A phase I study of targeted, dose-escalated intravenous busulfan in combination with etoposide as myeloablative therapy for autologous stem cell transplantation in acute myeloid leukemia

Background Busulfan and etoposide have been used as myeloablative therapy for autologous hematopoietic stem cell transplantation (HSCT) in adults with acute myeloid leukemia (AML) for > 20 years. The use of targeted intravenous (I.V.) busulfan has significantly improved the tolerability and efficacy of this regimen. We designed a dose-escalation study to examine the maximum tolerated dose (MTD) of targeted I.V. busulfan with bolus etoposide as preparative therapy for autologous HSCT in AML. Patients and Methods In this single-center, phase I study, adult AML patients received I.V. busulfan targeted to either an area under the curve (AUC) of 1250 (cohort 1) or 1400 (cohort 2) μmol/min over 16 doses. Dose adjustments based on plasma pharmacokinetics occurred before doses 2 and 11. Etoposide 60 mg/kg I.V. was administered 24 hours after the last busulfan dose and 3 days before stem cell infusion. Results Twelve patients with intermediate-risk AML in first complete remission were treated. All patients in cohort 1 and 5 patients (83%) in cohort 2 were within 10% of the target AUC. The MTD was not reached, although Grade ≥ 3 mucositis occurred in 3 patients (50%) in cohort 1 and in 4 patients (66%) in cohort 2, limiting further dose escalation. Two-year relapse-free survival was 33% in cohort 1 versus 67% in cohort 2 ( P = .08). Conclusion Etoposide and targeted, dose-escalated I.V. busulfan as myeloablative therapy for autologous HSCT in AML is safe, with mucositis being the most significant toxicity. A phase II study is warranted to further evaluate the activity and safety of busulfan targeted to AUC 1400 μmol/min.