Rigel's R406/788 shows promise for treating blood disorders, study finds

By Angela McDaniels

Seattle, Dec. 7 - Rigel Pharmaceuticals Inc. said a study found its R406 syk kinase inhibitor slowed tumor growth in a dose-dependent manner in a xenograft mouse model with a human acute mylelogenous leukemia FLT3 cell line.

This demonstrates that R406 may be beneficial in FLT3-type acute mylelogenous leukemia, the company said. The disease is characterized by the overproduction of immature white blood cells, which leads to a deficit of other normal blood cells.

Acute mylelogenous leukemia is the most common form of leukemia with more than 10,000 patients diagnosed annually, the company said. The FLT3-mutant is found in about 20% to 30% of all acute mylelogenous leukemia patients.

Rigel's R406/788 is also a known inhibitor of FLT3, the company said.

A second study found R788, the oral solid dosage form of R406, to be protective against immune thrombocytopenia and hemolytic anemia in a mouse model.

This suggests that R788 may be useful in the treatment of Immune Thrombocytopenic Purpura and improving autoimmune hemolytic anemia, the company said. Both are autoimmune-based hematological diseases characterized by the destruction of formed blood cells by auto-antibodies.

These study results will be presented at the 47th Annual Meeting of the American Society of Hematology, taking place Dec. 10 to Dec. 13 in Atlanta.

Recent phase 1 studies of R406/788 demonstrated that it was well tolerated in human volunteers at dose levels Rigel plans to use moving forward, the company said.

R788 is Rigel's lead product candidate and is being developed for rheumatoid arthritis and possibly cancer and hematological diseases. Rigel said it plans to retain ownership of R788 and will begin efficacy studies of the drug in 2006.

Rigel is a clinical-stage drug development company based in South San Francisco, Calif., that discovers and develops small-molecule drugs for the treatment of inflammatory diseases, cancer and viral diseases.

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