On March 9, 2018 CTI BioPharma Corp. (CTI BioPharma) (NASDAQ: CTIC) reported that results from the Phase 3 PERSIST-2 clinical trial of pacritinib (an investigational JAK2 inhibitor) have been published online in JAMA Oncology (Press release, CTI BioPharma, MAR 9, 2018, View Source;p=RssLanding&cat=news&id=2337281 [SID1234524602]). The randomized, international, multicenter study compared the efficacy and safety of pacritinib at two dose levels, compared with best available therapy (BAT), which included ruxolitinib (a JAK1/JAK2 inhibitor), in patients with myelofibrosis and thrombocytopenia (defined as platelet counts ≤100 x 109/L). The publication can be accessed at: View Source

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In the intent-to-treat patient population of the study, the combined pacritinib arms (400mg once daily and 200mg twice daily dosing, 149 patients total) demonstrated a significant improvement of 35% or more in spleen volume reduction (SVR) at 24 weeks of treatment in 27 patients (18%) compared to 2 patients (3%) out of 72 patients in the BAT arm, which included treatment with ruxolitinib (P=0.001). The combined pacritinib treatment arms also demonstrated a greater than 50% reduction in total symptom score (TSS) in 37 patients (25%), compared to 10 patients (14%) in the BAT arm (P=0.079). Additionally, an exploratory analysis of the 74 patients who received pacritinib 200mg twice daily showed an improvement of 35% or more reduction of SVR in 16 patients (22%; P=0.001 vs BAT) and 50% or greater reduction of TSS in 24 patients (32%; P=0.01 vs BAT).

Pacritinib was generally well tolerated. The most commonly reported (≥15%) nonhematologic adverse events with pacritinib were gastrointestinal events, fatigue, peripheral edema, and dizziness, and those with BAT (including 19 patients with watchful-waiting only) were abdominal pain, fatigue, diarrhea, and peripheral edema. The majority of common nonhematologic adverse events were grade 1 or 2 in severity. Diarrhea was the most frequently observed adverse event with pacritinib (53% grade 1/2; 4% grade 3) most often occurring during weeks 1 to 8. The incidence of diarrhea was lower with pacritinib twice daily dosing compared to once daily dosing (48% vs 67%, respectively). Diarrhea was manageable with standard antidiarrheal agents (e.g., loperamide) and generally resolved within 1 to 2 weeks. The rate of on-study death was lowest with pacritinib twice daily (6%) compared to BAT (9%) and pacritinib once daily (14%).

Cardiac events were reported at similar rates in all arms (32%, pacritinib once daily or twice daily; 28%, BAT) and were most commonly peripheral edema in all arms. Grade 3 or 4 cardiac events were reported in 13 patients (13%) treated with pacritinib once daily, 7 patients (7%) treated with pacritinib twice daily, and 9 patients (9%) treated with BAT.

Bleeding events were reported at similar rates in all arms (36%, 42%, and 41% of patients treated with pacritinib once daily, twice daily, and BAT, respectively) and were most commonly epistaxis in all arms. Grade 3 or 4 bleeding events were reported in 7 patients (7%), 15 patients (14%), and 7 patients (7%) treated with pacritinib once daily, twice daily, and BAT, respectively.

"Pacritinib was shown to reduce both spleen volume and total symptom score, two very important clinical measures, in myelofibrosis patients with thrombocytopenia including those patients who received prior treatment with ruxolitinib," stated John Mascarenhas, M.D., Adult Leukemia Program, Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai. "Clinical improvements in hemoglobin levels and reduction in transfusions were also seen in patients who received pacritinib, and pacritinib had a generally manageable safety profile."

Dr. Mascarenhas continued, "Myelofibrosis is a difficult and progressive disease, and patients with thrombocytopenia that have already received JAK2 inhibitor therapy have an especially poor prognosis. These study results indicate there is important potential clinical benefit of pacritinib for these patients."

The PERSIST-2 trial results were previously presented at the 58th American Society of Hematology (ASH) (Free ASH Whitepaper) Annual Meeting, in December 2016.

CTI BioPharma is currently enrolling patients in the PAC203 study, which is evaluating the safety and efficacy of three dosing schedules, including 200mg twice daily (BID), 100mg twice daily (BID), and 100mg once daily (QD).