Pre-clinical Assessment of the Absorption, Distribution, Metabolism, and Excretion of GDC-0449 (2-chloro-N-(4-chloro-3-(pyridin-2-yl)phenyl)-4-(methylsulfonyl)benzamide), an Orally Bioavailable Systemic Hedgehog Signaling Pathway Inhibitor

GDC-0449 (2-chloro-N-(4-chloro-3-(pyridin-2-yl)phenyl)-4-(methylsulfonyl)benzamide) is a potent, selective Hedgehog (Hh) signalling pathway inhibitor being developed for the treatment of various cancers. The in vivo clearance of GDC-0449 was estimated to be 23.0, 4.65, 0.338, and 19.3 ml min^-1 kg^-1 in mouse, rat, dog and monkeys, respectively. The volume of distribution ranged from 0.490 in rats to 1.68 l kg^-1 in mice. Oral bioavailability ranged from 13% in monkeys to 53% in dogs. Predicted human clearance using allometry was 0.096-0.649 ml min^-1 kg^-1 and the predicted volume of distribution was 0.766 l kg^-1. Protein binding was extensive with an unbound fraction less than or equal to 6%, and the blood-to-plasma partition ratio ranged from 0.6 to 0.8 in all species tested. GDC-0449 was metabolically stable in mouse, rat, dog and human hepatocytes and had a more rapid turnover in monkey hepatocytes. Proposed metabolites from exploratory metabolite identification in vitro (rat, dog and human liver microsomes) and in vivo (dog and rat urine) include three primary oxidative metabolites (M1-M3) and three sequential glucuronides (M4-M6). Oxidative metabolites identified in microsomes M1 and M3 were formed primarily by P4503A4/5 (M1) and P4502C9 (M3). GDC-0449 was not a potent inhibitor of P4501A2, P4502B6, P4502D6, and P4503A4/5 with IC₅₀ estimates greater than 20 µM. K_I‘s estimated for P4502C8, P4502C9 and P4502C19 and were 6.0, 5.4 and 24 µM, respectively. An evaluation with Simcyp® suggests that GDC-0449 has a low potential of inhibiting P4502C8 and P4502C9. Furthermore, GDC-0449 (15 µM) was not a potent P-glycoprotein/ABCB1 inhibitor in MDR1-MDCK cells. Overall, GDC-0449 has an attractive preclinical profile and is currently in Phase II clinical trials..