Rigel Initiates Phase 3 Studies Of Fostamatinib In ITP

Rigel Pharmaceuticals, Inc. RIGL today announced the initiation of a Phase 3 clinical program for its oral SYK inhibitor, fostamatinib, in patients with ITP (immune thrombocytopenic purpura). The focus of these clinical studies is to evaluate the potential of fostamatinib to increase the platelet counts of patients with chronic ITP. Fostamatinib may provide a novel therapeutic for the underlying cause of this autoimmune disease of the blood. "Based on our extensive clinical experience with this product candidate, which includes more than 4,500 patient-years of data, we hope to demonstrate that fostamatinib can provide a new treatment option for patients with chronic ITP," said James M. Gower, chairman and chief executive officer of Rigel. Results of Rigel's Phase 2 clinical study, published in Blood (volume 113, number 14), showed that fostamatinib significantly increased the platelet counts of certain ITP patients, including those who had failed other currently available agents. Fostamatinib in ITP Phase 3 Program Design A total of 150 ITP patients will be randomized into two identical multi-center, double-blind, placebo-controlled clinical studies. The patients will have been diagnosed with persistent or chronic ITP, and have blood platelet counts consistently below 30,000 per microliter of blood. Two thirds of the subjects will receive fostamatinib orally at 100 mg bid (twice daily), the other third will receive placebo on the same schedule. Subjects are expected to remain on treatment for 24 weeks. At week 4 of treatment, subjects who meet certain platelet count and tolerability thresholds will have their dosage of fostamatinib (or corresponding placebo) increased to 150 mg bid. The primary efficacy endpoint of this program is a stable platelet response by week 24 with platelet counts at or above 50,000 per microliter of blood for at least 4 of the final 6 qualifying blood draws. Results are expected at year-end 2015. Immune Thrombocytopenic Purpura Chronic ITP affects an estimated 60,000 – 125,000 people in the US. In patients with ITP, the immune system attacks and destroys the body's own blood platelets, which play an active role in blood clotting and healing. ITP patients can suffer extraordinary bruising, bleeding and fatigue as a result of low platelet counts. Current therapies for ITP include steroids, blood platelet production boosters (TPOs) and splenectomy. Fostamatinib is the only potential therapy that may address the autoimmune basis of the disease. Taken in tablet form, fostamatinib blocks the activation of SYK kinase inside immune cells. ITP causes the body to produce antibodies that attach to healthy platelets in the blood stream. Immune cells recognize these antibodies and affix to them, which activates the SYK enzyme inside the immune cell, and triggers the destruction of the antibody and the attached platelet. When SYK is inhibited by fostamatinib, it interrupts this immune cell function and allows the platelets to escape destruction.