Pelabresib Plus Ruxolitinib Improves Spleen Volume Reduction in JAK Inhibitor-Naive Myelofibrosis

John Mascarenhas, MD

Treatment with the combination of pelabresib (CPI-0610) and ruxolitinib (Jakafi) led to a statistically significant and clinically meaningful improvement in spleen volume reduction vs placebo plus ruxolitinib in patients with JAK inhibitor-naive myelofibrosis, meeting the primary end point of the phase 3 MANIFEST-2 trial (NCT04603495).¹

Findings showed that 66% of patients treated with the combination of pelabresib and ruxolitinib experienced a spleen volume reduction of at least 35% (SVR35) at week 24 vs 35% of patients treated with placebo plus ruxolitinib (31% difference; 95% CI, 21.6%- 39.3%; P < .001).

Furthermore, patients in the pelabresib and ruxolitinib group experienced a median reduction in total symptom score (TSS) of 15.99 points at week 24, reduced from 28.26 at baseline, compared with a reduction of 14.05 points, reduced from 27.36, in those treated with placebo plus ruxolitinib (delta, –1.94; 95% CI, –3.92 to 0.04; P = .0545).

Notably, findings revealed that a higher percentage of patients experienced a hemoglobin response of an increase of at least 1.5 g/dL from baseline when treated with the combination of pelabresib and ruxolitinib compared with those given placebo and ruxolitinib.

Detailed findings from MANIFEST-2 will be presented at the 2023 ASH Annual Meeting in December. MorphoSys, the developer of pelabresib, will continue to review data and plans to submit a new drug application to the FDA and a marketing authorization application to the European Medicines Agency for pelabresib in combination with ruxolitinib in myelofibrosis by the middle of 2024.

“I believe MANIFEST-2 provides us with valuable evidence that the addition of pelabresib offers meaningful improvements over JAK inhibitor monotherapy as a first-line approach for patients with myelofibrosis,” John Mascarenhas, MD, director of the Adult Leukemia Program at The Tisch Cancer Institute at Mount Sinai in New York, New York, said in a news release. “The pelabresib and ruxolitinib combination therapy significantly reduced spleen volume—the best prognostic indicator we have at our disposal for long-term outcomes [for patients with myelofibrosis]. Based on insights from MANIFEST-2, pelabresib represents a promising and well-tolerated therapeutic option for a community in need of innovation.”

The randomized, double-blind, placebo-controlled MANIFEST-2 trial enrolled patients at least 18 years of with a confirmed diagnosis of myelofibrosis with adequate hematologic, renal, and hepatic function. Furthermore, patients must have a prognostic risk-factor score of intermediate-1 or higher per the Dynamic International Prognostic Scoring System; a spleen volume of 450 cm3 or more; and an ECOG performance status 2 or less. Exclusion criteria include splenectomy or splenic irradiation in the previous 6 months; medication use that would prohibit treatment; or prior administration of any JAK or BET inhibitor for treatment of a myeloproliferative neoplasm.²

Eligible patients were randomly assigned 1:1 to receive pelabresib in combination with ruxolitinib or placebo plus ruxolitinib.

TSS response from baseline at week 24 and the proportion of patients with at least a 50% reduction in TSS (TSS50) were key secondary end points.¹

Patients with intermediate-risk disease comprised more than 90% of patients in the study population, and in this population, pelabresib plus ruxolitinib reduced by a median TSS by 15.18 points at week 24 from the baseline median TSS of 28.20, compared with a median reduction of 12.74 points at week 24 from a baseline TSS of 27.53 in the placebo plus ruxolitinib arm (delta, –2.44; 95% CI, –4.48 to –0.40; P < .02). This difference was statistically significant.

At week 24, 52% of patients in the pelabresib arm achieved at least a 50% reduction in TSS (TSS50) vs 46% in the placebo arm (6% difference; 95% CI, –3.5% to 15.5%; P = .216). In intermediate-risk patients, TSS50 was achieved by 55% of those in the pelabresib arm compared with 45% in the placebo arm (10% difference; 95% CI, 0.35%-19.76%; P < .05).

Regarding safety, pelabresib and ruxolitinib remained in line with the previously observed safety profile, and no new safety signals were reported. Notably, instances of anemia as an adverse effect were less frequent in patients treated with pelabresib plus ruxolitinib compared with those treated with placebo plus ruxolitinib.

“[Patients with] myelofibrosis experience a severely diminished quality of life due to symptoms such as severe fatigue, night sweats, bone pain and fever—symptoms that can leave them bedridden for days and with limited ability to participate in daily activities. Reducing symptom burden is a primary goal of myelofibrosis treatment,” Ruben A. Mesa, MD, FACP, president and executive director of Atrium Health Levine Cancer Center and Atrium Health Wake Forest Baptist Comprehensive Cancer Center, said in a news release.

References

1. Morphosys’ phase 3 study of pelabresib in myelofibrosis demonstrates statistically significant improvement in spleen volume reduction and strong positive trend in symptom reduction. News release. Morphosys. November 20, 2023. Accessed November 21, 2023.
2. Phase 3 study of pelabresib (CPI-0610) in myelofibrosis (MF) (MANIFEST-2). ClinicalTrials.gov. Updated September 25, 2023. Accessed November 21, 2023.