Rigel's Fostamatinib Meets Primary Endpoint in Phase 3 Chronic ITP Study

Rigel Pharmaceuticals announced that fostamatinib, its oral spleen tyrosine kinase (SYK) inhibitor, met the primary endpoint in the first of two double-blind studies in the FIT Phase 3 clinical program for the treatment of adult chronic/persistent immune thrombocytopenia (ITP). The study (n=76) showed that 18% of patients receiving fostamatinib achieved a stable platelet response compared to none receiving a placebo control (p=0.0261). A stable platelet response was defined as achieving greater than 50,000 platelets per uL of blood on at least four of the last six scheduled visits between weeks 14 and 24 of treatment. The results from the second FIT Phase 3 study are expected in October/November 2016.

The most frequent adverse events were gastrointestinal-related, and the safety profile of the product was consistent with prior clinical experience, and no new or unusual safety issues were discovered.

“These data demonstrate the potential benefit of fostamatinib for chronic ITP patients who are in need of new treatment options,” said Raul Rodriguez, president and chief executive officer of Rigel. “We believe that fostamatinib has significant commercial potential given that it has a unique mechanism of action that may work where other products have failed.”

“We are very encouraged by these results,” said Anne-Marie Duliege, M.D., executive vice president and chief medical officer of Rigel. “Consistent with the prior clinical study of fostamatinib in ITP, this FIT Phase 3 study demonstrated that fostamatinib provided a robust and enduring benefit for those patients who responded to the drug candidate.”

Patients who met the primary endpoint of this study typically had an increase in platelet counts to a level above 50,000/uL within the initial weeks of treatment, providing early feedback as to whether it was a viable option for treating their ITP.

In general, the clinical goal of ITP treatment is to raise platelet counts to more than 50,000/uL. Patients who met the primary endpoint in this study had their platelet counts increase from a median of 16,000/uL at baseline to a median of more than 100,000/uL at week 24, a robust response that potentially allows patients to remain above 50,000/uL more consistently.

All of the patients from this study who met the stable platelet response endpoint enrolled in the long-term, Phase 3 extension study and continued to maintain their platelet levels for months past the initial study period of 24 weeks. These data affirm similar results observed in two patients from the Rigel Phase 2 study of fostamatinib in ITP who have been taking fostamatinib for more than seven years and have maintained stable platelet levels over this extended time period.

Fostamatinib’s clinical safety profile includes more than 5,000 patient years of data across multiple autoimmune indications and has a well-defined and manageable safety profile, providing data that it may be suitable for long-term maintenance therapy in chronic ITP.

If these results are reproduced in the second Phase 3 study and are supported by the results of a planned interim analysis of the Phase 3 extension study, the company expects to submit a New Drug Application with the U.S. Food and Drug Administration in the first quarter of 2017. Further results from the FIT Phase 3 studies and long-term extension will be presented at future medical meetings.