Rigel anticipates phase 3 studies of fostamatinib, ends development of R333

Rigel Pharmaceuticals announced it has decided not to pursue indication for R333, a topical dermatological JAK/SYK inhibitor for treating discoid lupus erythematosus, but expects to initiate phase 3 studies of fostamatinib, an oral SYK inhibitor for treating patients with immune thrombocytopenic purpura.

In a recently completed phase 2 study, R333, which was being studied as a potential therapy for active skin lesions in patients with discoid lupus erythematosus, did not meet its primary endpoint, according to a press release. Proportion of patients who achieved at least 50% reduction from baseline at week 4 in the total combined Erythema and Scaling score of all treated lesions was the primary endpoint. R333 was relatively safe and well tolerated.

Rigel announced its representatives have met with the FDA for an end-of-phase 2 meeting for fostamatinib, which is being developed for treating patients with immune thrombocytopenic purpura (ITP), and it expects to begin two phase 3 studies in 2014. Approximately 75 patients are expected to enroll in each trial and be treated for 6 months with the option of enrolling in an extension study.

Patients with ITP in the randomized, placebo-controlled studies must have platelet counts below 30,000 platelets/mL. A durable platelet count increase to more than 50,000 platelets/mL will be the goal of the trials, with top line data expected in 2015, according to Rigel.

“We now have a clear picture of the phase 3 program for fostamatinib in ITP,” James M. Gower, chairman and chief executive officer of Rigel, said in the release. “Unfortunately, discoid lupus is a difficult indication and R333 didn’t provide the benefit we had hoped. However, this frees up resources to focus on our ITP and dry eye programs.”