Haematologica 2003 - Supplements

lesions. Initially, high doses of ZOL (15 µg single dose; 3 times
weekly) were tested given by the intravenous (i.v.) or
subcutaneous (s.c.) route. Six out of 12 treated animals (4/6 i.v.,
2/6 s.c.) did not show any signs of tumor formation at the end of
the 84-day observation period. Subsequently, single doses of 2 or
8 µg ZOL, more comparable to the human dose range, were
chosen. The treatment schedule of 3 i.v. injections/week was
maintained to achieve constant bisphosphonate availability. The
14 day treatment was tolerated without toxicity and the median
survival was significantly prolonged in the groups treated (2 µg
group: 84 days; 8 µg: 86 days, controls: 47 days). As a marker for
tumor growth, serum levels of soluble human IL-6 receptor were
measured at day 21 and found to be significantly higher in
untreated than in ZOL treated animals. Similar results were
obtained when treatment was started at a later time point, starting
at day 14 upon tumor cell inoculation. In summary, ZOL
possesses significant anti-tumor activity as demonstrated in this
study using a unique xenograft model for human plasmacytoma
with more than 50 SCID mice involved. Thus, nitrogencontaining
bisphosphonates given at frequent intervals may have
a therapeutical potential in multiple myeloma beyond the
treatment of osteolytic lesions.
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HSP90 INHIBITORS PROLONG SURVIVAL IN A
SCID/NOD MICE MODEL OF DIFFUSE MULTIPLE
MYELOMA: THERAPEUTIC IMPLICATIONS
Constantine S. Mitsiades, Nicholas Mitsiades, Vassiliki
Poulaki, Galinos Fanourakis, Ciaran J. McMullan, Teru
Hideshima, Dharminder Chauhan, Masaharu Akiyama,
Nikhil Munshi, Kenneth Anderson
Dana-Farber Cancer Institute, Harvard Medical School, Boston MA
The molecular chaperone hsp90 (heat shock protein-90) is critical
for the proper 3-dimensional structure and function of kinases
and receptors (e.g. HER2/neu, androgen or estrogen receptors)
with major role in proliferation/survival of solid tumor cells.
While these aforementioned prominent hsp90 targets are not
deemed major contributors to multiple myeloma (MM)
pathophysiology, we hypothesized that other hsp90 client
proteins could be major determinants of MM cell survival against
pro-apoptotic stimuli (e.g. anti-cancer drugs). We first studied the
in vitro anti-MM effect of a panel of small molecule inhibitors
(including geldanamycin and its analogs, e.g. 17-AAG) of the
ATP-binding pocket of hsp90. We found that hsp90 inhibitors
potently induce apoptosis of both drug-sensitive and -resistant
MM cell lines, and tumor cells from patients with relapsed
refractory MM (even PS-341- or IMiD-resistant); sensitize tumor
cells to other pro-apoptotic agents (e.g. PS-341, Apo2L/TRAIL,
HDAC inhibition); suppress cell surface expression and downstream
signaling (via PI-3K/Akt and Ras/Raf/MAPK) of both
IGF-1R and IL-6R; decrease intracellular levels of key kinases,
including Akt, Raf, IKK-α; increase activity of pro-apoptotic
Forkhead transcription factors; decrease constitutive and
cytokine-induced activity of NF-κB and telomerase; and suppress
expression of intracellular anti-apoptotic proteins (e.g. FLIP,
XIAP, cIAP2). We then evaluated the in vivo anti-MM activity of
17-AAG in a recently developed model of diffuse GFP+ MM
lesions in SCID/NOD mice.RPMI-8226/S MM cells stably
transfected with Green Fluorescent Protein (GFP) construct were
injected (5x106 cells, i.v. tail injection) in 40 SCID/NOD mice,
randomly assigned to 2 groups (of 20 mice each): a) mice
receiving 50 mg/kg i.p. of 17-AAG (daily i.p. injections for 5
consecutive days followed by 2 days off therapy, in each cycle)
for a total of 4 cycles, or b) control group. Mice in both cohorts
were followed up serially by whole body real-time fluorescence
imaging, which allows external visualization of GFP+ tumors in
internal organs and was previously validated in a separate study.
The primary endpoint of this study was overall survival (time
between injection of tumor cells and sacrifice for paralysis,
moribund state, or death, whichever occurred first). Kaplan-Meier
survival analysis showed that 17-AAG treatment significantly
prolonged median overall survival of mice (>250 days, with
14/20 of 17-AAG-treated mice surviving at the last interim
analysis, vs. 29 days median overall survival for control mice,
with 0/20 mice surviving) (p