Rigel Pharmaceuticals, Inc, of San Francisco, California, announced preliminary data from a phase I double-blind, placebo-controlled trial to investigate the safety and pharmacokinetics of R788 in combination with methotrexate (MTX) in rheumatoid arthritis (RA) patients. The data demonstrated that R788, an oral syk kinase inhibitor that blocks the activation of mast cells, macrophages, and B cells that promote swelling and an inflammatory response, was well tolerated when given in combination with MTX and had no significant adverse pharmacokinetic interactions.

The company also announced plans to initiate separate clinical efficacy studies of R788 in RA and Immune Thrombocytopenic Purpura (ITP) in the second half of 2006. In preclinical studies, R788 greatly diminished the swelling and tissue destruction associated with RA. The drug also increased platelet counts significantly in a murine model of ITP.

In preclinical studies, R788 was shown to improve platelet counts in mice treated with antiplatelet antibodies, mitigating the disease in an ITP mouse model. Rigel is focusing its ITP program on the chronic form of this disorder, targeting the underlying autoimmune cause of the disease rather than stimulating platelet production.

R788, an oral solid dosage formulation of R406, is Rigel's lead product candidate. It has a novel mechanism of action, blocking IgG receptor signaling in macrophages and B cells. ITP is a blood disorder in which the immune system attacks and destroys platelets in the blood, resulting in an abnormally low platelet count. Antibodies, usually of the IgG type, mediate the destruction in ITP.

— A. Techman