779 PRECLINICAL CHARACTERIZATION OF THE NOVEL HCV NS3 PROTEASE INHIBITOR GS-9256

Background: GS-9256 is an inhibitor of HCV NS3 protease with a macrocyclic structure and novel phosphinic acid pharmacophore. Methods: Key preclinical properties of GS-9256 including in vitro antiviral activity, cross-resistance and pharmacokinetic properties were investigated in non-human species. Results: In genotype (GT) 1b Huh-luc cells with a replicon encoding luciferase, GS-9256 had a mean 50% effective concentration (EC50) value of 20.0 nM, with minimal cytotoxicity. Antiviral activity was similar in a number of additional GT1b and GT1a replicon cell lines. Similar potency was observed in chimeric replicons encoding the NS3 protease of GT1 clinical isolates. GS-9256 was less active in GT2a replicon cells (14.2-fold increase in EC50). Additive to synergistic in vitro antiviral activity was observed when GS-9256 was combined with other agents including interferon-a, ribavirin, NS5B polymerase inhibitors GS-6620 and tegobuvir, as well as the NS5A inhibitor ledipasvir. GS-9256 retained wildtype activity against all tested NS5B and NS5A inhibitor resistance mutations. GS-9256 was metabolically stable in microsomes and hepatocytes of tested species, including rodents, dogs and humans. GS-9256 had high bioavailability in mice (near 100%) and moderate bioavailability in rats (14%), dogs (21%) and monkeys (14%). Elimination half-lives were approximately 2 h in mice, 0.6 h in rats, 5 h in dogs and 4 h in monkey. A study in bile duct-cannulated rats indicated that the major route of elimination is through biliary excretion of unmetabolized GS-9256. Conclusions: GS-9256 showed a favourable preclinical profile supportive of clinical development for the treatment of chronic HCV infection in GT1 patients.