press release archive

Rigel and Merck Collaboration Progress Triggers Milestone Payments from Merck in Ligase Partnership

SOUTH SAN FRANCISCO, Calif. - June 13, 2006

Rigel Pharmaceuticals, Inc. (Nasdaq: RIGL) announced today that it has received milestone payments totaling $1 million from Merck & Co., Inc. based on progress to date in the companies’ 2004 collaboration to explore ubiquitin ligases, a new class of drug target, to find treatments for cancer and potentially other diseases.

Rigel is a leader in investigating and characterizing the ubiquitin ligase system for the discovery and development of potential new therapeutics. The collaboration with Merck combines Rigel's capabilities in ubiquitin ligases with Merck's molecular profiling technology and downstream drug development capabilities.

“Merck and Rigel believe the ligase target class represents a potentially significant new source of oncology opportunities,” said Donald G. Payan, M.D., executive vice president and chief scientific officer of Rigel. “Rigel is pleased with the potency and selectivity of its hits against the various ligase targets and therefore with the potential for drug-ability of this target class.”

Under the terms of the 2004 agreement, Rigel received an initial cash payment from Merck and funding for Rigel research scientists for two and a half years. Rigel is also eligible to receive milestone payments for preclinical and clinical events. Merck is responsible for worldwide development and commercialization of any resulting compounds and will pay Rigel royalties on future product sales, if any. The collaboration is based on a number of new targets designated by Merck and does not include Rigel's current ligase targets. Additional terms were not disclosed.

About Ubiquitin Ligases
Ubiquitin ligases are enzymes that regulate protein degradation within the cell. Breakdown of proteins, in turn, affects many important cellular functions, including cell division. Targeting ligases represents a novel approach to treating diseases where normal cellular processes are out of balance. Because unchecked cell division is the hallmark of cancer, researchers believe that this part of the cell machinery represents a particularly compelling target for cancer therapies. Ubiquitin ligase targets are numerous and modular. This provides the potential for intervening in a highly specific fashion in a disease, potentially improving efficacy and minimizing side-effects.

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 file one new investigative new drug (IND) application in a significant indication 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 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

Media Contact: Carolyn Bumgardner Wang, WeissComm Partners, Inc.
Phone: 415.946.1065
Email: carolyn@weisscommpartners.com