Background

Clofarabine is a nucleoside analogue with activity in children with acute lymphoblastic leukemia (ALL). Based on the hypothesis that clofarabine inhibits DNA repair after exposure to DNA-damaging agents, we designed a phase I and extension study to evaluate the combination of clofarabine and cyclophosphamide in adult patients with relapsed/refractory ALL.

Methods

The continual reassessment method (CRM) was used to define the maximum tolerated dose (MTD).

Results

Fifty patients with a median age of 30 years (range, 21-72 years) were enrolled, 30 of whom were part of the phase I group. Clofarabine 40 mg/m(2) intravenously daily × 3 days and cyclophosphamide 200 mg/m(2) intravenously every 12 hours × 3 days were established as the MTDs. Dose limiting toxicity (DLT) included diarrhea, transaminase elevations, and skin rashes. The response rate of the whole study group was 14%, including 10% of patients who achieved complete remission (CR) or CR without platelet recovery (CRp). Three responses occurred in patients with primary refractory disease. Early mortality (< 30 days) was 6%. The median duration of response was 69 days (range, 5-315 days). Median overall survival was about 3 months. Compared with day 1 (cyclophosphamide alone), H2AX phosphorylation was increased on day 2 when clofarabine and cyclophosphamide were administered as a couplet (n = 8).

Conclusion

The combination of clofarabine plus cyclophosphamide at the doses used in this study in a group of heavily pretreated patients with ALL is only moderately effective. Other doses, alternative schedules, or a more favorable patient population may achieve better results.

Chemoimmunotherapy regimens have been the standard first-line therapy for patients with chronic lymphocytic leukemia (CLL). For young, fit patients the standard of care is combination of fludarabine, cyclophosphamide, and rituximab (FCR). Based on the preclinical work demonstrating that bendamustine combined with fludarabine resulted in increased DNA damage, we designed a phase I-II clinical trial with fludarabine, bendamustine, and rituximab (FBR) for patients with relapsed/refractory CLL. Treatment consisted of fludarabine 20 mg/m2 daily x 3 days and rituximab 375-500 mg/m2 x 1 day. Phase I included bendamustine at increasing doses of 20, 30, 40, or 50 mg/m2 daily x 3 days; phase II was with FR, and B at the selected dose. DNA damage response (H2AX phosphorylation) was evaluated in a subset of patients. Fifty-one patients were enrolled. The median age was 62 years; median number of prior therapies was 2; 40% had del(11q); and 41 patients had received prior FCR-based therapies. Hematologic toxicity was more common in ≥40 mg/m2 dose cohorts. Maximum tolerated dose (MTD) was not identified. Bendamustine-elicited H2AX phosphorylation was not dose-dependent, but markedly increased after fludarabine. We identified bendamustine 30 mg/m2 as the safe dose for phase II. The overall response rate (ORR) was 67% with 36% complete response (CR) / CR with incomplete count recovery (CRi). Younger patients (<65 years) had significantly higher ORR (81% vs. 50%; p=0.038). The median progression-free survival was 19 months, and the median overall survival was 52.5 months. FBR is an effective and tolerable CIT regimen for patients with relapsed CLL.