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Rigel Announces Presentation of Phase I Data on R406/788 at the American College of Rheumatology (ACR) Annual Meeting

Study Demonstrates Safety and Bioavailability Allowing for Further Investigation of Orally Delivered Compound for the Treatment of Rheumatoid Arthritis (RA)

South San Francisco and San Diego, Calif. - November 14, 2005

Rigel Pharmaceuticals, Inc. (Nasdaq: RIGL) today announced that data from a Phase I study of R406 will be presented at the American College of Rheumatology (ACR) Annual Meeting taking place in San Diego, California this week. This novel, oral syk kinase inhibitor blocks the activation of mast cells, B cells and macrophages, which promote swelling and inflammatory responses. Data from the Phase I study was used to inform the clinical study of R788, an oral solid dosage formulation of R406.

Elliott B. Grossbard, M.D., Rigel’s senior vice president of medical development, will present the Phase I findings in a presentation at ACR on Wednesday, November 16, 2005 at 3:30 p.m. PST.

“This data shows that R406 was well tolerated and a potent inhibitor of syk kinase, which may play a key role in the inflammation associated with RA,” said Dr. Grossbard. “We believe that R406/788 will inhibit the inflammatory cascade associated with the autoimmune response in this debilitating disease, and thus is a potentially promising new disease-modifying anti-rheumatic drug (DMARD).”

The Phase I study evaluated the safety and pharmacokinetics of R406 and was conducted at Guy’s Drug Research Unit (GDRU) in London, England in two sequential parts. Researchers first conducted a placebo-controlled, escalating single-dose human safety/pharmacokinetic clinical trial that included 35 healthy volunteers. Results showed that R406 was well tolerated and showed a prolonged biological effect. The second part of the study was a placebo-controlled, 7-day multiple-dose human safety clinical trial in an additional 24 volunteers. Results showed that R406 was well tolerated up to the 200 mg dose level and produced a prolonged biological effect with a half-life of over 12 hours. These studies established a strong correlation between R406 plasma levels and the inhibition of the target.

Rigel recently completed a study of R788 in a single center, double-blind, randomized, placebo-controlled trial investigating the safety and pharmacokinetics of escalating single and multiple doses of R788. The results from this study are expected later this year.

“R788 is a fundamentally new approach to treating RA and has shown great potential in providing an orally-delivered treatment option for those who suffer from this disease,” said Donald G. Payan, M.D., executive vice president and chief scientific officer of Rigel. “We plan to initiate further clinical studies of R788 and anticipate entering broader, longer-term safety, efficacy, and pharmacokinetic studies in 2006.”

Rheumatoid Arthritis: Current Treatments and Market Opportunity
Approximately 2.1 million people in the U.S. suffer from RA and the worldwide market for innovative RA drugs is projected to reach $10 billion by 2008. RA is a chronic inflammatory disease that affects multiple tissues, but typically produces its most pronounced symptoms in the joints. It is often progressive and debilitating, preventing people from living a symptom-free life. Ultimately the chronic inflammation of joints leads to the destruction of the soft tissue and erosion of the articular surfaces of the bone.

The current treatment options for RA have potentially significant side effects and other shortfalls, including gastrointestinal complications and kidney damage. Some RA patients currently receive multiple drugs depending on the extent and aggressiveness of the disease. Most RA patients require some form of DMARD— including methotrexate, an anti-cancer agent, or TNF-blocking agents such as Enbrel®. The TNF-blocking agents only inhibit the inflammatory mediator TNF, and are all delivered via injection. Rigel believes that there is a significant opportunity for an oral DMARD that can be used earlier in the course of the disease, preventing its progression prior to major bone and cartilage destruction; this is the product goal for R788.

About R406/R788
Rigel has focused its rheumatoid arthritis (RA) program on the development of oral, safe, disease modifying anti-rheumatic drugs (DMARD’s). Rigel’s product candidates are intended to be used early in the course of the disease to prevent the progression of major bone and cartilage destruction. R788 is Rigel’s lead product candidate. It has a novel mechanism of action, blocking IgG receptor signaling in macrophages and B-cells. Phase I trial results, completed to date, have demonstrated that R406 is well-tolerated, established a good biomarker, and showed good pharmaceutical properties. In preclinical studies, Rigel’s compound greatly diminished the swelling and tissue destruction associated with RA. Rigel plans to retain ownership of R788 and will begin efficacy studies of the drug in 2006.

About Rigel (www.rigel.com)
Rigel is a clinical-stage drug development company that discovers and develops novel, small-molecule drugs for the treatment of inflammatory diseases, cancer and viral diseases. Our goal is to move one new product candidate for a significant indication into the clinic each year. We have achieved this goal 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. We have product development programs in allergy/asthma, rheumatoid arthritis and cancer.

Enbrel® is a registered trademark of Amgen and Wyeth Pharmaceuticals, Inc.

This press release contains "forward-looking" statements, including statements related to Rigel's plans to pursue clinical development of product candidates and the timing thereof and the potential efficacy of product candidates. 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," "expects" 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 pre-clinical studies and clinical trials, as well as other risks detailed from time to time in Rigel's SEC reports, including its Quarterly Report on Form 10-Q for the quarter ended September 30, 2005. Rigel does not undertake any obligation to update forward-looking statements.

Contact: Raul Rodriguez
Phone: 650.624.1302
Email: invrel@rigel.com

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