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Results of a phase 3 trial suggest the JAK2/FLT3 inhibitor pacritinib may be more effective for patients with myelofibrosis (MF) than best available therapy (BAT), excluding JAK inhibitors.
Patients who received pacritinib were more likely than those who received BAT to see a reduction in spleen volume and to become transfusion-independent,
regardless of their platelet counts.
In fact, pacritinib proved particularly effective among patients with severe thrombocytopenia.
CTI Biopharma and Baxter International, Inc., the companies developing pacritinib, announced these results from the PERSIST-1 trial yesterday.
“Despite the introduction of JAK2 inhibitors as effective therapies for patients with myelofibrosis, there remains a treatment gap for patients with disease-related or treatment-emergent thrombocytopenia,” said study investigator Claire Harrison, MD, of Guy’s Hospital in London, UK.
“The currently approved drug [ruxolitinib] may require dose titration to less effective doses in this patient population, thus limiting our ability to effectively treat them. Results from the PERSIST-1 randomized trial demonstrate that pacritinib could address this unmet medical need.”
PERSIST-1 is a randomized (2:1), phase 3 trial comparing the safety and efficacy of pacritinib to BAT, other than JAK inhibitors. Investigators enrolled 327 patients with primary and secondary MF, post-polycythemia vera MF, or post-essential thrombocythemia MF.
The study’s primary endpoint was the proportion of patients achieving a 35% or greater reduction in spleen volume from baseline to week 24, as measured by MRI or CT, when compared with BAT. Once patients completed 24 weeks of treatment, or if their disease progressed, they could cross over from the BAT arm to the pacritinib arm.
Investigators found that PERSIST-1 met its primary endpoint in the intent-to-treat population. Pacritinib produced a significantly better rate of spleen volume reduction (P=0.0003) when compared to BAT.
The same was true among patients with platelet counts of less than 100,000/μL and less than 50,000/μL, both subgroups that were stratified at randomization.
The magnitude of treatment effect was consistent with previously reported phase 2 results, with the greatest reduction observed among the sickest patients (platelet counts <50,000/μL).
Fifty patients were transfusion-dependent at study entry (receiving ≥ 6 units of red blood cells over 90 days pre-entry). And, compared to BAT, pacritinib resulted in a clinically meaningful percentage of patients becoming transfusion-independent.
Ultimately, 79% of patients in the BAT arm crossed over to the pacritinib arm.
Investigators said the safety profile in the PERSIST-1 trial was consistent with prior phase 2 trials, as the most common treatment-emergent adverse events were diarrhea, nausea, and vomiting. However, the incidence of grade 3 events was lower than previously observed in phase 2 trials. And no grade 4 gastrointestinal adverse events were reported.
Three patients discontinued treatment with pacritinib, and 9 required dose reductions for diarrhea. A preliminary analysis suggested that few patients discontinued pacritinib or required a dose reduction due to treatment-related anemia or thrombocytopenia.
Additional data from ongoing analyses will be submitted for presentation at an upcoming scientific meeting, according to Baxter and CTI Biopharma.
