Rigel Pharmaceuticals R406/788 study showed promising results for treating immune thrombocytopenia, haemolytic, anaemia and myeloid leukaemia in preclinical studies.

According to a company release, 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 signalling. In the first study, R788 was found to be protective from immune thrombocytopenia and haemolytic anaemia in a mouse model. This study suggests that R788 may be useful in the treatment of immune thrombocytopenic purpura (ITP) as well as improving autoimmune haemolytic anaemia (AIHA). Both ITP and AIHA are autoimmune-based haematological diseases characterised by the destruction of formed blood cells by auto-antibodies.

In a second study, R406 inhibited tumour growth in a dose-dependent manner in a xenograft mouse model with a human acute mylelogenous leukaemia (AML) FLT3 cell line, demonstrating that R406 may be a beneficial in FLT3-type AML. AML is characterised by the overproduction of immature white blood cells, which causes deficits of other normal blood cells. AML is the most common form of leukaemia with over 10,000 patients diagnosed annually. With current therapy, only 20-40% of patients survive at least 5 years without any relapse. FLT3-mutant type AML is found in approximately 20-30% of all AML patients, and the prognosis for these patients is even poorer. Rigel’s R406/788 is also a known inhibitor of FLT3.

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, adds the release.

R788 is Rigel’s lead product candidate. It has a novel mechanism of action, blocking IgG receptor signalling in macrophages and B-cells. Phase I trial results, completed to date, have demonstrated that R406/788 is well-tolerated, established a good biomarker, and showed good pharmaceutical properties. Rigel is developing R788 for rheumatoid arthritis and possibly other diseases.

In preclinical studies, Rigel’s compound greatly diminished the swelling and tissue destruction associated with RA. In other preclinical models, R406/788 was shown to have potential in treating various cancers and haematological diseases. Rigel plans to retain ownership of R788 and will begin efficacy studies of the drug in 2006.

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.