Pelabresib Combo Improves Spleen/Symptom Burden in JAKi-Naïve Myelofibrosis

"[Pelabresib plus ruxolitinib] has the potential to improve the standard of care for treatment-naïve patients with myelofibrosis and warrants further investigation," according to the authors of the phase 2 MANIFEST study (NCT02158858).

Combination treatment with pelabresib (CPI-0610) and ruxolitinib (Jakafi) was well tolerated and demonstrated enduring improvements in spleen and symptom burden among patients with JAK inhibitor treatment–naïve patients with myelofibrosis, according to findings from arm 3 of the phase 2 MANIFEST study (NCT02158858).

At week 24, 68% (95% CI, 57%-78%) of patients who received the combination achieved a spleen volume reduction of at least 35% (SVR35), which included a median SVR of –50% (range, –84% to 28%). Additionally, SVR35 responses at 24 weeks were observed in 70% and 67% of patients with intermediate-1– and intermediate-2– or high-risk disease based on Dynamic International Prognostic Scoring System (DIPSS) criteria, respectively, and 82% and 66% of patients based on International Prognostic Scoring System (IPSS) criteria. Kaplan-Meier estimates indicated that 93.5% (95% CI, 87.4%-99.7%) of those with a SVR35 response maintained their response at 36 weeks after onset.

A total symptom score reduction of at least 50% (TSS50) was reported in 56% (95% CI, 45%-67%) of patients at week 24, with a best TSS50 response at any time of 83% and a median change in TSS of –59% (range, –100% to 225%). Additionally, 43% of patients had a TSS50 response at 48 weeks, which included a median change in TSS of –54.8% (range, –100% to 307.1%).

At 24 weeks, study treatment yielded an absolute change in hemoglobin levels from baseline between –1 and at least 1.5 g/dL in 55% of patients; hemoglobin levels improved in 36% of patients, including a mean change of 1.3 g/dL and a median of 0.8 g/dL. Moreover, 24% of patients had a mean hemoglobin increase of at least 1.5 g/dL from baseline over any 12-week period while forgoing red blood cell transfusions.

“To our knowledge, the MANIFEST trial in JAK inhibitor treatment-naïve patients is the first study with a rational combination of BET [inhibitor] pelabresib and ruxolitinib that showed clinically meaningful durable improvements in splenomegaly and symptoms, was associated with biomarker findings indicating potential disease modification, and demonstrated a generally favorable safety profile,” the study authors stated. “This combination has the potential to improve the standard of care for treatment-naïve patients with myelofibrosis and warrants further investigation.”

Investigators of the global, open-label, nonrandomized phase 2 MANIFEST study evaluated pelabresib in combination with ruxolitinib in a cohort of JAK inhibitor treatment-naïve patients with myelofibrosis. Patients received an initial dose of 125 mg of pelabresib once daily for 14 days followed by a 7-day pause in combination with continuous ruxolitinib twice a day. Patients could receive a maximum pelabresib dose of 175 mg once daily.

The study’s primary end point was SVR35 from baseline to 24 weeks measured by imaging. The secondary end point was TSS50, and exploratory end points included bone marrow fibrosis improvement based on blinded central hematopathologist review following European consensus guideline criteria for reticulin fibrosis grading and improvement in anemia and transfusion requirements.

Patients who had not been exposed to treatment with JAK inhibitors and BET inhibitors and had confirmed diagnoses of primary myelofibrosis, or post–essential thrombocythemia or post–polycythemia vera myelofibrosis were eligible for enrollment on the trial. Additional eligibility criteria included having a spleen volume of at least 450 cm³, intermediate-2– or high-risk disease based on DIPSS criteria, and at least 2 measurable symptoms using the Myelofibrosis Symptom Assessment Form v4.0.

Overall, 84 patients received at least 1 dose of the study treatment, 53 of whom remained on treatment at the time of data cutoff. The median patient age was 68 years (range, 37-85), and 70% were male. Additionally, 24% had intermediate-1, 61% had intermediate-2, and 16% had high-risk disease by DIPSS criteria. In terms of mutations, investigators most frequently observed JAK2V617F (74%), ASXL1 (46%), CALR (21%), and MPL (8%).

Blinded central pathology review of bone marrow samples indicated at least 1 grade improvement in reticulin fibrosis at week 24 in 28% of evaluable patients, including 7% who had improvements of 2 grades. Among 24 patients with grade 1 or 2 reticulin fibrosis at baseline, 4 had worsening conditions, including 2 patients each with grade 1 and 2 fibrosis. Investigators observed no significant relationship between reticulin fibrosis improvement and clinical end points in the study,

Overall, 96% of patients experienced at least 1 treatment-emergent adverse effect (TEAE), and 63% had grade 3 or higher TEAEs. The most frequent hematologic TEAEs included thrombocytopenia (52%) and anemia (42%), and the most common nonhematologic TEAEs included diarrhea (35%), fatigue (33%), musculoskeletal pain (30%), respiratory tract infection (29%), and constipation (25%).

Pelabresib dose reductions were necessary among 37% of patients, and 36% had ruxolitinib dose reductions due to TEAEs. There were 5 deaths during study treatment or within 30 days following the final pelabresib dose, including 4 determined to be unrelated to pelabresib treatment. One patient died to multiorgan failure due to sepsis secondary to pneumonia, which investigators deemed to be related to pelabresib.

Reference

Mascarenhas J, Kremyanskaya M, Patriarca A, et al. MANIFEST: pelabresib in combination with ruxolitinib for Janus kinase inhibitor treatment-naïve myelofibrosis. J Clin Oncol. Published online March 7, 2023. doi:10.1200/JCO.22.01972