Encequidar mesylate/Irinotecan

Irinotecan is a commonly used chemotherapeutic in solid tumor malignancies. Oratecan is an investigational product comprised of encequidar methanesulfonate, a novel minimally absorbed P-glycoprotein pump inhibitor, and irinotecan. This study sought to determine the maximum tolerated dose (MTD) of oratecan in patients with advanced malignancies.

Using a "3 + 3″ dose-escalation design, patients were treated with oratecan on day 1 every 21 days. The irinotecan dose was escalated from 20 to 320 mg/m². The encequidar methanesulfonate dose was fixed at 15 mg (12.9 mg free base). PK sampling for irinotecan, encequidar and its major metabolites was performed following a single dose of oratecan during cycle 1. Patients were treated until disease progression or unacceptable toxicity.

Thirty-five patients were treated. The MTD was determined to be 280 mg/m² every 21 days. Irinotecan and SN-38 plasma concentration-time profile showed that irinotecan exposure increased with dose and followed biexponential decay. Nine of 17 patients at oratecan dose levels 200 mg/m² and above had SN-38 exposures comparable to those with intravenous irinotecan at standard dosing. None of the 35 patients achieved a radiologic response, ten patients had SD for > 8 weeks; the median progression-free survival for all treated patients was 9 weeks (95% CI 8.6-13.9).

The MTD of oratecan was encequidar methanesulfonate 15 mg plus irinotecan 280 mg/m². Exposure for irinotecan and SN-38 increased with increased dose. Potential antitumor activity was observed at the 280 and 320 mg/m² dose levels. The safety profile of oratecan was comparable to that of intravenous irinotecan.