Phase I Study of Ixazomib in Addition to Chemotherapy for the Treatment of Acute Myeloid Leukemia in Older Adults

Introduction: Treatment of acute myeloid leukemia (AML) has remained largely unchanged for several decades despite the emergence of new agents. Long-term survival for patients aged >60 years is less than 10% (median survival 10.5 months). Targeting the proteasome in treating AML is attractive, since leukemia stem cells have demonstrated sensitivity to proteasome inhibition, perhaps through down regulation of nuclear NF-KB (Guzman, Blood 2001). Preclinical studies in leukemia cell lines revealed synergistic cytotoxicity when bortezomib, a proteasome inhibitor, was combined with the standard agents daunorubicin and cytarabine. We have shown that adding bortezomib to standard treatment in AML results in a high remission rate, although neurotoxicity was noted among treated patients, 12% grade 3 sensory (Attar, …, Amrein, et al. Clin Cancer Res 2008, Attar, … Amrein, J Clin Oncol 2012). The next generation proteasome inhibitor, ixazomib, which is less frequently associated with neurotoxicity, was therefore selected for combination with conventional chemotherapy in this phase I trial. The primary objective was to determine the maximum tolerated dose (MTD) in the combination, initially in induction, and then in combination with consolidation in a subsequent portion of the overall study. We report here the results of the induction portion of the study, which has been completed.

Methods: Adults >60 years of age with newly diagnosed AML were screened for eligibility. Patients with secondary AML were eligible, including those with prior hypomethylating agent therapy for myelodysplastic syndromes (MDS). We excluded those with promyelocytic leukemia. The induction treatment consisted of the following: cytarabine 100 mg/m2/day by continuous IV infusion, Days 1-7; daunorubicin 60 mg/m2/day IV, Days 1, 2, 3; ixazomib orally at the cohort dose, Days 2, 5, 9, and 12

A standard 3 + 3 patient cohort dose escalation design was used to determine whether the dose of ixazomib could be safely escalated in 3 cohorts (1.5 mg/day, 2.3 mg/day, 3.0 mg/day), initially in induction and subsequently in consolidation. The dose of 3.0 mg/day was the maximum planned for this study. The determined MTD of ixazomib in the first portion of the trial would be used during induction in the second portion, which seeks to test dose escalation of ixazomib during consolidation. Secondary objectives included rate of complete remission and disease-free survival.

Results: Fourteen patients have been analyzed for toxicity and activity during the induction portion of the study. There were 4 (28%) patients with either secondary AML or treatment related AML, 9 (64%) were male, and the median age was 67 years (range 62-80 years). There have been no grade 5 toxicities due to study drug. Three patients died early due to leukemia, 2 of which were replaced for assessment of the MTD. Nearly all the grade 3 and 4 toxicities were hematologic (Table). There was 1 DLT (grade 3 thrombocytopenia) indicated at the highest dose level. There has been no neurotoxicity with ixazomib to date. Among the 14 patients, there have been 10 complete remissions (CR's) and 1 CRi for a remission rate of 79%.

Conclusions: The highest dose level planned for this portion of the trial, 3.0 mg of ixazomib, was reached with 1 DLT and is the recommended dose for induction in the next portion of this study, which will seek to determine a safe ixazomib dose in combination with conventional consolidation therapy. That no neurotoxicity was encountered was reassuring, and the remission rate in this older adult population is favorable.

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