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.Hepatitis C virus (HCV) is a small, enveloped virus that contains a single-stranded, positive-sense RNA (2). The World Health Organization estimates that approximately 170 million people worldwide are infected with HCV (25). Of these, 130 million are chronic HCV carriers at risk for the development of liver cirrhosis and/or liver cancer. In the United States, HCV infection leading to liver failure is the major indication for liver transplantation (4, 12). The current standard of care, which consists of a combination of pegylated interferon and ribavirin, provides good clinical efficacy for patients infected with genotype 2 and 3 viruses but is less effective for patients infected with genotype 1 viruses. Subgenotypes 1a and 1b constitute the most commonly found isolates in the United States, Japan, and Western Europe; and thus, the development of effective treatments against genotype 1 viruses presents a pressing need.HCV nonstructural protein 5B (NS5B) encodes a viral RNA-dependent RNA polymerase, an essential enzyme responsible for the replication of the viral genome. NS5B shares very limited sequence homology with cellular polymerases; hence, it is an attractive target for the development of antiviral therapy. Several classes of inhibitors, including nucleosides, nonnucleosides, and pyrophosphate mimics, that target t...

Relative Replication Capacity and Selective Advantage Profiles of Protease Inhibitor-Resistant Hepatitis C Virus (HCV) NS3 Protease Mutants in the HCV Genotype 1b Replicon System

“…The usefulness of the replicon system for HCV mutant study has been demonstrated by previous work, and overall there is a good correlation between in vitro selection of drug-resistant variants in the replicon and mutants selected in drug-treated patients (1,5,6,13,20,22). Still, the results of this study are based on a genotype 1b N strain replicon system which does not represent the genetic backgrounds of all other strains and genotypes, and so the RC profiles of these mutants might change in different genetic backgrounds.…”

1a/1b Subtype Profiling of Nonnucleoside Polymerase Inhibitors of Hepatitis C Virus

“…Further assessment of these analogs, using enzyme isolates and intergenotypic chimeric replicons derived from clinical iso-lates, revealed that the genotypic coverage of the NNI-1 and -4 analogs extends beyond genotype 1, unlike the NNI-2 and -3 derivatives that typically inhibit genotype 1 only (16,38). An additional drawback stems from the lower genetic barrier of the NNI-2 and -3 analogs in genotype 1 (25) and the reduced susceptibility in subtype 1a of the NNI-3 series (7,16,34,38,43). This effect was mostly attributed to the Y415F polymorphism observed in the NNI-3 binding site in subtype 1a (38).…”

Comparative Study of the Genetic Barriers and Pathways towards Resistance of Selective Inhibitors of Hepatitis C Virus Replication

“…These include the poor fidelity and lack of exonucleolytic proofreading capacity of the reverse transcriptase (RT) enzyme in the case of HIV (error rate, 10 Ϫ5 mutations per nucleotide per genomic replication) (4) or the RdRp in the case of HCV (error rate, 10 Ϫ3 to 10 Ϫ5 mutations per nucleotide per genomic replication) (9) and the very high magnitude of replication (HCV, 10 12 virions/day [48]; HIV, 10 10 virions/day [51]). As a result, multiple viral variants known as quasispecies (4,59) are generated.…”