This is a dose-escalation study to determine the maximum tolerated dose and toxic effects of clofarabine in patients with chronic lymphocytic leukemia and other acute leukemias. Clofarabine is a synthesized hybrid nucleoside analog, which is believed to possess the better qualities of fludarabine and chlorodeoxyadenosine, the 2 most active agents against lymphoproliferative disorders. Thus, it is hoped that this drug will be more active and less toxic than similar drugs.

The first group of patients will be treated at the starting dose level of 2 mg/m2 over 1 hour daily for 5 days. Dosage escalation will be permitted in individual patients if no toxicity occurred during the preceding course. Subsequent dose escalations will be by 50% until Grade 2 toxicity, then by 35% until the maximum tolerated dose.

Completion date provided represents the completion date of the grant per OOPD records

Inclusion criteria:

• Diagnosis of chronic lymphocytic leukemia
• Diagnosis of other acute leukemia
• At least 2 weeks since prior chemotherapy, immunotherapy, and/or radiotherapy
• Recovered from toxic effects of prior therapy
• Bilirubin no greater than 2 mg/dL
• Creatinine no greater than 1.5 mg/dL

Exclusion criteria:

• Candidate for treatment of higher efficacy or priority
• Pregnant or nursing