Pharmacokinetic dose-scheduling study of hedgehog pathway inhibitor vismodegib (GDC-0449) in patients with locally advanced or metastatic solid tumors

Purpose: This study was designed to evaluate whether less frequent dosing [three times per week (TIW) or once weekly (QW)] of 150 mg vismodegib following a loading dose [150 mg once daily (QD) for 11 days] would result in similar safety, tolerability, and steady-state levels of total and unbound vismodegib as continuous QD dosing. Experimental Design: Sixty-seven patients with advanced solid tumors were stratified by baseline plasma alpha 1-acid glycoprotein (AAG) levels and randomized to one of three vismodegib 150 mg regimens:QD (n = 23), TIW (n = 22), orQW(n = 22) for up to 42 days after an 11-day loading phase (150 mgQD). Total and unbound (dialyzed) plasma vismodegib concentrations were determined by LC-MS/MS. Results: The most frequently reported adverse events were consistent with those in prior monotherapy trials, with similar incidence and severity regardless of dosing schedule. After the 150 mg QD loading phase, a concentration-dependent change in protein binding (3-fold increase in vismodegib fraction unbound) was observed at steady state compared with single dose. Mean total and unbound vismodegib steady-state concentrations were lower after TIW and QW than QD dosing, with an average intrasubject decrease of 50% and 80%, respectively, for unbound drug. Mechanism-based PK model simulations accurately and prospectively predicted the PK results. Conclusions: Vismodegib 150 mg TIW or QW failed to achieve unbound plasma concentrations previously associated with efficacy in patients with advanced basal cell carcinoma and medulloblastoma, even after a QD loading dose period. The 150 mg QD regimen is appropriate for vismodegib based on its clinical activity, tolerability, and favorable unbound concentrations.