Clofarabine ± fludarabine with once daily i.v. busulfan as pretransplant conditioning therapy for advanced myeloid leukemia and MDS

Abstract

Although a combination of i.v. busulfan (Bu) and fludarabine (Flu) is a safe, reduced-toxicity conditioning program for acute myelogenous leukemia/myelodysplastic syndromes (AML/MDS), recurrent leukemia posttransplantation remains a problem. To enhance the conditioning regimen's antileukemic effect, we decided to supplant Flu with clofarabine (Clo), and assayed the interactions of these nucleoside analogs alone and in combination with Bu in Bu-resistant human cell lines in vitro. We found pronounced synergy between each nucleoside and the alkylator but even more enhanced cytotoxic synergy when the nucleoside analogs were combined prior to exposing the cells to Bu. We then designed a 4-arm clinical trial in patients with myeloid leukemia undergoing allogeneic stem cell transplantation (allo-SCT). Patients were adaptively randomized as follows: Arm I-Clo:Flu 10:30 mg/m(2), Arm II-20:20 mg/m(2), Arm III-30:10 mg/m(2), and Arm IV-single-agent Clo at 40 mg/m(2). The nucleoside analog(s) were/was infused over 1 hour once daily for 4 days, followed on each day by Bu, infused over 3 hours to a pharmacokinetically targeted daily area under the curve (AUC) of 6000 μMol-min ± 10%. Fifty-one patients have been enrolled with a minimum follow-up exceeding 100 days. There were 32 males and 19 females, with a median age of 45 years (range: 6-59). Nine patients had chronic myeloid leukemia (CML) (BC: 2, second AP: 3, and tyrosine-kinase inhibitor refractory first chronic phase [CP]: 4). Forty-two patients had AML: 14 were induction failures, 8 in first chemotherapy-refractory relapse, 7 in untreated relapse, 3 in second or subsequent relapse, 4 were in second complete remission (CR), and 3 in second CR without platelet recovery (CRp), 2 were in high-risk CR1. Finally, 1 patient was in first CRp. Graft-versus-host disease (GVHD) prophylaxis was tacrolimus and mini-methorexate (MTX), and those who had an unrelated or 1 antigen-mismatched donor received low-dose rabbit-ATG (Thymoglobulin™). All patients engrafted. Forty-one patients had active leukemia at the time of transplant, and 35 achieved CR (85%). Twenty of the 42 AML patients and 5 of 9 CML patients are alive with a projected median overall survival (OS) of 23 months. Marrow and blood (T cell) chimerism studies at day +100 revealed that both in the lower-dose Clo groups (groups 1+2) and the higher-dose Clo groups (groups 3+4), the patients had a median of 100% donor (T cell)-derived DNA. There has been no secondary graft failure. In the first 100 days, 1 patient died of pneumonia, and 1 of liver GVHD. We conclude that (1) Clo ± Flu with i.v. Bu as pretransplant conditioning is safe in high-risk myeloid leukemia patients; (2) clofarabine is sufficiently immunosuppressive to support allo-SCT in myeloid leukemia; and (3) the median OS of 23 months in this high-risk patient population is encouraging. Additional studies to evaluate the antileukemic efficacy of Clo ± Flu with i.v. Bu as pretransplant conditioning therapy are warranted.

Copyright © 2011 American Society for Blood and Marrow Transplantation. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1

Effects of Clo, Flu and Bu on cell cycle, apoptosis DNA damage response in the KBM3/Bu2506 cells. (a) Cells were exposed to drugs, alone or in combination, for 48 hr and analyzed for cell cycle distribution. (b) Similarly treated cells were also evaluated by determining the proportion of cells with fragmented DNA using the TUNEL assay. (c) The DNA-damage response was further assessed by probing for the phosphorylation of histone 2AX and cleavage of PARP1.

Figure 2

Kaplan-Meier Estimates for the overall (red line) and progression-free (blue line) survival of all 51 patients treated on the Clo±Flu with IV Bu protocol.

Figure 3

Kaplan-Meier estimates for overall survival of the 42 AML/MDS patients. The low clofarabine group is Arms I and II (the lower doses of 10 or 20 mg/m2/day clofarabine together with fludarabine at 30 and 20 mg/m2/day respectively, blue line), and the high clofarabine group refers to Arms III and IV (30 or 40 mg/m2/day clofarabine with fludarabine at mg/m2/day and 0 mg/m2/day, respectively, red line). The numbers within the brackets refer to the number of events in the respective groups (5/12 in the low Clo group and 10/30 in the high Clo group).

Figure 4

Kaplan-Meier estimates for Progression-free survival in the 42 AML/MDS patients. The low clofarabine group is Arms I and II (the lower doses of 10 or 20 mg/m2/day clofarabine together with fludarabine at 30 and 20 mg/m2/day respectively, blue line), and the high clofarabine group refers to Arms III and IV (30 or 40 mg/m2/day clofarabine with fludarabine at 10 mg/m2/day and 0 mg/m2/day, respectively, red line). The numbers within the brackets refer to the number of events in the respective groups.