S*BIO plans to initiate a global phase III clinical program of its novel JAK2 inhibitor pacritinib (SB1518), in the first half of 2012 to further demonstrate its activity and tolerability for the treatment of myelofibrosis (MF). The company is actively exploring partnering opportunities for the advancement of its leading JAK2 program.

The primary objective of the double-blind, placebo-controlled phase III studies is to compare the efficacy of pacritinib versus placebo in achieving clinically significant reduction in spleen size in MF patients with splenomegaly. Secondary outcomes of both studies include patient-reported change in the most bothersome symptom identified at baseline, duration of response, as well as overall survival. The trials will enroll up to 500 MF patients.

In phase II studies, treatment with pacritinib resulted in sustained reduction in MF-associated splenomegaly with no evidence of myelosuppression and no exacerbation of cytopenias. Pacritinib is a small molecule JAK2-selective kinase inhibitor that demonstrated high potency in preclinical models against both the wild type JAK2 kinase and the JAK2 kinase with the V617F mutation. The V617F mutation is found in high frequency in myeloproliferative disorders such as MF. More than 50% of patients with MF possess the JAK2 mutation.