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Polycythemia vera is characterized by the acquisition of the JAK2V617F mutation. Recommended treatments include hydroxyurea and interferon-alpha. Several groups have reported a reduction in the JAK2 mutant allele burden in interferon-treated patients, but significance of this observation is questioned. We characterized the activity of ropeginterferon alpha-2b, a novel form of interferon-alpha recently shown to be safe and efficacious in polycythemia vera. Ropeginterferon was able to inhibit the proliferation of the HEL, UKE-1, and UT-7 JAK2-mutant cell lines while sparing JAK2-wild-type UT-7 and normal CD34+ cells growth. In vitro treatment of erythroid progenitors derived from PV patients showed that ropeginterferon could considerably inhibit the growth of endogenous erythroid colonies, a hallmark of polycythemia vera. Finally, we could study in sequential samples the clonal architecture of erythroid progenitors derived from patients included in a randomized study comparing hydroxyurea to ropeginterferon. After 1 year of treatment with ropeginterferon, the ratio of JAK2-mutated to wild-type colonies grown from bone marrow progenitors was reduced by 64%, compared to 25% in patients receiving hydroxyurea. This study shows that ropeginterferon has a potent targeted activity against JAK2-mutant cells and is able to drastically reduce the proportion of malignant progenitors in patients treated with this drug.

Background: Interferon alfa (IFNa) based therapies have been successfully applied in myeloproliferative neoplasms (MPN) for over thirty years. Several uncontrolled phase II trials have independently shown high rates of hematologic, splenic and sustained mutant JAK2 molecular responses in Polycythemia vera (PV) patients. However, a head-to-head assessment versus other treatment options in confirmatory trials has been lacking so far. Here we report 12 month data from a randomized controlled phase III trial comparing the novel, long-acting Ropeginterferon alfa-2b (AOP2014) with hydroxyurea (HU) in PV patients. Study design: Randomized, controlled, parallel group multicenter phase III trial assessing efficacy, safety and tolerability in patients diagnosed with PV according to WHO2008 criteria, either naïve to cytoreduction or HU experienced (but neither intolerant nor complete responders, cumulative HU exposure max. 3 years). The primary endpoint was non-inferiority of AOP2014 vs. HU at 12 months of therapy in terms of complete hematological response (CHR) rate. CHR was defined as normal hematocrit, leukocyte and platelet counts, spleen size and absence of phlebotomy in the preceding 3 months. As important secondary endpoint the effect of treatment on mutant JAK2 allele burden was assessed as rate of complete and partial molecular response (C/PMR) rate according to modified ELN criteria. Both cohorts are followed up further maintaining the original randomization for assessing effects of prolonged therapy. Results: 257 patients were randomized in 48 sites in 13 European countries and treated with response-driven escalating doses of either AOP2014, or HU. 62% of patients were naïve to cytoreduction, 38% HU experienced; 19% had a previous thrombotic event. Response-driven dose escalation was done in both treatment arms applying up to 10 dose levels (50-500µg AOP2014 every other week, or 250-3000 mg HU daily). Both treatments were well tolerated. The drop-out rate after 12 months was low with ~15% in both arms, the majority of drop-outs were due to administrative reasons (bi-weekly hospital visits). This presentation will provide the detailed analysis of primary and secondary endpoints of the trial, which is still blinded as of 4th Aug 2016. Preliminary pooled analysis revealed that at 12 months 45% of patients had a hematologic response: mean Hct values dropped from 48% to 42%, leukocyte counts from 12 to 6 *109/L and platelets from 530 to 260 *109/L. Need for phlebotomy within 3 months dropped from 86% to 6%. 37% of patients achieved a JAK2 molecular response (PMR or CMR), mean mutant JAK2 allele burden went from 42,5% to 28,7%. Conclusions: This is the first phase III trial formally assessing efficacy, safety and tolerability of Ropeginterferon alfa-2b versus HU. Both cohorts are followed-up for prolonged treatment duration, and it is expected that the currently available and emerging data will establish the role of Ropeginterferon alfa-2b as first-line treatment for PV. Disclosures Gisslinger: AOP Orphan Pharmaceuticals AG, Novartis, Celgene, Baxalta: Consultancy, Honoraria, Research Funding. Klade:AOP Orphan: Employment. Georgiev:Alnylam Pharmaceuticals: Consultancy. Illes:University of Debrecen faculty of medicine department of hematology: Employment. Mayer:AOP Orphan Pharmaceuticals: Research Funding; Novartis: Research Funding. Grohmann-Izay:AOP Orphan Pharmaceuticals AG: Employment. Kralovics:AOP Orphan: Research Funding; Qiagen: Membership on an entity's Board of Directors or advisory committees. Kiladjian:Novartis: Research Funding; AOP Orphan: Research Funding.

Background: Ropeginterferon alfa-2b (Ropeg) is a novel long-acting monopegylated IFN-alpha-2b. Due to reduced dosing frequencies, better tolerability and improved compliance, Ropeg may be a favorable treatment option for long-term therapy in patients with polycythemia vera (PV). Study design: PEGINVERA phase I/II (NCT: 2010-018768-18), a prospective, open-label, multicenter study, investigated the efficacy and safety of Ropeg for long-term treatment in 51 patients aged ≥18 years with a confirmed diagnosis of PV, regardless of prior cytoreductive therapy. Following ≥1 year of 2-weekly treatment, patients who responded well to Ropeg were permitted to switch to a 4-weekly dosing regimen. Results: Baseline characteristics of the study cohort and interim safety and efficacy data were presented previously (Gisslinger et al., Blood, 2015). Fifty-one patients were treated: Median exposure to Ropeg was approximately 5.1 years (61 months; range: 0 to 87 months). Patients were treated for a median of approximately 2 years (98.9 weeks; (Q1-Q3: 69.0 - 117.4 weeks) on the 2-weekly regimen and 4 years (207.1 weeks; Q1-Q3: 158.6 - 242.0 weeks) on the 4-weekly regimen. The best observed individual hematological response for patients in the efficacy analysis set (FAS) was a complete hematological response for 27/42 (64.3%) and a partial response for 14/42 (33.3%) patients. Patients required a median of 34 weeks (Q1-Q3: 10-96 weeks) treatment to achieve a complete hematological response, and 10 weeks (Q1-Q3: 10-20 weeks) to achieve any hematological response. Switch from 2 to 4-week dosing regimen had no apparent effect on maintenance of response. With respect to JAK-2 allele burden, the best observed individual molecular response was a complete response for 12/42 (28.6%) patients and a partial response for 19/42 (45.2%) patients. Lowest JAK-2 values relative to baseline are presented by patient in Figure 1. Patients required a median of 82 weeks (Q1-Q3: 44-115 weeks) treatment to achieve a complete molecular response and 34 weeks (Q1-Q3: 18-55 weeks) treatment to achieve any molecular response. Irrespective of dosing regimen, molecular responses tended to increase over time. Most patients reported at least one adverse reaction (AR) to treatment (409 ARs in 48/51 [94.1%]); however, the majority (296 in 44 [86.3%] patients) were mild; 102 (in 34 [66.7%] patients) were moderate and 11 (in 10 [19.6%] patients) were severe. The most frequently reported ARs (frequency >20%) were arthralgia, influenza-like illness and fatigue. Twelve serious treatment emergent adverse events (TEAE) reported by 8/51 patients (15.7%) were considered to be treatment related: 2 events of depression, 2 of positive anti-thyroid antibodies, and one each of acute stress disorder, increased antinuclear antibodies, arthralgia, atrial fibrillation, fatigue, influenza-like illness, pyrexia, and increased transaminases. 25 patients completed the trial. The majority of discontinuation due to TEAE (13/21 patients) occurred in the first year, when the recommended slow up-titration of Ropeg could not be applied because of the maximum-tolerated-dose design. After the first year, only 8 additional patients discontinued because of TEAE. Conclusions: The final results of this phase I/II study of Ropeg in patients with PV support the findings of the pivotal phase III clinical trial (Gisslinger et al., Blood 2015) with respect to safety and efficacy as determined by hematological, clinical and molecular parameters. In addition, these data provide evidence that treatment with Ropeginterferon alfa-2b for up to 7 years is efficacious, well-tolerated and disease-modifying at both the 2 week and 4 week maintenance treatment regimens. Disclosures Gisslinger: AOP Orphan Pharmaceuticals AG: Consultancy, Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Janssen Cilag: Consultancy, Honoraria; Shire: Consultancy, Honoraria. Kralovics:MyeloPro Diagnostics and Research GmbH: Equity Ownership. Krauth:BMS: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Janssen: Consultancy, Honoraria. Greil:MSD: Honoraria, Research Funding; Merck: Honoraria, Research Funding; Sandoz: Honoraria, Research Funding; Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Astra Zeneca: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Research Funding; Janssen: Other: TRAVEL, ACCOMMODATIONS, EXPENSES; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees. Zoerer:AOP Orphan Pharmaceuticals: Employment. Empson:AOP Orphan Pharmaceuticals: Employment. Grohmann-Izay:AOP Orphan Pharmaceuticals AG: Employment. Klade:AOP Orphan Pharmaceuticals AG: Employment.

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