ASH 2021 | Safety of full dose pacritinib versus BAT in patients with cytopenic myelofibrosis
John Mascarenhas, MD, The Mount Sinai Hospital, New York, NY, shares the findings of a study investigating the safety profile of pacritinib in patients with cytopenic myelofibrosis (MF). The treatment of cytopenic MF is challenging, as efficacious options are limited and often need to be given as reduced doses, further harming responses. Unlike other drugs, pacritinib, a novel JAK2/IRAK1 inhibitor, has shown clinically significant activity in patients with advanced cytopenic MF at the full recommended dose of 200mg twice daily. In this study, data from the Phase II PAC203 (NCT04884191) and Phase III PERSIST-2 (NCT02055781) studies were analyzed to characterize the safety profile of pacritinib for these patients. Patients with baseline platelet counts below 50 × 109/L treated with pacritinib were compared to those who received best available therapy (BAT). The results from over 70 patients in the pacritinib arm showed that dose intensity was sustained. A total of 44% in the pacritinib arm and 21% treated with BAT had drug exposure for 6 months or longer. The safety profile was comparable across the two arms. Further analysis directly comparing pacritinib and ruxolitinib in the PERSIST-2 trial showed that superior spleen and symptom improvements were achieved in those treated with pacritinib compared to ruxolitinib, and more patients were able to maintain full doses over time. Overall, these findings suggest pacritinib may represent the first fully dosed therapeutic option available to these patients. This interview took place at the 63rd ASH Annual Meeting and Exposition congress in Atlanta, GA.
Transcript (edited for clarity)
Pacritinib is a JAK2, IRAK1 inhibitor. It is an oral drug that can be given at 200 milligrams twice daily to afford patients spleen and symptom benefit. And what the PERSIST studies, which were the randomized Phase III studies, demonstrated was that this drug is tolerable and effective, and particularly so in patients with low platelets. And I think is an important message that there’s an unmet need of this cytopenic MF patient profile...
Pacritinib is a JAK2, IRAK1 inhibitor. It is an oral drug that can be given at 200 milligrams twice daily to afford patients spleen and symptom benefit. And what the PERSIST studies, which were the randomized Phase III studies, demonstrated was that this drug is tolerable and effective, and particularly so in patients with low platelets. And I think is an important message that there’s an unmet need of this cytopenic MF patient profile. These are patients typified by low platelets, often a low JAK 2 a little burden, frequently primary myelofibrosis, that are not ideal candidates for ruxolitinib or fedratinib as the label is for 50,000 or greater. So it leaves this unmet need where patients can benefit from an additional JAK inhibitor, and pacritinib has really distinguished itself from the pack in terms of less myelosuppression than the other drugs in early phase studies and in the PERSIST program.
So this was an analysis specifically looking at patients with low platelets, less than 50,000, that came from the PERSIST-2 and the PAC203 dose-finding study, and comparing them to the BAT arm in the PERSIST-2 study. And in a nutshell, what it confirms is that you can deliver the intended full dose of 200 milligrams twice daily, of pacritinib and maintain that dose with superior efficacy in terms of spleen and symptom benefit, but importantly, maintaining safety. So, although there are expected higher grade 3 / 4 treatment emergent adverse events with pacritinib compared to supportive care, the frequency of cardiac events, for example, which was an initial concern with the drug, was not elevated compared to BAT with these drugs. And what I think the PAC203 dose-finding study confirmed for us is that if one is careful about optimizing patients in terms of coagulopathy, and those patients that may have an inherent bleeding risk, you can minimize your grade three / four bleeding risk with pacritinib.
So although there may be a slight increase over BAT, there are ways to optimize or minimize that risk going forward, and the benefit typically outweighs the risk. So it was an analysis that basically confirmed the safety profile and tolerability, particularly in this vulnerable patient population that’s in need of JAK inhibitor therapy.
In a similar vein, in the PERSIST-2 study, in which there were patients who some were rux-exposed, some were rux-naive, were randomized to pacritinib at 200 milligrams twice daily, 400 milligrams once daily and BAT in which nearly half the patients received ruxolitinib. And these were patients who had a platelet count of less than 100,000, so the cytopenic MF profile. What we showed there was that if you specifically looked at the pacritinib 200 milligram twice daily and the rux-treated patients in BAT, again, you maintain dose intensity with pacritinib, where that was often lost with ruxolitinib due to cytopenias. And there was superiority in terms of both spleen and symptom improvement when looking at this extreme thrombocytopenia, less than 50,000 patient cohort with pacritinib compared to best available therapy.
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