Phase III clinical trial of SB 1518 (pacritinib) meets one co-endpoint in myelofibrosis - CTI BioPharma

CTI BioPharma Corp has announced top-line results from PERSIST-2, a randomized, controlled Phase III clinical trial comparing SB 1518 (pacritinib), an investigational oral multikinase inhibitor, with physician-specified best available therapy (BAT), including ruxolitinib, for the treatment of patients with myelofibrosis whose platelet counts are less than 100,000 per microliter -- a patient population with high-risk advanced disease. Three hundred eleven (311) patients were enrolled in the study, which formed the basis for the safety analysis. Two hundred twenty-one (221) patients who had a chance to reach Week 24 (the primary analysis time point) at the time the clinical hold was imposed and constituted the intent-to-treat (ITT) analysis population utilized for the evaluation of efficacy.

Preliminary results demonstrated that the PERSIST-2 trial met one of the co-primary endpoints showing a statistically significant response rate in spleen volume reduction (SVR) in patients with myelofibrosis treated with pacritinib compared to BAT, including the approved JAK2 inhibitor ruxolitinib. Although the PERSIST-2 trial did not meet the other co-primary endpoint of greater than 50 percent reduction in Total Symptom Score (TSS), the preliminary analysis approached marginal significance compared to BAT (p=0.0791). The co-primary endpoints of the trial were the proportion of patients achieving a 35 percent or greater reduction in spleen volume from baseline to Week 24 as measured by magnetic resonance imaging (MRI) or computerized tomography (CT) and the proportion of patients achieving a Total Symptom Score (TSS) reduction of 50 percent or greater using MPN-SAF TSS 2.0 diary from baseline to Week 24.

The most common treatment emergent adverse events for pacritinib were generally manageable diarrhea, nausea and vomiting. The incidence of cardiac and bleeding adverse events (all grades and grade 3-4 including deaths) were similar across the arms.

Comment: Pacritinib may offer an advantage over other JAK inhibitors through effective treatment of symptoms while having less treatment-emergent thrombocytopenia and anemia than has been seen in currently approved and in-development JAK inhibitors.