December 7, 2005

Rigel Pharmaceuticals has announced that two presentations related to R406/788 will be made at the upcoming American Society of Hematology 47th Annual Meeting and Exposition in Atlanta, Ga.

R788, the oral solid dosage formulation of R406, is a novel syk kinase inhibitor that blocks the activation of mast cells, B cells and macrophages by blocking IgG signaling. In the first study, R788 was found to be protective from immune thrombocytopenia and hemolytic anemia in a mouse model. This study suggests that R788 may be useful in the treatment of immune thrombocytopenic purpura as well as improving autoimmune hemolytic anemia (AIHA). Both ITP and AIHA are autoimmune-based hematological diseases characterized by the destruction of formed blood cells by auto-antibodies.

In a second study, R406 inhibited tumor growth in a dose-dependent manner in a xenograft mouse model with a human acute mylelogenous leukemia (AML) FLT3 cell line, demonstrating that R406 may be a beneficial in FLT3-type AML. AML is characterized by the overproduction of immature white blood cells, which causes deficits of other normal blood cells. AML is the most common form of leukemia, with over 10,000 patients diagnosed annually. With current therapy, only 20 percent to 40 percent of patients survive at least 5 years without any relapse.