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Rigel Receives Second Milestone Payment From Daiichi for Progress In Developing Novel Cancer Drug

One of the First Industry Collaborations to Focus on Ligases as Potential Drug Targets in Oncology

South San Francisco, Calif. - April 02, 2003

Rigel Pharmaceuticals, Inc. (Nasdaq: RIGL) announced that it has received a second milestone payment from Daiichi Pharmaceuticals Co., Ltd, in conjunction with the companies' partnership to develop a new type of oncology drug. The three-year research collaboration, which began in August 2002, is investigating a specific target from a novel class of drug targets called ligases that control cancer cell proliferation through protein degradation. The partnership between the two companies is one of the industry's first collaborations to focus on this emerging field in drug discovery. The second milestone marks the successful completion of a key step towards identifying potential drugs.

The collaboration benefits from Rigel's extensive oncology drug discovery experience which is based on Rigel's broader programs focusing on the inhibition of ligase drug targets. The company is currently moving potential products from its own programs into pre-clinical evaluation.

"We believe that our partnership with Daiichi has been extremely productive and efficient in our effort to identify promising potential cancer drugs," said James Gower, Rigel's chief executive officer. "The rapid progress that we have achieved through this collaboration, we believe, demonstrates our leadership and expertise in the use of ligases for drug development in oncology."

About Rigel Pharmaceuticals, Inc.
Rigel's mission is to become a source of novel, small-molecule drugs to meet large, unmet medical needs. Rigel has identified three lead product development programs: mast cell inhibition to treat immunologic diseases such as asthma/allergy and autoimmune disorders; antiviral agents 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 the treatment of allergic rhinitis, and plans to begin clinical trials of two additional drug candidates for the treatment of hepatitis C and rheumatoid arthritis within the next 12 months. 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 screen efficiently for those that are likely to be amenable to drug modulation. 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 partners for completion of clinical trials, regulatory approval and marketing.

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 risks associated with the success of ligase drug development for oncology, the further achievement of collaboration milestones and the continuation of collaborations with partners, the timing and success of clinical trials as well as 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, 2002. Rigel does not undertake any obligation to update forward-looking statements.