Population pharmacokinetics and dosing implications for cobimetinib in patients with solid tumors

To characterize cobimetinib pharmacokinetics and evaluate impact of clinically relevant covariates on cobimetinib pharmacokinetics.

Plasma samples (N = 4886) were collected from 487 patients with various solid tumors (mainly melanoma) in three clinical studies (MEK4592g, NO25395, GO28141). Cobimetinib was administered orally, once daily on either a 21-day-on/7-day-off, 14-day-on/14-day-off or 28-day-on schedule in a 28-day dosing cycle as single agent or in combination with vemurafenib. Cobimetinib doses ranged from 2.1 to 125 mg. NONMEM was used for pharmacokinetic analysis.

A linear two-compartment model with first-order absorption, lag time and first-order elimination described cobimetinib pharmacokinetics. The typical estimates (inter-individual variability) of apparent clearance (CL/F), central volume of distribution (V2/F) and terminal half-life were 322 L/day (58 %), 511 L (49 %) and 2.2 days, respectively. Inter-occasion variability on relative bioavailability was estimated at 46 %. CL/F decreased with age. V2/F increased with body weight (BWT). However, the impact of age and BWT on cobimetinib steady-state exposure (peak and trough concentrations and AUC following the recommended daily dose of 60 mg 21-day-on/7-day-off) was limited (<25 % changes across the distribution of age and BWT). No significant difference in cobimetinib pharmacokinetics or steady-state exposure was observed between patient subgroups based on sex, renal function, ECOG score, hepatic function tests, race, region, cancer type, and co-administration of moderate and weak CYP3A inducers or inhibitors and vemurafenib.

A population pharmacokinetic model was developed for cobimetinib in cancer patients. Covariates had minimal impact on steady-state exposure, suggesting no need for dose adjustments and supporting the recommended dose for all patients.