R763 in Oncology

[RandyW]

The Second Clinical Study Initiated With R763 in Oncology

SOUTH SAN FRANCISCO, Calif., Feb. 13 /PRNewswire/ -- Rigel

Pharmaceuticals, Inc. (Nasdaq: RIGL) announced today that its partner Merck

Serono has begun enrolling patients in a Phase 1 study evaluating the

safety and tolerability of R763, a highly potent, orally available

multi-Aurora kinase inhibitor, for the treatment of patients with

hematological malignancies. This is the second of several Phase 1 studies

to be conducted in order to evaluate the safety and initial efficacy of

R763 in different types of cancers, including solid tumors, hematological

malignancies, and in combination with standard therapies. Merck Serono

licensed development and commercialization rights to R763 and Rigel's

Aurora kinase program in October 2005.

This Phase 1, open-label, dose-escalation study is designed to evaluate

safety and tolerability at 2 different dosing regimens of the Aurora kinase

inhibitor R763. Up to 54 subjects with acute or chronic myeloid leukemia

(AML or CML) or myelodysplastic syndrome (MDS) will be enrolled in each

regimen and dosed orally with R763.

"We are excited with the prospect of testing R763 in these leukemias.

R763 has shown encouraging results in in vitro and in vivo models of

hematological malignancies where Aurora kinase is thought to play a role.

R763's ability to potently inhibit this enzyme is promising and we look

forward to reviewing the results of this trial", said Donald G. Payan,

M.D., executive vice president and chief scientific officer of Rigel.

Aurora Kinase and Cancer

The over-expression of Aurora kinase can cause cells to rapidly develop

an abnormal number of chromosomes. Elevated levels of Aurora kinase are

frequently associated with various human cancers and inhibition of this

enzyme disrupts cell division and promotes programmed cell death

(apoptosis). Increased knowledge of Aurora kinase and its regulation may

result in novel approaches to the treatment of cancer.

Rigel's lead oncology drug candidate, R763 (also known as AS703569), is

a highly potent inhibitor of Aurora kinase. It has exhibited potent

anti-tumor activity against a broad panel of cancer cell lines. Leukemia

cells, lung, breast, pancreas, ovarian and cervical carcinoma cells, and

histiocytic cells are particularly sensitive to R763. Rigel discovered R763

using its proprietary cell-based PAD (Proliferation, Apoptosis and DNA

content) assays applied to tumor cell lines.

About Rigel (http://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

investigational 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, 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," "promising," "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 September 30,

2006. Rigel does not undertake any obligation to update forward-looking

statements.

Contact:

Raul Rodriguez

Phone: 650-624-1302

Email: invrel@rigel.com