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Rigel Pharmaceuticals Presents Drug Development Programs in Oncology and Allergy/Inflammation at the Protein Phosphorylation Drug Discovery World Summit

South San Francisco, Calif. - March 05, 2003

Rigel Pharmaceuticals, Inc., (Nasdaq: RIGL, news) announced today that the company will present an update on two of its drug development programs, one in the area of Ubiquitin ligases and the other focused on kinases at the Protein Phosphorylation Drug Discovery World Summit to be held March 3-5, 2003 at the Wyndham Emerald Plaza in San Diego. Ligases, a class of enzymes that regulate cell proliferation, have recently become the subject of intense interest among researchers as a potential drug target for the treatment of cancer. Another of Rigel's programs focuses on a kinase drug target that is the subject of drug discovery efforts as a means to inhibit inflammatory responses in diseases such as asthma and rheumatoid arthritis. The company's first drug candidate in this class, R112, is currently in phase I/II clinical testing for the treatment of allergic rhinitis.

"We believe that we have made rapid progress in developing selected inhibitors against novel ligases and kinases, and our lead molecules are now showing significant efficacy in animal models of oncology and arthritis," said Donald G. Payan, M.D., Rigel's executive vice president and chief scientific officer. "We are currently selecting our near-term clinical candidates from these programs and expect to introduce an additional drug candidate from these programs into clinical testing in 2003."

Rigel's research in the area of Ubiquitin ligases is developing novel cancer therapeutics that selectively modulate the Ubiquitin-regulatory enzymes controlling oncogenic processes. Rigel believes that it has now identified potent drug candidates against this class of target, and the company is currently moving them into pre-clinical evaluation. Rigel's Ubiquitin ligase presentation will demonstrate that selected Rigel ligase inhibitors significantly inhibit tumor growth in animals.

Rigel's kinase presentation will focus on a class of compounds that inhibit Syk, a kinase important in antibody-mediated activation of mast cells that trigger an inflammatory response. The company is developing small molecule compounds that show promise for the treatment of asthma, rheumatoid arthritis, and multiple sclerosis.

"Rigel has made significant progress in developing drug candidates against two important target classes, kinases and ligases, which play key roles in human diseases. We believe that our strategy of discovering potent and selective small molecules through our functional genomics platform is bearing fruit," said Dr. Payan.

About Rigel Pharmaceuticals, Inc.
Rigel's mission is to become a source of novel, small-molecule drugs to meet large, unmet medical needs. The company's business model is to develop a portfolio of drug candidates and to take these through phase II clinical trials, after which Rigel intends to seek commercialization partners for completion of clinical evaluation, regulatory approval and marketing. Rigel has identified three areas for its lead product research programs: mast cell activation to treat immunologic diseases such as asthma/allergy and autoimmune disorders; an antiviral agent to treat hepatitis C; and Ubiquitin ligases, a new class of cancer drug target. Rigel has begun clinical testing of its first product candidate, for allergic rhinitis, and plans to follow this by advancing two additional drugs into the clinic by the end of 2003. Rigel's approach to drug discovery is based on advanced, proprietary functional genomics techniques that allow the company to identify targets with a demonstrable role in a disease pathway and to efficiently screen for those that are likely to be amenable to drug modulation.

This press release contains "forward-looking" statements, including statements related to Rigel's business strategy, drug development programs and clinical trial plans. 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 "plans," "intends," "believes," 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 the risks detailed from time to time in Rigel's SEC reports, including its Annual Report on Form 10-K for the year ended December 31, 2001 and Quarterly Report on Form 10-Q for the quarter ended September 30, 2002. Rigel does not undertake any obligation to update forward-looking statements.