Long Term Efficacy and Safety Results and Analysis of Dose Correlations from the Phase I/II Peginvera Study of Ropeginterferon Alfa-2b, a Novel IFNa-2b, in Polycythemia Vera Patient

Background Ropeginterferon alfa-2b (AOP2014/P1101) is a novel long-acting pegylated IFN-alpha-2b, composed of mainly one isoform, resulting in longer half-life and exposure time. Reduced dosing frequencies, better tolerability, improved compliance and more favorable long-term treatment outcomes in patients with polycythemia vera (PV) are expected. The drug has Orphan designation by EMA and FDA and is currently in the phase III stage of development.

Study design Efficacy and safety data are being collected in the follow-up extension stage of the study (collecting the data of both Phase I and Phase II portions of the study), after the maximum tolerated dose (MTD) of ropeginterferon alfa-2b, administered subcutaneously every 14 to 28 days, has been defined earlier. Patients with confirmed diagnosis of PV, age ≥18 years, both naïve and cytoreductively pre-treated were eligible. After establishing the MTD, an extended cohort of 25 additional patients has been planned to be recruited. Complete hematological response (CR) is defined by hematocrit (Hct)<45%, platelet count≤400*10⁹/L, WBC count≤10*10⁹/L, normal spleen size by sonography, and absence of thromboembolic events. Partial response (PR) is defined as Hct<45% without phlebotomy but with persistent splenomegaly or elevated (>400*10⁹/L) platelet count, or reduction of phlebotomy requirements by at least 50%. Complete molecular response has been defined as reduction of any molecular abnormality to undetectable levels; partial molecular response as: reduction ≥ 50% in patients with < 50% mutant allele burden, or a reduction ≥ 25% in patients with > 50% mutant allele burden. The present analysis was focused on long-term tolerability and safety in correlation with the dose of ropeginterferon alfa-2b in PV.

Results Data on treatment as by July, 24, 2015, are covered by the current analysis. Baseline characteristics of the study cohort during short-term treatment were already presented earlier (Gisslinger et al, ASH 2013). The full analysis set and efficacy set were composed of 51 and 47 patients, respectively. Currently, the median reported treatment duration is 138 weeks, 33 patients completed their follow up for two years, 19 for three years. Starting with the week 10, Hct-level, platelet- and WBC-counts could be constantly maintained within normal range in the majority of patients. In a group of patients with the mean administered dose of <300 µg (“low dose”, n=36), CR as best individual response was achieved in 20 (56%) patients, and PR in 14 (39%) compared to the CR and PR in the high dose (>300 µg, n=11) group of 8 (73%) and 3 (27%) respectively. However, no statistical significance can be observed if correlation between the dose and response status was analyzed. 30 patients are still being treated in the study. Similarly, no association between the dose and occurrence of adverse events in the study could be observed. Complete molecular response as best individual response was observed more frequently in the high dose group 4 (36%) compared to 8 (23%) in the low dose group, while partial molecular responses were equally frequent in both dose groups (in 6/55% and 20/57%, respectively). 21 patients discontinued the study, 18 being treated with AOP2014 doses corresponding to low, and 3 to the high dose arms, corresponding to the drop-out rate of 50% and 27% in the respective arms. Interestingly, all discontinuations in the high dose group occurred within the first year of treatment (at weeks 16, 18 and 32), while the drop-outs in the low dose group (6 patients, 33%) discontinued the study after completion of their first year of treatment.  

Conclusions Efficacy and safety profile remain in line with expectations from other (pegylated) interferons. Overall response rate of >80% with cumulative CRs in 45-50%, accompanied by phlebotomy independence, normalization of hematological parameters and spleen size reduction in majority of patients have been observed. Significant and sustained JAK2 allelic burden decrease, starting from week 28 of treatment, was seen. No significant difference between the two mean dose levels regarding response rates or adverse events even during long-term treatment and observation could be observed. These finding are to be further verified in a larger prospective setting.