Phase I and pharmacokinetic study of irofulven, a novel mushroom-derived cytotoxin, administered for five consecutive days every four weeks in patients with advanced solid malignancies

Purpose: To evaluate the toxicity and pharmacologic behavior of the novel mushroom-derived cytotoxin irofulven administered as a 5-minute intravenous (IV) infusion daily for 5 days every 4 weeks to patients with advanced solid malignancies. Patients and Methods: In this phase I trial, 46 patients were treated with irofulven doses ranging from 1.0 to 17.69 mg/m² as a 5-minute IV infusion (two patients received a 1-hour infusion) daily for 5 days every 4 weeks. The modified continual reassessment method was used for dose escalation. Pharmacokinetic studies were performed on days 1 and 5 to characterize the plasma disposition of irofulven. Results: Forty-six patients were treated with 92 courses of irofulven. The dose-limiting toxicities on this schedule were myelosuppression and renal dysfunction. At the 14.15-mg/m² dose level, renal dysfunction resembling renal tubular acidosis occurred in four of 10 patients and was ameliorated by prophylactic IV hydration. The 17.69-mg/m² dose level was not tolerated because of grade 4 neutropenia and renal toxicity, whereas the 14.15-mg/m² dose level was not tolerable with repetitive dosing because of persistent thrombocytopenia. Other common toxicities included mild to moderate nausea, vomiting, facial erythema, and fatigue. One partial response occurred in a patient with advanced, refractory metastatic pancreatic cancer lasting 7 months. Pharmacokinetic studies of irofulven revealed dose-proportional increases in both maximum plasma concentrations and area under the concentration-time curve, while the agent exhibited a rapid elimination half-life of 2 to 10 minutes. Conclusion: Given the results of this study, the recommended dose of irofulven is 10.64 mg/m² as a 5-minute IV infusion daily for 5 days every 4 weeks. The preliminary antitumor activity documented in a patient with advanced pancreatic cancer and the striking preclinical antitumor effects of irofulven observed on intermittent dosing schedules support further disease-directed evaluations of this agent on the schedule evaluated in this study.