June 11, 2023
Caroline Seymour
Rusfertide (PTG-300) demonstrated freedom from phlebotomy, sustained hematocrit control, and 12-week treatment completion in 69.2% (n = 18/26) vs 18.5% (n = 5/27) of patients with phlebotomy-dependent polycythemia vera who received placebo (P = .0003), meeting the primary end point of the phase 2 REVIVE trial (NCT04057040). Findings were presented at the 2023 EHA Congress.
“The REVIVE study demonstrated significantly higher efficacy with rusfertide compared with placebo in subjects with polycythemia vera,” said Marina Kremyanskaya, MD, PhD, lead study author and assistant professor of medicine, hematology, and medical oncology at the Icahn School of Medicine at Mount Sinai in New York, New York, in a presentation of the data. “Current standard-of-care therapy in polycythemia vera does not consistently maintain hematocrit below 45%, thereby potentially increasing the risk of thromboembolic events. Rusfertide has the potential to consistently maintain hematocrit [levels] below 45%.”
Polycythemia vera is a myeloproliferative neoplasm (MPN) that produces red blood cells in excess and is often marked by elevated hematocrit. Hematocrit, when uncontrolled, can lead to higher fatality from cardiovascular causes or thrombotic events. Although guidelines from the National Comprehensive Cancer Network and European LeukemiaNet state that hematocrit should be maintained below 45%, current standard-of-care therapy fails to do so in most patients.
Hepcidin is a peptide hormone that controls iron availability for red blood cell formation. Rusfertide is a novel hepcidin mimetic that mirrors the effects of hepcidin on erythropoiesis, representing a potential add-on therapy to standard therapy with improved activity. This hypothesis was tested in the phase 2 REVIVE trial.
To be eligible for enrollment in the study, patients had to have phlebotomy-dependent polycythemia vera per 2016 World Health Organization criteria, having received at least 3 phlebotomies in 28 weeks with or without concurrent cytoreductive therapy. Additionally, all patients had to be phlebotomized to hematocrit levels below 45% prior to the first dose of rusfertide to standardize the starting hematocrit.
The study consisted of 3 parts: dose finding, blinded randomized withdrawal, and open-label extension. Rusfertide was administered subcutaneously in doses ranging from 10 mg to 120 mg weekly. In part 1, rusfertide was titrated for the first 16 weeks to determine the clinically effective dose. Efficacy was evaluated in weeks 17 to 28. In part 2, patients were randomly assigned 1:1 to receive active or placebo doses of rusfertide in weeks 29 to 41. Study treatment continued in part 3 for up to 3 years.
Safety and efficacy served as key end points of the trial. Efficacy was characterized by the proportion of responders in part 2, defined by the proportion of patients who maintained hematocrit below 45% and the percentage reduction in phlebotomies. Patient outcomes were evaluated with the MPN Symptoms Assessment Form Total Symptom Score.
A total of 70 patients were included in the dose-finding portion of the research. Fifty-nine patients were treated in part 2, 53 of which were included in the primary efficacy analysis set. Fifty-two patients are ongoing treatment in part 3
Regarding baseline characteristics of those included in part 2, most patients were male, above the age of 50 years at diagnosis, had polycythemia vera for approximately 5 years, and received hydroxyurea as the primary means of cytoreductive therapy. Across the arms, 52.7% of patients were high risk and 47.4% were low risk. Body mass index was 30.1 ± 5.76 kg/m2 and 28.7 ± 4.55 kg/m2 in the placebo and rusfertide arms, respectively.
Additional findings demonstrated similar benefit in time to treatment failure with rusfertide in responders (P < .0001), patients ineligible for phlebotomy plus hydroxyurea (P < .0001), and those with hematocrit under 45% (P < .0001).
Kremyanskaya also explained that rusfertide led to meaningful reductions in the need for phlebotomy, both with phlebotomy only (n = 37) and phlebotomy plus cytoreductive therapy (n = 33).
Although the focus of the presentation centered around outcomes in part 2, investigators also evaluated symptom improvement in part 1. Notably, moderate or severe symptoms of problems with concentration (P =.0018), itching (P = .0054), fatigue (P =.0074), and inactivity (P =.0005) were all improved following treatment with rusfertide. Kremyanskaya noted that meaningful comparison of symptom improvement was not possible in part 2 because most patients who were randomized to placebo discontinued prior to the 12-week symptom assessment.
In terms of safety, Kremyanskaya stated that rusfertide was “generally well tolerated.” Treatment-emergent adverse effects (TEAEs) included injection site erythema (64.3%), injection site pain (41.4%), injection site pruritus (40.4%), fatigue (31.4%), injection site mass (25.7%), pruritus (25.7%), arthralgia (24.3%), injection site swelling (24.3%), dizziness (22.9%), headache (22.9%), nausea (22.9%), anemia (20.0%), COVID-19 (20.0%), injection site irritation (18.6%), and injection site bruising (15.7%). Most events were grade 1/2 (83%), and 17% of patients experienced grade 3 events. No grade 5 events occurred.
“Most common TEAEs were injection site reactions, which decreased in incidence with continued treatment,” Kremyanskaya noted. “Additionally, events were localized, grade 1 or 2 in severity, and generally did not lead to treatment discontinuation,”
Two treatment-related events of mild thrombocytosis and recurrent grade 1 injection site erythema led to treatment discontinuation.
Patients who completed the REVIVE study will be eligible to enroll in PTG-300-21, a separate, 2-year follow-on extension trial. The agent is also under evaluation in the phase 3 VERIFY trial (NCT05210790), where it is being compared with placebo in patients with polycythemia vera maintaining hematocrit control and in improving symptoms of disease.
Disclosures: Dr Kremyanskaya reported receiving honoraria and being on the advisory board for Protagonist Therapeutics, Inc.
Reference
Kremyanskaya M, Kuykendall A, Pemmaraju N, et al. Targeted therapy of uncontrolled erythrocytosis in polycythemia vera with the hepcidin mimetic, rusfertide: – blinded randomized withdrawal results of the REVIVE study. Presented at: 2023 EHA Congress; June 8-11, 2023; Frankfurt, Germany. Abstract LBA2710.