Abstract 1304: Clinical pharmacokinetics of GDC-0973, an oral MEK inhibitor, in cancer patients: data from a Phase 1 study

Abstract

Abstract Background: GDC 0973 is a potent, selective, orally administered MEK1/2 inhibitor. It has shown antitumor activity in preclinical models. A first-in-human, phase 1 dose escalation study in cancer patients was conducted using a 3+3 design with two dosing schedules, followed by an expansion at the MTD for each dosing schedule. The pharmacokinetic objective was to evaluate GDC-0973 PK in patients on both dosing schedules. Methods: GDC-0973 was administered orally, once daily on a 21 day on/7 day off (21/7) or on a 14 day on/14 day off (14/14) dosing schedule. Plasma samples for PK analysis were collected on Day 1 and Day 21 (for 21/7) or Day 14 (14/14) of Cycle 1, and during the dosing holiday to determine half-life of GDC-0973. Urine samples were collected on Day 1 and on Day 21 (21/7) or Day 14 (14/14) over a 24-hour period for exploratory analysis. Plasma samples were analyzed using a validated LC/MS/MS method. GDC-0973 pharmacokinetic data was analyzed using a non-compartmental approach with the program WinNonlin. Results: GDC-0973 pharmacokinetics was evaluated at doses administered in the 21/7 schedule (0.05, 0.1 and 0.2 mg/kg in a liquid solution and 10, 20, 40, 60, and 80 mg as capsules) and the 14/14 schedule (60, 80, 100 and 125 mg as capsules). Pharmacokinetic data was available in 41 patients on the 21/7 and 11 patients on the 14/14 schedule. GDC-0973 Cmax was observed at 1-4 hours post-dose, and was similar across the entire dose range. Cmax and AUC increased dose proportionally in the dose range up to 100 mg. The mean apparent oral clearance ranged from 4.30 to 11.7 L/h in the 0.05 mg/kg-100 mg dose range. The mean elimination half-life ranged from 31.6 to 53.5 hours in all dose levels in both schedules. Following daily oral dosing, the mean accumulation ratio was 2.0 to 4.0, which is consistent with its half-life and dosing interval, indicating that the PK was constant over time. Given the mean half-life of ∼40 hours, steady-state exposures are expected to be achieved in 8-10 days. Preliminary data suggest that approximately 1-8% of intact drug is excreted in urine; hence, renal excretion is a minor pathway for elimination. Exploratory analysis showed no clear association between exposure and demographic factors (age, weight, sex) or concomitant medications. PK was consistent between patients in the 21/7 and 14/14 dose escalation stages, as well as the expansion stages when compared at the same doses. Doses of 40 mg or higher in patients achieved steady-state concentrations consistent with antitumor activity observed in xenograft models. Conclusion: GDC-0973 preliminary PK analysis shows a moderate rate of absorption; with generally dose-proportional increases in Cmax and AUC. Updated data will be presented. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1304. doi:10.1158/1538-7445.AM2011-1304