Rigel Announces Initiation Of Phase 1 Clinical Trial Of R348 For Rheumatoid Arthritis, Psoriasis And Other Immune Disorders

Rigel
Pharmaceuticals, Inc. (Nasdaq: RIGL) announced that it has begun
enrolling patients in a Phase 1 study to evaluate the safety and
tolerability of R348, an orally available, potent inhibitor of Janus Kinase
3 (JAK3), as a potential treatment for patients with rheumatoid arthritis
(RA), psoriasis and other immune disorders. In preclinical studies, R348
was shown to be effective in reducing arthritic symptoms, bone destruction
and swelling. It has also shown efficacy in models of psoriasis and
transplant rejection. This is Rigel's fourth novel product candidate in
clinical trials.


"R348 enters the clinic at a time when Rigel's product portfolio is
demonstrating its potential contribution to the field of immunology," said
Donald G. Payan, M.D., executive vice president and chief scientific
officer at Rigel. "With R348 targeting T-cells and our oral syk kinase
inhibitor, R788, targeting B-cells and other immune cells, Rigel has
mounted a comprehensive assault on autoimmune disorders," he added.



This study will evaluate the safety and pharmacokinetics of R348 in
young, healthy males using a double blind, placebo controlled, single dose
and multiple rising doses of R348. Results are expected in mid-2008.



JAK3 in RA and Other Immune Disorders



RA affects approximately 1% of the population worldwide --
approximately 2.1 million Americans -- and is a debilitating and
degenerative autoimmune disease. Psoriasis affects approximately 7.5
million in the U.S. and an estimated 125 million worldwide, and is a
lifelong skin disease. About 10-30% of patients with psoriasis also develop
psoriatic arthritis, which causes pain, swelling and stiffness of the
joints. These diseases are mediated by activated T-cells, which rely on
JAK3 signaling.



Current treatments for these diseases include steroids, methotrexate
and various injectable biologic agents. Rigel's product candidate, R348, is
believed to be orally bio-available and may provide an attractive
alternative or supplement to currently used agents.



R348 is also being studied as a potential treatment for transplant
rejection and graft vs. host disease.



About Rigel



Rigel is a clinical-stage drug development company that discovers and
develops novel, small-molecule drugs for the treatment of
inflammatory/autoimmune diseases and cancer, as well as viral and metabolic
diseases. Our goal is to file one new investigational new drug (IND)
application in a significant indication each year. Rigel has achieved this
goal every year since 2002. Our pioneering research focuses on
intracellular signaling pathways and related targets that are critical to
disease mechanisms. Rigel's productivity has resulted in strategic
collaborations with large pharmaceutical partners to develop and market our
product candidates. Rigel has product development programs in
inflammatory/autoimmune diseases such as rheumatoid arthritis,
thrombocytopenia and asthma, as well as in cancer.



This press release contains "forward-looking" statements, including
statements related to the potential efficacy and commercial potential of
R348 and Rigel's plans to pursue further clinical development thereof. Any
statements contained in this press release that are not statements of
historical fact may be deemed to be forward-looking statements. Words such
as "believes," "plans," "potential," and similar expressions are intended
to identify these forward-looking statements. There are a number of
important factors that could cause Rigel's results to differ materially
from those indicated by these forward-looking statements, including risks
associated with the timing and success of clinical trials and the
commercialization of product candidates, potential problems that may arise
in the clinical testing and approval process and Rigel's need for
additional capital, as well as other risks detailed from time to time in
Rigel's SEC reports, including its Form 10-Q for the quarter ended
September 30, 2007. Rigel does not undertake any obligation to update
forward-looking statements.


Rigel Pharmaceuticals, Inc.

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