Safety and Efficacy of Combined Ruxolitinib and Decitabine in Patients with Blast-Phase MPN and Post-MPN AML: Results of a Phase I Study (Myeloproliferative Disorders Research Consortium 109 trial)

Background: The Philadelphia chromosome negative myeloproliferative neoplasms (MPN) includePolycythemia Vera (PV), Essential Thrombocythemia (ET) and Primary Myelofibrosis (PMF). These stem cell disorders carry a propensity to evolve into acute myeloid leukemia (MPN-blast phase [BP] or post-MPN AML) with a dismal prognosis not meaningfully improved by conventional anti-leukemia therapy. Thus, MPN-BP is an urgent unmet clinical need. Responses in patients with MPN-BP to hypomethylating agents and single agent ruxolitinib have been reported. More recently, combination of ruxolitnib and decitabine has demonstrated synergistic activity in vitro in cells derived from patients with MPN-BP and from a murine model of MPN-BP (Rampal et al PNAS 2014). These observations led us to explore the safety of combined decitabine and dose escalation of ruxolitinib in MPN-BP.

Objective: To establish the maximum tolerated dose (MTD) of ruxolitinib in combination with a fixed dose of decitabine (DEC-RUX).

Methods: We conducted an open label Phase I trial in patients with MPN acceleration phase (AP) as defined by 10%-19% blasts in the peripheral blood or bone marrow or a diagnosis of MPN-BP as defined by ≥ 20% blasts in the blood or bone marrow, following a previous diagnosis of ET, PV or PMF. Patients were enrolled in a standard 3+3 phase I design with an MTD defined as a dose <33% DLT. Ruxolitinib was administered at doses of 10mg, 15mg, 25mg, or 50mg every 12 hours in combination with concurrent decitabine at a dose of 20mg/m² daily intravenously over 5 days and repeated every 28 days. Adverse events were assessed using the NCI CTCAE v. 4.0. DLTs were defined as Grade 3 or higher non-hematologic toxicity events not clearly related to disease and grade 4 hematologic events with a bone marrow cellularity of ≤5% and no evidence of leukemia. Response assessment was carried out every cycle using modified Cheson criteria: CR required 0% peripheral blood blasts, WBC ≥4x10⁹/L, hemoglobin ≥10g/L, and platelets ≥100x10⁹/L; CRi required 0% peripheral blood blasts with incomplete count recovery; and PR required ≥50% decrease in peripheral blood blasts regardless of blood counts.

Results: A total of 21 patients were accrued to study (Table 1). The median age was 63 years (range 48-88). 52% carried a diagnosis of MPN-AP, and 48% carried a diagnosis of MPN-BP. 29% of patients and 24% of patients had prior exposure to ruxolitinb and decitabine, respectively. The median number of cycles received varied from 10.5 cycles in the 10mg BID cohort to 2 and 2.5 cycles in the 25mg BID and 50mg BID cohorts, respectively (Table 2). The most common Grade 3/4 non-hematologic AEs observed were due to infection in all dosing cohorts. In terms of hematologic toxicity, treatment emergent Grade 3/4 anemia was observed in 1 patient in each of the 10mg BID, 15mg BID, and 50mg BID cohorts. Grade 3/4 leukopenia was observed in only 1 patient at the 50mg BID cohort, and Grade 3/4 thrombocytopenia was observed in 2 patients in the 10mg BID cohort and 1 patient in the 15mg BID cohort. DLT rate was below 33% for all dose levels so the MTD was not reached. The most common reason for ending study treatment was toxicity/adverse events (33%) followed by disease progression (22%). 9 patients died during study or follow-up. Of those, 5 (56%, 2 in 10mg BID cohort, 1 in 15mg BID cohort, 2 in 50mg BID cohort) died of infection, 3 (33%, 1 in each of 10mg, 25mg, and 50mg BID cohorts) of progressive disease, and 1 (11%, 25mg BID cohort) of hemorrhage.

The median overall survival for patients on study was 10.4 months (95% CI 3.3 mo - not reached). CR/CRi as best response was observed in 7/21 patients (33%, 95% CI 15-57%; 2 CR, 5 CRi; Table 2).

Conclusions: DEC-RUX combination therapy was safely administered to patients with MPN-AP/BP and an MTD was not reached. Based on pre-clinical data, observed safety profile, duration of treatment, and clinical responses in this phase I trial, the Recommended Phase II Dose of RUX was selected as 25mg BID for an induction cycle followed by 10mg BID in all ensuing cycles. Molecular and bone marrow pathology responses will be presented at the meeting.

View largeDownload slide

View largeDownload slide

Close modal

View largeDownload slide

View largeDownload slide

Close modal