Preliminary Results from a Phase II Study of the Combination of Pevonedistat and Azacitidine in the Treatment of MDS and MDS/MPN after Failure of DNA Methyltransferase Inhibition

After failure of DNA methyltransferase inhibition (DNMTi) there is no standard of care therapy for high-risk myelodysplastic syndromes (MDS), and median survival for higher risk disease is less than 6 months (Prebet et al, JCO 2011; Jabbour et al, Cancer 2015). Pevonedistat, a first in human small molecule inhibitor of the NEDD8 activating enzyme (NAE), downregulates Cullin ring ligases (CRL) which interferes with the shuttling and degradation of proteins in the proteasome and leads to accumulation of CRL substrates. Combining pevonedistat (Pev) with azacitidine (AZA) resulted in synergistic cell killing in in vitro and xenograft models of acute myeloid leukemia (AML) (Smith et al, Blood 2011), elicited favorable response rates in treatment naïve elderly or unfit AML patients (Swords et al Blood 2018), and is currently under study in treatment-naïve MDS. The study presented herein (NCT03238248) investigates the utility of adding pevonedistat to azacitidine (PevAz) after DNMTi failure in MDS and MDS/MPN overlap syndromes. Methods: In this on-going single-arm phase II study, MDS and MDS/MPN patients were eligible if they were refractory to DNMTi treatment, progressing after at least 2 cycles of therapy; had failed to achieve a complete remission (CR) after at least 4 cycles of DNMTi therapy; or had relapsed after an initial response to DNMTi therapy. Enrolled subjects received AZA 75mg/m2 sc/iv daily on days 1-5 and Pev 20mg/m2 iv on days 1, 3 and 5 of each 28-day cycle. Survival is the primary endpoint and is assessed at regularly scheduled study visits and every 3 months after ending protocol-directed therapy. Hematologic and bone marrow response rates are secondary endpoints. Responses to treatment are determined by the MDS International Working Group (IWG) response criteria (Cheson et al, Blood 2006) or for MDS/MPN, by the modified MDS/MPN IWG response criteria (Savona et al, Blood 2015). Results: As of the data cutoff on 15 MAR 2019, 23 subjects (21 with MDS, 2 with MDS/MPN) had enrolled and initiated treatment. Subjects had previously been treated with AZA (n=11/23), decitabine (n=11/23), and ASTX727 (n=4/23); some subjects had been treated with more than one DNMTi prior to enrollment. Median number of cycles of any prior DNMTi therapy was 7 (range 2-35). 65% of subjects were female. Median age at enrollment was 67 years (range 51 - 85). 65% had Intermediate-2 or High risk disease by IPSS at time of enrollment. Median number of PevAz cycles completed p