A Phase I Study of CPX-351 in Combination with Busulfan and Fludarabine Conditioning and Allogeneic Stem Cell Transplantation in Adult Patients with Refractory Acute Leukemia

This phase I study evaluated the maximal tolerated dose of CPX-351 when administered sequentially with allogeneic hematopoietic stem cell transplantation (HSCT) in patients with refractory acute leukemia. CPX-351 is a novel liposomal formulation that combines cytosine arabinoside (ara-c) and daunorubicin in a fixed molar ratio of 5:1. Patients in cohorts of 3 were treated with CPX-351 followed by fludarabine and busulfan (Bu/Flu) conditioning at 4-week (schedule A) or 3-week (schedule B) intervals. CPX-351 doses were escalated in 20-U/m2 increments starting at 60 U/m2 for 3 doses. Of the 36 patients enrolled, 29 were able to undergo HSCT, and the other 7 (the majority on schedule A) did not proceed to HSCT because of rapid disease progression. The maximal tolerated dose of CPX-351 was not reached at the 120 U/m2 × 3 dose level. All 29 patients who proceeded to HSCT demonstrated adequate neutrophil and platelet engraftment. The median follow-up on the study for all 36 patients was 205 days (range, 20 to 996 days). The 1-year cumulative incidence of relapse for the 36 patients was 60.1% (95% confidence interval [CI], 43.4% to 77.3%), and that of nonrelapse mortality was 23.8% (95% CI, 10.9% to 47.4%). The 1-year overall survival and leukemia-free survival were 37% (95% CI, 21% to 53%) and 27% (95% CI, 13% to 43%), respectively. Our data suggest that a phase II trial should incorporate CPX-351 120 U/m2 × 3 dosing on schedule B. Patients with good performance status and those who achieve effective cytoreduction from CPX-351 derived the greatest benefit.