A Single-Arm, Open-Label, Multicenter Study to Assess Molecular Response of P1101 Therapy in Patients with Polycythemia Vera and Elevated Hematocrit

Background: Polycythemia Vera (PV) is the commonest myeloproliferative neoplasm, characterized by clonal stem cell proliferation of the erythroid, myeloid, and megakaryocytic lines, and risk for thrombotic events and transformation into post-PV myelofibrosis and acute myeloid leukemia. The excessive myeloproliferation in PV is driven by JAK2 somatic driver mutations. Although hydroxyurea (HU) remains the myelosuppressive agent of first choice, HU treatment can be associated with cytopenias and often unsatisfactory hematological control over time, aphthous and leg ulcers, and concern for the second primary malignancy. Recently, ropeginterferon alfa-2b, a monopegylated IFNa, which had an extended elimination half-life, enabling less frequent dosing and improved tolerability, developed and evaluated the efficacy and safety in comparison to hydroxyurea treatment. An open-label, randomised phase III study (PROUD-PV and CONTINUATION-PV) showed is more effective in achieving durable hematological and molecular remissions than hydroxyurea and is well tolerated during long-term application. However, there are limited data on the clinical relevance of molecular response during ropeginterferon alfa-2b and the efficacy and safety of ropeginterferon alfa-2b in Eastern Asian patients.

Aims: The aim of this study is to evaluate clinical and molecular responses, and the association between efficacy and molecular response as assessed by reduction in JAK2 Val617Phe allele burden. In addition, the safety and tolerability of ropeginterferon alfa-2b were also collected.

Methods: This single-arm, open-label, multicenter study has been performed in 13 hospitals in Korea. Patients were eligible if 19 years or older with PV diagnosed by WHO's 2016 criteria, requiring cytoreductive therapy and elevated hematocrit (hematocrit >45%). Patients were treated with ropeginterferon alfa-2b, subcutaneously every 2 weeks, at a starting dose of 250 µg, followed by 350 µg at week 2, 500 µg at week 4, and thereafter until week 48. The quantitative JAK2 Val617Phe allele burden was assessed every 3 months

Results: With a data cut-off date of 19 Jul 2022, a total of 74 patients were enrolled including 42 (56.8%) patients in HU naïve and 32 (43.2%) patients in HU-resistance/intolerance. The median age was 58 years (range, 26-81) and 58.1% were male. The percentages of patients with low and high risk were 55.4% and 44.6%, respectively. Among the 74 patients, 70 patients continue in the study, and 4 dropped out. Until now, 45, 20, and 6 patients were evaluable at 3, 6, and 9 months, respectively. During the dose escalation period, 4.44% of evaluable patients needed the dose reduction. At baseline, mean hematocrit (%) was 50.53 ± 3.99, which significantly decreased to 47.00 ± 5.58, 42.60 ± 5.92, and 41.68 ± 4.60 at 3, 6, and 9 months, respectively. WBC and PLT also decreased steadily over time; at baseline, mean WBC (x 10⁹/L) was 14.16 ± 6.01, which significantly decreased to 7.17 ± 3.40, 6.16 ± 3.50, and 4.45 ± 1.57 at 3, 6, and 9 months, respectively, and at baseline, mean PLT (x 10⁹/L) was 560.03 ± 299.21, which significantly decreased to 336.53 ± 234.11, 274 ± 167.59, and 249.50 ± 256.18 at 3, 6, and 9 months, respectively. The JAK2 Val617Phe allele burden changes, which were analyzed with available samples so far, showed a trend for rapid decreasing pattern; at baseline, mean JAK2 Val617Phe allele burden (%) was 59.70 ± 27.91(n=39), which significantly decreased to 42.41 ± 23.83 (n=16) and 37.14 ± 13.41 (n=5) at 3 and 6 months, respectively. Updated data with molecular response per individual patient will be presented in the meeting. In addition, although grade 1/2 adverse events (n=20) and grade 3 adverse events (n=4) were reported, there were no drug-related serious adverse events.

Conclusion: Our data demonstrated that ropeginterferon alfa-2b therapy with rapid dose optimization induced hematological response and reduction of JAK2 Val617Phe allele burden, and was well tolerated in Korean patients with polycythemia vera and elevated hematocrit. Updated data with longer follow-up will be presented in the meeting.

Yoon:Chugai Pharmaceutical: Consultancy; Celgene: Consultancy; Novartis: Consultancy; Amgen: Consultancy; Kyowa Kirin: Research Funding; Takeda: Consultancy; Yuhan Pharmaceutical: Research Funding; Astellas Pharma: Consultancy; Roche-Genetech: Research Funding; Tikaros: Consultancy; Janssen Pharmaceutical: Consultancy.