Phase I and pharmacokinetic study of the novel MDR1 and MRP1 inhibitor biricodar administered alone and in combination with doxorubicin

Purpose: To evaluate the safety, tolerability, and pharmacokinetics of biricodar (VX-710), an inhibitor of P-glycoprotein (P-gp) and multidrug resistance-associated protein (MRP1), alone and with doxorubicin in patients with advanced malignancies. The effect of VX-710 on the tissue distribution of ^99mTc-sestamibi, a P-gp and MRP1 substrate, was also evaluated. Patients and Methods: Patients with solid malignancies refractory to standard therapy first received a 96-hour infusion of VX-710 alone at 20 to 160 mg/m²/h. After a 3-day washout, a second infusion of VX-710 was begun, on the second day of which doxorubicin 45 mg/m² was administered. Cycles were repeated every 21 to 28 days. ^99mTc-sestamibi scans were performed before and during administration of VX-710 alone. Results: Of the 28 patients who enrolled, 25 patients were eligible for analysis. No dose-limiting toxicity (DLT) was observed in the nine assessable patients who received 120 mg/m²/h or less. Among seven patients receiving VX-710 160 mg/m²/h, two DLTs were seen: reversible CNS toxicity and febrile neutropenia. All other adverse events were mild to moderate and reversible. Plasma concentrations of VX-710 in patients who received at 120 and 160 mg/m²/h were two- to fourfold higher than concentrations required to fully reverse drug resistance in vitro. VX-710 exhibited linear pharmacokinetics with a harmonic mean half-life of 1.1 hours. VX-710 enhanced hepatic uptake and retention of ^99mTc-sestamibi in all patients. Conclusion: A 96-hour infusion of VX-710 at 120 mg/m²/h plus doxorubicin 45 mg/m² has acceptable toxicity in patients with refractory malignancies. The safety and pharmacokinetics of VX-710 plus doxorubicin warrant efficacy trials in malignancies expressing P-gp and/or MRP1.