press release archive

Rigel Initiates Phase II Clinical Trial of R112 for Allergic Rhinitis

South San Francisco, CA - April 20, 2004

Rigel Pharmaceuticals, Inc. (NASDAQ: RIGL) today announced that it has initiated a Phase II study for R112, the company’s lead candidate for the treatment of allergic rhinitis. R112, an intranasal therapy, inhibits mast cell activation and thereby blocks the major pathways triggered in an allergic attack. Initiation of the Phase II trial follows the successful completion of a Phase I/II trial which demonstrated that R112 was well tolerated and showed favorable biological effects.

The Phase II, randomized, placebo-controlled “Park” study is taking place in two outdoor locations in different parts of the country. The study, which began in mid-April, is being conducted by researchers near Atlanta, Georgia and in San Diego, California. The study will enroll approximately 300 patients (approximately 150 patients per site) that have experienced seasonal allergic rhinitis during the spring pollen season for the previous two years. The study endpoints include nasal symptom scores, time to the onset of the effect and safety measures. Results are expected in the second half of 2004.

“The initiation of this clinical trial represents a significant step in the development of R112 as a first-line allergy therapeutic for the treatment of allergic rhinitis,” stated Elliott B. Grossbard, M.D., Senior Vice President of Medical Development. “This trial will evaluate R112’s comprehensive approach to treating the major symptoms of allergic rhinitis.”

About Allergic Rhinitis
Allergic rhinitis is a common condition that affects nearly 59 million people in the United States—nearly 20 percent of the population. Allergic 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. The U.S. market for allergic rhinitis therapies approaches $4 billion.*

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 allergen (e.g., pollen) 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, which can ultimately lead to common allergic symptoms such as nasal congestion, sneezing, itching and rhinorrhea. These mediators include histamine, tryptase, chymase, kinins, heparin, leukotrienes and PGD2. PGD2 is the immune mediator most commonly associated with the chronic symptoms of allergic rhinitis.

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 slow onset of action, sometimes requiring multiple days of treatment before a positive effect is seen. In the phase I/II trial, R112 began to diminish chemical mediator release within minutes after allergen challenge. R112 is delivered intranasally, and no systemic exposure to R112 has been detected in any intranasal administration in any human trials completed 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. We have three initial clinical development programs: asthma/allergy, hepatitis C and rheumatoid arthritis. 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.

* Decision Resources, Allergic Rhinitis Report

This press release contains “forward-looking” statements, including statements related to the potential efficacy and applicability of drug candidate and the timing and subject matter of future clinical trials. 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,” “believes,” “hopes” and similar expressions are intended to identify these forward-looking statements. There are a number of important factors that could cause Rigel’s results and plans 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: Melinda Bagatelos or Ayanna Anderson (415) 512-0770 rigel@schwartz-pr.com