Clinical study of an organic arsenical, melarsoprol, in patients with advanced leukemia

Inorganic arsenic trioxide (As₂O₃) induces a high proportion of complete remissions in relapsed patients with acute promyelocytic leukemia (APL). Previously, we have shown that both As₂O₃ and melarsoprol, an organic arsenical used for the treatment of trypanosomiasis, exhibit broad antileukemic activity against both chronic and acute myeloid and lymphoid leukemia cell lines. Given the breadth of this activity, we initiated a clinical study to evaluate the pharmacokinetics, safety, and potential efficacy of melarsoproI in patients with refractory or resistant leukemia. Using the antitrypanosomal dose and schedule, patients received escalating intravenous doses daily for 3 days, repeated weekly for 3 weeks. Doses were 1 mg/kg on day 1, 2 mg/kg on day 2, and 3.6 mg/kg on day 3 and on all days thereafter, up to a maximum daily dose of 200 mg. Eight patients [6 AML (2 morphologic APL), 1 CML, 1 CLL] were treated. Mean peak plasma concentrations of the parent drug were obtained immediately after injection, ranged from 1.2 μg/ml on day 1 to 2.4 μg/ml on day 3, were dose proportional, and decayed with a t(1/2β) ≃ 15 min. A minor clinical response (regression of splenomegaly and lymphadenopathy) was observed in a patient with chronic lymphocytic leukemia. Central nervous system (CNS) toxicity proved limiting on this dose and schedule. Three patients experienced generalized grand mal seizures during the second week of therapy. We concluded that this dose and schedule of melarsoprol is associated with excessive CNS toxicity and that verification of the striking preclinical activity in patients with leukemia will require developing an alternative dose and schedule.