Activity of a potent hepatitis C virus polymerase inhibitor in the chimpanzee model

Abstract

A-837093 is a potent and specific nonnucleoside inhibitor of the hepatitis C virus (HCV) nonstructural protein 5B (NS5B) RNA-dependent RNA polymerase. It possesses nanomolar potencies in both enzymatic and replicon-based cell culture assays. In rats and dogs this compound demonstrated an oral plasma half-life of greater than 7 h, and its bioavailability was >60%. In monkeys it had a half-life of 1.9 h and 15% bioavailability. Its antiviral efficacy was evaluated in two chimpanzees infected with HCV in a proof-of-concept study. The design included oral dosing of 30 mg per kg of body weight twice a day for 14 days, followed by a 14-day posttreatment observation. Maximum viral load reductions of 1.4 and 2.5 log(10) copies RNA/ml for genotype 1a- and 1b-infected chimpanzees, respectively, were observed within 2 days after the initiation of treatment. After this initial drop in the viral load, a rebound of plasma HCV RNA was observed in the genotype 1b-infected chimpanzee, while the genotype 1a-infected chimpanzee experienced a partial rebound that lasted throughout the treatment period. Clonal analysis of NS5B gene sequences derived from the plasma of A-837093-treated chimpanzees revealed the presence of several mutations associated with resistance to A-837093, including Y448H, G554D, and D559G in the genotype 1a-infected chimpanzee and C316Y and G554D in the genotype 1b-infected chimpanzee. The identification of resistance-associated mutations in both chimpanzees is consistent with the findings of in vitro selection studies, in which many of the same mutations were selected. These findings validate the antiviral efficacy and resistance development of benzothiadiazine HCV polymerase inhibitors in vivo.

FIG. 1.

Chemical structure of A-837093.

FIG. 2.

HCV viral load changes during and after A-837093 treatment in the HCV genotype 1a- and genotype 1b-infected chimpanzees. Each animal was dosed with 30 mg/kg A-837093 BID for 14 days. Viral load determinations were done by a TaqMan quantitative RT-PCR assay. The samples chosen for genotypic and phenotypic analyses are circled.

FIG. 3.

Curves for inhibition by A-837093 of HCV subgenomic replicon containing NS5B cloned from the genotype 1a-infected chimpanzee samples before treatment and on days 5 and 16 after the initiation of treatment with A-837093. The dashed line indicates 50% inhibition level.