Compassionate Use of Ropeginterferon-Alfa-2b/P1101 for Treatment of High Risk Polycythemia Vera and Essential Thrombocythemia Patients Previously Controlled on Pegylated Interferon-Alfa-2a/Pegasys®
Authors: Gilreath Jeffrey A , Tashi Tsewang , Kim Soo Jin , Hickman Kimberly , Prchal Josef T. 
Published: October 2019

Abstract
Polycythemia vera (PV) and essential thrombocythemia (ET) are chronic myeloproliferative neoplasms (MPN) associated with morbidity and mortality resulting from thrombosis or transformation to myelofibrosis and/or secondary acute leukemia. The acquired somatic mutation JAK2V617Fhas been observed in 98% of PV patients, and around 50% of ET patients. Interferon is known to be an effective treatment for chronic MPNs, but unlike hydroxyurea (HU, Hydrea®), it has been shown to target the malignant clone by decreasing JAK2V617Fallelic burden, and in some patients restoring polyclonal hematopoiesis. (Liu et al, Blood. 2003;101:3294-3301). The covalent binding of polyethylene glycol to the interferon molecule, through pegylation, prolongs the half-life by lowering the clearance of interferon, thereby extending the duration of its therapeutic effects, permitting less frequent administration and fewer side-effects. Currently, there are two commercially available pegylated interferons in the U.S., peginterferon alfa-2b (PEG-Intron®, Merck) and peginterferon alfa-2a (Pegasys®, PEG, Roche), both with heterogeneous pegylation with multiple pegylation sites. Ropeginterferon-alfa 2b/P1101 (ROPEG) is a novel longer acting mono-pegylated recombinant proline-interferon alfa-2b which has shown good efficacy in PV and has successfully completed a phase III trial in PV patients comparing it against HU (PROUD-PV study) in Europe (ASH2016 Abstract;Blood. 2016;128:475).
Earlier, we had enrolled 53 high risk PV and ET patients to the Myeloproliferative Disorders Research Consortium (MPD-RC) trials #111 (refractory to HU) and #112 (randomized to HU vs PEG)(www.clinicaltrials.gov; NCT01259856 and NCT01259817). After the completion of these trials, PEG was no longer supplied by the study and not adequately covered by insurance for many of our patients. Therefore, ROPEG was procured under an FDA-approved expanded access program and used as a substitute for those controlled on PEG, and these patients are being transitioned from PEG to ROPEG according to the dosing strategy shown in Table 1.
Seven patients have been switched onto ROPEG as of writing this abstract (Table 2). After a mean follow-up of roughly 8 weeks (range: 2 - 10 weeks), all have maintained response to therapy and none have had a thrombotic event or new or increased interferon-related side effects thus far. Patient 002 experienced elevated AST/ALT while on PEG, which normalized after four q2 week doses of ROPEG (8 weeks of therapy). Patients 003 and 004 who had persistent fatigue on PEG, saw significant improvement of their symptoms after switching to ROPEG. In patient 005 who has ET, bone marrow cytogenetics at entry to PEG had a paracentric inversion of the long arm of chromosome 3, namely 3q21.3q26.2 (RPN1/MECOM, inv3; diagnostic of AML per WHO criteria), in 16/20 (80%) metaphases. Over the 4 ensuing years while on PEG, this cytogenetic abnormality progressively decreased. FISH assay was set up 2 years ago wherein 86/200 cells (46%) were positive with lowest achieved level of 36/200 cells (18%) without any evidence of emerging AML. Upon transition to ROPEG (2 fortnightly injections of 50 mcg), this response was maintained (23/200 cells scored (11.5%). Of the 3 patients who were JAK2V617Fpositive, one patient (patient 003) showed a decrease in the JAK2V617Fallelic burden (37% to 18%) after two months of ROPEG despite decreasing the dose to 50 mcg (from 100 mcg) 2 weeks after the first injection, while the other two patients had no statistically significant change in their JAK2V617Fallelic burden. Clonality will be followed in female subjects to see if clonal hematopoiesis is suppressed and normalizes with long-term administration of ROPEG.
Our early experience suggests ROPEG is a safe and effective alternative to PEG permitting less frequent administration for patients with high risk PV and ET. Notable observations include normalization of hepatic transaminases previously induced by PEG, maintenance or even suppression of one highly deleterious cytogenetic abnormality, maintenance of ET & PV remission, and amelioration of interferon side-effects with lower equivalent doses. In the future, we intend to increase the pool of patients by designing a protocol for newly diagnosed high risk ET and PV with randomization to HU versus ROPEG.

Disclosures
No relevant conflicts of interest to declare.