Target Discovery and Validation Reviews and Protocols

Target Discovery and Validation 9
As with transgenic animals, reverse genetics using mouse knockouts played
a crucial role in target validation and drug discovery. The lack of the target gene
will simulate the effect of complete target inhibition by the desired, future drug
lead. Interestingly, the 100 best-selling drugs of 2001 are directed at only 43
host proteins that have been validated in mouse knockouts (21). Chapter 11,
Volume 1, describes the utility of this technology in functional studies to understand
how mutations lead to diseases. It also provides excellent protocols and
guidelines for the generation of transgenic and knockout mice. Cre-lox system
has now been used in several successful studies to generate null mutations in
specific genes. Moreover, novel techniques are described that can create “conditional
knockout,” which is designed to model the more relevant therapeutic
intervention. Also, the major techniques to construct transgenic animals are
summarized in Chapter 10, Volume 1.
Animal models of autoimmune diseases have been developed that mimic
some aspects of the pathophysiology of human disease. These models have
increased our understanding of possible mechanisms of pathogenesis at the
molecular and cellular level and have been important in target validation and
testing of new immunotherapies. The most used model of rheumatoid arthritis
is the collagen-induced arthritis model in DBA/1 mice, which has both a
cellular and humoral component (30) (see Chapter 13, Volume 2). It seems
that local tumor necrosis factor is the driving force behind the chronic inflammation.
Given the chronic nature of autoimmune diseases and the complexity
and redundancy of the involved cytokines and cells, the therapeutic effects of
new molecules should be assessed thoroughly. Overviews of new treatment
options for rheumatic diseases are described in Chapter 14, Volume 2. However,
despite the discovery of new drugs, corticosteroids, which were life-saving
50 yr ago, remain a stable treatment in several autoimmune diseases, including
lupus (31).
For some diseases, it might not be possible to mimic the complete human
pathology in the mouse; for others, it might be more desirable to create a model
of specific pathological (e.g., metastasis) or physiological (e.g., angiogenesis)
processes. Chapter 12, Volume 1, describes the development of in vivo assay
that enables the study of angiogenesis and testing therapies. Also, a murine
model for studying hematopoiesis and immunity in heart failure is described in
Chapter 13, Volume 1. Using the innovative methods described above, several
therapeutic targets have been identified and validated in vitro and in vivo. Other
chapters in Volume 1 cover many important aspects of target validation and
clinical trials with some of the developed agents.
1.3. Drug Discovery
Once a target is validated, the next step is the drug discovery process in which
chemical agents with activity against a specified target or function are identified