A phase I, randomized, open-label, parallel-cohort, dose-finding study of elacridar (GF120918) and oral topotecan in cancer patients

Purpose: Breast cancer resistance protein (ABCG2) substantially limits the oral bioavailability of topotecan. Coadministration with elacridar, an inhibitor of breast cancer resistance protein mediated drug transport, increases the bioavailability of topotecan. The aim of this study was to establish the lowest effective dose of elacridar to obtain maximum oral bioavailability of topotecan and to determine the optimal schedule of coadministration of oral topotecan and elacridar. In the second part of this study, dose-limiting toxicities and maximum tolerated dose of oral topotecan coadministered with elacridar, at a daily times five regimen administered every 21 days, were established. Experimental Design: In part 1, 20 patients were randomized to receive 100, 300, 500,700, or 1,000 mg of elacridar on days 1 and 8 1 h before or simultaneously with 2.0 mg oral topotecan, which was also randomized. On day 15, all patients were treated with 1.5 mg/m(2) i.v. topotecan. In part 11 of the study, patients were treated daily with oral topotecan and with the lowest effective dose of elacridar following from part I. The maximum tolerated dose and dose-limiting toxicity were determined in cohorts of three patients. Blood samples were taken on days 1, 8, and 15 of part I and on day 1 of cycles 1 and 2 of part II. Results: Complete apparent oral bioavailability of topotecan (102 +/- 7%) for all treatment arms with elacridar in both schedules was seen in part I. In the topotecan dose escalation part, two dose-limiting toxicities were seen at the 2.5 mg topotecan dose level. Conclusion: The recommended schedule is 2.0 mg oral topotecan plus 100 mg elacridar administered concomitantly daily times five every 21 days.