Current Opinion in Investigational Drugs
Current Opinion in Investigational Drugs
Current Opinion in Investigational Drugs
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<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong><br />
<strong>Investigational</strong> <strong>Drugs</strong><br />
Mike Williams EDITOR<br />
Vol 7 No 1 January 2006<br />
Stanley Crooke, Annette Doherty, William Hagmann, John Kemp, Jacob J Plattner CO-EDITORS<br />
In this issue<br />
Central and peripheral nervous system<br />
• The genome: Five years on<br />
• Steroid therapy for exudative age-related<br />
macular degeneration<br />
• Nitrone sp<strong>in</strong> on cerebral ischemia<br />
• <strong>Drugs</strong> <strong>in</strong> development for Park<strong>in</strong>son's disease<br />
• The mechanism of action of gabapent<strong>in</strong> <strong>in</strong><br />
neuropathic pa<strong>in</strong><br />
• 5-HT 1A receptor activation <strong>in</strong> pa<strong>in</strong> relief<br />
• Glyc<strong>in</strong>e receptors: A new therapeutic target <strong>in</strong><br />
pa<strong>in</strong> pathways<br />
• Does VEGF represent a potential treatment for<br />
amyotrophic lateral sclerosis?<br />
• Ispronicl<strong>in</strong>e<br />
• AEOL-10150<br />
• Vivitrex
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> Vol 7 No 1 January 2006<br />
Editor <strong>in</strong> Chief Michael Williams USA<br />
Co-Editors Stanley Crooke USA Annette Doherty UK William Hagmann USA John<br />
Kemp GERMANY Jacob J Plattner USA<br />
Patent Editor Hermann AM Mucke AUSTRIA<br />
Thomson Scientific<br />
Middlesex House<br />
34-42 Cleveland Street<br />
London<br />
W1T 4JE<br />
UK<br />
Tel +44 (0)20 7070 6565<br />
Fax +44 (0)20 7070 6570<br />
Email: TS.Custserv.EMEA@thomson.<br />
com<br />
Manag<strong>in</strong>g Editor<br />
Barbara Chan<br />
Email: barbara.chan@thomson.com<br />
In-house Editors<br />
Tracey Coll<strong>in</strong>s (Anti-<strong>in</strong>fectives, Endocr<strong>in</strong>e<br />
and Metabolics, and Oncological)<br />
Email: tracey.coll<strong>in</strong>s@thomson.com<br />
Paula F<strong>in</strong>n (Anti-<strong>in</strong>flammatory,<br />
Cardiovascular and Renal, and Nervous<br />
System)<br />
Email: paula.f<strong>in</strong>n@thomson.com<br />
Editorial Board<br />
Janet Allen (UK)<br />
Rafael Apitz-Castro (Venezuela)<br />
John F Barrett (USA)<br />
Maria Belvisi (UK)<br />
Frank Bennett (USA)<br />
Andreas Billich (Austria)<br />
Norbert Bischofberger (USA)<br />
Roy Black (USA)<br />
Mel Blumenthal (USA)<br />
Frank Cerasoli (USA)<br />
Bruce Chabner (USA)<br />
Daniel Chu (USA)<br />
Kelv<strong>in</strong> Cooper (USA)<br />
Joseph Coyle (USA)<br />
Neal Cutler (USA)<br />
Mohsen Daneshtalab (Canada)<br />
Erik De Clercq (Belgium)<br />
Chet De Groat (USA)<br />
Errol DeSouza (Germany)<br />
Andy Dray (Canada)<br />
Mariano Elices (USA)<br />
Jilly Evans (USA)<br />
Tony Evans (Australia)<br />
Giora Feuerste<strong>in</strong> (USA)<br />
Alan C Foster (USA)<br />
W<strong>in</strong> Gutteridge (Switzerland)<br />
Jean Marc Herbert (France)<br />
Taff Jones (Canada)<br />
Loran Killar (USA)<br />
Gav<strong>in</strong> Kilpatrick (UK)<br />
George Koob (USA)<br />
Daniel Lane (USA)<br />
Alan Lewis (USA)<br />
John McCall (USA)<br />
Rodger McMillan (UK)<br />
He<strong>in</strong>z Moser (USA)<br />
Bo Öberg (Sweden)<br />
Jose Palacios (Spa<strong>in</strong>)<br />
Alan Palmer (UK)<br />
Michael Parnham (Croatia)<br />
Herbert P<strong>in</strong>edo (Netherlands)<br />
Yves Pommier (USA)<br />
John Reed (UK)<br />
Malcolm Richardson (F<strong>in</strong>land)<br />
Steve Rosenberg (USA)<br />
Alessandro Sette (USA)<br />
Jim Sikorski (USA)<br />
John Souness (USA)<br />
Paul Smith (New Zealand)<br />
Ken Tanaka (USA)<br />
Eugene Thorsett (USA)<br />
Section Editors<br />
January 2006/July 2006<br />
Central and Peripheral Nervous System<br />
Mike Briley (France), Mike Crowell (USA), Robert<br />
Davis (USA), Steve England (UK), Peter<br />
Goadsby (UK), Clifford Woolf (USA), Mike Wyllie<br />
(UK), Stev<strong>in</strong> Zorn (USA)<br />
February 2006/August 2006<br />
Anti-<strong>in</strong>fectives<br />
Rob<strong>in</strong> Cooper (USA), Simon Croft (Switzerland),<br />
Christian Hubschwerlen (Switzerland), Jeffrey H<br />
Toney (USA), Alan Johnson (UK), Barney<br />
Koszalka (USA), Nicholas Meanwell (USA), R<strong>in</strong>o<br />
Rappuoli (Italy), John Rex (UK), David A Stevens<br />
(USA)<br />
March 2006/September 2006<br />
Cardiovascular and Renal<br />
Frank Barone (USA), Tom Colatsky (USA), De-Zai<br />
Dai (Ch<strong>in</strong>a), Delv<strong>in</strong> Knight (USA), Brian Krause<br />
(USA), Keith E Suckl<strong>in</strong>g (UK), J Ruth Wu-Wong<br />
(USA)<br />
April 2006/October 2006<br />
Endocr<strong>in</strong>e and Metabolics<br />
Bruno Allolio (Germany), Franklyn Bolander (USA),<br />
Joy H<strong>in</strong>son (UK), Nigel Levens (France), Terry<br />
Opgenorth (USA)<br />
May 2006/November 2006<br />
Anti-<strong>in</strong>flammatory, Immunologicals and<br />
Biologicals<br />
Cynthia Darl<strong>in</strong>gton (New Zealand), Francis Dumont<br />
(USA), David Howat (France), Cees Korstanje<br />
(Netherlands), Tony Mann<strong>in</strong>g (USA), Randall Morris<br />
(USA), Neville Punchard (UK)<br />
June 2006/December 2006<br />
Oncological<br />
Suresh Ambudkar (USA), Andrew Dorr (USA),<br />
David Gewirtz (USA), Michael Lotze (USA), Ala<strong>in</strong><br />
Rolland (USA), Edward Sausville (USA), Ian<br />
Stratford (UK), Mario Sznol (USA), Paul<br />
Workman (UK)
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong><br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong><br />
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Aims and organization<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> is a monthly publication cover<strong>in</strong>g all therapeutic areas, <strong>in</strong> recognition of the<br />
<strong>in</strong>creas<strong>in</strong>gly multi-discipl<strong>in</strong>ary nature of modern drug discovery and development. With <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong><br />
<strong>Drugs</strong>, we aim to help the reader by provid<strong>in</strong>g <strong>in</strong> a systematic manner:<br />
• critical reviews of selected areas of <strong>in</strong>vestigational drug research<br />
• expert evaluation of selected drugs currently <strong>in</strong> cl<strong>in</strong>ical trials<br />
• selection of the most <strong>in</strong>terest<strong>in</strong>g papers and patents, annotated by experts.<br />
Subject division<br />
Six therapeutic categories are covered with each be<strong>in</strong>g featured <strong>in</strong> separate journal issues, and each therapeutic area be<strong>in</strong>g<br />
covered twice-yearly. The broad therapeutic categories and the specialist topics with<strong>in</strong> each are as follows:<br />
• Anti-<strong>in</strong>fectives Antifungals and antiparasitics; antibacterials (β-lactams, glycopeptides and other agents); antibacterials<br />
(qu<strong>in</strong>olones, macrolides and oxazolid<strong>in</strong>ones); vacc<strong>in</strong>es; antivirals (HIV); antivirals (non-HIV)<br />
• Anti-<strong>in</strong>flammatory, Immunologicals and Biologicals Musculoskeletal; respiratory; dermatology; nervous system;<br />
transplantation<br />
• Cardiovascular and Renal Hypertension and renal failure; stroke and ang<strong>in</strong>a; arrhythmia and heart failure;<br />
antithrombotics; hemostasis and hematological diseases; atherosclerosis, hypercholesterolemia and heart disease<br />
• Endocr<strong>in</strong>e and Metabolics Diabetes, reproductive endocr<strong>in</strong>ology, hormone disorders, bone metabolism and obesity<br />
• Central and Peripheral Nervous System Pa<strong>in</strong>; neuro-urology and neurogastroenterology; neurodegenerative and<br />
cognitive disorders; affective/behavioral/personality disorders and substance abuse; neurology and neuroprotection;<br />
schizophrenia and psychosis<br />
• Oncological Cell signal<strong>in</strong>g modulators; cytotoxic drugs; immunotherapeutic drugs and monoclonal antibodies; prote<strong>in</strong><br />
therapeutics, <strong>in</strong>clud<strong>in</strong>g growth factors; gene therapy; antisense <strong>in</strong>hibitors<br />
Each issue also conta<strong>in</strong>s a general alerts section which covers all therapeutic areas.<br />
Selection of topics to be reviewed Section Editors, who are major authorities <strong>in</strong> the field, are appo<strong>in</strong>ted by the Editors of<br />
the journal. They divide their section <strong>in</strong>to a number of topics, ensur<strong>in</strong>g that the field is comprehensively covered and that all<br />
issues of current importance are emphasized. Section Editors commission reviews from authorities on each topic that they<br />
have selected. Section Editors also identify compounds of significant promise and commission expert evaluations of these<br />
drugs. Submitted articles are peer reviewed before publication.<br />
Contents<br />
Patent alerts Brief commentaries on the scientific and/or commercial significance of new patents selected and written by<br />
experts with<strong>in</strong> their respective fields. These are presented beside the patent abstract from Patent fast-alert, published by<br />
Thomson <strong>Current</strong> <strong>Drugs</strong>.<br />
Paper alerts Expert commentary on a selection of recently published papers is provided.<br />
Therapeutic overviews Short m<strong>in</strong>i-reviews <strong>in</strong> which an area of <strong>in</strong>terest to the pharmaceutical <strong>in</strong>dustry is critically reviewed <strong>in</strong><br />
the context of recent developments. These pieces are <strong>in</strong>tended to be personal, thought-provok<strong>in</strong>g and controversial, where<br />
appropriate.<br />
Reviews Authors write concise reviews <strong>in</strong> which they present recent developments <strong>in</strong> their subject, emphasiz<strong>in</strong>g the aspects<br />
that, <strong>in</strong> their op<strong>in</strong>ion, are most important and provide short annotations to the papers and patents that they consider to be the<br />
most <strong>in</strong>terest<strong>in</strong>g from all those recently published <strong>in</strong> their topic. The reviews focus predom<strong>in</strong>antly on <strong>in</strong>vestigational drugs, or<br />
the therapeutic/commercial applications of new discoveries.<br />
Drug evaluations Expert commentary on the scientific and commercial potential of selected drugs <strong>in</strong> cl<strong>in</strong>ical trials are<br />
provided <strong>in</strong> each issue, <strong>in</strong> the form of drug evaluations. An evaluation is a review of the available literature (scientific and<br />
commercial) and acts as an expert guide to the bibliography, highlight<strong>in</strong>g references of particular <strong>in</strong>terest. <strong>Op<strong>in</strong>ion</strong> on the<br />
drug's potential, with a personal viewpo<strong>in</strong>t on its therapeutic and economic viability, are <strong>in</strong>cluded. The bibliographies conta<strong>in</strong><br />
only those papers referenced <strong>in</strong> the report, but readers may purchase the full bibliography, as it appears <strong>in</strong> <strong>Current</strong> <strong>Drugs</strong>'<br />
<strong>Investigational</strong> <strong>Drugs</strong> database (IDdb), if they wish.<br />
Literature classifications Key references relat<strong>in</strong>g to the drug are classified accord<strong>in</strong>g to a set of standard head<strong>in</strong>gs to<br />
provide a quick guide to the bibliography. These head<strong>in</strong>gs are as follows:<br />
Chemistry: References which discuss synthesis and structure-activity relationships.<br />
Metabolism: References which discuss metabolism, pharmacok<strong>in</strong>etics and toxicity.<br />
Biology: References which disclose aspects of the drug's pharmacology <strong>in</strong> animal models.<br />
Cl<strong>in</strong>ical: Reports of cl<strong>in</strong>ical phase studies <strong>in</strong> volunteers provid<strong>in</strong>g, where available, data on the follow<strong>in</strong>g: whether the<br />
experiment is placebo-controlled or double- or s<strong>in</strong>gle-bl<strong>in</strong>d, number of patients, dosage.<br />
Literature annotations Throughout the journal, a bullet<strong>in</strong>g system is used to denote <strong>in</strong>formation deemed by the author or<br />
editor to be either: • of special <strong>in</strong>terest; or •• of outstand<strong>in</strong>g <strong>in</strong>terest.<br />
Bi-annual <strong>in</strong>dexes Every six months, follow<strong>in</strong>g completion of coverage of each therapeutic area, cumulative <strong>in</strong>dexes of<br />
contents are provided.
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> Vol 7 No 1 January 2006<br />
Paper alert<br />
1 Mohsen Daneshtalab, Mariano J Elices & Robert E Hurst<br />
Patent selection<br />
4 Hermann AM Mucke<br />
Patent alert<br />
7 Hermann AM Mucke, Peter Norman & Clifford Whelan<br />
Central and Peripheral Nervous System<br />
Mike Briley, Mike Crowell, Robert Davis, Steve England,<br />
Peter Goadsby, Clifford Woolf, Mike Wyllie & Stev<strong>in</strong> Zorn<br />
14 Michael Williams<br />
Editorial overview: The genome: Five years on<br />
18 Maneli Mozaffarieh & Andreas Wedrich<br />
Editorial overview: Steroid therapy for exudative age-related<br />
macular degeneration: Bridg<strong>in</strong>g the gap until a cure is found<br />
20 Sheila A Doggrell<br />
Nitrone sp<strong>in</strong> on cerebral ischemia<br />
25 Tom H Johnston & Jonathan M Brotchie<br />
<strong>Drugs</strong> <strong>in</strong> development for Park<strong>in</strong>son's disease: An update<br />
33 J Kenneth Baillie & Ian Power<br />
The mechanism of action of gabapent<strong>in</strong> <strong>in</strong> neuropathic pa<strong>in</strong><br />
40 Francis C Colpaert<br />
5-HT1A receptor activation: New molecular and neuroadaptive<br />
mechanisms of pa<strong>in</strong> relief<br />
48 Joseph W Lynch & Robert J Callister<br />
Glyc<strong>in</strong>e receptors: A new therapeutic target <strong>in</strong> pa<strong>in</strong> pathways<br />
54 Joanna Iłżecka<br />
Does VEGF represent a potential treatment for amyotrophic<br />
lateral sclerosis?<br />
60 Hugo Geerts<br />
Ispronicl<strong>in</strong>e (Targacept)<br />
70 Richard W Orrell<br />
AEOL-10150 (Aeolus)<br />
81 Christ<strong>in</strong>e E Head<strong>in</strong>g<br />
Vivitrex (Alkermes/Cephalon)<br />
89 Erratum
The next issue of this journal (Vol 7 No 2 February 2006)<br />
Will conta<strong>in</strong>:<br />
Anti-<strong>in</strong>fectives<br />
Rob<strong>in</strong> Cooper, Simon Croft, Christian Hubschwerlen, Jeffrey H<br />
Toney, Alan Johnson, Barney Koszalka, Nicholas Meanwell, R<strong>in</strong>o<br />
Rappuoli, John Rex & David A Stevens<br />
Barney Koszalka & Nicholas Meanwell<br />
Editorial overview: Viral entry mechanisms<br />
Mark Erion<br />
HepDirect prodrugs for target<strong>in</strong>g nucleotide-based antiviral drugs to<br />
the liver<br />
Asim Kumar Debnath<br />
Prospects and strategies for the discovery and development of<br />
small-molecule <strong>in</strong>hibitors of six-helix bundle formation <strong>in</strong> class 1 viral<br />
fusion prote<strong>in</strong>s<br />
Robert Smolic, Mart<strong>in</strong>a Volarevic, Cather<strong>in</strong>e H Wu & George Y<br />
Wu<br />
Potential applications of siRNA <strong>in</strong> hepatitis C virus therapy<br />
Larry Boone<br />
Next generation non-nucleoside reverse transcriptase <strong>in</strong>hibitors for<br />
the treatment of HIV<br />
Maria Zambon<br />
Influenza immunization strategies<br />
David Koelle<br />
Novel treatment options for herpes simplex virus<br />
Ursula Theuretzbacher & Jeffrey H Toney<br />
Nature's clarion call of antibacterial resistance: Are we listen<strong>in</strong>g?<br />
David Shlaes<br />
Novel tetracycl<strong>in</strong>es<br />
David Kaufman<br />
Veronate (Inhibitex)<br />
Joseph Jao-Yiu Sung & Henry Lik-Yuen Chan<br />
HBV-ISS (Dynavax)<br />
David McMillan<br />
StreptAvax (ID Biomedical)
Paper alert<br />
A selection of <strong>in</strong>terest<strong>in</strong>g recently published papers from<br />
major journals relat<strong>in</strong>g to drug discovery and research.<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 7(1):1-3<br />
© The Thomson Corporation ISSN 1472-4472<br />
Contents<br />
1 Anti-<strong>in</strong>fectives<br />
2 Endocr<strong>in</strong>e & metabolic<br />
2 Oncological<br />
Anti-<strong>in</strong>fectives<br />
Selected by Mohsen Daneshtalab (Memorial University, St<br />
John's, NL, Canada)<br />
In vitro and <strong>in</strong> vivo antibacterial activities of SM-216601, a<br />
new broad-spectrum parenteral carbapenem.<br />
Ueda Y, Kanazawa K, Eguchi K, Takemoto K, Eriguchi Y,<br />
Sunagawa M (Sumitomo Pharmaceuticals Research Division,<br />
Osaka, Japan).<br />
Antimicrob Agents Chemother (2005) 49(10):4185-4196.<br />
•• Significance The emergence of multidrug-resistant, Grampositive<br />
bacteria such as methicill<strong>in</strong>-resistant Staphylococcus<br />
aureus (MRSA), penicill<strong>in</strong>-resistant Streptococcus pneumoniae<br />
(PRSP) and vancomyc<strong>in</strong>-resistant enterococci (VRE), has<br />
affected the usefulness of antibacterial chemotherapy <strong>in</strong> recent<br />
years. Resistance to β-lactam antibiotics is a serious concern<br />
because this class of compounds exhibits several advantages<br />
over other antibacterials. Thus, there is an urgent need for new<br />
β-lactam agents effective aga<strong>in</strong>st resistant pathogens. These<br />
researchers previously reported that 2-(4-arylthiazole-2-ylthio)-<br />
1β-methylcarbapenems, such as SM-17466 (Sumitomo Seika<br />
Chemicals Co Ltd/F Hoffmann-La Roche Ltd) and its<br />
derivatives, showed potent activity aga<strong>in</strong>st MRSA ow<strong>in</strong>g to<br />
their high aff<strong>in</strong>ity for penicill<strong>in</strong>-b<strong>in</strong>d<strong>in</strong>g prote<strong>in</strong> (PBP)2a.<br />
SM-17466 was also effective aga<strong>in</strong>st Enterococcus faecium<br />
compared with other carbapenems. These observations<br />
prompted the search for novel carbapenems with potent<br />
activity aga<strong>in</strong>st MRSA and VRE. SM-216601 (Sumitomo Seika<br />
Chemicals Co Ltd/F Hoffmann-La Roche Ltd), a<br />
dihydropyrrolyl thiazole analog of SM-17466, was identified,<br />
which demonstrated broad-spectrum antibacterial activity<br />
aga<strong>in</strong>st Gram-positive and Gram-negative bacteria. This paper<br />
describes <strong>in</strong> vitro studies <strong>in</strong>vestigat<strong>in</strong>g the activity of SM-216601<br />
aga<strong>in</strong>st different cl<strong>in</strong>ical isolates compared with vancomyc<strong>in</strong>,<br />
l<strong>in</strong>ezolid and several other β-lactams. In addition, the efficacy of<br />
SM-216601 aga<strong>in</strong>st systemic <strong>in</strong>fections <strong>in</strong> mice caused by<br />
methicill<strong>in</strong>-sensitive S aureus, MRSA, Escherichia coli,<br />
Pseudomonas aerug<strong>in</strong>osa and experimental E faecium<br />
subcutaneous abscesses is described.<br />
F<strong>in</strong>d<strong>in</strong>gs This study <strong>in</strong>vestigated the <strong>in</strong> vitro antibacterial<br />
activity, aff<strong>in</strong>ity for bacterial PBPs and resistance to<br />
hydrolysis by dehydropeptidase (DHP)-1 of SM-216601, and<br />
evaluated its <strong>in</strong> vivo efficacy aga<strong>in</strong>st Gram-positive and<br />
Gram-negative bacteria and pharmacok<strong>in</strong>etics <strong>in</strong> mice.<br />
SM-216601 exhibited potent activity aga<strong>in</strong>st MRSA, PRSP,<br />
VRE, ampicill<strong>in</strong>-resistant Haemophilus <strong>in</strong>fluenzae, Moraxella<br />
catarrhalis, E coli, Klebsiella pneumoniae and Proteus mirabilis.<br />
In addition, SM-216601 was highly efficacious aga<strong>in</strong>st<br />
experimentally <strong>in</strong>duced <strong>in</strong>fections <strong>in</strong> mice caused by<br />
S aureus, E faecium, E coli and P aerug<strong>in</strong>osa. Its sensitivity aga<strong>in</strong>st<br />
renal DHP-1 was similar to that of meropenem and superior to<br />
that of imipenem. SM-216601 exhibited improved<br />
pharmacok<strong>in</strong>etics compared with imipenem and meropenem<br />
<strong>in</strong> mice, rats, dogs and cynomolgus monkeys.<br />
Design, synthesis, and biological activity of m-tyros<strong>in</strong>ebased<br />
16- and 17-membered macrocyclic <strong>in</strong>hibitors of<br />
hepatitis C virus NS3 ser<strong>in</strong>e protease.<br />
Chen KX, Njoroge FG, Pichardo J, Prongay A, Butkiewicz N, Yao<br />
N, Madison V, Girijavallabhan V (Scher<strong>in</strong>g-Plough Research<br />
Institute, Kenilworth, NJ, USA).<br />
J Med Chem (2005) 48(20):6229-6235.<br />
• Significance The worldwide spread of hepatitis C virus<br />
(HCV) <strong>in</strong>fection has caused a global health crisis. The only<br />
therapies currently available for the treatment of HCV <strong>in</strong>fection<br />
are subcutaneous <strong>in</strong>terferon (IFN)α or pegylated IFNα<br />
monotherapy, or the comb<strong>in</strong>ation of IFNα or pegylated IFNα<br />
and oral ribavir<strong>in</strong>. These therapies have limited efficacies and<br />
cause considerable side effects <strong>in</strong> patients. Therefore, the search<br />
for small molecules with high efficacy and less toxicity<br />
cont<strong>in</strong>ues. The viral NS3 prote<strong>in</strong> and its correspond<strong>in</strong>g enzyme,<br />
NS3 protease, are attractive drug targets <strong>in</strong> HCV. Many<br />
protease <strong>in</strong>hibitors that have peptidic molecular structures have<br />
been developed <strong>in</strong> recent years. However, because of low<br />
bioavailability and poor pharmacok<strong>in</strong>etics, most of these<br />
<strong>in</strong>hibitors have failed to make it onto the market.<br />
Peptidomimetics are peptidic analogs that resist hydrolytic<br />
enzymes while exhibit<strong>in</strong>g the same enzyme <strong>in</strong>hibitory<br />
characteristics as the correspond<strong>in</strong>g peptides. The potential of<br />
cyclic hexapeptides as <strong>in</strong>hibitors of the HCV NS3 protease have<br />
been reported <strong>in</strong> a number of studies. Based on these<br />
discoveries, novel 16- and 17-membered r<strong>in</strong>g analogs were<br />
synthesized and evaluated for HCV NS3 protease <strong>in</strong>hibitory<br />
activity.<br />
F<strong>in</strong>d<strong>in</strong>gs The synthesis of these cyclic peptides began with<br />
the coupl<strong>in</strong>g of the commercially available N-Boccyclohexylglyc<strong>in</strong>e<br />
and m-tyros<strong>in</strong>e methyl ester, which <strong>in</strong> five<br />
steps gave rise to methyl 11(S)-cyclohexyl-9.12-dioxo-2-oxa-<br />
10,13-diazabicyclo[14.3.1]eicosa-1(20),16,18-triene-14(S)carboxylate.<br />
Hydrolysis of this <strong>in</strong>termediate followed by<br />
coupl<strong>in</strong>g with [2-(3-am<strong>in</strong>o-2-hydroxy-hexanoylam<strong>in</strong>o)acetylam<strong>in</strong>o]-phenylacetic<br />
acid tert-butyl ester hydrochloride<br />
afforded the desired 17-membered macrocyclic compounds<br />
as either O-tert-butyl ester, free carboxylic acid, or the<br />
correspond<strong>in</strong>g mono- or dimethylamide analogs. The<br />
correspond<strong>in</strong>g 16-membered analogs were synthesized <strong>in</strong><br />
the same manner as above. In an HCV protease cont<strong>in</strong>uous<br />
assay, the 16-membered analogs were less active than the<br />
correspond<strong>in</strong>g 17-membered analogs. This study confirmed<br />
the potential of these 17-membered macrocycles as lead<br />
compounds for further development of anti-HCV drugs.<br />
Synthesis and structure-activity relationships of novel<br />
anti-hepatitis C agents: N 3 ,5'-cyclo-4-(β-D-ribofuranosyl)vic-triazolo[4,5-b]pyrid<strong>in</strong>-5-one<br />
derivatives.<br />
Wang P, Du J, Rachakonda S, Chun B-K, Tharnish PM, Stuyver<br />
LJ, Otto MJ, Sch<strong>in</strong>azi RF, Watanabe KA (Pharmasset Inc,<br />
Pr<strong>in</strong>ceton, NJ, USA).<br />
J Med Chem (2005) 48(20):6454-6460.<br />
• Significance Chronic hepatitis C virus (HCV) <strong>in</strong>fection is<br />
1
2 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
predicted to become a major challenge for healthcare providers,<br />
especially as the currently asymptomatic carriers of this virus<br />
may develop hepatocellular carc<strong>in</strong>oma. Furthermore, the death<br />
rate due to HCV <strong>in</strong>fection is predicted to triple <strong>in</strong> the next ten to<br />
20 years. <strong>Current</strong> treatment protocols <strong>in</strong>volve either the<br />
adm<strong>in</strong>istration of <strong>in</strong>terferon (IFN)α or its pegylated form alone<br />
or <strong>in</strong> comb<strong>in</strong>ation with ribavir<strong>in</strong> (RBV). IFNα causes<br />
neuropsychiatric adverse effects and anemia is the most<br />
common side effect of RBV. In addition, the response rate for<br />
both therapeutic approaches is < 50%. Thus, the identification<br />
of new and effective drugs for the treatment of HCV <strong>in</strong>fection is<br />
critical. These researchers previously identified a novel<br />
compound, N 3,5'-cyclo-4-(β-D-ribofuranosyl)-vic-triazolo[4,5b]pyrid<strong>in</strong>-5-one<br />
(CRTP), which exhibited moderate anti-HCV<br />
activity <strong>in</strong> a subgenomic RNA replicon system. In an effort to<br />
discover more potent anti-HCV agents, a series of 6- and 7substituted<br />
derivatives of CRTP were synthesized. In this<br />
study, different 5-thiono, 6-halo, 7-alkylam<strong>in</strong>o and 7-methyl<br />
analogs of CRTP were synthesized and their anti-HCV activity<br />
and cytotoxicity evaluated. Some of the newly synthesized<br />
compounds exhibited 8- to 40-fold more potent anti-HCV<br />
activity than that of CRTP.<br />
F<strong>in</strong>d<strong>in</strong>gs CRTP was <strong>in</strong>itially synthesized from 1-(2,3,5-tri-Obenzoyl-β-D-ribofuranosyl)-5-nitropyrid<strong>in</strong>-2-one<br />
us<strong>in</strong>g either<br />
a five-step traditional synthetic method or a one-pot<br />
synthetic method. Further synthetic procedures <strong>in</strong>volv<strong>in</strong>g<br />
CRTP resulted <strong>in</strong> 5-thiono, 6-chloro/bromo, 7-am<strong>in</strong>o or 7alkylam<strong>in</strong>o<br />
analogs. The 7-methyl analog of CRTP was<br />
prepared us<strong>in</strong>g a different methodology. The synthesized<br />
compounds were tested for their ability to <strong>in</strong>hibit HCV RNA<br />
<strong>in</strong> a subgenomic replicon Huh-7 cell l<strong>in</strong>e. Cytotoxicity was<br />
determ<strong>in</strong>ed us<strong>in</strong>g an MTS assay. Among the compounds<br />
tested, the 5-thiono, 6-chloro, 6-bromo, 7-am<strong>in</strong>o, 7methylam<strong>in</strong>o<br />
and 7-methyl analogs exhibited more potent<br />
anti-HCV activity than CRTP, with the 6-chloro and 6-bromo<br />
analogs be<strong>in</strong>g the most potent. This study suggests a direct<br />
correlation between the anti-HCV activity and the<br />
cytotoxicity of these compounds.<br />
Endocr<strong>in</strong>e & metabolics<br />
Selected by Mariano J Elices (PharmaMar USA, Cambridge,<br />
MA, USA)<br />
Normal fast<strong>in</strong>g plasma glucose levels and type 2<br />
diabetes <strong>in</strong> young men.<br />
Tirosh A, Shai I, Tekes-Manova D, Israeli E, Pereg D, Shochat<br />
T, Kochba I, Rudich A; Israeli Diabetes Research Group<br />
(Medical Corps Headquarters, Tel-Hashomer, Israel).<br />
N Engl J Med (2005) 353(14):1454-1462.<br />
• Significance Science textbooks generally list the range of<br />
fast<strong>in</strong>g plasma glucose values for healthy <strong>in</strong>dividuals<br />
(normoglycemic) as be<strong>in</strong>g 70 to 110 mg/dl. However, <strong>in</strong><br />
2003, an expert committee at the American Diabetes<br />
Association (ADA) revised this long-held view and<br />
suggested that fast<strong>in</strong>g blood glucose levels of 101 to 109<br />
mg/dl represent impairment of glucose metabolism and<br />
thus pose a risk for the development of type 2 diabetes. In<br />
general, the <strong>in</strong>cidence of type 2 diabetes has <strong>in</strong>creased <strong>in</strong><br />
developed countries, <strong>in</strong>clud<strong>in</strong>g among younger members of<br />
the population that have traditionally not been considered to<br />
be at risk; thus it is of significant value to uncover risk<br />
factors for this illness.<br />
F<strong>in</strong>d<strong>in</strong>gs In order to address which risk factors contribute to<br />
the development of type 2 diabetes, the <strong>in</strong>vestigators exam<strong>in</strong>ed<br />
a computerized database that was established <strong>in</strong> 1992 to<br />
capture data from the MELANY (MEtabolic, Lifestyle, And<br />
Nutrition assessment <strong>in</strong> Young adults) trial. This trial was<br />
conducted among military personnel over 25 years of age <strong>in</strong><br />
Israel who received periodic exam<strong>in</strong>ations every three to five<br />
years. At the time of their periodic visit, each <strong>in</strong>dividual gave a<br />
blood sample after a 14-h fast<strong>in</strong>g period, and received a medical<br />
exam<strong>in</strong>ation; a detailed questionnaire was also completed by<br />
each <strong>in</strong>dividual. The primary endpo<strong>in</strong>t of the study was a new<br />
diagnosis of type 2 diabetes dur<strong>in</strong>g the trial (based on criteria<br />
outl<strong>in</strong>ed by the ADA expert committee) which <strong>in</strong>volved the<br />
record<strong>in</strong>g of two fast<strong>in</strong>g plasma glucose levels of at least 126<br />
mg/dl. Of 13,163 male <strong>in</strong>dividuals with fast<strong>in</strong>g blood glucose<br />
levels of ≤ 100 mg/dl, there were 208 new cases of type 2<br />
diabetes (ie, a 1.6% <strong>in</strong>cidence) spann<strong>in</strong>g an average of 5.7 years<br />
of follow-up. Multivariate models showed that males with<br />
fast<strong>in</strong>g blood glucose at the high end of the normal range (91 to<br />
99 mg/dl), comb<strong>in</strong>ed with serum triglyceride levels of ≥ 150<br />
mg/dl, had an 8.23-fold higher risk of develop<strong>in</strong>g type 2<br />
diabetes compared with <strong>in</strong>dividuals with fast<strong>in</strong>g plasma<br />
glucose and serum triglyceride levels of ≤ 86 and < 150 mg/dl,<br />
respectively. In a similar manner, hazard ratios revealed a 8.29fold<br />
higher risk of develop<strong>in</strong>g type 2 diabetes <strong>in</strong> obese men<br />
(body mass <strong>in</strong>dex ≥ 30) even when they had a normal, albeit<br />
high, fast<strong>in</strong>g blood glucose (91 to 99 mg/dl), compared with<br />
control <strong>in</strong>dividuals with fast<strong>in</strong>g plasma glucose levels and a<br />
body mass <strong>in</strong>dex of ≤ 86 mg/dl and < 25, respectively. These<br />
data strongly suggest that normoglycemic <strong>in</strong>dividuals with<br />
either serum triglyceride levels > 150 mg/dl or exhibit<strong>in</strong>g<br />
relative obesity (ie, body mass <strong>in</strong>dex ≥ 30) are at an <strong>in</strong>creased<br />
risk of develop<strong>in</strong>g type 2 diabetes later <strong>in</strong> life. From a healthcare<br />
standpo<strong>in</strong>t, these f<strong>in</strong>d<strong>in</strong>gs expose a host of opportunities <strong>in</strong><br />
diagnostic, preventive and therapeutic areas <strong>in</strong> type 2 diabetes.<br />
Oncological<br />
Selected by Robert E Hurst (Oklahoma University Health<br />
Sciences Center, OK, USA)<br />
A potential synergistic anticancer effect of paclitaxel<br />
and amifost<strong>in</strong>e on endometrial cancer.<br />
Dai D, Holmes AM, Nguyen T, Davies S, Theele DP,<br />
Verschraegen C, Leslie KK (University of New Mexico Health<br />
Sciences Center, Albuquerque, NM, USA).<br />
Cancer Res (2005) 65(20):9517-9524.<br />
• Significance Although the prognosis for endometrial cancer<br />
is generally good, advanced or recurrent cases have a poor<br />
prognosis, with chemotherapy offer<strong>in</strong>g mostly palliative<br />
therapy. Amifost<strong>in</strong>e has been proven to protect normal cells<br />
aga<strong>in</strong>st a number of chemotherapeutic agents, <strong>in</strong>clud<strong>in</strong>g<br />
paclitaxel. Amifost<strong>in</strong>e not only allows the adm<strong>in</strong>istration of<br />
higher doses of paclitaxel but, <strong>in</strong> this study, the drug also had a<br />
direct effect on endometrial cancer cells, and acted<br />
synergistically with paclitaxel. Thus, comb<strong>in</strong>ation therapy<br />
with these two drugs may be more effective than paclitaxel<br />
alone.
F<strong>in</strong>d<strong>in</strong>gs In vitro studies with poorly differentiated Hec50co<br />
endometrial cancer cells demonstrated that amifost<strong>in</strong>e had<br />
direct anticancer effects, produc<strong>in</strong>g G1 arrest of the cell cycle<br />
and <strong>in</strong>duc<strong>in</strong>g apoptosis. Amifost<strong>in</strong>e was also active <strong>in</strong> a<br />
flank xenograft model <strong>in</strong> nude mice. A s<strong>in</strong>gle dose of<br />
Paper alert 3<br />
amifost<strong>in</strong>e (178 µM) reduced the IC50 value of paclitaxel<br />
from 14 to 2 nM, and amifost<strong>in</strong>e acted synergistically with<br />
paclitaxel to <strong>in</strong>duce G2 to M growth arrest and apoptosis.<br />
The survival of mice was improved significantly over either<br />
agent alone <strong>in</strong> a flank xenograft model.
4<br />
Patent selection<br />
The follow<strong>in</strong>g recently issued patents have been pre-selected<br />
as be<strong>in</strong>g of particular <strong>in</strong>terest from the <strong>Current</strong> Patents<br />
Gazette. Full alerts will appear <strong>in</strong> forthcom<strong>in</strong>g issues of<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong>.<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 7(1):4-6<br />
© The Thomson Corporation ISSN 1472-4472<br />
Oncologic, endocr<strong>in</strong>e and metabolic<br />
NOVARTIS AG Inhibitors of IAP. WO-2005097791 (20<br />
October 2005)<br />
• Compounds that <strong>in</strong>hibit the b<strong>in</strong>d<strong>in</strong>g of Smac prote<strong>in</strong> to<br />
<strong>in</strong>hibitors of apoptosis prote<strong>in</strong>s (IAPs), thereby promot<strong>in</strong>g the<br />
apoptosis of rapidly divid<strong>in</strong>g cells are described. These<br />
compounds are useful for the treatment of proliferation diseases<br />
such as cancer. This application represents cont<strong>in</strong>uation of<br />
research by this group on Smac and IAPs (see also WO-<br />
2004005248 and WO-2005074989); a May 2005 press release<br />
from Novartis gives details of the Smac mimetic project. Some<br />
of the <strong>in</strong>ventors have previously worked on k<strong>in</strong>ase <strong>in</strong>hibitors<br />
and <strong>in</strong>tegr<strong>in</strong> receptor antagonists.<br />
UNIVERSITY OF WESTERN AUSTRALIA Osteoblast growth<br />
factor. WO-2005100389 (27 October 2005)<br />
• Caltr<strong>in</strong> (calcium transport <strong>in</strong>hibitor), a small cyste<strong>in</strong>e-rich<br />
secretory prote<strong>in</strong> isolated from a hematopoietic macrophage<br />
cell l<strong>in</strong>e, elevates cytosolic calcium levels and may be used<br />
for treat<strong>in</strong>g or prevent<strong>in</strong>g bone disorders. The <strong>in</strong>ventors are<br />
named on prior applications from Verigen Transplantation<br />
Service International AG, for example, WO-03026689,<br />
concern<strong>in</strong>g the use of growth factors from chondrocytes for<br />
the treatment of osteogenesis.<br />
MEDIQUEST THERAPEUTICS INC Polyam<strong>in</strong>e analogs that<br />
activate antizyme frameshift<strong>in</strong>g. WO-2005105729 (10<br />
November 2005)<br />
• Polyam<strong>in</strong>e analogs that activate antizyme frameshift<strong>in</strong>g to<br />
downregulate production of endogenous polyam<strong>in</strong>es by<br />
ornith<strong>in</strong>e decarboxylase and transport via the correspond<strong>in</strong>g<br />
polyam<strong>in</strong>e transporter are claimed. These compounds are<br />
useful <strong>in</strong> the treatment of cellular proliferation-associated<br />
<strong>in</strong>dications, particularly alopecia. This application claims<br />
several polyam<strong>in</strong>es, of which two compounds have previously<br />
been specifically claimed <strong>in</strong> US-06914079 (by the same<br />
<strong>in</strong>ventors). MediQuest, <strong>in</strong> collaboration with researchers at the<br />
University of Utah, is <strong>in</strong>vestigat<strong>in</strong>g a series of polyam<strong>in</strong>e<br />
analogs. The company is also <strong>in</strong>vestigat<strong>in</strong>g a polyam<strong>in</strong>e<br />
transporter <strong>in</strong>hibitor ORI-1202.<br />
PFIZER INC Inhibitors of checkpo<strong>in</strong>t k<strong>in</strong>ases (Wee1 and<br />
Chk1). US-20050250836 (10 November 2005)<br />
• Novel substituted <strong>in</strong>dacene molecules that specifically <strong>in</strong>hibit<br />
one or both of the checkpo<strong>in</strong>t k<strong>in</strong>ases Wee1 and Chk1 and are<br />
useful <strong>in</strong> the treatment of proliferative disorders are described.<br />
Pfizer is <strong>in</strong>vestigat<strong>in</strong>g PD-166285, a prote<strong>in</strong> k<strong>in</strong>ase <strong>in</strong>hibitor.<br />
Results presented at the American Association for Cancer<br />
Research meet<strong>in</strong>g <strong>in</strong> April 2000 <strong>in</strong>dicated that PD-166285<br />
<strong>in</strong>hibited Wee1 tyros<strong>in</strong>e k<strong>in</strong>ase. Pfizer (formerly Agouron) is<br />
also <strong>in</strong>vestigat<strong>in</strong>g a series of Chk1 <strong>in</strong>hibitors for the potential<br />
treatment of cancer. As of May 2005, <strong>in</strong>vestigations were<br />
ongo<strong>in</strong>g (see WO-03091255).<br />
SMITHKLINE BEECHAM CORP; CYTOKINETICS INC Certa<strong>in</strong><br />
chemical entities, compositions, and methods. WO-<br />
2005107762 (17 November 2005)<br />
• Substituted heterocyclic amides as <strong>in</strong>hibitors of CENP-E<br />
k<strong>in</strong>es<strong>in</strong> activity for the treatment of cellular proliferative<br />
disorders are described. This cont<strong>in</strong>ues the collaboration<br />
between Cytok<strong>in</strong>etics and GlaxoSmithKl<strong>in</strong>e (formerly<br />
SmithKl<strong>in</strong>eBeecham), although this appears to be a new<br />
research direction as previous research relates to KSP<br />
k<strong>in</strong>es<strong>in</strong> (see WO-2005060692, which names three of the<br />
present <strong>in</strong>ventors). Cytok<strong>in</strong>etics and GlaxoSmithKl<strong>in</strong>e have<br />
two KSP <strong>in</strong>hibitors <strong>in</strong> phase I and II trials for cancer.<br />
BUCK INSTITUTE; TOURO UNIVERSITY; THE BURNHAM INSTITUTE<br />
Artificially designed pore-form<strong>in</strong>g prote<strong>in</strong>s with<br />
antitumor effects. US-20050256040 (17 November 2005)<br />
• Use of a small globular prote<strong>in</strong> (SGP) to disrupt a biological<br />
membrane is claimed. SGP is established as the prototype for a<br />
new class of artificial prote<strong>in</strong>s designed for therapeutic<br />
application. SGP can be used for disrupt<strong>in</strong>g tumor growth (eg,<br />
Kaposi's sarcoma, breast carc<strong>in</strong>oma, malignant melanoma of<br />
the sk<strong>in</strong>, lung and prostate cancer and metastases). This<br />
application cont<strong>in</strong>ues the <strong>in</strong>ventors' cancer research (eg, WO-<br />
2005094383). One of the <strong>in</strong>ventors is associated with the<br />
Burnham Institute and the other with the University of Touro.<br />
E MERCK PATENT GMBH GM3 synthase as a therapeutic<br />
target <strong>in</strong> microvascular complications of diabetes. WO-<br />
2005108600 (17 November 2005)<br />
• GM3 synthase <strong>in</strong>hibitors to treat microvascular complications<br />
of diabetes (eg, diabetic nephropathy) are claimed. Also claimed<br />
is a method for screen<strong>in</strong>g for GM3 synthase <strong>in</strong>hibitors. See also<br />
WO-00234201 and WO-09936396 for previous applications<br />
by members of this team.<br />
Pulmonary-allergy, dermatological,<br />
gastro<strong>in</strong>test<strong>in</strong>al and anti-<strong>in</strong>flammatory<br />
ONO PHARMACEUTICAL CO LTD Novel BLT2-mediated<br />
disease, and BLT2 b<strong>in</strong>d<strong>in</strong>g agent and compound. WO-<br />
2005102388 (03 November 2005)<br />
• A compound capable of selective b<strong>in</strong>d<strong>in</strong>g to BLT2 is<br />
disclosed. Its use as a therapeutic agent for BLT2-mediated<br />
disease, <strong>in</strong>clud<strong>in</strong>g cutaneous disorders, bowel disease and<br />
HIV <strong>in</strong>fection, is described. This application may be related<br />
to the company's ONO-4057, a dual antagonist of two<br />
leukotriene B4 receptors, BLT1 and BLT2, for the potential<br />
treatment of Behcet's disease, psoriasis and <strong>in</strong>flammatory<br />
bowel disease. WO-2004031118 (by different <strong>in</strong>ventors) is<br />
cited as relevant <strong>in</strong> the search report.<br />
NOVARTIS AG CRTH2 receptor antagonists. WO-<br />
2005105727 (10 November 2005)<br />
• Novel compounds as CRTH2 (G-prote<strong>in</strong>-coupled<br />
chemoattractant receptor expressed on Th2 cells) receptor<br />
antagonists, useful for the treatment of respiratory and<br />
<strong>in</strong>flammatory conditions, are disclosed. CRTH2 appears to<br />
be a new target for Novartis and the <strong>in</strong>ventors, this be<strong>in</strong>g<br />
their only patent application on the receptor. Oxagen and<br />
Ortho-McNeil are currently lead<strong>in</strong>g this field, with both<br />
companies hav<strong>in</strong>g programs <strong>in</strong> precl<strong>in</strong>ical development.
Anti-<strong>in</strong>fectives<br />
JANSSEN PHARMACEUTICA NV Inhibitors of bacterial type III<br />
prote<strong>in</strong> secretion systems. US-20050250819 (10<br />
November 2005)<br />
• Novel triaz<strong>in</strong>e compounds as <strong>in</strong>hibitors of bacterial type III<br />
prote<strong>in</strong> secretion systems, useful for the treatment and<br />
prevention of bacterial <strong>in</strong>fections, particularly Gramnegative<br />
bacterial <strong>in</strong>fections, are described. The <strong>in</strong>ventors<br />
have been named on other applications disclos<strong>in</strong>g<br />
antibacterials. However, this specific action appears to be a<br />
new target.<br />
Biological and immunological<br />
CATALYST BIOSCIENCES INC Cleavage of VEGF and VEGF<br />
receptor by wild-type and mutant proteases. WO-<br />
2005100556 (27 October 2005)<br />
• Mutated granzyme B polypeptides (mute<strong>in</strong>s) that cleave<br />
vascular endothelial growth factor (VEGF) or the VEGF<br />
receptor and <strong>in</strong>hibit angiogenesis are claimed. The mute<strong>in</strong>s<br />
may be used for the treatment of angiogenesis-related<br />
disorders (eg, cancer, <strong>in</strong>flammation, diabetes and macular<br />
degeneration). This is only the company's second<br />
application and cont<strong>in</strong>ues its development of modified<br />
enzymes (see WO-2004031733). In July 2005, Catalyst<br />
exclusively licensed <strong>in</strong>tellectual property cover<strong>in</strong>g protease<br />
eng<strong>in</strong>eer<strong>in</strong>g from Torrey P<strong>in</strong>es.<br />
CURTIN UNIVERSITY OF TECHNOLOGY Therapeutic hepar<strong>in</strong>s<br />
and their b<strong>in</strong>d<strong>in</strong>g to <strong>in</strong>terleuk<strong>in</strong>s 4 and 5, and PECAM-1.<br />
WO-2005100374 (27 October 2005)<br />
• These glycosam<strong>in</strong>oglycan oligosaccharides are claimed for<br />
use <strong>in</strong> the treatment of a wide range of conditions. The<br />
British <strong>in</strong>ventor appears to be based at the National<br />
Institute for Biological Standards and Control.<br />
Bassiri A, Das A, Dillon S, Duffy K, Seideman J, Mbow ML,<br />
Karlsson L, Sun S, Zhu J, Cunn<strong>in</strong>gham M Toll-like receptor<br />
9 effector agents and uses thereof. US-20050244410 (03<br />
November 2005)<br />
• Cell-surface toll-like receptor 9 (TLR9) effector agents, such<br />
as TLR9 receptor b<strong>in</strong>d<strong>in</strong>g agents and TLR9 ligand b<strong>in</strong>d<strong>in</strong>g<br />
agents (namely antibodies and other prote<strong>in</strong>s), and their use<br />
<strong>in</strong> modulat<strong>in</strong>g immune responses for the treatment of, for<br />
example, <strong>in</strong>fections, cancer and <strong>in</strong>flammation, are described.<br />
The <strong>in</strong>ventors appear to be based at Centocor and feature on<br />
a related application, WO-2004096156.<br />
E MERCK PATENT GMBH Dihydrobenzothiophenes. WO-<br />
2005108355 (17 November 2005)<br />
• Dihydrobenzothiophenes as modulators of mitotic motor<br />
prote<strong>in</strong>s, particularly Eg5, useful for the treatment of, for<br />
example, angiogenesis, cancers, arteriosclerosis, eye<br />
disorders and <strong>in</strong>flammation, are disclosed. See WO-<br />
2005063735 for substituted tetrahydroqu<strong>in</strong>ol<strong>in</strong>e derivatives<br />
with the same action.<br />
Central and peripheral nervous system<br />
Patent selection 5<br />
BIOCORTECH Derivatives of 14,15-dihydro 20,21d<strong>in</strong>oreburnamen<strong>in</strong>-14-ol,<br />
and applications thereof. WO-<br />
2005103047 (03 November 2005)<br />
• 14,15-Dihydro 20,21-d<strong>in</strong>oreburnamen<strong>in</strong>-14-ol derivatives<br />
are targeted at the treatment of depression. A similar use of<br />
the parent nucleus was claimed <strong>in</strong> WO-2005082365. This<br />
application is possibly l<strong>in</strong>ked to BC-19, an orally active<br />
small molecule believed to reactivate the norep<strong>in</strong>ephr<strong>in</strong>e<br />
pathways, which Biocortech is develop<strong>in</strong>g for the potential<br />
treatment of depression. By April 2005, phase II trials of<br />
BC-19 were underway.<br />
SANGAMO BIOSCIENCES INC Treatment of neuropathic pa<strong>in</strong><br />
with z<strong>in</strong>c f<strong>in</strong>ger prote<strong>in</strong>s. WO-2005100392 (27 October<br />
2005)<br />
• Use of a nucleic acid consist<strong>in</strong>g of a z<strong>in</strong>c f<strong>in</strong>ger DNAb<strong>in</strong>d<strong>in</strong>g<br />
doma<strong>in</strong> eng<strong>in</strong>eered to b<strong>in</strong>d target genes and<br />
modulate overexpression of dorsal root ganglia genes (eg,<br />
VR1, TRKA and Nav1.8) of pa<strong>in</strong> patients, and a<br />
transcriptional repression doma<strong>in</strong>, are described. This<br />
application appears to be related to the company's ZFP TF<br />
(pa<strong>in</strong>) gene therapy, us<strong>in</strong>g Avigen's adeno-associated virus<br />
gene delivery system for the potential treatment of<br />
neuropathic pa<strong>in</strong>. See US-20040091991 and WO-<br />
2005028630.<br />
ELI LILLY & CO BACE <strong>in</strong>hibitors. WO-2005108358/WO-<br />
2005108358 (17 November 2005)<br />
• Alkylamide-substituted pyrrolid<strong>in</strong>e and related<br />
ethanolam<strong>in</strong>e derivatives are disclosed. These compounds<br />
are β-amyloid precursor prote<strong>in</strong> cleav<strong>in</strong>g enzyme (BACE)<br />
<strong>in</strong>hibitors, and appear to be some of the first small molecules<br />
to emerge from the program. See WO-00068266 and WO-<br />
00069262 for related drug screen<strong>in</strong>g methods and<br />
technology. Lilly is <strong>in</strong>vestigat<strong>in</strong>g ethanolam<strong>in</strong>e-conta<strong>in</strong><strong>in</strong>g<br />
peptide-based BACE <strong>in</strong>hibitors, <strong>in</strong>clud<strong>in</strong>g LY-2070103, for<br />
the potential treatment of Alzheimer's disease. In August<br />
2005, one of the <strong>in</strong>ventors from this team presented<br />
precl<strong>in</strong>ical data from this program at the 230th American<br />
Chemical Society meet<strong>in</strong>g <strong>in</strong> Wash<strong>in</strong>gton DC.<br />
Cardiovascular, ocular and renal<br />
ARYX THERAPEUTICS INC New 4-hydroxycoumar<strong>in</strong><br />
derivatives are vitam<strong>in</strong> K epoxide reductase <strong>in</strong>hibitors -<br />
useful for the treatment of coagulation disorders. WO-<br />
2005100336 (27 October 2005)<br />
• 3-Substituted 4-hydroxy-2-oxo-2H-chrom-3-ene derivatives<br />
are claimed. See WO-02085882 for related warfar<strong>in</strong><br />
analogs. ARYx is <strong>in</strong>vestigat<strong>in</strong>g ATI-5000, a warfar<strong>in</strong><br />
analog identified us<strong>in</strong>g its RetroMetabolic platform<br />
technology, for the potential treatment of deep ve<strong>in</strong><br />
thrombosis and prevention of stroke <strong>in</strong> atrial fibrillation<br />
patients.
6 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
JAPAN HEALTH SCIENCE FOUNDATION; UNIVERSITY OF<br />
TOKUSHIMA Agent for controll<strong>in</strong>g cholesterol<br />
homeostasis-associated gene transcription activity<br />
mediated by FXR activation. WO-2005097097 (20 October<br />
2005)<br />
• Two of the <strong>in</strong>ventors are based at Tokushima Bunri<br />
University, and all are named on WO-2005092328, which<br />
disclosed bis(bibenzyl) cyclic ether derivatives as farnesoid<br />
X-receptor (FXR) activators, useful for the treatment of<br />
hyperlipidemia.<br />
THERAPTOSIS SA Caspase-2 <strong>in</strong>hibitors and their biological<br />
applications. WO-2005105829 (10 November 2005)<br />
• Novel caspase-2 <strong>in</strong>hibitors and their use for treat<strong>in</strong>g<br />
ischemia are claimed. Several of these <strong>in</strong>ventors claimed<br />
double-stranded RNA molecules with this activity <strong>in</strong> WO-<br />
2004103389.
Patent alert<br />
Patent alert provides abstracts and expert commentary on a<br />
selection of recent patents that have been identified as be<strong>in</strong>g<br />
of particular <strong>in</strong>terest. Selections are based on patent abstracts<br />
featured <strong>in</strong> patent products published by Thomson<br />
Scientific. <strong>Current</strong> op<strong>in</strong>ions are provided based on the<br />
novelty of the <strong>in</strong>vention and its potential application.<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 7(1):7-13<br />
© The Thomson Corporation ISSN 1472-4472<br />
Contents<br />
7 Anti-<strong>in</strong>flammatory & immunomodulatory<br />
8 Cardiovascular & renal<br />
9 Central & peripheral nervous system<br />
10 Endocr<strong>in</strong>e & metabolics<br />
12 Oncological<br />
Anti-<strong>in</strong>flammatory & immunomodulatory<br />
Selected by Clifford Whelan (Phlogopharm Ltd, Hatfield,<br />
Hertfordshire, UK)<br />
New C5a receptor <strong>in</strong>hibitory compounds - useful for<br />
treat<strong>in</strong>g, eg, <strong>in</strong>flammation and S aureus <strong>in</strong>fections<br />
ALLIGATOR BIOSCIENCE AB (PUBL) (Van Strijp JAD, De Haas<br />
CJC, Kemm<strong>in</strong>k J, Van Kessel KPM)<br />
WO-2005100385, 27 October 2005<br />
Compounds for prevent<strong>in</strong>g <strong>in</strong>tramolecular contact of Nterm<strong>in</strong>al<br />
residues 10 to 18 of human C5aR with the extracellular<br />
loops, are claimed. Also claimed are further compositions and<br />
use of the compounds for treat<strong>in</strong>g conditions <strong>in</strong>volv<strong>in</strong>g the C5a<br />
receptor on cells other than neutrophils, monocytes and<br />
endothelial cells, for example, <strong>in</strong>flammation, and for use <strong>in</strong><br />
therapeutic vacc<strong>in</strong>es for <strong>in</strong>fections caused by chemotaxis<br />
<strong>in</strong>hibitory prote<strong>in</strong> from Staphylococcus aureus (CHIPS)produc<strong>in</strong>g<br />
bacteria. The agents are stated to be small enough for<br />
use <strong>in</strong> therapy. U937 cells express<strong>in</strong>g C5aR were <strong>in</strong>cubated with<br />
<strong>in</strong>creas<strong>in</strong>g concentrations of CHIPS31-121 or CHIPS31-121<br />
mutant compounds. The samples were further <strong>in</strong>cubated with<br />
10 µg/ml of FITC-labeled anti-C5aR S5/1 monoclonal antibody.<br />
The IC50 values of the CHIPS31-121 mutants, <strong>in</strong> which s<strong>in</strong>gle<br />
am<strong>in</strong>o acids were substituted <strong>in</strong>to alan<strong>in</strong>es, were calculated.<br />
The CHIPS31-121 mutants with the lowest IC50 values (ng/ml)<br />
were N47 (5), R46 (10), Y121 deleted (10), K54 (10), K50 (10),<br />
G102 (12) and K101 (15). Chemical sequences are provided <strong>in</strong><br />
the source document.<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong><br />
S aureus is a common member of the bacterial flora on human<br />
sk<strong>in</strong>. Although its presence is usually symptom free, it can<br />
cause a number of pathologies, rang<strong>in</strong>g from superficial<br />
pustules to major life-threaten<strong>in</strong>g <strong>in</strong>fections. Furthermore, the<br />
evolution of stra<strong>in</strong>s of S aureus that are resistant to antibiotic<br />
therapy makes the development of novel approaches to the<br />
treatment of <strong>in</strong>fection an important therapeutic target.<br />
Neutrophil accumulation at the site of <strong>in</strong>flammation and<br />
<strong>in</strong>fection is a hallmark of acute <strong>in</strong>flammation. Neutrophil<br />
chemotaxis can result from a wide range of compounds and<br />
this may have physiological importance. However, major<br />
chemoattractants <strong>in</strong> acute <strong>in</strong>flammation are complement<br />
products formed from plasma prote<strong>in</strong>. This disclosure describes<br />
a series of prote<strong>in</strong>s that <strong>in</strong>hibit b<strong>in</strong>d<strong>in</strong>g of the complement<br />
product C5a to its receptor. The prote<strong>in</strong>s described are based on<br />
an endogenous prote<strong>in</strong> released by S aureus. Such prote<strong>in</strong>s are<br />
likely to reduce neutrophil accumulation <strong>in</strong> vivo and may even<br />
be of benefit <strong>in</strong> <strong>in</strong>flammatory diseases, such as chronic<br />
obstructive pulmonary disease, <strong>in</strong> which products released by<br />
activated neutrophils appear to <strong>in</strong>itiate changes that are not<br />
beneficial. However, <strong>in</strong> <strong>in</strong>fection, particularly that characterized<br />
by abscess formation, neutrophil chemotaxis appears to conta<strong>in</strong><br />
the <strong>in</strong>fection, and patients who are deficient <strong>in</strong> complement<br />
products seem to suffer severe <strong>in</strong>fections. Thus, further research<br />
is required to determ<strong>in</strong>e whether the prote<strong>in</strong>s described will<br />
have utility <strong>in</strong> the treatment of <strong>in</strong>fection, and to determ<strong>in</strong>e how<br />
they can be utilized as anti-<strong>in</strong>flammatory agents.<br />
New imidazole compounds are H4 receptor <strong>in</strong>hibitors -<br />
useful for the <strong>in</strong>hibition of leukocyte recruitment and for<br />
the treatment of <strong>in</strong>flammation and immune disorders<br />
JANSSEN PHARMACEUTICA NV (Buzard DJ, Edwards JP,<br />
K<strong>in</strong>drachuk DE, Venable JD)<br />
WO-2005092066, 06 October 2005<br />
New imidazole compounds are claimed, as well as their use<br />
as H4 receptor <strong>in</strong>hibitors for the <strong>in</strong>hibition of leukocyte<br />
recruitment and for the treatment of <strong>in</strong>flammation. The<br />
compounds are claimed to be useful for the treatment of<br />
<strong>in</strong>flammatory response (eg, to chemotherapy or <strong>in</strong>fection),<br />
allergy, dermatological disorders, autoimmune disease,<br />
lymphatic disorders, immunodeficiency, asthma, chronic<br />
obstructive pulmonary disease, atherosclerosis, rheumatoid<br />
arthritis, multiple sclerosis and <strong>in</strong>flammatory bowel disease<br />
(eg, Crohn's disease or ulcerative colitis). The compounds<br />
can also be isotopically labeled and used <strong>in</strong> diagnostic<br />
imag<strong>in</strong>g. No suitable advantage is given. The illustrated<br />
compound had a Ki value of 6 nM when tested <strong>in</strong> vitro for its<br />
ability to b<strong>in</strong>d to human histam<strong>in</strong>e H4 receptors expressed<br />
by SK-N-MC or COS7 cells. Seventy specific compounds are<br />
claimed, <strong>in</strong>clud<strong>in</strong>g 1-(3-[4-[4,5-bis-(3-methoxyphenyl)-1Himidazol-2-yl]-3-chlorophenoxy]propyl)-4-methyl[1,4]diazepane.<br />
C<br />
H 3<br />
O<br />
O CH3<br />
H<br />
N<br />
Cl O<br />
N<br />
WO-2005092066<br />
(Janssen)<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong><br />
Leukocyte accumulation is one of the hallmarks of<br />
<strong>in</strong>flammation. Generally <strong>in</strong> the lesion, granulocytes and<br />
macrophages act as effector cells and lymphocytes act to<br />
orchestrate the response. Many reports <strong>in</strong> the literature suggest<br />
N<br />
N<br />
CH 3<br />
7
8 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
that histam<strong>in</strong>e may have a role <strong>in</strong> the process of leukocyte<br />
recruitment by act<strong>in</strong>g on leukocytes to promote chemotaxis,<br />
and by act<strong>in</strong>g on endothelial cells to <strong>in</strong>crease P-select<strong>in</strong><br />
expression and promote leukocyte adhesion. Until recently,<br />
research <strong>in</strong> this area was unclear, partly because the histam<strong>in</strong>e<br />
receptors mediat<strong>in</strong>g these events were not well def<strong>in</strong>ed. The<br />
f<strong>in</strong>d<strong>in</strong>g that leukocytes, such as eos<strong>in</strong>ophils, express histam<strong>in</strong>e<br />
H4 receptors that mediate histam<strong>in</strong>e-<strong>in</strong>duced chemotaxis has<br />
provided researchers with an additional therapeutic target that<br />
this disclosure seeks to exploit.<br />
Eos<strong>in</strong>ophils are thought to be the effector cells responsible for<br />
the <strong>in</strong>flammatory changes that underlie asthma, atopic<br />
dermatitis and other pathologies. Thus, it seems reasonable to<br />
propose that compounds that <strong>in</strong>hibit eos<strong>in</strong>ophil accumulation<br />
<strong>in</strong> tissues will have therapeutic utility. However, a degree of<br />
redundancy exists <strong>in</strong> the <strong>in</strong>flammatory process, which may<br />
enable the body to mount a response <strong>in</strong> the absence of one<br />
pathway. The same appears to be the case with eos<strong>in</strong>ophil<br />
recruitment, where many factors appear to be chemotactic<br />
agents for eos<strong>in</strong>ophils. For example, <strong>in</strong>terleuk<strong>in</strong> (IL)-5 is an<br />
important factor <strong>in</strong> eos<strong>in</strong>ophil recruitment, yet antibodies to<br />
IL-5 failed to produce a cl<strong>in</strong>ically beneficial effect when<br />
adm<strong>in</strong>istered to patients with asthma.<br />
The compounds described <strong>in</strong> this disclosure, if developed,<br />
will enable the role of histam<strong>in</strong>e H4 receptors <strong>in</strong> the process<br />
of leukocyte recruitment to be tested <strong>in</strong> humans. Such trials<br />
will determ<strong>in</strong>e the therapeutic potential of such compounds.<br />
Use of a composition compris<strong>in</strong>g a nicot<strong>in</strong>e ligand and<br />
an antidepressant - for treat<strong>in</strong>g ulcerative colitis<br />
THE JOYCE CLARKE LIVING TRUST AGREEMENT (Clarke DE)<br />
US-20050234024, 20 October 2005<br />
A method for treat<strong>in</strong>g ulcerative colitis <strong>in</strong> a patient hav<strong>in</strong>g<br />
<strong>in</strong>flammatory bowel disease, emphysema, chronic heart<br />
failure, lung cancer and esophageal cancer by adm<strong>in</strong>ister<strong>in</strong>g<br />
a composition compris<strong>in</strong>g a comb<strong>in</strong>ation of nicot<strong>in</strong>e, its<br />
analog or an antagonist, and an antidepressant is claimed. A<br />
substitute for smok<strong>in</strong>g compris<strong>in</strong>g the composition and a kit<br />
compris<strong>in</strong>g the composition are also claimed. No suitable<br />
advantage is given, and no suitable biological data are<br />
presented. The antidepressant is claimed to be bupropion.<br />
N<br />
CH 3<br />
N<br />
US-20050234024<br />
(Joyce Clarke Liv<strong>in</strong>g Trust)<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong><br />
Ulcerative colitis is a common <strong>in</strong>flammatory condition of the<br />
colon that affects <strong>in</strong>dividuals of all ages <strong>in</strong> the developed<br />
world. It has a major impact on the quality of life of those<br />
affected and has an impact on the economy of developed<br />
countries. Furthermore, ulcerative colitis is not well treated,<br />
thus there is a need for an effective therapy, particularly one<br />
that reduces the frequency of hospital admissions.<br />
It is well documented that the <strong>in</strong>cidence of ulcerative colitis<br />
among non-smokers is 3- to 4-fold greater than among smokers<br />
and that nicot<strong>in</strong>e appears to be responsible for this protective<br />
effect. In addition, when tobacco smokers cease smok<strong>in</strong>g,<br />
ulcerative colitis is often precipitated. While nicot<strong>in</strong>e can be<br />
used to treat ulcerative colitis, it is addictive and has many<br />
actions on the cardiovascular system. Some laboratories have<br />
<strong>in</strong>vestigated whether the mechanism of the addictive effect of<br />
nicot<strong>in</strong>e is dist<strong>in</strong>ct from the beneficial action with a view to<br />
develop<strong>in</strong>g a selective agent, although none of these projects<br />
has resulted <strong>in</strong> a cl<strong>in</strong>ically useful agent.<br />
Bupropion is used when smokers are attempt<strong>in</strong>g to reduce<br />
their dependence on nicot<strong>in</strong>e (tobacco), although this drug is<br />
not without adverse events. This disclosure describes an<br />
<strong>in</strong>terest<strong>in</strong>g comb<strong>in</strong>ation for the treatment of ulcerative<br />
colitis, <strong>in</strong> which nicot<strong>in</strong>e is used to treat colitis and<br />
bupropion is used to prevent the depression that occurs on<br />
withdrawal of the nicot<strong>in</strong>e. Whether or not bupropion will<br />
prevent nicot<strong>in</strong>e addiction is unclear. Furthermore, it seems<br />
unlikely that the addition of bupropion will prevent adverse<br />
cardiovascular effects. Thus, much research is required to<br />
see if this approach to the treatment of a disease with much<br />
unmet medical need will have utility.<br />
Cardiovascular & renal<br />
Selected by Hermann AM Mucke (Pharmaceutical<br />
Consultant and Analyst, Vienna, Austria) and Clifford<br />
Whelan (Phlogopharm Ltd, Hatfield, Hertfordshire, UK)<br />
New 4-hydroxycoumar<strong>in</strong> derivatives are vitam<strong>in</strong> K<br />
epoxide reductase <strong>in</strong>hibitors - useful for the treatment of<br />
coagulation disorders<br />
ARYX THERAPEUTICS (Druzgala P, Becker C)<br />
WO-2005100336, 27 October 2005<br />
Novel 4-hydroxycoumar<strong>in</strong> derivatives, their salts and<br />
compositions conta<strong>in</strong><strong>in</strong>g them are claimed. The compounds<br />
are disclosed to be useful for the treatment of coagulation<br />
disorders and to act by <strong>in</strong>hibit<strong>in</strong>g vitam<strong>in</strong> K epoxide<br />
reductase. The compounds are stable, and have a shorter<br />
half-life and a lower <strong>in</strong>cidence of side effects and toxicity<br />
compared with prior art anticoagulants. The effect of several<br />
compounds on vitam<strong>in</strong> K epoxide reductase activity was<br />
determ<strong>in</strong>ed. The specified compound displayed an IC50<br />
value of 5.07 µM. The stability of the compounds to<br />
metabolism by pooled human liver microsomes, conta<strong>in</strong><strong>in</strong>g<br />
both CYP450 and esterase, with or without an NADPH cofactor,<br />
was also determ<strong>in</strong>ed. The specified compound had<br />
stabilities at 90 m<strong>in</strong> of 91 and 96%, respectively, and stability<br />
<strong>in</strong> buffer of 92% at 90 m<strong>in</strong>; both the compound and its<br />
correspond<strong>in</strong>g acid metabolite had no <strong>in</strong>hibitory effect on<br />
human IKr <strong>in</strong> stably transfected HEK-293 cells, nor <strong>in</strong> a broad<br />
cellular and biochemical receptor screen<strong>in</strong>g assay. The<br />
specified compound, 1,1,1,3,3,3-hexafluoro-2-methylpropan-<br />
2-yl 4-((4-hydroxy-2-oxo-2H-chromen-3-yl)methyl)benzoate,<br />
is the only compound specifically claimed for use.
OH<br />
O O<br />
WO-2005100336<br />
(Aryx)<br />
C<br />
H 3<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong><br />
Vitam<strong>in</strong> K epoxide reductase recycles the epoxide created by<br />
γ-glutamyl carboxylase before vitam<strong>in</strong> K can be re-used as an<br />
essential cofactor for the post-translational γ-carboxylation of<br />
several blood coagulation factors. Genetic polymorphisms of<br />
this quite recently uncovered enzyme complex could be partly<br />
responsible for the variable response to warfar<strong>in</strong> therapy, but<br />
polymorphisms <strong>in</strong> the CYP2C9 gene, affect<strong>in</strong>g S-warfar<strong>in</strong><br />
clearance, are probably more important. This has<br />
spurred development of warfar<strong>in</strong> analogs (<strong>in</strong>clud<strong>in</strong>g<br />
4-hydroxycoumar<strong>in</strong>s) as more predictable anticoagulants. The<br />
compounds of the <strong>in</strong>vention conta<strong>in</strong> a halogenated ester group,<br />
which makes them more susceptible to degradation by<br />
hydrolases, while reduc<strong>in</strong>g or elim<strong>in</strong>at<strong>in</strong>g their CYP450<br />
metabolism. This should greatly alleviate the problem of drug<br />
<strong>in</strong>teraction, which is also typical for warfar<strong>in</strong>. Such designed<br />
compounds could offer powerful alternatives to the current<br />
platelet aggregation <strong>in</strong>hibitors.<br />
Use of a composition to <strong>in</strong>hibit PUMA function <strong>in</strong><br />
cardiomyocytes - for prevent<strong>in</strong>g or reduc<strong>in</strong>g<br />
ischemia/reperfusion-<strong>in</strong>duced myocardial cell death<br />
BOSTON BIOMEDICAL RESEARCH INSTITUTE (Erhardt P, Toth A)<br />
WO-2005099772, 27 October 2005<br />
The use of a composition to <strong>in</strong>hibit p53 upregulated modulator<br />
of apoptosis (PUMA) function <strong>in</strong> cardiomyocytes is claimed for<br />
prevent<strong>in</strong>g or reduc<strong>in</strong>g ischemia/reperfusion <strong>in</strong>duced<br />
myocardial cell death. The composition is adm<strong>in</strong>istered dur<strong>in</strong>g<br />
or after an ischemic attack, and <strong>in</strong>hibits b<strong>in</strong>d<strong>in</strong>g of PUMA to<br />
Bcl-2 or Bcl-xL. It is claimed that the <strong>in</strong>vention is also useful for<br />
screen<strong>in</strong>g for <strong>in</strong>hibitors of PUMA expression, for prevent<strong>in</strong>g<br />
cell death <strong>in</strong> stem-cell explants <strong>in</strong>tended to restore cardiac<br />
function. The <strong>in</strong>vention provides an effective means of<br />
protect<strong>in</strong>g cardiomyocytes from cell death follow<strong>in</strong>g<br />
myocardial <strong>in</strong>farction. The hearts of PUMA-deficient mice<br />
showed significantly better functional recovery at the end of<br />
reperfusion than hearts from wild-type litter mates, <strong>in</strong>clud<strong>in</strong>g<br />
recovery of left ventricular developed pressure, first derivatives<br />
of left ventricular pressure, and left ventricular end-diastolic<br />
pressure. In addition, the functional recovery of PUMAdeficient<br />
hearts accompanies correspond<strong>in</strong>g <strong>in</strong>hibition of<br />
apoptosis and necrosis as well as reduced <strong>in</strong>farct size. Chemical<br />
structures are provided <strong>in</strong> the source document.<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong><br />
Follow<strong>in</strong>g stroke or myocardial <strong>in</strong>farction, cells that are<br />
deprived of a blood supply die. On reperfusion, many cells<br />
that are at risk also die, often as a result of free radical<br />
damage. Whereas cells killed as a direct result of the <strong>in</strong>farct<br />
die from necrosis, those exposed to free radicals may<br />
undergo apoptosis. Thus, an agent that <strong>in</strong>hibits apoptosis<br />
may have utility <strong>in</strong> the acute therapy of ischemic disease.<br />
The p53 gene modulates apoptosis and offers an attractive<br />
O<br />
O<br />
F<br />
F<br />
F<br />
F<br />
F<br />
F<br />
Patent alert 9<br />
target for the development of agents that modulate this<br />
process.<br />
This disclosure describes some experiments <strong>in</strong> which mice<br />
deficient <strong>in</strong> the p53 upregulated modulator of apoptosis, a<br />
factor that promotes apoptosis, developed smaller <strong>in</strong>farcts<br />
and showed better recovery <strong>in</strong> a model of myocardial<br />
<strong>in</strong>farction than their wild-type litter mates. Thus, <strong>in</strong><br />
pr<strong>in</strong>ciple, <strong>in</strong>hibition of apoptosis leads to a reduction <strong>in</strong><br />
<strong>in</strong>farct size and improved recovery. The disclosure claims<br />
the use of antisense oligonucleotides as a means of <strong>in</strong>hibit<strong>in</strong>g<br />
apoptosis, although it is not clear how these agents would be<br />
used therapeutically. Patients present cl<strong>in</strong>ically with an<br />
<strong>in</strong>farct, thus any therapy with a long onset of action may not<br />
have utility. Alternatively, the use of such compounds as<br />
prophylactic agents <strong>in</strong> patients with a history of<br />
cardiovascular disease may render these patients susceptible<br />
to the development of tumors, given that many tumors do<br />
not undergo apoptosis as a result of mutations <strong>in</strong> the p53<br />
gene. Thus, while this disclosure is an <strong>in</strong>terest<strong>in</strong>g concept,<br />
further research is required before the utility of the<br />
hypothesis can be tested cl<strong>in</strong>ically.<br />
Central & peripheral nervous system<br />
Selected by Hermann AM Mucke (Pharmaceutical<br />
Consultant and Analyst, Vienna, Austria)<br />
Use of an annex<strong>in</strong> II <strong>in</strong>hibitor - for treat<strong>in</strong>g<br />
neurodegenerative diseases or CNS disorders<br />
QUARK BIOTECH INC/FUJISAWA PHARMACEUTICAL CO LTD<br />
(Fe<strong>in</strong>ste<strong>in</strong> EM, Mett I, Shtutman M)<br />
WO-2005091716, 06 October 2005<br />
A method for treat<strong>in</strong>g neurodegenerative diseases, central<br />
nervous system (CNS) disorders or <strong>in</strong>jury to CNS, for example,<br />
sp<strong>in</strong>al cord <strong>in</strong>jury and traumatic bra<strong>in</strong> <strong>in</strong>jury, compris<strong>in</strong>g<br />
adm<strong>in</strong>ister<strong>in</strong>g a composition of an annex<strong>in</strong> II <strong>in</strong>hibitor is<br />
claimed. The use of an annex<strong>in</strong> II <strong>in</strong>hibitor for promot<strong>in</strong>g or<br />
enhanc<strong>in</strong>g recovery from the claimed diseases and an <strong>in</strong>hibitor<br />
of annex<strong>in</strong> II are also claimed. The neurodegenerative diseases<br />
are claimed to be stroke, hypertension, cerebral vascular<br />
disease, systemic hypotension, Park<strong>in</strong>son's disease, epilepsy,<br />
depression, amyotrophic lateral sclerosis, Alzheimer's disease,<br />
Hunt<strong>in</strong>gton's disease and HIV-<strong>in</strong>duced dementia. A method for<br />
diagnos<strong>in</strong>g neurodegenerative diseases and ischemic events by<br />
detect<strong>in</strong>g the levels of annex<strong>in</strong> II polypeptide is disclosed. The<br />
annex<strong>in</strong> II <strong>in</strong>hibitor is disclosed to <strong>in</strong>hibit neurotoxic-stress<strong>in</strong>duced<br />
apoptosis. No suitable advantage is given, and no<br />
suitable biological data are presented. The annex<strong>in</strong> II <strong>in</strong>hibitor is<br />
claimed to be a compound, for example, sodium nitroprusside<br />
or Tyrphost<strong>in</strong> AG1024, or an antisense polynucleotide.<br />
Chemical sequences are provided <strong>in</strong> the source document.<br />
C<br />
H 3<br />
C<br />
H 3<br />
HO<br />
CH 3<br />
Br<br />
N<br />
WO-2005091716<br />
(Quark Biotech/Fujisawa)<br />
N
10 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong><br />
The annex<strong>in</strong>s are a family of highly homologous calcium<br />
and phospholipid b<strong>in</strong>d<strong>in</strong>g prote<strong>in</strong>s. Annex<strong>in</strong> II serves as a<br />
co-receptor for both plasm<strong>in</strong>ogen and tissue plasm<strong>in</strong>ogen<br />
activator on endothelial cells and greatly facilitates the<br />
generation of plasm<strong>in</strong>. Its primary role is believed to be <strong>in</strong><br />
coagulation, although <strong>in</strong>volvement <strong>in</strong> cell-membrane fusion<br />
and cancer <strong>in</strong>vasion has also been demonstrated. This<br />
<strong>in</strong>vention relates to the discovery that the expression of<br />
annex<strong>in</strong> II is <strong>in</strong>volved <strong>in</strong> neuronal apoptosis <strong>in</strong>duced by<br />
oxidative or ischemic stress. Us<strong>in</strong>g stroke-specific neuronal<br />
cDNA subtraction libraries on microarrays prepared from<br />
rats before and after middle cerebral artery occlusion, the<br />
<strong>in</strong>ventors determ<strong>in</strong>ed that the annex<strong>in</strong> II gene is upregulated<br />
with<strong>in</strong> 6 h of ischemia, reaches a maximum at 48 h and can<br />
be repressed <strong>in</strong> vivo by pre-treatment with a specific siRNA.<br />
In situ hybridization demonstrated <strong>in</strong>duction of prote<strong>in</strong><br />
expression on leukocytes and macrophages, but not <strong>in</strong><br />
neurons, which makes the <strong>in</strong>vention less surpris<strong>in</strong>g because<br />
this <strong>in</strong>dicates that the neurotoxic action of annex<strong>in</strong> II is not a<br />
direct one; rather it ties <strong>in</strong>to known mechanisms. Only<br />
detailed functional studies can reveal if this prote<strong>in</strong> could<br />
actually become a drug target or rather should be 'better left<br />
alone' (Blood (2005) 105(5):1845-1846).<br />
New g<strong>in</strong>kgolide derivatives and compositions are<br />
amyloid β prote<strong>in</strong> <strong>in</strong>hibitors - useful for the treatment of<br />
Alzheimer's disease<br />
THE TRUSTEES OF COLUMBIA UNIVERSITY IN THE CITY OF NEW<br />
YORK (Vitolo OV, Nakanishi K, Shelanski ML, Krane S, Arancio<br />
O, Jaracz S, Berova ND)<br />
WO-2005092324, 06 October 2005<br />
Novel g<strong>in</strong>kgolide derivatives, compositions conta<strong>in</strong><strong>in</strong>g<br />
them, optionally <strong>in</strong> comb<strong>in</strong>ation with an antioxidant,<br />
compositions compris<strong>in</strong>g a mixture of g<strong>in</strong>kgolides, a process<br />
for the extraction of G<strong>in</strong>kgo biloba, and the use of the<br />
compositions for the treatment of neurological and<br />
neurodegenerative disease, especially Alzheimer's disease,<br />
are claimed. The composition produced by the claimed<br />
process is stated to be more efficacious than the currently<br />
available standardized extract Egb-761. Compounds were<br />
tested as <strong>in</strong>hibitors of β-amyloid (1-42) prote<strong>in</strong>-<strong>in</strong>duced<br />
long-term potentiation (LTP) <strong>in</strong> a hippocampal slice assay.<br />
At concentrations of 1 µM, g<strong>in</strong>kgolide J and g<strong>in</strong>kgolide A<br />
both restored long-term potentiation values to control levels,<br />
while neither g<strong>in</strong>kgolide B nor g<strong>in</strong>kgolide C was effective.<br />
Several compounds are specifically claimed for use, for<br />
example, g<strong>in</strong>kgolide J. Compositions conta<strong>in</strong><strong>in</strong>g g<strong>in</strong>kgolide J<br />
and g<strong>in</strong>kgolide A are also claimed.<br />
O<br />
O<br />
H<br />
CH 3<br />
OH CH3 CH<br />
OH 3<br />
O<br />
CH 3<br />
O<br />
O<br />
OH O H<br />
O<br />
WO-2005092324<br />
(Trustees of Columbia University)<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong><br />
When extracts from G<strong>in</strong>kgo biloba were first offered as<br />
cognition enhancers several decades ago, their scientific<br />
foundation was extremely narrow, and even a decade ago<br />
our knowledge at the molecular level was limited. Today,<br />
hardly a month passes <strong>in</strong> which the peer-reviewed and<br />
patent literature does not carry new, well-founded<br />
contributions concern<strong>in</strong>g G<strong>in</strong>kgo compounds. That<br />
g<strong>in</strong>kgolide B can block β-amyloid (1-42)-<strong>in</strong>duced<br />
neurotoxicity had been published before, but scientists from<br />
Columbia University have now extended this to g<strong>in</strong>kgolides<br />
A and J. More importantly, they have shown that these<br />
molecules also <strong>in</strong>hibit β-amyloid blockade of neuronal LTP.<br />
At concentrations of 1 µM, g<strong>in</strong>kgolides A and J both restored<br />
LTP <strong>in</strong> hippocampal slices to control levels, while the B- and<br />
C-type molecules were <strong>in</strong>effective. Less than a month before<br />
the pert<strong>in</strong>ent March 2004 priority date, a Ukra<strong>in</strong>ian research<br />
group had published the f<strong>in</strong>d<strong>in</strong>g that 5 µM of g<strong>in</strong>kgolide B<br />
(but not J) completely <strong>in</strong>hibited the <strong>in</strong>duction of<br />
hippocampal LTP (Neurochem Int (2004) 44(3):171-177). LTP<br />
modulation has much more profound therapeutic<br />
implications than simple neuroprotection, and <strong>in</strong> the case of<br />
the g<strong>in</strong>kgolides it might be caused by the <strong>in</strong>terplay of two<br />
mechanisms: blockade of glyc<strong>in</strong>e b<strong>in</strong>d<strong>in</strong>g sites and<br />
antagonism of receptors for platelet-activat<strong>in</strong>g factor, a<br />
bioactive lipid that has been proposed to be a retrograde<br />
mediator of LTP.<br />
Endocr<strong>in</strong>e & metabolics<br />
Selected by Peter Norman (Norman Consult<strong>in</strong>g, Burnham,<br />
Bucks, UK)<br />
New sulfonamide derivatives are PPARα agonists -<br />
useful for the treatment of, eg, lipid disorders and<br />
atherosclerosis<br />
PFIZER PRODUCTS INC (Hamanaka ES, Kehrli ME Jr)<br />
WO-2005092845, 06 October 2005<br />
Novel sulfonamide derivatives, their salts or prodrugs,<br />
compositions conta<strong>in</strong><strong>in</strong>g them, optionally <strong>in</strong> comb<strong>in</strong>ation<br />
with additional active <strong>in</strong>gredients, and methods of their use for<br />
the treatment of dyslipidemia, obesity, hypertriglyceridemia,<br />
hyperlipidemia, hypoalphalipoprote<strong>in</strong>emia, metabolic<br />
syndrome, diabetes mellitus, hyper<strong>in</strong>sul<strong>in</strong>emia, impaired<br />
glucose tolerance, <strong>in</strong>sul<strong>in</strong> resistance, diabetic complications,<br />
atherosclerosis, hypertension, coronary heart disease,<br />
hypercholesterolemia, <strong>in</strong>flammation, osteoporosis,<br />
thrombosis, peripheral vascular disease, cognitive<br />
dysfunction or congestive heart failure are claimed. These<br />
compounds are stated to be peroxisome proliferatoractivated<br />
receptor (PPAR) agonists, particularly PPARα<br />
agonists. No suitable advantage is given. The ability of the<br />
compounds to reduce postpartum serum non-esterified fatty<br />
acid (NEFA) and liver triglyceride levels was determ<strong>in</strong>ed <strong>in</strong><br />
calv<strong>in</strong>g dairy cattle follow<strong>in</strong>g dos<strong>in</strong>g (route unspecified) on<br />
alternate days <strong>in</strong> the week prior to calv<strong>in</strong>g and for 8 days<br />
follow<strong>in</strong>g. Several compounds are specifically claimed, for<br />
example, 2-methyl-5-(4'-trifluoromethoxybiphenyl-4-ylsulfamoyl)-benzoic<br />
acid, which significantly (p < 0.01)
educed serum NEFA and liver triglyceride levels at a dose<br />
of 0.5 mg/kg. Functional and anti-atherosclerotic studies are<br />
additionally described, but no result<strong>in</strong>g data are presented.<br />
F<br />
F<br />
F<br />
O<br />
H<br />
N<br />
S<br />
O O<br />
WO-2005092845<br />
(Pfizer)<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong><br />
PPAR agonists of vary<strong>in</strong>g specificities have attracted<br />
considerable attention for the treatment of various metabolic<br />
disorders. However, their development has encountered<br />
many problems ow<strong>in</strong>g to side effects and toxicity, lead<strong>in</strong>g to<br />
the abandonment of many compounds and caus<strong>in</strong>g the Food<br />
and Drug Adm<strong>in</strong>istration (FDA) to impose additional<br />
toxicology requirements for this class of compounds. The<br />
FDA's rejection of the dual PPAR agonist muraglitazar has<br />
prompted Bristol-Myers Squibb Co and Merck & Co Inc to<br />
consider discont<strong>in</strong>u<strong>in</strong>g development of the drug. This<br />
application is notable for two reasons: first, Pfizer has shown<br />
limited <strong>in</strong>terest <strong>in</strong> the development of PPAR agonists, and<br />
second, because the acid head group <strong>in</strong> the claimed<br />
compounds is present as a benzoic acid rather than the more<br />
common phenylpropionic acid or its isosteres.<br />
Use of alkyne MCH antagonists - for the treatment of,<br />
eg, obesity, metabolic disorders or diabetes<br />
BOEHRINGER INGELHEIM INTERNATIONAL GMBH (Stenkamp D,<br />
Mueller SG, Lustenberger P, Lehmann-L<strong>in</strong>tz T, Roth GJ, Rudolf<br />
K, Sch<strong>in</strong>dler M, Thomas L, Lotz R)<br />
US-20050234101, 20 October 2005<br />
The use of alkyne derivatives, their tautomers, enantiomers<br />
or salts, or compositions compris<strong>in</strong>g them, to <strong>in</strong>fluence<br />
eat<strong>in</strong>g behavior, reduce body weight or prevent or treat a<br />
metabolic disorder is claimed. The metabolic disorder is<br />
claimed to be selected from the group consist<strong>in</strong>g of bulimia,<br />
bulimia nervosa, cachexia, anorexia, anorexia nervosa or<br />
hyperphagia. The compounds are also claimed to be useful<br />
for the treatment of diabetes, diabetic ret<strong>in</strong>opathy,<br />
neuropathy or nephropathy, <strong>in</strong>sul<strong>in</strong> resistance, cardiac<br />
<strong>in</strong>sufficiency, arteriosclerosis, high blood pressure, arthritis,<br />
hyperlipidemia, mastocytosis, emotional disorders, affective<br />
disorders, depression, anxiety, sleep disorders, reproductive<br />
disorders, sexual disorders, memory disorders, epilepsy,<br />
dementia, hormonal disorders, ur<strong>in</strong>ary <strong>in</strong>cont<strong>in</strong>ence,<br />
hyperactive ur<strong>in</strong>ary bladder, urgency or enuresis, and<br />
dependencies or withdrawal symptoms. The compounds are<br />
stated to act as melan<strong>in</strong> concentrat<strong>in</strong>g hormone (MCH)<br />
antagonists. No specific advantage is given. The activity of<br />
these compounds was assessed <strong>in</strong> an MCH-1 receptorb<strong>in</strong>d<strong>in</strong>g<br />
test. Several compounds are specifically claimed, for<br />
example, (2-{4-[5-(4-chlorophenyl)pyrid<strong>in</strong>-2-ylethynyl]-2methylphenoxy}ethyl)(cyclohexyl)cyclopentylam<strong>in</strong>e,<br />
which<br />
had an IC50 value of 6.2 nM.<br />
O<br />
OH<br />
CH 3<br />
N<br />
O<br />
C<br />
H 3<br />
US-20050234101<br />
(Boehr<strong>in</strong>ger Ingelheim)<br />
N<br />
Patent alert 11<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong><br />
Obesity is a major problem <strong>in</strong> all developed countries and is<br />
an underly<strong>in</strong>g causal factor <strong>in</strong> the development of many<br />
other conditions, such as type 2 diabetes and heart disease.<br />
Despite this, there are few approved therapeutic agents for<br />
the treatment of obesity, and none of the currently marketed<br />
drugs are well tolerated. A number of new approaches for<br />
the treatment of obesity are under <strong>in</strong>vestigation and the<br />
development of MCH antagonists is prom<strong>in</strong>ent <strong>in</strong> this<br />
regard. Boehr<strong>in</strong>ger has not previously shown an <strong>in</strong>terest <strong>in</strong><br />
this target; however, this application and WO-2005085221<br />
suggest that this is another research area <strong>in</strong> which the<br />
company is actively <strong>in</strong>volved, and that it is seek<strong>in</strong>g to<br />
expand its metabolic disease portfolio.<br />
New substituted pyrimid<strong>in</strong>e derivatives are DPP-IV<br />
<strong>in</strong>hibitors - useful for treat<strong>in</strong>g, eg, diabetes, cancer,<br />
autoimmune disease, HIV <strong>in</strong>fection and immunodeficiency<br />
SYRRX INC (Feng J, Gwaltney SL, Stafford JA, Zhang Z)<br />
WO-2005095381, 13 October 2005<br />
Novel substituted pyrimid<strong>in</strong>e and related derivatives, a<br />
process for their preparation and methods of their use for<br />
<strong>in</strong>hibit<strong>in</strong>g dipeptidyl peptidase (DPP)-IV and for the<br />
treatment of types 1 and 2 diabetes, cancer (particularly<br />
colorectal, prostate, breast, thyroid, sk<strong>in</strong>, lung or head and<br />
neck cancer), autoimmune disorders (<strong>in</strong>clud<strong>in</strong>g rheumatoid<br />
arthritis, psoriasis and multiple sclerosis), HIV <strong>in</strong>fection,<br />
<strong>in</strong>adequate lymphocyte or hematopoietic cell levels,<br />
chemotherapy or radiation therapy side effects (particularly<br />
kidney failure and bone marrow disorders) and<br />
immunodeficiency are claimed. The compounds are<br />
selective for DPP-IV over other proteases. Protocols for<br />
protease <strong>in</strong>hibition assays are described. The compounds are<br />
stated to exhibit selective DPP-IV <strong>in</strong>hibitory activity at<br />
concentrations of at least 50-fold less than those required to<br />
<strong>in</strong>hibit fibroblast activation prote<strong>in</strong>-α, with Ki values<br />
rang<strong>in</strong>g between 10 -9 and 10 -5 M, but no specific data are<br />
presented. Several compounds are specifically claimed,<br />
<strong>in</strong>clud<strong>in</strong>g 2-(6-[3(R)-am<strong>in</strong>opiperid<strong>in</strong>-1-yl]-3-methyl-2,4-dioxo-<br />
3,4-dihydro-2H-pyrimid<strong>in</strong>-1-ylmethyl)benzonitrile.<br />
N<br />
H 2<br />
N<br />
N<br />
N<br />
O<br />
N<br />
WO-2005095381<br />
(Syrrx)<br />
O<br />
CH 3<br />
Cl
12 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong><br />
A number of new approaches to the treatment of diabetes<br />
are be<strong>in</strong>g pursued. Of these, the development of DPP-IV<br />
<strong>in</strong>hibitors is by far the most advanced, with three<br />
compounds (MK-431 (Merck & Co Inc/Banyu<br />
Pharmaceutical Co Ltd/Ono Pharmaceutical Co Ltd),<br />
saxaglipt<strong>in</strong> (Bristol-Myers Squibb Co) and vildaglipt<strong>in</strong><br />
(Novartis Institutes for BioMedical Research Inc)) currently<br />
<strong>in</strong> phase III cl<strong>in</strong>ical trials. These compounds, like nearly all<br />
other DPP-IV <strong>in</strong>hibitors, are based on the almost ubiquitous<br />
2-pyrrolonitrile chemotype. Few other chemotypes have<br />
been described, and the compounds claimed <strong>in</strong> this<br />
application represent a considerable variation <strong>in</strong> this regard.<br />
This difference may be due to the successful exploitation of<br />
structure-aided drug design that is the focus of research at<br />
Takeda San Diego (formerly Syrrx).<br />
Oncological<br />
Selected by Peter Norman (Norman Consult<strong>in</strong>g, Burnham,<br />
Bucks, UK)<br />
New 6-phenylfuro[2,3-d]pyrimid<strong>in</strong>e derivatives are DDR2<br />
tyros<strong>in</strong>e k<strong>in</strong>ase <strong>in</strong>hibitors - useful for the treatment of<br />
rheumatoid arthritis, cirrhosis and cancer<br />
KOREA INSTITUTE OF SCIENCE AND TECHNOLOGY/JEIL<br />
PHARMACEUTICAL CO LTD (Yang B-S, Yang K-M, Kim H-J, Park<br />
I-S, Park S-D, Lee J-H, Kwon H-M, Woo B-Y)<br />
WO-2005092896, 06 October 2005<br />
Novel 6-phenylfuro[2,3-d]pyrimid<strong>in</strong>e derivatives and their<br />
salts, compositions conta<strong>in</strong><strong>in</strong>g them, their use as <strong>in</strong>hibitors<br />
of the discoid<strong>in</strong> doma<strong>in</strong> receptor (DDR)2 tyros<strong>in</strong>e k<strong>in</strong>ase,<br />
and <strong>in</strong> the treatment of hepatocirrhosis, rheumatism and<br />
cancer are claimed. The DDR prote<strong>in</strong> has been reported to<br />
enhance the development of fibroblasts and to show<br />
<strong>in</strong>creased expression <strong>in</strong> metastatic cancer cells. The claimed<br />
compounds are the first low-molecular-weight <strong>in</strong>hibitors of<br />
DDR2 k<strong>in</strong>ase described. In a rat cannulated bile duct model<br />
of cirrhosis, adm<strong>in</strong>istration of one compound (10<br />
mg/kg/day for 2 weeks) <strong>in</strong>hibited hydroxy furor<strong>in</strong><br />
production from 4.93 to 2.23 mg/g (the normal level).<br />
Approximately 200 compounds are exemplified. No<br />
compounds are specifically claimed.<br />
Cl<br />
O<br />
N<br />
CH3 HN<br />
WO-2005092896<br />
(Korea Institute of Science and Technology/Jeil)<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong><br />
DDR2 is a widely expressed member of a subfamily of<br />
receptor tyros<strong>in</strong>e k<strong>in</strong>ases whose ligands are fibrillar<br />
collagens. Studies <strong>in</strong> knockout mice suggest that it acts to<br />
regulate cellular proliferation and, for example, fibroblast<br />
signal<strong>in</strong>g. Tyros<strong>in</strong>e k<strong>in</strong>ases <strong>in</strong> this subfamily have attracted<br />
little attention until now, thus the appearance of this<br />
application claim<strong>in</strong>g the first documented <strong>in</strong>hibitors of<br />
N<br />
S<br />
N<br />
N<br />
DDR2 k<strong>in</strong>ase is likely to evoke considerable efforts <strong>in</strong> the<br />
field. The claimed compounds also represent a novel<br />
chemotype of tyros<strong>in</strong>e k<strong>in</strong>ase <strong>in</strong>hibitor, which may have<br />
enhanced selectivity compared with the better characterized<br />
tyros<strong>in</strong>e k<strong>in</strong>ases.<br />
New thioalkeneamide derivatives are transketolase<br />
<strong>in</strong>hibitors - useful for the treatment of cancer<br />
ARRAY BIOPHARMA INC (Boyd SA)<br />
WO-2005095344, 13 October 2005<br />
Novel thioalkeneamide derivatives and their use, either<br />
alone or <strong>in</strong> comb<strong>in</strong>ation with a thiam<strong>in</strong>e-restricted diet<br />
and/or other therapeutic agents, to <strong>in</strong>hibit transketolase<br />
activity and cellular nucleic acid synthesis, and to reduce the<br />
cellular levels of ribulose/ribose-5-phosphate are claimed.<br />
These compounds are also claimed to <strong>in</strong>crease apoptosis <strong>in</strong><br />
tumor cells and to reduce tumor growth. They are stated to<br />
be additionally useful as <strong>in</strong>hibitors of metastasis and<br />
angiogenesis. No suitable advantage is given. Several<br />
compounds are specifically claimed, <strong>in</strong>clud<strong>in</strong>g N-(2-am<strong>in</strong>o-6methylpyrid<strong>in</strong>-3-ylmethyl)-N-{2-[2-[(2-am<strong>in</strong>o-6-methylpyrid<strong>in</strong>-3ylmethyl)formylam<strong>in</strong>o]-1-(2-hydroxyethyl)-propenyl-disulfanyl]-<br />
4-hydroxy-1-methylbut-1-enyl}formamide (AR-00342632), which<br />
had an IC50 value of 10 nM aga<strong>in</strong>st HCT116 colon carc<strong>in</strong>oma<br />
cells <strong>in</strong> vitro.<br />
C<br />
H 3<br />
N<br />
NH 2<br />
C<br />
H 3<br />
N<br />
O<br />
H<br />
S S<br />
OH<br />
OH<br />
H<br />
WO-2005095344<br />
(Array)<br />
N<br />
CH 3<br />
O NH 2<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong><br />
Transketolase is a metabolic enzyme that plays a crucial role<br />
<strong>in</strong> tumor cell nucleic acid synthesis, us<strong>in</strong>g glucose through<br />
the elevated non-oxidative pentose phosphate pathway.<br />
Thus, <strong>in</strong>hibitors of this enzyme constitute a novel approach<br />
to the treatment of cancer. To date, this possibility has been<br />
almost completely neglected, with only Array's disclosure of<br />
the activity of AR-00342632 at the 2005 American Chemical<br />
Society meet<strong>in</strong>g, and S*BIO and Chiron's description of the<br />
identification of lead compounds via high-throughput<br />
screen<strong>in</strong>g <strong>in</strong>dicat<strong>in</strong>g any <strong>in</strong>terest. This application was one<br />
of two from Array (see also WO-2005095391). AVEO<br />
Pharmaceuticals published WO-2005094803 claim<strong>in</strong>g such<br />
<strong>in</strong>hibitors on the same day.<br />
New 2-am<strong>in</strong>omethylthiazole-5-carboxamide derivatives<br />
are prote<strong>in</strong> k<strong>in</strong>ase modulators - useful for the treatment<br />
of, eg, neurological disease and cancer<br />
LEXICON GENETICS INC (J<strong>in</strong> H, Shi Z-C, Theis H, Kolb H)<br />
WO-2005097766, 20 October 2005<br />
New 2-am<strong>in</strong>omethylthiazole-5-carboxamide derivatives,<br />
their compositions, and their use for the treatment of, for<br />
example, allergy, cardiovascular disease, cancer, dental<br />
disease, dermatological disease, endocr<strong>in</strong>e disease,<br />
metabolic disorder, gastro<strong>in</strong>test<strong>in</strong>al disease, genitour<strong>in</strong>ary<br />
N<br />
CH 3
disease, hematological disease, hepatobiliary disease,<br />
<strong>in</strong>fection, musculoskeletal disease, neurological disease,<br />
nutritional disorder, ocular disease, psychiatric disorder,<br />
pulmonary disease and leukemia are claimed. It is disclosed<br />
that the compounds can be used for the treatment of<br />
diseases mediated by prote<strong>in</strong> k<strong>in</strong>ase <strong>in</strong>hibition. No suitable<br />
advantage is given. No biological data are presented. The<br />
specified compound is one of several 2-am<strong>in</strong>omethylthiazole-5-carboxamide<br />
compounds specifically claimed.<br />
C<br />
H 3<br />
N<br />
N<br />
S<br />
N<br />
N<br />
H<br />
O<br />
WO-2005097766<br />
(Lexicon Genetics)<br />
CH 3<br />
O CH3<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong><br />
Lexicon Genetics is one of several genomics companies that<br />
has switched its bus<strong>in</strong>ess strategy to pursue the<br />
development of small-molecule therapeutics. In January<br />
2005, Lexicon Genetics <strong>in</strong>dicated that it had identified two<br />
small-molecule candidates, the more advanced of which<br />
(LX-1521) is an anti-apoptotic k<strong>in</strong>ase <strong>in</strong>hibitor discovered<br />
from Lexicon's LG152 k<strong>in</strong>ase target program. Until October<br />
2005, Lexicon Genetics had not published any patent<br />
applications claim<strong>in</strong>g k<strong>in</strong>ase <strong>in</strong>hibitors. The appearance of<br />
this application and WO-2005095420, which claims<br />
thiazolopyrazoles, provides the first <strong>in</strong>dication as to the<br />
chemical strategy that is be<strong>in</strong>g pursued.<br />
New 3-am<strong>in</strong>opyrazole derivatives are tropomyos<strong>in</strong>related<br />
k<strong>in</strong>ase <strong>in</strong>hibitors - useful for the treatment of<br />
cancer and fibroproliferative/differentiative disorders<br />
ASTRAZENECA AB/ASTRAZENECA UK LTD (Lyne P, Wang B,<br />
Wang T)<br />
WO-2005103010, 03 November 2005<br />
Novel 3-am<strong>in</strong>opyrazole derivatives, their salts, processes for<br />
their preparation, compositions conta<strong>in</strong><strong>in</strong>g them and<br />
methods of their use as tropomyos<strong>in</strong>-related k<strong>in</strong>ase (Trk)<br />
<strong>in</strong>hibitors for the treatment of cancers, fibroproliferative/<br />
differentiative disorders, psoriasis, rheumatoid arthritis,<br />
Patent alert 13<br />
Kaposi's sarcoma, hemangioma, nephropathy, atheroma,<br />
atherosclerosis, arterial restenosis, autoimmune disease,<br />
<strong>in</strong>flammation, bone disease or ocular disease with ret<strong>in</strong>al<br />
vessel proliferation are claimed. The compounds are<br />
particularly stated to <strong>in</strong>hibit TrkA and TrkB activity. No<br />
suitable advantage is given. The ability of compounds to<br />
<strong>in</strong>hibit TrkA and TrkB activity was determ<strong>in</strong>ed <strong>in</strong> vitro us<strong>in</strong>g<br />
an amplified lum<strong>in</strong>escent proximity assay and appropriate<br />
biot<strong>in</strong>ylated polypeptide substrates. Compounds are stated<br />
to have IC50 values of 0.01 to 10 µM aga<strong>in</strong>st TrkB activity. No<br />
specific biological data aga<strong>in</strong>st TrkB are presented. Six<br />
compounds are specifically claimed, for example, (R)-4-(5cyclopropyl-1H-pyrazol-3-ylam<strong>in</strong>o)-2-[1-(4-fluorophenyl)-<br />
2-hydroxyethylam<strong>in</strong>o]-5-nitrobenzonitrile, which had an<br />
IC50 value of 0.859 µM aga<strong>in</strong>st TrkA.<br />
F<br />
HO<br />
N<br />
H<br />
N<br />
H<br />
N<br />
N<br />
WO-2005103010<br />
(AstraZeneca)<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong><br />
TrkA and TrkB are two members of the Trk proto-oncogene<br />
family and thus constitute logical targets for the<br />
development of novel anticancer agents. Despite this,<br />
relatively few small-molecule <strong>in</strong>hibitors of these k<strong>in</strong>ases<br />
have been described to date, and, of those that have, a<br />
number are broad-spectrum k<strong>in</strong>ase <strong>in</strong>hibitors. AstraZeneca<br />
is the first company to describe compounds that appear to<br />
be specific <strong>in</strong>hibitors of these k<strong>in</strong>ases, and which also<br />
represent a fairly novel k<strong>in</strong>ase <strong>in</strong>hibitor chemotype. This<br />
application claims compounds similar to those<br />
claimed <strong>in</strong> the application WO-2005049033, but employs<br />
pyrazolyl-am<strong>in</strong>obenzene derivatives rather than pyrazolylam<strong>in</strong>opyrimid<strong>in</strong>es.<br />
NH<br />
N +<br />
O<br />
O
14<br />
Editorial overview<br />
The genome: Five years on<br />
Michael Williams<br />
Address<br />
Department of Molecular Pharmacology and Biological Chemistry<br />
Fe<strong>in</strong>berg School of Medic<strong>in</strong>e<br />
Northwestern University<br />
Chicago<br />
IL 60611<br />
USA<br />
Email: mazar<strong>in</strong>e1643@comcast.net<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 7(1):14-17<br />
© The Thomson Corporation ISSN 1472-4472<br />
In 2001, one of the major milestones <strong>in</strong> the history of<br />
biomedical research was achieved, namely the publication of<br />
draft maps of the human genome [1,2], an activity that was<br />
reportedly completed <strong>in</strong> 2003 [3]. This was <strong>in</strong>evitably<br />
accompanied by various predictions that the discrete<br />
molecular source of all human diseases would soon be<br />
known [4-6] and, as a consequence, that the path to the<br />
discovery of novel, more efficacious and safer drugs, based<br />
on as yet unknown and unproven targets resident <strong>in</strong> the<br />
genome, would be exponentially more facile, more<br />
productive, faster and cheaper, ow<strong>in</strong>g to the unique diseaseassociation<br />
of the targets. The then US President, Bill<br />
Cl<strong>in</strong>ton, predicted that 'with this new found knowledge,<br />
humank<strong>in</strong>d is on the verge of ga<strong>in</strong><strong>in</strong>g immense new power<br />
to heal' [7]. Conversely, recent research by Accenture/CMR<br />
International notes that 'only 3% of projects aimed at new<br />
targets will enter precl<strong>in</strong>ical development compared with<br />
17% for projects on established targets' [8].<br />
Almost five years later, an <strong>in</strong>formal survey of 500 scientists<br />
<strong>in</strong>volved <strong>in</strong> the drug discovery process found that 67% were<br />
unconv<strong>in</strong>ced that the genome maps had 'even moderate<br />
effects on drug research' [9]. Similarly, biotechnology<br />
<strong>in</strong>dustry observers and genomic scientists cautioned that the<br />
promised 'fruits of genomics' [10] are unlikely to emerge <strong>in</strong><br />
the near future, with a 10 to 20 year timeframe be<strong>in</strong>g<br />
considered more likely [11].<br />
Additionally, <strong>in</strong> follow<strong>in</strong>g the theme of us<strong>in</strong>g novel<br />
approaches to f<strong>in</strong>d<strong>in</strong>g new drugs, <strong>in</strong> this same group of 500<br />
scientists, 64% 'considered that their organization, at best,<br />
only supported <strong>in</strong>novation to a moderate extent' [9], echo<strong>in</strong>g<br />
similar comments made by Drews [12] and Vagelos [13].<br />
This f<strong>in</strong>d<strong>in</strong>g <strong>in</strong>dicated a disconnect between the concept of<br />
<strong>in</strong>novation−'the act of <strong>in</strong>troduc<strong>in</strong>g someth<strong>in</strong>g new'−that is<br />
religiously cited as the driver for drug discovery [8,14], and<br />
the rampant technology acquisition and implementation <strong>in</strong><br />
the biotech and pharmaceutical <strong>in</strong>dustries over the past<br />
decade. Clearly, the acquisition of enabl<strong>in</strong>g technologies is<br />
very dist<strong>in</strong>ct from their effective use and subsequent ability<br />
to impact the way th<strong>in</strong>gs are done. In reflect<strong>in</strong>g on the<br />
contributions of the late Paul Janssen to the pharmaceutical<br />
<strong>in</strong>dustry, Black noted that successful drug discovery should<br />
avoid 'wishful th<strong>in</strong>k<strong>in</strong>g' and superficiality, and focus <strong>in</strong>stead<br />
on conception, concentration, commitment and creativity<br />
[15]. In this context, the strategic management of the<br />
drug-discovery process appears critical to support the<br />
process of <strong>in</strong>novation and entrepreneurship [16] to ensure<br />
that the enabl<strong>in</strong>g technologies actually contribute to, rather<br />
than diffuse, the focus.<br />
As with many of the new technologies <strong>in</strong> biomedical<br />
research, the expectations for genome-based <strong>in</strong>formation<br />
have far outweighed their fledgl<strong>in</strong>g status with 'overhyp<strong>in</strong>g'<br />
be<strong>in</strong>g a frequently expressed concern [17-20]. Genetics was<br />
described as a 'science of exceptions' by Jones <strong>in</strong> 2000, with<br />
human life expectancy far more dependent on the<br />
environment (epigenetics) than the genome (genetics) [17].<br />
Jones also noted that geneticists have made promises<br />
regard<strong>in</strong>g the deliverables <strong>in</strong> genetics for decades,<br />
controversially suggest<strong>in</strong>g that four letters of the genetic<br />
code might more reasonably be H, Y, P and E.<br />
However, hype related to new technology <strong>in</strong>troductions is not<br />
unique to either the genome or biomedical research and has<br />
been formalized <strong>in</strong> Fenn's 'hype cycle' (Figure 1) [21]. Initially<br />
used <strong>in</strong> 1995, the concept has been more broadly extended to<br />
the maturity and adoption rates of a wide range of emerg<strong>in</strong>g<br />
technologies <strong>in</strong> different <strong>in</strong>dustries. The question for the<br />
genome-based, biomedical research enterprise <strong>in</strong> 2006 is where<br />
genome-based drug discovery currently lies on the maturity<br />
scale. One may argue that the thought leaders <strong>in</strong> genomics are<br />
still operat<strong>in</strong>g <strong>in</strong> the 'peak of <strong>in</strong>flated expectations', while those<br />
reduc<strong>in</strong>g the genome to practice (by fiat or choice) <strong>in</strong> pharma<br />
and biotech are operat<strong>in</strong>g <strong>in</strong> the 'trough of disillusionment'<br />
(Figure 1) [9]. The sceptics are at least ahead of the pundits on<br />
the hype cycle abscissa of maturity.<br />
While many heritable disorders have already been identified <strong>in</strong><br />
which a mutation <strong>in</strong> a s<strong>in</strong>gle gene is necessary and sufficient to<br />
produce a disease, critics of genome-based drug discovery have<br />
po<strong>in</strong>ted out that the genetic associations for Hunt<strong>in</strong>gton's<br />
disease [22], sickle cell anemia [23] and cystic fibrosis [24] were<br />
known before the mapp<strong>in</strong>g of the genome and, despite the<br />
identification of discrete molecular lesions <strong>in</strong>volv<strong>in</strong>g these<br />
associations, have yet to yield effective treatments. Similarly, <strong>in</strong><br />
the Alzheimer's disease (AD) field, the two key mechanisms<br />
thought to contribute to disease progression and neuronal<br />
death−amyloid β deposition and tau hyperphosphorylation<br />
[25]−together with the genetic association of AD with<br />
apolipoprote<strong>in</strong> E alleles [26], have been active research targets<br />
for many years with, aga<strong>in</strong>, little progress hav<strong>in</strong>g been made <strong>in</strong><br />
either understand<strong>in</strong>g the orig<strong>in</strong> and contribution of the<br />
molecular lesion to disease etiology or how this knowledge can<br />
be used to f<strong>in</strong>d effective treatments. Of additional concern <strong>in</strong><br />
the area of AD therapeutics is that the National Institute for<br />
Health and Cl<strong>in</strong>ical Excellence <strong>in</strong> the UK has recently<br />
recommended that the drugs currently approved for use <strong>in</strong> the<br />
treatment of AD (eg, donezepil) are no longer prescribed,<br />
because their benefit to the patient does not justify their cost<br />
[27]; the implications of this recommendation represent part of<br />
a much broader debate [28].
Figure 1. The hype cycle.<br />
Visibility<br />
Technology<br />
trigger<br />
Positive<br />
hype<br />
Don't jo<strong>in</strong> <strong>in</strong> just because it's '<strong>in</strong>'<br />
Peak of <strong>in</strong>flated<br />
expectations<br />
Negative<br />
hype<br />
Don't miss out just because it's 'out'<br />
Trough of<br />
disillusionment<br />
Maturity<br />
Slope of<br />
enlightenment<br />
Plateau of<br />
productivity<br />
Editorial overview 15<br />
Technology trigger: a breakthrough technology that generates significant <strong>in</strong>terest and rampant acquisition and deal mak<strong>in</strong>g and claims to<br />
revolutionize the future of drug discovery.<br />
Peak of <strong>in</strong>flated expectations: a phase of over enthusiasm and unrealistic predictions <strong>in</strong> the press, dur<strong>in</strong>g which successes <strong>in</strong> terms of<br />
<strong>in</strong>vestigational new drugs are <strong>in</strong>frequent. Conference organizers reap the benefits from organiz<strong>in</strong>g frequent 'updates' on the usefulness and<br />
utilization of the technology with speakers who spend the majority of their time attend<strong>in</strong>g such conferences and are thus removed from the<br />
practicalities of try<strong>in</strong>g to use the technology effectively.<br />
Trough of disillusionment: the technology s<strong>in</strong>ks from the limelight as it did not live up to its over-<strong>in</strong>flated expectations; technocrats and<br />
research management move onto the next technology trigger <strong>in</strong> the hope that this will be 'the one'. The phenomenon of hype addiction is<br />
apparent.<br />
Slope of enlightenment: additional focused research leads to a true understand<strong>in</strong>g of the utility of the technology (eg, parallel synthesis<br />
versus comb<strong>in</strong>atorial chemistry).<br />
Plateau of productivity: the practical benefits of the technology are widely demonstrated and accepted. It is found to make a big difference<br />
just as those who are long gone said they thought it would (modified from reference [45]).<br />
(Reproduced with permission from Gartner and L<strong>in</strong>den A, Fenn J: Understand<strong>in</strong>g Gartner's Hype Cycles. Research ID R-20-197, Gartner,<br />
Stamford, CT, USA. © 2003 Gartner) [21].<br />
Additional examples of tantaliz<strong>in</strong>g gene associations with<br />
disease phenotypes that have already been established, yet<br />
rema<strong>in</strong> controversial, are: the dopam<strong>in</strong>e transporter and<br />
attention-deficit hyperactivity disorder [29], the breast<br />
cancer gene and cancer [30], the cystic fibrosis<br />
transmembrane conductance regulator and cystic fibrosis<br />
[31], and α1 antitryps<strong>in</strong> deficiency and chronic obstructive<br />
pulmonary disease [32].<br />
An <strong>in</strong>terest<strong>in</strong>g observation regard<strong>in</strong>g the perceived<br />
commercial value of the genome, albeit an extremely shortterm<br />
view, is that the majority of the high-profile<br />
genomic/genetics companies founded <strong>in</strong> the 1990s<br />
[33]−Celera, Human Genome Sciences, Incyte, Millennium,<br />
Exelexis, Curagen and Genset−have either dramatically<br />
changed their bus<strong>in</strong>ess model toward that of more<br />
traditional biotechs (eg, small-molecule and/or biologicals<br />
drug discovery) or ceased to exist, leav<strong>in</strong>g only Myriad<br />
Genetics <strong>in</strong> Salt Lake City, USA and DeCode genetics, based<br />
primarily <strong>in</strong> Reykjavik, Iceland, as the rema<strong>in</strong><strong>in</strong>g two<br />
players of note <strong>in</strong> the field of genome-based medic<strong>in</strong>e, each<br />
build<strong>in</strong>g on unique access to discrete patient populations<br />
with extensive genealogical and genetic records: members of<br />
the Mormon Church <strong>in</strong> Salt Lake City, and the population of<br />
Iceland <strong>in</strong> Reykjavik.<br />
With an <strong>in</strong>creas<strong>in</strong>g recognition of the significant challenges<br />
<strong>in</strong>herent <strong>in</strong> translat<strong>in</strong>g genomic <strong>in</strong>formation to practice (the<br />
99% perspiration part of the def<strong>in</strong>ition of genius ascribed to<br />
Thomas Edison), thought leaders have had no compunction<br />
<strong>in</strong> leav<strong>in</strong>g the <strong>in</strong>complete bus<strong>in</strong>ess of the genome beh<strong>in</strong>d to<br />
focus their attentions on the many other 'omics' that exist<br />
beyond the genome. These <strong>in</strong>clude proteomics [34], which<br />
provides even bigger technical challenge than genomics,<br />
given an <strong>in</strong>f<strong>in</strong>itely more complex data set full of labile<br />
unknowns dependent on post-translational modification<br />
(such as phosphorylation, glycosylation and splic<strong>in</strong>g) and<br />
the need for extensive subproteomic analysis based on the<br />
current limitations of mass spectrometroscopic-based<br />
analytical capabilities that lag far beh<strong>in</strong>d the questions be<strong>in</strong>g<br />
posed [35,36].<br />
The latest of the 'omic' sciences is that of the '<strong>in</strong>teractome'<br />
[37], an evolv<strong>in</strong>g collection of b<strong>in</strong>ary prote<strong>in</strong>-prote<strong>in</strong>
16 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
<strong>in</strong>teractions that may form the scaffold for functional genomics<br />
and proteomics, that has emerged from the recently published<br />
draft of the human haplotype map (HapMap) [37,38]. HapMap<br />
is anticipated to 'provide <strong>in</strong>sight <strong>in</strong>to development and disease<br />
mechanisms at a systems level' and to facilitate genome-wide<br />
association studies, represent<strong>in</strong>g a major step forward <strong>in</strong><br />
understand<strong>in</strong>g human disease etiology, provided that the same<br />
concerns regard<strong>in</strong>g data replication that are prevalent <strong>in</strong> the<br />
genome [39], and more so <strong>in</strong> the proteome [36], are not a<br />
function of the enhanced complexity and practice of the<br />
<strong>in</strong>teractome [40].<br />
While there is early enthusiasm for the promise of the<br />
<strong>in</strong>teractome (the 'technology trigger' phase of the hype cycle)<br />
Sharon Begley of the Wall Street Journal (who brought the<br />
world the parts model of the Boe<strong>in</strong>g 777 as a metaphor for<br />
the reductionistic approach to decipher<strong>in</strong>g the genome) [41]<br />
has questioned the 'limited' value of the HapMap [19] <strong>in</strong> the<br />
context of tw<strong>in</strong> studies [42] <strong>in</strong> which identical DNA and<br />
haplotypes lead to different phenotypes.<br />
Dur<strong>in</strong>g the course of this year, <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong><br />
<strong>Investigational</strong> <strong>Drugs</strong> hopes to present a series of Editorials,<br />
written or suggested by members of its Editorial Board, that<br />
are focused on the challenges and progress <strong>in</strong> utiliz<strong>in</strong>g<br />
<strong>in</strong>formation from the genome and its 'omic' progeny <strong>in</strong> the<br />
context of both discrete therapeutic areas and genomeassociated<br />
technology platforms. In an era of considerable<br />
scepticism as to the value of new biologies [9,18] and their<br />
ability to be <strong>in</strong>tegrated with more traditional approaches to<br />
drug discovery [43], the capacity of these discipl<strong>in</strong>es to add<br />
to the solutions, rather than the problems that are deemed to<br />
be contribut<strong>in</strong>g to the dearth of new drug <strong>in</strong>troductions [8,<br />
43,44], will be reviewed.<br />
Suggested read<strong>in</strong>g<br />
1. Lander ES, L<strong>in</strong>ton LM, Birren B, Nusbaum C, Zody MC, Baldw<strong>in</strong> J,<br />
Devon K, Dewar K, Doyle M, Fitz Hugh W, Funke R et al: Initial<br />
sequenc<strong>in</strong>g and analysis of the human genome. Nature (2001)<br />
409(6822):860-921.<br />
2. Venter JC, Adams MD, Myers EW, Li PW, Mural RJ, Sutton GG, Smith<br />
HO, Yandell M, Evans CA, Holt RA, Gocayne JD et al: The sequence<br />
of the human genome. Science (2001) 291(5507):1304-1351.<br />
3. Coll<strong>in</strong>s FS, Morgan M, Patr<strong>in</strong>os A: The human genome project:<br />
Lessons from large-scale biology. Science (2003) 300(5617):286-<br />
290.<br />
4. Moore SD: Biotechnology executives discuss the impact of the<br />
genetic revolution. Wall Street Journal (2000) July 24:B10-B11.<br />
5. Coll<strong>in</strong>s FS, Green ED, Guttmacher AE, Guyer MS: A vision for the<br />
future of genomics research. Nature (2003) 422(6934):835-847.<br />
6. Stoughton RB, Friend SH: How molecular profil<strong>in</strong>g could<br />
revolutionize drug discovery. Nat Rev Drug Discov (2005) 4(4):345-<br />
350.<br />
7. Belk<strong>in</strong> L: A doctor for the future. New York Times Magaz<strong>in</strong>e (2005)<br />
November 06:68-115.<br />
8. Carney S: How can we avoid the productivity gap? Drug Disc Today<br />
(2005) 10(15):1011-1013.<br />
9. Carney S: Question: What do you call 500 scientists com<strong>in</strong>g<br />
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10. Lehman Brothers/McK<strong>in</strong>sey & Co: The Fruits of Genomics. New York,<br />
NY, USA (2001) January.<br />
11. Weatherall D: Personalised medic<strong>in</strong>es: Hopes and realities. Royal<br />
Society, London, UK (2005):1-52.<br />
12. Drews J: Strategic trends <strong>in</strong> the drug <strong>in</strong>dustry. Drug Disc Today<br />
(2003) 8(9):411-420.<br />
13. Osbourne E: After plateau, 'big growth phase' due for<br />
biotechnology: Vagelos. BioWorld Today (2005): May 25.<br />
14. Frantz S: Europe fiddles while <strong>in</strong>novation burns. Nat Rev Drug<br />
Discov (2005) 4(9):704-705.<br />
15. Black J: A personal perspective on Dr Paul Janssen. J Med Chem<br />
(2005) 48(6):1687-1688.<br />
16. Sams-Dodd F: Optimiz<strong>in</strong>g the discovery organization for<br />
<strong>in</strong>novation. Drug Disc Today (2005) 10(15):1049-1056.<br />
17. Jones S: Genetics <strong>in</strong> Medic<strong>in</strong>e: Real Promises, Unreal<br />
Expectations. Milbank Memorial Fund Report (2000) 9:June.<br />
18. Kub<strong>in</strong>yi H: Drug research: Myths, hype and reality. Nat Rev Drug<br />
Discov (2003) 2(8):665-668.<br />
19. Guttmacher AE, Coll<strong>in</strong>s FS: Realiz<strong>in</strong>g the promise of genomics <strong>in</strong><br />
biomedical research. J Am Med Assoc (2005) 294(11):1399-1402.<br />
20. Begley S: L<strong>in</strong>k<strong>in</strong>g DNA profiles to diseases may not lead to<br />
prevention. Wall Street Journal (2005) November 04:B1.<br />
21. L<strong>in</strong>den A, Fenn J: Understand<strong>in</strong>g Gartner's hype cycles. Research ID<br />
R-20-197, Gartner, Stamford, CT, USA (2003).<br />
22. Marx J: Neurodegeneration: Hunt<strong>in</strong>gton's research po<strong>in</strong>ts to<br />
possible new therapies. Science (2005) 310(5745):43-45.<br />
23. Edwards CL, Scales MT, Loughl<strong>in</strong> C, Bennett GG, Harris-Peterson S,<br />
De Castro LM, Whitworth E, Abrams M, Feliu M, Johnson S, Wood M et<br />
al: A brief review of the pathophysiology, associated pa<strong>in</strong>, and<br />
psychosocial issues <strong>in</strong> sickle cell disease. Int J Behav Med (2005)<br />
12(3):171-179.<br />
24. Rubenste<strong>in</strong> RC: Novel, mechanism-based therapies for cystic<br />
fibrosis. Curr Op<strong>in</strong> Pediatr (2005) 17(3):385-392.<br />
25. Forman MS, Trojanowski JQ, Lee VM-Y: Neurodegenerative<br />
diseases: A decade of discoveries paves the way for therapeutic<br />
breakthroughs. Nat Med (2004) 10(10):1055-1063.<br />
26. Fenili D, McLaur<strong>in</strong> J: Cholesterol and ApoE: A target for Alzheimer's<br />
disease therapeutics. Curr Drug Targets CNS Neurol Disord (2005)<br />
4(5):553-567.<br />
27. Whalen J: Brita<strong>in</strong> stirs outcry by weigh<strong>in</strong>g benefits of drugs versus<br />
price. Wall Street Journal (2005) November 27:A1-A11.<br />
28. Avorn J: Powerful Medic<strong>in</strong>es: The Benefits, Risks and Costs of<br />
Prescription <strong>Drugs</strong>. Knopf, New York, NY, USA (2004):1-464.<br />
29. Langley K, Turic D, Peirce TR, Mills S, Van Den Bree MB, Owen MJ,<br />
O'Donovan MC, Thapar A: No support for association between the<br />
dopam<strong>in</strong>e transporter (DAT1) gene and ADHD. Am J Med Genetics<br />
Part B: Neuropsychiatric Genetics (2005) 139(1):7-10.<br />
30. Couz<strong>in</strong> J: Choices−and uncerta<strong>in</strong>ties−for women with BRCA<br />
mutations. Science (2003) 302(5645):592.<br />
31. Des Georges M, Guittard C, Altieri J-P, Templ<strong>in</strong> C, Sarles J, Sarda P,<br />
Claustres M: High heterogeneity of CFTR mutations and unexpected<br />
low <strong>in</strong>cidence of cystic fibrosis <strong>in</strong> Mediterranean France. J Cystic<br />
Fibrosis (2004) 3(4):265-272.<br />
32. DeMeo DL, Silverman EK: Genetics of chronic obstructive pulmonary<br />
disease. Sem<strong>in</strong> Respir Crit Care Med (2003) 24(2):151-160.<br />
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USA (1999).<br />
34. Figuys D: Proteomics: The basic overview. In: Industrial Proteomics:<br />
Applications for Biotechnology and Pharmaceuticals. John Wiley & Sons<br />
Inc, New York, NY, USA (2005):1-62.
35. Huber LA: Is proteomics head<strong>in</strong>g <strong>in</strong> the wrong direction? Nat Rev<br />
Mol Cell Biol (2003) 4(1):74-80.<br />
36. Kopec K, Bozyczko-Coyne D, Williams M: Target identification and<br />
validation <strong>in</strong> drug discovery: The role of proteomics. Biochem<br />
Pharmacol (2005) 69(8):1133-1139.<br />
37. Rual J-F, Venkatesan K, Hao T, Hirozane-Kishikawa T, Dricot A, Li N,<br />
Berriz GF, Gibbons FD, Dreze M, Ayivi-Guedehoussou N, Klitgord M et<br />
al: Towards a proteome-scale map of the human prote<strong>in</strong>-prote<strong>in</strong><br />
<strong>in</strong>teraction network. Nature (2005) 437(7062):1173-1178.<br />
38. Altshuler D, Brooks LD, Chakravarti A, Coll<strong>in</strong>s FS, Daly MJ, Donnelly P,<br />
International HapMap Consortium: A haplotype map of the human<br />
genome. Nature (2005) 437(7063):1299-1320.<br />
39. Williams M: Genome-based drug discovery: Prioritiz<strong>in</strong>g disease<br />
susceptibility/disease-associated genes as novel drug targets for<br />
schizophrenia. Curr Op<strong>in</strong> Investig <strong>Drugs</strong> (2003) 4(1):31-36.<br />
Editorial overview 17<br />
40. Kruglyak L: Power tools for human genetics. Nat Genet (2005)<br />
37(12):1299-1300.<br />
41. Begley S: Biologists hail dawn of a new approach: Don't shoot the<br />
radio. Wall Street Journal Marketplace (2003) February 21:B1.<br />
42. Wong AHC, Gottesman II, Petronis A: Phenotypic differences <strong>in</strong><br />
genetically identical organisms: The epigenetic perspective. Hum<br />
Mol Genet (2005) 14(1):R11-R18.<br />
43. Williams M: Systems and <strong>in</strong>tegrative biology as alternative guises<br />
for pharmacology: Prime time for an iPharm concept? Biochem<br />
Pharmacol (2005) 70(12):1707-1716.<br />
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45. McFedries P: Hype cycle. Word Spy (2001) November 29.<br />
www.wordspy.com/words/hypecycle.asp
18<br />
Editorial overview<br />
Steroid therapy for exudative age-related macular degeneration: Bridg<strong>in</strong>g<br />
the gap until a cure is found<br />
Maneli Mozaffarieh & Andreas Wedrich*<br />
Address<br />
Department of Ophthalmology<br />
Medical University of Graz<br />
Auenbruggerplatz 4<br />
A-8036 Graz<br />
Austria<br />
Email: andreas.wedrich@meduni-graz.at<br />
* To whom correspondence should be addressed<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 7(1):18-19<br />
© The Thomson Corporation ISSN 1472-4472<br />
Age-related macular degeneration (AMD) is a devastat<strong>in</strong>g<br />
disease affect<strong>in</strong>g <strong>in</strong>dividuals of over 50 years of age, and is<br />
the lead<strong>in</strong>g cause of irreversible bl<strong>in</strong>dness <strong>in</strong> the developed<br />
world [1,2]. It is estimated that 1.6% of the population <strong>in</strong> the<br />
50- to 65-year-old age group is affected, and <strong>in</strong> the UK there<br />
are 16,000 new cases per year. The implications of this<br />
untreatable disease <strong>in</strong> terms of social impact, healthcare<br />
costs and personal misery are considerable. <strong>Current</strong><br />
treatments for both the wet and dry forms of the disease are<br />
of limited efficacy [3], and, therefore, there is keen <strong>in</strong>terest<br />
among scientists and physicians to develop new therapies.<br />
Corticosteroids have long been the cornerstone of ocular<br />
anti-<strong>in</strong>flammatory therapy. In addition, they can suppress<br />
cell proliferation. Consequently, steroids have been used for<br />
the treatment of several ocular diseases, adm<strong>in</strong>istered either<br />
locally or systemically. In recent years, one particular<br />
steroid, triamc<strong>in</strong>olone acetonide, has received much<br />
attention from scientists. Various researchers studied the<br />
possibility of <strong>in</strong>ject<strong>in</strong>g this corticosteroid directly <strong>in</strong>to the<br />
eye, firstly <strong>in</strong> animals [4,5] and later <strong>in</strong> selected patients. The<br />
<strong>in</strong>travitreal use of this corticosteroid ga<strong>in</strong>ed popularity<br />
amongst ophthalmologists for the treatment of a wide range<br />
of ret<strong>in</strong>al diseases, <strong>in</strong>clud<strong>in</strong>g diabetic and cystoid macular<br />
edema and exudative AMD.<br />
Steroids, along with the majority of other drugs, do not exert<br />
solely beneficial effects. One common side effect is the rise of<br />
<strong>in</strong>traocular pressure (IOP) that is associated with steroid use.<br />
This issue was addressed <strong>in</strong> a study where a group of<br />
known steroid responders were treated with four different<br />
steroids topically [6]. The results of this study showed that<br />
IOP did not beg<strong>in</strong> to <strong>in</strong>crease until after 3 and 5 weeks of<br />
treatment. The beauty of this f<strong>in</strong>d<strong>in</strong>g for ophthalmologists<br />
was that <strong>in</strong> the worst-case scenario, there rema<strong>in</strong>s a 3-week<br />
w<strong>in</strong>dow of relative safety when treat<strong>in</strong>g with a topical<br />
ophthalmic corticosteroid. Moreover, almost all patients<br />
with primary-care conditions respond to treatment <strong>in</strong> less<br />
than 2 weeks when the steroid is applied topically.<br />
Therefore, should we be concerned about the risk of IOP<br />
elevation after triamc<strong>in</strong>olone acetonide <strong>in</strong>travitreal use for<br />
exudative AMD? Furthermore, do we <strong>in</strong>crease the chances<br />
of improved vision for patients <strong>in</strong> the long term when<br />
<strong>in</strong>ject<strong>in</strong>g this steroid through the <strong>in</strong>travitreal route? The<br />
results of some of the research that has been conducted <strong>in</strong><br />
this area show that even 4 mg of <strong>in</strong>travitreal triamc<strong>in</strong>olone<br />
significantly raises IOP [7,8]. In one particular study, the<br />
researchers describe us<strong>in</strong>g 25 mg of triamc<strong>in</strong>olone for<br />
<strong>in</strong>travitreal <strong>in</strong>jections [9], which may <strong>in</strong>crease IOP even more<br />
significantly. The <strong>in</strong>vestigators suggested that the advantage of<br />
a higher dose would be the longer <strong>in</strong>traocular availability of the<br />
drug [10], rather than the temporary visual improvements<br />
encountered <strong>in</strong> patients after <strong>in</strong>travitreal <strong>in</strong>jections [8], despite<br />
the possible side effects. It appears that our scientific<br />
enthusiasm for possible visual improvements <strong>in</strong> exudative<br />
AMD with steroid <strong>in</strong>jections has forced us to step sideways.<br />
Indeed, various studies suggest that <strong>in</strong> exudative AMD, the<br />
modes of action of triamc<strong>in</strong>olone are l<strong>in</strong>ked to the<br />
downregulation of <strong>in</strong>flammatory markers and endothelial<br />
cell permeability [11,12]. However, moderate-to-high<br />
concentrations of this drug would be required at the site of<br />
action <strong>in</strong> order to prevent further growth of subret<strong>in</strong>al<br />
neovascular tissue. For patients, this requirement would mean<br />
that triamc<strong>in</strong>olone must be <strong>in</strong>jected repeatedly, otherwise visual<br />
improvements would only occur <strong>in</strong> the short term [8]. The<br />
question that then arises is up to how many <strong>in</strong>travitreal<br />
<strong>in</strong>jections of this steroid can be tolerated by the eye of each<br />
patient? Unfortunately, most of the research that has been<br />
conducted <strong>in</strong> this area to date has not been associated with a<br />
long enough follow-up time, one of the longer follow-up times<br />
be<strong>in</strong>g 18 months [7]. We therefore do not have a fair idea of the<br />
actual long-term outcome (ie, visual improvement or the side<br />
effects of this drug), particularly when <strong>in</strong>ject<strong>in</strong>g via the<br />
<strong>in</strong>travitreal route more than once.<br />
Another concern when us<strong>in</strong>g <strong>in</strong>travitreal steroids is the<br />
association of steroid use with an <strong>in</strong>crease <strong>in</strong> lens opacity. In<br />
one particular study <strong>in</strong> which <strong>in</strong>travitreal <strong>in</strong>jections of<br />
triamc<strong>in</strong>olone were adm<strong>in</strong>istered for the treatment of diffuse<br />
diabetic macular edema [13], a 3-fold <strong>in</strong>crease of the posterior<br />
subcapsular cataract score among phakic patients occurred.<br />
This trend toward cataract progression suggests that cataract is<br />
a likely risk of steroid <strong>in</strong>jections. Cataracts <strong>in</strong>fluence quality-oflife<br />
measures [14], and therefore a delay of cataract onset could<br />
have a tremendous <strong>in</strong>fluence on the health of patients and on<br />
healthcare costs. The issue of cataract progression is also of<br />
particular <strong>in</strong>terest for patients with AMD, because there is<br />
controversy regard<strong>in</strong>g the possible benefits or risks of cataract<br />
surgery <strong>in</strong> these patients. While some reports suggest that<br />
cataract surgery may worsen the progression of AMD [15,16],<br />
others describe a benefit [17,18]. It may therefore be more<br />
justified to resist the temptation to treat patients with multiple<br />
<strong>in</strong>travitreal steroid <strong>in</strong>jections as there is currently no evidence<br />
of long-term benefits and, by <strong>in</strong>creas<strong>in</strong>g the chances of<br />
cataracts, patients may become more vulnerable to possible<br />
side effects after surgery.<br />
A further side effect of corticosteroid <strong>in</strong>jections is steroid<strong>in</strong>duced<br />
<strong>in</strong>fection [19,20]. Some researchers have reported
cases of pseudo-endophthalmitis [21], which appear to<br />
resolve without any specific treatment. At this po<strong>in</strong>t we can<br />
only postulate that, <strong>in</strong> case of true <strong>in</strong>fectious<br />
endophthalmitis, the course of the disease may be altered <strong>in</strong><br />
the presence of a moderate-to-high dose (25 mg) of<br />
triamc<strong>in</strong>olone acetonide, which may necessitate patients<br />
be<strong>in</strong>g treated aggressively. Placebo-controlled cl<strong>in</strong>ical trials<br />
<strong>in</strong> large multicenter populations, with a long-term followup,<br />
could provide evidence of the efficacy of this drug and<br />
assess possible side effects and complications. However, it<br />
may be difficult to design effective placebo-controlled trials<br />
<strong>in</strong> a study for which an <strong>in</strong>vasive procedure is required.<br />
Overall, there is still no strong body of scientific evidence to<br />
support the benefits of <strong>in</strong>travitreal <strong>in</strong>jections of steroids <strong>in</strong><br />
the prevention of age-related eye disease. Additional data<br />
regard<strong>in</strong>g the toxic effects of steroids on the ret<strong>in</strong>a and optic<br />
nerve, the optimum dosage and the number of <strong>in</strong>travitreal<br />
<strong>in</strong>jections that can be tolerated by the eyes of the patients, as<br />
well as the perceptions of the patients themselves and<br />
quality-of-life measures, could provide physicians with<br />
more <strong>in</strong>sight and help them to understand the long-term<br />
risks and benefits for patients.<br />
So why should we proceed with caution <strong>in</strong> view of the<br />
possibility that <strong>in</strong>travitreal <strong>in</strong>jections of steroids may have<br />
important benefits? Firstly, mak<strong>in</strong>g recommendations before<br />
there is adequate knowledge to support long-term effects<br />
erodes the credibility of science <strong>in</strong> the eyes of the public.<br />
Moreover, <strong>in</strong>travitreal triamc<strong>in</strong>olone acetonide <strong>in</strong>jections<br />
may not promote additional ga<strong>in</strong> <strong>in</strong> the quality of life or<br />
overall health of the patients. We suggest that physicians<br />
effectively educate their patients with regard to all benefits<br />
and possible side effects of steroids <strong>in</strong> order for the patients<br />
to establish realistic expectations. In particular, they should<br />
be <strong>in</strong>formed that there is no firm scientific knowledge as to<br />
whether steroid <strong>in</strong>jections are at all beneficial <strong>in</strong> the longterm<br />
for the treatment of exudative AMD. Further careful<br />
<strong>in</strong>vestigations of the pathogenesis of AMD, <strong>in</strong> addition to<br />
studies of the effects of <strong>in</strong>travitreal steroid <strong>in</strong>jections, are<br />
required <strong>in</strong> order to ga<strong>in</strong> a greater understand<strong>in</strong>g of the<br />
treatment possibilities for this debilitat<strong>in</strong>g disease. Until<br />
then, <strong>in</strong>travitreal steroid <strong>in</strong>jections will rema<strong>in</strong> a bridge over<br />
the therapy gap until a cure is found.<br />
Suggested read<strong>in</strong>g<br />
1. Bressler NM, Bressler SB, F<strong>in</strong>e SL: Age-related macular<br />
degeneration. Surv Ophthalmol (1988) 32(6):375-413.<br />
2. Kle<strong>in</strong> R, Kle<strong>in</strong> BE, L<strong>in</strong>ton KL: Prevalence of age-related maculopathy.<br />
The Beaver Dam Eye Study. Ophthalmology (1992) 99(6):933-943.<br />
3. Mozaffarieh M, Sacu S, Wedrich A: The role of the carotenoids, lute<strong>in</strong><br />
and zeaxanth<strong>in</strong>, <strong>in</strong> protect<strong>in</strong>g aga<strong>in</strong>st age-related macular<br />
degeneration: A review based on controversial evidence. Nutr J<br />
(2003) 2:20.<br />
4. Ciulla TA, Criswell MH, Danis RP, Hill TE: Intravitreal triamc<strong>in</strong>olone<br />
acetonide <strong>in</strong>hibits choroidal neovascularization <strong>in</strong> a laser-treated<br />
rat model. Arch Ophthalmol (2001) 119(3):399-404.<br />
Editorial overview 19<br />
5. Danis RP, B<strong>in</strong>gaman DP, Yang Y, Ladd B: Inhibition of preret<strong>in</strong>al and<br />
optic nerve head neovascularization <strong>in</strong> pigs by <strong>in</strong>travitreal<br />
triamc<strong>in</strong>olone acetonide. Ophthalmology (1996) 103(12):2099-2104.<br />
6. Leibowitz HM, Bartlett JD, Rich R, McQuirter H, Stewart R, Assil K:<br />
Intraocular pressure-rais<strong>in</strong>g potential of 1.0% rimexolone <strong>in</strong><br />
patients respond<strong>in</strong>g to corticosteroids. Arch Ophthalmol (1996)<br />
114(8):933-937.<br />
7. Challa JK, Gillies MC, Penfold PL, Gyory JF, Hunyor AB, Billson FA:<br />
Exudative macular degeneration and <strong>in</strong>travitreal triamc<strong>in</strong>olone: 18<br />
month follow up. Aust N Z J Ophthalmol (1998) 26(4):277-281.<br />
8. Danis RP, Ciulla TA, Pratt LM, Anliker W: Intravitreal triamc<strong>in</strong>olone<br />
acetonide <strong>in</strong> exudative age-related macular degeneration. Ret<strong>in</strong>a<br />
(2000) 20(3):244-250.<br />
9. Jonas JB, Kreissig I, Hugger P, Sauder G, Panda-Jonas S, Degenr<strong>in</strong>g<br />
R: Intravitreal triamc<strong>in</strong>olone acetonide for exudative age related<br />
macular degeneration. Br J Ophthalmol (2003) 87(4):462-468.<br />
10. Rodriguez-Coleman H, Yuan P, Kim H, Gravl<strong>in</strong> L, Srivastava S, Csaky<br />
KG, Rob<strong>in</strong>son MR: Intravitreal <strong>in</strong>jection of triamc<strong>in</strong>olone for diffuse<br />
macular edema. Arch Ophthalmol (2004) 122(7):1085-1086.<br />
11. Penfold PL, Wen L, Madigan MC, Gillies MC, K<strong>in</strong>g NJ, Provis JM:<br />
Triamc<strong>in</strong>olone-acetonide modulates permeablility and <strong>in</strong>tercellular<br />
adhesion molecule-1 (ICAM-1) expression of the ECV304 cell l<strong>in</strong>e:<br />
Implications for macular degeneration. Cl<strong>in</strong> Exp Immunol (2000)<br />
121(3):458-465.<br />
12. Penfold PL, Wong JG, Gyory J, Billson FA: Effects of triamc<strong>in</strong>olone<br />
acetonide on microglial morphology quantitative expression of<br />
MHC-II <strong>in</strong> exudative age-related macular degeneration. Cl<strong>in</strong><br />
Experiment Ophthalmol (2001) 29(3):188-192.<br />
13. Jonas JB, Kreissig I, Sofker A, Degenr<strong>in</strong>g RF: Intravitreal <strong>in</strong>jection of<br />
triamc<strong>in</strong>olone for diffuse diabetic macular edema. Arch Ophthalmol<br />
(2003) 121(1):57-61.<br />
14. Mozaffarieh M, Krepler K, He<strong>in</strong>zl H, Sacu S, Wedrich A: Visual<br />
function, quality of life and patient satisfaction after ophthalmic<br />
surgery: A comparative study. Ophthalmologica (2004) 218(1):26-30.<br />
15. Pollack A, Bukelman A, Zalish M, Leiba H, Oliver M: The course of<br />
age-related macular degeneration follow<strong>in</strong>g bilateral cataract<br />
surgery. Ophthalmic Surg Lasers (1998) 29(4):286-294.<br />
16. Van de Schaft TL, Mooy CM, de Bruijn WC, Mulder PG, Pameyer JH, de<br />
Jong PT: Increased prevalence of disciform macular degeneration<br />
after cataract extraction with implantation of an <strong>in</strong>traocular lens. Br<br />
J Ophthalmol (1994) 78(6):441-445.<br />
17. Shuttleworth GN, Luhishi EA, Harrad RA: Do patients with age related<br />
maculopathy and cataract benefit from cataract surgery? Br J<br />
Ophthalmol (1998) 82(6):611-616.<br />
18. Armbrecht AM, F<strong>in</strong>dlay C, Kaushal S, Asp<strong>in</strong>all P, Hill AR, Dhillon B: Is<br />
cataract surgery justified <strong>in</strong> patients with age related macular<br />
degeneration? A visual function and quality of life assessment. Br J<br />
Ophthalmol (2000) 84(12):1343-1348.<br />
19. Engelman CJ, Palmer JD, Egbert P: Orbital abscess follow<strong>in</strong>g<br />
subtenon triamc<strong>in</strong>olone <strong>in</strong>jection. Arch Ophthalmol (2004)<br />
122(4):654-655.<br />
20. Nelson ML, Tennant MT, Sival<strong>in</strong>gam A, Regillo CD, Belmont JB,<br />
Martidis A: Infectious and presumed non<strong>in</strong>fectious endophthalmitis<br />
after <strong>in</strong>travitreal triamc<strong>in</strong>olone acetonide <strong>in</strong>jection. Ret<strong>in</strong>a (2003)<br />
23(5):686-691.<br />
21. Sutter FK, Gillies MC: Pseudo-endophthalmitis after <strong>in</strong>travitreal<br />
<strong>in</strong>jection of triamc<strong>in</strong>olone. Br J Ophthalmol (2003) 87(8):972-974.
20<br />
Nitrone sp<strong>in</strong> on cerebral ischemia<br />
Sheila A Doggrell<br />
Address<br />
Division of Health Practice<br />
Auckland University of Technology-Akoranga Campus<br />
90 Akoranga Drive<br />
Northcote<br />
Auckland<br />
New Zealand<br />
Email: s.doggrell@xtra.co.nz<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 7(1):20-24<br />
© The Thomson Corporation ISSN 1472-4472<br />
Cl<strong>in</strong>ical trials with radical scaveng<strong>in</strong>g antioxidants have<br />
shown little or no benefit <strong>in</strong> the treatment of ischemic stroke.<br />
The sp<strong>in</strong> trap nitrones covalently b<strong>in</strong>d with short-lived reactive<br />
radicals to <strong>in</strong>activate them for longer than the conventional<br />
scaveng<strong>in</strong>g antioxidants. One of these agents, NXY-059, is<br />
effective <strong>in</strong> animal models of cerebral ischemia, and is <strong>in</strong> phase<br />
III cl<strong>in</strong>ical trials for ischemic stroke by AstraZeneca, under<br />
license from Renovis. Second-generation nitrones (azulenyl<br />
nitrones) have also been described and shown to be<br />
neuroprotective <strong>in</strong> animal models. Thus, at last, it seems that<br />
antioxidants that are potent enough to have considerable<br />
potential for the treatment of cerebral ischemia are <strong>in</strong><br />
development.<br />
Keywords Animal model, azulenyl nitrone, cerebral ischemia,<br />
cl<strong>in</strong>ical trial, NXY-059, PBN, S-PBN, stilbazulenyl nitrone<br />
Introduction<br />
Stroke is the lead<strong>in</strong>g cause of disability and the third lead<strong>in</strong>g<br />
cause of death <strong>in</strong> the western world. Approximately 750,000<br />
new cases occur <strong>in</strong> the US each year, and although strokes<br />
are more prevalent <strong>in</strong> the elderly, they can occur at all ages,<br />
and are more common <strong>in</strong> African-Americans than<br />
Caucasians. The only pharmacological treatment for acute<br />
ischemic stroke currently used is tissue plasm<strong>in</strong>ogen<br />
activator (tPA) to dissolve the clot.<br />
As the most common cause of ischemic stroke <strong>in</strong> humans is<br />
an <strong>in</strong>farct <strong>in</strong> the middle cerebral artery [1], animal stroke<br />
models should ideally <strong>in</strong>volve occlusion of this artery.<br />
Although cerebral <strong>in</strong>farcts can reperfuse, a considerable<br />
amount of time may elapse before this occurs [2];<br />
consequently it is appropriate to study potential<br />
neuroprotective drugs <strong>in</strong> both transient and permanent<br />
occlusion animal models.<br />
The bra<strong>in</strong> is a highly oxygenated organ that consumes<br />
approximately a fifth of the total oxygen of the body, and<br />
which derives most of its energy from oxidative metabolism<br />
of the mitochondrial respiratory cha<strong>in</strong>. It is extremely<br />
sensitive to oxidative damage from free radicals, which<br />
occurs dur<strong>in</strong>g ischemia/reperfusion <strong>in</strong>sult and ultimately<br />
leads to neuronal cell death. Plasma levels of the antioxidant<br />
vitam<strong>in</strong> C are lowered, whereas markers of oxidative stress<br />
are <strong>in</strong>creased <strong>in</strong> patients with ischemic stroke [3], <strong>in</strong>dicat<strong>in</strong>g<br />
that antioxidants may be useful <strong>in</strong> the prevention and<br />
treatment of this disorder. However, antioxidant vitam<strong>in</strong><br />
supplementation is <strong>in</strong>effective <strong>in</strong> prevent<strong>in</strong>g stroke [4], and<br />
limited success has been achieved with free-radical<br />
scavengers (reviewed <strong>in</strong> reference [5]).<br />
Free-radical scavengers, such as vitam<strong>in</strong> E, donate a<br />
hydrogen ion to a radical to form a second radical−the<br />
tocopherol radical with vitam<strong>in</strong> E−which is relatively stable.<br />
However, the tocopherol radical can generate radicals itself<br />
under certa<strong>in</strong> circumstances, for example, exposure to<br />
reduc<strong>in</strong>g metals. Nitrone sp<strong>in</strong> traps are so-called because<br />
they covalently b<strong>in</strong>d with short-lived reactive radicals, such<br />
as hydroxyl radicals, as stable nitroxides. Historically, the<br />
nitrones were used to identify and elucidate free radicals<br />
and associated chemical and biological mechanisms. More<br />
recently, the therapeutic potential of nitrones as<br />
neuroprotective agents has been considered. In the first part<br />
of this review, the effects of the first generation of nitrones <strong>in</strong><br />
animal models of cerebral ischemia are discussed. One of<br />
these nitrones, NXY-059 (AstraZeneca plc/Renovis Inc;<br />
Figure 1), is undergo<strong>in</strong>g phase III cl<strong>in</strong>ical trials for the<br />
treatment of stroke and is discussed <strong>in</strong> more detail <strong>in</strong> this<br />
review. F<strong>in</strong>ally, the second-generation nitrones, the azulenyl<br />
nitrones, which are much more potent sp<strong>in</strong> traps than the<br />
first-generation nitrones, are considered as neuroprotective<br />
agents <strong>in</strong> a variety of animal models, <strong>in</strong>clud<strong>in</strong>g cerebral<br />
ischemia.<br />
First-generation nitrones<br />
PBN, S-PBN, MDL-101002 and S-34176<br />
The first nitrone sp<strong>in</strong> trap agent to demonstrate<br />
neuroprotective properties was α-phenyl-tert-butyl nitrone<br />
(PBN; Figure 1). Interest<strong>in</strong>gly, it was found that nitrone sp<strong>in</strong><br />
trap agents were effective when adm<strong>in</strong>istered after the<br />
ischemic event. Thus, when PBN was adm<strong>in</strong>istered 30 m<strong>in</strong><br />
prior to, or 30 m<strong>in</strong> after, a 5-m<strong>in</strong> bilateral occlusion of the<br />
carotid artery <strong>in</strong> the gerbil, it reduced the subsequent<br />
damage to the hippocampal CAI pyramidal cell layer [6•,7],<br />
and this protection was associated with the ability to<br />
prevent a cascade of free radical generation by form<strong>in</strong>g sp<strong>in</strong><br />
adducts [8]. Subsequently, PBN was shown to reduce<br />
cortical <strong>in</strong>farction when <strong>in</strong>jected before and after transient<br />
middle cerebral artery occlusion <strong>in</strong> the rat, a standard model<br />
of ischemic stroke [9]. In the focal embolic cerebral ischemia<br />
model <strong>in</strong> the rat, both PBN and N-tert-butyl-(2-sulfophenyl)nitrone<br />
(S-PBN; AstraZeneca plc/Renovis Inc; Figure 1)<br />
reduced the neurological deficit and cerebral <strong>in</strong>farct volume<br />
when commenced 2 h after the <strong>in</strong>troduction of an<br />
autologous thrombus <strong>in</strong>to the right-side middle coronary<br />
artery [10].<br />
The next group of nitrone sp<strong>in</strong> traps had a cyclic structure<br />
and demonstrated improved activity over PBN. These<br />
<strong>in</strong>cluded MDL-101002 (Figure 1), which is more potent than<br />
PBN <strong>in</strong> <strong>in</strong>hibit<strong>in</strong>g iron-<strong>in</strong>duced peroxidation <strong>in</strong> liposomes,<br />
as well as <strong>in</strong> trapp<strong>in</strong>g superoxide anions and hydroxyl<br />
radicals [11]. Furthermore, the hydroxyl radical adducts<br />
formed with MDL-101002 had a longer half-life (5 m<strong>in</strong>) than<br />
adducts formed with PBN [11]. MDL-101002 was reported to
Figure 1. The structures of selected first generation nitrones.<br />
C<br />
H 3<br />
C<br />
H 3<br />
HO<br />
Na<br />
CH 3<br />
N +<br />
O<br />
S<br />
O<br />
O<br />
O<br />
S<br />
O<br />
OH<br />
NXY-059<br />
(AstraZeneca/Renovis)<br />
Na<br />
C<br />
H 3<br />
C<br />
H 3<br />
C<br />
H 3<br />
C<br />
H 3<br />
be neuroprotective <strong>in</strong> the transient and permanent middle<br />
cerebral artery ligation models of stroke <strong>in</strong> rats [12],<br />
however, there have been no further reports of its<br />
development for the treatment of stroke.<br />
The chemical structures of some imidazolyl nitrones have been<br />
described [13], with the <strong>in</strong> vivo activity of one of these agents,<br />
S-34176 (Servier; Figure 1), reported <strong>in</strong> 2005. When<br />
adm<strong>in</strong>istered at a dose of 75 mg/kg <strong>in</strong>traperitoneally 30 m<strong>in</strong><br />
before transient global ischemia, S-34176 prevented delayed<br />
neuronal death <strong>in</strong> the hippocampal CA1 area <strong>in</strong> the rat [14]. The<br />
effects of S-34176 when adm<strong>in</strong>istered after cerebral <strong>in</strong>farction <strong>in</strong><br />
an animal model have not been reported to date.<br />
NXY-059: Animal and cellular studies<br />
The nitrone compound that has been studied most to date is<br />
NXY-059 (reviewed <strong>in</strong> reference [15]). In the rat transient<br />
focal cerebral ischemia model (2 h of middle cerebral artery<br />
occlusion), NXY-059 reduced <strong>in</strong>farct volume when<br />
adm<strong>in</strong>istered at 30 mg/kg/h commenc<strong>in</strong>g 3 to 6 h after the<br />
start of reperfusion [16]. This agent was more water soluble<br />
than PBN, but also proved more efficacious despite hav<strong>in</strong>g<br />
less ability to penetrate the blood-bra<strong>in</strong> barrier (BBB) [16].<br />
This f<strong>in</strong>d<strong>in</strong>g suggests that one of the benefits of NXY-059 is<br />
its ability to <strong>in</strong>hibit free radical damage to the endothelium<br />
with<strong>in</strong> the blood vessel. A subsequent study, us<strong>in</strong>g the same<br />
model, showed that when NXY-059 treatment (1, 10 and 30<br />
mg/kg/h) was commenced 2.75 h after occlusion, both the<br />
neurological deficit (scored from forelimb flexion,<br />
spontaneous rotation and absence of response to<br />
contralateral whisker stimulation) and <strong>in</strong>farct size were<br />
reduced <strong>in</strong> a dose-dependent manner at 24 h [17].<br />
In permanent focal cerebral ischemia <strong>in</strong> the spontaneously<br />
hypertensive rat (clip on middle cerebral artery), there was a<br />
22.6% <strong>in</strong>farct of the contralateral hemisphere 24 h after<br />
occlusion [18]. The <strong>in</strong>farct size was reduced to 17.4% with a<br />
cont<strong>in</strong>uous <strong>in</strong>fusion of NXY-059 (30 mg/kg/h) commenced<br />
5 m<strong>in</strong> after occlusion, but this did not reach significance [18].<br />
At 60 mg/kg/h NXY-059, the <strong>in</strong>farct size was reduced to<br />
14.5%, which was a significant reduction [18]. A subsequent<br />
study us<strong>in</strong>g permanent ischemia <strong>in</strong> normotensive rats showed<br />
that with a load<strong>in</strong>g dose of 32.5 mg NXY-059 adm<strong>in</strong>istered<br />
subcutaneously, followed by 30 mg/kg/h of NXY-059<br />
adm<strong>in</strong>istered via an osmotic m<strong>in</strong>ipump (commenced 5 m<strong>in</strong><br />
after occlusion), there was a reduction <strong>in</strong> the damage to the<br />
sub-cortex, but not the cortex, and that higher doses reduced<br />
the damaged area <strong>in</strong> both the cortex and sub-cortex<br />
CH 3<br />
N +<br />
O<br />
CH 3<br />
N +<br />
O<br />
O<br />
S<br />
O<br />
OH<br />
Na<br />
Nitrone sp<strong>in</strong> on cerebral ischemia Doggrell 21<br />
PBN S-PBN<br />
MDL-101002<br />
S-34176<br />
(AstraZeneca/Renovis)<br />
(Servier)<br />
N +<br />
O<br />
CH 3<br />
CH 3<br />
H3C<br />
C<br />
H 3<br />
CH 3<br />
N +<br />
O<br />
H<br />
N<br />
N<br />
F F<br />
[17]. A further experiment showed that a 50-mg/kg/h dose<br />
of NXY-059 gave some neuroprotection <strong>in</strong> both the cortex<br />
and sub-cortex when the <strong>in</strong>fusion was commenced 2 h after<br />
the occlusion [17].<br />
In humans, agents that improve functional disability after<br />
stroke are required. Thus, the f<strong>in</strong>d<strong>in</strong>g that NXY-059 reduces<br />
the functional disability result<strong>in</strong>g from ischemic stroke <strong>in</strong><br />
monkeys was welcomed. At a dose of 28 mg/kg for 48 h,<br />
commenced 5 m<strong>in</strong> after middle cerebral artery occlusion,<br />
NXY-059 improved the reach of monkeys with their<br />
hemiparetic arm, lessened spatial perceptual neglect at 3 and<br />
10 weeks, and reduced bra<strong>in</strong> damage [19]. Of more <strong>in</strong>terest<br />
was a subsequent study <strong>in</strong> the monkey middle cerebral<br />
artery occlusion model show<strong>in</strong>g that if a higher dose of<br />
NXY-059 was adm<strong>in</strong>istered, the commencement of <strong>in</strong>fusion<br />
could be delayed for 4 h after occlusion while ma<strong>in</strong>ta<strong>in</strong><strong>in</strong>g<br />
the beneficial effect [20•]. In conclusion, NXY-059 treatment<br />
ameliorated long-term motor impairment, improved the use<br />
of the contralateral stroke-affected arm, and lessened spatial<br />
neglect, while reduc<strong>in</strong>g <strong>in</strong>farct size [20•].<br />
Several drugs that have shown efficacy <strong>in</strong> animal models of<br />
stroke, <strong>in</strong>clud<strong>in</strong>g the γ-am<strong>in</strong>obutyric acid mimetic<br />
clomethiazole [21] and N-methyl-D-aspartate antagonists<br />
(eg, AR-R15896AR (AstraZeneca plc)) [22], have been<br />
unsuccessful <strong>in</strong> cl<strong>in</strong>ical trials because of a lack of efficacy or<br />
tolerability [21,22]. In the monkey model of stroke, NXY-059<br />
was more efficacious than clomethiazole or AR-R15896AR,<br />
produc<strong>in</strong>g a greater reduction <strong>in</strong> <strong>in</strong>farct size follow<strong>in</strong>g<br />
middle cerebral artery occlusion [23]. Of the three drugs,<br />
only NXY-059 improved motor deficit and reduced spatial<br />
neglect after 10 weeks [23].<br />
At present, the only effective treatment for ischemic stroke is<br />
the fibr<strong>in</strong>olytic agent tPA, which acts by dissolv<strong>in</strong>g the clot.<br />
The efficacy of NXY-059 has been studied <strong>in</strong> embolic models<br />
of cerebral ischemia alone and <strong>in</strong> comb<strong>in</strong>ation with tPA; the<br />
number of small clots that had to be adm<strong>in</strong>istered to rabbits<br />
to <strong>in</strong>duce neurological deficits was <strong>in</strong>creased by both<br />
NXY-059 and tPA when adm<strong>in</strong>istered alone 3 h after<br />
external carotid ligation [24]. When used as a comb<strong>in</strong>ation<br />
therapy, NXY-059 and tPA had an additive effect on<br />
<strong>in</strong>creas<strong>in</strong>g the number of small clots required to cause<br />
neurological deficits [24]. Subsequently, it was shown that<br />
the late co-adm<strong>in</strong>istration (6 h) of NXY-059 and the synthetic<br />
tPA tenecteplase was associated with an improvement <strong>in</strong><br />
behavioral deficits [25].<br />
F
22 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
PBN has effective BBB penetration, but questions have<br />
rema<strong>in</strong>ed about whether NXY-059 penetrates the BBB<br />
sufficiently for it to have a central mechanism of action. In a coculture<br />
of endothelial cells and primary astrocytes as a model of<br />
the BBB, uptake of PBN was high, but uptake of S-PBN and<br />
NXY-059 was not [26]. However, the permeability of BBB by<br />
NXY-059 <strong>in</strong>creased with <strong>in</strong>creas<strong>in</strong>g length of ischemia,<br />
although there was no uptake <strong>in</strong>to endothelial cells [26].<br />
In addition to act<strong>in</strong>g as a sp<strong>in</strong> trap for free radicals, NXY-059<br />
may be neuroprotective by <strong>in</strong>hibit<strong>in</strong>g the release of<br />
cytochrome C, a key <strong>in</strong>itiator of apoptosis. Cytochrome C<br />
levels <strong>in</strong>creased dur<strong>in</strong>g reperfusion after a 2-h occlusion of<br />
the rat cerebral artery, and NXY-059 treatment prevented<br />
this <strong>in</strong>crease [27].<br />
NXY-059: Cl<strong>in</strong>ical studies<br />
NXY-059 was well tolerated by healthy volunteers at an<br />
<strong>in</strong>fusion rate of 1.1 to 1.5 mg/kg/h for up to 72 h [28].<br />
Excretion of NXY-059 occurred via the renal route and, <strong>in</strong><br />
<strong>in</strong>dividuals with renal impairment, plasma clearance was<br />
directly proportional to glomerular filtration rate [29].<br />
NXY-059 usually has a half-life of 2 to 4 h, but this was<br />
extended to 10 to 12 h <strong>in</strong> <strong>in</strong>dividuals with moderate and<br />
severe renal impairment [29]. Consequently, <strong>in</strong> patients with<br />
renal impairment, the dose of NXY-059 needs to be adjusted<br />
on the basis of creat<strong>in</strong><strong>in</strong>e clearance [29].<br />
When adm<strong>in</strong>istered to patients with<strong>in</strong> 24 h of stroke,<br />
NXY-059 (250 mg over 1 h, followed by 85 mg/h for 71 h, or<br />
500 mg over 1 h, followed by 170 mg/h for 71 h) was well<br />
tolerated [30]. In this small study of tolerability, the cl<strong>in</strong>ical<br />
outcome scores were collected for descriptive purposes only,<br />
and no improvement <strong>in</strong> cl<strong>in</strong>ical outcome was demonstrated<br />
for these doses, possibly because the study was not designed<br />
to measure efficacy [30]. Furthermore, the doses of NXY-059<br />
used gave plasma levels (25 and 40 µmol/l) that were lower<br />
than those associated with neuroprotection <strong>in</strong> animal studies<br />
(200 µmol/l) [30], and thus may have been too low to be<br />
efficacious. Subsequently, higher doses of NXY-059 were<br />
tested <strong>in</strong> patients with<strong>in</strong> 24 h of stroke onset (915 mg over 1<br />
h, followed by 420 mg/h for 71 h, or 1820 mg over 1 h,<br />
followed by 844 mg/h for 71 h), with the higher dose<br />
achiev<strong>in</strong>g a steady-state plasma level of 260 µmol/l, which<br />
Figure 2. The structures of STAZN and lipid- and water-soluble AZNs.<br />
C<br />
H 3<br />
C<br />
H 3<br />
C<br />
H 3<br />
CH 3<br />
N +<br />
CH 3<br />
O<br />
C<br />
H 3<br />
CH 3<br />
_<br />
O<br />
STAZN<br />
(University of Miami)<br />
CH 3<br />
N +<br />
C<br />
H 3<br />
CH 3<br />
CH 3<br />
CH 3<br />
C<br />
H 3<br />
was above that associated with therapeutic benefit <strong>in</strong><br />
animals [31]. Furthermore, the higher doses were also well<br />
tolerated [31]. Although these studies were not conducted to<br />
determ<strong>in</strong>e effectiveness, at day 30, 58% of the 38 patients<br />
adm<strong>in</strong>istered the 844-mg dose of NXY-059 were assessed as<br />
good on the Barthel Index Score, compared with 47% of<br />
patients from the placebo group [31].<br />
NXY-059 (as Cerovive) is currently undergo<strong>in</strong>g phase III cl<strong>in</strong>ical<br />
trials for the treatment of ischemic stroke. The Stroke Acute<br />
Ischemia NXY Treatment (SAINT-1) trial is evaluat<strong>in</strong>g the effect<br />
of NXY-059 on disability and neurological recovery <strong>in</strong> acute<br />
ischemic stroke patients [32]. The Independent Data and Safety<br />
Monitor<strong>in</strong>g Board that reviewed the outcome after a 3-month<br />
follow-up <strong>in</strong> 1000 patients recommended that the trial be<br />
cont<strong>in</strong>ued [32]. In May 2005, AstraZeneca announced that the<br />
first analysis of data from the SAINT-1 trial <strong>in</strong> 1700 patients<br />
showed a significant reduction (p = 0.038) for patients treated<br />
with NXY-059 compared with those receiv<strong>in</strong>g placebo, based<br />
on the Modified Rank<strong>in</strong> Scale for neurological impairment [33].<br />
However, there was no significant difference between<br />
NXY-059 and placebo on the National Institutes of Health<br />
Stroke Scale [33].<br />
Second-generation nitrones<br />
Azulenyl nitrones<br />
Azulenyl nitrones (AZNs) are a class of compounds that can<br />
be synthesized from the natural product guaiazulene [34]<br />
and possess oxidation potentials far lower than that of firstgeneration<br />
nitrones [35•]. For example, the nitronylsubstituted<br />
hydrocarbon stilbazulenyl nitrone (STAZN,<br />
University of Miami; Figure 2) is 300-fold more potent at<br />
<strong>in</strong>hibit<strong>in</strong>g the free radical-mediated aerobic peroxidation of<br />
cumene than PBN or NXY-059 [36•]. Furthermore, because<br />
STAZN is lipid soluble, it is likely to cross the BBB.<br />
STAZN has neuroprotective activity <strong>in</strong> a rat model of<br />
traumatic bra<strong>in</strong> <strong>in</strong>jury. Anesthetized rats were subjected to a<br />
right parietoccipital parasagittal fluid-percussion <strong>in</strong>jury, and<br />
neurological status was evaluated on days 1, 2 and 7 [37•]. At a<br />
dose of 30 mg/kg, when adm<strong>in</strong>istered 5 m<strong>in</strong> and 4 h after the<br />
trauma, STAZN improved neurological scores on days 2 and<br />
7 compared with vehicle [37•]. The mean contusion area was<br />
CH 3<br />
C<br />
H 3<br />
_<br />
O<br />
CH 3<br />
N +<br />
O<br />
CH3 CH3 H<br />
O<br />
CH 3<br />
C<br />
H 3<br />
CH 3<br />
C<br />
H 3<br />
_<br />
O<br />
CH 3<br />
N +<br />
H<br />
CH3 CH3 C<br />
H 3<br />
H<br />
N +<br />
O<br />
CH 3<br />
lipid-soluble AZN water-soluble AZN<br />
CH 3
4.8 mm 2 <strong>in</strong> vehicle-treated rats, which was reduced by 63%<br />
to 1.8 mm 2 follow<strong>in</strong>g treatment with STAZN [37•]. This<br />
reduction was <strong>in</strong> the deep cortical contusion, with the<br />
hippocampal cell loss <strong>in</strong> the CA3 sector be<strong>in</strong>g unaffected by<br />
STAZN [37•].<br />
STAZN was also neuroprotective <strong>in</strong> animal models of<br />
Park<strong>in</strong>son's disease and Hunt<strong>in</strong>gton's disease. The<br />
neurotox<strong>in</strong> 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrid<strong>in</strong>e<br />
(MPTP) causes Park<strong>in</strong>sonian syndrome <strong>in</strong> humans, and is<br />
commonly used to create animal models of Park<strong>in</strong>son's<br />
disease. The toxic metabolite of MPTP accumulates <strong>in</strong> the<br />
mitochondria of dopam<strong>in</strong>ergic nerves, where it impairs<br />
energy production and <strong>in</strong>creases free radical production to<br />
ultimately lead to dopam<strong>in</strong>ergic nerve death. In the MPTP<br />
model <strong>in</strong> mice, both a lipid-soluble and a water-soluble<br />
azulenyl nitrone (Figure 2), adm<strong>in</strong>istered prior to and after<br />
MPTP adm<strong>in</strong>istration, protected aga<strong>in</strong>st dopam<strong>in</strong>e<br />
depletion, and were more efficacious than S-PBN [35•].<br />
In 1998, AZNs were shown to be neuroprotective <strong>in</strong> cerebral<br />
ischemia. The hippocampal neurons of gerbils are<br />
particularly sensitive to ischemia, and after 7 m<strong>in</strong> of bilateral<br />
carotid occlusion followed by 5 days of reperfusion, a 70%<br />
loss of neurons <strong>in</strong> the CA1 hippocampus resulted [34]. This<br />
loss was reduced to 36% by an <strong>in</strong>traperitoneal<br />
adm<strong>in</strong>istration of 100 mg/kg of AZN 30 m<strong>in</strong> prior to the<br />
occlusion [34].<br />
STAZN (10 or 20 mg/kg) adm<strong>in</strong>istered <strong>in</strong>traperitoneally 30 m<strong>in</strong><br />
before and 3, 12 and 24 h after MPTP adm<strong>in</strong>istration, reduced<br />
the depletion of dopam<strong>in</strong>ergic nerves <strong>in</strong> the substantia nigra<br />
pars compacta <strong>in</strong> animal models of Hunt<strong>in</strong>gton's and<br />
Park<strong>in</strong>son's diseases [38•]. In this study, the mitochondrial<br />
<strong>in</strong>hibitor 3-nitropropionic acid was used to create an animal<br />
model of Hunt<strong>in</strong>gton's disease. Treatment with STAZN (before<br />
and dur<strong>in</strong>g the adm<strong>in</strong>istration of 3-nitropropionic acid)<br />
reduced levels of the lipid peroxidation product<br />
melondialdehyde and the lesion volumes [38•].<br />
Importantly, STAZN was shown to be neuroprotective <strong>in</strong><br />
cerebral ischemia when adm<strong>in</strong>istered after occlusion. A<br />
standard neurobehavioral assessment demonstrated that<br />
after 2 h of middle coronary artery occlusion, rats improved<br />
modestly over a 72-h period [39••]. This improvement was<br />
quicker and more extensive when rats were treated with<br />
STAZN at <strong>in</strong>traperitoneal doses of 0.6 mg/kg at onset and<br />
repeated after 2 h of reperfusion [39••]. STAZN treatment<br />
also reduced the <strong>in</strong>farct volume, with the neuroprotection<br />
be<strong>in</strong>g predom<strong>in</strong>antly <strong>in</strong> the cortical region; <strong>in</strong> 13 of 22<br />
STAZN-treated rats, the cortical <strong>in</strong>farct was almost<br />
completely prevented [39••]. The researchers commented<br />
that the neuroprotection seen with STAZN exceeded that<br />
observed with many other agents <strong>in</strong> a similar model [39••].<br />
The doses of STAZN needed for a neuroprotective effect<br />
were 300- to 600-fold lower than those needed to <strong>in</strong>duce<br />
neuroprotection with NXY-059 [38•].<br />
Pharmacok<strong>in</strong>etic studies showed that STAZN was slowly<br />
absorbed after <strong>in</strong>traperitoneal <strong>in</strong>jection <strong>in</strong> the rat, with a<br />
Nitrone sp<strong>in</strong> on cerebral ischemia Doggrell 23<br />
computed half-life of 13.9 h [40]. After <strong>in</strong>travenous <strong>in</strong>jection<br />
of STAZN, a two-component decay occurred, with half-lives<br />
of 28 m<strong>in</strong> and 6.7 h [40]. STAZN permeated the bra<strong>in</strong>, where<br />
levels <strong>in</strong> the whole forebra<strong>in</strong> of the rat were 2.5% of blood<br />
levels, and also accumulated <strong>in</strong> rat liver [40].<br />
Conclusion<br />
The effectiveness of free radical-scaveng<strong>in</strong>g antioxidants <strong>in</strong><br />
cl<strong>in</strong>ical trials for the prevention and treatment of cerebral<br />
ischemia has been disappo<strong>in</strong>t<strong>in</strong>g. The sp<strong>in</strong> trap nitrones<br />
covalently b<strong>in</strong>d with short-lived reactive radicals to<br />
<strong>in</strong>activate them for longer than the conventional scaveng<strong>in</strong>g<br />
antioxidants. The first nitrone sp<strong>in</strong> trap agent shown to be<br />
neuroprotective was PBN. More importantly, it was<br />
discovered that nitrone sp<strong>in</strong> trap agents were effective when<br />
adm<strong>in</strong>istered after onset of ischemia. One of these agents,<br />
NXY-059, has demonstrated efficacy <strong>in</strong> animal models of<br />
cerebral ischemia and is undergo<strong>in</strong>g cl<strong>in</strong>ical trials for<br />
ischemic stroke. Second-generation nitrones (AZNs) with a<br />
greater ability to remove reactive radicals have been<br />
<strong>in</strong>vestigated <strong>in</strong> studies, <strong>in</strong> which neuroprotection <strong>in</strong> animal<br />
models of traumatic bra<strong>in</strong> <strong>in</strong>jury, Park<strong>in</strong>son's disease,<br />
Hunt<strong>in</strong>gton's disease and cerebral ischemia have been<br />
demonstrated. Thus, at last, it seems that potent antioxidants<br />
that have considerable potential for the treatment of cerebral<br />
ischemia are <strong>in</strong> development.<br />
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• This paper describes the efficacy of NXY-059 <strong>in</strong> a monkey model of stroke.<br />
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23. Marshall JW, Green AR, Ridley RM: Comparison of the neuroprotective<br />
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972(1-2):119-126.<br />
24. Lapchak PA, Araujo DM, Song D, Wei J, Ziv<strong>in</strong> JA: Neuroprotective effects<br />
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N-oxide (generic NXY-059) <strong>in</strong> a rabbit small clot embolic<br />
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25. Lapchak PA, Song D, Wei J, Ziv<strong>in</strong> JA: Coadm<strong>in</strong>istration of NXY-059<br />
and tenecteplase six hours follow<strong>in</strong>g embolic strokes <strong>in</strong> rabbits<br />
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26. Dehouck MP, Cecchelli R, Richard Green A, Renftel M, Lundquist S: In<br />
vitro blood-bra<strong>in</strong> barrier permeability and cerebral endothelial cell<br />
uptake of the neuroprotective nitrone compound NXY-059 <strong>in</strong><br />
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(1-2):229-235.<br />
27. Han M, He QP, Yong G, Siesjo BK, Li PA: NXY-059, a nitrone with<br />
free radical trapp<strong>in</strong>g properties <strong>in</strong>hibits release of cytochrome C<br />
after cerebral ischemia. Cell Mol Biol (Noisy-le-grand) (2003)<br />
49(8):1249-1252.<br />
28. Edenius C, Strid S, Breitholtz-Emanuelsson A, Dal<strong>in</strong> L, Jerl<strong>in</strong>g M,<br />
Fransson B: NXY-059, the first nitrone be<strong>in</strong>g developed for stroke, is<br />
safe and well tolerated <strong>in</strong> young and elderly healthy volunteers.<br />
Cerebrovasc Dis (1999) 9:102.<br />
29. Strid S, Borga O, Edenius C, Jostell KG, Odergren T, Weil A:<br />
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treatment of acute stoke. Eur J Cl<strong>in</strong> Pharmacol (2002) 58(6):409-415.<br />
30. Lees KR, Sharma AK, Barer D, Ford GA, Kostulas V, Cheng Y-F,<br />
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NXY-059 <strong>in</strong> patients with acute stroke. Stroke (2001) 32(3):675-680.<br />
31. Lees KR, Barer D, Ford GA, Hacke W, Kostulas V, Sharma AK,<br />
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32. Renovis Inc: Phase III trials for CEROVIVE (NXY-059) will cont<strong>in</strong>ue<br />
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October 14.<br />
33. AstraZeneca plc: First results from SAINT-1 trial show<br />
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(2005):May 04.<br />
34. Althaus JS, Fleck TJ, Becker DA, Hall ED, Vonvoigtlander PF: Azulenyl<br />
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model. Free Radic Biol Med (1998) 24(5):738-744.<br />
35. Klivenyi P, Matthews RT, Wermer M, Yang L, MacGarvey U, Becker<br />
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MPTP neurotoxicity. Exp Neurol (1998) 152(1):163-166.<br />
• This paper describes the neuroprotective effect of azulenyl nitrones <strong>in</strong> an<br />
animal model of Park<strong>in</strong>son's disease.<br />
36. Becker DA, Ley JJ, Echegoyen L, Alvarado R: Stilbazulenyl nitrone<br />
(STAZN): A nitronyl-substituted hydrocarbon with the potency of<br />
classical phenolic cha<strong>in</strong>-break<strong>in</strong>g antioxidants. J Am Chem Soc<br />
(2002) 124(17):4678-4684.<br />
• This study demonstrated that STAZN has higher antioxidant activity than<br />
PBN and NXY-059.<br />
37. Belayev L, Becker DA, Alonso OF, Liu Y, Busto R, Ley JJ, G<strong>in</strong>sberg<br />
MD: Stilbazulenyl nitrone, a novel azulenyl nitrone antioxidant:<br />
Improved neurological deficit and reduced contusion size after<br />
traumatic bra<strong>in</strong> <strong>in</strong>jury <strong>in</strong> rats. J Neurosurg (2002) 96(6):1077-1083.<br />
• This study demonstrated the neuroprotective effect of STAZN <strong>in</strong> an animal<br />
model of traumatic bra<strong>in</strong> <strong>in</strong>jury.<br />
38. Yang L, Cal<strong>in</strong>gasan NY, Chen J, Ley JJ, Becker DA, Beal MF: A novel<br />
azulenyl nitrone antioxidant protects aga<strong>in</strong>st MPTP and 3nitropropionic<br />
acid neurotoxicities. Exp Neurol (2005) 191(1):86-93.<br />
• This study demonstrated the neuroprotective effect of STAZN <strong>in</strong> an animal<br />
model of Hunt<strong>in</strong>gton's disease.<br />
39. G<strong>in</strong>sberg MD, Becker DA, Busto R, Belayev A, Zhang Y, Khoutorova L,<br />
Ley JJ, Zhao W, Belayev L: Stilbazulenyl nitrone, a novel<br />
antioxidant, is highly neuroprotective <strong>in</strong> focal ischemia. Ann Neurol<br />
(2003) 54(3):330-342.<br />
•• This paper describes the neuroprotective effect of STAZN <strong>in</strong> an animal<br />
model of ischemic stroke.<br />
40. Ley JJ, Vigdorchik A, Belayev K, Zhao W, Busto R, Khoutorova L, Becker<br />
DA, G<strong>in</strong>sberg MD: Stilbazulenyl nitrone, a second-generation azulenyl<br />
nitrone antioxidant, confers endur<strong>in</strong>g neuroprotection <strong>in</strong> experimental<br />
focal cerebral ischemia <strong>in</strong> the rat: Neurobehavior, histopathology, and<br />
pharmacok<strong>in</strong>etics. J Pharmacol Exp Ther (2005) 313(3):1090-1100.
<strong>Drugs</strong> <strong>in</strong> development for Park<strong>in</strong>son's disease: An update<br />
Tom H Johnston 1 & Jonathan M Brotchie 1,2 *<br />
Addresses<br />
1 Toronto Western Research Institute<br />
Toronto Western Hospital<br />
University Health Network<br />
399 Bathurst Street, MC 11-419<br />
Toronto<br />
ON M5T 2S8<br />
Canada<br />
Email: brotchie@uhnres.utoronto.ca<br />
2Atuka Ltd<br />
37th Floor<br />
First Canadian Place<br />
100 K<strong>in</strong>g Street West<br />
Toronto<br />
ON M5X 1C9<br />
Canada<br />
*To whom correspondence should be addressed<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 7(1):25-32<br />
© The Thomson Corporation ISSN 1472-4472<br />
The current development of emerg<strong>in</strong>g pharmacological<br />
treatments for Park<strong>in</strong>son's disease (PD), from precl<strong>in</strong>ical to<br />
launch, is summarized. Advances over the past year are<br />
highlighted, <strong>in</strong>clud<strong>in</strong>g the significant progress of several drugs<br />
through various stages of development. Several agents have<br />
been discont<strong>in</strong>ued from development, either because of adverse<br />
effects or lack of cl<strong>in</strong>ical efficacy. The methyl-esterified form of<br />
L-DOPA (melevodopa) and the monoam<strong>in</strong>e oxidase type B<br />
<strong>in</strong>hibitor rasagil<strong>in</strong>e have both been launched. With regard to<br />
the monoam<strong>in</strong>e re-uptake <strong>in</strong>hibitors, many changes have been<br />
witnessed, with new agents reach<strong>in</strong>g precl<strong>in</strong>ical development<br />
and pre-exist<strong>in</strong>g ones be<strong>in</strong>g discont<strong>in</strong>ued or hav<strong>in</strong>g no<br />
development reported. Of the dopam<strong>in</strong>e agonists, many<br />
cont<strong>in</strong>ue to progress successfully through cl<strong>in</strong>ical trials.<br />
Others have struggled to demonstrate a significant advantage<br />
over currently available treatments and have been<br />
discont<strong>in</strong>ued. The field of non-dopam<strong>in</strong>ergic treatments<br />
rema<strong>in</strong>s dynamic. The α2 adrenergic receptor antagonists and<br />
the adenos<strong>in</strong>e A2A receptor antagonists rema<strong>in</strong> <strong>in</strong> cl<strong>in</strong>ical<br />
trials. Trials of the neuronal synchronization modulator<br />
levetiracetam are at an advanced stage, and there has also been<br />
a new addition to the class (ie, seletracetam). There has been a<br />
change <strong>in</strong> the landscape of neuroprotective agents that<br />
modulate disease progression. Candidates from the classes of<br />
growth factors and glyceraldehyde-3-phosphate dehydrogenase<br />
<strong>in</strong>hibitors have been discont<strong>in</strong>ued, or no development has been<br />
reported, and the mixed l<strong>in</strong>eage k<strong>in</strong>ase <strong>in</strong>hibitor CEP-1347 has<br />
been discont<strong>in</strong>ued for PD treatment. Other drugs <strong>in</strong> this field,<br />
such as neuroimmunophil<strong>in</strong>s, estrogens and α-synucle<strong>in</strong><br />
oligomerization <strong>in</strong>hibitors, rema<strong>in</strong> <strong>in</strong> development.<br />
Keywords Adenos<strong>in</strong>e A2A, antipark<strong>in</strong>sonian, monoam<strong>in</strong>e<br />
oxidase <strong>in</strong>hibitors, non-dopam<strong>in</strong>ergic<br />
Introduction<br />
A summary of select antipark<strong>in</strong>sonian, antidysk<strong>in</strong>etic and<br />
neuroprotective/neurorestorative agents discussed <strong>in</strong> this<br />
review is presented <strong>in</strong> Tables 1 to 3. For a detailed<br />
discussion of the rationale for the majority of drugs <strong>in</strong><br />
development, refer to our orig<strong>in</strong>al review [1]. It should be<br />
25<br />
noted that, for commercial reasons, much of the <strong>in</strong>formation<br />
that relates to the development of these compounds is not<br />
available <strong>in</strong> the public doma<strong>in</strong> and our understand<strong>in</strong>g is<br />
derived from a variety of media reports of vary<strong>in</strong>g levels of<br />
reliability (eg, scientific literature, websites and company<br />
annual reports).<br />
Antipark<strong>in</strong>sonian symptomatic agents<br />
In the field of antipark<strong>in</strong>sonian therapies, the development of<br />
two dopam<strong>in</strong>e-replac<strong>in</strong>g compounds, etilevodopa and<br />
sumanirole, has been discont<strong>in</strong>ued [2,3]. In both <strong>in</strong>stances, it<br />
seems that this was not due to a lack of antipark<strong>in</strong>sonian<br />
efficacy, but rather because of a lack of any advantage over<br />
compet<strong>in</strong>g products. The discont<strong>in</strong>uation of Pfizer's sumanirole<br />
is disappo<strong>in</strong>t<strong>in</strong>g because it represented the first truly dopam<strong>in</strong>e<br />
D2-selective agonist [4], and thus had great promise as an agent<br />
that might avoid some of the complications that are associated<br />
with traditional dopam<strong>in</strong>e replacement therapy, such as<br />
dysk<strong>in</strong>esia and psychosis [5]. The reason beh<strong>in</strong>d the failure is<br />
unclear, and the entirety of Pfizer's precl<strong>in</strong>ical data on this agent<br />
may never enter the public doma<strong>in</strong>. However, from what has<br />
been made public, it appears that the precl<strong>in</strong>ical <strong>in</strong>vestigations<br />
to def<strong>in</strong>e the advantageous properties of sumanirole over its<br />
competitors, especially with respect to development/<br />
expression of dysk<strong>in</strong>esia and/or psychosis, were quite limited.<br />
This was particularly so <strong>in</strong> studies <strong>in</strong> 1-methyl-4-phenyl-1,2,3,6tetrahydropyrid<strong>in</strong>e<br />
(MPTP) primates, where little beyond<br />
antipark<strong>in</strong>sonian efficacy appears to have been presented<br />
publicly [6,7]. Cl<strong>in</strong>ical trials designed to maximize the potential<br />
advantages of sumanirole might thus have been overlooked.<br />
Another significant change <strong>in</strong> the field with<strong>in</strong> the last year<br />
is the decl<strong>in</strong>e <strong>in</strong> optimism regard<strong>in</strong>g monoam<strong>in</strong>e uptake<br />
<strong>in</strong>hibitors. Although the concept of enhanc<strong>in</strong>g rema<strong>in</strong><strong>in</strong>g<br />
levels of dopam<strong>in</strong>e with such compounds was supported<br />
by studies <strong>in</strong> MPTP-lesioned marmosets [8,9], the<br />
development of brasofens<strong>in</strong>e, SPD-473 and SPD-451 has<br />
been discont<strong>in</strong>ued [10]. The reasons beh<strong>in</strong>d these failures<br />
vary, but <strong>in</strong>clude, for example, lack of efficacy (SPD-473)<br />
[11]. In light of these developments, the results of the<br />
ongo<strong>in</strong>g phase II trial of NS-2330 (NeuroSearch<br />
A/S/Boehr<strong>in</strong>ger Ingleheim Corp) [12] and the<br />
development of SEP-226330 (Sepracor Inc), an agent<br />
claimed to reduce dopam<strong>in</strong>e and noradrenal<strong>in</strong>e, but not<br />
seroton<strong>in</strong>, re-uptake, are awaited with <strong>in</strong>terest [13].<br />
Advances <strong>in</strong> the development of patch and controlledrelease<br />
formulations of agonists have been made. Lead<strong>in</strong>g<br />
the way are studies with the rotigot<strong>in</strong>e patch (Schwarz<br />
Pharma AG/Otsuka Pharmaceutical Co Ltd), which is at the<br />
pre-registration stage, while the lisuride transcutaneous<br />
patch (Neurobiotec GmbH/Prestwick Pharmaceuticals Inc)<br />
has advanced to phase III cl<strong>in</strong>ical trials [14]. A controlledrelease<br />
version of the D2 agonist rop<strong>in</strong>irole<br />
(GlaxoSmithKl<strong>in</strong>e plc/SkyePharma plc) is undergo<strong>in</strong>g phase<br />
III cl<strong>in</strong>ical trials [15].
26 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
Table 1. Examples of antipark<strong>in</strong>sonian agents.<br />
Compound Develop<strong>in</strong>g company/<br />
<strong>in</strong>stitution<br />
Class of<br />
compound<br />
Dopam<strong>in</strong>ergic<br />
L-DOPA <strong>in</strong>haled<br />
(Inhaled levodopa)<br />
O-1369<br />
Boston Life Sciences Inc Dopam<strong>in</strong>e<br />
(BLS-602/BLS-605)<br />
uptake <strong>in</strong>hibitor<br />
SEP-226330 Sepracor Inc Dopam<strong>in</strong>e/<br />
norep<strong>in</strong>ephr<strong>in</strong>e<br />
reuptake<br />
<strong>in</strong>hibitor<br />
H<br />
O CH 3<br />
Cl<br />
Cl<br />
HO<br />
O<br />
O<br />
OH O<br />
OH<br />
OH<br />
Phase of<br />
cl<strong>in</strong>ical<br />
development<br />
Other potential<br />
actions<br />
Alkermes Inc - Precl<strong>in</strong>ical -<br />
Reference<br />
[35•]<br />
Precl<strong>in</strong>ical - [36]<br />
Precl<strong>in</strong>ical - [13]<br />
Rotigot<strong>in</strong>e nasal spray Schwarz Pharma AG D2 agonist Phase I Neuroprotective [37]<br />
BIA 3202<br />
(BIA-3-270)<br />
BIAL Group COMT <strong>in</strong>hibitor Phase I Neuroprotective [38]<br />
Cell therapy (dopam<strong>in</strong>e<br />
Titan<br />
Human ret<strong>in</strong>al Phase II - [39]<br />
producers, Park<strong>in</strong>son's)<br />
Pharmaceuticals Inc/ pigment<br />
(Spheram<strong>in</strong>e)<br />
Scher<strong>in</strong>g AG epithelial cells<br />
on microcarrier<br />
beads that<br />
produce<br />
L-DOPA<br />
NS-2330<br />
NeuroSearch A/S/ Monam<strong>in</strong>e Phase II Cognitive [40]<br />
H C 3<br />
Boehr<strong>in</strong>ger Ingelheim reuptake<br />
enhancement.<br />
N H<br />
Corp<br />
<strong>in</strong>hibitor<br />
Antidepressant<br />
Rop<strong>in</strong>irole<br />
GlaxoSmithKl<strong>in</strong>e plc/<br />
(ReQuip CR)<br />
SkyePharma plc<br />
Lisuride transdermal patch Prestwick<br />
Pharmaceuticals Inc/<br />
NeuroBiotech GmbH<br />
Saf<strong>in</strong>amide<br />
Newron Pharmaceuticals<br />
(PNU-151774E)<br />
SpA<br />
N<br />
H 2<br />
O<br />
CH 3<br />
H<br />
N<br />
Bifeprunox<br />
(DU-127090)<br />
N<br />
H<br />
N<br />
O<br />
O<br />
SLV-308<br />
(SME-308)<br />
CH 3<br />
N<br />
O<br />
N<br />
H<br />
Rotigot<strong>in</strong>e<br />
(N-0923/SPM-962)<br />
OH<br />
N<br />
N<br />
N<br />
O<br />
O<br />
CH 3<br />
HCl<br />
S<br />
F<br />
Solvay SA/<br />
H Lundbeck A/S/<br />
Wyeth Pharmaceuticals<br />
D3/weak D2<br />
agonist<br />
Phase III Neuroprotective [15]<br />
D2/D1 agonist Phase III - [14]<br />
MAO-B<br />
<strong>in</strong>hibitor/Na + and<br />
K + channel<br />
modulator<br />
D2 partial<br />
agonist/5-HT1A<br />
agonist<br />
Solvay SA D2 partial<br />
Schwarz Pharma AG/<br />
Otsuka Pharmaceutical<br />
Co Ltd<br />
agonist/5-HT1A<br />
agonist<br />
Phase III Neuroprotective [41,42,43••,<br />
44]<br />
Phase III - [45]<br />
Phase III Antidepressant [46]<br />
D2 agonist Pre-registered Neuroprotective [47]
Table 1. Examples of antipark<strong>in</strong>sonian agents (cont<strong>in</strong>ued).<br />
Compound Develop<strong>in</strong>g company/<br />
<strong>in</strong>stitution<br />
Piribedil<br />
(Trivastal)<br />
Zonisamide<br />
(Zonegran)<br />
Rasagil<strong>in</strong>e<br />
(TVP-1012/Agilect (US)/Azilect<br />
(Europe)<br />
<strong>Drugs</strong> <strong>in</strong> development for Park<strong>in</strong>son's disease: An update Johnston & Brotchie 27<br />
Class of<br />
compound<br />
Servier D2/3 agonist/α2<br />
antagonist<br />
Da<strong>in</strong>ippon Sumitomo<br />
Pharma Co Ltd/<br />
Donga Pharmaceutical<br />
Co Ltd/Eisai Co Ltd<br />
Teva Pharmaceutical<br />
Industries Ltd/<br />
Eisai Co Ltd/<br />
H Lundbeck A/S<br />
Complex<br />
dopam<strong>in</strong>ergic<br />
Irreversible MAO-<br />
B <strong>in</strong>hibitor<br />
Zandopa<br />
Zandu Complex<br />
(HP-200/Mucuna pruriens)<br />
dopam<strong>in</strong>ergic<br />
SPD-451 Shire plc Monam<strong>in</strong>e<br />
reuptake <strong>in</strong>hibitor<br />
Brasofens<strong>in</strong>e<br />
(NS-2214)<br />
C<br />
H 3<br />
N<br />
H<br />
SPD-473<br />
(BTS-74398)<br />
O CH 3<br />
N Cl<br />
Cl<br />
O<br />
O<br />
OH<br />
OH<br />
NeuroSearch A/S Monam<strong>in</strong>e<br />
reuptake <strong>in</strong>hibitor<br />
Shire plc Monam<strong>in</strong>e<br />
reuptake <strong>in</strong>hibitor<br />
Phase of<br />
cl<strong>in</strong>ical<br />
development<br />
Launched but<br />
new adjunct<br />
trials underway<br />
Other potential<br />
actions<br />
Reference<br />
- [48]<br />
Launched Neuroprotective [49-51]<br />
Launched Neuroprotective [52]<br />
Launched Neuroprotective [53-56]<br />
No development<br />
reported<br />
Cognitive<br />
enhancement.<br />
Antidepressant<br />
Discont<strong>in</strong>ued Cognitive<br />
enhancement.<br />
Antidepressant<br />
Discont<strong>in</strong>ued Cognitive<br />
enhancement.<br />
Antidepressant<br />
Sumanirole<br />
(PNU-95666)<br />
Non-dopam<strong>in</strong>ergic<br />
Pfizer Inc D2 agonist Discont<strong>in</strong>ued - [3]<br />
Adenos<strong>in</strong>e A2A blocker Adenos<strong>in</strong>e<br />
Therapeutics LLC<br />
A2A antagonist Precl<strong>in</strong>ical Neuroprotective [58]<br />
Adenos<strong>in</strong>e A2A receptor<br />
Neurocr<strong>in</strong>e<br />
A2A antagonist Precl<strong>in</strong>ical Neuroprotective [59]<br />
antagonists<br />
Biosciences Inc/<br />
Almirall Prodesfarma<br />
SA<br />
V-2006 Biogen IDEC Inc A2A antagonist Phase I Neuroprotective [25]<br />
AVE-1625 sanofi-aventis CB1 antagonist Phase I - [60]<br />
Sch-58261 analogs Scher<strong>in</strong>g-Plough Corp A2A antagonist Phase II Neuroprotective [61]<br />
Istradefyll<strong>in</strong>e<br />
Kyowa Hakko Kogyo A2A antagonist Phase III Neuroprotective [62-64]<br />
(KW-6002)<br />
Co Ltd<br />
CH 3<br />
O<br />
N<br />
C<br />
H 3<br />
O CH 3<br />
N<br />
Aricept<br />
(Donepezil/E-2020)<br />
N<br />
N<br />
Alt<strong>in</strong>icl<strong>in</strong>e<br />
(SIB-1508Y)<br />
HC<br />
N<br />
H<br />
CH 3<br />
N<br />
O<br />
CH 3<br />
O<br />
CH 3<br />
Eisai Co Ltd/Pfizer Inc AchE <strong>in</strong>hibitor Launched<br />
(pre-registered<br />
for PD-related<br />
dementia)<br />
SIBIA Neurosciences<br />
Inc<br />
α4β2 selective<br />
nicot<strong>in</strong>ic agonist<br />
No development<br />
reported<br />
Cognitive<br />
enhancement<br />
Cognitive<br />
enhancement<br />
AchE acetylchol<strong>in</strong>esterase, CB cannab<strong>in</strong>oid, COMT catechol-O-methyltransferase, MAO monoam<strong>in</strong>e oxidase, PD Park<strong>in</strong>son's disease.<br />
[10]<br />
[57]<br />
[11]<br />
[65]<br />
[66]
28 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
Table 2. Examples of antidysk<strong>in</strong>etic agents for Park<strong>in</strong>son's disease.<br />
Compound Develop<strong>in</strong>g<br />
company/<br />
<strong>in</strong>stitution<br />
Fipamezole<br />
(JP-1730)<br />
F<br />
CH 3<br />
Talampanel<br />
(K<strong>in</strong>ampa/LY-300164)<br />
C<br />
H 3<br />
BP-897<br />
(ST-280)<br />
O<br />
C<br />
H 3<br />
O<br />
N<br />
N<br />
N<br />
H<br />
Sarizotan<br />
(EMD-128130)<br />
F<br />
N<br />
NH 2<br />
HCl<br />
N<br />
H<br />
N<br />
NH<br />
O<br />
O<br />
N<br />
HCl<br />
C<br />
H 3<br />
O<br />
O<br />
N<br />
Class of<br />
compound<br />
Phase of<br />
development<br />
Other potential<br />
actions<br />
Juvantia Pharma Ltd α2 antagonist Phase II Extended 'on'<br />
time<br />
Reference<br />
IVAX Corp AMPA antagonist Phase II Neuroprotective [68]<br />
Bioprojet Pharma D3 partial agonist Phase II - [69]<br />
Merck KGaA 5-HT1A agonist Phase II Extended 'on'<br />
time<br />
Seletracetam<br />
(UCB-44212)<br />
UCB SA SV2A modulator Phase II - [29]<br />
ACP-103<br />
ACADIA<br />
Pharmaceuticals Inc<br />
5-HT2A <strong>in</strong>verse<br />
agonist<br />
Phase II Antipsychotic [70,71]<br />
E-2007 Eisai Co Ltd AMPA antagonist Phase II Neuroprotective [72]<br />
Seroquel<br />
(Quetiap<strong>in</strong>e)<br />
AstraZeneca plc 5-HT2A/C/D2/3<br />
antagonist<br />
Phase II for PD<br />
(launched for<br />
schizophrenia)<br />
Antipsychotic [73,74]<br />
AMPA α-am<strong>in</strong>o-3-hydroxy-5-methyl-4-isoxazolepropionic acid.<br />
Intense <strong>in</strong>terest is now focused on the area of monoam<strong>in</strong>e oxidase<br />
(MAO) <strong>in</strong>hibitors. In the past year, many data have accrued with<br />
regard to the antipark<strong>in</strong>sonian actions of the MAO-B <strong>in</strong>hibitor<br />
rasagil<strong>in</strong>e [11-15,16••], which has now been launched <strong>in</strong> the UK.<br />
Also approved for launch across Europe under the brand name<br />
Azilect, the results of two large cl<strong>in</strong>ical trials have demonstrated<br />
that rasagil<strong>in</strong>e is efficacious both as a monotherapy <strong>in</strong> early-stage<br />
Park<strong>in</strong>son's disease (PD) patients [16••,17••], and as an adjunct to<br />
L-DOPA therapy <strong>in</strong> advanced PD patients with motor<br />
fluctuations [18,19]. Precl<strong>in</strong>ical data suggest a potential<br />
neuroprotective action of rasagil<strong>in</strong>e [20] that might be reflected <strong>in</strong><br />
the f<strong>in</strong>d<strong>in</strong>gs of the TVP-1012 <strong>in</strong> Early Monotherapy for<br />
Park<strong>in</strong>son's disease Outpatients (TEMPO) study. In TEMPO,<br />
early-stage PD patients who commence treatment with rasagil<strong>in</strong>e<br />
as adjunctive therapy are associated with better outcomes at one<br />
year than those patients who delay the start of treatment [21].<br />
However, equally plausible explanations that are unrelated to<br />
neuroprotection could underlie the f<strong>in</strong>d<strong>in</strong>gs of TEMPO.<br />
Whatever the explanation, evidence is accumulat<strong>in</strong>g for the<br />
<strong>in</strong>itiation of rasagil<strong>in</strong>e therapy early after diagnosis.<br />
[67]<br />
[26••]<br />
In the field of non-dopam<strong>in</strong>ergic anti-park<strong>in</strong>sonian agents, the<br />
spotlight rema<strong>in</strong>s on harness<strong>in</strong>g the undoubted potential of<br />
adenos<strong>in</strong>e A2A antagonists. Progress with istradefyll<strong>in</strong>e (Kyowa<br />
Hakko Kogyo Co Ltd) rema<strong>in</strong>s relatively slow, although new<br />
f<strong>in</strong>d<strong>in</strong>gs show<strong>in</strong>g that its action is ma<strong>in</strong>ta<strong>in</strong>ed have been<br />
presented [22], and several phase III trials are now underway<br />
[23,24]. Biogen Idec Inc is develop<strong>in</strong>g the non-xanth<strong>in</strong>e A2A<br />
antagonist V-2006 under license from Vernalis plc [25].<br />
Development by both companies represents a potentially<br />
powerful comb<strong>in</strong>ation that could drive the development of<br />
V-2006 so that it is at the same level as istradefyll<strong>in</strong>e with<strong>in</strong> the<br />
next year. New entrants to this field <strong>in</strong>clude Adenos<strong>in</strong>e<br />
Therapeutics, Neurocr<strong>in</strong>e Biosciences and Almirall Prodesfarma,<br />
although little is known about their developmental candidates<br />
at this stage. It is not clear how the adenos<strong>in</strong>e A2A field will<br />
develop; istradefyll<strong>in</strong>e has prime-mover advantage at present,<br />
but if one of the emerg<strong>in</strong>g molecules can build on the lessons<br />
learned from the development of istradefyll<strong>in</strong>e, or prove useful<br />
as a monotherapy and not just an adjunct to dopam<strong>in</strong>e<br />
replacement (as seems likely to be the case with istradefyll<strong>in</strong>e),<br />
then this advantage could rapidly be negated.
Table 3. Examples of neuroprotective/neurorestorative agents for Park<strong>in</strong>son's disease.<br />
C<br />
H 3<br />
C<br />
H 3<br />
OH<br />
<strong>Drugs</strong> <strong>in</strong> development for Park<strong>in</strong>son's disease: An update Johnston & Brotchie 29<br />
Compound Develop<strong>in</strong>g company/<br />
Class of<br />
Phase of Other potential Reference<br />
<strong>in</strong>stitution<br />
compound development actions<br />
PAN-408 and PAN-527 Panacea Pharmaceuticals Inc α-Synucle<strong>in</strong><br />
oligomerization<br />
<strong>in</strong>hibitors<br />
Precl<strong>in</strong>ical -<br />
[75]<br />
Sonic hedgehog prote<strong>in</strong><br />
Curis Inc/<br />
Hh agonist Precl<strong>in</strong>ical -<br />
[76]<br />
agonists<br />
Wyeth Pharmaceuticals<br />
GYKI-47261 IVAX Corp AMPA antagonist Precl<strong>in</strong>ical Anti-dysk<strong>in</strong>etic [77]<br />
FR-255595 Astellas Pharma Inc PARP-1 <strong>in</strong>hibitor Precl<strong>in</strong>ical - [78]<br />
CERE-120<br />
(Neurtur<strong>in</strong>)<br />
Ceregene Inc GDNF analog Phase I - [79]<br />
MX-4509<br />
(MITO-4509)<br />
MIGENIX Inc Estrogen analog Phase I/II - [80]<br />
Cereact<br />
Ono Pharmaceutical Co Ltd/ Astrocyte modulator Phase II for PD<br />
-<br />
[81,82]<br />
(ONO-2506/arundic acid)<br />
Merck & Co Inc<br />
(phase III for<br />
O<br />
cerebral<br />
<strong>in</strong>farction)<br />
PYM-50028<br />
(P-63)<br />
Phytopharm plc Not known Phase II - [83]<br />
GPI-1485 MGI Pharma Inc/Symphony Neuroimmunophil<strong>in</strong> Phase II -<br />
[84]<br />
Neuro Development Co<br />
ligand<br />
SR-57667 sanofi-aventis Non-peptide<br />
neurotrophic<br />
Phase IIb Neuroprotective [85]<br />
Creat<strong>in</strong>e<br />
Avicena Group Inc Mitochondrial<br />
Phase III<br />
[86]<br />
NH<br />
permeability<br />
-<br />
H N 2 N<br />
OH<br />
transition pore<br />
<strong>in</strong>hibitor<br />
CH 3<br />
Liaterm<strong>in</strong>e<br />
(GDNF)<br />
Omigapil<br />
(CGP-3466/TCH-346)<br />
H C 3<br />
N<br />
O<br />
O<br />
CH<br />
Amgen Inc Endogenous<br />
neurotrophic factor<br />
Discont<strong>in</strong>ued -<br />
[30]<br />
Novartis AG GAPDH <strong>in</strong>hibitor Discont<strong>in</strong>ued - [87]<br />
AMPA α-am<strong>in</strong>o-3-hydroxy-5-methyl-4-isoxazolepropionic acid, GAPDH glyceraldehyde-3-phosphate dehydrogenase, GDNF glial-derived<br />
neurotrophic factor, PARP poly(ADP-ribose) polymerase, PD Park<strong>in</strong>son's disease.<br />
Antidysk<strong>in</strong>etic agents<br />
Developments <strong>in</strong> the field of non-dopam<strong>in</strong>ergic<br />
antidysk<strong>in</strong>etic drugs have generally been positive. Two<br />
agents, the α2 adrenoceptor antagonist fipamezole<br />
(Juvantia Pharma Ltd) and the 5-hydroxytryptam<strong>in</strong>e (5-<br />
HT)1A agonist sarizotan (Merck KGaA) [26••], have both<br />
successfully demonstrated antidysk<strong>in</strong>etic efficacy <strong>in</strong> phase<br />
IIa studies. Preparations for phase III trials of sarizotan are<br />
now underway [27]. It is unclear as to how UCB SA<br />
<strong>in</strong>tends to develop the anticonvulsant levetiracetam for L-<br />
DOPA-<strong>in</strong>duced dysk<strong>in</strong>esia, s<strong>in</strong>ce it has been suggested<br />
that there will be significant issues of tolerability ow<strong>in</strong>g to<br />
somnolence [28]; however, if it can be tolerated <strong>in</strong> an<br />
<strong>in</strong>dividual, antidysk<strong>in</strong>etic actions are achievable.<br />
Precl<strong>in</strong>ical data on a next-generation analog of<br />
levetiracetam, seletracetam (UCB SA), have been reported<br />
[29], demonstrat<strong>in</strong>g the apparent commitment of UCB to<br />
both the target and therapeutic area.<br />
Neuroprotective/neurorestorative agents<br />
In the research of disease-modify<strong>in</strong>g compounds, many<br />
potential agents cont<strong>in</strong>ue to vie for the opportunity to<br />
demonstrate efficacy. The field rema<strong>in</strong>s characterized by a<br />
lack of any s<strong>in</strong>gle target recognized as be<strong>in</strong>g more favorable<br />
than another, and the likelihood that several classes of<br />
compounds will eventually occupy this space may become a<br />
reality. The logistics of conduct<strong>in</strong>g cl<strong>in</strong>ical trials of diseasemodify<strong>in</strong>g<br />
agents rema<strong>in</strong> challeng<strong>in</strong>g [30], and development<br />
of some compounds for PD has been discont<strong>in</strong>ued, for<br />
example, the glial-derived neurotrophic factor, liaterm<strong>in</strong>e<br />
(Amgen Inc) [31]; the neurotroph<strong>in</strong> synthesis-enhancer,<br />
mixed l<strong>in</strong>eage k<strong>in</strong>ase <strong>in</strong>hibitor CEP-1347 (Cephalon Inc/H<br />
Lundbeck A/S/ Kyowa Hakko Kogyo Co Ltd) [32]; and the<br />
glyceraldehyde-3-phosphate dehydrogenase <strong>in</strong>hibitor<br />
TCH-346 (Novartis AG) [33]. In a similar manner to<br />
rasagil<strong>in</strong>e, much attention has also been focused on the<br />
neuroprotective potential of other pre-exist<strong>in</strong>g symptomatic
30 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
antipark<strong>in</strong>sonian agents. For example, data were recently<br />
presented <strong>in</strong> support of a protective action of rotigot<strong>in</strong>e<br />
whereby the progression of disability was attenuated <strong>in</strong> those<br />
patients with early-stage PD who received this agent [34].<br />
Conclusion<br />
In conclusion, the area of drug development <strong>in</strong> PD rema<strong>in</strong>s<br />
active and there is realistic hope of new therapies reach<strong>in</strong>g<br />
the market <strong>in</strong> the short to mid term.<br />
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2. Teva Pharmaceutical Ltd: Teva & Lundbeck announce phase III trials<br />
did not demonstrate etilevodopa superiority over standard<br />
levodopa. Press Release (2003):January 06.<br />
www.tevapharm.com/pr/2003/pr_371.asp<br />
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http://en.sanofi-aventis.com/rd/molecules/p_rd_molecules.asp<br />
86. NINDS: A multi-center, double-bl<strong>in</strong>d, pilot study of m<strong>in</strong>ocycl<strong>in</strong>e and<br />
creat<strong>in</strong>e <strong>in</strong> subjects with early untreated Park<strong>in</strong>son's disease.<br />
NINDS Park<strong>in</strong>son's disease neuroprotection trial (2003):May.<br />
http://www.cl<strong>in</strong>icaltrials.gov/ct/show/NCT00063193?order=1<br />
87. Novartis AG: Novartis shows dynamic momentum <strong>in</strong> <strong>in</strong>dustrylead<strong>in</strong>g<br />
pipel<strong>in</strong>e. Press Release (2005):January 20.
The mechanism of action of gabapent<strong>in</strong> <strong>in</strong> neuropathic pa<strong>in</strong><br />
J Kenneth Baillie* & Ian Power<br />
Address<br />
Department of Anaesthesia, Critical Care and Pa<strong>in</strong> Medic<strong>in</strong>e<br />
University of Ed<strong>in</strong>burgh<br />
Royal Infirmary of Ed<strong>in</strong>burgh<br />
51 Little France Street<br />
Ed<strong>in</strong>burgh<br />
EH16 4SA<br />
UK<br />
Email: j.k.baillie@doctors.org.uk<br />
*To whom correspondence should be addressed<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 7(1):33-39<br />
© The Thomson Corporation ISSN 1472-4472<br />
Neuropathic pa<strong>in</strong> is a common and potentially treatable cause<br />
of considerable lifelong morbidity. Effective pharmacological<br />
treatments are scarce, but one group of drugs that has shown<br />
promise is the antiepileptics. Gabapent<strong>in</strong> has become popular as<br />
a first-l<strong>in</strong>e treatment for neuropathic pa<strong>in</strong> because of its<br />
efficacy as an ant<strong>in</strong>europathic agent and relatively benign sideeffect<br />
profile. However, its mechanism of action is far from<br />
clear. This review discusses the available evidence for the<br />
postulated mechanisms of action of gabapent<strong>in</strong>. Understand<strong>in</strong>g<br />
the mechanism of action of this agent may well lead to the<br />
development of safer and more effective ant<strong>in</strong>europathic drugs.<br />
Keywords Allodynia, hyperalgesia, gabapent<strong>in</strong>,<br />
γ-am<strong>in</strong>obutyric acid, mechanism of action, neuropathic pa<strong>in</strong>,<br />
voltage-gated calcium channel<br />
Introduction<br />
Neuropathic pa<strong>in</strong> results from abnormal fir<strong>in</strong>g of damaged<br />
peripheral nerves, often associated with direct nerve <strong>in</strong>jury<br />
or nerve damage from diabetic, post-herpetic or alcoholic<br />
neuropathy. It has a considerable socioeconomic impact [1],<br />
affect<strong>in</strong>g more than 500,000 people <strong>in</strong> the UK alone [2], the<br />
great majority of whom will require lifelong drug treatment<br />
to control otherwise <strong>in</strong>tolerable suffer<strong>in</strong>g. There has been<br />
much recent <strong>in</strong>terest <strong>in</strong> novel anti-epileptic agents as<br />
potentially useful treatments for neuropathic pa<strong>in</strong>. This<br />
review will summarize the available evidence regard<strong>in</strong>g the<br />
mechanism of action of one such anti-epileptic drug,<br />
gabapent<strong>in</strong> (Figure 1).<br />
The etiologies of neuropathic pa<strong>in</strong> are dist<strong>in</strong>ct from<br />
nociceptive pa<strong>in</strong>, and several drugs that are effective for one<br />
type of pa<strong>in</strong> are relatively <strong>in</strong>effective for the other.<br />
Neuropathic pa<strong>in</strong> may be entirely <strong>in</strong>dependent of any<br />
peripheral nerve stimulus, or it may be manifest as an<br />
abnormal sensation of pa<strong>in</strong> <strong>in</strong> response to stimulation of<br />
other sensory modalities. A series of gene transcription<br />
factors are activated lead<strong>in</strong>g to a wide range of phenotypic<br />
alterations, <strong>in</strong>clud<strong>in</strong>g a reduction <strong>in</strong> the <strong>in</strong>hibitory<br />
neurotransmitter γ-am<strong>in</strong>obutyric acid (GABA), downregulation<br />
of GABA receptors [3••], and loss of GABAergic neurons [4].<br />
At a cellular level, there are many physiological and<br />
biochemical similarities with epilepsy. Direct <strong>in</strong>jury to the<br />
peripheral nerves leads to recurrent abnormal ectopic<br />
33<br />
discharges [5,6], and many of the excitatory neurotransmitters<br />
released <strong>in</strong> neuropathic pa<strong>in</strong> are also implicated <strong>in</strong> the<br />
propagation of seizure activity. Alterations <strong>in</strong> membrane ion<br />
channels can be found <strong>in</strong> both conditions, predispos<strong>in</strong>g the<br />
membranes to abnormal depolarization [7••]. Furthermore,<br />
anti-epileptic medications are often also effective <strong>in</strong> the<br />
treatment of neuropathic pa<strong>in</strong> [8].<br />
Designed as an analog of GABA that would cross the bloodbra<strong>in</strong><br />
barrier [9], gabapent<strong>in</strong> (1-(am<strong>in</strong>omethyl)-cyclohexane<br />
acetic acid) was orig<strong>in</strong>ally marketed worldwide as an antiepileptic.<br />
Other anti-epileptics, such as carbamazep<strong>in</strong>e and<br />
phenyto<strong>in</strong>, have also been effective treatments for neuropathic<br />
pa<strong>in</strong> [8]. The ma<strong>in</strong> problem with the use of these older antiepileptics<br />
is the wide range of side effects. When gabapent<strong>in</strong><br />
was also found to have ant<strong>in</strong>europathic activity, it quickly<br />
became popular because of its relatively mild and dosedependent<br />
side-effect profile, and annual worldwide sales<br />
are now <strong>in</strong> excess of US $2 billion [10•]. Other new<br />
anticonvulsants, such as pregabal<strong>in</strong> (Figure 1), a structural<br />
analog of gabapent<strong>in</strong>, may also prove to be useful<br />
treatments <strong>in</strong> neuropathic pa<strong>in</strong> [11].<br />
Figure 1. The structures of gabapent<strong>in</strong> and pregabal<strong>in</strong>.<br />
NH 2<br />
O<br />
OH<br />
C<br />
H 3<br />
N<br />
H 2<br />
CH 3<br />
gabapent<strong>in</strong> pregabal<strong>in</strong><br />
Efficacy, safety and pharmacok<strong>in</strong>etics<br />
Gabapent<strong>in</strong> is effective <strong>in</strong> reduc<strong>in</strong>g pa<strong>in</strong>-related behavior<br />
patterns <strong>in</strong> a variety of animal models of neuropathic pa<strong>in</strong>,<br />
<strong>in</strong>clud<strong>in</strong>g static allodynia [12], mechanical hyperalgesia [13],<br />
thermal hyperalgesia [13], mechanical allodynia [14,15] and<br />
thermal allodynia [16]. In humans, gabapent<strong>in</strong> reduces<br />
neuropathic pa<strong>in</strong> caused by diabetes mellitus [17], postherpetic<br />
neuralgia [18], cancer [19] and a variety of other<br />
neuropathic pa<strong>in</strong> syndromes [20]. Gabapent<strong>in</strong> is <strong>in</strong>effective<br />
<strong>in</strong> acute post-operative pa<strong>in</strong> follow<strong>in</strong>g mastectomy [21] and,<br />
<strong>in</strong>terest<strong>in</strong>gly, the analgesic efficacy of this agent is<br />
dependent on the presence of some pathological state, such<br />
as nerve <strong>in</strong>jury or <strong>in</strong>flammation [22]. A recent systematic<br />
meta analysis of randomized, controlled trials of gabapent<strong>in</strong><br />
yielded a comb<strong>in</strong>ed number of patients needed to treat<br />
(NNT) with the drug for an improvement <strong>in</strong> neuropathic<br />
pa<strong>in</strong> of 4.3 [10•], comparable with those for carbamazep<strong>in</strong>e<br />
and phenyto<strong>in</strong> [8].<br />
There is also encourag<strong>in</strong>g evidence of an additive effect of<br />
gabapent<strong>in</strong> with other ant<strong>in</strong>europathic and analgesic agents<br />
<strong>in</strong> rat models of neuropathic pa<strong>in</strong> [12,23,24] and healthy<br />
human volunteers [25]. Furthermore, gabapent<strong>in</strong> prevents<br />
the development of opiate tolerance <strong>in</strong> rats [26]. In an<br />
elegantly designed cl<strong>in</strong>ical trial, Gilron et al showed that the<br />
O<br />
OH
34 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
comb<strong>in</strong>ation of gabapent<strong>in</strong> and morph<strong>in</strong>e achieves a<br />
significant further reduction <strong>in</strong> pa<strong>in</strong> scores <strong>in</strong> a large<br />
majority of patients with neuropathic pa<strong>in</strong> [27•].<br />
Importantly, gabapent<strong>in</strong> has relatively m<strong>in</strong>or side effects<br />
and, as supported by the data from the available trials,<br />
withdrawal of treatment ow<strong>in</strong>g to side effects has not been<br />
significantly more common than <strong>in</strong> placebo groups. The<br />
numbers needed to harm (NNH) for m<strong>in</strong>or harm (tolerable<br />
adverse effects) was 3.7. The relative frequencies of adverse<br />
effects <strong>in</strong>cluded dizz<strong>in</strong>ess (24%), somnolence (20%),<br />
headache (10%), diarrhea (10%), confusion (7%) and nausea<br />
(8%) [18]. Dose titrations up to 3600 mg/day have been used<br />
<strong>in</strong> trials, although the maximum licensed dose <strong>in</strong> the UK is<br />
1800 mg/day. The available evidence suggests little<br />
potential for adverse <strong>in</strong>teractions with other agents.<br />
Although gabapent<strong>in</strong> exists at physiological pH as a<br />
zwitterion, and hence would be expected to exhibit limited<br />
permeability across membrane barriers, radiolabel<strong>in</strong>g<br />
studies have shown that it accumulates rapidly with<strong>in</strong><br />
neuronal cytosol [28]. This accumulation may be expla<strong>in</strong>ed<br />
by the carriage of gabapent<strong>in</strong> by system L am<strong>in</strong>o acid<br />
transporters, which operate across gut membranes [29] and<br />
neuronal and glial cell membranes [30]. This system<br />
becomes saturated at higher doses, which accounts for the<br />
non-l<strong>in</strong>ear relationship between oral doses and plasma<br />
concentration [29]. Gabapent<strong>in</strong> competes with am<strong>in</strong>o acids<br />
such as L-leuc<strong>in</strong>e, L-phenylalan<strong>in</strong>e and L-val<strong>in</strong>e at this<br />
transporter [30], although this is unlikely to be directly<br />
related to its mechanism of action [15].<br />
Gabapent<strong>in</strong> exhibits very little prote<strong>in</strong> b<strong>in</strong>d<strong>in</strong>g [31] and is<br />
excreted unchanged by the kidneys, with a first-order<br />
elim<strong>in</strong>ation pattern. Its plasma half-life is predictable and<br />
correlates with creat<strong>in</strong><strong>in</strong>e clearance [32].<br />
Anatomical site of action<br />
B<strong>in</strong>d<strong>in</strong>g sites for gabapent<strong>in</strong> are concentrated <strong>in</strong> the outer layer<br />
of the rat cerebral cortex [33] and <strong>in</strong> the superficial lam<strong>in</strong>ae of<br />
the dorsal horn [34••]. Peak anti-epileptic activity <strong>in</strong> rats occurs<br />
approximately 2 h after peak bra<strong>in</strong> <strong>in</strong>terstitial concentration<br />
[28]. The time course of ant<strong>in</strong>europathic activity after<br />
<strong>in</strong>trathecal <strong>in</strong>jection is similar [35], suggest<strong>in</strong>g that <strong>in</strong>traneural<br />
transport is prerequisite for both actions of gabapent<strong>in</strong>.<br />
In isolated slices of rat bra<strong>in</strong>stem, gabapent<strong>in</strong> <strong>in</strong>hibits<br />
substance P-mediated release of the excitatory neurotransmitter<br />
Figure 2. The structures of anti-epileptic drugs used to treat neuropathic pa<strong>in</strong>.<br />
O<br />
H<br />
N<br />
N<br />
H<br />
O<br />
N<br />
H N 2 O H N N<br />
2<br />
Cl<br />
Cl<br />
N<br />
N<br />
glutamate [36]. Furthermore, <strong>in</strong> vivo experiments have<br />
shown that gabapent<strong>in</strong> prevents the release of excitatory<br />
neurotransmitters, <strong>in</strong>clud<strong>in</strong>g glutamate, <strong>in</strong> sp<strong>in</strong>al cord<br />
microdialysate follow<strong>in</strong>g nociceptive stimulation by<br />
<strong>in</strong>traperitoneal acetic acid [37] or neuropathic pa<strong>in</strong> caused<br />
by sciatic nerve ligation [13].<br />
Possible mechanisms of action<br />
Does the mechanism of ant<strong>in</strong>europathic action of gabapent<strong>in</strong><br />
differ from its anti-epileptic action? Until both mechanisms<br />
are elucidated, we can <strong>in</strong>fer from the widely differ<strong>in</strong>g<br />
chemical structures of those anti-epileptic drugs that are<br />
used for neuropathic pa<strong>in</strong> (gabapent<strong>in</strong>, phenyto<strong>in</strong>,<br />
carbamazep<strong>in</strong>e, lamotrig<strong>in</strong>e, clonazepam and valproate;<br />
Figure 2) [10•] that it is unlikely that they all act at the same<br />
site. It would therefore be unlikely that all of these drugs<br />
each act at two dist<strong>in</strong>ct sites to produce two different, but<br />
common, effects; control of seizures and relief of<br />
neuropathic pa<strong>in</strong>. Given the relative specificity of these<br />
agents for neuropathic pa<strong>in</strong>, and the epileptiform activity<br />
observed <strong>in</strong> damaged sensory afferent fibers [5], it seems<br />
more plausible that both effects are mediated through a<br />
s<strong>in</strong>gle mechanism of action.<br />
Receptor-mediated actions<br />
Although gabapent<strong>in</strong> was orig<strong>in</strong>ally designed as an analog of<br />
the central <strong>in</strong>hibitory neurotransmitter GABA [9], no conclusive<br />
evidence has been found of a direct <strong>in</strong>teraction with any of the<br />
key receptors <strong>in</strong> central pa<strong>in</strong> transmission. Initial studies<br />
demonstrated that it has no direct agonist activity at GABA<br />
receptors [38] and does not b<strong>in</strong>d with high aff<strong>in</strong>ity to any<br />
GABA receptor subtype [39••]. More recent <strong>in</strong>vestigations<br />
us<strong>in</strong>g cloned receptors have found evidence of selective agonist<br />
activity at a subtype of presynaptic GABAB receptors on<br />
excitatory neurons [40•] (discussed below).<br />
Although D-ser<strong>in</strong>e, which acts as an agonist at the <strong>in</strong>hibitory<br />
glyc<strong>in</strong>e b<strong>in</strong>d<strong>in</strong>g site on N-methyl-D-aspartate (NMDA)<br />
receptors, reverses some of the actions of gabapent<strong>in</strong> [41], it<br />
has been shown that gabapent<strong>in</strong> itself does not directly<br />
<strong>in</strong>teract with the glyc<strong>in</strong>e-NMDA complex [39••,42] and<br />
gabapent<strong>in</strong> reduces downstream excitatory neurotransmitter<br />
release from rat bra<strong>in</strong> slices, even after NMDA receptorblock<strong>in</strong>g<br />
drugs have been adm<strong>in</strong>istered [43]. F<strong>in</strong>ally,<br />
gabapent<strong>in</strong> exhibits a profound synergistic anti-allodynic<br />
action with the AMPA receptor antagonist 6-cyano-7nitroqu<strong>in</strong>oxal<strong>in</strong>e-2,3-dione<br />
(CNQX) [35], suggest<strong>in</strong>g that the<br />
two drugs do not act at the same site.<br />
NH 2<br />
H<br />
N<br />
N N +<br />
O<br />
phenyto<strong>in</strong> carbamazep<strong>in</strong>e lamotrig<strong>in</strong>e clonazepam valproate<br />
O<br />
Cl<br />
O<br />
C<br />
H 3<br />
O<br />
OH<br />
CH 3
A specific b<strong>in</strong>d<strong>in</strong>g site on voltage-gated Ca 2+<br />
channels<br />
The search for the site of action of the new anti-epileptic<br />
agent was significantly advanced by Suman-Chauhan et al,<br />
who identified a new, high-aff<strong>in</strong>ity b<strong>in</strong>d<strong>in</strong>g site for<br />
gabapent<strong>in</strong> <strong>in</strong> rat bra<strong>in</strong> homogenate [39••]. Interest<strong>in</strong>gly,<br />
the b<strong>in</strong>d<strong>in</strong>g of gabapent<strong>in</strong> to this site was dependent on<br />
the system L transporter, suggest<strong>in</strong>g that gabapent<strong>in</strong> may<br />
have to cross a cell membrane <strong>in</strong> order to take effect. The<br />
b<strong>in</strong>d<strong>in</strong>g site has been identified as the α2δ subunit of<br />
voltage-gated Ca 2+ channels [34••]. This auxiliary subunit<br />
is upregulated after nerve <strong>in</strong>jury [44-46] and, when coexpressed<br />
with the α1 subunit, br<strong>in</strong>gs about a substantial<br />
<strong>in</strong>crease <strong>in</strong> transmembrane Ca 2+ current [47]. The <strong>in</strong>flux of<br />
Ca 2+ ions through voltage-gated Ca 2+ channels is<br />
necessary for excitatory neurotransmitter release (see<br />
Figure 3) [48-50]. The α2δ subunit has been the subject of<br />
much recent <strong>in</strong>terest as a potential target for novel drug<br />
development [51].<br />
Figure 3. Relevant mechanisms of pa<strong>in</strong> transmission <strong>in</strong> dorsal columns.<br />
GABA γ-am<strong>in</strong>obutyric acid, NMDA N-methyl-D-aspartate [7••,40•,49,57••,60••,82].<br />
The mechanism of action of gabapent<strong>in</strong> <strong>in</strong> neuropathic pa<strong>in</strong> Baillie & Power 35<br />
A gabapent<strong>in</strong> analog, 3-methyl gabapent<strong>in</strong>, has one isomeric<br />
form with high aff<strong>in</strong>ity at α2δ subunits and another with much<br />
lower aff<strong>in</strong>ity. Field et al have shown that the high-aff<strong>in</strong>ity<br />
isomer is an effective ant<strong>in</strong>europathic agent, whereas the lowaff<strong>in</strong>ity<br />
isomer did not have ant<strong>in</strong>europathic activity <strong>in</strong> two<br />
different rat models [52].<br />
Gabapent<strong>in</strong> b<strong>in</strong>ds to α2δ subunits [34••,53] and <strong>in</strong>hibits highthreshold<br />
neuronal Ca 2+ currents [54,55], and <strong>in</strong> cultured dorsal<br />
root ganglion cells, whole-cell Ca 2+ current is reduced by this<br />
agent [56]. Gabapent<strong>in</strong>-mediated Ca 2+ channel blockade<br />
appears to preferentially affect presynaptic P/Q-type voltagegated<br />
Ca 2+ channels, reduc<strong>in</strong>g the release of the excitatory<br />
am<strong>in</strong>o acids glutamate and aspartate; this effect occurs at<br />
therapeutically relevant concentrations <strong>in</strong> rat [57••] and human<br />
bra<strong>in</strong> [43]. As the α2δ subunit is expressed <strong>in</strong> all subtypes of<br />
voltage-gated Ca 2+ channels [58], the apparent selectivity of<br />
gabapent<strong>in</strong> for P/Q-type channels [57••] does not fit with the<br />
hypothesis that gabapent<strong>in</strong> acts by directly <strong>in</strong>hibit<strong>in</strong>g Ca 2+<br />
channels, and has yet to be expla<strong>in</strong>ed.
36 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
Several studies have shown that magnesium chloride and the<br />
synthetic polyam<strong>in</strong>e sperm<strong>in</strong>e <strong>in</strong>hibit the b<strong>in</strong>d<strong>in</strong>g of gabapent<strong>in</strong><br />
to high-aff<strong>in</strong>ity b<strong>in</strong>d<strong>in</strong>g sites, presumably α2δ subunits, <strong>in</strong> rats<br />
[39••], mice [59] and pigs [42]. Intrathecal <strong>in</strong>fusion of<br />
magnesium chloride effectively attenuates the anti-allodynic<br />
effect of gabapent<strong>in</strong> <strong>in</strong> a rat model [60••]. Nevertheless, the role<br />
of the α2δ subunit <strong>in</strong> the ant<strong>in</strong>europathic action of gabapent<strong>in</strong> is<br />
far from clear. Sperm<strong>in</strong>e had no effect on the efficacy of<br />
gabapent<strong>in</strong> <strong>in</strong> the same study [60••]. Furthermore, both<br />
magnesium chloride and sperm<strong>in</strong>e can promote gabapent<strong>in</strong><br />
b<strong>in</strong>d<strong>in</strong>g to purified α2δ subunit prote<strong>in</strong> and appear to have a<br />
temperature-dependent effect on the drug <strong>in</strong> mice, stimulat<strong>in</strong>g<br />
b<strong>in</strong>d<strong>in</strong>g at 30°C, and <strong>in</strong>hibit<strong>in</strong>g b<strong>in</strong>d<strong>in</strong>g at 4°C [59]. F<strong>in</strong>ally, both<br />
magnesium chloride and sperm<strong>in</strong>e are allosteric modulators of<br />
NMDA receptors and could <strong>in</strong>teract with gabapent<strong>in</strong> through a<br />
different site altogether [61].<br />
K + channel activation<br />
There have been some reports that gabapent<strong>in</strong> activates<br />
<strong>in</strong>wardly rectify<strong>in</strong>g K + channels, result<strong>in</strong>g <strong>in</strong> membrane<br />
hyperpolarization and decreased excitability [40•,62]. Ng et<br />
al found that gabapent<strong>in</strong> activates post-synaptic K + currents<br />
<strong>in</strong> rat bra<strong>in</strong> slices and Xenopus oocytes [40•]. However, this<br />
activation was dependent on expression of a specific cloned<br />
GABAB receptor subtype (gb1a-gb2). Furthermore, GABA<br />
had a similar effect on Xenopus oocytes express<strong>in</strong>g GABAB<br />
receptors, suggest<strong>in</strong>g that activation of K + currents is a<br />
receptor-mediated effect.<br />
Selective agonism at GABAB receptors (gb1a-gb2)<br />
GABA receptors are of two types; the multi-subunit chloride<br />
channel receptor GABAA subtype, at which gabapent<strong>in</strong> does<br />
not b<strong>in</strong>d <strong>in</strong> significant quantities [39••], and the G-prote<strong>in</strong>coupled<br />
GABAB receptor [63]. Although several studies have<br />
not found that gabapent<strong>in</strong> b<strong>in</strong>ds to any subtype of GABAB<br />
receptors to a significant degree [39••,64••,65], one group has<br />
provided evidence that expression of gb1a-gb2 GABAB<br />
receptors is prerequisite for gabapent<strong>in</strong> to alter membrane ion<br />
permeability [40•,66]. This is of particular <strong>in</strong>terest because<br />
agonism at GABAB receptors may account for both the<br />
gabapent<strong>in</strong>-mediated <strong>in</strong>hibition of voltage-gated Ca 2+ channels<br />
and activation of <strong>in</strong>wardly rectify<strong>in</strong>g K + channels [67••,68].<br />
A recent pharmacological study provides further evidence<br />
that an important <strong>in</strong>teraction occurs between gabapent<strong>in</strong><br />
and the subtype of GABAB receptors constitutively<br />
expressed on pre-synaptic regions of excitatory <strong>in</strong>terneurons<br />
to <strong>in</strong>hibit excitatory neurotransmitter release [69••].<br />
Importantly, GABAergic neurons were spared, and the<br />
effect of gabapent<strong>in</strong> on excitatory neurotransmitter release<br />
was sensitive to specific GABAB receptor antagonists. It is<br />
possible that GABAB receptor blockade prevented<br />
gabapent<strong>in</strong> action by <strong>in</strong>direct physiological antagonism [70],<br />
as residual GABA is likely to have been present <strong>in</strong> the rat<br />
bra<strong>in</strong> slices used for this experiment. However, this<br />
postulation does not expla<strong>in</strong> the direct effect of gabapent<strong>in</strong><br />
on a GABAB subtype expressed on Xenopus oocytes [40•].<br />
Increased GABA synthesis or release<br />
GABA is an important <strong>in</strong>hibitory neurotransmitter with<br />
numerous pharmacological <strong>in</strong>teractions [71]. Blockade of<br />
GABA causes hypersensitivity and allodynia consistent with<br />
neuropathic pa<strong>in</strong> [72], and partial nerve <strong>in</strong>jury reduces<br />
dorsal horn synaptic <strong>in</strong>hibition ow<strong>in</strong>g to apoptosis of<br />
GABAergic <strong>in</strong>terneurons [4]. As discussed previously,<br />
gabapent<strong>in</strong> does not have a direct action at GABAA receptors<br />
[38], GABA-receptor-block<strong>in</strong>g drugs do not alter the<br />
ant<strong>in</strong>europathic efficacy of gabapent<strong>in</strong> [73], and gabapent<strong>in</strong><br />
has no effect on GABA reuptake [74]. However, synthesis<br />
and release of GABA <strong>in</strong> the bra<strong>in</strong> are <strong>in</strong>creased by<br />
gabapent<strong>in</strong> [75,76], and magnetic resonance imag<strong>in</strong>g<br />
spectroscopy of epileptic patients tak<strong>in</strong>g gabapent<strong>in</strong><br />
demonstrated a global <strong>in</strong>crease <strong>in</strong> bra<strong>in</strong> GABA [77]. This<br />
observation may be because of <strong>in</strong>hibition of GABAtransam<strong>in</strong>ase<br />
[78], activation of glutamic acid decarboxylase<br />
[79] that is sufficient to <strong>in</strong>crease GABA synthesis by 50 to<br />
100% [80], or promotion of non-vesicular GABA release [81].<br />
In an <strong>in</strong>terest<strong>in</strong>g contrast with the f<strong>in</strong>d<strong>in</strong>g of Parker et al that<br />
gabapent<strong>in</strong> acts on pre-synaptic GABAB receptors to <strong>in</strong>hibit<br />
excitatory neurotransmitter release while spar<strong>in</strong>g<br />
GABAergic neurons [69••], gabapent<strong>in</strong> <strong>in</strong>creased the<br />
extrasynaptic NMDA-mediated current <strong>in</strong> GABAergic, but<br />
not non-GABAergic, neurons <strong>in</strong> a rat model of <strong>in</strong>flammatory<br />
pa<strong>in</strong> [82,83]. This action may <strong>in</strong>crease activity <strong>in</strong> <strong>in</strong>hibitory<br />
sp<strong>in</strong>al cord <strong>in</strong>terneurons, thus releas<strong>in</strong>g GABA under<br />
conditions associated with neuropathic pa<strong>in</strong>. However,<br />
neither NMDA receptor modulation [60••] nor GABA<br />
receptor blockade [73] significantly alters the efficacy of<br />
gabapent<strong>in</strong> <strong>in</strong> rat models of pa<strong>in</strong>.<br />
Increase <strong>in</strong> peripheral whole-blood seroton<strong>in</strong><br />
Mood has a profound effect on perception of pa<strong>in</strong> [84], so it<br />
is a realistic possibility that some of the analgesic effects of<br />
gabapent<strong>in</strong> <strong>in</strong> humans may be mediated by global<br />
serotonergic activation [85]. Indeed, gabapent<strong>in</strong> has been<br />
used to treat a variety of mood and anxiety disorders,<br />
although randomized cl<strong>in</strong>ical trials have so far been<br />
disappo<strong>in</strong>t<strong>in</strong>g [86]. Direct evidence from rats has<br />
contradicted this postulated mechanism; neither pretreatment<br />
of rats with a central nervous system seroton<strong>in</strong>deplet<strong>in</strong>g<br />
compound [73] nor blockade of seroton<strong>in</strong><br />
receptors [87] had any effect on the antihyperalgesic efficacy<br />
of gabapent<strong>in</strong>. We conclude that seroton<strong>in</strong> is unlikely to be<br />
central to the mechanism of action of gabapent<strong>in</strong>.<br />
Conclusions<br />
Despite its orig<strong>in</strong>al conception as a drug designed to mimic<br />
a specific neurotransmitter, gabapent<strong>in</strong> has become widely<br />
established <strong>in</strong> cl<strong>in</strong>ical practice without a satisfactory<br />
explanation of how it works. As summarized above, debate<br />
regard<strong>in</strong>g its mechanisms of action now centers on the<br />
apparent discrepancy between the high-aff<strong>in</strong>ity b<strong>in</strong>d<strong>in</strong>g site<br />
on α2δ subunits of voltage-gated Ca 2+ channels [34••], and<br />
persuasive evidence of a direct action at GABAB receptors<br />
[40•].<br />
It has been difficult to dist<strong>in</strong>guish between direct effects of<br />
the drug at Ca 2+ channels and receptor-mediated <strong>in</strong>hibition<br />
of Ca 2+ current because of an apparently ubiquitous<br />
physiological <strong>in</strong>terdependence. Both actions occur at<br />
therapeutically relevant concentrations, and both may
prevent the release of excitatory neurotransmitters and thus<br />
account for the mechanism of action of gabapent<strong>in</strong> <strong>in</strong><br />
neuropathic pa<strong>in</strong>. The presence of a high-aff<strong>in</strong>ity b<strong>in</strong>d<strong>in</strong>g site<br />
for gabapent<strong>in</strong> on Ca 2+ channels, and the fact that the<br />
obliteration of the effect of gabapent<strong>in</strong> when b<strong>in</strong>d<strong>in</strong>g at this site<br />
is prevented [60••], constitute persuasive evidence <strong>in</strong> favor of a<br />
direct effect on Ca 2+ channel activity. However, the deliberate<br />
structural similarity with GABA, and the demonstration that<br />
gabapent<strong>in</strong> can mimic the effect of GABA on a cloned subtype<br />
of GABAB receptors to alter membrane ion permeability [66],<br />
suggest that the mechanism of action of gabapent<strong>in</strong> may be<br />
much closer to that for which it was orig<strong>in</strong>ally designed. Even<br />
before the mechanism of action of gabapent<strong>in</strong> has been fully<br />
elucidated, the candidate mechanisms described here may<br />
become rich resources for novel drug development.<br />
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40 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
5-HT1A receptor activation: New molecular and neuroadaptive mechanisms<br />
of pa<strong>in</strong> relief<br />
Francis C Colpaert<br />
Address<br />
Institut de Recherche Pierre Fabre<br />
3 rue des Satellites<br />
BP 94244<br />
31432 Toulouse Cedex 4<br />
France<br />
Email: francis.colpaert@pierre-fabre.com<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 7(1):40-47<br />
© The Thomson Corporation ISSN 1472-4472<br />
Guided by an understand<strong>in</strong>g of signal transduction <strong>in</strong> pa<strong>in</strong>process<strong>in</strong>g<br />
systems, high-efficacy 5-hydroxytryptam<strong>in</strong>e (5-<br />
HT)1A receptor activation, by means of F-13640, has been<br />
discovered as a new molecular mechanism of pa<strong>in</strong> relief <strong>in</strong><br />
laboratory animals, <strong>in</strong>duc<strong>in</strong>g two neuroadaptive phenomena.<br />
Firstly, this activation cooperates with nociceptive stimulation,<br />
paradoxically caus<strong>in</strong>g analgesia, and secondly, <strong>in</strong>verse<br />
tolerance develops so that the result<strong>in</strong>g analgesia grows rather<br />
than decays. As an apparent result of these novel<br />
neuroadaptive mechanisms, F-13640 exerts an analgesic action<br />
<strong>in</strong> rat models of acute, tonic and chronic nociceptive pa<strong>in</strong> that<br />
is rivaled only by large doses of high-efficacy µ-opioid receptor<br />
agonists. In models of neuropathic allodynia of peripheral or<br />
central orig<strong>in</strong>, chronic F-13640 adm<strong>in</strong>istration causes an<br />
analgesia that surpasses that observed with morph<strong>in</strong>e or other<br />
agents exemplify<strong>in</strong>g other central nervous system drug<br />
mechanisms of pa<strong>in</strong> relief (eg, ketam<strong>in</strong>e, imipram<strong>in</strong>e and<br />
gabapent<strong>in</strong>). Indeed, F-13640 produces long-last<strong>in</strong>g, preemptive<br />
and, most remarkably, curative-like actions <strong>in</strong><br />
neuropathic allodynia. Although await<strong>in</strong>g proof-of-concept<br />
evidence <strong>in</strong> humans, high-efficacy 5-HT1A receptor activation<br />
may uniquely challenge the opioids for pa<strong>in</strong> therapy.<br />
Keywords 5-HT1A receptors, analgesia, neuropathic pa<strong>in</strong>,<br />
nociceptive pa<strong>in</strong>, opioids, tolerance<br />
Introduction<br />
Neuroanatomical and physiological studies have long<br />
implicated seroton<strong>in</strong> (5-hydroxytryptam<strong>in</strong>e; 5-HT) <strong>in</strong> the<br />
central nervous system (CNS) control of pa<strong>in</strong> (eg, descend<strong>in</strong>g<br />
<strong>in</strong>hibition) [1], and while a host of 5-HT receptors are known to<br />
mediate the cellular actions of seroton<strong>in</strong> [2], the 5-HT1A<br />
seroton<strong>in</strong> receptor subtype has not traditionally been<br />
considered as a molecular target for pa<strong>in</strong> therapy [3-8].<br />
However, it will be argued here that high-efficacy activation of<br />
CNS 5-HT1A receptors may perhaps now beg<strong>in</strong> to challenge the<br />
opioids as an option for the treatment of pa<strong>in</strong>, although the<br />
latter have been the ma<strong>in</strong>stay treatment of pa<strong>in</strong> for over<br />
thousands of years. Somewhat ironically, this stark<br />
development results from studies <strong>in</strong>to opioid tolerance <strong>in</strong> the<br />
1970s, and from a well-accepted concept that attempted to<br />
account for tolerance to opioid analgesia.<br />
Signal transduction <strong>in</strong> pa<strong>in</strong>-process<strong>in</strong>g systems<br />
The concept account<strong>in</strong>g for opioid analgesia tolerance specifies<br />
that any <strong>in</strong>put to pa<strong>in</strong>-process<strong>in</strong>g systems causes not a s<strong>in</strong>gle<br />
effect, but dual effects that are bidirectional, or opposite, <strong>in</strong> sign<br />
[9,10•,11,12]. Thus, morph<strong>in</strong>e causes not only analgesia as a<br />
'first-order' effect, but also a 'second-order' hyperalgesia that<br />
outlasts opioid receptor activation for some time. The first-order<br />
analgesia results directly from receptor activation, but the<br />
second-order effect is an <strong>in</strong>direct consequence of this analgesia<br />
and follows <strong>in</strong> time. Upon chronic opioid exposure, the secondorder<br />
pa<strong>in</strong>, or sensitization to nociceptive <strong>in</strong>put, grows and<br />
counteracts the first-order analgesia. Thus, opioid tolerance is<br />
due, paradoxically, to opioid pa<strong>in</strong> [10•,13,14].<br />
Intrigu<strong>in</strong>gly, the concept of high-efficacy activation of 5-HT1A<br />
receptors as an option for the treatment of pa<strong>in</strong> suggested that a<br />
mechanism wholly different from opioid receptor activation<br />
could possibly exist, whereby analgesia could be produced.<br />
Indeed, accord<strong>in</strong>g to this concept, the stimulation of peripheral<br />
nociceptors would <strong>in</strong>itially produce pa<strong>in</strong> as a first-order effect,<br />
but also hypoalgesia as a second-order effect; with chronicity,<br />
this second-order hypoalgesia should grow, counteract the firstorder<br />
pa<strong>in</strong> and, remarkably, develop <strong>in</strong>to an <strong>in</strong>creas<strong>in</strong>gly<br />
powerful analgesia (ie, <strong>in</strong>verse tolerance). Of equal importance,<br />
accord<strong>in</strong>g to the concept, is that one nociceptive stimulation<br />
should cooperate with another, concomitant stimulation of<br />
nociceptors to paradoxically <strong>in</strong>duce second-order hypoalgesia<br />
[4,9]. The potential of such an <strong>in</strong>tervention is considerable; it<br />
would be most effective <strong>in</strong> the treatment of severe pa<strong>in</strong> and<br />
would resolve <strong>in</strong>accessible, opioid-resistant, chronic pa<strong>in</strong>s.<br />
Thus, s<strong>in</strong>ce the 1970s, researchers currently at Pierre Fabre SA<br />
have employed an <strong>in</strong>creas<strong>in</strong>g array of neuropharmacological<br />
tools <strong>in</strong> an attempt to identify a mammalian prote<strong>in</strong> and a<br />
molecular action by which the central effects of peripheral<br />
nociceptive stimulation can be mimicked. This prote<strong>in</strong> should<br />
<strong>in</strong>itiate the neuroadaptive mechanisms of <strong>in</strong>verse tolerance and<br />
nociceptor cooperation, and its effects should constitute the<br />
opposite of those of opioids. 5-HT1A receptor activation has<br />
now been identified as the neuropharmacological <strong>in</strong>tervention<br />
whereby those neuroadaptive and therapeutic objectives can<br />
possibly be achieved [15•].<br />
F-13640<br />
F-13640 (Pierre Fabre SA; Figure 1) is a newly synthesized<br />
methylam<strong>in</strong>o-pyrid<strong>in</strong>e that has nanomolar and selective aff<strong>in</strong>ity<br />
for both rat and human G-prote<strong>in</strong>-coupled 5-HT1A receptors; at<br />
1000-fold higher concentrations the compound does not <strong>in</strong>teract<br />
with many other neurotransmitter receptors, uptake sites, ion<br />
channels and enzymes. Importantly, F-13640 has strong activity<br />
at 5-HT1A receptors and stimulates [ 35S]GTPγS b<strong>in</strong>d<strong>in</strong>g by a<br />
magnitude far greater than that observed with the 5-HT1A<br />
agonists buspirone and 8-hydroxy-2-di-n-propylam<strong>in</strong>o-tetral<strong>in</strong><br />
(8-OH-DPAT), and more recently identified selective 5-HT1A<br />
agonists [15•,16,17]. This comb<strong>in</strong>ation of potency, selectivity<br />
and high efficacy can also be observed <strong>in</strong> vivo; after<br />
<strong>in</strong>traperitoneal <strong>in</strong>jection <strong>in</strong> rat, F-13640 readily penetrates the<br />
bra<strong>in</strong> [18], <strong>in</strong>hibits sp<strong>in</strong>al-cord-wide dynamic neuron and<br />
s<strong>in</strong>gle motor unit responses to nociceptive electrical<br />
stimulation [19], and exerts analgesia from (ED50) doses of<br />
0.029 mg/kg upwards [20•]. Its effects are consistently
antagonized by the selective 5-HT1A antagonist WAY-100636<br />
[15•,20•,21,22] and the amplitude of its 5-HT1A receptormediated<br />
actions is unrivaled by other selective 5-HT1A<br />
receptor ligands [15•,20•].<br />
Figure 1. The structure of F-13640.<br />
C<br />
H 3<br />
N<br />
N<br />
H<br />
O<br />
F-13640<br />
(Pierre Fabre)<br />
Cooperation and <strong>in</strong>verse tolerance: Acute<br />
actions<br />
Studies have probed the sensitivity of normal rats to<br />
nociceptive stimulation by means of the Randall-Selitto<br />
technique, which determ<strong>in</strong>es the threshold mechanical<br />
stimulation of the h<strong>in</strong>dpaw required to <strong>in</strong>duce vocalization<br />
[15•]. While a subcutaneous <strong>in</strong>jection of 5 mg/kg morph<strong>in</strong>e<br />
produced an <strong>in</strong>itial hypoalgesia followed by hyperalgesia, 0.63<br />
mg/kg of <strong>in</strong>traperitoneal F-13640 caused hyperalgesia followed<br />
by hypoalgesia; these data <strong>in</strong>dicate bidirectional signal<br />
transduction and 5-HT1A receptor activation-produc<strong>in</strong>g effects<br />
that are the <strong>in</strong>verse of µ-opioid receptor activation. Repeated<br />
<strong>in</strong>jection of morph<strong>in</strong>e caused hyperalgesia and tolerance to its<br />
analgesic effect; repeated F-13640 <strong>in</strong>jection caused hypoalgesia<br />
and tolerance to its pro-algesic effect. After a 2-week<br />
subcutaneous <strong>in</strong>fusion of either 5 mg/day morph<strong>in</strong>e or 0.63<br />
mg/day F-13640, rats demonstrated a normal sensitivity to the<br />
mechanical stimulation. In morph<strong>in</strong>e-<strong>in</strong>fused animals, acute<br />
<strong>in</strong>jection of the opioid antagonist naloxone at this po<strong>in</strong>t caused<br />
hyperalgesia; mirror<strong>in</strong>g this action, the <strong>in</strong>jection of the 5-HT1A<br />
antagonist WAY-100635 <strong>in</strong> F-13640-<strong>in</strong>fused animals caused<br />
powerful hypoalgesia [15•]. The latter f<strong>in</strong>d<strong>in</strong>g offers a stark<br />
demonstration of the second-order nature of the analgesic effect<br />
of F-13640 and <strong>in</strong>itial evidence that high-efficacy 5-HT1A<br />
receptor stimulation may exert a pre-emptive action on pa<strong>in</strong> of<br />
nociceptive orig<strong>in</strong>.<br />
As discussed, an acute, <strong>in</strong>traperitoneal <strong>in</strong>jection of F-13640<br />
<strong>in</strong>itially produces hyperalgesia. Remarkably, and<br />
demonstrat<strong>in</strong>g cooperation, at the same time after the <strong>in</strong>jection<br />
of the same dose of F-13640, the compound produces analgesia<br />
<strong>in</strong> rats receiv<strong>in</strong>g an <strong>in</strong>traplantar formal<strong>in</strong> <strong>in</strong>jection <strong>in</strong> a model of<br />
tonic nociceptive pa<strong>in</strong>. Similar pro- and hypoalgesic effects<br />
occur with a host of other 5-HT1A receptor ligands [15•] <strong>in</strong> a<br />
manner that is behaviorally specific [23]. However, the<br />
magnitude of both of these effects depends on the extent to<br />
which the ligands activate the receptor; thus, the low-efficacy<br />
5-HT1A agonist buspirone is essentially <strong>in</strong>active, and<br />
F-13640 produces profound effects. These agents and another<br />
seven 5-HT1A receptor ligands produced pro- and hypoalgesic<br />
effects with a rank order that correlates highly (p < 0.001) with<br />
the extent to which they stimulate [ 35S]GTP-γS b<strong>in</strong>d<strong>in</strong>g [15•].<br />
Indeed, with the exception of the high-efficacy opioid agonist<br />
morph<strong>in</strong>e, none of the available analgesics exert<strong>in</strong>g their actions<br />
by peripheral or central mechanisms rivals the magnitude of<br />
N<br />
F<br />
Cl<br />
F<br />
5-HT1A receptor activation Colpaert 41<br />
analgesia that F-13640 produces <strong>in</strong> this model [20•]. Tables 1<br />
and 2 provide comparative data on the ability of various agents<br />
to <strong>in</strong>hibit formal<strong>in</strong>-<strong>in</strong>duced paw lick<strong>in</strong>g and paw elevation,<br />
respectively [20•]. Although several agents <strong>in</strong>hibited paw<br />
lick<strong>in</strong>g to vary<strong>in</strong>g degrees, only F-13640 fully <strong>in</strong>hibited both<br />
behaviors at the early and late phases after formal<strong>in</strong> <strong>in</strong>jection.<br />
Formal<strong>in</strong> <strong>in</strong>jection causes c-Fos prote<strong>in</strong> expression <strong>in</strong> sp<strong>in</strong>al<br />
cord dorsal horn neurons as well as pa<strong>in</strong> behaviors; an<br />
<strong>in</strong>traperitoneal dose of morph<strong>in</strong>e as high as 20 mg/kg is<br />
required to match the extent to which 0.63 mg/kg of<br />
<strong>in</strong>traperitoneal F-13640 suppresses formal<strong>in</strong>-<strong>in</strong>duced c-Fos<br />
prote<strong>in</strong> expression [24].<br />
The exceptionally powerful analgesia that F-13640 produces <strong>in</strong><br />
the formal<strong>in</strong> model of tonic nociceptive pa<strong>in</strong> led the research<br />
group to exam<strong>in</strong>e its possible effectiveness for <strong>in</strong>tra- and postoperative<br />
pa<strong>in</strong> associated with orthopedic surgery <strong>in</strong> rats that<br />
received an <strong>in</strong>cision of the sk<strong>in</strong>, fascia and plantar muscle of the<br />
foot [25], and underwent drill<strong>in</strong>g of a hole <strong>in</strong> the calcaneus [26].<br />
As with a pre-operative <strong>in</strong>traperitoneal <strong>in</strong>jection of the shortact<strong>in</strong>g<br />
opioid remifentanil (0.63 mg/kg), the same dose of<br />
<strong>in</strong>traperitoneal F-13640 lowered the requirement for <strong>in</strong>traoperative<br />
isoflurane anesthesia, <strong>in</strong>dicat<strong>in</strong>g that the<br />
5-HT1A agonist exerted analgesia equivalent to that of the<br />
opioid <strong>in</strong> this model. When adm<strong>in</strong>istered after surgery, F-13640<br />
suppressed post-operative pa<strong>in</strong> behaviors (ie, paw flexion and<br />
elevation) <strong>in</strong> a last<strong>in</strong>g manner; <strong>in</strong> contrast, remifentanil<br />
produced a short-lived analgesia that was followed by a longerlived<br />
hyperalgesia [22]. The peri-operative use of opioids <strong>in</strong><br />
humans often produces a hyperalgesia and tolerance that have<br />
been well documented <strong>in</strong> the immediate postoperative episode<br />
[27-29]. However, surgery conducted under opioid analgesia<br />
may also be followed by a chronic pa<strong>in</strong> state [30,31] that may<br />
perhaps result from long-last<strong>in</strong>g opioid (second-order)<br />
hyperalgesia. Thus, high-efficacy 5-HT1A receptor activation<br />
might rival the <strong>in</strong>tra- and post-operative analgesia that is offered<br />
by opioids and also obviate (and pre-empt) the short- and longterm<br />
<strong>in</strong>creases <strong>in</strong> post-operative pa<strong>in</strong> that opioids may <strong>in</strong>duce.<br />
Long-term neuroadaptive actions<br />
The studies considered here exam<strong>in</strong>ed the effects of agents that<br />
were cont<strong>in</strong>uously <strong>in</strong>fused by means of subcutaneously<br />
implanted osmotic pumps, for 2 weeks or longer, <strong>in</strong> rats that<br />
were subjected to manipulations that model chronic pa<strong>in</strong> of<br />
nociceptive or neuropathic orig<strong>in</strong>.<br />
Chronic nociceptive pa<strong>in</strong><br />
The oral self adm<strong>in</strong>istration of a fentanyl solution offers a<br />
measure of the spontaneous, persistent and severe chronic<br />
nociceptive pa<strong>in</strong> that is associated with adjuvant arthritis <strong>in</strong> the<br />
rat [32]. While normal rats demonstrate hyperalgesia early after<br />
F-13640 (0.63 mg/day) pump implantation, the agent produces<br />
a dose-dependent, full analgesia <strong>in</strong> arthritic rats that is at least<br />
equivalent to that found with 5 mg/day of morph<strong>in</strong>e [15•],<br />
the dose at which morph<strong>in</strong>e produces dependence. The<br />
f<strong>in</strong>d<strong>in</strong>g that 2 weeks of morph<strong>in</strong>e treatment produces<br />
analgesia is surpris<strong>in</strong>g, because <strong>in</strong> normal rats the same<br />
treatment results <strong>in</strong> complete analgesic tolerance with<strong>in</strong> 8 h<br />
of pump implantation [15•]. However, the concept that<br />
guided this research also suggests that nociceptive<br />
stimulation hampers the development of opioid tolerance <strong>in</strong>
42 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
Table 1. Quantification of the ability of various analgesic agents to <strong>in</strong>hibit formal<strong>in</strong>-<strong>in</strong>duced paw lick<strong>in</strong>g dur<strong>in</strong>g the early and late phases follow<strong>in</strong>g <strong>in</strong>traplantar formal<strong>in</strong> <strong>in</strong>jection <strong>in</strong><br />
rats.<br />
Drug Dose range Inhibition of formal<strong>in</strong>-<strong>in</strong>duced paw lick<strong>in</strong>g<br />
Early phase Late phase<br />
ED50 95% CL MSD Lowest mean score ED50 95% CL MSD Lowest mean score<br />
Morph<strong>in</strong>e 1.25 to 40 2.4 1.1 to 5.4 10 1 ± 0.49 (10) < 1.25 - 1.25 0 ± 0 (10)<br />
Buprenorph<strong>in</strong>e 0.01 to 10 0.25 0.051 to 1.1 0.63 0.86 ± 0.46 (2.5) 0.051 0.0075 to 0.35 0.16 0.43 ± 0.3 (0.63)<br />
Imipram<strong>in</strong>e 2.5 to 40 7.6 2.5 to 23 10 0 ± 0 (40) 3.6 1.5 to 8.6 10 0 ± 0 (40)<br />
Amitryptyl<strong>in</strong>e 2.5 to 40 15 7.5 to 30 10 0 ± 0 (40) 5.1 3 to 8.7 10 0 ± 0 (40)<br />
Paroxet<strong>in</strong>e 2.5 to 40 13 6 to 28 10 0.57 ± 0.29 (40) 4.4 1.2 to 16 10 0 ± 0 (40)<br />
Aspir<strong>in</strong> 160 > 160 - > 160 5 ± 0.62 (160) > 160 - 160 5.8 ± 0.59 (160)<br />
Diclofenac 40 to 160 > 160 - 160 0.86 ± 0.34 (160) > 160 - 160 0 ± 0 (160)<br />
Paracetamol 10 to 160 > 160 - > 160 4.7 ± 0.61 (160) 93.1 a 9.9 to 872 160 4.0 ± 1.2 (160)<br />
Rofecoxib 40 to 160 > 160 - > 160 5.7 ± 0.42 (40) > 160 - > 160 6.7 ± 0.57 (40)<br />
Celecoxib 40 to 160 > 160 - > 160 5.1 ± 0.7 (40) > 160 - > 160 5.4 ± 0.78 (40)<br />
Gabapent<strong>in</strong> 10 to 640 > 640 - 40 4.1 ± 0.86 (40) < 10 - 10 2.3 ± 0.68 (160)<br />
Baclofen 0.63 to 2.5 > 2.5 - > 2.5 3.1 ± 1.3 (2.5) > 2.5 - 2.5 2.6 ± 1.3 (2.5)<br />
Carbamazep<strong>in</strong>e 40 > 40 - > 40 5.7 ± 1.1 (40) < 40 - > 40 5 ± 1.4 (40)<br />
Ketam<strong>in</strong>e 10 to 40 22 a<br />
ND 40 0.57 ± 0.57 (40) 22 a<br />
ND 40 1.6 ± 1.0 (40)<br />
Sumatriptan<br />
40 > 40 - 40 5.7 ± 0.64 (40) > 40 - 40 6.5 ± 0.3 (40)<br />
ABT-594 0.01 to 0.16 0.033 0.012 to 0.092 0.16 0.57 ± 0.57 (0.16) 0.013 0.0021 to 0.086 0.16 1.4 ± 1.4 (0.16)<br />
F-13640 0.01 to 2.5 0.081 0.051 to 0.13 0.16 0 ± 0 (0.16) 0.081 0.051 to 0.13 0.16 0 ± 0 (0.16)<br />
All compounds were <strong>in</strong>jected <strong>in</strong>traperitoneally 15 m<strong>in</strong> before formal<strong>in</strong> <strong>in</strong>jection. ED50 values, confidence limits (CL) and all drug doses are <strong>in</strong> mg/kg. The maximal drug effect is represented by the<br />
lowest mean (± SEM) score found with any dose (dose between brackets). a the ED50 was not calculated but was found by l<strong>in</strong>ear <strong>in</strong>terpolation. MSD m<strong>in</strong>imal significant dose, ND not determ<strong>in</strong>ed<br />
because of <strong>in</strong>sufficient data.<br />
42 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1
5-HT1A receptor activation Colpaert 43<br />
Table 2. Quantification of the ability of various analgesic agents to <strong>in</strong>hibit formal<strong>in</strong>-<strong>in</strong>duced paw elevation dur<strong>in</strong>g the early and late phases follow<strong>in</strong>g <strong>in</strong>traplantar formal<strong>in</strong> <strong>in</strong>jection <strong>in</strong><br />
rats.<br />
Drug Dose range Inhibition of formal<strong>in</strong>-<strong>in</strong>duced paw elevation<br />
Early phase Late phase<br />
ED50 95% CL MSD Lowest mean score ED50 95% CL MSD Lowest mean score<br />
Morph<strong>in</strong>e 1.25 to 40 4.2 2.2 to 7.8 10 3.1 ± 1.2 (40) 2.1 1.1 to 3.7 10 0 ± 0 (10)<br />
Buprenorph<strong>in</strong>e 0.01 to 10 > 10 - > 10 9.1 ± 0.7 (10) 5.8 0.51 to 70 0.63 5.4 ± 1.9 (0.63)<br />
Imipram<strong>in</strong>e 2.5 to 40 14 3.9 to 48 40 3.4 ± 1.3 (40) 7.2 2.8 to 19 10 0 ± 0 (40)<br />
Amitryptyl<strong>in</strong>e 2.5 to 40 18 9.2 to 36 40 0 ± 0 (40) 18 9.2 to 36 40 0 ± 0 (40)<br />
Paroxet<strong>in</strong>e 2.5 to 40 > 40 - > 40 9.3 ± 0.47 (40) 16 6.1 to 41 40 2.7 ± 1.8 (40)<br />
Aspir<strong>in</strong> 160 > 160 - > 160 8.8 ± 0.55 (160) > 160 - > 160 9.8 ± 0.14 (160)<br />
Diclofenac 40 to 160 > 160 - 160 4.1 ± 0.77 (160) > 160 - 160 0.43 ± 0.43 (160)<br />
Paracetamol 10 to 160 > 160 - > 160 9.7 ± 0.29 (160) 55 16 to 192 160 5.2 ± 1.5 (160)<br />
Rofecoxib 40 to 160 > 160 - > 160 9.6 ± 0.2 (160) > 160 - > 160 9.4 ± 0.43 (40)<br />
Celecoxib 40 to 160 > 160 - > 160 9.7 ± 0.18 (160) > 160 - > 160 10 ± 0 (160)<br />
Gabapent<strong>in</strong> 10 to 640 > 640 - > 640 9.5 ± 0.3 (40) > 640 - > 640 8.5 ± 1.2 (160)<br />
Baclofen 0.63 to 2.5 > 2.5 - > 2.5 7 ± 1.6 (2.5) > 2.5 - 2.5 4.3 ± 1.4 (2.5)<br />
Carbamazep<strong>in</strong>e 40 > 40 - > 40 10 ± 0 (40) > 40 - > 40 10 ± 0 (40)<br />
Ketam<strong>in</strong>e 10 to 40 > 40 - > 40 9.7 ± 0.29 (40) > 40 - 40 5.7 ± 2 (40)<br />
Sumatriptan 40 > 40 - > 40 9.7 ± 0.29 (40) > 40 - > 40 10 ± 0 (40)<br />
ABT-594 0.01 to 0.16 0.041 0.014 to 0.12 0.16 1.4 ± 1.4 (0.16) 0.068 0.027 to 0.18 0.16 1.4 ± 1.4 (0.16)<br />
F-13640 0.01 to 2.5 0.029 0.0075 to 0.11 0.16 0 ± 0 (0.63) 0.081 0.051 to 0.13 0.16 0 ± 0 (0.16)<br />
All compounds were <strong>in</strong>jected <strong>in</strong>traperitoneally 15 m<strong>in</strong> before formal<strong>in</strong> <strong>in</strong>jection. ED50 values, confidence limits (CL) and all drug doses are <strong>in</strong> mg/kg. The maximal drug effect is represented by the<br />
lowest mean (± SEM) score found with any dose (dose between brackets). MSD m<strong>in</strong>imal significant dose.<br />
Table 3. Comparative data on the effects of F-13640 and four other centrally act<strong>in</strong>g analgesics <strong>in</strong> rat models of chronic nociceptive or neuropathic pa<strong>in</strong>.<br />
Parameter (unit) Treatment (mg/rat/day)<br />
Vehicle<br />
Morph<strong>in</strong>e<br />
Ketam<strong>in</strong>e<br />
Imipram<strong>in</strong>e Gabapent<strong>in</strong> (10) F-13640<br />
(0)<br />
Chronic nociceptive pa<strong>in</strong> (adjuvant arthritis)<br />
(5)<br />
(20)<br />
(2.5)<br />
(0.63)<br />
FSA (g) 60 (40 to 72) 42* (21 to 63) 52 (34 to 88) 47* (18 to 51) 49 (36 to 70) 35** (20 to 54)<br />
Chronic neuropathic pa<strong>in</strong> (sp<strong>in</strong>al cord <strong>in</strong>jury)<br />
Response to brush (score) 2.2 (0.07) 2.7 (0.07) 2.5 (0.09) 2.3 (0.12) 2.2 (0.10) 1.0*** (0.11)<br />
Response to cold (score) 2.7 (0.05) 2.8 (0.07) 2.7 (0.07) 2.8 (0.05) 2.5 (0.07) 2.0** (0.09)<br />
von Frey threshold (g) 1.4 (0.05) 3.7 (0.04) 4.3 (0.03) 3.9 (0.04) 4.6 (0.05) 5.7* (0.07)<br />
Chronic neuropathic pa<strong>in</strong> (sciatic nerve constriction)<br />
von Frey threshold (g) 17 (0.89) 20 (1.30) 20 (3.80) 22 (3.80) 23* (4.40) 24** (2.30)<br />
Data are based on observations that were made dur<strong>in</strong>g 2 weeks after the subcutaneous implantation of osmotic m<strong>in</strong>ipumps that <strong>in</strong>fused vehicle or agents at a constant rate. Doses (expressed <strong>in</strong><br />
mg/rat/day) for the four reference analgesics correspond to the highest dose (concentration) that could be adm<strong>in</strong>istered <strong>in</strong> the experimental conditions. Results are expressed as the median (and<br />
<strong>in</strong>ter-quartile range for fentanyl self adm<strong>in</strong>istered; FSA) or the mean (+SEM for other parameters). (*p < 0.05; **p < 0.01; ***p < 0.001).<br />
5-HT1A receptor activation Colpaert 43
44 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
both an <strong>in</strong>tensity- and duration-dependent manner [10•]. Thus,<br />
the susta<strong>in</strong>ed, <strong>in</strong>tense nociception associated with adjuvant<br />
arthritis may have sufficiently <strong>in</strong>hibited opioid analgesia<br />
tolerance development for morph<strong>in</strong>e analgesia to have<br />
rema<strong>in</strong>ed significant, at least over the 2-week period. Agents<br />
exemplify<strong>in</strong>g other central mechanisms of analgesia (eg, the 5-<br />
HT and noradrenal<strong>in</strong>e re-uptake <strong>in</strong>hibitor imipram<strong>in</strong>e (2.5<br />
mg/day), the excitatory am<strong>in</strong>o acid antagonist ketam<strong>in</strong>e (20<br />
mg/day), and the anticonvulsant gabapent<strong>in</strong> (10 mg/day))<br />
were <strong>in</strong>active (Table 3). Similar to tonic nociceptive pa<strong>in</strong>, the<br />
data suggest that high-efficacy 5-HT1A receptor activation<br />
produces an analgesia with chronic nociceptive pa<strong>in</strong> that is<br />
rivaled only, if at all, by morph<strong>in</strong>e-like opioids.<br />
Chronic neuropathic pa<strong>in</strong><br />
In a model of peripheral neuropathic pa<strong>in</strong>, rats undergo a<br />
unilateral chronic constriction <strong>in</strong>jury of the common sciatic<br />
nerve and demonstrate a lowered threshold for von Frey<br />
filament stimulation to <strong>in</strong>duce paw withdrawal [33]. A 2-week<br />
<strong>in</strong>fusion of morph<strong>in</strong>e, ketam<strong>in</strong>e or imipram<strong>in</strong>e produced a<br />
slight, non-significant <strong>in</strong>crease of the ipsilateral reduced<br />
threshold <strong>in</strong> sal<strong>in</strong>e-treated rats (17 g), while gabapent<strong>in</strong> exerted<br />
a significant effect (Table 3). F-13640 produced a larger, highly<br />
significant <strong>in</strong>crease, suggest<strong>in</strong>g robust efficacy <strong>in</strong> this model<br />
[15•]. This effect on ipsilateral threshold was behaviorally<br />
specific, <strong>in</strong> that F-13640 did not modify the contralateral<br />
threshold <strong>in</strong> sal<strong>in</strong>e-treated rats (69 g).<br />
In a model of central neuropathic pa<strong>in</strong>, rats received a<br />
photochemical, ischemic <strong>in</strong>jury of sp<strong>in</strong>al cord dorsal segments<br />
L3 to L5 and developed allodynic responses to cutaneous<br />
stimulations such as von Frey filament application, a gentle<br />
brush or a cold spray [34]. Interest<strong>in</strong>gly, and as with sciatic<br />
nerve constriction, subcutaneously <strong>in</strong>fused morph<strong>in</strong>e,<br />
ketam<strong>in</strong>e, imipram<strong>in</strong>e and gabapent<strong>in</strong> <strong>in</strong>creased the von Frey<br />
threshold to some extent, although not significantly so; these<br />
agents also exerted no significant effect <strong>in</strong> response to a gentle<br />
brush or a cold spray (Table 3). In contrast, F-13640 robustly<br />
<strong>in</strong>hibited all three responses [15•]. The effects of F-13640 grew<br />
<strong>in</strong> the course of the 2-week treatment period, demonstrat<strong>in</strong>g<br />
<strong>in</strong>verse analgesic tolerance.<br />
The acute <strong>in</strong>jection of F-13640, as well as that of morph<strong>in</strong>e,<br />
can counteract allodynic responses to von Frey filament<br />
stimulation <strong>in</strong> rats susta<strong>in</strong><strong>in</strong>g a chronic constriction <strong>in</strong>jury of<br />
the <strong>in</strong>fra-orbital nerve (IoN-CCI), a model of trigem<strong>in</strong>al<br />
neuropathic pa<strong>in</strong> [35]. The effects of F-13640 <strong>in</strong> this model<br />
are aga<strong>in</strong> behaviorally specific [36]. In these rats, morph<strong>in</strong>e<br />
<strong>in</strong>fusion <strong>in</strong>itially produces a robust, significant analgesia to<br />
which complete tolerance develops after 2 weeks; the effects<br />
of F-13640 <strong>in</strong>creased rather than decl<strong>in</strong>ed dur<strong>in</strong>g the 2-week<br />
period, aga<strong>in</strong> demonstrat<strong>in</strong>g <strong>in</strong>verse tolerance [37•,38,39,40•].<br />
Collectively, these data suggest that high-efficacy 5-HT1A<br />
receptor activation may produce exceptionally powerful and<br />
susta<strong>in</strong>ed, 'symptomatic' analgesia with chronic neuropathic<br />
pa<strong>in</strong> of peripheral or central orig<strong>in</strong>.<br />
Pre-emptive and curative-like analgesia<br />
Much as opioids <strong>in</strong>duce a hyperalgesia and tolerance that<br />
may outlast µ-opioid receptor activation for a long time (eg,<br />
a year [10•,41]), the signal-transduction concept suggests<br />
that a neuropharmacological manipulation that generates<br />
the <strong>in</strong>verse of opioid actions should <strong>in</strong>duce analgesia (and<br />
cont<strong>in</strong>ue to demonstrate <strong>in</strong>verse tolerance) long after its<br />
implementation has been discont<strong>in</strong>ued.<br />
Rats were <strong>in</strong>fused with 0.63 mg/day of F-13640 for 8 weeks<br />
start<strong>in</strong>g 24 h before the sp<strong>in</strong>al cord <strong>in</strong>jury described<br />
previously; with all three cutaneous stimulations the<br />
treatment effect persisted unabated for 2 months follow<strong>in</strong>g<br />
discont<strong>in</strong>uation of treatment [42]. These data, together with<br />
the consideration that F-13640 is effective <strong>in</strong> neuropathic<br />
pa<strong>in</strong> regardless of its peripheral or central orig<strong>in</strong>, suggest<br />
that high-efficacy 5-HT1A receptor activation may<br />
powerfully 'pre-empt' pa<strong>in</strong> ensu<strong>in</strong>g from neuronal damage,<br />
such as that result<strong>in</strong>g from surgical nerve <strong>in</strong>jury or diabetes.<br />
To explore this suggestion, rats hav<strong>in</strong>g susta<strong>in</strong>ed sp<strong>in</strong>al cord<br />
<strong>in</strong>jury and hav<strong>in</strong>g fully developed allodynia were then<br />
<strong>in</strong>fused with F-13640 (0.63 mg/day) for 56 days. The<br />
treatment <strong>in</strong>creas<strong>in</strong>gly alleviated and eventually normalized<br />
the allodynic responses, thereby demonstrat<strong>in</strong>g <strong>in</strong>verse<br />
tolerance. More importantly, dur<strong>in</strong>g the 70-day period that<br />
ensued, the effects of F-13640 persisted, demonstrat<strong>in</strong>g an<br />
unprecedented 'curative-like' action on allodynic pa<strong>in</strong> [40•].<br />
It rema<strong>in</strong>s to be determ<strong>in</strong>ed whether these pre-emptive and<br />
curative-like actions are mediated by the neuron-protective<br />
and astroglial reaction-<strong>in</strong>hibitory effects that 5-HT1A<br />
agonists may produce <strong>in</strong> ischemic bra<strong>in</strong> tissue [43].<br />
Although it might be of <strong>in</strong>terest to similarly exam<strong>in</strong>e the<br />
potential pre-emptive and curative-like actions of morph<strong>in</strong>e,<br />
ketam<strong>in</strong>e, imipram<strong>in</strong>e and gabapent<strong>in</strong>, the absence of<br />
significant symptomatic effects with these agents <strong>in</strong> the<br />
sp<strong>in</strong>al cord <strong>in</strong>jury model has prevented the research group<br />
from do<strong>in</strong>g so. Indeed, any such pre-emptive actions<br />
reported so far have concerned pa<strong>in</strong> parameters that<br />
respond <strong>in</strong> a symptomatic manner to the agents be<strong>in</strong>g<br />
considered [44,45]. Prom<strong>in</strong>ent among these agents are<br />
opioids, and the largest symptomatic effects observed to<br />
date with cont<strong>in</strong>uous, 2-week <strong>in</strong>fusion of any comparable<br />
analgesic <strong>in</strong> any model of neuropathic pa<strong>in</strong> were obta<strong>in</strong>ed<br />
with 5 mg/day of morph<strong>in</strong>e <strong>in</strong> the IoN-CCI model [37•,38].<br />
As <strong>in</strong>dicated, soon after the <strong>in</strong>itiation of morph<strong>in</strong>e <strong>in</strong>fusion,<br />
a robust analgesia occurs <strong>in</strong> this model, to which tolerance<br />
develops with<strong>in</strong> 2 weeks. At that stage, discont<strong>in</strong>uation of<br />
morph<strong>in</strong>e <strong>in</strong>fusion does not afford analgesia, and <strong>in</strong> fact<br />
causes hyperallodynia [53].<br />
Tolerability<br />
Although the data discussed previously allow assessment of<br />
the comparative therapeutic potential of F-13640 relative to<br />
currently available treatments to a considerable extent, the<br />
evidence available so far offers only little <strong>in</strong> the way of an<br />
evaluation of the relative tolerability of the compound.<br />
Regard<strong>in</strong>g the opioids, however, one issue stands out; it is<br />
now recognized that the chronic use of opioids <strong>in</strong>duces an<br />
analgesic tolerance that not only limits, or dissipates their<br />
therapeutic usefulness, but is also accompanied by<br />
hyperalgesia and opioid-<strong>in</strong>duced pa<strong>in</strong> [10•,13,14]. In<br />
addition to the well-known side effects of opioids, this drug<strong>in</strong>duced<br />
pa<strong>in</strong> may become 'excruciat<strong>in</strong>g', thus severely
compromis<strong>in</strong>g the tolerability of opioids; <strong>in</strong>deed, the<br />
discont<strong>in</strong>uation of opioid treatment <strong>in</strong> these conditions may<br />
act to alleviate pa<strong>in</strong> [46]. The precl<strong>in</strong>ical data discussed<br />
suggest that, <strong>in</strong> contrast, chronic adm<strong>in</strong>istration of F-13640<br />
produces an analgesia that grows rather than decays. Of<br />
particular concern, is that agents that <strong>in</strong>teract with<br />
serotonergic neurotransmission (eg, 5-HT re-uptake<br />
<strong>in</strong>hibitors and opioids) may <strong>in</strong>duce 'seroton<strong>in</strong> syndrome' <strong>in</strong><br />
humans [47]. In several animal species, 5-HT1A agonists,<br />
<strong>in</strong>clud<strong>in</strong>g F-13640, <strong>in</strong>duce behavioral effects such as the<br />
retraction of the lower lip and postural movements <strong>in</strong> rats,<br />
forepaw tread<strong>in</strong>g, splayed h<strong>in</strong>dlimbs, flat body posture and<br />
locomotion [48-50]. Among the agents that <strong>in</strong>duce at least<br />
some of those signs <strong>in</strong> rats are antidepressant uptake<br />
<strong>in</strong>hibitors of 5-HT and noradrenal<strong>in</strong>e and buspirone [49,51],<br />
yet while the occurrence of seroton<strong>in</strong> syndrome is<br />
sporadically reported with several 5-HT and noradrenal<strong>in</strong>e<br />
uptake <strong>in</strong>hibitors and opioids [47], no such occurrence has<br />
been observed with buspirone, <strong>in</strong> spite of the considerable<br />
evidence of the syndrome that has now accumulated with<br />
regard to this agent <strong>in</strong> humans. However, no cl<strong>in</strong>ical data<br />
are currently available regard<strong>in</strong>g selective, higher-efficacy<br />
5-HT1A agonists such as F-13640.<br />
Clearly, however, with repeated or cont<strong>in</strong>uous adm<strong>in</strong>istration,<br />
the analgesic action of F-13640 grows, while at the same time<br />
tachyphylaxis develops to the ability of the drug to <strong>in</strong>duce<br />
behavioral and other signs, for example, hypothermia<br />
[15•,37•,38,39,40•,42], <strong>in</strong>dicat<strong>in</strong>g that, <strong>in</strong> the rat, the<br />
tolerability of 5-HT1A agonists <strong>in</strong>creases considerably <strong>in</strong><br />
conditions of chronic drug adm<strong>in</strong>istration.<br />
Neurobiology of hyper- and hypoalgesia<br />
The evidence discussed <strong>in</strong> this review is consistent with<br />
recent data <strong>in</strong>dicat<strong>in</strong>g that both 5-HT1A and µ-opioid<br />
receptor agonists produce apparently complex, paradoxical<br />
hypo- and hyperalgesic actions (see references [10•,11-14]<br />
for reviews). To a considerable extent, this apparent<br />
complexity is likely resolved by tak<strong>in</strong>g <strong>in</strong>to account the<br />
'base-l<strong>in</strong>e' stimulation to which pa<strong>in</strong>-process<strong>in</strong>g systems are<br />
exposed. Thus, both 5-HT1A receptor-mediated and opioid<br />
hyperalgesia are counteracted <strong>in</strong> a duration- and <strong>in</strong>tensitydependent<br />
manner by nociceptive stimulation, which<br />
enhances the analgesia produced by both 5-HT1A and opioid<br />
receptor agonists [10•]. Thus, while 5-HT1A agonists may<br />
counteract opioid hypoalgesia <strong>in</strong> animals that are exposed to<br />
limited nociceptive stimulation [52], F-13640 counteracts the<br />
hyper-allodynia that develops follow<strong>in</strong>g long-term opioid<br />
treatment <strong>in</strong> IoN-CCI-lesioned, chronically allodynic rats<br />
[53].<br />
The 5-HT1A receptor, like µ-opioid receptors, is an <strong>in</strong>hibitory<br />
G-prote<strong>in</strong>-coupled receptor. It is located with high density<br />
post-synaptically to 5-HT neurons <strong>in</strong> the hippocampus and<br />
neocortex and, as a pre-synaptic autoreceptor, <strong>in</strong> the raphe<br />
nuclei from where projections descend to pa<strong>in</strong>-process<strong>in</strong>g<br />
neurons <strong>in</strong> the sp<strong>in</strong>al cord dorsal horn where 5-HT1A<br />
receptors are located post-synaptically [2,54]. Marked<br />
regional differences <strong>in</strong> the functional adaptation of 5-HT1A<br />
receptors occur after long-term stimulation; chronic<br />
exposure to direct or <strong>in</strong>direct (ie, 5-HT uptake <strong>in</strong>hibitors)<br />
5-HT1A receptor activation Colpaert 45<br />
agonists desensitizes 5-HT1A presynaptic autoreceptors <strong>in</strong><br />
the raphe nuclei without alter<strong>in</strong>g the response properties of<br />
post-synaptic 5-HT1A receptors <strong>in</strong> the projection areas (eg,<br />
the sp<strong>in</strong>al cord dorsal horn) of raphe neurons [55]. Thus,<br />
with chronic exposure, the 5-HT1A autoreceptor-mediated<br />
<strong>in</strong>hibitory feedback control of serotonergic neurotransmission<br />
decays, enabl<strong>in</strong>g serotonergic signal<strong>in</strong>g at post-synaptic<br />
5-HT1A receptors [55]. This desensitization of presynaptic<br />
5-HT1A autoreceptors may conceivably play a role <strong>in</strong> the<br />
tachyphylaxis that develops to 5-HT1A agonist-<strong>in</strong>duced<br />
hyperalgesia, but further research is required to elucidate<br />
this po<strong>in</strong>t.<br />
Conclusions<br />
The precl<strong>in</strong>ical evidence summarized here suggests that<br />
high-efficacy 5-HT1A receptor stimulation presents a new<br />
molecular and neuroadaptive approach to the treatment of<br />
acute and chronic, nociceptive and neuropathic pa<strong>in</strong> states,<br />
as well as achiev<strong>in</strong>g pa<strong>in</strong> relief <strong>in</strong> conditions that have<br />
rema<strong>in</strong>ed <strong>in</strong>accessible, even after opioid or other treatment.<br />
Hav<strong>in</strong>g never been studied <strong>in</strong> humans, cl<strong>in</strong>ical<br />
<strong>in</strong>vestigations are now <strong>in</strong> order to assess the efficacy of<br />
compounds such as F-13640 <strong>in</strong> patients.<br />
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48<br />
Glyc<strong>in</strong>e receptors: A new therapeutic target <strong>in</strong> pa<strong>in</strong> pathways<br />
Joseph W Lynch 1 * & Robert J Callister 2<br />
Addresses<br />
1 School of Biomedical Sciences<br />
University of Queensland<br />
Brisbane<br />
QLD 4072<br />
Australia<br />
Email: j.lynch@uq.edu.au<br />
2School of Biomedical Sciences<br />
Faculty of Health and Hunter Medical Research Institute<br />
University of Newcastle<br />
Callaghan<br />
NSW 2308<br />
Australia<br />
*To whom correspondence should be addressed<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 7(1):48-53<br />
© The Thomson Corporation ISSN 1472-4472<br />
Although glyc<strong>in</strong>e receptor Cl − channels (GlyRs) have long been<br />
known to mediate <strong>in</strong>hibitory neurotransmission onto sp<strong>in</strong>al<br />
nociceptive neurons, their therapeutic potential for peripheral<br />
analgesia has received little attention. However, it has been shown<br />
that α3-subunit-conta<strong>in</strong><strong>in</strong>g GlyRs are concentrated <strong>in</strong>to regions of<br />
the sp<strong>in</strong>al cord dorsal horn where nociceptive afferents term<strong>in</strong>ate.<br />
Furthermore, <strong>in</strong>flammatory mediators specifically <strong>in</strong>hibit α3conta<strong>in</strong><strong>in</strong>g<br />
GlyRs, and deletion of the mur<strong>in</strong>e α3 gene confers<br />
<strong>in</strong>sensitivity to chronic <strong>in</strong>flammatory pa<strong>in</strong>. This strongly<br />
implicates GlyRs <strong>in</strong> the <strong>in</strong>flammation-mediated dis<strong>in</strong>hibition of<br />
centrally project<strong>in</strong>g nociceptive neurons. Future therapies aimed<br />
at specifically <strong>in</strong>creas<strong>in</strong>g current flux through α3-conta<strong>in</strong><strong>in</strong>g<br />
GlyRs may prove effective <strong>in</strong> provid<strong>in</strong>g analgesia.<br />
Keywords Analgesia, chloride channel, drug discovery,<br />
<strong>in</strong>flammatory pa<strong>in</strong>, <strong>in</strong>hibitory neurotransmission,<br />
neuropathic pa<strong>in</strong>, sp<strong>in</strong>al cord<br />
Introduction<br />
Pa<strong>in</strong> is a complex and highly modifiable sensory experience.<br />
Over the past 50 years our view of pa<strong>in</strong> mechanisms and<br />
treatment has changed considerably. The current paradigm<br />
is that pa<strong>in</strong> results from the complex <strong>in</strong>teraction of a variety<br />
of synaptic <strong>in</strong>puts <strong>in</strong> a pathway that beg<strong>in</strong>s at peripheral<br />
receptors, ascends the neural axis, and f<strong>in</strong>ally reaches the<br />
cerebral cortex and limbic structures, such as the amygdala<br />
[1•]. The majority of current approaches to treat<strong>in</strong>g pa<strong>in</strong> are<br />
based on the idea that <strong>in</strong>creas<strong>in</strong>g the level of <strong>in</strong>hibitory drive<br />
or tone at key central nervous system (CNS) regions <strong>in</strong> the<br />
pa<strong>in</strong> pathway can alter pa<strong>in</strong> perception [2-4,5•]. Because<br />
γ-am<strong>in</strong>obutyric acid (GABA)A and glyc<strong>in</strong>e receptor Cl −<br />
channels (GABAARs and GlyRs) mediate <strong>in</strong>hibitory<br />
neurotransmission <strong>in</strong> the CNS, they represent key targets for<br />
pharmacologically manipulat<strong>in</strong>g <strong>in</strong>hibitory drive.<br />
Until recently, <strong>in</strong>vestigation of <strong>in</strong>hibitory mechanisms <strong>in</strong><br />
pa<strong>in</strong> process<strong>in</strong>g focused on the role of GABAARs <strong>in</strong> various<br />
regions of the pa<strong>in</strong> pathway, particularly <strong>in</strong> the dorsal horn<br />
of the sp<strong>in</strong>al cord and <strong>in</strong> the bra<strong>in</strong>stem [2,3,5•,6]. The role of<br />
GlyRs <strong>in</strong> pa<strong>in</strong> process<strong>in</strong>g has largely been ignored because<br />
of the lack of pharmaceutical agents that specifically<br />
modulate them <strong>in</strong> a therapeutically useful way. However, this<br />
situation has changed with the demonstration that α3 subunitconta<strong>in</strong><strong>in</strong>g<br />
GlyRs expressed <strong>in</strong> sp<strong>in</strong>al cord dorsal horn synapses<br />
are specifically <strong>in</strong>hibited by <strong>in</strong>flammatory mediators [7••].<br />
These GlyRs, which are sparsely expressed outside the sp<strong>in</strong>al<br />
cord dorsal horn, represent a new analgesic target. Molecules<br />
that can specifically enhance (or potentiate) Cl − current flow<br />
through this particular GlyR isoform offer promise as<br />
therapeutic lead compounds. The challenge now is to identify<br />
such molecules. This review summarizes our current<br />
understand<strong>in</strong>g of GlyRs <strong>in</strong> terms of their distribution <strong>in</strong> regions<br />
of the CNS important <strong>in</strong> pa<strong>in</strong> process<strong>in</strong>g, their subunit<br />
composition, and mechanisms by which they may be<br />
modulated.<br />
The ascend<strong>in</strong>g pa<strong>in</strong> pathway<br />
Although there is much conjecture and disagreement regard<strong>in</strong>g<br />
the specific details of ascend<strong>in</strong>g pa<strong>in</strong> pathways [1•,8-11], any<br />
approach to the treatment of pa<strong>in</strong>ful conditions requires an<br />
understand<strong>in</strong>g of the elements and circuitry of the pathway.<br />
The classic pa<strong>in</strong>-process<strong>in</strong>g pathway <strong>in</strong>volves numerous<br />
neuron clusters (hereafter termed 'nodes') located <strong>in</strong><br />
anatomically discrete regions of the CNS (Figure 1A). The<br />
nodes, especially those <strong>in</strong> the sp<strong>in</strong>al cord and bra<strong>in</strong>stem, are<br />
known to conta<strong>in</strong> sub-synaptic GlyRs and GABAARs that<br />
participate <strong>in</strong> Cl − -mediated fast <strong>in</strong>hibitory synaptic<br />
transmission [12,13,14•,15-17]. Immunohistochemical and<br />
electrophysiological studies have also shown that cortical and<br />
sub-cortical centers conta<strong>in</strong> extra-synaptic GlyRs (for examples,<br />
see below). Because these extra-synaptic receptors are located <strong>in</strong><br />
bra<strong>in</strong> regions known to be important <strong>in</strong> pa<strong>in</strong> process<strong>in</strong>g, the<br />
specific target<strong>in</strong>g of extra-synaptic GlyRs may, <strong>in</strong> pr<strong>in</strong>cipal,<br />
offer a therapeutic route for the treatment of pa<strong>in</strong>. However, as<br />
the role of non-synaptic GlyRs <strong>in</strong> bra<strong>in</strong> function is not yet<br />
understood, we focus on synaptic GlyRs as potential targets for<br />
pa<strong>in</strong> therapies.<br />
Nociceptors located <strong>in</strong> the sk<strong>in</strong>, deep tissues and viscera signal<br />
the presence of potentially harmful (or noxious) stimuli (Figure<br />
1B and C) [1•]. Central projections from these peripheral<br />
receptors enter the sp<strong>in</strong>al cord dorsal horn via small-diameter<br />
(Aδ- and C-fiber) primary afferents [18•,19•]. Other sensory<br />
receptors also provide signals to the dorsal horn regard<strong>in</strong>g nonnoxious<br />
stimuli <strong>in</strong> both cutaneous and deep tissues, via largediameter,<br />
myel<strong>in</strong>ated Aβ fibers [1•]. Inputs from both small-<br />
and large-diameter afferents make synaptic connections with<br />
various neuronal types <strong>in</strong> specific stratified zones (or lam<strong>in</strong>ae)<br />
of the dorsal horn (Figure 1C). Neurons <strong>in</strong> lam<strong>in</strong>ae I and II (the<br />
outermost strata) receive both monosynaptic and polysynaptic<br />
<strong>in</strong>put from Aδ- and C-fibers. Neurons <strong>in</strong> lam<strong>in</strong>ae III to IV<br />
receive <strong>in</strong>put almost exclusively from large-diameter Aβ-fibers,<br />
and neurons <strong>in</strong> lam<strong>in</strong>a V receive <strong>in</strong>put from Aδ-, C- and Aβfibers.<br />
Projection neurons <strong>in</strong> lam<strong>in</strong>ae I and V relay this<br />
<strong>in</strong>formation onto ascend<strong>in</strong>g pa<strong>in</strong> pathways [8].<br />
Classic textbook views of dorsal horn circuitry overly focus<br />
on projection neurons because they are the output neurons<br />
of the dorsal horn, contribute to ascend<strong>in</strong>g pathways, and
Figure 1. Important components of the pa<strong>in</strong> pathway.<br />
A<br />
Cortex<br />
Thalamus<br />
PAG, LC<br />
PB<br />
RVM<br />
DH<br />
B<br />
C<br />
Glyc<strong>in</strong>e receptors Lynch & Callister 49<br />
(A) Key process<strong>in</strong>g nodes <strong>in</strong> the pa<strong>in</strong> pathway. Spike tra<strong>in</strong>s carry<strong>in</strong>g <strong>in</strong>formation regard<strong>in</strong>g noxious and <strong>in</strong>nocuous stimuli are processed <strong>in</strong><br />
the dorsal horn (DH) of the sp<strong>in</strong>al cord and further processed <strong>in</strong> various nodes (ellipses) as they ascend the neural axis to eventually reach<br />
the thalamus and cortical regions. Midbra<strong>in</strong> nodes, such as the periaqueductal gray (PAG), locus coeruleus (LC), and para-brachial nucleus<br />
(PB), exert powerful descend<strong>in</strong>g modulatory effects on the DH via their projections to another pa<strong>in</strong> node, the rostral ventromedial medulla<br />
(RVM sp<strong>in</strong>al projection: thick arrow). (B) Sp<strong>in</strong>al cord cross-section show<strong>in</strong>g peripheral sensory afferents enter<strong>in</strong>g the DH, the first process<strong>in</strong>g<br />
node <strong>in</strong> the pa<strong>in</strong> pathway. Projection neurons (black stars) provide the output of the dorsal horn and are located <strong>in</strong> lam<strong>in</strong>ae I and V. (C)<br />
Expanded view (region circled <strong>in</strong> B) of the DH emphasis<strong>in</strong>g the role of excitatory (gray circles) and <strong>in</strong>hibitory (white circles) <strong>in</strong>terneurons <strong>in</strong><br />
DH circuitry. In the superficial strata (lam<strong>in</strong>ae I and II) of the DH, Aδ- and C-fibers contact projection neurons (black stars) as well as<br />
excitatory and <strong>in</strong>hibitory <strong>in</strong>terneurons. These <strong>in</strong>terneurons contact other <strong>in</strong>terneurons and also receive <strong>in</strong>put from descend<strong>in</strong>g pathways (not<br />
shown; see Figure 1A). Neurons <strong>in</strong> deeper lam<strong>in</strong>ae (IV to VI) receive <strong>in</strong>put from Aδ- and C-fibers <strong>in</strong> addition to large-diameter Aβ-fibers. In<br />
some chronic pa<strong>in</strong> states, it is believed that sp<strong>in</strong>al cord circuits are altered so that the <strong>in</strong>fluence of large-diameter afferents on the excitability<br />
of projection neurons <strong>in</strong>creases. Numerous studies have shown that reduced <strong>in</strong>hibition <strong>in</strong> DH circuits plays a key role, however, the exact<br />
circuitry and mechanisms are unknown.<br />
provide different qualities to pa<strong>in</strong> perception [8,20].<br />
However, it must be emphasized that the neuron population<br />
of the dorsal horn is highly heterogeneous. Most neurons<br />
are, <strong>in</strong> fact, excitatory or <strong>in</strong>hibitory <strong>in</strong>terneurons [21••,22].<br />
The <strong>in</strong>hibitory <strong>in</strong>terneurons can be broadly grouped <strong>in</strong>to<br />
those that express GABAARs and those that express both<br />
GABAARs and GlyRs [12,13]. Importantly, their activity can<br />
dramatically alter the excitability of projection neurons<br />
[14•,21••,22-25]. Thus, understand<strong>in</strong>g <strong>in</strong>hibitory <strong>in</strong>terneuron<br />
function is central to pa<strong>in</strong> mechanisms, pa<strong>in</strong> perception and<br />
pa<strong>in</strong> therapy (Figure 1C).<br />
Descend<strong>in</strong>g pathways<br />
A major pr<strong>in</strong>ciple of sensory system neurobiology is that the<br />
CNS itself exerts powerful control over the flow of<br />
<strong>in</strong>formation from peripheral receptors [2,3,8]. The first<br />
experimental evidence for such an 'endogenous pa<strong>in</strong> control<br />
mechanism' came <strong>in</strong> the late 1960s, when it was reported<br />
that stimulation of the midbra<strong>in</strong> periaqueductal gray (PAG)<br />
reduced responses to pa<strong>in</strong>ful stimuli <strong>in</strong> rats [26]. Subsequent<br />
studies have reported that stimulation of analogous bra<strong>in</strong><br />
regions <strong>in</strong> humans can produce analgesia <strong>in</strong> patients<br />
suffer<strong>in</strong>g from <strong>in</strong>tractable cancer pa<strong>in</strong> [27]. Accord<strong>in</strong>gly,<br />
there has been considerable cl<strong>in</strong>ical <strong>in</strong>terest <strong>in</strong> this<br />
mechanism [28]. Indeed, opiate adm<strong>in</strong>istration, currently a<br />
major therapeutic approach to the treatment of both acute<br />
C<br />
Aδ<br />
Aβ<br />
and chronic pa<strong>in</strong>, relies on the recruitment of endogenous<br />
(<strong>in</strong>hibitory) pa<strong>in</strong> control mechanisms [29,30].<br />
The importance of descend<strong>in</strong>g pathways <strong>in</strong> blunt<strong>in</strong>g or<br />
<strong>in</strong>hibit<strong>in</strong>g responses to pa<strong>in</strong>ful stimuli is now well accepted<br />
[2,6,29]. Unfortunately, some studies <strong>in</strong> animal models of<br />
chronic pa<strong>in</strong> have shown that activation of descend<strong>in</strong>g<br />
pathways can also enhance pa<strong>in</strong> responses [31,32]. Thus, the<br />
role of descend<strong>in</strong>g <strong>in</strong>puts is more complex than previously<br />
thought and this could help expla<strong>in</strong> why the treatment of<br />
chronic pa<strong>in</strong> has been so problematic.<br />
Several bra<strong>in</strong>stem nuclei are well recognized as midbra<strong>in</strong><br />
pa<strong>in</strong> process<strong>in</strong>g nodes (Figure 1A). These <strong>in</strong>clude the PAG,<br />
the locus coeruleus (LC), the parabrachial nucleus (PB) and<br />
the rostral ventromedial medulla (RVM) [2,3]. Although<br />
these regions conta<strong>in</strong> GlyRs [33,34••,35-37], the exact<br />
circuitry and synaptic l<strong>in</strong>kages <strong>in</strong>volved are extremely<br />
complex and are poorly understood. The available<br />
electrophysiological, anatomical and behavioral data suggest<br />
that the more rostral nuclei exert their modulatory effects on<br />
sp<strong>in</strong>al cord process<strong>in</strong>g via relays to the RVM (Figure 1A).<br />
RVM <strong>in</strong>puts arrive at all cell types <strong>in</strong> the dorsal horn of the<br />
sp<strong>in</strong>al cord [19•,34••,38]; however, little is known about<br />
specific descend<strong>in</strong>g connections with glyc<strong>in</strong>ergic<br />
<strong>in</strong>terneurons.
50 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
Inhibitory mechanisms <strong>in</strong> the sp<strong>in</strong>al cord and<br />
the gate theory of pa<strong>in</strong><br />
In 1965, Melzack and Wall proposed the 'gate control' theory<br />
of pa<strong>in</strong> [39••]. At the time there was great <strong>in</strong>terest <strong>in</strong><br />
descend<strong>in</strong>g <strong>in</strong>hibitory pathways and their capacity to <strong>in</strong>hibit<br />
sp<strong>in</strong>al reflexes [40]. Simplistically, this theory stated that<br />
<strong>in</strong>hibitory synaptic mechanisms <strong>in</strong> the sp<strong>in</strong>al cord dorsal<br />
horn play a key role <strong>in</strong> determ<strong>in</strong><strong>in</strong>g whether peripheral<br />
stimuli on small-diameter afferent fibers (Aδ- and C-fibers)<br />
can raise the level of excitability <strong>in</strong> projection neurons and<br />
subsequently be perceived as pa<strong>in</strong>ful. Even though the<br />
orig<strong>in</strong>al theory has been criticized, its <strong>in</strong>fluence has persisted<br />
because it emphasized the importance of <strong>in</strong>hibitory<br />
mechanisms.<br />
Under normal conditions, <strong>in</strong>hibitory drive <strong>in</strong> sp<strong>in</strong>al<br />
projection and local circuit neurons is mediated by both<br />
GABAAergic and glyc<strong>in</strong>ergic synapses [5•,14•,25,34••,35,41].<br />
Although the exact contribution of these two forms of<br />
<strong>in</strong>hibition is unknown, the faster k<strong>in</strong>etics of glyc<strong>in</strong>ergic<br />
<strong>in</strong>hibitory post-synaptic currents implies that they have<br />
dist<strong>in</strong>ct roles <strong>in</strong> synaptic <strong>in</strong>tegration [12,13,42]. It is also<br />
important to note that these receptors may cease to be<br />
<strong>in</strong>hibitory <strong>in</strong> neuropathic pa<strong>in</strong>; an <strong>in</strong>crease <strong>in</strong> <strong>in</strong>tracellular<br />
Cl − <strong>in</strong> lam<strong>in</strong>a I neurons follow<strong>in</strong>g peripheral nerve <strong>in</strong>jury<br />
results <strong>in</strong> depolarization and action potential generation<br />
follow<strong>in</strong>g GABAAR activation [43].<br />
Follow<strong>in</strong>g both peripheral <strong>in</strong>flammation and nerve <strong>in</strong>jury,<br />
there is an extensive physiological and morphological<br />
reorganization <strong>in</strong> dorsal horn circuitry, which ultimately<br />
leads to a net reduction <strong>in</strong> <strong>in</strong>hibitory tone [5•,44•,45-48] and<br />
<strong>in</strong>creased excitability <strong>in</strong> ascend<strong>in</strong>g pathways. Likewise,<br />
descend<strong>in</strong>g <strong>in</strong>hibitory mechanisms act<strong>in</strong>g via pre- and postsynaptic<br />
mechanisms are known to be important <strong>in</strong> sett<strong>in</strong>g<br />
excitability levels <strong>in</strong> both normal and pathological<br />
conditions [1•,2,8].<br />
GlyR subunit composition and distribution<br />
GlyRs belong to the cyste<strong>in</strong>e-loop family of ligand-gated ion<br />
channel receptors. A total of five GlyR subunits (α1 to α4<br />
and β) plus several splice variants have been identified [49•].<br />
Functional receptors comprise either α homomeric<br />
pentamers or α:β heteromers <strong>in</strong> a 2:3 stoichiometry [50••].<br />
The cytoplasmic prote<strong>in</strong> gephyr<strong>in</strong> b<strong>in</strong>ds only to the βsubunit<br />
and is essential for cluster<strong>in</strong>g GlyRs at post-synaptic<br />
densities [51].<br />
Homomeric α2 GlyRs are abundantly and evenly distributed<br />
over the membrane surface of embryonic neurons [52].<br />
Because <strong>in</strong>tracellular Cl − concentration is high, activation of<br />
embryonic GlyRs <strong>in</strong>duces neuronal depolarization and a<br />
subsequent calcium <strong>in</strong>flux that is important for neuronal<br />
differentiation [53,54]. Glyc<strong>in</strong>ergic synapses beg<strong>in</strong> to form<br />
before birth <strong>in</strong> the rat, with their appearance correlat<strong>in</strong>g with<br />
the expression of the β-subunit [55]. By the third postnatal<br />
week, most α2 homomers have been replaced by α1β<br />
heteromers [52]. This isoform predom<strong>in</strong>ates at sp<strong>in</strong>al cord<br />
<strong>in</strong>hibitory synapses and also mediates <strong>in</strong>hibitory<br />
neurotransmission <strong>in</strong> several bra<strong>in</strong>stem nuclei, as well as at<br />
def<strong>in</strong>ed synapses <strong>in</strong> the cerebellum and ret<strong>in</strong>a [49•]. The α2<br />
and α3 subunits are expressed at lower levels <strong>in</strong> the adult<br />
and exhibit dist<strong>in</strong>ct synaptic expression patterns that are<br />
particularly evident <strong>in</strong> the ret<strong>in</strong>a [56,57•]. The α3 subunit is<br />
also <strong>in</strong>corporated <strong>in</strong>to GlyRs on neurons <strong>in</strong> lam<strong>in</strong>a II of the<br />
dorsal horn [7••]. The α4 subunit is a pseudo-gene <strong>in</strong><br />
humans [58].<br />
Non-synaptic GlyRs are more widely distributed throughout<br />
the adult nervous system. They have so far been found <strong>in</strong><br />
the cortex [53], dorsal midbra<strong>in</strong> [59••], hippocampus [60],<br />
caudatoputamen [61] and basolateral amygdala [62]. As<br />
stated previously, little is known about their roles. However,<br />
one study, published <strong>in</strong> 2005, demonstrated that α3 subunit<br />
transcripts undergo RNA edit<strong>in</strong>g, result<strong>in</strong>g <strong>in</strong> a P185L<br />
substitution <strong>in</strong> the external ligand-b<strong>in</strong>d<strong>in</strong>g doma<strong>in</strong> [59••].<br />
This mutation dramatically <strong>in</strong>creases glyc<strong>in</strong>e sensitivity,<br />
with the result that non-synaptic α3-conta<strong>in</strong><strong>in</strong>g GlyRs <strong>in</strong> the<br />
superior colliculus are held open by ambient glyc<strong>in</strong>e,<br />
result<strong>in</strong>g <strong>in</strong> strong tonic <strong>in</strong>hibition [59••]. The amount of<br />
mutant transcript <strong>in</strong> immature bra<strong>in</strong> is <strong>in</strong>creased by bra<strong>in</strong><br />
slic<strong>in</strong>g, suggest<strong>in</strong>g that the RNA edit<strong>in</strong>g process may be an<br />
adaptive mechanism to compensate for excessive<br />
excitability. Many questions rema<strong>in</strong> about this mechanism.<br />
For example, its anatomical distribution and subunitspecificity<br />
are not known, and the extent to which it occurs<br />
<strong>in</strong> vivo under physiological or realistic pathological<br />
(<strong>in</strong>clud<strong>in</strong>g pa<strong>in</strong>) conditions also rema<strong>in</strong>s to be elucidated.<br />
GlyR α3 subunits and pa<strong>in</strong><br />
Although GlyR α3 subunits are sparsely distributed, some<br />
research has identified a specific role for them <strong>in</strong> sp<strong>in</strong>al cord<br />
pa<strong>in</strong> process<strong>in</strong>g. First it was shown that the <strong>in</strong>flammatory<br />
mediator prostagland<strong>in</strong> E2 (PGE2) reduced <strong>in</strong>hibitory<br />
glyc<strong>in</strong>ergic neurotransmission onto lam<strong>in</strong>a II neurons [63••].<br />
This effect, mediated via activation of the EP2 receptor,<br />
<strong>in</strong>volved the activation of a cholera-tox<strong>in</strong>-sensitive G prote<strong>in</strong><br />
and a cAMP-dependent prote<strong>in</strong> k<strong>in</strong>ase. This important<br />
f<strong>in</strong>d<strong>in</strong>g implied that <strong>in</strong>flammatory pa<strong>in</strong> sensitization is<br />
mediated, at least <strong>in</strong> part, by an <strong>in</strong>hibition of sp<strong>in</strong>al<br />
glyc<strong>in</strong>ergic neurotransmission.<br />
A subsequent study demonstrated that α1 and α3 subunits<br />
were equally represented at glyc<strong>in</strong>ergic synapses <strong>in</strong> lam<strong>in</strong>a<br />
II neurons [7••]. Recomb<strong>in</strong>antly expressed α3 GlyRs were<br />
<strong>in</strong>hibited by PGE2 via a prote<strong>in</strong> k<strong>in</strong>ase (PK)A-dependent<br />
phosphorylation [7••]. However, α1 GlyRs, which do not<br />
have PKA-dependent phosphorylation sites, were not<br />
affected. This prompted the hypothesis that the α3 subunit<br />
was specifically modulated by <strong>in</strong>flammatory stimuli. A GlyR<br />
α3 knockout mouse was used to test this theory further.<br />
Although the mice displayed no overt behavioral<br />
phenotype, the PGE2-dependent decrease of lam<strong>in</strong>a II<br />
glyc<strong>in</strong>ergic currents was abolished [7••]. Behaviorally,<br />
normal and GlyR α3 -/- mice responded similarly to acute<br />
pa<strong>in</strong> stimuli. However, peripheral <strong>in</strong>flammation produced<br />
pa<strong>in</strong> sensitization <strong>in</strong> normal animals, but not <strong>in</strong> the GlyR α3<br />
-/- animals [7••]. These f<strong>in</strong>d<strong>in</strong>gs show that the currents<br />
carried by α3-conta<strong>in</strong><strong>in</strong>g GlyRs are specifically <strong>in</strong>hibited <strong>in</strong><br />
an animal model of <strong>in</strong>flammatory pa<strong>in</strong>. Such an effect would
educe the <strong>in</strong>hibitory drive onto nociceptive projection<br />
neurons, thereby <strong>in</strong>creas<strong>in</strong>g the transmission of nociceptive<br />
stimuli to the bra<strong>in</strong>.<br />
The GlyR α3 subunit as a therapeutic target<br />
In pr<strong>in</strong>cipal, there are several ways to compensate for the<br />
effects of <strong>in</strong>flammation on α3-conta<strong>in</strong><strong>in</strong>g GlyRs. One is to<br />
<strong>in</strong>crease the magnitude or slow the decay rate of glyc<strong>in</strong>ergic<br />
synaptic currents <strong>in</strong> lam<strong>in</strong>a II neurons (Figure 1C), and<br />
another is to <strong>in</strong>crease the magnitude of non-synaptic GlyRs<br />
(or other Cl − channels) <strong>in</strong> these neurons. Although<br />
<strong>in</strong>creas<strong>in</strong>g the current through α1-conta<strong>in</strong><strong>in</strong>g GlyRs should<br />
compensate for the decrease <strong>in</strong> current through α3conta<strong>in</strong><strong>in</strong>g<br />
GlyRs, the risk of side effects is higher given that<br />
α1 subunits are more widespread outside lam<strong>in</strong>a II. Ideally,<br />
therapeutic <strong>in</strong>terventions should selectively <strong>in</strong>crease current<br />
through the downregulated (ie, phosphorylated) α3conta<strong>in</strong><strong>in</strong>g<br />
GlyRs.<br />
Unfortunately, very little is known about the pharmacology of<br />
α3-conta<strong>in</strong><strong>in</strong>g GlyRs. Until publication of the study by Harvey<br />
et al [7••], this subunit was virtually ignored because of its low<br />
expression and limited distribution. The physiology and<br />
molecular pharmacology of α1, α2, α1β and α2β GlyRs have<br />
been studied <strong>in</strong> much more detail, and several classes of<br />
compounds (eg, trope<strong>in</strong>es, alcohols and volatile anesthetics,<br />
butyrolactones, neurosteroids and dihydropyrid<strong>in</strong>es) are<br />
known to potentiate these receptors <strong>in</strong> a subunit-specific<br />
manner [49•]. These compound families may provide a start<strong>in</strong>g<br />
po<strong>in</strong>t for identify<strong>in</strong>g α3-specific potentiat<strong>in</strong>g agents.<br />
An alternative therapeutic approach might <strong>in</strong>volve <strong>in</strong>terfer<strong>in</strong>g<br />
with post-translational modifications that affect the magnitude<br />
or sensitivity of glyc<strong>in</strong>ergic currents. One potential mechanism<br />
<strong>in</strong>volves the previously described RNA edit<strong>in</strong>g process that<br />
leads to the α3 subunit P185L mutation. If the glyc<strong>in</strong>e sensitivity<br />
of sp<strong>in</strong>al α3 GlyRs could be <strong>in</strong>creased via this mechanism, the<br />
result<strong>in</strong>g enhanced <strong>in</strong>hibition may effect some degree of relief<br />
from chronic pa<strong>in</strong> syndromes.<br />
Conclusion<br />
Pa<strong>in</strong>-process<strong>in</strong>g circuitry <strong>in</strong>creases <strong>in</strong> complexity as it<br />
ascends the neural axis. A great deal is now known<br />
regard<strong>in</strong>g the neuronal types and distribution of GlyR<br />
subunits <strong>in</strong> sp<strong>in</strong>al cord pa<strong>in</strong>-process<strong>in</strong>g circuits, but rather<br />
less is known about their role <strong>in</strong> higher bra<strong>in</strong> regions. Thus,<br />
the sp<strong>in</strong>al cord dorsal horn would appear to be the best<br />
place to focus efforts on us<strong>in</strong>g GlyR modulation to alter pa<strong>in</strong><br />
process<strong>in</strong>g. As sp<strong>in</strong>al GlyR α3 subunits are specifically<br />
<strong>in</strong>hibited by <strong>in</strong>flammatory mediators <strong>in</strong> an animal model of<br />
chronic pa<strong>in</strong>, this receptor provides an excellent candidate<br />
therapeutic target.<br />
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Edition. Kluwer Academic/Plenum Publishers, New York, NY, USA (2004).<br />
• This classic text summarizes the anatomy, physiology and pharmacology of<br />
the sp<strong>in</strong>al cord dorsal horn.<br />
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by <strong>in</strong>troduc<strong>in</strong>g antagonists of GABAA and GlyRs, exaggerated responses to<br />
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Smart TG, Harvey K, Schutz B, Abo-Salem OM, Zimmer A et al: GlyR<br />
α3: An essential target for sp<strong>in</strong>al PGE2-mediated <strong>in</strong>flammatory pa<strong>in</strong><br />
sensitization. Science (2004) 304(5672):884-887.<br />
•• This is a landmark paper implicat<strong>in</strong>g the GlyR α3 subunit as a therapeutic<br />
target for <strong>in</strong>flammatory pa<strong>in</strong>.<br />
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of dorsal horn neuron activity <strong>in</strong>volves GABA and/or glyc<strong>in</strong>e release <strong>in</strong> the<br />
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39. Melzack R, Wall PD: Pa<strong>in</strong> mechanisms: A new theory. Science (1965)<br />
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•• This is a classic paper propos<strong>in</strong>g the importance of <strong>in</strong>hibitory mechanisms<br />
<strong>in</strong> the sp<strong>in</strong>al cord dorsal horn for understand<strong>in</strong>g the treatment of pa<strong>in</strong>. It also<br />
provides an historical account of arguments for 'specificity' and 'patterned<br />
activity' theories of pa<strong>in</strong> process<strong>in</strong>g and perception.<br />
40. Lundberg A, Norrssell U, Voorhoeve P: Effects from the sensory<br />
motor cortex on ascend<strong>in</strong>g sp<strong>in</strong>al pathways. Acta Physiol Scand<br />
(1963) 59:462-473.<br />
41. Yoshimura M, Nishi S: Primary afferent-evoked glyc<strong>in</strong>e- and GABAmediated<br />
IPSPs <strong>in</strong> substantia gelat<strong>in</strong>osa neurones <strong>in</strong> the rat sp<strong>in</strong>al<br />
cord <strong>in</strong> vitro. J Physiol (1995) 482(1):29-38.<br />
42. Keller AF, Coull JA, Chery N, Poisbeau P, De Kon<strong>in</strong>ck Y: Regionspecific<br />
developmental specialization of GABA-glyc<strong>in</strong>e cosynapses<br />
<strong>in</strong> lam<strong>in</strong>as I-II of the rat sp<strong>in</strong>al dorsal horn. J Neurosci (2001)<br />
21(20):7871-7880.<br />
43. Coull JA, Boudreau D, Bachand K, Prescott SA, Nault F, Sik A, De<br />
Kon<strong>in</strong>ck P, De Kon<strong>in</strong>ck Y: Trans-synaptic shift <strong>in</strong> anion gradient <strong>in</strong><br />
sp<strong>in</strong>al lam<strong>in</strong>a I neurons as a mechanism of neuropathic pa<strong>in</strong>.<br />
Nature (2003) 424(6951):938-942.<br />
44. Sork<strong>in</strong> LS, Puig S: Neuronal model of tactile allodynia produced by<br />
sp<strong>in</strong>al strychn<strong>in</strong>e: Effects of excitatory am<strong>in</strong>o acid receptor antagonists<br />
and a µ-opiate receptor agonist. Pa<strong>in</strong> (1996) 68(2-3):283-292.<br />
• This study showed the importance of GlyR-mediated <strong>in</strong>hibitory tone <strong>in</strong><br />
chronic pa<strong>in</strong> syndromes, such as tactile allodynia.<br />
45. Sork<strong>in</strong> LS, Puig S, Jones DL: Sp<strong>in</strong>al bicucull<strong>in</strong>e produces<br />
hypersensitivity of dorsal horn neurons: Effects of excitatory<br />
am<strong>in</strong>o acid antagonists. Pa<strong>in</strong> (1998) 77(2):181-190.<br />
46. Wall PD, Lidierth M, Hillman P: Brief and prolonged effects of Lissauer<br />
tract stimulation on dorsal horn cells. Pa<strong>in</strong> (1999) 83(3):579-589.<br />
47. Baba H, Doubell TP, Woolf CJ: Peripheral <strong>in</strong>flammation facilitates Aβ<br />
fiber-mediated synaptic <strong>in</strong>put to the substantia gelat<strong>in</strong>osa of the<br />
adult rat sp<strong>in</strong>al cord. J Neurosci (1999) 19(2):859-867.<br />
48. Kont<strong>in</strong>en VK, Stanfa LC, Basu A, Dickenson AH: Electrophysiologic<br />
evidence for <strong>in</strong>creased endogenous gabaergic but not glyc<strong>in</strong>ergic<br />
<strong>in</strong>hibitory tone <strong>in</strong> the rat sp<strong>in</strong>al nerve ligation model of neuropathy.<br />
Anesthesiology (2001) 94(2):333-339.<br />
49. Lynch JW: Molecular structure and function of the glyc<strong>in</strong>e receptor<br />
chloride channel. Physiol Rev (2004) 84(4):1051-1095.<br />
• This paper <strong>in</strong>cludes a reasonably comprehensive review of GlyR molecular<br />
pharmacology.<br />
50. Grudz<strong>in</strong>ska J, Schemm R, Haeger S, Nicke A, Schmalz<strong>in</strong>g G, Betz H,<br />
Laube B: The β subunit determ<strong>in</strong>es the ligand b<strong>in</strong>d<strong>in</strong>g properties of<br />
synaptic glyc<strong>in</strong>e receptors. Neuron (2005) 45(5):727-739.<br />
•• This paper calls <strong>in</strong>to question two long-stand<strong>in</strong>g dogmas <strong>in</strong> the GlyR field.<br />
First, it shows that the α subunit conta<strong>in</strong>s high-aff<strong>in</strong>ity glyc<strong>in</strong>e b<strong>in</strong>d<strong>in</strong>g sites.<br />
Second, it makes a strong case for revis<strong>in</strong>g the heteromeric GlyR<br />
stoichiometry from 3α:2β to 2α:3β.<br />
51. Kneussel M, Betz H: Receptors, gephyr<strong>in</strong> and gephyr<strong>in</strong>-associated<br />
prote<strong>in</strong>s: Novel <strong>in</strong>sights <strong>in</strong>to the assembly of <strong>in</strong>hibitory<br />
postsynaptic membrane specializations. J Physiol (2000) 525(1):1-9.<br />
52. Becker CM, Hoch W, Betz H: Glyc<strong>in</strong>e receptor heterogeneity <strong>in</strong> rat<br />
sp<strong>in</strong>al cord dur<strong>in</strong>g postnatal development. EMBO J (1988)<br />
7(12):3717-3726.<br />
53. Fl<strong>in</strong>t AC, Liu X, Kriegste<strong>in</strong> AR: Nonsynaptic glyc<strong>in</strong>e receptor<br />
activation dur<strong>in</strong>g early neocortical development. Neuron (1998)<br />
20(1):43-53.<br />
54. Tapia JC, Mentis GZ, Navarrete R, Nualart F, Figueroa E, Sanchez A,<br />
Aguayo LG: Early expression of glyc<strong>in</strong>e and GABAA receptors <strong>in</strong><br />
develop<strong>in</strong>g sp<strong>in</strong>al cord neurons. Effects on neurite outgrowth.<br />
Neuroscience (2001) 108(3):493-506.<br />
55. Aguayo LG, van Zundert B, Tapia JC, Carrasco MA, Alvarez FJ:<br />
Changes on the properties of glyc<strong>in</strong>e receptors dur<strong>in</strong>g neuronal<br />
development. Bra<strong>in</strong> Res Bra<strong>in</strong> Res Rev (2004) 47(1-3):33-45.<br />
56. Haverkamp S, Muller U, Harvey K, Harvey RJ, Betz H, Wassle H:<br />
Diversity of glyc<strong>in</strong>e receptors <strong>in</strong> the mouse ret<strong>in</strong>a: Localization of<br />
the α3 subunit. J Comp Neurol (2003) 465(4):524-539.<br />
57. Haverkamp S, Muller U, Zeilhofer HU, Harvey RJ, Wassle H: Diversity<br />
of glyc<strong>in</strong>e receptors <strong>in</strong> the mouse ret<strong>in</strong>a: Localization of the α2<br />
subunit. J Comp Neurol (2004) 477(4):399-411.<br />
• This paper and reference [56] provide detailed, high-quality analyses of the<br />
differential distribution patterns of GlyR α1, α2 and α3 subunits <strong>in</strong> the ret<strong>in</strong>ae<br />
of normal and GlyR α3 knockout mice.
58. Simon J, Wakimoto H, Fujita N, Lalande M, Barnard EA: Analysis of<br />
the set of GABAA receptor genes <strong>in</strong> the human genome. J Biol Chem<br />
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59. Meier JC, Henneberger C, Melnick I, Racca C, Harvey RJ, He<strong>in</strong>emann<br />
U, Schmieden V, Grantyn R: RNA edit<strong>in</strong>g produces glyc<strong>in</strong>e receptor<br />
α3(P185L), result<strong>in</strong>g <strong>in</strong> high agonist potency. Nat Neurosci (2005)<br />
8(6):736-744.<br />
•• This study not only shows that RNA edit<strong>in</strong>g results <strong>in</strong> a mutation affect<strong>in</strong>g<br />
the agonist sensitivity of α3 GlyR subunit, but it demonstrates a physiological<br />
role for this mechanism.<br />
60. Mori M, Gahwiler BH, Gerber U: β-Alan<strong>in</strong>e and taur<strong>in</strong>e as<br />
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vitro. J Physiol (2002) 539(1):191-200.<br />
Glyc<strong>in</strong>e receptors Lynch & Callister 53<br />
61. Darste<strong>in</strong> M, Landwehrmeyer GB, Kl<strong>in</strong>g C, Becker CM, Feuerste<strong>in</strong> TJ:<br />
Strychn<strong>in</strong>e-sensitive glyc<strong>in</strong>e receptors <strong>in</strong> rat caudatoputamen are<br />
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96(1):33-39.<br />
62. McCool BA, Farroni JS: Subunit composition of strychn<strong>in</strong>e-sensitive<br />
glyc<strong>in</strong>e receptors expressed by adult rat basolateral amygdala<br />
neurons. Eur J Neurosci (2001) 14(7):1082-1090.<br />
63. Ahmadi S, Lippross S, Neuhuber WL, Zeilhofer HU: PGE2 selectively<br />
blocks <strong>in</strong>hibitory glyc<strong>in</strong>ergic neurotransmission onto rat<br />
superficial dorsal horn neurons. Nat Neurosci (2002) 5(1):34-40.<br />
•• This study provided the first evidence that <strong>in</strong>flammatory mediators<br />
specifically downregulate glyc<strong>in</strong>ergic synaptic currents <strong>in</strong> the superficial dorsal<br />
horn.
54<br />
Does VEGF represent a potential treatment for amyotrophic lateral<br />
sclerosis?<br />
Joanna Iłżecka<br />
Address<br />
Department of Neurology<br />
Medical University<br />
Jaczewskiego 8<br />
20-954 Lubl<strong>in</strong><br />
Poland<br />
Email: ilzecka@onet.pl<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 7(1):54-59<br />
© The Thomson Corporation ISSN 1472-4472<br />
Amyotrophic lateral sclerosis (ALS) is a progressive<br />
neurodegenerative disease. The pathogenesis of ALS is unclear<br />
and there is no effective treatment. Vascular endothelial growth<br />
factor (VEGF) is a cytok<strong>in</strong>e that has a protective function via<br />
angiogenic, neurotrophic, gliotrophic and anti-apoptotic<br />
activity. Data <strong>in</strong>dicate that VEGF can <strong>in</strong>hibit neurodegeneration<br />
<strong>in</strong> ALS and may have therapeutic potential <strong>in</strong> this disease. The<br />
use of gene therapy to deliver VEGF <strong>in</strong>to the central nervous<br />
system is be<strong>in</strong>g evaluated.<br />
Keywords Amyotrophic lateral sclerosis, neurodegeneration,<br />
neuroprotection, therapy, vascular endothelial growth factor<br />
Introduction<br />
Amyotrophic lateral sclerosis (ALS) is a progressive<br />
neurodegenerative disease affect<strong>in</strong>g motor neurons <strong>in</strong> the<br />
sp<strong>in</strong>al cord, bra<strong>in</strong> stem and motor cortex. The pathogenesis<br />
of ALS is still obscure, but there is evidence that oxidative<br />
stress, glutamate-<strong>in</strong>duced toxicity and withdrawal of trophic<br />
factors may play an important role [1]. It was previously<br />
revealed that mutations <strong>in</strong> the superoxide dismutase<br />
(SOD)1 gene are implicated <strong>in</strong> pathogenesis of familial ALS<br />
[2] and <strong>in</strong>vestigations have shown that apoptosis appears to<br />
be the primary mechanism of cell death <strong>in</strong> this disease. In<br />
the past few years, attention has been paid to the potential<br />
role of vascular endothelial growth factor (VEGF) <strong>in</strong> the<br />
pathogenesis of ALS. Data from the literature <strong>in</strong>dicate that<br />
VEGF can play a protective and reparative function <strong>in</strong> the<br />
central nervous system (CNS) via angiogenic, neurotrophic,<br />
gliotrophic and anti-apoptotic activity.<br />
VEGF is a glycoprote<strong>in</strong> act<strong>in</strong>g via receptors VEGFR1 (Flt-1),<br />
VEGFR2 (KDR/Flk-1), VEGFR3 (Flt-4) and neuropil<strong>in</strong>-1 and<br />
-2 [3,4]. Spliet et al demonstrated an altered expression of<br />
VEGFRs <strong>in</strong> human sp<strong>in</strong>al cord <strong>in</strong> ALS, <strong>in</strong>dicat<strong>in</strong>g their<br />
significant role <strong>in</strong> sp<strong>in</strong>al cord pathology [5]. VEGF-1<br />
expression is <strong>in</strong>creased <strong>in</strong> reactive astroglial cells and <strong>in</strong> the<br />
blood vessels of ALS sp<strong>in</strong>al cord. The higher expression of<br />
VEGFR2 <strong>in</strong> blood vessels of sp<strong>in</strong>al cord and lower<br />
expression of VEGF-3 <strong>in</strong> neuropil was also observed.<br />
The <strong>in</strong>teractions between neuronal, astrocytic and<br />
endothelial cells are important for metabolic bra<strong>in</strong> functions.<br />
Blood vessels can modulate the activity of neurons and the<br />
<strong>in</strong>fluence of neurons on blood vessel function. The vascular<br />
tone of the blood vessels is regulated through excitatory<br />
signal transmissions, and astrocytes play a critically<br />
important role <strong>in</strong> this process. It is known that VEGF is a<br />
major regulator of angiogenesis, and both angiogenesis and<br />
neurogenesis are regulated by systemic coord<strong>in</strong>ations.<br />
Neuroangiogenic factors, <strong>in</strong>clud<strong>in</strong>g VEGF, <strong>in</strong>fluence the<br />
proliferation and differentiation of neuronal and endothelial<br />
cells [6]. This growth factor <strong>in</strong>duces endothelial regeneration<br />
and <strong>in</strong>fluences nitric oxide and prostacycl<strong>in</strong> production,<br />
result<strong>in</strong>g <strong>in</strong> vasodilatation, <strong>in</strong>hibition of vascular smoothmuscle<br />
cell proliferation and aggregation of platelets [7,8].<br />
VEGF <strong>in</strong>fluences vascularization and reduces retrograde<br />
degeneration of transected corticosp<strong>in</strong>al tract axons [9]. It<br />
can promote collateral vessel growth <strong>in</strong> animal models of<br />
ischemia [10]. VEGF can also protect regression of vasa<br />
nervorum, which improves the function of peripheral nerves<br />
[11]. A previous study revealed that local production of<br />
VEGF by microvessels supports the survival and<br />
regeneration of motor nerves [12].<br />
VEGF and neuroprotection<br />
Previous data have shown that VEGF may <strong>in</strong>fluence<br />
neuronal and glial cells [13], and it was demonstrated that<br />
VEGF expressed by neurons can serve both paracr<strong>in</strong>e and<br />
autocr<strong>in</strong>e functions <strong>in</strong> the CNS [14]. Studies have shown that<br />
VEGF and its receptors, localized on neurons and astrocytes,<br />
play a neuroprotective role aga<strong>in</strong>st ischemia and sp<strong>in</strong>al cord<br />
<strong>in</strong>jury. The functions of vascular and nervous tissue are<br />
l<strong>in</strong>ked because VEGF shares common receptor signal<strong>in</strong>g<br />
with SEMA3A [15].<br />
Accord<strong>in</strong>g to Sun and Guo, the mechanisms by which VEGF<br />
exerts neuroprotection <strong>in</strong>clude the modulation of the<br />
phosphatidyl<strong>in</strong>ositol 3'-k<strong>in</strong>ase (PI3K)/Akt/nuclear factor<br />
(NF)κB signal<strong>in</strong>g pathway, <strong>in</strong>duction of neural progenitor<br />
proliferation, activation of neuron maturation <strong>in</strong> adult rat<br />
bra<strong>in</strong> and <strong>in</strong>hibition of apoptosis [16]. However, these<br />
neuroprotective mechanisms have not been confirmed <strong>in</strong><br />
human studies and it is difficult to assess the molecular<br />
activity of VEGF <strong>in</strong> ALS patients. Thus far, it is still<br />
uncerta<strong>in</strong> whether apoptosis plays a role <strong>in</strong> cell death <strong>in</strong><br />
ALS, or if the <strong>in</strong>hibition of apoptosis by VEGF has a<br />
protective effect <strong>in</strong> this disease. Studies have demonstrated<br />
that VEGF is a mitogen for astrocytes [17], and VEGF has<br />
been shown to stimulate neurogenesis <strong>in</strong> the proliferative<br />
zones of the human bra<strong>in</strong> [18]. VEGF also has a neurotrophic<br />
effect, via <strong>in</strong>duction of motor neurons that confer protection<br />
aga<strong>in</strong>st hypoxia [19•], and can reduce the hypoxic death of<br />
cultured cerebral cortical neurons via activation of VEGFR2<br />
[20]. In endothelial cells, VEGF attenuates oxidative <strong>in</strong>jury<br />
through <strong>in</strong>hibition of reactive species production and by<br />
<strong>in</strong>duction of SOD2 expression [21,22]. It was also observed<br />
that VEGF has a neuroprotective effect on hippocampal<br />
neurons [23,24]. Another <strong>in</strong>vestigation showed that the<br />
<strong>in</strong>activation of VEGF <strong>in</strong> the nervous system leads to<br />
dim<strong>in</strong>ish<strong>in</strong>g vessel density, result<strong>in</strong>g <strong>in</strong> ischemia and severe<br />
degeneration [25]. It is also known that manganese<br />
superoxide dismutase (Mn-SOD) plays a protective role
aga<strong>in</strong>st oxidative stress <strong>in</strong>jury. VEGF can stimulate<br />
expression of Mn-SOD through the negative PI3K/Aktforkhead<br />
pathway and the positive prote<strong>in</strong> k<strong>in</strong>ase C-NFκB<br />
pathway [26]. VEGFR and Akt offer protection <strong>in</strong><br />
experimental models of hypoxic cerebellar granule neurons<br />
[27], and VEGF also protects motor neurons aga<strong>in</strong>st<br />
glutamate and N-methyl-D-aspartate toxicity. VEGF <strong>in</strong>hibits<br />
glutamate-mediated toxicity through PI3K/Akt and<br />
MEK/ERK anti-apoptotic pathways [28••], and it has also<br />
been revealed that VEGF plays an important role <strong>in</strong> the<br />
growth and structural stability of neurons [29]. A protective<br />
effect was observed <strong>in</strong> hippocampal, cortical, cerebellar,<br />
dopam<strong>in</strong>ergic and other neurons, along with a<br />
neuroprotective role <strong>in</strong> cerebral ischemic stroke [30,31],<br />
offer<strong>in</strong>g protection via enhanc<strong>in</strong>g angiogenesis <strong>in</strong> the<br />
penumbra and reduc<strong>in</strong>g <strong>in</strong>farct volume [32,33]. Previous<br />
studies demonstrated that VEGF <strong>in</strong>fluences apoptosis,<br />
exert<strong>in</strong>g anti-apoptotic activity through <strong>in</strong>hibition of<br />
caspase-3 pathways and via VEGFR2-mediated activation of<br />
PI3K, Akt and NFκB pathways [34,35]. One study,<br />
conducted on cerebral cortical neurons and other cell l<strong>in</strong>es,<br />
showed that VEGF <strong>in</strong>hibits apoptosis through the activation<br />
<strong>in</strong>hibitor of apoptosis prote<strong>in</strong> (XIAP) and Bcl-2 [36]. VEGF<br />
has a protective role aga<strong>in</strong>st oxidative stress and mutant<br />
SOD1-mediated motor neuron death via activation of the<br />
PI3K/Akt pathway [37].<br />
It has been observed that glia may have an important role <strong>in</strong><br />
neurodegeneration <strong>in</strong> ALS. VEGF <strong>in</strong>fluences the growth and<br />
differentiation of astrocytes <strong>in</strong> the CNS; it has gliotrophic<br />
effects via the mitogen-activated prote<strong>in</strong> k<strong>in</strong>ase/<br />
extracellular signal-related k<strong>in</strong>ase and PI3K signal<strong>in</strong>g pathways<br />
[38]. Krum and Khaibull<strong>in</strong>a demonstrated that <strong>in</strong>hibition of<br />
endogenous VEGF <strong>in</strong>fluences the revascularization and<br />
proliferation of astroglia <strong>in</strong> the bra<strong>in</strong> [39]. This f<strong>in</strong>d<strong>in</strong>g<br />
<strong>in</strong>dicates a significant role for VEGF <strong>in</strong> the repair of CNS<br />
tissue after <strong>in</strong>jury. VEGF also <strong>in</strong>duces the proliferation of<br />
microglial cells <strong>in</strong> the bra<strong>in</strong> [40]. The ma<strong>in</strong> problem with the<br />
above <strong>in</strong>vestigations is that they were conducted on<br />
experimental animal models and all of the protective<br />
functions of VEGF have not yet been confirmed <strong>in</strong> humans.<br />
The activities of VEGF warrant further cl<strong>in</strong>ical research<br />
and/or neuropathological studies of human ALS because it<br />
is not certa<strong>in</strong> that VEGF has a protective effect <strong>in</strong> this<br />
context.<br />
It appears that migration of neural progenitors is an<br />
important process for repair<strong>in</strong>g the CNS. VEGF can<br />
<strong>in</strong>fluence stem cells, <strong>in</strong>clud<strong>in</strong>g neural progenitors, and it is<br />
also known that VEGF mRNA and its receptors are<br />
expressed <strong>in</strong> neural stem cells [41]. Zhang et al showed that<br />
progenitor cells may express VEGF receptors and that<br />
VEGFR2 mediates the effect of VEGF on progenitor<br />
migration [42]. Accord<strong>in</strong>g to Brusselmans et al, VEGF is a<br />
survival factor for embryonic stem cells dur<strong>in</strong>g hypoxia [43].<br />
Experiments showed that hypoxia <strong>in</strong>creases the expression<br />
of VEGF and its receptor <strong>in</strong> neural stem cells, result<strong>in</strong>g <strong>in</strong> the<br />
<strong>in</strong>hibition of apoptosis [44]. Additionally, it has been<br />
demonstrated that the gene transfer of VEGF <strong>in</strong>to neural<br />
stem cells reduces apoptosis caused by hypoxia [45]. This<br />
f<strong>in</strong>d<strong>in</strong>g <strong>in</strong>dicates that VEGF has a protective role on neural<br />
Does VEGF represent a potential treatment for amyotrophic lateral sclerosis? Iłżecka 55<br />
stem cells and neurogenesis <strong>in</strong> the adult nervous system.<br />
The <strong>in</strong>vestigation of VEGF function <strong>in</strong> the develop<strong>in</strong>g bra<strong>in</strong><br />
showed that the <strong>in</strong>activation of this growth factor leads to<br />
neural damage of the bra<strong>in</strong> tissue [46].<br />
Judg<strong>in</strong>g by these protective effects of VEGF, this growth factor<br />
may have cl<strong>in</strong>ical utility <strong>in</strong> the treatment of different diseases,<br />
<strong>in</strong>clud<strong>in</strong>g ischemic disorders such as stroke or myocardial<br />
<strong>in</strong>farction. It may also have an application <strong>in</strong> the therapy of<br />
different neurodegenerative diseases, <strong>in</strong>clud<strong>in</strong>g ALS. However,<br />
there are some concerns with the cl<strong>in</strong>ical use of this growth<br />
factor and, furthermore, the protective effects of VEGF<br />
described above have not yet been confirmed <strong>in</strong> humans.<br />
VEGF and ALS<br />
There is evidence to suggest that VEGF may play a<br />
protective role <strong>in</strong> ALS. It is known that the expression of<br />
VEGF is upregulated by hypoxia, which <strong>in</strong>creases<br />
transcription because of the higher stability of VEGF mRNA,<br />
and through the b<strong>in</strong>d<strong>in</strong>g of the transcription factor hypoxia<strong>in</strong>ducible<br />
factor-1 to the 5'-promoter region [47]. In contrast,<br />
it has been demonstrated that the hypoxic <strong>in</strong>duction of<br />
VEGF <strong>in</strong> SOD1 transgenic mice (an animal model of ALS) is<br />
selectively impaired from a very early stage. The high<br />
basel<strong>in</strong>e and the low hypoxia-<strong>in</strong>duced expression of VEGF<br />
has been observed <strong>in</strong> the sp<strong>in</strong>al cord of SOD1 mutant mice<br />
[48]. Downregulation of VEGF expression <strong>in</strong> the sp<strong>in</strong>al cord<br />
of G93A SOD1 rats has also been shown [49]. One study<br />
showed that deletion of the hypoxia-responsive element <strong>in</strong><br />
the promoter region of the VEGF gene <strong>in</strong> transgenic mice<br />
leads to degeneration of motor neurons [50••]. The <strong>in</strong>crease<br />
<strong>in</strong> reactive oxygen species production observed <strong>in</strong> ALS can<br />
activate hypoxia-<strong>in</strong>ducible factors, result<strong>in</strong>g <strong>in</strong> the <strong>in</strong>creased<br />
transcription of VEGF [51]. As previously described,<br />
glutamate-mediated toxicity may play an important role <strong>in</strong><br />
the pathogenesis of ALS. It is possible that the impairment of<br />
VEGF expression <strong>in</strong> ALS caused by hypoxia can augment<br />
sensitivity of motor neurons for glutamate-mediated<br />
toxicity. It is also known that glial cells <strong>in</strong>fluence VEGF<br />
expression, and a high basel<strong>in</strong>e VEGF level observed <strong>in</strong><br />
transgenic SOD1 mice might be the result of astrogliosis or<br />
changes <strong>in</strong> pro-<strong>in</strong>flammatory cytok<strong>in</strong>es <strong>in</strong> the ALS sp<strong>in</strong>al<br />
cord [52]. Thus, changes <strong>in</strong> VEGF may be due to the<br />
pathomorphological status of glia caused by the <strong>in</strong>fluence of<br />
harmful factors, <strong>in</strong>clud<strong>in</strong>g ischemia and <strong>in</strong>flammation.<br />
Human genetic studies have shown that there is an<br />
association between VEGF and ALS; two at-risk VEGF<br />
genotypes <strong>in</strong>fluence risk for ALS. Moreover, the human<br />
haplotypes that are associated with low VEGF levels<br />
<strong>in</strong>crease the risk for ALS [53••]. Huez et al determ<strong>in</strong>ed two<br />
homozygous recessive haplotypes of VEGF that are def<strong>in</strong>ed<br />
by s<strong>in</strong>gle nucleotide polymorphisms <strong>in</strong> the promoter and <strong>in</strong><br />
the 5'-untranslated region (5'-UTR) of exon 1 as risk haplotypes<br />
of ALS [54]. Moreover, it was revealed that haplotypes<br />
AAG/AAG and AGG/AGG <strong>in</strong>fluence the expression of<br />
VEGF by <strong>in</strong>hibit<strong>in</strong>g VEGF mRNA transcription and<br />
translation, result<strong>in</strong>g <strong>in</strong> dim<strong>in</strong>ish<strong>in</strong>g VEGF levels that could<br />
lead to motor neuron death. It has also been suggested that<br />
other regulators of the VEGF pathway, such as VEGFR2 and<br />
NRP1 and their effectors, might <strong>in</strong>fluence risk for ALS.
56 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
The results of these genetic studies must be confirmed <strong>in</strong><br />
future experiments as it is not clear whether primary genetic<br />
factors are responsible for the effects of VEGF expression.<br />
The fact that oxidative stress also primarily <strong>in</strong>fluences<br />
expression and levels of VEGF <strong>in</strong> these cases cannot be<br />
excluded. Data have shown decreased VEGF plasma levels<br />
<strong>in</strong> ALS patients compared with controls, but no correlation<br />
was found with the cl<strong>in</strong>ical parameters of the disease. In<br />
contrast, Nygren et al observed that VEGF levels rema<strong>in</strong>ed<br />
unchanged <strong>in</strong> the sp<strong>in</strong>al cord of ALS patients compared<br />
with controls, but that serum VEGF levels were <strong>in</strong>creased <strong>in</strong><br />
ALS patients, probably due to hypoxia [55]. It was observed<br />
that CSF VEGF levels were <strong>in</strong>creased <strong>in</strong> ALS patients with<br />
long duration of disease and <strong>in</strong> limb-onset ALS [56].<br />
Another study showed low cerebrosp<strong>in</strong>al fluid VEGF levels<br />
dur<strong>in</strong>g the first year of ALS, which were <strong>in</strong>dependent of<br />
VEGF promoter polymorphism [57]. Thus, there are<br />
discrepancies <strong>in</strong> the data from human studies and it is<br />
difficult to conclude that changes <strong>in</strong> VEGF levels may lead to<br />
neurodegeneration <strong>in</strong> ALS. It is possible that such diverse<br />
results are caused by different haplotypes <strong>in</strong> the ALS<br />
patients studied. Thus, it is difficult to compare the results<br />
from different studies and to draw the correct conclusions.<br />
The pathomorphological studies conducted on the sp<strong>in</strong>al<br />
cord and bra<strong>in</strong> of ALS patients could provide further<br />
<strong>in</strong>formation concern<strong>in</strong>g VEGF expression and function <strong>in</strong><br />
the CNS.<br />
It was hypothesized that decreased VEGF levels could<br />
<strong>in</strong>fluence the neurotrophic and angiogenic activity of this<br />
growth factor. The mechanism of motor neuron loss <strong>in</strong> ALS<br />
has not been elucidated, but it appears that decreased VEGF<br />
levels could affect blood flow <strong>in</strong> the sp<strong>in</strong>al cord, which<br />
<strong>in</strong>fluences the life span of motor neurons. It is possible that<br />
reduced neural perfusion caused by decreased VEGF levels<br />
may be due to affected vasoregulation, possibly via nitric<br />
oxide activity. Conversely, decreased VEGF levels may also<br />
affect the activity of perivascular autonomic nerves that can<br />
lead to the impairment of vascular tone and sp<strong>in</strong>al cord<br />
perfusion [58•]. Additionally, decreased VEGF levels might<br />
dim<strong>in</strong>ish its neurotrophic activity on motor neurons. There<br />
is evidence that impaired VEGF regulation <strong>in</strong> mice leads to<br />
reduction of sp<strong>in</strong>al cord VEGF levels, especially dur<strong>in</strong>g<br />
hypoxia, result<strong>in</strong>g <strong>in</strong> a neural blood flow reduction of 50%.<br />
Motor neurons are more vulnerable to hypoperfusion, and<br />
chronic ischemia of the sp<strong>in</strong>al cord can cause motor neuron<br />
degeneration. Decreased regional cerebral blood flow has<br />
been observed <strong>in</strong> ALS patients [59], yet its connection to<br />
VEGF levels has not been <strong>in</strong>vestigated. Accord<strong>in</strong>g to<br />
Lambrechts et al, sufficient VEGF levels <strong>in</strong> humans with high<br />
VEGF-produc<strong>in</strong>g genotypes protect the perfusion of<br />
neurons, but the low levels of this cytok<strong>in</strong>e may be a risk<br />
factor for ALS [60•]. It seems that the above mentioned<br />
mechanism might play a role <strong>in</strong> neurodegeneration <strong>in</strong> ALS,<br />
but this requires further research.<br />
Muscle atrophy is one of the signs of disease <strong>in</strong> ALS. It was<br />
revealed that VEGF stimulates the regeneration of skeletal<br />
muscles via the protection of myogenic cells from apoptosis<br />
and the stimulation of growth of myogenic fibers. On<br />
balance, it was observed that progenitor cells from bone<br />
marrow, which are <strong>in</strong>duced by VEGF, can also <strong>in</strong>fluence the<br />
regeneration of muscle [61]. Thus, theoretically, VEGF could<br />
<strong>in</strong>hibit muscle damage <strong>in</strong> ALS and might be useful for<br />
muscle protection therapy <strong>in</strong> this disease, but no cl<strong>in</strong>ical<br />
studies have yet confirmed this.<br />
The protective effects of VEGF that have been demonstrated<br />
<strong>in</strong> experimental studies have not been confirmed <strong>in</strong> cl<strong>in</strong>ical<br />
trials. Data have shown that treatment with a variety of<br />
different growth factors, <strong>in</strong>clud<strong>in</strong>g ciliary neurotrophic<br />
factor, <strong>in</strong>sul<strong>in</strong> growth factor, glial cell-derived neurotrophic<br />
factor (GDNF) and bra<strong>in</strong>-derived neurotrophic factor, did<br />
not significantly <strong>in</strong>fluence ALS. It was suggested that the<br />
<strong>in</strong>efficiency of treatment us<strong>in</strong>g growth factors was caused by<br />
the subcutaneous route of their adm<strong>in</strong>istration and was the<br />
result of the limited ability of the growth factors to cross the<br />
blood-bra<strong>in</strong> barrier (BBB) [62]. It is possible that the transfer<br />
of VEGF across the BBB us<strong>in</strong>g viral vectors might be the best<br />
route of adm<strong>in</strong>istration, and it is suspected that VEGF<br />
therapy could be most effective <strong>in</strong> the earliest phase after the<br />
cl<strong>in</strong>ical signs of ALS onset. Experiments conducted on a<br />
transgenic mouse model of ALS showed that VEGF may be<br />
an effective treatment after disease onset and can delay<br />
<strong>in</strong>itiation and slow progression of the disease [63••,64••].<br />
Thus, the application of this therapy to humans, especially<br />
<strong>in</strong> the earliest phase of the disease, requires evaluation <strong>in</strong><br />
extensive cl<strong>in</strong>ical studies. Storkebaum et al [65] showed that<br />
<strong>in</strong>tracerebroventricular delivery of recomb<strong>in</strong>ant VEGF <strong>in</strong> the<br />
transgenic SOD1 rat model of ALS delays disease onset and<br />
prolongs survival of animals. Based on available data, the<br />
transplantation of genetically modified cells <strong>in</strong>to the CNS<br />
may be a promis<strong>in</strong>g strategy for the delivery and expression<br />
of different neurotrophic factors, <strong>in</strong>clud<strong>in</strong>g VEGF. It has<br />
been suggested that the specific promoters may control the<br />
gene expression that is required for dose-specific and timespecific<br />
therapy [66]. VEGF can be delivered <strong>in</strong>to the CNS by<br />
several routes, <strong>in</strong>clud<strong>in</strong>g as a recomb<strong>in</strong>ant prote<strong>in</strong>, and<br />
through delivery of the gene as a naked plasmid or via viral<br />
vector [67]; these routes of adm<strong>in</strong>istration are promis<strong>in</strong>g for<br />
cl<strong>in</strong>ical therapy. Studies are cont<strong>in</strong>u<strong>in</strong>g, and it has been<br />
demonstrated that us<strong>in</strong>g adeno-associated virus as a vector<br />
for gene delivery <strong>in</strong>to motor neuron-like cells may be an<br />
important strategy <strong>in</strong> the future treatment of ALS [68]. Kle<strong>in</strong><br />
et al showed GDNF delivery us<strong>in</strong>g human neural progenitor<br />
cells <strong>in</strong> a rat model of ALS [69]. Another potential treatment<br />
option is via the adm<strong>in</strong>istration of the heat shock prote<strong>in</strong> co<strong>in</strong>ducers,<br />
which <strong>in</strong>fluence cell stress response to cell<br />
protection [70]. However, it is difficult to evaluate the effect<br />
of such therapy <strong>in</strong> human ALS.<br />
Stem cells<br />
Human embryonic stem cells and neural stem cells can be<br />
used <strong>in</strong> reparative therapy <strong>in</strong> ALS. Human neural stem-cellderived<br />
chol<strong>in</strong>ergic neurons can <strong>in</strong>nervate muscle <strong>in</strong> motor<br />
neuron-deficient adult rats [71], and Vastag observed<br />
partially reversed paralysis <strong>in</strong> a rat model of ALS after stemcell<br />
therapy [72]. However, there are no data concern<strong>in</strong>g the<br />
<strong>in</strong>fluence of stem cells on cl<strong>in</strong>ical signs <strong>in</strong> human ALS,<br />
although stem-cell transplantation had a protective effect <strong>in</strong><br />
animal models. The mechanisms of stem-cell protection are<br />
unclear, but it has been suggested that cell fusion,
neurotrophic factor release, <strong>in</strong>clud<strong>in</strong>g VEGF, endogenous<br />
stem-cell proliferation and transdifferentiation may all play<br />
a role [73].<br />
Stem-cell therapy may be a promis<strong>in</strong>g treatment for ALS<br />
[74]. It is known that VEGF promotes the maturation of<br />
neurons and endothelial cells by <strong>in</strong>fluenc<strong>in</strong>g stem cells that<br />
support reparative processes <strong>in</strong> the nervous system. The<br />
therapeutic effect exerted by embryonic and neural stem<br />
cells might, at least <strong>in</strong> part, be mediated by the secretion of<br />
VEGF. The protective effect of non-<strong>in</strong>vasive cell-based<br />
therapy of ALS has been observed by us<strong>in</strong>g <strong>in</strong>travenous<br />
adm<strong>in</strong>istration of human umbilical cord blood cells <strong>in</strong> a<br />
mouse model of ALS [75]. It might be <strong>in</strong>terest<strong>in</strong>g to apply<br />
such non-<strong>in</strong>vasive therapy <strong>in</strong> humans, but there are no data<br />
concern<strong>in</strong>g cl<strong>in</strong>ical trials of this nature. The transplantation<br />
of neurons and glia us<strong>in</strong>g human motor neuronal progenitor<br />
cells or xenografts of animal cells has also been proposed.<br />
However, <strong>in</strong> a rat model, Li et al demonstrated that grafted<br />
cells do not migrate and die by apoptosis [76]. One cl<strong>in</strong>ical<br />
study showed that the <strong>in</strong>trasp<strong>in</strong>al cord implantation of<br />
autologous mesenchymal stem cells was safe [77], but this<br />
result needs confirmation <strong>in</strong> other studies. Accord<strong>in</strong>g to<br />
Silani et al, stem-cell therapy should be used <strong>in</strong> comb<strong>in</strong>ation<br />
with other treatments, such as trophic factors, <strong>in</strong>clud<strong>in</strong>g<br />
VEGF [78]. Moreover, it was demonstrated that comb<strong>in</strong>ed<br />
cord blood stem cells and gene therapy <strong>in</strong>duced<br />
angiogenesis and improved cardiac performance <strong>in</strong> a mouse<br />
model of acute myocardial <strong>in</strong>farction [79]. Thus, this<br />
comb<strong>in</strong>ed therapy could be promis<strong>in</strong>g for the future <strong>in</strong> ALS,<br />
although there are no data concern<strong>in</strong>g cl<strong>in</strong>ical trials of such<br />
therapy. However, <strong>in</strong> the past, different comb<strong>in</strong>ed therapies<br />
have been applied <strong>in</strong> ALS patients and their effect did not<br />
br<strong>in</strong>g any significant cl<strong>in</strong>ical improvement.<br />
Prote<strong>in</strong> aggregates<br />
The aggregation of prote<strong>in</strong>s is a typical pathomorphological<br />
hallmark of different neurodegenerative diseases, <strong>in</strong>clud<strong>in</strong>g<br />
ALS [80]. Some publications <strong>in</strong>dicate that the toxicity of prote<strong>in</strong><br />
aggregates may be responsible for neurodegeneration. Yang et<br />
al demonstrated that VEGF dim<strong>in</strong>ishes β-amyloid-<strong>in</strong>duced<br />
neurotoxicity <strong>in</strong> Alzheimer's disease through the <strong>in</strong>hibition<br />
of β-amyloid aggregation and the production of reactive<br />
oxygen species [81]. VEGF may also attenuate toxicity of<br />
prote<strong>in</strong> aggregates <strong>in</strong> ALS. This needs cl<strong>in</strong>ical <strong>in</strong>vestigation,<br />
but it appears that us<strong>in</strong>g VEGF for the <strong>in</strong>hibition of<br />
aggregates <strong>in</strong> ALS might be an <strong>in</strong>terest<strong>in</strong>g therapeutic<br />
strategy. It is also possible that other components of the<br />
VEGF pathway might play a role <strong>in</strong> motor neuron death.<br />
These <strong>in</strong>clude other VEGF receptors and their signal<strong>in</strong>g<br />
effectors [82].<br />
Conclusions<br />
In recent years, attention has been focused on the role of<br />
gene therapy and stem-cell therapy for ALS. Based on<br />
available data, it seems that VEGF could be an important<br />
growth factor for ALS therapy. The protective function that<br />
VEGF exerts via its angiotrophic, neurotrophic and<br />
gliotrophic effects might <strong>in</strong>hibit neurodegeneration <strong>in</strong> ALS.<br />
Additionally, the protective effect of VEGF on stem cells of<br />
adult CNS tissue could support reparative processes <strong>in</strong> ALS<br />
Does VEGF represent a potential treatment for amyotrophic lateral sclerosis? Iłżecka 57<br />
and slow neurodegeneration. It is known that endogenous<br />
precursors or stem cells can differentiate <strong>in</strong>to new<br />
corticosp<strong>in</strong>al motor neurons <strong>in</strong> the adult bra<strong>in</strong> and<br />
molecular modification of their activity by VEGF might<br />
<strong>in</strong>fluence cell death. However, there are some limitations to<br />
us<strong>in</strong>g this cytok<strong>in</strong>e cl<strong>in</strong>ically, <strong>in</strong> that the beneficial effect of<br />
VEGF therapy that has been observed <strong>in</strong> animal models has<br />
not been confirmed <strong>in</strong> cl<strong>in</strong>ical trials. Moreover, there are<br />
some technical difficulties surround<strong>in</strong>g the delivery of VEGF<br />
<strong>in</strong>to the human CNS. It is known that the application of<br />
different growth factors <strong>in</strong> cl<strong>in</strong>ical trials did not have a<br />
significant effect, but gene therapy to deliver VEGF <strong>in</strong>to<br />
sp<strong>in</strong>al cord and bra<strong>in</strong>, or comb<strong>in</strong>ed therapy with stem cells,<br />
should be considered as a future treatment for ALS.<br />
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60<br />
Ispronicl<strong>in</strong>e Targacept<br />
Hugo Geerts<br />
Address<br />
In Silico Biosciences Inc<br />
3741 Walnut Street #609<br />
Philadelphia<br />
PA 19104<br />
USA<br />
Email: Hugo-Geerts@In-Silico-Biosciences.com<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 7(1):60-69<br />
© The Thomson Corporation ISSN 1472-4472<br />
Targacept (formerly a subsidiary of RJ Reynolds) is develop<strong>in</strong>g<br />
ispronicl<strong>in</strong>e, the lead <strong>in</strong> a series of nicot<strong>in</strong>ic acetylchol<strong>in</strong>e<br />
(nACh) ligands, as a potential oral treatment for cognitive<br />
impairment, <strong>in</strong>clud<strong>in</strong>g a variety of non-Alzheimer's dementias.<br />
In July 2005, Targacept was prepar<strong>in</strong>g for a phase II study <strong>in</strong><br />
patients with mild-to-moderate Alzheimer's disease.<br />
Introduction<br />
With the observation that a nicot<strong>in</strong>ic acetylchol<strong>in</strong>e receptor<br />
(nAChR) deficit occurs <strong>in</strong> neurodegenerative conditions,<br />
such as Alzheimer's disease (AD), and <strong>in</strong> psychiatric<br />
conditions, such as schizophrenia, there came a considerable<br />
<strong>in</strong>terest <strong>in</strong> develop<strong>in</strong>g nicot<strong>in</strong>ic receptor modulators with a<br />
less addictive and toxic profile than nicot<strong>in</strong>e [624142],<br />
[624143]. Although different nAChR subtypes exist <strong>in</strong> the<br />
central nervous system (CNS) as hetero- or homomeric<br />
assemblies of α and β subunits, there is evidence that α7<br />
homomeric and β2-conta<strong>in</strong><strong>in</strong>g (β2*) receptor subunits<br />
predom<strong>in</strong>ate <strong>in</strong> the human bra<strong>in</strong>, as do α3β4 subunits to a<br />
lesser extent [638395], [638396], [638398]. The majority of the<br />
β2* subunits are of the α4β2 nAChR subtype and positron<br />
emission tomography (PET) imag<strong>in</strong>g data <strong>in</strong> humans have<br />
<strong>in</strong>dicated a high density of this subtype <strong>in</strong> the cortex and<br />
thalamus [638427]. Although the majority of data suggest<br />
that β2* nAChR subtypes are selectively affected <strong>in</strong> AD,<br />
other results suggest that α7 nAChR subtypes are also<br />
<strong>in</strong>volved. It is of particular <strong>in</strong>terest to note that <strong>in</strong><br />
schizophrenic patients, both genetic and neuropathological<br />
f<strong>in</strong>d<strong>in</strong>gs suggest that the cognitive deficit is sensitive to<br />
nicot<strong>in</strong>ic receptor modulation. The National Institutes of<br />
Health-sponsored MATRICS (Measurement And Treatment<br />
Research to Improve Cognition <strong>in</strong> Schizophrenia) project<br />
developed a standardized battery of cognitive tests and<br />
identified a number of pharmacological approaches,<br />
<strong>in</strong>clud<strong>in</strong>g nAChR modulation [624144], [624147]. The<br />
follow-up project, called TURNS (Treatment Units for<br />
Research on Neurocognition <strong>in</strong> Schizophrenia), selected<br />
ispronicl<strong>in</strong>e (TC-1734; Targacept Inc) for a pilot phase II<br />
study as an add-on medication with a neuroleptic agent<br />
[631107]. Ispronicl<strong>in</strong>e is currently undergo<strong>in</strong>g phase II<br />
trials by Targacept for the potential treatment of ageassociated<br />
memory impairment (AAMI) and mild<br />
cognitive impairment (MCI) [545766]. A phase II study <strong>in</strong><br />
AD has also commenced [611220]. Targacept is consider<strong>in</strong>g<br />
ispronicl<strong>in</strong>e for cl<strong>in</strong>ical development <strong>in</strong> <strong>in</strong>dications such as<br />
cognitive impairment (associated with schizophrenia and<br />
follow<strong>in</strong>g coronary artery bypass graft<strong>in</strong>g), attention<br />
deficit hyperactivity disorder (ADHD) and some forms of<br />
dementia [624033].<br />
Orig<strong>in</strong>ator Targacept Inc<br />
Status Phase II Cl<strong>in</strong>ical<br />
.<br />
Indication Cognitive disorder<br />
.<br />
Actions Neuroprotectant, Nicot<strong>in</strong>ic ACh agonist, Nootropic<br />
agent<br />
Synonyms & Analogs CLZ-52, CLZ-59, nicot<strong>in</strong>ic ACh<br />
ligands (cognitive disorder), nicot<strong>in</strong>ic ACh ligands (memory<br />
enhancers), RJR-1594, RJR-1595, RJR-1734, RJR-2559,<br />
TC-01695, TC-1698, TC-1707, TC-1709, TC-1734, TC-<br />
2248, TC-2258, TC-01706, TC-01707, TC-01714, TC-<br />
01893, TC-02116, TC-02123, TC-02248, TC-02258, TC-<br />
02531<br />
Registry No: 252870-53-4<br />
C<br />
H 3<br />
CH 3<br />
O<br />
N<br />
It has also been proposed that nicot<strong>in</strong>ic receptor stimulation can<br />
provide neuroprotection aga<strong>in</strong>st some aspects of AD (βamyloid<br />
and glutamate pathology) [622041]. The fact that<br />
galantam<strong>in</strong>e, a chol<strong>in</strong>ergic drug that also has an allosteric<br />
potentiat<strong>in</strong>g ligand effect on nAChRs, is used to treat AD<br />
patients, opens a w<strong>in</strong>dow onto the possible cl<strong>in</strong>ical potential of<br />
nicot<strong>in</strong>ic receptor modulation. As a consequence, the<br />
modulation of nicot<strong>in</strong>ic receptors is an <strong>in</strong>terest<strong>in</strong>g therapeutic<br />
approach that is be<strong>in</strong>g pursued by a number of laboratories<br />
because, <strong>in</strong> pr<strong>in</strong>ciple, it comb<strong>in</strong>es symptomatic treatment with<br />
neuroprotection [516203], [634638].<br />
Synthesis and SAR<br />
Compounds modulat<strong>in</strong>g nAChRs were identified us<strong>in</strong>g<br />
Targacept's proprietary Pentad <strong>in</strong> silico technology [430095],<br />
[512600]. A number of compounds with low nanomolar<br />
aff<strong>in</strong>ities for the nAChR were identified, but the <strong>in</strong> vivo halflives<br />
of these compounds were estimated to be too short. An αmethyl<br />
group was identified as be<strong>in</strong>g essential for <strong>in</strong>creas<strong>in</strong>g<br />
the half-life of these compounds from 0.5 to 1.4 h <strong>in</strong> rodents, as<br />
illustrated by the fact that RJR-2403 (Targacept Inc/Dr Falk<br />
Pharma GmbH), a neuronal nicot<strong>in</strong>ic receptor ligand <strong>in</strong><br />
development for the treatment of ulcerative colitis, was rapidly<br />
metabolized through N-demethylation and oxidation. As a<br />
result of a 'use-patent' problem, cl<strong>in</strong>ical development of RJR-<br />
2403 was suspended and the <strong>in</strong> vitro nicot<strong>in</strong>ic receptor α4β2<br />
specificity of ispronicl<strong>in</strong>e was <strong>in</strong>vestigated. Ispronicl<strong>in</strong>e is the 3isopropoxy-pyrid<strong>in</strong>e<br />
analog of RJR-2403 synthesized to prevent<br />
N-demethylation. It conferred potent neuroprotection and<br />
dopam<strong>in</strong>e release <strong>in</strong> rat striatum, without react<strong>in</strong>g with any<br />
other ganglionic or muscle receptors [345007], [557048].<br />
In order to prepare ispronicl<strong>in</strong>e, (S)-N-methyl-N-(tertbutoxycarbonyl)-4-penten-2-am<strong>in</strong>e<br />
and 3-bromo-5-isopropoxy-<br />
CH 3<br />
H<br />
N<br />
CH 3
pyrid<strong>in</strong>e were coupled via a palladium-catalyzed Heck<br />
coupl<strong>in</strong>g reaction. The result<strong>in</strong>g <strong>in</strong>termediate, (S)-(E)-Nmethyl-N-(tert-butoxycarbonyl)-5-[3-(5-isopropoxy-pyrid<strong>in</strong>)yl]-4-penten-2-am<strong>in</strong>e,<br />
was subsequently treated with 6 M<br />
hydrochloric acid <strong>in</strong> dimethylformamide to give the free<br />
base of ispronicl<strong>in</strong>e [559979].<br />
Precl<strong>in</strong>ical development<br />
Ispronicl<strong>in</strong>e is a high-aff<strong>in</strong>ity (Ki = 11 nM) agonist of nicot<strong>in</strong>ic<br />
receptors <strong>in</strong> rat bra<strong>in</strong> membrane preparations (nicot<strong>in</strong>e Ki = 4<br />
nM) [306443], [363337] and reportedly has specificity for α4β2<br />
nAChRs [306443]; <strong>in</strong> one study <strong>in</strong> rat hippocampal membranes,<br />
ispronicl<strong>in</strong>e was <strong>in</strong>effective at displac<strong>in</strong>g [ 125I]α-bungarotox<strong>in</strong><br />
b<strong>in</strong>d<strong>in</strong>g to α7 nAChRs (Ki > 50,000 nM) [559979]. No further<br />
data on the aff<strong>in</strong>ities for other bra<strong>in</strong> nAChR subtypes are<br />
available.<br />
Ispronicl<strong>in</strong>e did not b<strong>in</strong>d to muscle-type (α1β1δγ) or<br />
ganglion-type (α3β4) peripheral nAChRs at concentrations<br />
up to 100 µM, as determ<strong>in</strong>ed by isotopic ion efflux <strong>in</strong> the<br />
human TE671/RD and rat pheochromocytoma PC12 cell<br />
l<strong>in</strong>es, which express the respective receptors. Conversely,<br />
nicot<strong>in</strong>e activated nAChRs <strong>in</strong> the human and rat cells with<br />
EC50 values of 60 and 20 µM, respectively, suggest<strong>in</strong>g that<br />
ispronicl<strong>in</strong>e has considerable CNS/peripheral nervous<br />
system specificity [306443], [376757]. No other data were<br />
provided regard<strong>in</strong>g human nAChRs.<br />
Induction of dopam<strong>in</strong>e release <strong>in</strong> rat striatal synaptosomes<br />
showed that ispronicl<strong>in</strong>e had a profile comparable to that of<br />
nicot<strong>in</strong>e at these receptors (EC50 = 106 nM and Emax = 85%).<br />
In thalamic synaptosomes, ispronicl<strong>in</strong>e <strong>in</strong>creased ion <strong>in</strong>flux<br />
to an Emax of 58% with an EC50 value of 220 nM, compared<br />
with an Emax of 100% and an EC50 value of 590 nM for<br />
nicot<strong>in</strong>e [306443], [376757]. These data are <strong>in</strong> agreement with<br />
observations that striatal dopam<strong>in</strong>e release is regulated by<br />
β2* nAChRs [636359] and confirm the preference of<br />
ispronicl<strong>in</strong>e for the α4β2 nAChR subtype. Given the<br />
preferential localization of α4β2 nAChRs <strong>in</strong> the thalamus<br />
[638427], the effect of ispronicl<strong>in</strong>e on thalamic synaptosomes<br />
is also very likely mediated via these receptor subtypes.<br />
Ispronicl<strong>in</strong>e improved performance <strong>in</strong> a rat radial arm maze<br />
model <strong>in</strong> vivo, and significant improvements <strong>in</strong> cognition were<br />
observed follow<strong>in</strong>g oral adm<strong>in</strong>istration of ispronicl<strong>in</strong>e (0.1, 0.3,<br />
0.6, 3.0 and 6.0 µmol/kg) <strong>in</strong> both acute (presumed to be s<strong>in</strong>gledose)<br />
and chronic (daily for 6 days) schedules [306443]. The<br />
effects on short- and long-term memory <strong>in</strong> this model<br />
reportedly lasted for 18 to > 24 h [325629], [363337], [363536].<br />
In a mur<strong>in</strong>e behavioral despair model, ispronicl<strong>in</strong>e showed<br />
significant activity follow<strong>in</strong>g <strong>in</strong>traperitoneal adm<strong>in</strong>istration of 1<br />
and 3 µmol/kg, but not 10 µmol/kg, and was more effective<br />
than the dibenzazep<strong>in</strong>e antidepressant imipram<strong>in</strong>e (40<br />
µmol/kg ip), show<strong>in</strong>g its potential for additional beneficial<br />
effects as an antidepressant [559979].<br />
Ispronicl<strong>in</strong>e (0.6, 1.0 and 3.0 µmol/kg) [559979] reversed<br />
scopolam<strong>in</strong>e-<strong>in</strong>duced cognitive deficits <strong>in</strong> a rat passive<br />
avoidance model (ED50 = 0.89 µmol/kg) with an <strong>in</strong>verted Ushaped<br />
dose response. This result suggests a possible effect<br />
Ispronicl<strong>in</strong>e Geerts 61<br />
on pre-synaptic ACh release and the subsequent stimulation<br />
of post-synaptic muscar<strong>in</strong>ic receptors, because scopolam<strong>in</strong>e<br />
is not documented to have any effect on nicot<strong>in</strong>ic receptors.<br />
This f<strong>in</strong>d<strong>in</strong>g is corroborated by the observation that a<br />
synergistic effect was achieved <strong>in</strong> this model when a suboptimal<br />
dose of ispronicl<strong>in</strong>e (0.6 µmol/kg) was comb<strong>in</strong>ed<br />
with <strong>in</strong>effective doses of the acetyl chol<strong>in</strong>esterase (AChE)<br />
<strong>in</strong>hibitors tacr<strong>in</strong>e and donepezil. Ispronicl<strong>in</strong>e comb<strong>in</strong>ed with<br />
each <strong>in</strong>hibitor resulted <strong>in</strong> an enhanced step-through latency<br />
compared with sole ispronicl<strong>in</strong>e adm<strong>in</strong>istration. Stepthough<br />
latencies (as % of control) were as follows:<br />
unlesioned, 69%; scopolam<strong>in</strong>e lesioned, 8%; ispronicl<strong>in</strong>e (1.0<br />
µmol/kg), 55%; tacr<strong>in</strong>e (12 µmol/kg), 36%; donepezil (1.0<br />
µmol/kg), 53%; suboptimal ispronicl<strong>in</strong>e (0.6 µmol/kg),<br />
tacr<strong>in</strong>e (1.2 µmol/kg) or donepezil (0.1 µmol/kg), 21, 6 and<br />
21%, respectively; and suboptimal ispronicl<strong>in</strong>e plus tacr<strong>in</strong>e<br />
or donepezil: 37 and 39%, respectively [345774], [559979].<br />
Ispronicl<strong>in</strong>e (7 to 14 days at an unstated dose) reduced<br />
spontaneous locomotor activity <strong>in</strong> rats <strong>in</strong> a monophasic<br />
manner, unlike the biphasic activity of nicot<strong>in</strong>e, for the<br />
duration of the test (90 m<strong>in</strong>). Chronic adm<strong>in</strong>istration of the<br />
compound resulted <strong>in</strong> rapid tolerance [345791]. This<br />
property might necessitate <strong>in</strong>novative dosage schedul<strong>in</strong>g <strong>in</strong><br />
the cl<strong>in</strong>ic.<br />
Acute oral adm<strong>in</strong>istration of ispronicl<strong>in</strong>e dose-dependently<br />
<strong>in</strong>creased levels of free ACh <strong>in</strong> the cortex of rats [475601],<br />
[557048]. The lowest active dose was 5 mg/kg and the<br />
maximally effective dose was 10 mg/kg, and these yielded<br />
<strong>in</strong>creases of 36 and 70% over the basal ACh values,<br />
respectively. The maximal effect was observed at the 10mg/kg<br />
dose. A larger dose of ispronicl<strong>in</strong>e (20 mg/kg)<br />
<strong>in</strong>creased the duration of ACh release (to 4 h), but did not<br />
<strong>in</strong>crease the amplitude significantly (84%). With different<br />
doses of nicot<strong>in</strong>e (1.0, 2.5 and 5.0 mg/kg po), the amplitude<br />
of the stimulated ACh response did not change, and the<br />
maximal <strong>in</strong>creases over the basal levels of ACh were 47, 44<br />
and 56%, respectively, 40 to 80 m<strong>in</strong> after treatment. The nonselective<br />
nAChR antagonist mecamylam<strong>in</strong>e (Targacept Inc),<br />
which is <strong>in</strong> development for the potential treatment of<br />
various neuropsychiatric disorders, <strong>in</strong>hibited the ACh<br />
release <strong>in</strong>duced by ispronicl<strong>in</strong>e and nicot<strong>in</strong>e (maximal<br />
effective doses) at a dose of 1 mg/kg when adm<strong>in</strong>istered<br />
subcutaneously 40 m<strong>in</strong> before dos<strong>in</strong>g with ispronicl<strong>in</strong>e and<br />
nicot<strong>in</strong>e. Oral adm<strong>in</strong>istration of ispronicl<strong>in</strong>e improved object<br />
recognition <strong>in</strong> mice after 24 h. The recognition <strong>in</strong>dex (RI) <strong>in</strong><br />
mice treated with the vehicle was 72 ± 5 after 3 h and 45 ± 2<br />
after 24 h; however, after treatment with 0.5 and 1 mg/kg<br />
ispronicl<strong>in</strong>e, the RI at 24 h improved to 72 ± 3 and 55 ± 3,<br />
respectively. Both these effects, the <strong>in</strong>creases <strong>in</strong> ACh<br />
concentration and improved object recognition, were also<br />
countered by mecamylam<strong>in</strong>e [475601]. After a repeated<br />
treatment of 4 days with ispronicl<strong>in</strong>e (10 mg/kg) or nicot<strong>in</strong>e<br />
(1 mg/kg), no tolerance was observed regard<strong>in</strong>g ACh<br />
release [376757].<br />
Ispronicl<strong>in</strong>e was neuroprotective <strong>in</strong> an N-methyl-D-aspartate<br />
(NMDA)-<strong>in</strong>duced cell-death paradigm and may be<br />
synergistic with current AD therapies [325629]. In a<br />
hippocampal slice model (a mature culture of fetal rat<br />
neurons) subjected to a 15-m<strong>in</strong> hypoxia/glucose deprivation
62 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
episode, ispronicl<strong>in</strong>e prevented the loss of synaptic<br />
transmission <strong>in</strong> a concentration-dependent manner, with a<br />
maximal effect of > 70% protection at 10 µM. The effect was<br />
mediated through nAChRs because mecamylam<strong>in</strong>e, blocked<br />
the neuroprotective effect [583306]. This effect is somewhat<br />
unexpected given the proposed l<strong>in</strong>k between specific α7<br />
nAChR activation and neuroprotection. Neurotoxicity<br />
stimulated by glutamate is prevented by nicot<strong>in</strong>e <strong>in</strong> primary<br />
cultures of cerebellar neurons and is generally thought to be<br />
mediated by α7 nAChR activation. However <strong>in</strong> acutely<br />
dissociated slices, neuroprotection by nicot<strong>in</strong>e can be mediated<br />
by activation of α4β2 nAChRs and <strong>in</strong>hibition of α7 nAChRs<br />
[638430]. Therefore, neuroprotection by ispronicl<strong>in</strong>e can be<br />
expla<strong>in</strong>ed by its preferential activation of the α4β2 nAChR.<br />
The mechanism of ispronicl<strong>in</strong>e neuroprotection reportedly<br />
utilizes a signal transduction pathway <strong>in</strong>volv<strong>in</strong>g JAK2, PI3<br />
k<strong>in</strong>ase, Akt and Bcl-2 [467878]. Ispronicl<strong>in</strong>e (unstated dosage)<br />
was orally active <strong>in</strong> vivo and <strong>in</strong>duced susta<strong>in</strong>ed ACh release<br />
from the cortex, show<strong>in</strong>g potency <strong>in</strong> animal models of cognition<br />
and attention, and additivity/synergy with AChE <strong>in</strong>hibitors. It<br />
demonstrated neuroprotective effects <strong>in</strong> chemically <strong>in</strong>duced<br />
neuronal excitotoxicity models and <strong>in</strong> hypoxia/glucose<br />
deprivation models. Additionally, ispronicl<strong>in</strong>e showed<br />
antidepressant activity; however, no details were provided for<br />
these studies [513286].<br />
Metabolism and pharmacok<strong>in</strong>etics<br />
Metabolism studies conducted <strong>in</strong> vitro with liver microsome<br />
preparations from mice, rats, gu<strong>in</strong>ea pigs, dogs, monkeys<br />
and humans identified five metabolites; the O-dealkyl<br />
derivative endogenous conjugate was the primary<br />
metabolite <strong>in</strong> humans and monkeys, while the N-oxide<br />
metabolite was present <strong>in</strong> all other species [559979]. The<br />
aff<strong>in</strong>ities of the 3-alkylcarbonate and N-desalkylated<br />
metabolites for α4β2 nAChRs were approximately 20- and<br />
40-fold higher than for ispronicl<strong>in</strong>e; other metabolites had<br />
aff<strong>in</strong>ities > 100-fold over ispronicl<strong>in</strong>e. In Sprague Dawley<br />
rats that were adm<strong>in</strong>istered 20 mg/kg of ispronicl<strong>in</strong>e, mass<br />
spectroscopy identified 12 metabolites <strong>in</strong> the plasma, the Odealkyl<br />
derivative be<strong>in</strong>g the major metabolite. No<br />
metabolites were detected <strong>in</strong> fecal extracts, although a small<br />
amount of the parent compound was present [559979].<br />
Ispronicl<strong>in</strong>e had a half-life of 1 to 2 h <strong>in</strong> rodents [557048],<br />
[634416]; however, given that the beneficial effect of a s<strong>in</strong>gle<br />
oral adm<strong>in</strong>istration of ispronicl<strong>in</strong>e on cognition <strong>in</strong> precl<strong>in</strong>ical<br />
models persisted for 18 to 48 h [363337], [634416], this halflife<br />
does not seem to present much of a problem for efficacy.<br />
This unexpected long-term potentiation effect might be<br />
because of a much higher retention of the compound <strong>in</strong> the<br />
bra<strong>in</strong>, an elaborate downstream effect lead<strong>in</strong>g to transient<br />
<strong>in</strong>tracellular plasticity changes, or both. In Sprague Dawley<br />
rats, oral adm<strong>in</strong>istration of ispronicl<strong>in</strong>e (10 mg/kg)<br />
produced high systemic levels, with a maximal plasma<br />
concentration (Cpmax) of 370 ng/ml and Tmax value of 0.25 h.<br />
The compound was cleared rapidly, with a term<strong>in</strong>ation halflife<br />
of 1.1 h. The bioavailability of ispronicl<strong>in</strong>e was 73.3%.<br />
Whole-bra<strong>in</strong> ispronicl<strong>in</strong>e levels at this dose were high<br />
(maximal bra<strong>in</strong> concentration (Cbmax) = 659 ng/g; Tmax = 0.5<br />
to 2 h), show<strong>in</strong>g that the drug readily penetrated the bra<strong>in</strong>.<br />
After <strong>in</strong>travenous adm<strong>in</strong>istration of 1 mg/kg, ispronicl<strong>in</strong>e had<br />
a half-life of 0.8 h and was cleared rapidly (7.1 l/h/kg<br />
compared with the hepatic plasma flow of 2 to 4 l/h/kg)<br />
[559979].<br />
In dogs, ispronicl<strong>in</strong>e had a half-life of 2 h follow<strong>in</strong>g a 1mg/kg<br />
<strong>in</strong>travenous dose. A high total plasma clearance of<br />
3.2 l/h/kg was achieved compared with the hepatic plasma<br />
flow of 1.2 to 2.4 l/h/kg. Follow<strong>in</strong>g oral adm<strong>in</strong>istration of 1<br />
mg/kg ispronicl<strong>in</strong>e, low systemic plasma levels were<br />
achieved (Cpmax = 35 ng/ml at 0.5 to 2 h). The elim<strong>in</strong>ation<br />
half-life of ispronicl<strong>in</strong>e was 1.3 h and its estimated<br />
bioavailability was 31.4% [559979].<br />
In a crossover study <strong>in</strong> six healthy male volunteers,<br />
ispronicl<strong>in</strong>e (2 to 320 mg po) had a Tmax at 2 h and an<br />
elim<strong>in</strong>ation half-life of 4 h; follow<strong>in</strong>g a 320-mg dose,<br />
ispronicl<strong>in</strong>e had a Cmax of 120 ng/ml, a plasma concentration<br />
5- to 10-fold greater than that expected to produce maximal<br />
cognitive effects [559979].<br />
In elderly AAMI patients (> 60 years of age), a 50-mg oral dose<br />
of ispronicl<strong>in</strong>e gave rise to a plasma Cmax range of 4 to 25 ng/ml<br />
[612281], and oral doses of 25 to 75 mg ispronicl<strong>in</strong>e produced<br />
plasma Cmax values <strong>in</strong> the range of 4 to 55 ng/ml [634952].<br />
These low Cmax values might be due to extensive metabolism,<br />
high plasma clearance or low bioavailability. A complete<br />
pharmacok<strong>in</strong>etic study of a s<strong>in</strong>gle 80-mg dose of ispronicl<strong>in</strong>e<br />
was performed <strong>in</strong> six elderly volunteers to assess its absorption,<br />
distribution, metabolism and excretion properties. Cognitive<br />
improvement was evident after 36 to 48 h, which was<br />
comparable to the long duration of action observed <strong>in</strong> animal<br />
models, thus <strong>in</strong>dicat<strong>in</strong>g the suitability of a once-daily dos<strong>in</strong>g<br />
schedule [615362]. The study showed that ispronicl<strong>in</strong>e had a<br />
half-life of 5 to 7 h <strong>in</strong> humans [634416]. Another study <strong>in</strong> six<br />
fed/fasted volunteers exam<strong>in</strong>ed food <strong>in</strong>teraction follow<strong>in</strong>g an<br />
80-mg dose of ispronicl<strong>in</strong>e, although the results from this study<br />
have apparently not yet been reported [615362].<br />
Toxicity<br />
The results of studies <strong>in</strong> rats, dogs and rabbits <strong>in</strong>dicated that<br />
ispronicl<strong>in</strong>e was free from toxic effects at the doses tested. In<br />
rats, no effect was observed on diaphragm contraction,<br />
respiratory function or gastric empty<strong>in</strong>g after oral<br />
adm<strong>in</strong>istration of up to 50, 250 and 500 mg/kg, respectively.<br />
In rats and dogs that were chronically adm<strong>in</strong>istered<br />
ispronicl<strong>in</strong>e for 13 weeks (50 and 30 mg/kg, respectively),<br />
the only side effect was slight and transient bradycardia <strong>in</strong><br />
dogs at the highest dose, possibly mediated by autonomic<br />
nerve stimulation [512176]. Overall, ispronicl<strong>in</strong>e was well<br />
tolerated <strong>in</strong> animals and there was no <strong>in</strong>dication of<br />
reproductive, cellular or genetic toxicity [513286].<br />
Other prelim<strong>in</strong>ary toxicology studies showed a low toxicity<br />
for ispronicl<strong>in</strong>e, with observable adverse effects occurr<strong>in</strong>g <strong>in</strong><br />
normal male and female rats at doses of 5 to 200 mg/kg,<br />
compared with cognitive enhancement at 0.034 mg/kg. At a<br />
dose of 1400 mg/kg, significant toxicity was produced<br />
without caus<strong>in</strong>g death <strong>in</strong> rats [325629]. Thus, the therapeutic<br />
effects of ispronicl<strong>in</strong>e <strong>in</strong> animals are dissociated from its side<br />
effects by four to five orders of magnitude [467878].
In a study conducted <strong>in</strong> rats tra<strong>in</strong>ed to discrim<strong>in</strong>ate nicot<strong>in</strong>e,<br />
ispronicl<strong>in</strong>e and the known addictive properties of nicot<strong>in</strong>e<br />
were compared. Nicot<strong>in</strong>e engaged appropriate respond<strong>in</strong>g <strong>in</strong><br />
70% of animals at a dose of 1.9 µmol/kg compared with<br />
ispronicl<strong>in</strong>e, which engaged an equivalent response only at a<br />
dose of 40 µmol/kg; this result <strong>in</strong>dicates an approximately 20fold-reduced<br />
propensity for dependence of ispronicl<strong>in</strong>e<br />
compared with nicot<strong>in</strong>e [559979].<br />
Cl<strong>in</strong>ical development<br />
Phase I<br />
Four phase I trials of ispronicl<strong>in</strong>e, which assessed safety,<br />
pharmacok<strong>in</strong>etics and cognitive enhancement, have been<br />
completed. One study tested eight escalat<strong>in</strong>g s<strong>in</strong>gle oral doses<br />
of ispronicl<strong>in</strong>e (2, 4, 10, 20, 40, 80, 160 and 320 mg) <strong>in</strong> 48 healthy<br />
volunteers [559979], and a multiple escalat<strong>in</strong>g-dose trial (50, 100<br />
and 200 mg) was conducted <strong>in</strong> 24 healthy volunteers over a 10day<br />
period [511071], [615362]. A pharmacok<strong>in</strong>etic study that<br />
tested food <strong>in</strong>teraction <strong>in</strong> six elderly volunteers was also<br />
completed. The rapid absorption, dose proportionality and<br />
favorable plasma half-life of ispronicl<strong>in</strong>e <strong>in</strong> these trials<br />
suggested the suitability of a once-daily dos<strong>in</strong>g schedule. No<br />
safety issues were reportedly encountered and dose-specific<br />
enhancement of both direct and surrogate measures of memory<br />
and attention was observed. No differences <strong>in</strong> the quality of<br />
work<strong>in</strong>g memory factor were observed. Less pronounced<br />
improvements were observed <strong>in</strong> the 100-mg group, compared<br />
with all other doses, <strong>in</strong>dicative of a possible <strong>in</strong>verted U-shaped<br />
dose-response curve [615362].<br />
In the s<strong>in</strong>gle and multiple escalat<strong>in</strong>g-dose trials, ispronicl<strong>in</strong>e<br />
dose-dependently <strong>in</strong>duced electrical bra<strong>in</strong> activity characteristic<br />
of a nicot<strong>in</strong>e agonist, and electroencephalogram (EEG) analysis<br />
confirmed its CNS penetration and activity. In addition, dosespecific<br />
effects were observed on direct and surrogate measures<br />
of memory <strong>in</strong> a computerized cognitive test battery [615362]. In<br />
l<strong>in</strong>e with precl<strong>in</strong>ical observations, the compound <strong>in</strong>duced longlast<strong>in</strong>g<br />
cognitive enhancement for up to 48 h <strong>in</strong> elderly<br />
volunteers [592125]. In the s<strong>in</strong>gle and multiple escalat<strong>in</strong>g-dose<br />
trials, EEG analysis showed that orally adm<strong>in</strong>istered<br />
ispronicl<strong>in</strong>e caused a shift <strong>in</strong> relative and absolute power from<br />
lower to higher frequency bands. Specifically, power shifted<br />
from the α1 to the α2 band. The shift <strong>in</strong> dom<strong>in</strong>ant α suggested<br />
that the compound had entered the bra<strong>in</strong> and was typical of a<br />
nicot<strong>in</strong>e agonist. Similar effects were observed <strong>in</strong> both trials on<br />
day 1 and <strong>in</strong> the multiple escalat<strong>in</strong>g-dose trial on day 10. No<br />
tolerance to ispronicl<strong>in</strong>e occurred over the 10-day dos<strong>in</strong>g period<br />
[634416]. In the multiple escalat<strong>in</strong>g-dose trial <strong>in</strong> healthy<br />
volunteers, 10 days of dos<strong>in</strong>g with ispronicl<strong>in</strong>e produced<br />
efficacy <strong>in</strong> the 'power of attention' measure of the cognitive<br />
drug research (CDR) test battery [634952]. The 100-mg dose of<br />
ispronicl<strong>in</strong>e improved memory (notably immediate and<br />
delayed word recall) <strong>in</strong> volunteers, and a 200-mg dose<br />
improved picture and word recognition and enhanced<br />
vigilance [634416].<br />
In elderly volunteers, pharmaco-EEG changes resembled<br />
those seen <strong>in</strong> younger <strong>in</strong>dividuals; the changes were of an<br />
acceleration type, with power shift<strong>in</strong>g from low to high<br />
frequency bands. In CDR cognitive tests, significant<br />
Ispronicl<strong>in</strong>e Geerts 63<br />
differences between ispronicl<strong>in</strong>e and placebo on measures of<br />
immediate and delayed recall, picture recognition and<br />
quality of episodic memory were achieved. There was good<br />
correlation between plasma levels of the drug and<br />
pharmaco-EEG changes [634416]. Correlations of<br />
pharmacodynamic and pharmacok<strong>in</strong>etic data <strong>in</strong>dicated that<br />
plasma Cmax values <strong>in</strong> the range 4 to 55 ng/ml were<br />
associated with greatest cognitive improvement; Cmax values<br />
<strong>in</strong> this range would be achieved with oral doses of 25 to 75<br />
mg, levels at which ispronicl<strong>in</strong>e has tolerability equivalent to<br />
placebo [634952].<br />
Phase II<br />
In a randomized, double-bl<strong>in</strong>d, placebo-controlled, phase<br />
IIa/II study <strong>in</strong> an undisclosed number of AAMI patients<br />
(aged > 60 years), a s<strong>in</strong>gle dose of 80 mg ispronicl<strong>in</strong>e was<br />
superior to placebo <strong>in</strong> improv<strong>in</strong>g quality of episodic<br />
secondary memory factor score up to 48 h after dos<strong>in</strong>g. After 3<br />
weeks of treatment at 50 mg, significant improvements were<br />
observed <strong>in</strong> CDR measures of the power and cont<strong>in</strong>uity of<br />
attention, episodic memory and speed of th<strong>in</strong>k<strong>in</strong>g, compared<br />
with patients receiv<strong>in</strong>g placebo [612281], [634952].<br />
Targacept reports that a phase II trial with ispronicl<strong>in</strong>e has<br />
been completed <strong>in</strong> elderly <strong>in</strong>dividuals with AAMI (n = 76).<br />
Positive effects on various aspects of cognition were<br />
observed and the drug was well tolerated at doses up to 150<br />
mg [624033].<br />
Data were presented recently for the double-bl<strong>in</strong>d, placebocontrolled,<br />
crossover phase II study of ispronicl<strong>in</strong>e <strong>in</strong><br />
volunteers with MCI [641513]. Volunteers (aged > 60 years)<br />
with MCI (m<strong>in</strong>i-mental state exam<strong>in</strong>ation (MMSE) score ≥ 24<br />
and Wechsler memory scale-R, paired associate learn<strong>in</strong>g test<br />
score ≥ 1.5 standard deviations lower than age matched<br />
controls) were randomized <strong>in</strong>to cohorts of 20 to sequentially<br />
receive 3 weeks oral treatment with 50 and 100 mg of<br />
ispronicl<strong>in</strong>e or placebo, with a 2-week washout between<br />
treatments. Cognitive assessment was performed at 0, 2 and 4 h<br />
post-dos<strong>in</strong>g on the CDR test battery. No effect was observed<br />
with 50 mg of ispronicl<strong>in</strong>e (n = 19), at which placebo was<br />
superior to drug on measures of work<strong>in</strong>g memory and memory<br />
speed. The 100-mg dose of ispronicl<strong>in</strong>e (n = 17) was superior to<br />
placebo <strong>in</strong> the power of attention and episodic memory factors<br />
(p < 0.05), and on the work<strong>in</strong>g memory and speed of memory<br />
tests (p < 0.1). Analysis of data from both dose groups showed<br />
that ispronicl<strong>in</strong>e produced greater cognitive improvement <strong>in</strong><br />
more severely impaired (MMSE 23 to 27) volunteers than those<br />
with lesser impairment (MMSE = 28 to 30). Ispronicl<strong>in</strong>e was<br />
well tolerated and demonstrated a favorable safety profile at<br />
both doses [641513].<br />
A randomized, double-bl<strong>in</strong>d, placebo-controlled phase II<br />
cl<strong>in</strong>ical trial of ispronicl<strong>in</strong>e is ongo<strong>in</strong>g <strong>in</strong> elderly <strong>in</strong>dividuals<br />
(aged 50 to 80 years) with AAMI. Recruitment has been<br />
completed (174 participants were expected), and the study is<br />
scheduled for completion <strong>in</strong> February 2006<br />
[www.cl<strong>in</strong>icaltrials.gov]. A further phase II trial is planned for<br />
mid 2006, and is designed to evaluate ispronicl<strong>in</strong>e as a<br />
monotherapy treatment for mild AD or add-on therapy to<br />
approved medications for moderate AD. Cl<strong>in</strong>ical development
64 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
is also be<strong>in</strong>g considered for cognitive impairment associated<br />
with schizophrenia and follow<strong>in</strong>g coronary artery bypass<br />
graft<strong>in</strong>g, ADHD and certa<strong>in</strong> forms of dementia [624033]. In<br />
summary, ispronicl<strong>in</strong>e was well tolerated and demonstrated<br />
cognitive enhanc<strong>in</strong>g effects <strong>in</strong> the phase I and phase II cl<strong>in</strong>ical<br />
trials to date (n = 200) [611220].<br />
Side effects and contra<strong>in</strong>dications<br />
In phase I/II studies assess<strong>in</strong>g the effect of ispronicl<strong>in</strong>e on<br />
central activity and cognitive enhancement, adverse events<br />
were only detected at the maximum tolerated dose of<br />
ispronicl<strong>in</strong>e (150 mg <strong>in</strong> the elderly and 320 mg <strong>in</strong> the young).<br />
These <strong>in</strong>cluded headache, dizz<strong>in</strong>ess and light-headedness<br />
and occasional nausea/vomit<strong>in</strong>g. These side effects were<br />
attributed to the central pharmacology of ispronicl<strong>in</strong>e<br />
because they were not accompanied by changes <strong>in</strong><br />
cardiovascular variables as would be expected if peripheral<br />
nAChR <strong>in</strong>hibition were occurr<strong>in</strong>g [615362].<br />
In phase IIa/b trials, ispronicl<strong>in</strong>e had an effective dose of 50 to<br />
100 mg, and no toxic effects were observed at 320 mg,<br />
suggest<strong>in</strong>g a broad therapeutic w<strong>in</strong>dow [541084]. Ispronicl<strong>in</strong>e<br />
was well tolerated and demonstrated a favorable safety profile<br />
[612281].<br />
In a phase II study of 50 or 100 mg ispronicl<strong>in</strong>e <strong>in</strong> volunteers<br />
with MCI, the drug was well tolerated at both doses. The<br />
most common adverse event was light-headedness. No<br />
significant effects were recorded on biochemical,<br />
hematological or ur<strong>in</strong>ary measures, vital signs or cardiac<br />
monitor<strong>in</strong>g [641513].<br />
Patent summary<br />
In January 2002, Targacept and Aventis Pharma SA<br />
published WO-00205798, a PCT application that covered<br />
salts of ispronicl<strong>in</strong>e and their use <strong>in</strong> the prevention or<br />
treatment of CNS disorders.<br />
Four US patents (US-06432975, US-06624173, US-06440970<br />
and US-06525065) relate to composition of matter of the<br />
chemical family of the hetero-aryl azabicyclo alkanes. In the<br />
composition patents, a broad application doma<strong>in</strong> has been<br />
stated, <strong>in</strong>clud<strong>in</strong>g the treatment of other CNS conditions and<br />
disorders, such as schizophrenia, <strong>in</strong> provid<strong>in</strong>g neuroprotection,<br />
the management of stroke, and <strong>in</strong> treat<strong>in</strong>g patients<br />
susceptible to convulsions, depression, autism and certa<strong>in</strong><br />
neuroendocr<strong>in</strong>e disorders.<br />
WO-2005037832 was published by Targacept <strong>in</strong> April 2005,<br />
and claims the use of ispronicl<strong>in</strong>e for the treatment of<br />
Park<strong>in</strong>son's disease, Tourette's syndrome, ADHD,<br />
schizophrenia, drug/nicot<strong>in</strong>e addiction, pa<strong>in</strong> and obesity. In<br />
addition, appropriately radiolabeled compounds are<br />
claimed for use as selective probes for nAChR subtypes <strong>in</strong><br />
neuroimag<strong>in</strong>g applications <strong>in</strong> US-06432975.<br />
<strong>Current</strong> op<strong>in</strong>ion<br />
Specific stimulation of α4β2 versus α7 nAChRs will likely<br />
lead to different effects on cognitive scales because of the<br />
differential distribution of nAChR subtypes (preferentially<br />
striatal-thalamic versus cortical), and differential sensitivity<br />
to pathological conditions (eg, AD versus psychiatric<br />
diseases). In this regard, perhaps someth<strong>in</strong>g can be learned<br />
from the cl<strong>in</strong>ical expertise ga<strong>in</strong>ed from the study of ABT-418<br />
(an nAChR agonist that was discont<strong>in</strong>ued from<br />
development by Abbott Laboratories <strong>in</strong> 2002 because of<br />
safety concerns) <strong>in</strong> a number of medical conditions<br />
<strong>in</strong>volv<strong>in</strong>g lack of attention and cognitive deficits. The<br />
compounds have a similar profile <strong>in</strong> terms of their nAChR<br />
selectivity. Interest<strong>in</strong>gly, unlike ABT-418, ispronicl<strong>in</strong>e<br />
produces a susta<strong>in</strong>ed cognitive effect <strong>in</strong> both precl<strong>in</strong>ical and<br />
human models long after its clearance from the body. This<br />
prolonged action might be the result of changes <strong>in</strong><br />
<strong>in</strong>tracellular signal<strong>in</strong>g, the nature of which is still unclear. At<br />
the maximal cl<strong>in</strong>ical tolerable dose, ispronicl<strong>in</strong>e will most<br />
probably also stimulate the α7 nAChR. For α7 nAChRmediated<br />
neuroprotection aga<strong>in</strong>st β-amyloid, it has been<br />
shown that Janus k<strong>in</strong>ase/Akt pathways are <strong>in</strong>volved <strong>in</strong><br />
<strong>in</strong>tracellular activation [621830]. As a possible caveat,<br />
precl<strong>in</strong>ical data suggest that as well as possibly reduc<strong>in</strong>g βamyloid<br />
pathology [622041], long-term activation of<br />
nicot<strong>in</strong>ic receptors <strong>in</strong> transgenic animals can exacerbate tau<br />
pathology [621828]. Whether this is the case for ispronicl<strong>in</strong>e<br />
is currently unknown.<br />
The specific activation of neuronal nAChRs is advantageous<br />
because gastro<strong>in</strong>test<strong>in</strong>al side effects, such as vomit<strong>in</strong>g and<br />
diarrhea, currently occur <strong>in</strong> many AD patients dur<strong>in</strong>g the<br />
titration phase of their treatment with AChE <strong>in</strong>hibitors, and<br />
are assumed to be related to peripheral muscar<strong>in</strong>ic receptor<br />
activation. Nausea is a more typical nicot<strong>in</strong>ic-receptormediated<br />
side effect, and whether the effects are a<br />
consequence of central activity is still a matter for debate. In<br />
any case, no data have described the <strong>in</strong>cidence of nausea <strong>in</strong><br />
ispronicl<strong>in</strong>e-treated patients.<br />
The cl<strong>in</strong>ical experience with galantam<strong>in</strong>e <strong>in</strong> AD patients<br />
suggests a superior effect of nAChR modulators <strong>in</strong><br />
enhanc<strong>in</strong>g attention [516203] and work<strong>in</strong>g memory [622036]<br />
over and above that attributable to AChE <strong>in</strong>hibition alone. In<br />
addition, specific behavioral improvements can be expected<br />
<strong>in</strong> agitation/aggression, anxiety, dis<strong>in</strong>hibition and aberrant<br />
motor behaviors [622040]. This f<strong>in</strong>d<strong>in</strong>g is <strong>in</strong> l<strong>in</strong>e with the<br />
observed effects of ispronicl<strong>in</strong>e on CDR battery scales <strong>in</strong><br />
cognitively impaired elderly <strong>in</strong>dividuals. This cl<strong>in</strong>ical effect<br />
is probably because the stimulation of nicot<strong>in</strong>ic receptors,<br />
which diffusely project out of the nucleus basalis of Meynert<br />
and the pedunculopont<strong>in</strong>e nucleus, modulates their<br />
activation <strong>in</strong> a large part of the bra<strong>in</strong>. This is likely mediated<br />
by an <strong>in</strong>crease <strong>in</strong> dopam<strong>in</strong>e, seroton<strong>in</strong>, norep<strong>in</strong>ephr<strong>in</strong>e,<br />
acetylchol<strong>in</strong>e and even glutamate and γ-am<strong>in</strong>obutyric acid<br />
(GABA) levels. As a specific example, β2* nAChR<br />
stimulation <strong>in</strong>creases dopam<strong>in</strong>e release <strong>in</strong> the striatum<br />
[636359]. One could argue that <strong>in</strong>creased dopam<strong>in</strong>e release<br />
<strong>in</strong> a slightly deficient striatum could enhance the saliency of<br />
stimuli and positively <strong>in</strong>fluence reward stimuli. However,<br />
the specific nAChR subtype responsible for the other effects<br />
has not been identified <strong>in</strong> all cases, and specific questions<br />
rema<strong>in</strong> regard<strong>in</strong>g the k<strong>in</strong>etics of activation, desensitization<br />
and reactivation of the nAChRs responsible, result<strong>in</strong>g, for<br />
example, <strong>in</strong> spatial and temporal differences <strong>in</strong> excitatory
glutamatergic and <strong>in</strong>hibitory GABA modulation <strong>in</strong> complex<br />
<strong>in</strong>teract<strong>in</strong>g networks [621790], [621822].<br />
Whether this effect will be sufficient for pure nAChR<br />
agonists to improve cognitive scales such as the Alzheimer's<br />
disease assessment scale cognitive subscale (ADAS-Cog) or<br />
MMSE is at present unknown. Computer simulation of a<br />
virtual synaptic cleft suggests that suboptimal AChE<br />
<strong>in</strong>hibition can be synergistically amplified by nicot<strong>in</strong>ic<br />
receptor stimulation [621742]. This effect was illustrated <strong>in</strong> a<br />
number of <strong>in</strong> vivo precl<strong>in</strong>ical studies <strong>in</strong> which a dose of<br />
galantam<strong>in</strong>e had similar or superior effects on behavior or<br />
neurophysiology compared with an identical dose of<br />
donepezil, a pure AChE <strong>in</strong>hibitor [621831], [621833], despite<br />
the fact that donepezil produces a 3- to 4-fold higher bra<strong>in</strong><br />
AChE <strong>in</strong>hibition under these conditions [621785]. This<br />
f<strong>in</strong>d<strong>in</strong>g suggests that the activation of nAChR through the<br />
comb<strong>in</strong>ation of nAChR modulation with a low bra<strong>in</strong> AChE<br />
<strong>in</strong>hibition can actually lead to the same (or even superior)<br />
behavioral or neurochemical changes as direct stimulation <strong>in</strong><br />
the context of a much higher bra<strong>in</strong> AChE <strong>in</strong>hibition.<br />
There is a high probability that ispronicl<strong>in</strong>e will be tested <strong>in</strong><br />
comb<strong>in</strong>ation with an AChE <strong>in</strong>hibitor dur<strong>in</strong>g cl<strong>in</strong>ical<br />
development. Interest<strong>in</strong>gly, comb<strong>in</strong>ation with a suboptimal<br />
dose of an AChE <strong>in</strong>hibitor could lead to superior cl<strong>in</strong>ical<br />
efficacy on primary endpo<strong>in</strong>ts, such as ADAS-Cog, while<br />
simultaneously limit<strong>in</strong>g the development of tolerance ow<strong>in</strong>g to<br />
the upregulation of the AChE enzyme as a consequence of<br />
high-level cont<strong>in</strong>uous AChE <strong>in</strong>hibition [622031]. Furthermore,<br />
muscar<strong>in</strong>ic receptor stimulation result<strong>in</strong>g from limited AChE<br />
<strong>in</strong>hibition can provide additional benefits for a number of<br />
behavioral problems, as suggested by the cl<strong>in</strong>ical experience<br />
with muscar<strong>in</strong>ic M1 agonists (for a review, see reference<br />
[624153]). In addition, muscar<strong>in</strong>ic M1 receptor stimulation can<br />
provide neuroprotection aga<strong>in</strong>st both amyloid and tau<br />
pathology beyond nicot<strong>in</strong>e receptor activation (reviewed <strong>in</strong><br />
reference [621786]). Because the <strong>in</strong>tracellular pathways of both<br />
approaches differ, there may be the possibility of an additive or<br />
synergistic action.<br />
Ispronicl<strong>in</strong>e Geerts 65<br />
Ispronicl<strong>in</strong>e is also currently <strong>in</strong> development for the<br />
treatment of pre-Alzheimer's conditions such as MCI and<br />
AAMI. A reactive upregulation of ACh-synthesiz<strong>in</strong>g<br />
enzymes has been documented <strong>in</strong> this patient population,<br />
probably as a consequence of dysfunctional chol<strong>in</strong>ergic<br />
nerve term<strong>in</strong>als [622042]. This upregulation might reduce<br />
the beneficial effect of direct nAChR stimulation by<br />
modulators such as ispronicl<strong>in</strong>e. In this regard, it is<br />
<strong>in</strong>terest<strong>in</strong>g to note that <strong>in</strong> terms of delay<strong>in</strong>g the diagnosis<br />
of AD, the cl<strong>in</strong>ical benefits of AChE <strong>in</strong>hibition <strong>in</strong> MCI<br />
patients are, at best, limited [622044]. MCI and AAMI<br />
have not yet been recognized by the Food and Drug<br />
Adm<strong>in</strong>istration as medical conditions, but the regulatory<br />
landscape might change substantially over the next few<br />
years.<br />
An <strong>in</strong>terest<strong>in</strong>g development is the cl<strong>in</strong>ical proof-of-pr<strong>in</strong>ciple<br />
study of ispronicl<strong>in</strong>e as an add-on <strong>in</strong> the treatment of<br />
cognitive deficits <strong>in</strong> schizophrenia. This study was carried<br />
out by the TURNS project, as presented at the 2005<br />
International Conference on Schizophrenia Research<br />
[631107]. Although the neuropathology and genetics of<br />
schizophrenia suggest a specific α7 nAChR deficit <strong>in</strong> this<br />
case, a well-balanced modulation of both major bra<strong>in</strong><br />
nAChR subtypes, such as that provided by ispronicl<strong>in</strong>e,<br />
might be of great value.<br />
In summary, the pharmacological profile of available data<br />
for ispronicl<strong>in</strong>e <strong>in</strong>dicate that this compound may provide<br />
an <strong>in</strong>terest<strong>in</strong>g new mechanism for treat<strong>in</strong>g cognitive<br />
deficits <strong>in</strong> both schizophrenia and AD. Extrapolat<strong>in</strong>g from<br />
the precl<strong>in</strong>ical data for galantam<strong>in</strong>e, a compound with a<br />
similar pharmacology (reviewed <strong>in</strong> reference [634638]), <strong>in</strong><br />
theory we can expect that ispronicl<strong>in</strong>e will comb<strong>in</strong>e<br />
symptomatic cognitive improvement with general<br />
neuroprotection aga<strong>in</strong>st β-amyloid pathology. We believe<br />
that the best effects of the drug will be observed <strong>in</strong><br />
patients with AD and when it is comb<strong>in</strong>ed with a<br />
suboptimal dose of an AChE <strong>in</strong>hibitor.<br />
Development history<br />
Developer Country Status Indication Date Reference<br />
Targacept Inc UK Phase II Cognitive disorder 11-NOV-03 512600<br />
Targacept Inc US Phase II Cognitive disorder 06-JUL-05 611220<br />
Literature classifications<br />
Chemistry<br />
Study type Result Reference<br />
SAR. A number of compounds with low nanomolar aff<strong>in</strong>ity for nAChRs were identified, but were metabolized<br />
through N-demethylation and oxidation, result<strong>in</strong>g <strong>in</strong> a half-life of 30 m<strong>in</strong>. The 3-isopropoxy-pyrid<strong>in</strong>e analog<br />
of RJR-2403 had an improved half-life of 1.4 h <strong>in</strong> rodents, and was later named ispronicl<strong>in</strong>e. An α-methyl<br />
group was identified as be<strong>in</strong>g essential for <strong>in</strong>creas<strong>in</strong>g the half-life.<br />
557048<br />
Synthesis. Ispronicl<strong>in</strong>e was prepared by coupl<strong>in</strong>g (S)-N-methyl-N-(tert-butoxycarbonyl)-4-penten-2-am<strong>in</strong>e and 3bromo-5-isopropoxy-pyrid<strong>in</strong>e<br />
via a palladium-catalyzed Heck coupl<strong>in</strong>g reaction. The result<strong>in</strong>g <strong>in</strong>termediate,<br />
(S)-(E)-N-methyl-N-(tert-butoxycarbonyl)-5-[3-(5-isopropoxy-pyrid<strong>in</strong>)yl]-4-penten-2-am<strong>in</strong>e, was<br />
subsequently treated with 6 M hydrochloric acid <strong>in</strong> dimethylformamide to give the free base of ispronicl<strong>in</strong>e.<br />
559979
66 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
Biology<br />
Study type Effect studied Model Result Reference<br />
In vitro Activity. Rat bra<strong>in</strong> membrane preparations, Ispronicl<strong>in</strong>e was a high-aff<strong>in</strong>ity agonist of<br />
306443<br />
or muscle- or ganglion-type nicot<strong>in</strong>ic receptors <strong>in</strong> rat bra<strong>in</strong> membranes (Ki =<br />
nAChRs.<br />
11 nM; nicot<strong>in</strong>e Ki = 4 nM), and reportedly had<br />
specificity for nAChRs. Ispronicl<strong>in</strong>e did not b<strong>in</strong>d<br />
to the muscle-type (α1β1δγ) or ganglion-type<br />
(α3β4) peripheral nAChRs at concentrations up<br />
to 100 µM. Conversely, nicot<strong>in</strong>e activated<br />
nAChRs <strong>in</strong> human and rat cells, with EC50<br />
values of 60 and 20 µM, respectively, <strong>in</strong>dicat<strong>in</strong>g<br />
greater CNS/peripheral nervous system<br />
specificity for ispronicl<strong>in</strong>e.<br />
In vitro Efficacy. Rat striatal and thalamic<br />
In striatal synaptosomes, ispronicl<strong>in</strong>e had a 306443<br />
synaptosomes treated with<br />
dopam<strong>in</strong>e-release profile comparable to that of<br />
ispronicl<strong>in</strong>e or nicot<strong>in</strong>e (unstated nicot<strong>in</strong>e (EC50 = 106 nM and Emax = 85%). In<br />
concentrations).<br />
thalamic synaptosomes, ispronicl<strong>in</strong>e <strong>in</strong>creased<br />
ion <strong>in</strong>flux to an Emax of 58% with an EC50 value of<br />
220 nM, compared with an Emax of 100% and an<br />
EC50 value of 590 nM for nicot<strong>in</strong>e. Given the<br />
preferential localization of α4β2 nAChRs <strong>in</strong> the<br />
thalamus, this effect is likely mediated by this<br />
receptor subtype.<br />
In vivo Efficacy. Radial arm maze model. Rats were Both schedules of ispronicl<strong>in</strong>e significantly<br />
306443<br />
orally adm<strong>in</strong>istered ispronicl<strong>in</strong>e improved both work<strong>in</strong>g and reference memory<br />
(0.1, 0.3, 0.6, 3.0 and 6.0 µmol/kg)<br />
<strong>in</strong> both acute (presumed to be<br />
s<strong>in</strong>gle-dose) and chronic (daily for 6<br />
days) schedules.<br />
performance.<br />
In vivo Efficacy. Scopolam<strong>in</strong>e-<strong>in</strong>duced deficits <strong>in</strong> the Ispronicl<strong>in</strong>e improved performance both alone 345774<br />
passive avoidance task <strong>in</strong> rats. (ED50 = 0.89 µmol/kg) and at a suboptimal dose<br />
(0.6 µmol/kg) <strong>in</strong> comb<strong>in</strong>ation with tacr<strong>in</strong>e and<br />
donepezil.<br />
Ex vivo Activity. Synaptic transmission after Ispronicl<strong>in</strong>e prevented the loss of synaptic<br />
583306<br />
oxygen/glucose deprivation <strong>in</strong> a rat transmission <strong>in</strong> a concentration-dependent<br />
bra<strong>in</strong> hippocampal slice model manner, with a maximal effect of > 70%<br />
<strong>in</strong>cubated with ispronicl<strong>in</strong>e. protection at 10 µM. The effect was mediated by<br />
nAChRs because mecamylam<strong>in</strong>e, a nonselective<br />
antagonist, blocked the neuroprotective<br />
effect.<br />
Metabolism<br />
Study type Effect studied Model Result Reference<br />
In vivo Pharmacok<strong>in</strong>etics. Sprague Dawley rats adm<strong>in</strong>istered Values for Cpmax and Tmax were 370 ng/ml and 559979<br />
a s<strong>in</strong>gle oral dose of ispronicl<strong>in</strong>e 0.25 h, respectively. The compound was<br />
(10 mg/kg).<br />
cleared rapidly, with a term<strong>in</strong>ation half-life of<br />
1.1 h. The bioavailability was 73.3%. Wholebra<strong>in</strong><br />
ispronicl<strong>in</strong>e levels were high (Cbmax =<br />
659 ng/g; Tmax = 0.5 to 2 h), <strong>in</strong>dicat<strong>in</strong>g ready<br />
bra<strong>in</strong> penetration. After <strong>in</strong>travenous<br />
adm<strong>in</strong>istration of 1 mg/kg, ispronicl<strong>in</strong>e had a<br />
half-life of 0.8 h and was cleared rapidly (7.1<br />
l/h/kg compared with the hepatic plasma flow<br />
of 2 to 4 l/h/kg).<br />
In vivo Pharmacok<strong>in</strong>etics. Dogs adm<strong>in</strong>istered a 1-mg/kg A high total plasma clearance of 3.2 l/h/kg 559979<br />
<strong>in</strong>travenous or oral dose of<br />
was achieved compared with the hepatic<br />
ispronicl<strong>in</strong>e.<br />
plasma flow of 1.2 to 2.4 l/h/kg. Follow<strong>in</strong>g oral<br />
adm<strong>in</strong>istration of 1 mg/kg, low systemic<br />
plasma levels were achieved (Cpmax = 35<br />
ng/ml at 0.5 to 2 h). The elim<strong>in</strong>ation half-life of<br />
ispronicl<strong>in</strong>e was 1.3 h and its estimated<br />
bioavailability was 31.4%.<br />
In vivo Pharmacok<strong>in</strong>etics. Elderly AAMI patients (aged > 60 Plasma Cmax values ranged from 4 to 25<br />
612281<br />
years) adm<strong>in</strong>istered 50 mg of oral<br />
ispronicl<strong>in</strong>e.<br />
ng/ml.<br />
In vivo Pharmacok<strong>in</strong>etics. Elderly volunteers (aged > 60 Plasma Cmax values ranged from 4 to 55<br />
634952<br />
years) orally adm<strong>in</strong>istered<br />
ng/ml. Ispronicl<strong>in</strong>e <strong>in</strong>duced long-last<strong>in</strong>g<br />
ispronicl<strong>in</strong>e (25 to 75 mg).<br />
cognitive enhancement for up to 48 h.
Metabolism (cont<strong>in</strong>ued)<br />
Ispronicl<strong>in</strong>e Geerts 67<br />
Study type Effect studied Model Result Reference<br />
In vivo Pharmacok<strong>in</strong>etics. A food-<strong>in</strong>teraction trial <strong>in</strong> six No food <strong>in</strong>teraction was observed. S<strong>in</strong>gle 615362<br />
fed/fasted elderly volunteers doses of ispronicl<strong>in</strong>e achieved CNS<br />
adm<strong>in</strong>istered an 80-mg oral dose of penetration. The rapid absorption, dose<br />
ispronicl<strong>in</strong>e.<br />
proportionality and favorable plasma half-life<br />
of ispronicl<strong>in</strong>e <strong>in</strong> this trial suggested the<br />
suitability of a once-daily dos<strong>in</strong>g schedule.<br />
Cl<strong>in</strong>ical<br />
Effect studied Model Result Reference<br />
Safety and efficacy. A phase I, 10-day multiple<br />
Ispronicl<strong>in</strong>e was well tolerated and no safety issues were 615362<br />
escalat<strong>in</strong>g-dose study of<br />
encountered up to 200 mg. Dose-specific enhancement of<br />
ispronicl<strong>in</strong>e (50, 100 and 200 mg) <strong>in</strong> both direct and surrogate measures of memory and<br />
young volunteers (n = 24).<br />
attention was observed. No differences were observed on<br />
the quality of work<strong>in</strong>g memory factor. Less pronounced<br />
improvements were seen <strong>in</strong> the 100-mg group, <strong>in</strong>dicative<br />
of an <strong>in</strong>verted U-shaped dose-response curve.<br />
Efficacy and tolerability. A phase I, s<strong>in</strong>gle and multiple Ispronicl<strong>in</strong>e dose-dependently <strong>in</strong>duced electrical bra<strong>in</strong> 634416<br />
escalat<strong>in</strong>g-dose trial of ispronicl<strong>in</strong>e activity on EEG, characteristic of a nicot<strong>in</strong>e agonist,<br />
<strong>in</strong> young volunteers (n = 48 and 24, caus<strong>in</strong>g a shift <strong>in</strong> relative and absolute power from<br />
respectively).<br />
lower to higher frequency bands. No tolerance to<br />
ispronicl<strong>in</strong>e occurred over the 10-day dos<strong>in</strong>g period.<br />
Efficacy and tolerability. A phase I trial of ispronicl<strong>in</strong>e <strong>in</strong> Pharmacodynamic and pharmacok<strong>in</strong>etic data<br />
634952<br />
elderly patients with AAMI (aged > suggested that Cmax values <strong>in</strong> the range of 4 to 55 ng/ml<br />
60 years).<br />
caused the greatest cognitive improvement. Oral doses<br />
of 25 to 75 mg of ispronicl<strong>in</strong>e gave rise to values <strong>in</strong> this<br />
range, at which ispronicl<strong>in</strong>e was tolerated <strong>in</strong> a similar<br />
manner to placebo.<br />
Efficacy. A phase II, randomized, double- A s<strong>in</strong>gle dose of 80 mg ispronicl<strong>in</strong>e was superior to 612281<br />
bl<strong>in</strong>d, placebo-controlled trial <strong>in</strong> placebo <strong>in</strong> improv<strong>in</strong>g quality of episodic secondary<br />
elderly AAMI patients (aged > 60 memory factor score up to 48 h after dos<strong>in</strong>g. Three<br />
years).<br />
weeks of treatment with 50 mg ispronicl<strong>in</strong>e improved<br />
CDR measures of the power and cont<strong>in</strong>uity of attention,<br />
episodic memory and speed of th<strong>in</strong>k<strong>in</strong>g, compared with<br />
patients receiv<strong>in</strong>g placebo.<br />
Efficacy and tolerability. Phase II trials <strong>in</strong> elderly AAMI Positive effects on various aspects of cognition were 624033<br />
patients (n = 76).<br />
observed, and the drug was well tolerated at doses up<br />
to 150 mg.<br />
Associated patent<br />
Title Pharmaceutical compositions and methods for use.<br />
Assignee Targacept Inc; Aventis Pharma SA<br />
Publication WO-00205798 24-JAN-02<br />
Priority US-20000616743 14-JUL-00<br />
Inventors Dull GM, Leconte J-P, Kabir H.<br />
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624143 Dementia rat<strong>in</strong>g and nicot<strong>in</strong>ic receptor expression <strong>in</strong> the<br />
prefrontal cortex <strong>in</strong> schizophrenia. Mart<strong>in</strong>-Ruiz CM, Haroutunian VH, Long<br />
P, Young AH, Davis KL, Perry EK, Court JA BIOL PSYCHIATRY 2003 54 11<br />
1222-1223<br />
624144 Measurement and treatment research to improve cognition <strong>in</strong><br />
schizophrenia: NIMH MATRICS <strong>in</strong>itiative to support the development of<br />
agents for improv<strong>in</strong>g cognition <strong>in</strong> schizophrenia. Marder SR, Fenton W<br />
SCHIZOPHR RES 2004 72 1 5-9<br />
624147 Alpha-7 nicot<strong>in</strong>ic receptor agonists: Potential new candidates for<br />
the treatment of schizophrenia. Mart<strong>in</strong> LF, Kem WR, Freedman R<br />
PSYCHOPHARMACOLOGY 2005 174 1 54-64<br />
624153 The utility of muscar<strong>in</strong>ic agonists <strong>in</strong> the treatment of Alzheimer's<br />
disease. Messer WS Jr J MOL NEUROSCI 2002 19 1-2 187-193<br />
631107 Cognition <strong>in</strong> schizophrenia: The MATRICS <strong>in</strong>itiative. White RF,<br />
Compton M INT CONGR SCHIZOPH RES 2005 April 4-6 Symposium 4-6<br />
634416 Cognitive enhancement <strong>in</strong> man with ispronicl<strong>in</strong>e a nicot<strong>in</strong>ic<br />
partial agonist us<strong>in</strong>g surrogate markers. Dunbar GC, Kuchibhatla R INT<br />
SYMP CHOLINERGIC MECH 2005 October 01-05 SO33<br />
634638 Indicators of neuroprotection with galantam<strong>in</strong>e. Geerts H BRAIN<br />
RES BULL 2005 64 6 519-524<br />
634952 Cognitive enhancement <strong>in</strong> early studies with TC-1734, a<br />
partial agonist at the NNR receptor. Dunbar GC, Kuchibhatla R,<br />
Wamsley JK INT CONF ALZHEIMER PARKINSONS DIS, Sorrento, Italy<br />
2005 March 9-13<br />
636359 Endogenous nicot<strong>in</strong>ic chol<strong>in</strong>ergic activity regulates dopam<strong>in</strong>e<br />
release <strong>in</strong> the striatum. Zhou FM, Liang Y, Dani JA NAT NEUROSCI 2001 4<br />
12 1224-1229<br />
638395 Nicot<strong>in</strong>ic receptors and schizophrenia. Ripoll N, Bronnec M, Bour<strong>in</strong><br />
M CURR MED RES OPIN 2004 20 7 1057-1074<br />
638396 Nicot<strong>in</strong>ic receptors and Alzheimer's disease. Bour<strong>in</strong> M, Ripoll N,<br />
Dailly E CURR MED RES OPIN 2003 19 3 169-177
638398 The nicot<strong>in</strong>ic acetylchol<strong>in</strong>e receptor subtypes and their function<br />
<strong>in</strong> the hippocampus and cerebral cortex. Alkondon M, Albuquerque EX<br />
PROG BRAIN RES 2004 145 109-120<br />
638427 In vivo imag<strong>in</strong>g of human cerebral nicot<strong>in</strong>ic acetylchol<strong>in</strong>e<br />
receptors with 2-18F-fluoro-A-85380 and PET. Gallezot JD, Bottlaender M,<br />
Gregoire MC, Roumenov D, Deverre JR, Coulon C, Ottaviani M, Dolle F,<br />
Syrota A, Valette H J NUCL MED 2005 46 2 240-247<br />
Ispronicl<strong>in</strong>e Geerts 69<br />
638430 Nicot<strong>in</strong>ic receptors differentially regulate N-methyl-D-aspartate<br />
damage <strong>in</strong> acute hippocampal slices. Ferchm<strong>in</strong> PA, Perez D, Eterovic VA,<br />
de Vellis J J PHARMACOL EXP THER 2003 305 3 1071-1078<br />
641513 Ispronicl<strong>in</strong>e, a neuronal nicot<strong>in</strong>ic receptor partial agonist <strong>in</strong> the<br />
treatment of subjects with mild cognitive impairment (MCI). Dunbar GC,<br />
Kuchibhatla R CONG INT PSYCHOGERIATR ASSOC Stockholm, Sweden<br />
2005 September 21 Abs 105
70<br />
AEOL-10150 Aeolus<br />
Richard W Orrell<br />
Address<br />
Department of Cl<strong>in</strong>ical Neurosciences<br />
Royal Free and University College Medical School<br />
University College London<br />
Rowland Hill Street<br />
London<br />
NW3 2PF<br />
UK<br />
Email: r.orrell@medsch.ucl.ac.uk<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 7(1):70-80<br />
© The Thomson Corporation ISSN 1472-4472<br />
AEOL-10150, a small-molecule antioxidant analogous to the<br />
catalytic site of superoxide dismutase, is under development by<br />
Aeolus (formerly Incara) as a potential subcutaneous treatment<br />
for amyotrophic lateral sclerosis (ALS), stroke, sp<strong>in</strong>al cord<br />
<strong>in</strong>jury, lung <strong>in</strong>flammation and mucositis. The compound is<br />
currently undergo<strong>in</strong>g a phase I cl<strong>in</strong>ical trial for ALS. In<br />
October 2005, the company had applied for Fast Track status,<br />
and planned to submit a special protocol assessment for a<br />
pivotal phase II/III trial.<br />
Introduction<br />
AEOL-10150 is a manganese metalloporphyr<strong>in</strong> catalytic<br />
oxidant, a small-molecule antioxidant that has structural and<br />
functional similarities to the catalytic site of superoxide<br />
dismutase (SOD). Metalloporphyr<strong>in</strong>s are a novel class of<br />
antioxidants that 'scavenge' a wide range of oxidative species,<br />
<strong>in</strong>clud<strong>in</strong>g superoxide, peroxide, peroxynitrite and lipid peroxyl<br />
radicals [449960], [625113]. AEOL-10150 is under development<br />
by Aeolus Pharmaceuticals Inc (formerly Incara<br />
Pharmaceuticals) as a potential subcutaneous treatment,<br />
primarily for amyotrophic lateral sclerosis (ALS) [505222], but is<br />
also under <strong>in</strong>vestigation for a range of conditions, <strong>in</strong>clud<strong>in</strong>g<br />
stroke [428437], sp<strong>in</strong>al cord <strong>in</strong>jury [616364], lung <strong>in</strong>flammation<br />
[616377] and mucositis [432294].<br />
ALS is a neurodegenerative disorder affect<strong>in</strong>g men and<br />
women of all ages and ethnic orig<strong>in</strong>s worldwide. ALS may<br />
also be called motor neuron disease. This disorder has an<br />
annual <strong>in</strong>cidence rate of approximately two per 100,000 of<br />
the population, and a prevalence of six per 100,000. The<br />
<strong>in</strong>cidence <strong>in</strong>creases with age, with the mean age of onset<br />
be<strong>in</strong>g approximately 60 years, although it can affect<br />
<strong>in</strong>dividuals from early adulthood (from approximately 20<br />
years) onwards. Men are slightly more likely to be affected<br />
than women (1.4:1) [478835], [638196], [638197]. The<br />
progression of the disease is typically rapid, with the earliest<br />
symptom often be<strong>in</strong>g a muscle weakness <strong>in</strong> the arms or legs<br />
of a patient, co<strong>in</strong>cid<strong>in</strong>g with an <strong>in</strong>creased tendency to drop<br />
objects, stumble, twitch or experience abnormal fatigue <strong>in</strong><br />
the limbs. Further weaken<strong>in</strong>g and paralysis can spread to<br />
the muscles <strong>in</strong>volved <strong>in</strong> breath<strong>in</strong>g, swallow<strong>in</strong>g and speech,<br />
lead<strong>in</strong>g to immobility, an <strong>in</strong>ability to eat, dr<strong>in</strong>k and speak,<br />
and respiratory failure. Early respiratory or bulbar<br />
symptoms are adverse prognostic <strong>in</strong>dicators of the disease.<br />
Respiratory failure is the most common cause of death <strong>in</strong><br />
ALS, and usually occurs with<strong>in</strong> three to five years of onset<br />
[478835], [638197], [638203]. Follow<strong>in</strong>g the onset of<br />
symptoms, over 50% of ALS sufferers will die with<strong>in</strong> three<br />
Orig<strong>in</strong>ator Aeolus Pharmaceuticals Inc<br />
Status Phase I Cl<strong>in</strong>ical<br />
.<br />
Indications Cerebrovascular ischemia, Lung <strong>in</strong>flammation,<br />
Motor neuron disease (amytrophic lateral sclerosis),<br />
Mucositis,.Sp<strong>in</strong>al cord <strong>in</strong>jury.<br />
.<br />
Actions Antioxidant agent, Neuroprotectant<br />
.<br />
Technology Subcutaneous formulation<br />
Registry No: 286475-30-7<br />
C<br />
H 3<br />
C<br />
H 3<br />
N +<br />
N +<br />
N<br />
N<br />
CH 3<br />
N<br />
N<br />
N<br />
N<br />
N N<br />
CH 3<br />
Mn 3+<br />
CH 3<br />
CH 3<br />
N +<br />
N +<br />
Cl Cl Cl Cl Cl<br />
years, with < 10% liv<strong>in</strong>g beyond five years. Disease<br />
progression can be either more rapid or greatly reduced <strong>in</strong><br />
some cases, with around 10% of patients liv<strong>in</strong>g for > 10 years<br />
[634304].<br />
The cause of ALS rema<strong>in</strong>s unknown, although free-radicalmediated<br />
neurotoxicity is one proposed mechanism<br />
[638229], [638230]. Free-radical-mediated toxicity has been<br />
implicated <strong>in</strong> a wide range of diseases, <strong>in</strong>clud<strong>in</strong>g<br />
neurodegenerative diseases, stroke, acute myocardial<br />
<strong>in</strong>farction, <strong>in</strong>flammatory disorders and carc<strong>in</strong>ogenesis<br />
[449960], [638218]. In addition, a proportion of patients with<br />
ALS (approximately 2%) have mutations of the gene<br />
encod<strong>in</strong>g the copper/z<strong>in</strong>c SOD1 enzyme [400330], [638203],<br />
[638220], [638223]. <strong>Current</strong> evidence suggests that <strong>in</strong> patients<br />
with SOD1 mutations, the disease is not related to deficiency<br />
of SOD activity, but is caused by a toxic ga<strong>in</strong> of function,<br />
possibly related to prote<strong>in</strong> accumulation or other<br />
mechanisms [638223], [638233].<br />
<strong>Current</strong> treatment for ALS is largely supportive, and only<br />
one medication has been licensed. Riluzole is orally<br />
adm<strong>in</strong>istered, and is proposed to <strong>in</strong>hibit glutamate release.<br />
Although well tolerated, the drug has limited efficacy.<br />
Glutamate-<strong>in</strong>duced neuronal excitotoxicity is one<br />
hypothesized cause of ALS, hence the <strong>in</strong>itial study of<br />
riluzole. The therapeutic mechanism of action rema<strong>in</strong>s<br />
uncerta<strong>in</strong>, however, and other possibilities <strong>in</strong>clude an effect<br />
on modulation of sodium, potassium or AMPA/ka<strong>in</strong>ate<br />
channels [262608]. Evidence from cl<strong>in</strong>ical trials <strong>in</strong>dicates a<br />
CH 3<br />
CH 3
prolongation of survival of approximately 2 months, after 12<br />
months of riluzole treatment. This represents a 9% ga<strong>in</strong> <strong>in</strong><br />
the probability of surviv<strong>in</strong>g for one year (57% <strong>in</strong> the placebo<br />
and 66% <strong>in</strong> the riluzole group) [625097]. Despite the<br />
prolongation of survival, there is no clear cl<strong>in</strong>ical evidence of<br />
slow<strong>in</strong>g of functional decl<strong>in</strong>e, and the basis of the prolonged<br />
survival is uncerta<strong>in</strong>. Riluzole has not been demonstrated to<br />
alter the rate of disease progression or preserve muscle<br />
strength [636040].<br />
AEOL-10150 has progressed through a series of precl<strong>in</strong>ical<br />
studies <strong>in</strong> models represent<strong>in</strong>g a range of diseases, <strong>in</strong>clud<strong>in</strong>g<br />
ALS, sp<strong>in</strong>al cord <strong>in</strong>jury, islet-cell transplantation for<br />
diabetes, cancer and stroke. The demonstration of a<br />
beneficial effect of AEOL-10150 on survival and delayed<br />
disease progression <strong>in</strong> the SOD1 mutant mouse model of<br />
ALS led to phase I studies <strong>in</strong> patients with ALS, and phase<br />
II/III studies <strong>in</strong> ALS have also been proposed, together with<br />
plans for cl<strong>in</strong>ical studies <strong>in</strong> stroke and radiation-<strong>in</strong>duced<br />
mucositis.<br />
Synthesis and SAR<br />
Metalloporphyr<strong>in</strong>s are low-molecular-weight complexes<br />
that have antioxidant scaveng<strong>in</strong>g properties for superoxide,<br />
peroxynitrite and lipid peroxyl radicals. They are water<br />
soluble, manganese meso-porphyr<strong>in</strong>s that are stable and nontoxic<br />
[616369]. Aeolus synthesized AEOL-10150 as a cationic<br />
manganese porphyr<strong>in</strong>, manganese(III) mesotetrakis(N,N'diethylimidazolium-2-yl)porphyr<strong>in</strong><br />
[625100], which can be<br />
abbreviated as Mn IIITDE-2-ImP 5+ [554429]. Accord<strong>in</strong>g to<br />
Bat<strong>in</strong>ic-Haberle et al [625100], AEOL-10150 has been<br />
erroneously referred to <strong>in</strong> a number of publications as<br />
[5,10,l5,20-tetrakis(1,3-diethylimidazolium-2-yl)porphyr<strong>in</strong>ato]<br />
manganese(III) pentachloride [616156], manganese(III)<br />
mesotetrakis (di-N-ethylimidazole) porphyr<strong>in</strong> [616360], and<br />
manganese(III)meso-tetrakis(N,N'-diethyl-1,3-imidazolium-<br />
2-yl) porphyr<strong>in</strong> [616370]. In these cases the '1' and '3'<br />
<strong>in</strong>dicated the imidazolyl nitrogens, rather than position 2<br />
where the imidazolyl is attached to the porphyr<strong>in</strong> r<strong>in</strong>g<br />
[625100].<br />
AEOL-10150 was produced alongside AEOL-10113, the<br />
other lead compound from Aeolus' catalytic antioxidants<br />
pipel<strong>in</strong>e [465629]. AEOL-10113 (manganese (III) tetrakis (Nethylpyrid<strong>in</strong>ium-2-yl)<br />
porphyr<strong>in</strong> or MnTE-2-PyP 5+) is<br />
composed of several stereoisomers, mak<strong>in</strong>g a pharmaceutically<br />
acceptable formulation difficult to achieve and limit<strong>in</strong>g the<br />
ability to analyze tissue levels and perform pharmacok<strong>in</strong>etic<br />
studies. AEOL-10113 and related compounds were<br />
synthesized through β-chlor<strong>in</strong>ation of 5,10,15,20-tetrakis (2pyridyl)<br />
porphyr<strong>in</strong> (H2T-2-PyP) followed by N-ethylation<br />
and metallation [625109]. In contrast, AEOL-10150 is a<br />
structurally different metalloporphyr<strong>in</strong> catalytic antioxidant,<br />
with imidazole side cha<strong>in</strong> substitutions. AEOL-10150 does<br />
not exist as a stereoisomer, is relatively easy to synthesize,<br />
and can be readily analyzed <strong>in</strong> tissues [465629].<br />
AEOL-10150 was synthesized on the basis of the structureactivity<br />
relationships of AEOL-10113. The metal-centered<br />
redox potential and electrostatics of these compounds have a<br />
key effect on the ability to dismutase superoxides [625100].<br />
AEOL-10150 Orrell 71<br />
AEOL-10150 had a metal-centered redox potential (E1/2)<br />
value of +346 mV, and a catalytic rate constant (log kcat) of<br />
7.83. AEOL-10113 has cationic ortho-N-ethylpyridyl groups<br />
on the meth<strong>in</strong>e bridge carbons of the porphyr<strong>in</strong> r<strong>in</strong>g system<br />
that provides electrostatic guidance for superoxide. The nonplanarity<br />
dim<strong>in</strong>ishes the <strong>in</strong>teraction of AEOL-10113 with<br />
DNA and hence reduces the <strong>in</strong> vivo toxicity of the compound<br />
[413580]. AEOL-10150 has ethyl cha<strong>in</strong>s <strong>in</strong> substitution for<br />
both the ortho-imidazolyl nitrogens of AEOL-10113. This<br />
delocalizes the positive charge over both nitrogens,<br />
provid<strong>in</strong>g greater proximity to the mesoporphyr<strong>in</strong> carbons,<br />
and creates a stronger electron-withdraw<strong>in</strong>g effect than the<br />
positively charged ortho-pyridyl nitrogens [625100].<br />
Separation and detection of these compounds has been<br />
described by high-performance liquid chromatography, with<br />
electrochemical detection apparently offer<strong>in</strong>g greater<br />
quantitative sensitivity than spectrophotometric detection,<br />
although less specificity for <strong>in</strong> vivo applications [625112].<br />
Precl<strong>in</strong>ical development<br />
Mechanism<br />
AEOL-10150 can catalytically decompose biological<br />
oxidants, such as peroxynitrite, by its ability to cycle<br />
between Mn(II) and Mn(IV) states [616156]. The compound<br />
has a +5 charge, with SOD activity between 5000 and 8500<br />
units/g and catalase activity equivalent to approximately<br />
1% of purified bov<strong>in</strong>e catalase (weight/<br />
weight basis) [616360], [616369].<br />
Alternative mechanisms of action have been proposed for<br />
the metallophorphyr<strong>in</strong>s, <strong>in</strong>clud<strong>in</strong>g neuroprotective effects<br />
mediated by suppression of oxygen-glucose deprivation<br />
(OGD) or N-methyl-D-aspartate (NMDA)-<strong>in</strong>duced rises <strong>in</strong><br />
<strong>in</strong>tracellular Ca 2+ concentration [634340], <strong>in</strong>duction of antiapoptotic<br />
prote<strong>in</strong> synthesis [634341], and <strong>in</strong>hibition of lipid<br />
peroxidation [634325]. However, to date, studies of<br />
AEOL-10150 have focused on antioxidant mechanisms, and<br />
the possibility of other mechanisms rema<strong>in</strong>s undef<strong>in</strong>ed.<br />
ALS<br />
The effects of AEOL-10150 were demonstrated <strong>in</strong> mice that<br />
overexpress the human Cu/Zn SOD1 mutant G93A, which<br />
develop a progressive motor neuron disease; this is<br />
currently considered the best animal model of ALS [505222],<br />
[616156]. Three studies were performed and described <strong>in</strong> a<br />
s<strong>in</strong>gle paper [616156]. In the first study, AEOL-10150 (5<br />
mg/kg) was adm<strong>in</strong>istered <strong>in</strong>traperitoneally as a load<strong>in</strong>g<br />
dose after the first day of symptom onset, followed by daily<br />
ma<strong>in</strong>tenance doses of 2.5 mg/kg. A second study<br />
used a similar regime and adm<strong>in</strong>istered <strong>in</strong>traperitoneal<br />
AEOL-10150 (2.5 mg/kg) every day follow<strong>in</strong>g the onset of<br />
symptoms; <strong>in</strong> addition, creat<strong>in</strong>e and the selective COX-2<br />
<strong>in</strong>hibitor rofecoxib were also adm<strong>in</strong>istered (at 2 and 0.005%<br />
<strong>in</strong> the diet, respectively). The third experiment tested the<br />
same dose of AEOL-10150 (2.5 mg/kg/day) via<br />
subcutaneous adm<strong>in</strong>istration. The survival <strong>in</strong>terval was<br />
calculated from the onset of symptoms (typically around 90<br />
days of age) until sacrifice at a predeterm<strong>in</strong>ed late stage of<br />
disease. After calculat<strong>in</strong>g the survival <strong>in</strong>terval of treated<br />
mice relative to sal<strong>in</strong>e-treated controls (the <strong>in</strong>creased<br />
survival result<strong>in</strong>g from treatment), a survival <strong>in</strong>terval ratio
72 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
was determ<strong>in</strong>ed. The mean survival <strong>in</strong>tervals for G93A mice<br />
treated with <strong>in</strong>traperitoneal AEOL-10150 (2.5 mg/kg/day)<br />
<strong>in</strong>traperitoneal AEOL-10150 (2.5 mg/kg/day) plus<br />
creat<strong>in</strong>e and rofecoxib, and subcutaneous AEOL-10150<br />
(2.5 mg/kg/day) were 40.0, 38.8 and 40.5 days, respectively,<br />
<strong>in</strong> the first study; survival ratios <strong>in</strong> the same groups were<br />
2.96, 2.87 and 2.43, respectively [616156].<br />
Specific deficits were absent <strong>in</strong> the AEOL-10150-treated<br />
mice, with an absence of h<strong>in</strong>d-limb paralysis until a late<br />
stage compared with control mice. The relative <strong>in</strong>frequency<br />
of h<strong>in</strong>d-limb paralysis <strong>in</strong> AEOL-10150-treated mice<br />
compared with complete h<strong>in</strong>d-limb paralysis <strong>in</strong> almost all<br />
control mice suggests that AEOL-10150 alters the course of<br />
the disease and helps to ma<strong>in</strong>ta<strong>in</strong> overall motor function<br />
dur<strong>in</strong>g the period of extended survival [616156]. These<br />
effects correlate with the preservation of sp<strong>in</strong>al motor<br />
neurons. Neuron counts <strong>in</strong> the sp<strong>in</strong>al cord demonstrated<br />
<strong>in</strong>creased cellular survival, with 53% of sp<strong>in</strong>al cord neurons<br />
surviv<strong>in</strong>g at 100 days <strong>in</strong> AEOL-10150-treated mice compared<br />
with 38% <strong>in</strong> untreated mice. Immunosta<strong>in</strong><strong>in</strong>g for glial<br />
fibrillary acidic prote<strong>in</strong> was reduced <strong>in</strong> treated mice,<br />
suggest<strong>in</strong>g that gliosis or neuronal <strong>in</strong>jury is reduced. Levels<br />
of prote<strong>in</strong>-bound nitrotyros<strong>in</strong>e (a marker of oxidative <strong>in</strong>jury)<br />
and malondialdehyde (a marker of lipid oxidation) were<br />
reduced <strong>in</strong> AEOL-10150-treated G93A mice [616156].<br />
In a follow-up study, AEOL-10150 was tested both as a<br />
s<strong>in</strong>gle agent and <strong>in</strong> comb<strong>in</strong>ation with the histone deacetylase<br />
<strong>in</strong>hibitor phenylbutyrone <strong>in</strong> a mur<strong>in</strong>e G93A SOD1<br />
transgenic model [633859]. The neurodegenerative effects of<br />
phenylbutyrate (400 mg/kg/day) and phenylbutyrate (400<br />
mg/kg/day) comb<strong>in</strong>ed with AEOL-10150 (2.5 mg/kg/day)<br />
were compared with a control. Treatments were<br />
adm<strong>in</strong>istered <strong>in</strong>traperitoneally, commenc<strong>in</strong>g at disease onset<br />
(between 85 and 92 days of age). In mice treated with<br />
AEOL-10150 alone there was a significant <strong>in</strong>crease <strong>in</strong><br />
survival, from 132 ± 5 to 146 ± 15 days (11%). Mice<br />
adm<strong>in</strong>istered with phenylbutyrone alone showed an<br />
<strong>in</strong>crease <strong>in</strong> survival from 126 ± 4 to 143 ± 9 days (13%).<br />
When AEOL-10150 was adm<strong>in</strong>istered together with<br />
phenylbutyrone, survival <strong>in</strong>creased to 150 ± 13 days (19%).<br />
The comb<strong>in</strong>ation therapy was significantly more effective<br />
than phenylbutyrone alone (p < 0.05). Motor performance <strong>in</strong><br />
mice treated with AEOL-10150 alone was not significantly<br />
<strong>in</strong>creased, whereas mice treated with phenylbutyrone, both<br />
alone and <strong>in</strong> comb<strong>in</strong>ation with AEOL-10150, showed a<br />
significantly improved motor performance compared with<br />
control. Loss of motor neurons <strong>in</strong> the lumbar sp<strong>in</strong>al cord<br />
was assessed histologically and was significantly reduced<br />
with all treatment comb<strong>in</strong>ations. Immunohistochemical<br />
analysis of malondialdehyde and 3-nitrotyros<strong>in</strong>e, thought to<br />
be relatively specific markers of oxidative damage, showed<br />
<strong>in</strong>creased expression <strong>in</strong> control mice, and a marked<br />
reduction at 115 days <strong>in</strong> all other treatment groups [633859].<br />
The mechanism of action of AEOL-10150 <strong>in</strong> G93A mice is<br />
unlikely to be due to SOD-like activity, as these mice<br />
overexpress SOD. Prevention of the formation of prote<strong>in</strong>bound<br />
nitrotyros<strong>in</strong>e and malondialdehyde suggests an<br />
antioxidant effect on the preservation of sp<strong>in</strong>al motor<br />
neurons [616156]. As it is currently unknown whether the<br />
best possible survival effects have been achieved, further<br />
studies to rigorously exam<strong>in</strong>e dose, route and frequency of<br />
adm<strong>in</strong>istration of AEOL-10150 <strong>in</strong> ALS models are ongo<strong>in</strong>g.<br />
Sp<strong>in</strong>al cord <strong>in</strong>jury<br />
C57BL/6J mice were subjected to sp<strong>in</strong>al cord compression<br />
for 60 m<strong>in</strong> at the T11 vertebral level. In the first experiment<br />
of a two-part study, AEOL-10150 was adm<strong>in</strong>istered as a 0.5mg/kg<br />
bolus dose, followed by a 1.0 mg/kg <strong>in</strong>travenous<br />
<strong>in</strong>fusion every hour for 24 h, beg<strong>in</strong>n<strong>in</strong>g 5 m<strong>in</strong> after onset of<br />
sp<strong>in</strong>al cord compression (n = 25). In the second experiment,<br />
AEOL-10150 was adm<strong>in</strong>istered as an <strong>in</strong>trathecal <strong>in</strong>jection<br />
(2.5 or 5.0 µg/kg; total n = 18). Rotarod performance<br />
demonstrated that <strong>in</strong>trathecal adm<strong>in</strong>istration of 5 µg of<br />
AEOL-10150 was associated with an approximately 30%<br />
improvement <strong>in</strong> neurological behavior (p < 0.05), and a<br />
reduction was observed <strong>in</strong> histological total damage score<br />
(19 ± 8; p = 0.03) compared with controls (26 ± 10).<br />
Intravenous adm<strong>in</strong>istration of AEOL-10150 produced no<br />
significant changes <strong>in</strong> these tests compared with controls<br />
[554429], [616364].<br />
Stroke<br />
AEOL-10150 was adm<strong>in</strong>istered <strong>in</strong> a C57BL/6J mouse model<br />
of stroke [616369]. Mice were subjected to transient (60 m<strong>in</strong>)<br />
middle cerebral artery occlusion (MCAO; n = 6) or sham<br />
surgery (n = 6), and were then treated with AEOL-10150 5<br />
m<strong>in</strong> after reperfusion. A bolus dose of AEOL-10150 (0.5<br />
mg/kg) was followed by cont<strong>in</strong>uous <strong>in</strong>travenous <strong>in</strong>fusion of<br />
1.0 mg/kg/h for 6 h. At this time, the bra<strong>in</strong>s were studied<br />
and mRNA expression was analyzed us<strong>in</strong>g an Affymetrix<br />
mur<strong>in</strong>e microarray. AEOL-10150 attenuated the <strong>in</strong>jury<strong>in</strong>duced<br />
<strong>in</strong>crease <strong>in</strong> expression of pro-<strong>in</strong>flammatory cytok<strong>in</strong>e<br />
genes. For example, MCAO caused a 12-fold upregulation <strong>in</strong><br />
macrophage <strong>in</strong>flammatory prote<strong>in</strong> (MIP)-2 <strong>in</strong> untreated<br />
animals, compared with a 6-fold <strong>in</strong>crease follow<strong>in</strong>g<br />
AEOL-10150 treatment. However, AEOL-10150 had no<br />
apparent effect on the expression of stress response genes,<br />
suggest<strong>in</strong>g that the protective effect of the drug may be<br />
<strong>in</strong>dependent of any stress response pathways. A possible<br />
explanation is that AEOL-10150 is compartmentalized to the<br />
extracellular space because of its +5 charge, and therefore<br />
produces no effect on the stress response genes, which are<br />
regulated by <strong>in</strong>tracellular events. However, studies with a<br />
range of manganese porphyr<strong>in</strong>s, <strong>in</strong>clud<strong>in</strong>g AEOL-10113<br />
(which also has a +5 charge), <strong>in</strong>dicated that they penetrated<br />
mitochondrial and cytosolic fractions of cortical cells <strong>in</strong><br />
concentrations sufficient for antioxidant activity [634343].<br />
Slight changes were observed <strong>in</strong> the expression of<br />
antioxidant genes, <strong>in</strong>clud<strong>in</strong>g glutathion<strong>in</strong>e transferase,<br />
neuronal nitric oxide synthase, Cu/Zn SOD, extracellular<br />
SOD and mitochondrial SOD. No significant changes were<br />
recorded <strong>in</strong> the expression of apoptosis and growth factor<br />
genes, suggest<strong>in</strong>g that AEOL-10150 has no effect on these<br />
pathways [616369].<br />
In a study <strong>in</strong> rats, AEOL-10150 and AEOL-10113 were<br />
adm<strong>in</strong>istered <strong>in</strong>tracerebroventricularly 90 m<strong>in</strong> after a 90-m<strong>in</strong><br />
MCAO [465629]. Dose escalation was performed, <strong>in</strong> which<br />
the <strong>in</strong>itial 300-ng dose of AEOL-10150 was doubled until
side effects were observed. The maximal dose of<br />
AEOL-10150 <strong>in</strong> rats that was clearly devoid of adverse<br />
behavioral effects was 4500 ng. AEOL-10113 caused<br />
behavioral side effects at twice the neuroprotective dose, but<br />
AEOL-10150 caused similar changes at 15-fold the<br />
neuroprotective dose [413580]. AEOL-10150 and<br />
AEOL-10113 reduced <strong>in</strong>farct size by 35% when adm<strong>in</strong>istered<br />
90 m<strong>in</strong> after occlusion. When AEOL-10150 was adm<strong>in</strong>istered<br />
6 h after occlusion, <strong>in</strong>farct size was reduced by 43% [465629].<br />
In a similar study, AEOL-10150 reduced <strong>in</strong>farct size by 40%,<br />
but with no associated functional improvement [468211].<br />
AEOL-10113 was not reported at 6 h, but <strong>in</strong> previous<br />
experiments a 54% reduction <strong>in</strong> <strong>in</strong>farct volume was<br />
reported, together with a reduction <strong>in</strong> neurological deficit<br />
[413580]. In another study, us<strong>in</strong>g the same dos<strong>in</strong>g schedule<br />
<strong>in</strong> mice, neuroprotective effects were observed <strong>in</strong> bra<strong>in</strong><br />
parenchymal prote<strong>in</strong> expression where AEOL-10150<br />
<strong>in</strong>hibited changes <strong>in</strong> prote<strong>in</strong> expression that were<br />
attributable to MCAO [428437].<br />
A comparable study of <strong>in</strong>travenous AEOL-10150 was<br />
conducted <strong>in</strong> a mur<strong>in</strong>e model [465629]. A similar doseescalation<br />
design was implemented <strong>in</strong> two cohorts,<br />
follow<strong>in</strong>g either MCAO or sham surgery, followed by an<br />
<strong>in</strong>travenous bolus dose of 0.5 mg/kg AEOL-10150 and a<br />
cont<strong>in</strong>uous <strong>in</strong>travenous <strong>in</strong>fusion at 1.0 mg/kg/h for 24 h<br />
(n = 6/group). A 25% reduction <strong>in</strong> <strong>in</strong>farct size and a<br />
reduction <strong>in</strong> neurological deficit were demonstrated<br />
[465629]. Uptake of AEOL-10150 <strong>in</strong>to the bra<strong>in</strong> was slow,<br />
dose- and time-dependent and greater <strong>in</strong> the ischemic<br />
hemisphere. AEOL-10150 had direct effects on bra<strong>in</strong><br />
parenchymal prote<strong>in</strong> expression, support<strong>in</strong>g the hypothesis<br />
that a potent catalytic antioxidant can <strong>in</strong>dependently cause<br />
diverse changes <strong>in</strong> prote<strong>in</strong> expression and ameliorate<br />
changes <strong>in</strong>duced by ischemic <strong>in</strong>sult [465629].<br />
One further <strong>in</strong> vitro study by Sheng et al exam<strong>in</strong>ed the ability of<br />
AEOL-10150 to reduce cell death <strong>in</strong> conditions of oxidative<br />
stress [465629]. Neuronal and glial cell cultures were prepared<br />
from embryonic (day 18) rat cerebral hemispheres, and<br />
AEOL-10150 was applied to the assays 30 m<strong>in</strong> prior to<br />
placement <strong>in</strong> oxygen/glucose deprivation (OGD). AEOL-10150<br />
<strong>in</strong>hibited cell death <strong>in</strong> a concentration-dependent manner (p <<br />
0.0001) follow<strong>in</strong>g OGD. The optimal effect of the drug occurred<br />
at 10 µM, at which 48% of the OGD-<strong>in</strong>duced lactate<br />
dehydrogenase release was <strong>in</strong>hibited. AEOL-10150 selectively<br />
<strong>in</strong>hibited aconitase <strong>in</strong>activation (measured 8 h after OGD)<br />
[465629]. The preservation of aconitase activity is used as a<br />
marker of specific <strong>in</strong>hibition of superoxide-mediated <strong>in</strong>jury<br />
[638331].<br />
Transplantation<br />
In human pancreatic islet-cell allotransplantation, a<br />
treatment be<strong>in</strong>g developed for diabetes mellitus, the<br />
mechanical and chemical <strong>in</strong>sults caused to transplanted cells<br />
by oxidative stresses significantly reduce their viability and<br />
function. In an experiment by Bott<strong>in</strong>o et al, AEOL-10150 was<br />
added to the culture medium of purified human islet cells,<br />
and also at the isolation phase [463528]. After 24 h, there was<br />
a 3-fold <strong>in</strong>crease <strong>in</strong> the mass of AEOL-10150-treated cells<br />
compared with untreated control cells. When transplanted<br />
AEOL-10150 Orrell 73<br />
to diabetic mice, glucose levels were normalized <strong>in</strong> n<strong>in</strong>e of<br />
n<strong>in</strong>e mice receiv<strong>in</strong>g AEOL-10150-treated islet cell cultures,<br />
but only five of eight animals receiv<strong>in</strong>g untreated cells. The<br />
<strong>in</strong> vitro glucose responsiveness and <strong>in</strong> vivo function of the<br />
cells that survived demonstrated that AEOL-10150 does not<br />
impair islet functional performance. AEOL-10150 seemed to<br />
protect the human islets from oxidative and free radical<br />
stresses, improv<strong>in</strong>g the preservation of the isolated tissue,<br />
suggest<strong>in</strong>g that the drug may be usefully applied to the<br />
procurement solution dur<strong>in</strong>g organ perfusion to obta<strong>in</strong> a<br />
more successful protective effect before transplant [463528].<br />
Pancreatic islet β-cells are reported to be highly susceptible<br />
to oxidative stress because of reduced endogenous<br />
antioxidant levels [632736]. Under conditions of extreme<br />
stress, for example, islet-cell isolation procedures follow<strong>in</strong>g<br />
cl<strong>in</strong>ical transplantation, the antioxidant defenses of the βcells<br />
may be overwhelmed, which may lead to a state of<br />
redox imbalance and the production of reactive oxygen<br />
species (ROS). A potential ROS-dependent target is nuclear<br />
factor (NF)κB. In a second study, Bott<strong>in</strong>o et al demonstrated<br />
that AEOL-10150 reduced the level of NFκB <strong>in</strong> treated islet<br />
β-cells, correlat<strong>in</strong>g with reduced production of cytok<strong>in</strong>es<br />
and chemok<strong>in</strong>es, and reduced activation of apoptosis and<br />
necrosis, further support<strong>in</strong>g the use of AEOL-10150 <strong>in</strong> the<br />
protection of pancreatic islet cells used for transplantation<br />
treatment of diabetes [632736].<br />
Hemorrhage-<strong>in</strong>duced lung <strong>in</strong>jury<br />
The effect of hemorrhage-<strong>in</strong>duced lung <strong>in</strong>jury was studied<br />
<strong>in</strong> extracellular (EC)-SOD knockout mice, with and without<br />
pre-treatment with a s<strong>in</strong>gle subcutaneous dose of<br />
AEOL-10150 (24 mg/kg) [616360]. Compared with wild-type<br />
mice, EC-SOD-deficient mice had <strong>in</strong>creased lung neutrophil<br />
accumulation, a 3.9-fold <strong>in</strong>crease <strong>in</strong> myeloperoxidase<br />
activity, a 1.5-fold <strong>in</strong>crease <strong>in</strong> NFκB activation, and a 1.5-fold<br />
<strong>in</strong>crease <strong>in</strong> lipid peroxidation 1 h after hemorrhage. Pretreatment<br />
with AEOL-10150 did not attenuate neutrophil<br />
accumulation <strong>in</strong> the lungs, but reduced NFκB activation and<br />
isoprostane formation <strong>in</strong> both wild-type and EC-SODdeficient<br />
mice. However, the beneficial effects of<br />
AEOL-10150 were moderate and no reduction <strong>in</strong> neutrophil<br />
recruitment to the lungs was observed, suggest<strong>in</strong>g that<br />
AEOL-10150 can attenuate markers of oxidative stress, but<br />
may not reduce lung <strong>in</strong>jury as measured by neutrophil<br />
accumulation [616360].<br />
Radiation-<strong>in</strong>duced lung <strong>in</strong>jury<br />
The effects of radiation-<strong>in</strong>duced <strong>in</strong>jury were exam<strong>in</strong>ed <strong>in</strong> 344<br />
Fisher rats. Follow<strong>in</strong>g the adm<strong>in</strong>istration of a s<strong>in</strong>gle<br />
irradiation dose (26 Gy) to the right hemithorax, rats were<br />
treated with AEOL-10150 (1, 10 or 30 mg/kg/day) for 10<br />
weeks, via a subcutaneous osmotic pump. Follow-up<br />
exam<strong>in</strong>ations at 20 weeks showed significantly improved<br />
breath<strong>in</strong>g rates <strong>in</strong> both the 10 and 30 mg/kg/day groups. In<br />
the same two groups, a reduction <strong>in</strong> oxidative stress (as<br />
measured by levels of 8-hydroxydeoxyguanos<strong>in</strong>e; 8OHdG),<br />
a reduction <strong>in</strong> macrophage levels and a significant decrease<br />
<strong>in</strong> structural disease were observed, compared with the<br />
control and 1-mg/kg/day groups. The doses and route of<br />
adm<strong>in</strong>istration used <strong>in</strong> this study were implemented <strong>in</strong>to a
74 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
phase I study of AEOL-10150 <strong>in</strong> ALS patients [629090],<br />
[638411].<br />
Tobacco-smoke-<strong>in</strong>duced lung <strong>in</strong>flammation<br />
Cigarette smokers experience airway <strong>in</strong>flammation and<br />
epithelial damage, which is thought to be caused by the<br />
formation of free radicals by chemicals <strong>in</strong> the smoke, lead<strong>in</strong>g<br />
to oxidative stress. AEOL-10150 (either 5 mg/kg<br />
adm<strong>in</strong>istered approximately 2 h before a 2-day toxicity<br />
study, or as eight weekly doses of 2 mg/kg <strong>in</strong> a long-term<br />
toxicity model) was adm<strong>in</strong>istered by <strong>in</strong>tratracheal<br />
<strong>in</strong>stillation to rats exposed to filtered air or tobacco smoke<br />
[616370], [616377]. A lower dose was used for the 8-week<br />
study <strong>in</strong> order to m<strong>in</strong>imize potential long-term toxicity.<br />
AEOL-10150 significantly reduced bronchoalveolar lavage<br />
cell numbers <strong>in</strong> tobacco-smoke-treated rats, with reductions<br />
<strong>in</strong> counts of neutrophils, macrophages and lymphocytes at<br />
different time po<strong>in</strong>ts. Squamous cell metaplasia was reduced<br />
from 12% of total airway epithelial area to 2% after 8 weeks<br />
of treatment with AEOL-10150. AEOL-10150 was also<br />
observed to attenuate decreases <strong>in</strong> levels of MIP-2 and<br />
<strong>in</strong>tracellular adhesion molecule-1, important prote<strong>in</strong>s <strong>in</strong> the<br />
migration and presentation of neutrophils and<br />
macrophages. The expression of these two prote<strong>in</strong>s is<br />
mediated by NFκB and, therefore, it was suggested<br />
that AEOL-10150 decreases tobacco-smoke-<strong>in</strong>duced<br />
<strong>in</strong>flammation <strong>in</strong> the lungs of rats by reduc<strong>in</strong>g oxidative<br />
stress and the resultant activation of NFκB [616370].<br />
Autoimmune disease<br />
The effect of AEOL-10150 (and AEOL-10113) on<br />
lipopolysaccharide-stimulated macrophages was studied to<br />
determ<strong>in</strong>e the role of oxidation-reduction reactions <strong>in</strong> the<br />
activation of the immune system. In the presence of<br />
AEOL-10150, the cells failed to elicit a pro-<strong>in</strong>flammatory<br />
response, and levels of the pro-<strong>in</strong>flammatory cytok<strong>in</strong>es tumor<br />
necrosis factor α and <strong>in</strong>terleuk<strong>in</strong>-1β were decreased. There was<br />
also a reduced ability to generate reactive oxygen species, with<br />
decreased superoxide and peroxynitrite production. These<br />
effects led to the <strong>in</strong>hibition of the NFκB pathway at the DNA<br />
b<strong>in</strong>d<strong>in</strong>g level, which, if mediated by the catalytic antioxidant<br />
<strong>in</strong>hibition, suggests that this pathway is dependent on the<br />
redox state with<strong>in</strong> the cell. This f<strong>in</strong>d<strong>in</strong>g implies that immune<br />
activation might not be an on/off response, but one that is<br />
mediated to some degree by free-radical signal<strong>in</strong>g. The<br />
potential of AEOL-10150 to suppress this immune response<br />
suggests long-term applications <strong>in</strong> prevent<strong>in</strong>g the activation of<br />
the adaptive immune response <strong>in</strong> organ-specific autoimmune<br />
diseases <strong>in</strong> which chronic <strong>in</strong>flammation causes delayed-type<br />
hypersensitivity and tissue destruction [616358].<br />
Mucositis<br />
AEOL-10150 was reported to reduce the <strong>in</strong>cidence and<br />
duration of radiation-<strong>in</strong>duced oral mucositis <strong>in</strong> a hamster<br />
model [432294]. Intraperitoneal (0.05, 0.2 and 0.3 mg/ml) or<br />
topical (0.05, 0.2, 0.3 and 1.0 mg/ml) AEOL-10150 was<br />
adm<strong>in</strong>istered three-times daily for 20 days, commenc<strong>in</strong>g a<br />
day before a s<strong>in</strong>gle 40 Gy dose of radiation. Relative to<br />
vehicle-treated control animals, <strong>in</strong>traperitoneal AEOL-10150<br />
reduced the number of days of severe mucositis (ulceration)<br />
by 35 to 59% at all doses, and topical adm<strong>in</strong>istration (of 1.0<br />
mg/ml) reduced the number of days by 36%. The drug also<br />
protected aga<strong>in</strong>st conditions that commonly arise <strong>in</strong> association<br />
with oxidative free radical damage, reduc<strong>in</strong>g mitochondrial<br />
aconitase <strong>in</strong>activation (by 4-fold with topical adm<strong>in</strong>istration<br />
and 2.5-fold with <strong>in</strong>traperitoneal adm<strong>in</strong>istration) and 8OHdG<br />
formation (by 1.5-fold follow<strong>in</strong>g either topical or <strong>in</strong>traperitoneal<br />
adm<strong>in</strong>istration) [432294]. These data have been presented <strong>in</strong><br />
abstract form only, with no <strong>in</strong>dication of dos<strong>in</strong>g based on<br />
weight. Total daily doses were equivalent to 0.03, 0.12, 0.18 and<br />
0.6 mg/day [432294].<br />
Cancer<br />
A more recent study exam<strong>in</strong>ed the effect of AEOL-10150 on<br />
the efficacy and toxicity of anticancer radiation therapy<br />
[595706]. Male C57BL/6 mice were <strong>in</strong>jected subcutaneously<br />
with RM9 prostate tumor cells before be<strong>in</strong>g treated with<br />
<strong>in</strong>traperitoneal AEOL-10150 (6 mg/kg) for 16 days.<br />
Radiation (10 Gy) was delivered on day 8. Three days after<br />
the application of irradiation, hematological analysis<br />
showed that radiation alone significantly slowed tumor<br />
progression (p ≤ 0.05) and that a slight antitumor response<br />
was observed with AEOL-10150 treatment alone. The most<br />
potent effect was observed when AEOL-10150 was<br />
comb<strong>in</strong>ed with radiation, after which tumor volumes were<br />
significantly reduced on days 8 and 10 to 14, compared with<br />
untreated controls. It was also suggested that AEOL-10150<br />
<strong>in</strong>creased the efficacy of radiation because smaller tumor<br />
volumes were recorded on days 10, 13 and 16 <strong>in</strong> the<br />
AEOL-10150 plus radiation group than <strong>in</strong> animals receiv<strong>in</strong>g<br />
radiation alone (p ≤ 0.05). Record<strong>in</strong>gs of body mass were<br />
similar among all groups dur<strong>in</strong>g the majority of the study.<br />
These f<strong>in</strong>d<strong>in</strong>gs support the utilization of AEOL-10150 as a<br />
possible therapy <strong>in</strong> slow<strong>in</strong>g tumor progression and suggest<br />
that greater tumor control may be possible when the<br />
compound is comb<strong>in</strong>ed with radiation [595706].<br />
Metabolism and pharmacok<strong>in</strong>etics<br />
Pharmacok<strong>in</strong>etic parameters were determ<strong>in</strong>ed <strong>in</strong> a rat study<br />
of AEOL-10150 (300 ng) <strong>in</strong>jected <strong>in</strong>tracerebroventricularly 90<br />
m<strong>in</strong> after reperfusion from MCAO [465629]. No compound<br />
was detected <strong>in</strong> the liver. Plasma concentrations were<br />
generally negligible, but reached levels of 4.6 and 3.2 ng/ml<br />
<strong>in</strong> two rats. Bra<strong>in</strong> parenchymal AEOL-10150 peaked with<strong>in</strong> 1<br />
h of <strong>in</strong>jection, and the tissue half-life was calculated to be<br />
approximately 10 h [465629].<br />
In a mouse model of MCAO and reperfusion, AEOL-10150<br />
was adm<strong>in</strong>istered as an <strong>in</strong>travenous bolus of 2.5 mg/kg,<br />
followed by <strong>in</strong>fusion of 1 mg/kg/h. The plasma<br />
concentration of AEOL-10150 was stable at 3 to 4 µg/ml. The<br />
drug concentration <strong>in</strong> both ipsilateral and contralateral bra<strong>in</strong><br />
regions <strong>in</strong>creased with time, but was 2- to 4-fold greater <strong>in</strong><br />
the ischemic hemisphere [468211].<br />
Model<strong>in</strong>g based on animal and human data predicted the<br />
efficacious dose of AEOL-10150 <strong>in</strong> humans with ALS to be<br />
approximately 12 mg daily. It therefore appears that a wide<br />
therapeutic w<strong>in</strong>dow exists for AEOL-10150, accord<strong>in</strong>g to<br />
current safety data and dose-l<strong>in</strong>ear pharmacok<strong>in</strong>etics <strong>in</strong> animals<br />
and humans [616116].<br />
A multicenter, double-bl<strong>in</strong>d, randomized, placebo-controlled,<br />
escalat<strong>in</strong>g-dose study of subcutaneously adm<strong>in</strong>istered s<strong>in</strong>gle<br />
doses of AEOL-10150 (3, 12, 30, 45, 60 and 75 mg) to 25 patients
(n = 3 or 4 per cohort) has been conducted [621716].<br />
Pharmacok<strong>in</strong>etic data from the study showed that responses<br />
were dose-dependent, AUC values rang<strong>in</strong>g from 354 to 12,167<br />
ng.h/ml (follow<strong>in</strong>g 3- and 75-mg doses). Cmax values ranged<br />
from 114.8 to 1584 ng/ml, Tmax values ranged from 1 to 2 h and<br />
mean half-life values from 2.6 to 6.4 h (3 and 75 mg) [621716].<br />
Toxicity<br />
A study <strong>in</strong> rats compared the relative behavioral neurotoxicity<br />
of AEOL-10113 and AEOL-10150 [465629]. Animals were<br />
exam<strong>in</strong>ed for 2 h after <strong>in</strong>jection, and if no adverse behavioral<br />
responses were observed the dose was doubled <strong>in</strong> a new set of<br />
rats. In animals treated with AEOL-10113, a behavioral<br />
syndrome with susta<strong>in</strong>ed proptosis (a protuberance of the<br />
eyeball out of its socket), ataxia (impaired muscle function or<br />
movement) and hypersensitivity to sound was observed. For<br />
AEOL-10113, an <strong>in</strong>tracerebroventricular dose of 600 ng was<br />
reached before m<strong>in</strong>or behavioral side effects became noticeable<br />
compared with 9 µg for AEOL-10150, a 15-fold reduction <strong>in</strong><br />
toxicity. No effect of the drugs on body temperature was<br />
detected [465629].<br />
When adm<strong>in</strong>istered to mice for 16 days, alone or <strong>in</strong><br />
comb<strong>in</strong>ation with radiation, AEOL-10150 (6 mg/kg/day)<br />
did not produce any detectable toxicities affect<strong>in</strong>g body<br />
mass, behavior or hematological analyses [595706].<br />
In male Wistar rats, <strong>in</strong>travenous AEOL-10150 <strong>in</strong> doses of<br />
> 0.1 mg/kg produced a reduction of mean arterial pressure<br />
of > 20%. The duration of hypotension was dose dependent,<br />
with 0.5 mg/kg caus<strong>in</strong>g irreversible profound hypotension,<br />
but smaller doses produc<strong>in</strong>g only transient effects. No<br />
change <strong>in</strong> mean arterial pressure was observed when an<br />
<strong>in</strong>tracerebroventricular route was used [465629].<br />
In a mur<strong>in</strong>e prostate cancer model, animals treated with<br />
AEOL-10150 (6 mg/kg) for 16 days had a significantly elevated<br />
white blood cell count due to granulocytosis (p ≤ 0.05) [595706].<br />
Levels of red blood cells and platelets, hemoglob<strong>in</strong> and<br />
hematocrit were similar among groups tested. A trend of<br />
elevated white blood cells was observed <strong>in</strong> the spleens of mice<br />
treated with AEOL-10150 (p < 0.1), with <strong>in</strong>creases <strong>in</strong> both<br />
granulocytes and macrophages (p < 0.05). Additional studies<br />
are needed to understand the biological significance, if any, of<br />
the <strong>in</strong>creased white blood cell counts [595706].<br />
Cl<strong>in</strong>ical development<br />
Phase I<br />
A multicenter, double-bl<strong>in</strong>d, randomized, placebo-controlled<br />
study evaluated escalat<strong>in</strong>g, subcutaneous s<strong>in</strong>gle doses of<br />
AEOL-10150 (3, 12, 30, 45, 60 and 75 mg) <strong>in</strong> 25 ALS patients<br />
[592224], [621716]. Recently reported pharmacok<strong>in</strong>etic data<br />
from the trial are detailed above, and side effects/<br />
tolerability detailed <strong>in</strong> the side effects and contra<strong>in</strong>dications<br />
section below.<br />
A second multicenter, multiple-dose study was expected to<br />
enroll 18 ALS patients to receive subcutaneous <strong>in</strong>jections of<br />
40, 60 or 75 mg of AEOL-10150 (n = 4/dose) or placebo<br />
(n = 6), twice daily for 6 days, with a s<strong>in</strong>gle <strong>in</strong>jection on the<br />
seventh day. The trial was to collect efficacy, safety and<br />
AEOL-10150 Orrell 75<br />
pharmacok<strong>in</strong>etic data, and was expected to be completed by<br />
the end of 2005 or early <strong>in</strong> 2006 [629382].<br />
Aeolus has announced plans to <strong>in</strong>itiate trials <strong>in</strong> other<br />
<strong>in</strong>dications. In February 2005, the company was to file an<br />
<strong>in</strong>vestigational new drug application prior to <strong>in</strong>itiat<strong>in</strong>g a<br />
phase I study of AEOL-10150 <strong>in</strong> radiation-<strong>in</strong>duced mucositis<br />
[583926].<br />
The company had announced <strong>in</strong> April 2004 that, depend<strong>in</strong>g<br />
on the results of phase I trials <strong>in</strong> ALS, a pivotal phase II/III<br />
trial <strong>in</strong> this <strong>in</strong>dication could be <strong>in</strong>itiated by the first half of<br />
2005 [533629]. In February 2005, the company stated its<br />
<strong>in</strong>tention to <strong>in</strong>itiate an efficacy study of AEOL-10150 <strong>in</strong><br />
stroke patients [583926]. At the time of publication, however,<br />
no further details of these studies were available.<br />
Side effects and contra<strong>in</strong>dications<br />
The most common side effects that have been reported<br />
from phase I trials of ALS patients were <strong>in</strong>jection-site<br />
reactions, dizz<strong>in</strong>ess and headache [592224]. The adverse<br />
events were considered mild <strong>in</strong> severity, and<br />
approximately 50% of these events were possibly related<br />
to the study medication. No serious adverse events,<br />
laboratory abnormalities or cardiovascular issues were<br />
observed [621716]. Initial observations from the multipledose<br />
study <strong>in</strong> ALS patients have demonstrated no serious<br />
adverse events [629382].<br />
S<strong>in</strong>gle doses of AEOL-10150 rang<strong>in</strong>g from 3 to 30 mg were<br />
well tolerated [592224], and no serious adverse events were<br />
reported. No cl<strong>in</strong>ically mean<strong>in</strong>gful abnormalities were noted<br />
<strong>in</strong> safety laboratory tests, vital signs, unified Park<strong>in</strong>son's<br />
disease rat<strong>in</strong>g scale, functional ALS assessments or<br />
electrocardiogram data. Further studies of up to 75 mg of<br />
AEOL-10150 <strong>in</strong> humans revealed no serious adverse events<br />
or laboratory abnormalities [616116].<br />
Patent summary<br />
WO-09510185, published <strong>in</strong> April 1995 by Duke University and<br />
the University of Melbourne Research Foundation, describes<br />
novel mimetics of SOD and <strong>in</strong>hibitors of xanth<strong>in</strong>e. Claims are<br />
made for various manganic derivatives of meth<strong>in</strong>e-substituted<br />
porphyr<strong>in</strong>s, prepared by conventional methods, <strong>in</strong>clud<strong>in</strong>g the<br />
products AEOL-10113 and AEOL-10150. In December 1996, the<br />
University of Alabama Research Foundation and Duke<br />
University published WO-09640223, describ<strong>in</strong>g the modulation<br />
of <strong>in</strong>tra- or extracellular levels of oxidants, such as superoxide<br />
radicals, hydrogen peroxides and peroxynitrite; potential was<br />
claimed <strong>in</strong> the therapy of ischemia, myocardial <strong>in</strong>farction,<br />
reperfusion <strong>in</strong>jury, and <strong>in</strong>flammatory disorders, such as asthma<br />
and rheumatoid arthritis.<br />
In July 2000, AEOL-10150 was first claimed <strong>in</strong> WO-00043395,<br />
which is expected to be granted as EP-01155019 <strong>in</strong> December<br />
2005, describ<strong>in</strong>g the modulation of cellular levels of oxidants<br />
us<strong>in</strong>g substituted porphyr<strong>in</strong>s. AEOL-10150 is specifically<br />
claimed <strong>in</strong> US-06544975. Both the European and US cases are <strong>in</strong><br />
the name of the National Jewish Medical & Research Center,<br />
Aeolus Pharmaceuticals Inc and Duke University. AEOL-10150<br />
should have solid patent protection at least until January 2020.
76 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
Further patents associated with the drug <strong>in</strong>clude WO-02060383<br />
(published <strong>in</strong> August 2002), which claims the use of a list of<br />
SOD mimetics, <strong>in</strong>clud<strong>in</strong>g AEOL-10150, for treat<strong>in</strong>g cancer, and<br />
WO-02098431 (published <strong>in</strong> December 2002), which specifically<br />
claims AEOL-10150 for the treatment of diabetes.<br />
<strong>Current</strong> op<strong>in</strong>ion<br />
Oxidative stress and free-radical-mediated damage have<br />
been implicated <strong>in</strong> a broad range of diseases. Many of these<br />
diseases, namely stroke, myocardial <strong>in</strong>farction, cancer, and<br />
neurodegenerative and <strong>in</strong>flammatory diseases, are common,<br />
especially <strong>in</strong> later life, and cause significant disability as a<br />
result of the tissue damage. In particular, if free-radicalmediated<br />
damage can be dim<strong>in</strong>ished or halted after the<br />
immediate <strong>in</strong>sult, for example, <strong>in</strong> stroke or myocardial<br />
<strong>in</strong>farction, there is the prospect of significantly improv<strong>in</strong>g<br />
survival and reduc<strong>in</strong>g disability. Nevertheless, to date, the<br />
results of cl<strong>in</strong>ical studies of other antioxidant (eg, vitam<strong>in</strong>s C<br />
and E, selegil<strong>in</strong>e and N-acetylcyste<strong>in</strong>e) and neuroprotective<br />
compounds (eg, β-lactam antibiotics and m<strong>in</strong>ocycl<strong>in</strong>e) have<br />
been largely disappo<strong>in</strong>t<strong>in</strong>g [625121], [638229]. This may be a<br />
consequence of the animal and tissue models used, and the<br />
difficulty <strong>in</strong> apply<strong>in</strong>g the therapeutic <strong>in</strong>terventions<br />
sufficiently early <strong>in</strong> cl<strong>in</strong>ical practice. The lack of efficacy may<br />
also relate to the compounds be<strong>in</strong>g <strong>in</strong>appropriate.<br />
Questions rema<strong>in</strong> as to the mechanism of action of<br />
metalloporphyr<strong>in</strong>s, <strong>in</strong>clud<strong>in</strong>g AEOL-10150. The therapeutic<br />
mechanism may not be their antioxidant properties, and more<br />
studies should be conducted <strong>in</strong> precl<strong>in</strong>ical models to determ<strong>in</strong>e<br />
alternative mechanisms, study<strong>in</strong>g markers other than those of<br />
oxidative stress. For example, heat shock prote<strong>in</strong>s are also<br />
implicated <strong>in</strong> the pathogenesis of ALS, and their modulation<br />
has produced some benefit <strong>in</strong> precl<strong>in</strong>ical studies [634318],<br />
[634320]. This f<strong>in</strong>d<strong>in</strong>g may have significant implications for<br />
target<strong>in</strong>g diseases, and determ<strong>in</strong><strong>in</strong>g the most effective<br />
compound for further studies. Also, the free-radical-scaveng<strong>in</strong>g<br />
ability of the metalloporphyr<strong>in</strong>s may be reduced or abolished<br />
by structural modifications. Includ<strong>in</strong>g such modified<br />
compounds as controls <strong>in</strong> studies of AEOL-10150 is important<br />
to clarify the therapeutic mechanisms.<br />
SOD mimetics and similar compounds that affect free radicals<br />
and oxidative stress have the potential for cl<strong>in</strong>ical efficacy.<br />
AEOL-10150 was apparently tolerated <strong>in</strong> phase I studies, and<br />
has the advantage of be<strong>in</strong>g subcutaneously adm<strong>in</strong>istered. For<br />
treatment of a chronic disease process, such as ALS, where<br />
oxidative damage is presumed to be ongo<strong>in</strong>g throughout the<br />
disease, treatment would presumably require regular<br />
adm<strong>in</strong>istration of the compound and access to the central<br />
nervous system. ALS would appear to be a sensible choice of<br />
disease <strong>in</strong> which to study the cl<strong>in</strong>ical effects of AEOL-10150<br />
because of the presumption of oxidative stress as a component<br />
of the pathology, and also because the rapid progression of the<br />
disease allows cl<strong>in</strong>ical efficacy to be studied <strong>in</strong> a relatively short<br />
time period. ALS is a serious and fatal disease <strong>in</strong> urgent need of<br />
effective treatment. A range of antioxidants have been<br />
evaluated <strong>in</strong> the treatment of this disorder, with no proven<br />
efficacy [625121], but these have usually been of low potency<br />
and specificity, and evaluated <strong>in</strong> poorly designed studies. The<br />
only current licensed medication for ALS, riluzole, has only<br />
slight efficacy [625097], [625122], and there is the expectation<br />
that other medications will have a more significant effect <strong>in</strong> the<br />
future, either alone or <strong>in</strong> comb<strong>in</strong>ation with riluzole and other<br />
compounds. The observation of an additive therapeutic effect of<br />
AEOL-10150 when comb<strong>in</strong>ed with sodium phenylbutyrate<br />
supports this view [633859], and is important when design<strong>in</strong>g<br />
precl<strong>in</strong>ical and cl<strong>in</strong>ical studies, and determ<strong>in</strong><strong>in</strong>g the eventual<br />
utility of the compound.<br />
Some caution is needed <strong>in</strong> the <strong>in</strong>terpretation of therapeutic<br />
studies <strong>in</strong> SOD1 transgenic mice, as a range of compounds have<br />
been demonstrated to have efficacy on survival, but this efficacy<br />
has not been translated to effects <strong>in</strong> humans [638229]. Also, a<br />
range of different SOD1 transgenic mouse models exist, with<br />
different mutations, different expression loads and different<br />
background survival, mak<strong>in</strong>g comparison of survival times or<br />
efficacy difficult. An important study <strong>in</strong> a mouse model would<br />
be to exam<strong>in</strong>e a comb<strong>in</strong>ation of riluzole and AEOL-10150,<br />
compar<strong>in</strong>g the comb<strong>in</strong>ation with the effects on animals treated<br />
with the <strong>in</strong>dividual agents and placebo. It is probable that any<br />
cl<strong>in</strong>ical trial <strong>in</strong> humans with ALS will require the patients to be<br />
tak<strong>in</strong>g riluzole as well as AEOL-10150, for ethical reasons. A<br />
criticism that may be raised concern<strong>in</strong>g the treatment of<br />
degenerative conditions, such as ALS (and other conditions<br />
such as cancer, stroke and heart disease), is that <strong>in</strong> prolong<strong>in</strong>g<br />
survival, suffer<strong>in</strong>g or disability may also be prolonged. Hence,<br />
the observation that mice treated with AEOL-10150 reta<strong>in</strong>ed<br />
their ability to walk on all four limbs and perform other normal<br />
activities throughout the extended period of survival, rather<br />
than experience a gradual deterioration or prolongation of<br />
lifespan <strong>in</strong> significant physical disability, is potentially<br />
important [616116], [616156].<br />
More effective antioxidants are also be<strong>in</strong>g synthesized, for<br />
example, through the modification of AEOL-10150 by <strong>in</strong>clud<strong>in</strong>g<br />
oxygen atoms [625100]. Three new Mn(III) porphyr<strong>in</strong> SOD-like<br />
catalysts, with ether oxygen atoms <strong>in</strong> the side cha<strong>in</strong>s, have been<br />
synthesized and characterized by the same laboratory [625100].<br />
When compared with AEOL-10113 and AEOL-10150,<br />
MnTDMOE-2-ImP 5+ (where all eight ethyl groups are replaced<br />
by methoxyethyl groups) was the most effective catalyst of<br />
SOD, while AEOL-10150 was stated to be of low efficacy<br />
[625100]. Comparative studies of these antioxidants <strong>in</strong> the G93A<br />
SOD1 mutant mouse would be of <strong>in</strong>terest because it is the best<br />
available ALS model. In one study, the synthetic superoxide<br />
dismutase/catalase mimetics (salen manganese complexes),<br />
EUK-8 and EUK-134 (Proteome Systems Ltd) were<br />
adm<strong>in</strong>istered <strong>in</strong>traperitoneally to low-express<strong>in</strong>g G93A mice,<br />
110 days before onset. Disease onset occurs later <strong>in</strong> these mice<br />
(170 days), and prolongation of up to 6 days occurs <strong>in</strong> the<br />
EUK-8-treated group, a 1.1-fold <strong>in</strong>crease <strong>in</strong> total life span. Us<strong>in</strong>g<br />
the survival <strong>in</strong>terval ratio, values of 1.2-fold for EUK-8 and<br />
1.6-fold for EUK-134 were calculated [625120]. In another<br />
study, iron porphyr<strong>in</strong> (FeTCPP) 5,10,15,20-tetrakis-4carboxyphenylporphyr<strong>in</strong><br />
was adm<strong>in</strong>istered to G93A SOD1<br />
mutant mice. The mean survival time was <strong>in</strong>creased by 7 days<br />
<strong>in</strong> treated mice compared with controls [625101].<br />
If cl<strong>in</strong>ical efficacy of AEOL-10150 is demonstrated <strong>in</strong> any one<br />
of the proposed treatment <strong>in</strong>dications, the possibilities of<br />
efficacy <strong>in</strong> the rema<strong>in</strong><strong>in</strong>g <strong>in</strong>dications would appear to be good.
Although subcutaneous adm<strong>in</strong>istration is of benefit for chronic<br />
conditions, <strong>in</strong>travenous adm<strong>in</strong>istration with access to<br />
appropriate tissues, especially bra<strong>in</strong> <strong>in</strong> stroke and sp<strong>in</strong>al cord <strong>in</strong><br />
trauma, is important. The recurrent problem <strong>in</strong> treat<strong>in</strong>g these<br />
acute conditions is diagnos<strong>in</strong>g and adm<strong>in</strong>ister<strong>in</strong>g the<br />
medication with<strong>in</strong> the first few hours of the <strong>in</strong>sult.<br />
Development history<br />
AEOL-10150 Orrell 77<br />
Precl<strong>in</strong>ical trials of AEOL-10150 have shown promise of<br />
efficacy <strong>in</strong> a range of diseases that cause significant<br />
mortality, disability and suffer<strong>in</strong>g. However, the<br />
mechanisms of action and relative efficacy of<br />
AEOL-10150 and other metalloporphyr<strong>in</strong>s require further<br />
study.<br />
Developer Country Status Indication Date Reference<br />
Aeolus Pharmaceuticals Inc US Phase I Motor neuron disease 31-OCT-04 583926<br />
Aeolus Pharmaceuticals Inc US Discovery Cerebrovascular ischemia 24-NOV-00 391004<br />
Aeolus Pharmaceuticals Inc US Discovery Lung <strong>in</strong>flammation 01-AUG-01 616377<br />
Aeolus Pharmaceuticals Inc US Discovery Mucositis 01-OCT-01 432294<br />
Aeolus Pharmaceuticals Inc US Discovery Sp<strong>in</strong>al cord <strong>in</strong>jury 04-MAR-04 554429<br />
Literature classifications<br />
Chemistry<br />
Study type Result Reference<br />
SAR. A number of related manganese (III) compounds were studied and compared. AEOL-10150, a stable<br />
and non-toxic manganese mesoporphyr<strong>in</strong>, was selected on the basis of its redox potentials (E1/2 value<br />
of +346 mV and log kcat value of 7.83).<br />
625100<br />
Biology<br />
Study type Effect studied Model Result Reference<br />
In vitro Efficacy. AEOL-10150 was added dur<strong>in</strong>g the After 24 h, there was a 3-fold <strong>in</strong>crease <strong>in</strong> 463528<br />
isolation and culture of purified human the mass of AEOL-10150-treated cells<br />
pancreatic islet cells.<br />
compared with untreated cells. When<br />
transplanted to diabetic mice, glucose<br />
levels were normalized <strong>in</strong> n<strong>in</strong>e out of n<strong>in</strong>e<br />
mice receiv<strong>in</strong>g AEOL-10150-treated isletcell<br />
cultures but <strong>in</strong> only five out of eight<br />
animals receiv<strong>in</strong>g untreated cells.<br />
In vivo Efficacy. SOD1-overexpress<strong>in</strong>g G93A mice Compared with placebo, the mean<br />
616156<br />
adm<strong>in</strong>istered one of three schedules <strong>in</strong>creases <strong>in</strong> survival for mice treated with<br />
(5 mg/kg AEOL-10150<br />
<strong>in</strong>traperitoneal AEOL-10150,<br />
<strong>in</strong>traperitoneally as a load<strong>in</strong>g dose <strong>in</strong>traperitoneal AEOL-10150 plus creat<strong>in</strong>e<br />
followed by daily ma<strong>in</strong>tenance doses and rofecoxib, and subcutaneous<br />
of 2.5 mg/kg; 2.5 mg/kg AEOL-10150 AEOL-10150 were 40.0, 38.8 and 40.5<br />
<strong>in</strong>traperitoneally with creat<strong>in</strong>e and days, respectively; survival ratios <strong>in</strong> the<br />
rofecoxib (2 and 0.005% <strong>in</strong> diet, same groups were 2.96, 2.87 and 2.43,<br />
respectively); or 2.5 mg/kg/day<br />
AEOL-10150 via subcutaneous<br />
adm<strong>in</strong>istration) were treated from the<br />
first day of symptom onset<br />
(~ 90 days of age).<br />
respectively.<br />
In vivo Efficacy. SOD1-overexpress<strong>in</strong>g G93A mice Compared with placebo, the mean<br />
633859<br />
adm<strong>in</strong>istered one of three dos<strong>in</strong>g survival of mice treated with AEOL-10150<br />
schedules <strong>in</strong>traperitoneally<br />
alone, with phenylbutyrate alone, and with<br />
(AEOL-10150 (2.5 mg/kg/day), the comb<strong>in</strong>ation of AEOL-10150 and<br />
phenylbutyrate (400 mg/kg/day), and phenylbutyrate <strong>in</strong>creased by 11, 13 and<br />
a comb<strong>in</strong>ation of AEOL-10150<br />
and phenylbutyrate at the same<br />
doses). Animals were treated from the<br />
first day of symptom onset (~ 90 days<br />
of age).<br />
19%, respectively.<br />
In vivo Efficacy. C57BL/6J mice (n = 18) subjected to Rotarod performance demonstrated that 554429<br />
sp<strong>in</strong>al cord compression for 60 m<strong>in</strong>, <strong>in</strong>trathecal adm<strong>in</strong>istration of AEOL-10150<br />
with AEOL-10150 or placebo<br />
was associated with ~ 30% improvement<br />
adm<strong>in</strong>istered 5 m<strong>in</strong> later. In two <strong>in</strong> neurological behavior (p < 0.05), and a<br />
studies, AEOL-10150 was<br />
reduction was seen <strong>in</strong> histological total<br />
adm<strong>in</strong>istered as a 0.5-mg/kg bolus damage score (19 ± 8; p = 0.03)<br />
dose followed by a 1.0-mg/kg<br />
<strong>in</strong>travenous <strong>in</strong>fusion every hour for 24<br />
compared with controls (26 ± 10).<br />
Intravenous adm<strong>in</strong>istration of<br />
h (n = 25), or as an <strong>in</strong>trathecal<br />
<strong>in</strong>jection (2.5 or 5.0 µg/kg).<br />
AEOL-10150 showed no significant<br />
changes compared with the control group.
78 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
Biology (cont<strong>in</strong>ued)<br />
Study type Effect studied Model Result Reference<br />
In vivo Efficacy. MCAO or sham surgery <strong>in</strong> mice A 25% reduction <strong>in</strong> <strong>in</strong>farct size and a<br />
465629<br />
(n = 6/group) followed by an<br />
reduction <strong>in</strong> neurological deficit were<br />
<strong>in</strong>travenous bolus dose of<br />
AEOL-10150 (0.5 mg/kg) and a<br />
cont<strong>in</strong>uous <strong>in</strong>travenous <strong>in</strong>fusion at<br />
1.0 mg/kg/h for 24 h (n = 6/group).<br />
demonstrated.<br />
Metabolism<br />
Study type Effect studied Model Result Reference<br />
In vivo Pharmacok<strong>in</strong>etics. AEOL-10150 (300 ng)<br />
The drug was not detected <strong>in</strong> the liver.<br />
465629<br />
adm<strong>in</strong>istered<br />
Plasma concentrations were generally<br />
<strong>in</strong>tracerebroventricularly 90 m<strong>in</strong> negligible, but reached 4.6 and 3.2 ng/ml <strong>in</strong><br />
after MCAO <strong>in</strong> rats.<br />
two rats. Bra<strong>in</strong> parenchymal AEOL-10150<br />
peaked with<strong>in</strong> 1 h of <strong>in</strong>jection, and the<br />
tissue half-life was calculated to be ~ 10 h.<br />
In vivo Pharmacok<strong>in</strong>etics. Post MCAO or sham surgery, mice<br />
received an <strong>in</strong>travenous bolus<br />
dose of AEOL-10150 (0.5 mg/kg)<br />
and a cont<strong>in</strong>uous <strong>in</strong>travenous<br />
<strong>in</strong>fusion of AEOL-10150 at 1.0<br />
mg/kg/h for 24 h.<br />
In vivo Pharmacok<strong>in</strong>etics. A phase I, double-bl<strong>in</strong>d,<br />
randomized, placebo-controlled,<br />
s<strong>in</strong>gle escalat<strong>in</strong>g-dose study of<br />
subcutaneous AEOL-10150 (3, 12,<br />
30, 45, 60 and 75 mg) <strong>in</strong> 25 ALS<br />
patients.<br />
Cl<strong>in</strong>ical<br />
Uptake of the drug <strong>in</strong>to the bra<strong>in</strong> was slow,<br />
dose- and time- dependent, and greater <strong>in</strong><br />
the ischemic hemisphere.<br />
Responses were dose dependent, with AUC<br />
values rang<strong>in</strong>g from 354 to 12,167 ng.h/ml<br />
(follow<strong>in</strong>g 3- and 75-mg doses, respectively).<br />
Cmax values ranged from 114.8 to 1584 ng/ml,<br />
Tmax ranged from 1 to 2 h, and mean half-lives<br />
from 2.6 to 6.4 h (follow<strong>in</strong>g doses of 3 and 75<br />
mg, respectively).<br />
465629<br />
621716<br />
Effect studied Model Result Reference<br />
Safety. A phase I, multicenter, double-bl<strong>in</strong>d, randomized, No serious adverse effects, laboratory<br />
621716<br />
placebo-controlled, s<strong>in</strong>gle escalat<strong>in</strong>g-dose study of abnormalities or cardiovascular issues were<br />
subcutaneous AEOL-10150 (3, 12, 30, 45, 60 and recorded. The most common adverse effects were<br />
75 mg) <strong>in</strong> 25 ALS patients.<br />
<strong>in</strong>jection-site reactions, dizz<strong>in</strong>ess and headache.<br />
Associated patent<br />
Title Substituted porphyr<strong>in</strong>s.<br />
Assignee National Jewish Medical and Research Center<br />
Publication WO-00043395 27-JUL-00<br />
Priority US-19990117010 25-JAN-99<br />
Inventors Crapo JD, Day BJ, Trova MP, Gauuan PJF, Kitchen DB.<br />
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Calvi CL, Bat<strong>in</strong>ic Haberle I, Day BJ, Liang LP, Fridovich I, Crapo JD,<br />
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449960 Metalloporphyr<strong>in</strong> class of therapeutic catalytic antioxidants.<br />
Patel M, Day BJ TRENDS PHARMACOL SCI 1999 20 9 359-364<br />
463528 Preservation of human islet cell functional mass by antioxidative<br />
action of a novel SOD mimic compound. Bott<strong>in</strong>o R,<br />
Balamurugan AN, Bertera S, Pietropaolo M, Trucco M, Piganelli JD<br />
DIABETES 2002 51 8 2561- 2567<br />
465629 Effects of metalloporphyr<strong>in</strong> catalytic antioxidants <strong>in</strong><br />
experimental bra<strong>in</strong> ischemia. Sheng H, Enghild JJ, Bowler R, Patel M,<br />
Bat<strong>in</strong>i-Haberle I, Calvi CL, Day BJ, Pearlste<strong>in</strong> RD, Crapo JD, Warner DS<br />
FREE RADIC BIOL MED 2002 33 7 947-961<br />
468211 Intravenous adm<strong>in</strong>istration of the Mn metalloporphyr<strong>in</strong> catalytic<br />
antioxidant AEOL 10150 protects aga<strong>in</strong>st ischemic bra<strong>in</strong> <strong>in</strong>jury <strong>in</strong> mice.<br />
Warner DS, Homi H, Crapo JD, Pearlste<strong>in</strong> RD, Sheng H ABSTR SOC<br />
NEUROSCI 2002 28 Abs 201.18<br />
478835 The natural history of amyotrophic lateral sclerosis. R<strong>in</strong>gel SP,<br />
Murphy JR, Alderson MK, Bryan W, England JD, Miller RG, Petajan JH, Smith<br />
SA, Roelofs RI, Ziter F NEUROLOGY 1993 43 7 1316-1322<br />
505222 Organometallics adm<strong>in</strong>istered at onset of disease enhance<br />
survival and preserve motor function of ALS transgenic mice. Crow JP,<br />
Hill JL, Jones P ACS 2003 226 INOR 615<br />
533629 Incara Pharmaceuticals closes on $10.26 million f<strong>in</strong>anc<strong>in</strong>g. Incara<br />
Pharmaceuticals Inc PRESS RELEASE 2004 April 19<br />
554429 Mouse sp<strong>in</strong>al cord compression <strong>in</strong>jury is ameliorated by<br />
<strong>in</strong>trathecal cationic manganese (III) porphyr<strong>in</strong> catalytic antioxidant<br />
therapy. Sheng H, Spasojevic I, Warner DS, Haberle IB NEUROSCI LETT<br />
2004 366 2 220-225
583926 Aeolus Pharmaceuticals announces first quarter f<strong>in</strong>ancial<br />
results. Aeolus Pharmaceuticals Inc PRESS RELEASE 2005 February 08<br />
592224 Aeolus Pharmaceuticals Inc announces optimistic AEOL 10150<br />
phase 1 cl<strong>in</strong>ical trial <strong>in</strong>terim results <strong>in</strong> patients with Lou Gehrig's<br />
disease. Aeolus Pharmaceuticals Inc PRESS RELEASE 2005 March 29<br />
595706 Effect of AEOL 10150 on prostate tumor response to radiation.<br />
Mak<strong>in</strong>de AY, Rizvi A, Luo X, Andres ML, Archambeau JO, Pearlste<strong>in</strong> RD,<br />
Slater JM, Gridley DS PROC AM ASSOC CANCER RES 2005 46 Abs 1991<br />
616116 Aeolus Pharmaceuticals Inc announces publication of results of<br />
AEOL 10150 studies <strong>in</strong> Annals of Neurology. Aeolus Pharmaceuticals Inc<br />
PRESS RELEASE 2005 August 04<br />
616156 Manganese porphyr<strong>in</strong> given at symptom onset markedly extends<br />
survival of ALS mice. Crow JP, Cal<strong>in</strong>gasan NY, Chen J, Hill J, Beal MF ANN<br />
NEUROL 2005 58 2 258-265<br />
616358 Mechanistic analysis of the immunomodulatory effects of a<br />
catalytic antioxidant on antigen-present<strong>in</strong>g cells: Implication for their<br />
use <strong>in</strong> target<strong>in</strong>g oxidation-reduction reactions <strong>in</strong> <strong>in</strong>nate immunity. Tse<br />
HM, Milton MJ, Piganelli JD FREE RADIC BIOL MED 2004 36 2 233-247<br />
616360 Evidence for extracellular superoxide dismutase as a mediator of<br />
hemorrhage-<strong>in</strong>duced lung <strong>in</strong>jury. Bowler RP, Aracoli J, Abraham E, Patel<br />
M, Chang LY, Crapo JD AM J PHYSIOL - LUNG CELL MOL PHYSIOL 2003<br />
284 4 L680-L687<br />
616364 Mn(III) meso tetrakis(N,N'-diethylimidazolium-2-yl)porphyr<strong>in</strong><br />
(AEOL-10150) offers protection <strong>in</strong> mouse model of sp<strong>in</strong>al cord <strong>in</strong>jury.<br />
Sheng H, Spasojevic I, Warner DS, Bat<strong>in</strong>ic-Haberle I FREE RADIC BIOL<br />
MED 2003 35 Suppl 1 S154<br />
616369 A catalytic antioxidant (AEOL 10150) attenuates expression of<br />
<strong>in</strong>flammatory genes <strong>in</strong> stroke. Bowler RP, Sheng H, Enghild JJ, Pearlste<strong>in</strong><br />
RD, Warner AS, Crapo JD FREE RADIC BIOL MED 2002 33 8 1141-1152<br />
616370 Inhibition of tobacco smoke-<strong>in</strong>duced lung <strong>in</strong>flammation by a<br />
catalytic antioxidant. Smith KR, Uyem<strong>in</strong>ami DL, Kodavanti UP, Chang LY,<br />
Crapo JD, P<strong>in</strong>kerton KE FREE RADIC BIOL MED 2002 33 8 1106-1114<br />
616377 Attenuation of cigarette smoke-<strong>in</strong>duced lung <strong>in</strong>flammation and<br />
remodel<strong>in</strong>g by treatment with the metalloporphyr<strong>in</strong> (AEOL 10150).<br />
P<strong>in</strong>kerton KE, Smith KR, Kodavanti U, Chang LY, Crapo JD FREE RADIC<br />
BIOL MED 2001 31 10 S49<br />
621716 Aeolus Pharmaceuticals reports positive safety results from<br />
completed phase I s<strong>in</strong>gle dose study of AEOL 10150 <strong>in</strong> 25 patients with<br />
ALS (Lou Gehrig's disease). Aeolus Pharmaceuticals Inc PRESS RELEASE<br />
2005 September 07<br />
625097 Riluzole for amyotrophic lateral sclerosis (ALS)/motor neuron<br />
disease (MND). Miller RG, Mitchell JD, Lyon M, Moore DH COCHRANE<br />
DATABASE SYST REV 2001 4 CD001447<br />
625100 New class of potent catalysts of O2 dismutation. Mn(III) orthomethoxyethylpyridyl-<br />
and di-ortho-methoxyethylimidazolylporphyr<strong>in</strong>s.<br />
Bat<strong>in</strong>ic-Haberle I, Spasojevic I, Stevens RD, Hambright P, Neta P, Okado-<br />
Matsumoto A, Fridovich I DALTON TRANS 2004 11 1696-1702.<br />
625101 Wu AS, Kiaei M, Aguirre N, Crow JP, Cal<strong>in</strong>gasan NY, Browne SE,<br />
Beal MF Iron porphyr<strong>in</strong> treatment extends survival <strong>in</strong> a transgenic animal<br />
model of amyotrophic lateral sclerosis. J NEUROCHEM 2003 85 1 142-<br />
150<br />
625109 Syntheses and superoxide dismut<strong>in</strong>g activities of partially (1-4)<br />
β-chlor<strong>in</strong>ated derivatives of manganese (III) meso-tetrakis (-ethylpyrid<strong>in</strong>ium-2-yl)<br />
porphyr<strong>in</strong>. Kachadourian R, Bat<strong>in</strong>ic-Haberle I, Fridovich I<br />
INORG CHEM 1999 38 2 391-396<br />
625112 High-performance liquid chromatography with<br />
spectrophotometric and electrochemical detection of a series of<br />
manganese (III) cationic porphyr<strong>in</strong>s. Kachadourian R, Menzeleev R, Agha<br />
B, Bocck<strong>in</strong>o SB, Day BJ J CHROMATOGR B ANAL TECHNOL BIOMED LIFE<br />
SCI 2002 767 1 61-67<br />
625113 Peroxynitrite scaveng<strong>in</strong>g by metalloporphyr<strong>in</strong>s and thiolates.<br />
Crow JP FREE RADIC BIOL MED 2000 28 10 1487-1494.<br />
625120 Synthetic superoxide dismutase/catalase mimetics reduce<br />
oxidative stress and prolong surival <strong>in</strong> a mouse amyotrophic lateral<br />
sclerosis model. Jung C, Rong Y, Doctrow S, Baudry M, Malfroy B, Xu Z<br />
NEUROSCI LETT 2001 304 3 157-160<br />
AEOL-10150 Orrell 79<br />
625121 Antioxidant treatment for amyotrophic lateral sclerosis/motor<br />
neuron disease. Orrell RW, Lane JM, Ross M COCHRANE DATABASE<br />
SYST REV 2004 18 4 CD002829<br />
625122 Dose-rang<strong>in</strong>g study of riluzole <strong>in</strong> amyotrophic lateral sclerosis.<br />
Lacomblez L, Bensimon G, Leigh PN, Guillet P, Me<strong>in</strong><strong>in</strong>ger V LANCET 1996<br />
347 9013 1425-1431<br />
629090 Protection of normal tissue from radiation-<strong>in</strong>duced <strong>in</strong>jury us<strong>in</strong>g<br />
AEOL 10150 presented at the annual meet<strong>in</strong>g of the American Society<br />
for Therapeutic Radiology and Oncology. Aeolus Pharmaceuticals Inc<br />
PRESS RELEASE 2005 October 18<br />
629382 Aeolus Pharmaceuticals announces <strong>in</strong>itiation of multiple dose<br />
study of AEOL 10150 <strong>in</strong> patients with Lou Gehrig's disease. Aeolus<br />
Pharmaceuticals Inc PRESS RELEASE 2005 October 19<br />
632736 Response of human islets to isolation stress and the effect of<br />
antioxidant treatment. Bott<strong>in</strong>o R, Balamurugan AN, Tse H,<br />
Thirunavvukarasu C, Ge X, Profozich J, Milton M, Ziegenfuss A, Trucco M,<br />
Piganeli JD DIABETES 2004 53 10 2559-2568<br />
633859 Additive neuroprotective effects of a histone deacetylase<br />
<strong>in</strong>hibitor and a catalytic antioxidant <strong>in</strong> a transgenic mouse model of<br />
amyotrophic lateral sclerosis. Petri S, Kiaei M, Kipiani K, Chen J,<br />
Cal<strong>in</strong>gasan NY, Damiano M, Manfredi G, Crow JP, Beal MF ABSTR SOC<br />
NEUROSCI 2005 35 Abs 213.15<br />
634304 Management of motor neuron disease. Howard RS, Orrell RW<br />
POSTGRAD MED J 2002 78 926 736-741<br />
634318 Mutant Cu/Zn superoxide dismutase prote<strong>in</strong>s have altered<br />
solubility and <strong>in</strong>teract with heat shock/stress prote<strong>in</strong>s <strong>in</strong> models of<br />
amyotrophic lateral sclerosis. Sh<strong>in</strong>der GA, Lacourse MC, M<strong>in</strong>otti S, Durham<br />
HD J BIOL CHEM 2001 276 16 12791-12796<br />
634320 Treatment with arimoclomol, a co<strong>in</strong>ducer of heat shock prote<strong>in</strong>s,<br />
delays disease progression <strong>in</strong> ALS mice. Kieran D, Kalmar B, Dick JR,<br />
Riddoch-Contreras J, Burnstock G, Greensmith L NAT MED 2004 10 4 402-<br />
405<br />
634325 Flav<strong>in</strong>-dependent antioxidant properties of a new series of meso-<br />
N,N'-dialkyl-imidazolium substituted manganese(III) porphyr<strong>in</strong>s.<br />
Kachadourian R, Johnson CA, M<strong>in</strong> E, Spasojevic I, Day BJ BIOCHEM<br />
PHARMACOL 2004 67 1 77-85<br />
634340 An alternative Ca 2+ -dependent mechanism of neuroprotection by<br />
the metalloporphyr<strong>in</strong> class of superoxide dismutase mimetics. Tauskela<br />
JS, Brunette E, O'Reilly N, Meal<strong>in</strong>g G, Comas T, Gendron TF, Monette R,<br />
Morley P FASEB J 2005 19 12 1734-1736<br />
634341 Paradoxical effects of metalloporphyr<strong>in</strong>s on doxorubic<strong>in</strong>-<strong>in</strong>duced<br />
apoptosis: Scaveng<strong>in</strong>g of reactive oxygen species versus <strong>in</strong>duction of<br />
heme oxygenase-1. Konorev EA, Kotamraju S, Zhao H, Kalivendi S, Joseph<br />
J, Kalyanaraman B FREE RADIC BIOL MED 2002 33 7 988-997<br />
634343 Dependence of excitotoxic neurodegeneration on mitochondrial<br />
aconitase <strong>in</strong>activation. Li Q-Y, Pedersen C, Day BJ, Patel M J<br />
NEUROCHEM 2001 78 47 746-755<br />
636040 Therapeutic developments <strong>in</strong> the treatment of amyotrophic<br />
lateral sclerosis. Jackson M, Llado J, Rothste<strong>in</strong> JD EXPERT OPIN INVEST<br />
DRUGS 2002 11 10 1343-1364<br />
638196 Natural history of amyotrophic lateral sclerosis <strong>in</strong> a database<br />
population. Validation of a scor<strong>in</strong>g system and a model for survival<br />
prediction. Haverkamp LJ, Appel V, Appel SH BRAIN 1995 118 3 707-719<br />
638197 Prognostic <strong>in</strong>dicators of survival <strong>in</strong> ALS. Stambler N, Charatan M,<br />
Cedarbaum JM NEUROLOGY 1998 50 1 66-72<br />
638203 Orrell RW, Habgood JJ, Gard<strong>in</strong>er I, K<strong>in</strong>g AW, Bowe FA, Hallewell RA,<br />
Marklund SL, Greenwood J, Lane RJ, deBelleroche J Cl<strong>in</strong>ical and functional<br />
<strong>in</strong>vestigation of 10 missense mutations and a novel frameshift <strong>in</strong>sertion<br />
mutation of the gene for copper-z<strong>in</strong>c superoxide dismutase <strong>in</strong> UK<br />
families with amyotrophic lateral sclerosis. NEUROLOGY 1997 48 3 746-<br />
751<br />
638218 Catalytic antioxidants: A radical approach to new therapeutics.<br />
Day BJ DRUG DISC TODAY 2004 9 13 557-566<br />
638220 Amyotrophic lateral sclerosis: Copper/z<strong>in</strong>c superoxide<br />
dismutase (SOD1) gene mutations. Orrell RW NEUROMUSCULAR<br />
DISORD 2000 10 1 63-68
80 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
638223 The genetics of motor neuron disease. Figlewicz DA, Orrell RW<br />
AMYOTROPHIC LATERAL SCLEROSIS OTHER MOTOR NEURON<br />
DISORD 2003 4 4 225-231<br />
638229 Amyotrophic lateral sclerosis: Recent advances and future<br />
therapies. Nirmalananthan N, Greensmith L CURR OPIN NEUROL 2005 18<br />
6 712-719<br />
638230 Oxidatively modified prote<strong>in</strong>s <strong>in</strong> ag<strong>in</strong>g and disease. Beal MF<br />
FREE RADIC BIOL MED 2002 32 9 797-803<br />
638233 Unravel<strong>in</strong>g the mechanisms <strong>in</strong>volved <strong>in</strong> motor neuron<br />
degeneration <strong>in</strong> ALS. Bruijn LJ, Miller TM, Cleveland DW ANNU REV<br />
NEUROSCI 2004 27 723-749<br />
638331 Inactivation-reactivation of aconitase <strong>in</strong> Escherichia coli. A<br />
sensitive measure of superoxide radical. Gardner PR, Fridovich I J BIOL<br />
CHEM 1992 267 13 8757-8763<br />
638411 Long term adm<strong>in</strong>istration of a small molecular weight catalytic<br />
metalloporphyr<strong>in</strong> antioxidant AEOL 10150 protects lungs from radiation<strong>in</strong>duced<br />
<strong>in</strong>jury. Aeolus Pharmaceuticals Inc COMPANY PRESENTATION<br />
2005 October 16-20
Vivitrex Alkermes/Cephalon<br />
Christ<strong>in</strong>e E Head<strong>in</strong>g<br />
Address<br />
Faculty of Science<br />
The Open University <strong>in</strong> the North<br />
Eldon House<br />
Regent Centre<br />
Gosforth<br />
Newcastle-upon-Tyne<br />
NE3 3PW<br />
UK<br />
Email: moore11@globalnet.co.uk<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 7(1):81-88<br />
© The Thomson Corporation ISSN 1472-4472<br />
Vivitrex, an <strong>in</strong>jectable, susta<strong>in</strong>ed-release formulation of the<br />
opioid antagonist naltrexone, is be<strong>in</strong>g developed by Alkermes<br />
and Cephalon for the potential once-monthly treatment of<br />
alcoholism and opiate use disorder. Alkermes and Cephalon are<br />
currently await<strong>in</strong>g Food and Drug Adm<strong>in</strong>istration review of<br />
the Vivitrex new drug application, which was granted Priority<br />
Review <strong>in</strong> May 2005.<br />
Introduction<br />
Vivitrex is an <strong>in</strong>jectable, extended-release naltrexone<br />
product that is currently <strong>in</strong> development by Alkermes Inc<br />
and licensee Cephalon Inc for alcohol and opiate<br />
dependence. Pharmacotherapies for substance-dependent<br />
conditions have traditionally focused on the substance itself;<br />
substitutes for the substance of abuse, plus receptor<br />
antagonists and agents that <strong>in</strong>terfere with the<br />
pharmacok<strong>in</strong>etics of the substance (eg, methadone and<br />
naltrexone for opiate dependence and disulfiram for alcohol<br />
dependence) have all proved useful <strong>in</strong> treat<strong>in</strong>g these<br />
conditions, and cont<strong>in</strong>ue to be developed. However, there is<br />
reliable evidence to suggest that certa<strong>in</strong> loci <strong>in</strong> the bra<strong>in</strong><br />
function abnormally <strong>in</strong> all dependencies, regardless of their<br />
cause [636843]. With<strong>in</strong> the mesolimbic dopam<strong>in</strong>e system<br />
(MLDS) is the nucleus accumbens (NA), which is associated<br />
with reward and drug-seek<strong>in</strong>g behavior caused by the<br />
elevation of dopam<strong>in</strong>e levels at the site. Both alcohol and<br />
opiates can raise levels of dopam<strong>in</strong>e <strong>in</strong> the NA, and the<br />
available evidence suggests that alcohol causes this by<br />
<strong>in</strong>creas<strong>in</strong>g the release of endogenous opioids [631895].<br />
Therefore, <strong>in</strong>hibition of opioid receptors by naltrexone is a<br />
rational way of reduc<strong>in</strong>g the rewards that both ethanol and<br />
opiates <strong>in</strong>duce.<br />
In 1984, the opioid receptor antagonist naltrexone was<br />
approved for the treatment of opiate dependence <strong>in</strong> the US;<br />
a decade later naltrexone was approved for the treatment of<br />
alcohol dependence [631898]. The drug has also been<br />
<strong>in</strong>vestigated for a variety of other dependencies. Naltrexone<br />
acts at µ-, δ- and κ-opioid receptors, each of which are<br />
implicated <strong>in</strong> one or more aspects of alcohol and opiate<br />
dependence. Of the three receptors, the µ-opioid receptor is<br />
believed to be the most significant regard<strong>in</strong>g alcohol and<br />
opioid self adm<strong>in</strong>istration, and its absence or blockade tends<br />
to be l<strong>in</strong>ked with dim<strong>in</strong>ished dependence [638453]. The<br />
general evidence support<strong>in</strong>g the use of naltrexone for<br />
alcohol dependence, as well as the relationship between<br />
Orig<strong>in</strong>ator Alkermes Inc<br />
Licensee Cephalon Inc<br />
Status Pre-registration<br />
.<br />
Indications Alcoholism, Opiate dependence.<br />
.<br />
Action Opioid antagonist<br />
.<br />
Technologies Controlled release formulation, Intramuscular<br />
formulation<br />
Synonym naltrexone (once-monthly controlled-release,<br />
Medisorb)<br />
Registry No: 16590-41-3<br />
N<br />
OH<br />
HO O H O<br />
81<br />
opioid receptors and alcoholism, can be found <strong>in</strong> a<br />
comprehensive review by Oswald and Wand [631895], and a<br />
broad overview of the actions of naltrexone and its use <strong>in</strong><br />
the treatment of opiate dependence can be found <strong>in</strong> a review<br />
by Kreek et al [638453].<br />
Several factors make the worldwide extent of abuse of<br />
and/or dependence on alcohol or opiates hard to quantify<br />
accurately. The dist<strong>in</strong>ction between heavy use and<br />
dependence is regularly blurred and the quoted figures are<br />
often outdated, but it has been claimed that around 10 to 14<br />
million <strong>in</strong>dividuals <strong>in</strong> the US are alcohol dependent<br />
[631992], [637673]. Several gender-l<strong>in</strong>ked differences are<br />
associated with alcohol use and dependence. One example<br />
of such a difference is <strong>in</strong> <strong>in</strong>cidence: an estimated 14% of men<br />
and 5% of women <strong>in</strong> the US will experience symptoms of<br />
alcohol abuse or dependence dur<strong>in</strong>g their lifetime [637682].<br />
Naltrexone is one of several therapeutic options for treat<strong>in</strong>g<br />
opiate or alcohol dependence. Despite its oral<br />
adm<strong>in</strong>istration, a major limitation with this treatment is poor<br />
patient compliance [593795]. One of several contributors to<br />
this poor compliance may be the high plasma levels of the<br />
metabolite 6β-naltrexol that result from first-pass<br />
metabolism [638460]. The presence of this metabolite has<br />
been correlated with both treatment dropout [638459] and<br />
an <strong>in</strong>creas<strong>in</strong>g <strong>in</strong>cidence of side effects [631898]. In a study by<br />
K<strong>in</strong>g et al, <strong>in</strong>dividuals who experienced more side effects<br />
had significantly higher ur<strong>in</strong>ary levels of 6β-naltrexol<br />
follow<strong>in</strong>g oral naltrexone treatment [638460]. In contrast,<br />
there is some evidence that the metabolite could be valuable<br />
<strong>in</strong> the treatment of opiate addicts; a reduction of the<br />
withdrawal effects associated with µ-opioid receptor
82 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
antagonism by 6β-naltrexol may offer an advantage <strong>in</strong><br />
treat<strong>in</strong>g opioid overdose and addiction [638466]. More<br />
certa<strong>in</strong> contributors to poor patient compliance with oral<br />
naltrexone <strong>in</strong>clude fluctuat<strong>in</strong>g levels of naltrexone <strong>in</strong> the<br />
body and a lack of susta<strong>in</strong>ed motivation for overcom<strong>in</strong>g the<br />
addiction [616446], [636722].<br />
Because of the problems with side effects and patient<br />
compliance, several long-act<strong>in</strong>g naltrexone preparations<br />
have been explored by various research laboratories and<br />
cl<strong>in</strong>ics s<strong>in</strong>ce the early 1970s [441894], [616446], [637696],<br />
[637699], but many rema<strong>in</strong>ed experimental and lack product<br />
licenses [636732]. Reported reasons for the failure to<br />
commercialize these products <strong>in</strong>clude a paucity of evidence<br />
of clear success, naltrexone-release problems and <strong>in</strong>jectionsite<br />
reactions [616446], but a lack of <strong>in</strong>terest <strong>in</strong> develop<strong>in</strong>g<br />
these products also seems to have played a role [636732].<br />
Despite these hurdles, the development of Vivitrex, a depotrelease<br />
naltrexone product, is almost complete, and the<br />
product is near<strong>in</strong>g approval <strong>in</strong> the US [624146]. Similar<br />
products <strong>in</strong> development <strong>in</strong>clude a susta<strong>in</strong>ed-release,<br />
<strong>in</strong>jectable depot formulation of naltrexone from DrugAbuse<br />
Sciences Inc, which had reached phase III cl<strong>in</strong>ical trials for<br />
opiate dependence by 2002 [455296], and an implant for<br />
opiate dependence (naltrexone-poly(DL-lactide)) which has<br />
been used experimentally for several years <strong>in</strong> Australia. By<br />
2003, the DrugAbuse Sciences product had successfully<br />
completed one phase III cl<strong>in</strong>ical trial for alcoholism [475512],<br />
[638704] and the Food and Drug Adm<strong>in</strong>istration has agreed<br />
on the protocol for a second, pivotal phase III cl<strong>in</strong>ical trial <strong>in</strong><br />
alcohol-dependent patients. If this trial is successful,<br />
DrugAbuse Sciences expects that the product could be<br />
approved <strong>in</strong> the US and <strong>in</strong> Europe <strong>in</strong> 2008 [638704]. The<br />
naltrexone implant product is <strong>in</strong> development by Go<br />
Medical Industries Pty Ltd and is currently undergo<strong>in</strong>g<br />
cl<strong>in</strong>ical trials [631995].<br />
To date, Vivitrex has only reached phase II cl<strong>in</strong>ical trials for<br />
opiate dependence and, because of a lack of results for this<br />
<strong>in</strong>dication, this review will concentrate primarily on alcohol<br />
dependence. Successful phase III cl<strong>in</strong>ical trial results have<br />
lead Alkermes to predict a 2006 launch of Vivitrex for<br />
alcohol dependence [632485], and the FDA was scheduled to<br />
rule on US approval for this <strong>in</strong>dication by the end of 2005<br />
[624146].<br />
Synthesis and SAR<br />
Vivitrex is an extended-release depot <strong>in</strong>jection of naltrexone<br />
<strong>in</strong> which the active <strong>in</strong>gredient is encapsulated <strong>in</strong>to<br />
biodegradable polymer microspheres. These are fabricated<br />
from poly-lactide co-glycolide (PLG), a common medical<br />
polymer used <strong>in</strong> absorbance and extended-release<br />
pharmaceuticals, to form microspheres approximately 100<br />
µm <strong>in</strong> diameter [616446]. Alkermes's proprietary Medisorb<br />
technology is used to produce microspheres that, follow<strong>in</strong>g<br />
subcutaneous or <strong>in</strong>tramuscular adm<strong>in</strong>istration, can ma<strong>in</strong>ta<strong>in</strong><br />
a steady release rate of naltrexone <strong>in</strong>to the bloodstream for<br />
up to 1 month [593795], [616446].<br />
Follow<strong>in</strong>g <strong>in</strong>jection <strong>in</strong>to the body, PLG hydrolyzes to lactic<br />
and glycolic acids. These naturally occurr<strong>in</strong>g metabolic<br />
<strong>in</strong>termediates are further metabolized <strong>in</strong>to carbon dioxide<br />
and water. The ratio of lactide to glycolide <strong>in</strong> the polymer,<br />
the molecular weight of the polymer, and other<br />
manufactur<strong>in</strong>g conditions all <strong>in</strong>fluence the rate of release of<br />
the drug from the microsphere [616443].<br />
Precl<strong>in</strong>ical development<br />
Studies conducted <strong>in</strong> animals confirmed that a s<strong>in</strong>gle dose of<br />
Vivitrex can antagonize the effects of morph<strong>in</strong>e over a<br />
period of at least 4 weeks [616446]. In the rat hot plate test,<br />
the effect of placebo or Vivitrex on morph<strong>in</strong>e-<strong>in</strong>duced<br />
analgesia was assessed over a period of up to 70 days.<br />
Basel<strong>in</strong>e test<strong>in</strong>g was conducted prior to rats be<strong>in</strong>g assigned<br />
to a treatment group. Every 5 days, analgesia was <strong>in</strong>duced<br />
with an <strong>in</strong>traperitoneal <strong>in</strong>jection of morph<strong>in</strong>e (1 mg/kg) and<br />
the latency of hot plate response was detected 30 m<strong>in</strong> later.<br />
Rats pre-dosed with Vivitrex (50 mg/kg) adm<strong>in</strong>istered<br />
subcutaneously or <strong>in</strong>tramuscularly showed a reduced<br />
latency from day 1 to day 28 follow<strong>in</strong>g <strong>in</strong>jection (40 ± 0.54 s<br />
and 36 ± 0.40 s follow<strong>in</strong>g subcutaneous and <strong>in</strong>tramuscular<br />
<strong>in</strong>jection, respectively) compared with placebo-treated rats<br />
(57 ± 0.60 s), suggest<strong>in</strong>g a substantial block of morph<strong>in</strong>e<br />
analgesia. Studies <strong>in</strong>volv<strong>in</strong>g a second <strong>in</strong>tramuscular<br />
<strong>in</strong>jection of Vivitrex (50 mg/kg), adm<strong>in</strong>istered on day 34,<br />
were conducted <strong>in</strong> the same model; an <strong>in</strong>tramuscular<br />
<strong>in</strong>jection was used because it was thought to be the best<br />
route for Vivitrex adm<strong>in</strong>istration to humans. This <strong>in</strong>jection<br />
produced a similar effect to the <strong>in</strong>itial treatment and<br />
suppressed morph<strong>in</strong>e-<strong>in</strong>duced analgesia up to day 68 of the<br />
study [616446].<br />
Vivitrex-<strong>in</strong>duced changes <strong>in</strong> µ-opioid receptor density and<br />
immunoreactivity were assessed <strong>in</strong> rats from the same<br />
experimental groups. As mentioned previously, the µ-opioid<br />
receptor appears to be the opioid receptor that is most<br />
strongly l<strong>in</strong>ked to alcohol and opiate dependencies [638453].<br />
Rats were sacrificed over a range of days (from day 3 to day<br />
40) and µ-opioid receptor density was exam<strong>in</strong>ed <strong>in</strong> saturation<br />
b<strong>in</strong>d<strong>in</strong>g assays us<strong>in</strong>g [ 3H]DAMGO (D-ala 2, N-methyl-phe 4,<br />
glycol 5-enkephal<strong>in</strong>) and us<strong>in</strong>g autoradiography and<br />
immunoreactivity [616446]. Receptor density <strong>in</strong>creased up to<br />
2-fold follow<strong>in</strong>g a s<strong>in</strong>gle <strong>in</strong>tramuscular <strong>in</strong>jection of Vivitrex<br />
(50 mg/kg). Receptor density <strong>in</strong> the midbra<strong>in</strong> and striatum<br />
<strong>in</strong>creased with<strong>in</strong> 7 days by 100 and 110%, respectively,<br />
compared with placebo treatment, whereas density <strong>in</strong> the<br />
cortex <strong>in</strong>creased by 120% between days 32 and 40 [616446].<br />
No specific reason is known for these regional differences,<br />
but the distribution, b<strong>in</strong>d<strong>in</strong>g and elim<strong>in</strong>ation characteristics<br />
of naltrexone <strong>in</strong> bra<strong>in</strong> tissue may be relevant <strong>in</strong> determ<strong>in</strong><strong>in</strong>g<br />
which regions of this organ are most closely l<strong>in</strong>ked to<br />
dependency [616446].<br />
Similar results were obta<strong>in</strong>ed us<strong>in</strong>g radioligand b<strong>in</strong>d<strong>in</strong>g<br />
autoradiography <strong>in</strong> rats receiv<strong>in</strong>g one or two <strong>in</strong>tramuscular<br />
<strong>in</strong>jections of Vivitrex (50 mg/kg) 34 days apart, monitored 1<br />
or 2 months after the <strong>in</strong>itial <strong>in</strong>jection [616446]. Radioligand<br />
b<strong>in</strong>d<strong>in</strong>g was significantly <strong>in</strong>creased <strong>in</strong> all bra<strong>in</strong> regions<br />
studied, rang<strong>in</strong>g from 90% <strong>in</strong> the habenular nucleus to 160%<br />
<strong>in</strong> the dorsal raphe nucleus after 1 month. In the majority of<br />
regions, density <strong>in</strong>creased further <strong>in</strong> the follow<strong>in</strong>g month,<br />
reach<strong>in</strong>g 120% <strong>in</strong> the habenular nucleus and 220% <strong>in</strong> the
dorsal raphe nucleus. Immunohistochemistry at adjacent<br />
bra<strong>in</strong> sections revealed <strong>in</strong>creased µ-opioid receptor<br />
immunoreactivity at both 1 and 2 months after Vivitrex<br />
<strong>in</strong>jection; however, the effect was less than <strong>in</strong> the<br />
autoradiography studies, with only two of the 15 bra<strong>in</strong><br />
regions exam<strong>in</strong>ed show<strong>in</strong>g significant <strong>in</strong>creases over control<br />
after 1 month. The <strong>in</strong>vestigators of the report <strong>in</strong>terpreted the<br />
large <strong>in</strong>crease <strong>in</strong> µ-opioid receptor density, but small<br />
<strong>in</strong>crease <strong>in</strong> µ-opioid receptor immunoreactivity, as evidence<br />
of recruitment of active µ-opioid receptors from a pool of<br />
receptors, rather than an <strong>in</strong>crease <strong>in</strong> µ-opioid receptor<br />
prote<strong>in</strong> expression [616446].<br />
Metabolism and pharmacok<strong>in</strong>etics<br />
A s<strong>in</strong>gle <strong>in</strong>tramuscular or subcutaneous <strong>in</strong>jection of Vivitrex (50<br />
mg/kg) produced stable, pharmacologically relevant plasma<br />
concentrations <strong>in</strong> rats for approximately 1 month. AUC values<br />
of 332 and 360 ng.day/ml were observed follow<strong>in</strong>g<br />
<strong>in</strong>tramuscular and subcutaneous adm<strong>in</strong>istration, respectively.<br />
Maximum naltrexone plasma levels (15 ± 1.4 and 19 ± 3.6<br />
ng/ml follow<strong>in</strong>g subcutaneous and <strong>in</strong>tramuscular<br />
adm<strong>in</strong>istration of Vivitrex, respectively) were produced with<strong>in</strong><br />
3 days, with half-maximum levels reached with<strong>in</strong> 24 h. By 35<br />
days, naltrexone plasma concentrations were approach<strong>in</strong>g<br />
undetectable levels (< 1 ng/ml), and a similar pattern was<br />
observed follow<strong>in</strong>g a second Vivitrex <strong>in</strong>jection [616446].<br />
Naltrexone is primarily metabolized by the liver, produc<strong>in</strong>g the<br />
major metabolite 6β-naltrexol. This metabolite can be detected<br />
<strong>in</strong> both conjugated and non-conjugated form <strong>in</strong> plasma.<br />
Follow<strong>in</strong>g oral adm<strong>in</strong>istration, 1% of unchanged naltrexone is<br />
excreted <strong>in</strong> ur<strong>in</strong>e [631898]. The half-life of oral naltrexone <strong>in</strong><br />
humans is 4 to 9 h, compared with 12 to 18 h for 6β-naltrexol<br />
[631895], but us<strong>in</strong>g the Vivitrex formulation, the half-lives of<br />
naltrexone and 6β-naltrexol are greatly extended, and are<br />
quoted as 5 to 8 days [636722]. The pharmacok<strong>in</strong>etic benefits of<br />
the extended-release <strong>in</strong>jection compared with oral dos<strong>in</strong>g<br />
<strong>in</strong>clude an absence of high peak plasma concentrations, a<br />
decrease <strong>in</strong> gastro<strong>in</strong>test<strong>in</strong>al exposure, and avoidance of firstpass<br />
hepatic metabolism [616446]. Compared with oral<br />
naltrexone, Vivitrex reduces the ratio of 6β-naltrexol to the<br />
parent compound <strong>in</strong> the body [593795], [616443], which is<br />
consistent with f<strong>in</strong>d<strong>in</strong>gs of studies with other extended-release<br />
preparations. This reduction is thought to result from<br />
avoidance of the first-pass effect [631898].<br />
In a phase I, double-bl<strong>in</strong>d cl<strong>in</strong>ical trial, 42 healthy volunteers<br />
were randomized to receive placebo or Vivitrex as a s<strong>in</strong>gle<br />
<strong>in</strong>tramuscular (150, 300, 600 or 900 mg) or subcutaneous<br />
(150, 300 or 600 mg) <strong>in</strong>jection [390669]. Prelim<strong>in</strong>ary data<br />
regard<strong>in</strong>g plasma levels of naltrexone showed that the AUC<br />
and Cmax values were dose proportional, with slightly higher<br />
values observed follow<strong>in</strong>g <strong>in</strong>tramuscular dos<strong>in</strong>g (at 150, 300<br />
and 600 mg; <strong>in</strong>tramuscular AUC values of 49 ± 9, 84 ± 12 and<br />
189 ± 27 ng.day/ml were observed compared with<br />
subcutaneous AUC values of 31 ± 11, 65 ± 13 and 145 ± 28<br />
ng.day/ml, respectively). The <strong>in</strong>itial drug 'burst' (with<strong>in</strong> 48<br />
h) demonstrated a peak concentration that was only<br />
approximately 3-fold higher than steady-state levels, which<br />
were dose proportional, with<strong>in</strong> expected therapeutic levels,<br />
and ma<strong>in</strong>ta<strong>in</strong>ed for a full month [390669].<br />
Vivitrex Head<strong>in</strong>g 83<br />
Results from a phase II cl<strong>in</strong>ical trial <strong>in</strong> 30 alcohol-dependent<br />
patients adm<strong>in</strong>istered <strong>in</strong>tramuscular Vivitrex (400 mg)<br />
showed that mean trough serum naltrexone concentrations<br />
rema<strong>in</strong>ed relatively constant throughout the study (1.23<br />
ng/ml). Mean serum trough levels of 6β-naltrexol (2.91<br />
ng/ml) were slightly higher than naltrexone, but<br />
substantially lower than those observed follow<strong>in</strong>g oral<br />
naltrexone adm<strong>in</strong>istration. As outl<strong>in</strong>ed above, lower levels<br />
of 6β-naltrexol are thought to reduce the chances of adverse<br />
events and improve patient compliance [616443].<br />
Because <strong>in</strong>dividuals who consume large quantities of<br />
alcohol often suffer from liver damage, the<br />
pharmacok<strong>in</strong>etics of Vivitrex were exam<strong>in</strong>ed <strong>in</strong> patients<br />
with mild-to-moderate hepatic impairment [636722]. Six<br />
<strong>in</strong>dividuals with mild (Child-Pugh grade A) or moderate<br />
(Child-Pugh grade B) hepatic impairment and 13 healthy<br />
<strong>in</strong>dividuals each received a s<strong>in</strong>gle <strong>in</strong>tramuscular dose of<br />
Vivitrex (190 mg). The total exposure (AUC0-∞) of naltrexone<br />
and 6β-naltrexol was similar across all groups over 63 days<br />
(treatment comparison ratios were 0.97 and 1.08 for mild<br />
and moderate hepatic impairment, respectively, compared<br />
with control), <strong>in</strong>dicat<strong>in</strong>g that no dosage adjustment would<br />
be needed for alcohol users with impaired liver function<br />
[636722].<br />
Toxicity<br />
No toxic effects have been reported <strong>in</strong> animal studies,<br />
although the <strong>in</strong>creased density of µ-opioid receptors<br />
observed <strong>in</strong> rats poses a theoretical risk <strong>in</strong> the context of<br />
opiate abuse. Similar, long-last<strong>in</strong>g receptor changes have<br />
been observed with other naltrexone formulations and can<br />
potentially enhance hypersensitivity to opiates. The effects<br />
have also been observed with other opiate antagonists, and<br />
it has been suggested that the change results from the<br />
recruitment of receptors from a pool of receptors <strong>in</strong> response<br />
to the presence of antagonists [616446]. From <strong>in</strong>direct<br />
evidence, it has been suggested that the enhanced<br />
hypersensitivity <strong>in</strong>duced by Vivitrex is unlikely to <strong>in</strong>crease<br />
the euphoria, respiratory depression and tolerance that can<br />
result from the <strong>in</strong>take of opiates [616446]. In contrast, there<br />
is long-stand<strong>in</strong>g experimental evidence that hypersensitivity<br />
to the analgesic effects of opiates can occur after naltrexone<br />
exposure [638481], [638482].<br />
Cl<strong>in</strong>ical development<br />
Phase I<br />
In the phase I, randomized, double-bl<strong>in</strong>d, placebo-controlled<br />
study <strong>in</strong> which 42 healthy volunteers received either placebo<br />
or s<strong>in</strong>gle doses of Vivitrex <strong>in</strong> an escalat<strong>in</strong>g-dose paradigm<br />
(<strong>in</strong>tramuscular <strong>in</strong>jections of 150, 300, 600 or 900 mg, or<br />
subcutaneous <strong>in</strong>jections of 150, 300 or 600 mg), therapeutic<br />
levels of naltrexone were susta<strong>in</strong>ed for 1 month. In order for<br />
equivalent plasma levels to be achieved over this period<br />
us<strong>in</strong>g oral naltrexone, the total naltrexone dose would need<br />
to be 5-fold higher [393208].<br />
Phase II<br />
A multicenter, randomized, double-bl<strong>in</strong>d, placebocontrolled<br />
pilot study was conducted with 30 patients with a<br />
DSM-IV diagnosis of alcohol-dependence. Vivitrex (400 mg)
84 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
was adm<strong>in</strong>istered <strong>in</strong>tramuscularly once a month for 4 months<br />
to 25 patients, and the rema<strong>in</strong><strong>in</strong>g patients were given placebo;<br />
both groups were offered psychosocial support [494451],<br />
[616443]. At the end of this period, the mean percentage of<br />
heavy dr<strong>in</strong>k<strong>in</strong>g days <strong>in</strong> the Vivitrex group was reduced to half<br />
that of the placebo group (11.7% compared with 25.3%).<br />
Patients treated with Vivitrex also showed an <strong>in</strong>crease <strong>in</strong> the<br />
mean percentage of days abst<strong>in</strong>ent from alcohol (69.4%<br />
compared with 39.2% pre-treatment) and a reduction <strong>in</strong> the<br />
number of dr<strong>in</strong>ks consumed per dr<strong>in</strong>k<strong>in</strong>g day (3.8 compared<br />
with 7.4 pre-treatment) [616443].<br />
A trial designed to determ<strong>in</strong>e the pharmacok<strong>in</strong>etics and<br />
safety of a range of Vivitrex doses <strong>in</strong> opiate-dependent<br />
<strong>in</strong>dividuals was <strong>in</strong>itiated <strong>in</strong> 2002 [445176], but by November<br />
2005, no results were apparently available.<br />
Phase III<br />
A 6-month, double-bl<strong>in</strong>d, placebo-controlled, randomized<br />
study was conducted at 24 centers <strong>in</strong> 624 patients (423 men<br />
and 201 women) with DSM-IV-diagnosed alcohol<br />
dependence [593795]. All study groups were matched for<br />
men and women and patients received monthly<br />
<strong>in</strong>tramuscular <strong>in</strong>jections of Vivitrex (190 or 380 mg; n = 210<br />
and 205, respectively) or placebo (n = 209). All groups also<br />
received low-<strong>in</strong>tensity counsel<strong>in</strong>g. Patients receiv<strong>in</strong>g 380 mg<br />
Vivitrex showed a 25% reduction <strong>in</strong> heavy dr<strong>in</strong>k<strong>in</strong>g (def<strong>in</strong>ed<br />
as five or more dr<strong>in</strong>ks per day for men and four dr<strong>in</strong>ks per<br />
day for women) compared with the placebo group (p =<br />
0.02). In patients receiv<strong>in</strong>g 190 mg Vivitrex, heavy dr<strong>in</strong>k<strong>in</strong>g<br />
was reduced by 17% compared with patients receiv<strong>in</strong>g<br />
placebo (p = 0.07). Overall, the median number of heavy<br />
dr<strong>in</strong>k<strong>in</strong>g days <strong>in</strong> the group receiv<strong>in</strong>g 380 mg Vivitrex was<br />
reduced from 19 to 3 days a month [593795].<br />
Consider<strong>in</strong>g each gender separately, the number of heavy<br />
dr<strong>in</strong>k<strong>in</strong>g days for males receiv<strong>in</strong>g the high dose of Vivitrex fell<br />
by 48% compared with males given placebo (p < 0.0001),<br />
whereas the results from females treated with Vivitrex did not<br />
differ from those given placebo. Similarly, males adm<strong>in</strong>istered<br />
low-dose Vivitrex showed a 25% reduction <strong>in</strong> heavy dr<strong>in</strong>k<strong>in</strong>g<br />
days compared with placebo (p < 0.03), but there was no<br />
difference between the results from females treated with either<br />
Vivitrex or placebo [516479], [593795].<br />
Results of an open-label, 12-month extension trial that enrolled<br />
85% of <strong>in</strong>dividuals who completed the <strong>in</strong>itial phase III trial<br />
were presented <strong>in</strong> May 2005 [603348]. The results confirmed the<br />
susta<strong>in</strong>ed efficacy of Vivitrex. The trial recruited 115 of the 380mg<br />
dose patients, 102 of the 190-mg group and 60 patients from<br />
the placebo group. Gender was not a recruitment criterion.<br />
Patients from the placebo group were randomized to receive<br />
either 380 or 190 mg Vivitrex by monthly <strong>in</strong>tramuscular<br />
<strong>in</strong>jection. Patients <strong>in</strong> the high-dose group showed a reduction<br />
(not claimed as significant) <strong>in</strong> the median number of heavy<br />
dr<strong>in</strong>k<strong>in</strong>g days per month from 2.6 to 1.6 days. Patients switched<br />
from placebo to 380 mg Vivitrex showed a reduction <strong>in</strong> heavy<br />
dr<strong>in</strong>k<strong>in</strong>g days from 5.2 to 1.8 days per month [603348].<br />
There was evidence of a physiological improvement<br />
secondary to the reduction of alcohol <strong>in</strong>take from both the<br />
phase II and III trials, as <strong>in</strong>dicated by a reduction <strong>in</strong> the level<br />
of the hepatic enzyme γ-glutamyl transferase (GGT; a liver<br />
enzyme raised <strong>in</strong> ~ 70% of alcohol abusers that is frequently<br />
used as a marker of reduced alcohol <strong>in</strong>take) [638730]. A<br />
mean reduction <strong>in</strong> serum activity of GGT was observed <strong>in</strong><br />
both the phase II cl<strong>in</strong>ical trial [616443] and <strong>in</strong> the phase III<br />
cl<strong>in</strong>ical trial [593795].<br />
Side effects and contra<strong>in</strong>dications<br />
As discussed, Vivitrex is designed to reduce a number of<br />
problems associated with other naltrexone formulations,<br />
<strong>in</strong>clud<strong>in</strong>g the high concentration of its primary metabolite,<br />
which may contribute significantly to the side effects<br />
observed with oral naltrexone. In studies with other<br />
naltrexone formulations, 6β-naltrexol was l<strong>in</strong>ked with<br />
subjective reports of headache, nausea and anxiety [631898].<br />
Prelim<strong>in</strong>ary analysis of the results from cl<strong>in</strong>ical trials<br />
<strong>in</strong>dicated that Vivitrex was well tolerated and demonstrated<br />
no serious adverse events <strong>in</strong> healthy volunteers [390669],<br />
f<strong>in</strong>d<strong>in</strong>gs that were subsequently confirmed <strong>in</strong> patient trials.<br />
However, the side effects of substance dependence<br />
treatments often depend on the substance be<strong>in</strong>g abused.<br />
Substance abusers often fail to adhere to the planned<br />
therapeutic program so that the treatment drug may at some<br />
po<strong>in</strong>t be used alongside the abused substance. Thus, the<br />
risks associated with the use of Vivitrex for alcohol<br />
dependence differ from those that arise when the product is<br />
used for opiate dependence. It is also noteworthy that<br />
abusers might <strong>in</strong>crease their level of usage <strong>in</strong> order to<br />
surmount a blockade of effect produced by Vivitrex.<br />
In a phase II trial of 30 patients with alcohol dependence, an<br />
<strong>in</strong>tramuscular <strong>in</strong>jection of Vivitrex (400 mg) was generally safe<br />
and well tolerated, and reported adverse effects were mild to<br />
moderate. Nausea and headache were the most common<br />
adverse events, and both occurred equally <strong>in</strong> the placebo- and<br />
Vivitrex-treated groups [432929]. However, two patients<br />
discont<strong>in</strong>ued participation <strong>in</strong> the study because of adverse<br />
events (<strong>in</strong>jection site <strong>in</strong>duration and angioedema). Both events<br />
occurred after the second, monthly dose of Vivitrex and were<br />
moderate <strong>in</strong> severity [616443].<br />
In the 6-month, 624-patient phase III trial <strong>in</strong>volv<strong>in</strong>g alcoholdependent,<br />
active dr<strong>in</strong>kers, trial discont<strong>in</strong>uation ow<strong>in</strong>g to<br />
adverse events occurred <strong>in</strong> 14.1% of the 380-mg naltrexone<br />
group, 6.7% of the 190-mg group, and 6.7% of the placebo<br />
group [593795]. At least 10% of patients experienced some<br />
form of adverse event follow<strong>in</strong>g Vivitrex treatment, but less<br />
than 2% of patients discont<strong>in</strong>ued treatment because of<br />
<strong>in</strong>jection-site reaction [534413]. The most common adverse<br />
effects <strong>in</strong> the ma<strong>in</strong> trial were nausea, headache and fatigue,<br />
all of which have been observed with oral naltrexone<br />
formulations [593795]. Nausea was mild or moderate <strong>in</strong> 95%<br />
of cases, and usually occurred dur<strong>in</strong>g the first month. As<br />
well as loss of appetite, this was the most common adverse<br />
event <strong>in</strong> the 380-mg dose group. The frequency of serious<br />
adverse effects dur<strong>in</strong>g the trial was similar <strong>in</strong> all treatment<br />
groups, the most common be<strong>in</strong>g hospitalization for alcohol<br />
<strong>in</strong>toxication. However, two cases of pneumonia occurred <strong>in</strong><br />
the 380-mg group and, although not observed with<br />
naltrexone or microsphere medications previously, may
have been related to Vivitrex. Mean levels of alan<strong>in</strong>e<br />
am<strong>in</strong>otransferase and aspartate am<strong>in</strong>otransferase did not<br />
change significantly, <strong>in</strong>dicat<strong>in</strong>g a lack of hepatotoxicity<br />
[593795]. The most common adverse effects <strong>in</strong> the 12-month<br />
extension trial were headache, nasopharyngitis and<br />
respiratory tract <strong>in</strong>fections [603348].<br />
Patent summary<br />
Naltrexone was orig<strong>in</strong>ally claimed by Endo Laboratories Inc<br />
<strong>in</strong> 1967 (US-03332950). This patent expired <strong>in</strong> 1984, and by<br />
the late 1980s, any basic product protection elsewhere had<br />
also expired. The Medisorb extended-release technology was<br />
first claimed <strong>in</strong> WO-09742940 and granted as US-05817343<br />
and EP-00914095 <strong>in</strong> July 2002. Orig<strong>in</strong>ally developed by<br />
Medisorb Technologies International LP, the method was<br />
acquired by Alkermes <strong>in</strong> 1996.<br />
The patent status for Vivitrex will be resolved when it has been<br />
granted FDA approval (which was expected <strong>in</strong> December 2005)<br />
and a selection of relevant patents is subsequently published <strong>in</strong><br />
the Orange Book. Alkermes has claims to various patents<br />
cover<strong>in</strong>g areas such as the <strong>in</strong>jectable, extended-release of<br />
naltrexone compositions (WO-2004103342) and amorphous and<br />
polymorphic forms of naltrexone, which are reported to be<br />
advantageous <strong>in</strong> extended-release formulations (WO-<br />
2004108084). Moreover, two further patent applications (WO-<br />
2005089449 and WO-2005089486) cover comb<strong>in</strong>ations of<br />
naltrexone with an anticonvulsant or a dopam<strong>in</strong>e D2 partial<br />
agonist for treat<strong>in</strong>g alcoholism.<br />
<strong>Current</strong> op<strong>in</strong>ion<br />
A full understand<strong>in</strong>g of how opioids <strong>in</strong>fluence reward<br />
pathways is not yet available, but occupancy of opioid<br />
receptors by endogenous peptides or opiate drugs is known<br />
to <strong>in</strong>fluence the MLDS [631895]. Most experts <strong>in</strong> the field of<br />
neuroscience consider that this pathway plays a major role<br />
<strong>in</strong> reward mechanisms and drug-seek<strong>in</strong>g behavior, and<br />
believe that the sensitization of the MLDS observed <strong>in</strong><br />
dependence reflects a form of learnt or conditioned<br />
behavior. The various behavioral hypotheses that attempt to<br />
expla<strong>in</strong> dependence generally share the view that the effect<br />
experienced after substance <strong>in</strong>take re<strong>in</strong>forces the substanceseek<strong>in</strong>g<br />
behavior [636843]. If the l<strong>in</strong>k between <strong>in</strong>take and<br />
effect is broken (eg, by pharmacotherapeutic means) the<br />
learnt behavior can be overcome [631895], [636843].<br />
Pharmacotherapy alone rarely succeeds <strong>in</strong> elim<strong>in</strong>at<strong>in</strong>g<br />
dependence, but where patients have the correct motivation<br />
and psychosocial support, reductions <strong>in</strong> dependence can be<br />
achieved. It is therefore reasonable for cl<strong>in</strong>ical trials to<br />
<strong>in</strong>corporate both pharmacological and psychological<br />
elements. However, when <strong>in</strong>terpret<strong>in</strong>g the results of the<br />
phase II and phase III cl<strong>in</strong>ical trials of Vivitrex to date, it<br />
should be noted that they are placebo-controlled trials and<br />
do not compare psychosocial therapy alone with<br />
psychosocial therapy plus Vivitrex. It is perfectly possible<br />
that psychological elements of a placebo effect contributed<br />
to the improvements <strong>in</strong> the placebo-treated groups, and the<br />
design of the studies has wisely avoided the need to<br />
establish whether this is the case. It is also possible that<br />
genders respond differently to the psychological elements of<br />
treatment and much here rema<strong>in</strong>s to be elucidated.<br />
Vivitrex Head<strong>in</strong>g 85<br />
As discussed previously, the value of oral naltrexone <strong>in</strong> the<br />
long-term treatment of alcohol or opiate dependence has been<br />
greatly underm<strong>in</strong>ed by the failure of the substance abusers to<br />
adhere to the daily dos<strong>in</strong>g schedule [593795]. A reliable<br />
extended-release preparation that uses the <strong>in</strong>tramuscular route<br />
should provide an answer to the fluctuat<strong>in</strong>g plasma levels of<br />
naltrexone and high plasma levels of the naltrexone metabolite,<br />
and circumvent the changeable motivation seen <strong>in</strong> the users.<br />
Vivitrex is therefore likely to be welcomed as a new treatment<br />
for alcohol dependence that can be <strong>in</strong>itiated <strong>in</strong> active dr<strong>in</strong>kers,<br />
especially when consider<strong>in</strong>g the current absence of any truly<br />
satisfactory alternative products. Disulfiram and acamprosate<br />
are options for therapeutic <strong>in</strong>tervention <strong>in</strong> alcohol abuse, but<br />
both have limitations and, <strong>in</strong> contrast to Vivitrex, are not<br />
considered suitable for <strong>in</strong>itiation <strong>in</strong> active alcohol users<br />
[631992], [638487]. Disulfiram relies on an aversive effect<br />
produced by altered metabolism of ethyl alcohol, but the<br />
adverse side effects associated with this drug can be severe and<br />
even fatal [631992], [638487]. Acamprosate is thought to act on<br />
γ-am<strong>in</strong>obutyric acid and glutam<strong>in</strong>ergic receptors, with at least<br />
some of its actions be<strong>in</strong>g focused on the NA [631992].<br />
To date, the efficacy of Vivitrex has been confirmed for<br />
alcohol dependence only and, specifically, only <strong>in</strong> men. The<br />
trial report suggests that the difference <strong>in</strong> efficacy may be a<br />
consequence of different patient characteristics (eg, weight,<br />
smok<strong>in</strong>g and use of antidepressants) rather than a<br />
fundamental gender difference, but establish<strong>in</strong>g widespread<br />
efficacy <strong>in</strong> women may be difficult. Cl<strong>in</strong>icians may also be<br />
reluctant to use depot preparations <strong>in</strong> women who might<br />
become pregnant because of the universal pr<strong>in</strong>cipal of<br />
m<strong>in</strong>imiz<strong>in</strong>g medication dur<strong>in</strong>g the first trimester. A nonchemical<br />
treatment or one that can be halted abruptly might<br />
be preferred for women of childbear<strong>in</strong>g age.<br />
Should Vivitrex be developed further for opiate dependence,<br />
the safety issues will be different to those for alcohol<br />
dependence. Naltrexone is currently prescribed only for<br />
opiate addicts who are not active users because this agent<br />
can precipitate opiate withdrawal effects <strong>in</strong> active opiate<br />
users [631992]. Thus, to combat opiate abuse, Vivitrex might<br />
be more suited to use <strong>in</strong> an <strong>in</strong>-patient, rather than<br />
community, environment, where it would be harder for<br />
users to <strong>in</strong>crease their opiate <strong>in</strong>take <strong>in</strong> an attempt to<br />
surmount the naltrexone-<strong>in</strong>duced opioid antagonism.<br />
F<strong>in</strong>ally, it should be acknowledged that a great deal rema<strong>in</strong>s<br />
to be understood regard<strong>in</strong>g dependence on opiates and<br />
alcohol as well as appropriate treatments. For example, µopioid<br />
receptors have been researched and implicated <strong>in</strong><br />
dependence far more than δ- and κ-opioid receptors, which<br />
may also be <strong>in</strong>volved. At the receptor level, adaptive<br />
responses to alcohol or opiates are known to occur, and<br />
adaptive responses to antagonists are also observed. These<br />
responses have been observed with Vivitrex treatment, and<br />
the implications of such responses are not yet clear. In<br />
addition, from the behavioral po<strong>in</strong>t of view, the possible<br />
beneficial action of Vivitrex on crav<strong>in</strong>g has not yet been<br />
explored. Overall, it seems probable that Vivitrex has the<br />
capacity to make a significant contribution to the treatment<br />
of dependence long before its detailed mode of action has<br />
been elucidated.
86 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
Commercial op<strong>in</strong>ion<br />
In November 2005, an analyst from SunTrust Rob<strong>in</strong>son<br />
Humphrey stated that they believed that it would take some<br />
time to build the market for Vivitrex for alcoholism, and that<br />
peak sales could reach US $250 million <strong>in</strong> the future.<br />
Predicted sales of Vivitrex <strong>in</strong> fiscal 2007 (beg<strong>in</strong>n<strong>in</strong>g <strong>in</strong><br />
the second quarter of 2006) were estimated at<br />
US $65 million, lead<strong>in</strong>g to sales of US $110 million <strong>in</strong><br />
fiscal 2008, ris<strong>in</strong>g to US $175 million <strong>in</strong> fiscal 2010<br />
[638339].<br />
Licens<strong>in</strong>g<br />
Cephalon Inc<br />
In June 2005, Cephalon agreed to jo<strong>in</strong>tly develop and commercialize Vivitrex <strong>in</strong> the US. Alkermes was to receive an <strong>in</strong>itial<br />
payment of US $160 million from Cephalon and will receive an additional US $110 million if Vivitrex is approved, and could<br />
also receive up to US $220 million <strong>in</strong> milestone payments based on sales. The responsibility for develop<strong>in</strong>g the commercial<br />
strategy for the product will be shared by a jo<strong>in</strong>t commercialization team formed from both companies. Alkermes will be<br />
responsible for manufactur<strong>in</strong>g Vivitrex and seek<strong>in</strong>g market<strong>in</strong>g approval and Cephalon will conduct the market<strong>in</strong>g and sales<br />
of the product. Alkermes will be responsible for any cumulative losses of up to US $120 million until December 31 2007, or<br />
for 18 months after FDA approval. Dur<strong>in</strong>g this period, Cephalon will be liable for cumulative losses exceed<strong>in</strong>g US $120<br />
million. After that time, any pretax profit or loss will be shared equally by both companies [609280].<br />
Development history<br />
Developer Country Status Indication Date Reference<br />
Alkermes Inc US Pre-registration Alcoholism 01-APR-05 592847<br />
Cephalon Inc US Pre-registration Alcoholism 24-JUN-05 609507<br />
Alkermes Inc US Phase II Opiate dependence 22-JAN-02 435928<br />
Literature classifications<br />
Chemistry<br />
Study type Result Reference<br />
Preparation. Naltrexone is encapsulated <strong>in</strong>to biodegradable polymer microspheres (100 µm diameter) fabricated<br />
from PLG. Follow<strong>in</strong>g subcutaneous or <strong>in</strong>tramuscular adm<strong>in</strong>istration, the microspheres can ma<strong>in</strong>ta<strong>in</strong> a<br />
steady release rate of naltrexone <strong>in</strong>to the bloodstream for up to 1 month.<br />
616446<br />
Biology<br />
Study type Effect studied Model Result Reference<br />
In vivo Efficacy. The latency of response <strong>in</strong> a hot plate test Reduced latency from day 1 to 28 616446<br />
was measured <strong>in</strong> rats 30 m<strong>in</strong> after a was observed <strong>in</strong> rats pre-dosed with<br />
1.0-mg/kg <strong>in</strong>traperitoneal morph<strong>in</strong>e Vivitrex (40 ± 0.54 s and 36 ± 0.40 s<br />
<strong>in</strong>jection (adm<strong>in</strong>istered every 5 days). follow<strong>in</strong>g subcutaneous and<br />
Rats were adm<strong>in</strong>istered a s<strong>in</strong>gle 50- <strong>in</strong>tramuscular <strong>in</strong>jection, respectively)<br />
mg/kg dose of Vivitrex either<br />
compared with placebo-treated rats<br />
subcutaneously or <strong>in</strong>tramuscularly prior to<br />
test<strong>in</strong>g.<br />
(57 ± 0.60 s).<br />
In vivo Efficacy. Post-sacrifice radioligand b<strong>in</strong>d<strong>in</strong>g<br />
autoradiography assays us<strong>in</strong>g<br />
[ 3 Increased radioligand b<strong>in</strong>d<strong>in</strong>g was 616446<br />
observed <strong>in</strong> all bra<strong>in</strong> regions<br />
H]DAMGO were used to measure exam<strong>in</strong>ed, reach<strong>in</strong>g 120% <strong>in</strong> the<br />
receptor density <strong>in</strong> rats for up to 2 months habenular nucleus and 220% <strong>in</strong> the<br />
follow<strong>in</strong>g a 50-mg/kg <strong>in</strong>tramuscular<br />
<strong>in</strong>jection of Vivitrex.<br />
dorsal raphe nucleus.<br />
In vivo Efficacy. Post-sacrifice immunohistochemistry The <strong>in</strong>crease <strong>in</strong> receptor<br />
616446<br />
us<strong>in</strong>g receptor-target<strong>in</strong>g antibodies <strong>in</strong> rats immunoreactivity was less than <strong>in</strong><br />
1 or 2 months follow<strong>in</strong>g a 50-mg/kg the autoradiography studies, with<br />
<strong>in</strong>tramuscular <strong>in</strong>jection of Vivitrex.<br />
only two of the 15 bra<strong>in</strong> regions<br />
exam<strong>in</strong>ed show<strong>in</strong>g significant<br />
<strong>in</strong>creases after 1 month compared<br />
with control.<br />
Metabolism<br />
Study type Effect studied Model Result Reference<br />
In vivo Pharmacok<strong>in</strong>etics. Circulat<strong>in</strong>g levels of naltrexone <strong>in</strong> AUC = 332 and 360 ng.day/ml and Cmax = 616446<br />
rats measured 1 to 35 days 15 ± 1.4 and 19 ± 3.6 ng/ml after<br />
follow<strong>in</strong>g subcutaneous or<br />
subcutaneous and <strong>in</strong>tramuscular<br />
<strong>in</strong>tramuscular adm<strong>in</strong>istration of adm<strong>in</strong>istration of Vivitrex, respectively. By<br />
Vivitrex (50 mg/kg).<br />
day 35, drug levels were almost<br />
undetectable (< 1 ng/ml).
Metabolism (cont<strong>in</strong>ued)<br />
Vivitrex Head<strong>in</strong>g 87<br />
Study type Effect studied Model Result Reference<br />
In vivo Pharmacok<strong>in</strong>etics. Phase I, double-bl<strong>in</strong>d study of 42 AUC and Cmax were dose proportional, with 390669<br />
healthy volunteers randomized to slightly higher values observed follow<strong>in</strong>g<br />
receive placebo or Vivitrex as a <strong>in</strong>tramuscular adm<strong>in</strong>istration (AUC = 49 ±<br />
s<strong>in</strong>gle <strong>in</strong>tramuscular (150, 300, 9, 84 ± 12 and 189 ± 27 ng.day/ml at 150,<br />
600 or 900 mg) or subcutaneous 300 and 600 mg, respectively) compared<br />
(150, 300 or 600 mg) <strong>in</strong>jection. with subcutaneous adm<strong>in</strong>istration (AUC =<br />
31 ± 11, 65 ± 13 and 145 ± 28 ng.day/ml at<br />
150, 300 and 600 mg, respectively).<br />
In vivo Pharmacok<strong>in</strong>etics. Phase I, double-bl<strong>in</strong>d study of 42 Therapeutic naltrexone levels were<br />
393208<br />
healthy volunteers randomized to susta<strong>in</strong>able for a full month. Sufficient<br />
receive placebo or Vivitrex as a doses were 5-fold less than the equivalent<br />
s<strong>in</strong>gle <strong>in</strong>tramuscular (150, 300, dose required through oral naltrexone<br />
600 or 900 mg) or subcutaneous<br />
(150, 300 or 600 mg) <strong>in</strong>jection.<br />
adm<strong>in</strong>istration.<br />
In vivo Pharmacok<strong>in</strong>etics. Phase II, double-bl<strong>in</strong>d study of 30 The mean trough serum naltrexone<br />
616443<br />
healthy volunteers randomized to concentration rema<strong>in</strong>ed relatively constant<br />
receive <strong>in</strong>tramuscular Vivitrex (400 throughout the study. Serum levels of 6β-<br />
mg) or placebo once a month for 4 naltrexol were substantially lower than<br />
months.<br />
those observed follow<strong>in</strong>g oral naltrexone<br />
adm<strong>in</strong>istration.<br />
In vivo Pharmacok<strong>in</strong>etics. Control-matched study <strong>in</strong><br />
<strong>in</strong>dividuals with mild or moderate<br />
Total exposure (AUC0-∞) of naltrexone and<br />
6β-naltrexol was similar across all groups<br />
636722<br />
hepatic impairment. Six <strong>in</strong>dividuals over 63 days (treatment comparison ratios<br />
from each test group and 13 were 0.97 and 1.08 for mild and moderate<br />
healthy volunteers each received a hepatic impairment, respectively,<br />
s<strong>in</strong>gle 190-mg <strong>in</strong>tramuscular dose compared with control) <strong>in</strong>dicat<strong>in</strong>g that no<br />
of Vivitrex.<br />
dosage adjustment would be needed for<br />
alcohol users with impaired liver function.<br />
Cl<strong>in</strong>ical<br />
Effect studied Model Result Reference<br />
Efficacy. Phase II, multicenter, randomized, The mean percentage of heavy dr<strong>in</strong>k<strong>in</strong>g days was<br />
616443<br />
double-bl<strong>in</strong>d pilot study conducted with 30 reduced to 11.7% <strong>in</strong> the Vivitrex group compared with<br />
alcohol-dependent patients who received 25.3% <strong>in</strong> the placebo group. An <strong>in</strong>crease <strong>in</strong> the mean<br />
a 400-mg <strong>in</strong>tramuscular <strong>in</strong>jection of percentage of days abst<strong>in</strong>ent from alcohol (69.4%<br />
Vivitrex (n = 25) or placebo (n = 5) once a compared with 39.2% pre-treatment) and a reduction <strong>in</strong><br />
month for 4 months. Both treatment the number of dr<strong>in</strong>ks consumed per dr<strong>in</strong>k<strong>in</strong>g day (3.8<br />
groups received counsel<strong>in</strong>g.<br />
compared with 7.4 pre-treatment) was seen with Vivitrex<br />
treatment.<br />
Safety and Phase II, multicenter, randomized, Vivitrex was well tolerated and adverse effects were 616443<br />
tolerability. double-bl<strong>in</strong>d study conducted with 30 mild to moderate. Nausea and headache occurred<br />
alcohol-dependent patients who received<br />
<strong>in</strong>tramuscular <strong>in</strong>jections of 400 mg<br />
Vivitrex (n = 25) or placebo (n = 5) once a<br />
month for 4 months.<br />
similarly <strong>in</strong> both patient groups.<br />
Efficacy. Phase III, double-bl<strong>in</strong>d, placebo-<br />
There was a 48% reduction <strong>in</strong> heavy dr<strong>in</strong>k<strong>in</strong>g days for 516479<br />
controlled, randomized cl<strong>in</strong>ical trial <strong>in</strong> 624 males adm<strong>in</strong>istered the 380-mg dose compared with<br />
alcohol-dependent patients. Patients were placebo (p < 0.0001), whereas <strong>in</strong> females the results did<br />
enrolled to receive Vivitrex (190 or 380 not differ from placebo. Similarly, males adm<strong>in</strong>istered<br />
mg) or placebo once a month for 6 190 mg Vivitrex showed a 25% reduction <strong>in</strong> heavy<br />
months. All patients received counsel<strong>in</strong>g. dr<strong>in</strong>k<strong>in</strong>g days compared with placebo (p < 0.03), but<br />
there was no difference <strong>in</strong> the results from females<br />
treated with either Vivitrex or placebo.<br />
Efficacy and A 12-month, open-label extension of a Patients who cont<strong>in</strong>ued on the 380-mg dose showed a 603348<br />
tolerability. phase III cl<strong>in</strong>ical trial <strong>in</strong> 277 patients susta<strong>in</strong>ed reduction <strong>in</strong> the median number of heavy<br />
adm<strong>in</strong>istered monthly <strong>in</strong>tramuscular dr<strong>in</strong>k<strong>in</strong>g days per month (2.6 to 1.6 days). Patients<br />
<strong>in</strong>jections of Vivitrex (380 or 190 mg). switched from placebo to the 380-mg drug dose showed<br />
Patients formerly on placebo were a reduction <strong>in</strong> the median number of heavy dr<strong>in</strong>k<strong>in</strong>g<br />
switched randomly to either the 380- or days from 5.2 to 1.8 days per month. Vivitrex was well<br />
190-mg Vivitrex groups.<br />
tolerated over the total 18-month period.<br />
Associated patent<br />
Title Method for fabricat<strong>in</strong>g polymer-based controlled-release devices.<br />
Assignee Alkermes Inc<br />
Publication WO-09742940 20-NOV-97<br />
Priority US-19960649128 14-MAY-96<br />
Inventor Burke PA.<br />
Associated references<br />
390669 Alkermes releases abstract regard<strong>in</strong>g cl<strong>in</strong>ical data for Medisorb<br />
naltrexone - data from first cl<strong>in</strong>ical trial of <strong>in</strong>jectable susta<strong>in</strong>ed release<br />
formulation of alcoholism drug to be presented at December 2000<br />
scientific meet<strong>in</strong>g. Alkermes Inc PRESS RELEASE 2000 November 21<br />
393208 Alkermes presents phase I results of Medisorb (naltrexone).<br />
Alkermes Inc PRESS RELEASE 2000 December 11
88 <strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> 2006 Vol 7 No 1<br />
432929 Alkermes reports positive results of phase II cl<strong>in</strong>ical trial of Vivitrex<br />
for alcohol dependency at Annual Meet<strong>in</strong>g of the American College of<br />
Neuropsychopharmacology. Alkermes Inc PRESS RELEASE 2001 December<br />
10<br />
435928 Product pipel<strong>in</strong>e. Alkermes Inc COMPANY WORLD WIDE WEB SITE<br />
2002 January 15<br />
441894 Susta<strong>in</strong>ed-release naltrexone for alcoholism treatment: A prelim<strong>in</strong>ary<br />
study. Kranzler HR, Modesto-Lowe V, Neuwayser ES ALCOHOL CLIN EXP RES<br />
1998 22 5 1074-1079<br />
445176 Alkermes beg<strong>in</strong>s phase III trial of Vivitrex. Alkermes Inc PRESS<br />
RELEASE 2002 April 01<br />
455296 DrugAbuse Sciences Inc. INT BIOTECHNOL CONV & EXHIB 2002<br />
Suppl June 09-12<br />
475512 Phase III study shows DrugAbuse Sciences naltrexone depot<br />
beneficial <strong>in</strong> treat<strong>in</strong>g alcoholism. DrugAbuse Sciences Inc PRESS RELEASE<br />
2003 January 06<br />
494451 Alkermes's Vivitrex reduces heavy dr<strong>in</strong>k<strong>in</strong>g days by 50%. Alkermes<br />
Inc PRESS RELEASE 2003 June 23<br />
534413 Alkermes completes enrollment <strong>in</strong> long-term safety study of Vivitrex,<br />
naltrexone, long-act<strong>in</strong>g <strong>in</strong>jection for the treatment of alcohol dependence.<br />
Alkermes Inc PRESS RELEASE 2004 April 22<br />
592847 Alkermes announces submission of new drug application for Vivitrex<br />
for treatment of alcohol dependence. Alkermes Inc PRESS RELEASE 2005<br />
April 01<br />
593795 Efficacy and tolerability of long-act<strong>in</strong>g <strong>in</strong>jectable naltrexone for<br />
alcohol dependence: A randomized controlled trial. Garbutt JC, Kranzler HR,<br />
O'Malley SO, Gastfriend DR, Pett<strong>in</strong>ati HM, Silverman BL, Loewy JW, Ehrich EW J<br />
AM MED ASSOC 2005 293 13 1617-1625<br />
•• A full report of the multicenter phase III trial of Vivitrex, cover<strong>in</strong>g efficacy,<br />
tolerability and safety.<br />
603348 Alkermes's Vivitrex gives long-term benefit to alcoholics. Alkermes Inc<br />
PRESS RELEASE 2005 May 23<br />
609280 Cephalon and Alkermes announce agreement for the<br />
commercialization of Vivitrex for the treatment of alcohol dependence.<br />
Cephalon Inc, Alkermes Inc PRESS RELEASE 2005 June 24<br />
609507 Cephalon - announces agreement with ALKS to market Vivitrex for<br />
alcohol dependence. Geller M, Holley B, Kassum T CIBC WORLD MARKETS<br />
CORP 2005 June 24 1-11<br />
616443 A pilot evaluation of the safety and tolerability of repeat dose<br />
adm<strong>in</strong>istration of long-act<strong>in</strong>g <strong>in</strong>jectable naltrexone (Vivitrex) <strong>in</strong> patients with<br />
alcohol dependence. Johnson BA, Ait-Daoud N, Aub<strong>in</strong> HJ, Van Den Br<strong>in</strong>k W,<br />
Guzzetta R, Loewy J, Silverman B, Ehrich E ALCOHOL CLIN EXP RES 2004 28 9<br />
1356-1361<br />
616446 Vivitrex, an <strong>in</strong>jectable, extended-release formulation of naltrexone,<br />
provides pharmacok<strong>in</strong>etic and pharmacodynamic evidence of efficacy for 1<br />
month <strong>in</strong> rats. Bartus RT, Emerich DF, Hotz J, Blauste<strong>in</strong> M, Dean RL, Perdomo B,<br />
Basile AS NEUROPSYCHOPHARMACOLOGY 2003 28 11 1973-1982<br />
•• This is a comprehensive report of animal studies with Vivitrex.<br />
624146 FDA extends PDUFA date for Vivitrex to December 30, 2005;<br />
Cephalon and Alkermes cont<strong>in</strong>ue to anticipate Vivitrex launch <strong>in</strong> first half of<br />
2006. Celphalon Inc, Alkermes Inc PRESS RELEASE 2005 September 20<br />
631895 Opioids and alcoholism. Oswald LM, Wand GS PHYSIOL BEHAV 2004<br />
81 2 339-358<br />
•• A major review of experimental evidence and theory relat<strong>in</strong>g to the relationship<br />
between opioids and alcohol abuse.<br />
631898 Pharmacok<strong>in</strong>etics, safety, and tolerability of a depot formulation of<br />
naltrexone <strong>in</strong> alcoholics: An open-label trial. Galloway GP, Koch M, Cello R,<br />
Smith DE BMC PSYCHIATRY 2005 5 1 18<br />
631992 Acamprosate for the treatment of alcohol dependence. Boothby LA,<br />
Doer<strong>in</strong>g PL CLIN THER 2005 27 6 695-714<br />
• A review of current treatment options for alcohol dependence <strong>in</strong>clud<strong>in</strong>g<br />
experiences of naltrexone use.<br />
631995 Histological changes over time around the site of susta<strong>in</strong>ed release<br />
naltrexone-poly(DL-lactide) implants <strong>in</strong> humans. Hulse GK, Stalenberg V,<br />
McCallum D, Smit W, O'Neil G, Morris N, Tait RJ J CONTROL RELEASE 2005<br />
108 1 43-55<br />
632485 Alkermes reports second quarter fiscal 2006 f<strong>in</strong>ancial results;<br />
company reports profitable quarter; f<strong>in</strong>ancial expectations for fiscal 2006<br />
improve. Alkermes Inc PRESS RELEASE 2005 November 03<br />
636722 Pharmacok<strong>in</strong>etics of long-act<strong>in</strong>g naltrexone <strong>in</strong> subjects with mild to<br />
moderate hepatic impairment. Turncliff RZ, Dunbar JL, Dong Q, Silverman BL,<br />
Ehrich EW, Dilzer SC, Lasseter KC J CLIN PHARMACOL 2005 45 11 1259-1267<br />
636732 Naltrexone implants for opiate addiction: New life for a middle-aged<br />
drug. Brewer C PHARM J 2001 267 7162 260<br />
636738 DrugAbuse Sciences Product Portfolio. DrugAbuse Sciences Inc<br />
COMPANY COMMUNICATION 2005 November 17<br />
636843 Drug addiction: Bad habits add up. Robb<strong>in</strong>s TW, Everitt BJ NATURE<br />
1999 398 6728 567-570<br />
• A comprehensive overview of biological and psychological theories concern<strong>in</strong>g<br />
the basis of substance dependence.<br />
637673 Prevalence and correlates of alcohol use and DSM-IV alcohol<br />
dependence <strong>in</strong> the United States: Results of the National Longitud<strong>in</strong>al<br />
Alcohol Epidemiologic Survey. Grant BF J STUD ALCOHOL 1997 58 5 464-473<br />
637682 Alcohol consumption, alcohol abuse and alcohol dependence. The<br />
United States as an example. Grant BF ADDICTION 1994 89 11 1357-1365<br />
637696 Naltrexone implants can completely prevent early (1-month) relapse<br />
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Erratum<br />
<strong>Current</strong> <strong>Op<strong>in</strong>ion</strong> <strong>in</strong> <strong>Investigational</strong> <strong>Drugs</strong> (2005) 6(7):686-689.<br />
Mario di Napoli & BethAnn McLaughl<strong>in</strong><br />
In the legend to Figure 1, PPi is an abbreviation of <strong>in</strong>organic pyrophosphate.<br />
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