Abstract: Background: Treatment of elderly AML patients considered unfit for conventional chemotherapy is inadequate and hypomethylating agents are commonly used alternatives. In the case of azacitidine, responses are typically seen after 3–6 cycles of therapy, and a recent large randomized trial in elderly unfit patients reported a complete response (CR)/CR with incomplete blood count recovery rate of 28% (Dombret et al, EHA 2014). Pevonedistat (MLN4924) is an investigational, first-in-class NEDD8-activating enzyme (NAE) inhibitor. A phase 1 trial previously reported pevonedistat single-agent clinical activity in relapsed/refractory AML patients. Preclinical studies of pevonedistat and azacitidine identified synergistic lethality in AML cell lines and murine xenografts. The current phase 1b dose-escalation study evaluated the safety and tolerability of pevonedistat combined with azacitidine in elderly AML patients considered unfit for conventional chemotherapy. Methods: The primary objective was to assess the safety and tolerability of pevonedistat combined with azacitidine. Secondary objectives included assessment of pevonedistat pharmacokinetics (PK) and clinical activity. Treatment-naïve AML patients aged ≥60 years who were considered unfit for standard induction therapy received pevonedistat via 1-hour IV infusion on days 1, 3, and 5 of 28-day cycles. Dose escalation began at 20 mg/m2 and used an adaptive Bayesian continual reassessment method. Azacitidine 75 mg/m2 was administered (IV or SC) on days 1–5 and 8–9. Patients were treated until disease progression or unacceptable toxicity. Adverse events (AEs) were graded per NCI-CTCAE v4.03. Responses were assessed according to International Working Group response criteria for AML. Serial blood samples were obtained for PK analysis following dosing on days 1 and 5 of cycle 1. Results: As of May 30, 2014, 25 patients (median age 75.0 years [range 63–85]; 16 [64%] male) had received pevonedistat 20 mg/m2 (n=22) and 30 mg/m2 (n=3). Primary diagnoses were 16 (64%) de novo AML and 9 (36%) secondary AML. Fourteen (56%) patients had intermediate- and 6 (24%) had adverse-risk cytogenetics (5 [20%] undetermined). During dose escalation, dose-limiting toxicity (DLT) at the 30 mg/m2 pevonedistat dose level included reversible grade 2 increased bilirubin (n=1) and grade 3/4 increased transaminases (n=1) without clinical sequelae. In 1 of the 22 patients treated at the maximum tolerated dose (20 mg/m2 pevonedistat plus 75 mg/m2 IV/SC azacitidine), 1 additional DLT (grade 4 AST/ALT elevation) was seen in the expansion cohort. This patient was successfully re-challenged with a reduced pevonedistat dose. The most common all-grade AEs are shown in table 1. Twelve (48%) patients experienced drug-related grade ≥3 AEs (table 1). The nature and frequency of the reported toxicities (excluding DLTs) were similar to previous reports for azacitidine alone. Preliminary PK data showed that addition of azacitidine did not alter the known PK profile of single-agent pevonedistat. In the 18 response-evaluable patients, there were 6 (33%) CRs and 4 (22%) PRs (table 2), for an overall response rate of 56%. Nine of the 10 responses occurred within the first two cycles of therapy and included 1 patient with bone marrow blasts 〉 80%. Conclusions: Combination therapy with pevonedistat and azacitidine was generally well-tolerated. The characteristics of the observed responses suggest added benefit from the addition of pevonedistat compared with azacitidine alone. Table 1 Common all-grade AEs n (%) Most frequent (≥10%) drug-related grade ≥3 AEs n (%) Febrile neutropenia 9 (36) Febrile neutropenia 4 (16) Constipation 8 (32) Thrombocytopenia 3 (12) Decreased appetite 7 (28) – – Thrombocytopenia 7 (28) – – Table 2 Responders* Tumor Type Cytogenetic Risk Group Current Status Response Molecular CR 1st Response 1st CR 1 De novo AML Adverse C12 C4 – – 2 Undetermined C4† C1 C1 Y 3 Adverse C9 C1 C1 Y 4 Undetermined C5‡ C1 C2 Y 5 Intermediate C5† C1 C2 N 6 Intermediate C7 C1 C4 Y 7 Intermediate C2 C2 – – 8 Secondary AML Undetermined C4 C2 C2 – 9 Normal C4 C1 – – 10 De novo AML – C1 C1 – – Molecular CR, complete remission confirmed by molecular studies *All received 20 mg/m2 pevonedistat except #4, who started on 30 mg/m2 and had a dose reduction to 20 mg/m2. †Patient off study ‡Patient off treatment and in follow-up Disclosures Swords: Novartis: Consultancy; KaloBios Pharmaceuticals, Inc.: Consultancy; Millennium: The Takeda Oncology Company: Consultancy. Savona:Novartis: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees; Gilead Sciences, Inc.: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Karyopharm Pharmaceuticals: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees. Erba:Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Consultancy, Research Funding; Incyte: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Takeda Pharmaceuticals International Co.: Research Funding; Astellas Pharma: Research Funding; Celgene: Honoraria, Speakers Bureau; Seattle Genetics: Consultancy, Research Funding. Foran:Takeda Pharmaceuticals International Co.: Research Funding. Hua:Takeda Pharmaceuticals International Co.: Employment. Faessel:Takeda Pharmaceuticals International Co.: Employment, Equity Ownership. Dash:Takeda Pharmaceuticals International Co.: Employment. Sedarati:Takeda Pharmaceuticals International Co.: Employment. Dezube:Takeda Pharmaceuticals International Co.: Employment. Medeiros:Millennium: The Takeda Oncology Company: Consultancy, Honoraria; Takeda Pharmaceuticals International Co.: Research Funding.