A Phase 1b, Dose-Finding Study Of Ruxolitinib Plus Panobinostat In Patients With Primary Myelofibrosis (PMF), Post–Polycythemia Vera MF (PPV-MF), Or Post–Essential Thrombocythemia MF (PET-MF): Identification Of The Recommended Phase 2 Dose

Myelofibrosis (MF) is a myeloproliferative neoplasm associated with progressive, debilitating symptoms that impact patient quality of life (QoL) and reduce survival. Ruxolitinib (RUX), a potent dual JAK1/JAK2 inhibitor, demonstrated superiority in spleen volume and symptom reduction, improved health-related QoL measures, and prolonged survival compared with traditional therapies or placebo in the phase 3 COMFORT studies. Panobinostat (PAN) is a potent oral pan-deacetylase inhibitor (DACi) that inhibits JAK pathway signaling through increased acetylation of the JAK2 protein chaperone HSP90. In phase 1/2 studies in MF, PAN has shown reduction in splenomegaly and JAK2 V617F allele burden, and improvement of marrow fibrosis. RUX and PAN demonstrated synergistic anti-MF activity in JAK2-mutation–driven MF murine models. Here, we present the results of a phase 1b study to determine the recommended phase 2 dose (RP2D) of the combination of RUX and PAN in MF patients.

Patients with intermediate-1, -2, or high-risk MF by International Prognostic Scoring System criteria and with palpable splenomegaly ≥ 5 cm below the costal margin were enrolled. Dose escalation was guided by a Bayesian logistic regression model with overdose control based on dose-limiting toxicities (DLTs) in the first cycle along with other safety findings. DLTs were defined as protocol-specified toxicities related to treatment but unrelated to disease progression, intercurrent illness, or concomitant medications, occurring up to and including cycle 1 day 28, that are considered severe enough to prevent continuation of treatment. Each dosing cohort consisted of ≥ 3 evaluable patients. Data for ≥ 9 patients were required to determine the preliminary RP2D and/or maximum tolerated dose (MTD). Following determination of the preliminary RP2D, additional patients were to be enrolled and treated at that dose in the safety-expansion phase. The range of dose levels tested for RUX was 5-15 mg twice daily (BID) and for PAN was 10-25 mg once daily, 3 times a week (TIW; days 2, 4, and 6), every other week (QOW) in a 28-day cycle. Serial blood samples collected following the first dose of RUX alone on day 1 and in combination with PAN on days 2 and 6 were evaluated for plasma concentrations of RUX (days 1, 2, and 6) and PAN (days 2 and 6) by LC-MS/MS. Pharmacokinetic parameters were derived using noncompartmental analysis. Spleen size was determined by palpation.

A total of 38 patients have been enrolled across 6 cohorts in the dose-escalation phase. Preliminary data presented here are based on a cutoff date of March 7, 2013. Thirteen patients (34.2%) have discontinued study treatment. Reasons for discontinuation include disease progression (n = 4), adverse events (n = 7), withdrawal of consent (n = 1), and death due to pulmonary embolism (n = 1). The most common grade 3/4 adverse events were anemia (34.2%), thrombocytopenia (21.2%), abdominal pain (7.9%), and diarrhea (7.9%). QTc prolongation of > 500 ms was observed in 1 patient in cohort 4. DLTs are summarized in the Table. An approximate 50% increase in plasma exposure of both RUX and PAN on day 6 from respective baselines suggested drug-drug interaction (DDI) at 15 mg RUX and 25 mg PAN. The RP2D was defined at the cohort 6 dose and schedule. Evidence of preliminary activity was observed across all cohorts with 28 patients (73.7%) showing ≥ 50% decrease in palpable spleen length at some point during the study.

The combination of RUX and PAN has a tolerable safety profile, with few DLTs and acceptable rates of grade 3/4 anemia and thrombocytopenia. Also, encouraging splenomegaly reduction was seen in the dose-escalation phase. The MTD was not reached; however, due primarily to findings of anemia and potential DDI in dose cohort 6, preliminary RP2D was identified at RUX 15 mg BID/PAN 25 mg TIW/QOW and will be confirmed in the dose-expansion phase. Additional safety and efficacy data from patients in the expansion phase will be presented.

Ribrag:Takeda: Membership on an entity’s Board of Directors or advisory committees; Bayer: Research Funding; Sanofi: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Johnson & Johnson : Honoraria, Membership on an entity’s Board of Directors or advisory committees; Servier: Membership on an entity’s Board of Directors or advisory committees, Research Funding. Off Label Use: Ruxolitinib is approved for MF but panobinostat is not approved anywhere globally at this time for any indication. Harrison:S Bio: Honoraria, Membership on an entity’s Board of Directors or advisory committees; Shire: Speakers Bureau; Celgene: Honoraria; YM Bioscience: Honoraria, Membership on an entity’s Board of Directors or advisory committees; Sanofi: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Speakers Bureau; Novartis: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; Gilead: Honoraria, Membership on an entity’s Board of Directors or advisory committees. Heidel:Novartis: Membership on an entity’s Board of Directors or advisory committees, Research Funding. Kiladjian:AOP Orphan: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Sanofi: Honoraria, Membership on an entity’s Board of Directors or advisory committees; Celgene: Research Funding; Novartis: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding. Acharyya:Novartis: Employment. Mu:Novartis: Employment. Liu:Novartis: Employment. Williams:Novartis: Employment. Giles:Novartis: Consultancy, Research Funding. Conneally:Pfizer: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; BMS: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Novartis: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding. Kindler:Novartis: Membership on an entity’s Board of Directors or advisory committees. Passamonti:sanofi-aventis: Honoraria; Incyte: Honoraria; Celgene: Honoraria; Novartis: Honoraria. Vannucchi:Novartis: Honoraria, Membership on an entity’s Board of Directors or advisory committees.