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Rigel Presents Positive Results of R112 Clinical Trial for Treatment of Allergic Rhinitis

Study Presented at the American Academy of Allergy, Asthma and Immunology Meeting

South San Francisco, CA - March 18, 2004

Rigel Pharmaceuticals, Inc. (NASDAQ: RIGL) today announced the presentation of clinical data for R112, the company’s lead candidate for the treatment of allergic rhinitis, during a poster session at the annual meeting of the American Academy of Allergy, Asthma and Immunology (AAAAI) in San Francisco, CA. The phase I/II single dose trial demonstrated that R112 was well tolerated and showed favorable biological effects.

The presentation entitled, “The Effect of a Novel Inhibitor of Mast Cell Activation on Mediators, Symptoms and Nasal Patency in Allergic Rhinitis,” reports data from the Phase I/II study, evaluating R112 for the treatment of allergic rhinitis. The study evaluated 20 patients in a randomized double blind crossover trial. One dose of R112 or vehicle control was given intranasally followed by nasal allergen challenge 15 minutes later. Chemical mediators and symptoms were then measured. Brenda Guyer, MD, will present the study results on Saturday, March 20, 2004.

The data demonstrated that subjects treated with R112 were indistinguishable from the vehicle controls across a wide range of clinical and laboratory safety tests. In addition to the positive safety data, the study demonstrated a statistically significant decrease in prostaglandin D2 (PGD2), a key immune mediator that was highly correlated with improvements in the allergic symptom of rhinorrhea. The study also showed other favorable responses.

“We are encouraged that the data demonstrates that R112 is well tolerated and has a positive safety profile,” said Donald Payan, MD, Rigel’s Chief Scientific Officer and Executive Vice President. “With these positive results and the promising decrease in PGD2, and other favorable changes, Rigel looks forward to further investigating R112 as a potential novel allergy therapeutic.”

Based on the success of this phase I/II trial, Rigel plans to initiate phase II efficacy trials in Q2, 2004. The randomized, placebo-controlled park study will provide broader indications of R112’s potential clinical value. The study will take place in two locations in different parts of the country, where patients will spend two days in an outdoor setting during the high-pollen season. Phase II results are expected in the second half of 2004.

About Allergic Rhinitis
Rhinitis is a common condition that affects nearly 40 million people in the United States—nearly 20 percent of the population. Rhinitis is characterized by inflammation of the nasal membranes accompanying symptoms that may include sneezing, nasal congestion, nasal itching and rhinorrhea. The eyes, ears, sinuses and throat can also be involved. Allergic rhinitis is the most common cause of rhinitis and while not a life-threatening condition, complications can occur and the condition can significantly impair quality of life.

How R112 Works and Its Possible Advantages
R112 enters mast cells, binds to an intracellular target and interrupts the signal from the IgE receptor, thus preventing downstream signaling and subsequent chemical mediator release. However, unlike common allergy drugs such as antihistamines or antileukotrienes that block only a single mediator, R112 is designed to block all of the major pathways that are triggered in an allergic attack, potentially making R112 a more effective and comprehensive drug. Currently, steroids are the major class of drugs that are able to block multiple mediators in the allergic response, but these have a comparatively slow onset of action. In the phase I/II trial, R112 began to diminish chemical mediator release within minutes after allergen challenge. R112 is delivered intra-nasally and no systemic exposure to R112 has been detected in any intra-nasal administration in any human trials conducted to date.

About Rigel (www.rigel.com)
Rigel’s mission is to become a source of novel, small-molecule drugs to meet large, unmet medical needs. Rigel has identified four disease areas with which to focus its lead product development programs: asthma/allergy, virology, immunology and oncology Rigel has begun clinical testing of its first two product candidates, R112 for allergic rhinitis and R803 for hepatitis C, and plans to begin clinical trials of two additional drug candidates, for the treatment of rheumatoid arthritis and asthma, by the end of 2004.

This press release contains “forward-looking” statements, including statements related to Rigel’s plans to pursue clinical development of drug candidates and the timing thereof and the potential efficacy of drug 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 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 Annual Report on Form 10-K for the year ended December 31, 2003. Rigel does not undertake any obligation to update forward-looking statements.

Rigel Contact:
Rigel Pharmaceuticals
Raul Rodriguez
(650) 624-1302

Media Contact:
Schwartz Communications
Melinda Bagatelos or Ayanna Anderson
(415) 512-0770
rigel@schwartz-pr.com