press release archive

Rigel Announces Pfizer Selection of R343, a Syk Kinase Inhibitor, for Advanced Preclinical Development in Allergic Asthma

SOUTH SAN FRANCISCO, Calif. - May 17, 2006

Rigel Pharmaceuticals, Inc. (Nasdaq: RIGL) announced today that Pfizer (NYSE: PFE) has selected R343, a novel small-molecule drug candidate, for advanced preclinical development in allergic asthma. Rigel will receive a $5 million milestone payment from Pfizer. The collaboration was established in 2005 and aims to investigate and develop syk kinase inhibitors via intrapulmonary delivery to find treatments for allergic asthma and chronic obstructive pulmonary disease.

“Pfizer’s decision to take R343 into development is significant because it supports the potential of syk inhibition in the treatment of allergic diseases such as allergic asthma,” said Donald G. Payan, M.D., executive vice president and chief scientific officer of Rigel. “It is also significant because Pfizer is committing substantial investment and scientific resources ahead of the clinical development of this new treatment approach.”

R343 is designed to block the major pathways that are triggered in allergic asthma. It appears to be particularly appropriate for intrapulmonary delivery due to its limited systemic exposure.

Under the terms of the agreement, Rigel received an initial cash payment and is eligible to receive milestone payments for preclinical and clinical events as well as royalties on any future product sales. Pfizer made an equity investment in Rigel and is responsible for worldwide development and commercialization of any resulting compounds. Additional terms were not disclosed.

Syk Inhibition in Allergic Asthma
Allergic asthma is a chronic inflammatory disorder of the airways whereby persistent inflammation of the airway passages results in airway obstruction. In some patients, allergens, such as pollen, trigger the production of immunoglobulin E antibodies, or IgE antibodies, which then bind to mast cells and cause an intracellular signal that results in the release of various chemical mediators.

Syk kinase is a protein tyrosine kinase that plays a pivotal role in high affinity IgE receptor signaling in mast cells. Rigel’s syk kinase inhibitors are designed to bind to syk in mast cells and interrupt the signal from the IgE receptor, thus preventing cellular activation and subsequent chemical mediator release, and potentially blocking an allergic response in allergic asthma.

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 inflammatory/autoimmune diseases such as rheumatoid arthritis, thrombocytopenia, and asthma and allergy, as well as in cancer.

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, the potential efficacy of product candidates and the sufficiency of financial resources. 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," “anticipates” 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, 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 March 31, 2006. Rigel does not undertake any obligation to update forward-looking statements.

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