Encephalopathy is the dose-limiting toxicity of intravenous hepsulfam: results of a phase I trial in patients with advanced hematological malignancies

Hepsulfam is a bisulfamic ester which is similar in structure to busulfan and is believed to act as a bifunctional alkylator inducing both DNA-DNA and DNA-protein crosslinks. Prior studies in patients with refractory solid tumors have identified the doselimiting toxicity of hepsulfam to be cumulative myelosuppression resulting in prolonged leukopenia and thrombocytopenia. This phase I trial was designed to determine the maximally tolerated dose of hepsulfam administered intravenously in patients with refractory leukemias and other advanced hematologic malignancies. Hepsulfam was administered as a 30-min or 2-h intravenous infusion to 21 patients with advanced leukemia or multiple myeloma. All patients had been extensively treated and had progressive disease. Cycles were repeated every 5 weeks. Cohorts of patients were treated at 360, 480, 640, and 800 mg/m². The doselimiting toxicity of intravenous hepsulfam was severe encephalopathy. The single patient treated at 800 mg/m² became comatose within 48 h and required 3 weeks for his mental status to return to baseline. There were, however, no irreversible neurological sequelae. Several patients treated at 640 mg/m² had clinical evidence of toxic deliriums and slowing of alpha rhythm waves on electroencephalograms indicative of a gray-matter encephalopathy. When hepsulfam was infused over 30 min, patients complained of uncomfortable parasthesias, but when the drug was administered over 2 h, these acute symptoms were less common. Myelosuppression was observed in most patients. Among those patients who had some suppression of their leukemia, peripheral blood counts recovered to pretreatment levels after 3-5 weeks. Apart from CNS toxicity, non-hematologic toxicity was minimal. Pharmacokinetic studies demonstrated rapid clearance of hepsulfam so that the drug was not reliably detected in the plasma after 24 h. The recommended phase II dose of hepsulfam as a single 2-h intravenous infusion is 480 mg/m², but this dose provided relatively little clinical benefit for patients with refractory leukemia. The dose-limiting toxicity is CNS toxicity with increasingly severe encephalopathy at doses ≥640 mg/m². It would be reasonable to investigate further dose escalation of hepsulfam in a divided dose schedule to minimize the peak concentrations which may be related to the encephalopathy. EEG monitoring is recommended for early detection of slowing of alpha rhythm waves. Hematopoietic stem cell support will probably be required at total doses exceeding 800 mg/m².