OBJECTIVE To assess the feasibility of administering NSC 655649, a water-soluble, rebeccamycin analog with topoisomerase inhibitory properties, as a brief intravenous (IV) infusion once every 3 weeks and to determine the maximum-tolerated dose (MTD) of NSC 655649, characterize its pharmacokinetic behavior, and seek preliminary evidence of antitumor activity. METHODS Patients with advanced solid malignancies were treated with escalating doses of NSC 655649 administered over 30 to 60 minutes IV once every 3 weeks. An accelerated dose-escalation method was used to guide dose escalation. After three patients were treated at the first dose level, doses were escalated in increments that ranged up to 150% using single patient cohorts until moderate toxicity was observed, when a more conservative dose-escalation scheme was invoked. MTD was defined as the highest dose level at which the incidence of dose-limiting toxicity did not exceed 20%. MTD was determined for both minimally pretreated (MP) and heavily pretreated (HP) patients. Plasma and urine were sampled to characterize the pharmacokinetic and excretory behavior of NSC 655649. RESULTS Forty-five patients were treated with 130 courses of NSC 655649 at doses ranging from 20 mg/m(2) to 744 mg/m(2). Myelosuppression was the principal toxicity. Severe neutropenia, which was often associated with thrombocytopenia, was unacceptably high in HP and MP patients treated at 572 mg/m(2) and 744 mg/m(2), respectively. Nausea, vomiting, and diarrhea were common but rarely severe. The pharmacokinetics of NSC 655649 were dose dependent and fit a three-compartment model. The clearance and terminal elimination half-lives for NSC 655649 averaged 7.57 (SD = 4.2) L/h/m(2) and 48.85 (SD = 23.65) hours, respectively. Despite a heterogeneous population of MP and HP patients, the magnitude of drug exposure correlated well with the severity of myelosuppression. Antitumor activity was observed in two HP ovarian cancer patients and one patient with a soft tissue sarcoma refractory to etoposide and doxorubicin. CONCLUSIONS Recommended phase II doses are 500 mg/m(2) and 572 mg/m(2) IV once every 3 weeks for HP and MP patients, respectively. The absence of severe nonhematologic toxicities, the encouraging antitumor activity in HP patients, and the unique mechanism of antineoplastic activity of NSC 655649 warrant further clinical development.