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Efficacy and Safety Clinical Data for Rigel's R112 Phase II Study Published in Journal of Allergy and Clinical Immunology

Rigel's R112 Compound, an Inhibitor of Syk Kinase, Shows Promise for the Treatment of Allergic Rhinitis

South San Francisco, CA - April 06, 2005

Rigel Pharmaceuticals, Inc. (Nasdaq: RIGL) today announced that the Journal of Allergy and Clinical Immunology has published the Phase II clinical data for R112, the company's lead candidate for the treatment of allergic rhinitis. The article titled, “An Intranasal Syk-kinase inhibitor (R112) improves the symptoms of seasonal allergic rhinitis in a park environment,” is included in the April 2005 issue of the Journal. The article reviews the clinical Phase II data results for R112, concluding that patients in a park-like setting demonstrated a significant improvement in their allergic rhinitis symptoms when treated with R112, and confirmed that the drug candidate was well tolerated and had a favorable safety profile. The article and abstract can be viewed and downloaded at http://www.aaaai.org/members/jaci.stm.

“R112 is a potential novel therapeutic for seasonal allergic rhinitis, which is one of the most prevalent illnesses in the U.S.,” stated Elliott B. Grossbard, M.D., Rigel's Senior Vice President of Medical Development and the article's co-author. “R112 may provide an attractive alternative to the many sufferers of allergies with the potential added benefit of an onset of action which is much faster than with the intranasal steroids which many sufferers currently use.”

The data demonstrated that R112 significantly improved the Global Symptom Complex (GSC) compared to placebo on both day 1 and day 2 (P=0.0005 and P=0.0016 respectively). The GSC is a composite measure of nasal allergy symptoms. All ten of the individual nasal allergy symptoms measured were also significantly improved in the R112 group compared to placebo (P<0.05). As early as 30-45 minutes after dosing, R112 showed a significant improvement in symptoms over placebo. Adverse effects were indistinguishable between the groups and were not clinically meaningful.

320 patients with seasonal allergic rhinitis were evaluated in the double-blind, randomized, placebo-controlled parallel-group trial conducted over two days at two different outdoor sites in Atlanta and San Diego during the high-pollen season of Spring of 2004. Patients were randomized into two groups of 160 in order to receive intranasal R112 or a vehicle placebo. Patients self-administered R112 or the placebo twice daily. Subjects were evaluated for symptoms of allergic rhinitis including sneezes, runny nose/sniffles, itchy nose and stuffy nose based on a possible maximum score of 32 for the GSC scale. The primary outcome evaluated was the difference in the reduction in GSC (area under the curve over 8 hours) from baseline between R112 and vehicle placebo.

The Role of Immune Mediators in Allergic Rhinitis
Allergic rhinitis involves inflammation of the mucous membranes of the nose, eyes, Eustachian tubes, middle ear, sinuses and pharynx. This inflammation is characterized by a complex interaction of inflammatory mediators but ultimately is triggered by an immunoglobulin E (IgE)-mediated response to a foreign allergen. When a specific protein (e.g., a pollen grain) is inhaled into the nose, it can bind to the IgE on the mast cells, leading to immediate and delayed release of a number of mediators, the release of which can ultimately lead to the symptoms of rhinorrhea. These mediators include histamine, tryptase, chymase, kinins, leukotrienes and prostaglandin D2.

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 an earlier trial, R112 began to diminish chemical mediator release within minutes after allergen challenge. In addition, steroids need to be used selectively due to their global blocking of immune function. 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 Allergic Rhinitis
Rhinitis is an extremely common condition, affecting 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.

About the Journal of Allergy and Clinical Immunology
The Journal of Allergy and Clinical Immunology is a peer reviewed journal and an official publication of the American Academy of Allergy, Asthma, and Immunology. The Journal of Allergy and Clinical Immunology brings timely clinical papers, instructive case reports, and detailed examinations of state-of-the-art equipment and techniques to clinical allergists, immunologists, dermatologists, internists, and other physicians concerned with clinical manifestations of allergies in their practice. Articles cover such topics as allergic and immunologic diseases, the latest therapies and treatment programs, occupational/industrial allergy, and studies of antigens, allergens, and the environment. The Journal ranks in the top 3% of the 5,684 scientific journals most frequently cited (2000 Science Citation Index).

About Rigel Rigel's mission is to become a source of novel, small-molecule drugs to address large, unmet medical needs. We have four research and development programs investigating treatments for asthma/allergy, rheumatoid arthritis, oncology and hepatitis C. Our strategy is to initiate clinical trials with at least one new product candidate annually and to pursue partnerships with pharmaceutical and biotechnology companies for late-stage clinical development and commercialization of those product candidates.

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 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, 2004. Rigel does not undertake any obligation to update forward-looking statements.

Rigel Contacts:
Rigel Pharmaceuticals
Raul Rodriguez
650-624-1302

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