Phase I Study of Cloretazine (VNP40101M), a Novel Sulfonylhydrazine Alkylating Agent, Combined with Cytarabine in Patients with Refractory Leukemia

Purpose: Cloretazine (VNP40101M) is a novel sulfonylhydrazine alkylating agent with significant antileukemia activity. A phase I study of cloretazine combined with cytarabine (1-β-d-arabinofuranosylcytosine, ara-C) was conducted in patients with refractory disease. Design: Ara-C was given i.v. at a fixed dose of 1.5 gm/m2/d by continuous infusion for 4 days (patients ages <65 years at time of diagnosis) or 3 days (patients ages ≥65 years). Cloretazine was given i.v. over 15 to 60 minutes on day 2 at a starting dose of 200 mg/m2, with escalation in 100 mg/m2 increments in cohorts of three to six patients until a maximum tolerated dose was established. The DNA repair enzyme O6-alkylguanine DNA alkyltransferase (AGT) was measured at baseline. Results: Forty patients, including 32 with acute myeloid leukemia, received 47 courses of treatment. Complete responses were seen at cloretazine dose levels of ≥400 mg/m2 in 10 of 37 (27%) evaluable patients, and in this patient subset, AGT activity was significantly lower in patients that responded to treatment than in patients who did not (P ≤ 0.027). Dose-limiting toxicities (gastrointestinal and myelosuppression) were seen with 500 and 600 mg/m2 of cloretazine combined with the 4-day ara-C schedule but not seen with the 3-day schedule. Conclusion: The recommended cloretazine dose schedule for future studies is 600 mg/m2 combined with 1.5 gm/m2/d continuous infusion of ara-C for 3 days. The cloretazine and ara-C regimen has significant antileukemic activity. AGT activity may be a predictor of response to cloretazine.