A Phase II and Pharmacokinetic Study of Ecteinascidin 743 in Patients with Gastrointestinal Stromal Tumors

Abstract

Abstract Learning Objectives After completing this course, the reader will be able to: Describe the mechanism of action, administration, and pharmacokinetics of ecteinascidin 743. Recognize the classification and pathophysiology of gastrointestinal stromal tumors. Appreciate that conventional cytotoxic chemotherapy has no efficacy in patients with gastrointestinal stromal tumors and that STI571 has dramatic efficacy. Access and take the CME test online and receive one hour of AMA PRA category 1 credit at CME.TheOncologist.com Purpose. To assess the efficacy, tolerability, and pharmacokinetics of ecteinascidin 743 (ET-743) in patients with advanced gastrointestinal stromal tumors (GISTs). Patients and Methods. The study was confined to adult patients with radiographically measurable GISTs. ET-743 was administered as a 24-hour continuous i.v. infusion at a dose of 1.5 mg/m2 repeated every 3 weeks. Pharmacokinetic blood sampling was performed during the first cycle of therapy. Tumors were restaged after every second cycle of therapy. Results. A total of 20 patients was enrolled in the study, 19 of whom were treated with 47 cycles of ET-743 (median 2, range 1-10). Severe toxicities were limited to reversible grade 3 transaminitis in 10 patients and grade 3 fatigue in one patient. There were no objective responses, and disease stabilization occurred in two patients lasting for periods of 4 and 10 months. The 1-year survival rate was 71.1%. Mean ± standard deviation values of the maximum plasma concentration and total plasma clearance were 1.1 ± 0.4 ng/ml and 44 ± 16 l/h/m2, respectively, for 19 of the 20 patients. Conclusion. This study is the first report of a prospective phase II trial to evaluate a cytotoxic agent in patients with GISTs. This study underscores the primary resistance of GISTS to chemotherapy and stands in stark contrast to the encouraging results recently achieved with STI571. The lack of response may be associated with a therapeutically ineffective exposure to the drug based upon the lower incidence of severe toxicities and greater clearance than described in phase I and II trials of ET-743.