Protease inhibitors (PIs) have proven to be effective adjuncts to interferon/ribavirin treatment of hepatitis C virus (HCV) infections. Little clinical or in vitro data exists, however, on their effectiveness for nontype 1 genotypes that predominate in Europe, the Middle East, Africa, and most of Asia. NS3 protease and NS4A genes from genotypes 1-6 were inserted into the JFH clone to generate replication-competent intergenotype chimeras. Susceptibility to PIs was determined by replication and infectivity assays. To study resistance development, chimeras were cultured in subinhibitory concentrations of PIs and mutations phenotypically characterized. Marked differences in susceptibility of different genotypes to danoprevir and telaprevir (VX-950) were observed. Genotypes 1, 4, and 6 showed median inhibitory concentration (IC 50 ) values of 2-3 nM, >100-fold lower than genotypes 2/3/5 (250-750 nM). Telaprevir susceptibilities varied over a 4-fold range, with genotypes 1 and 2 being most susceptible and genotypes 4 and 5 most resistant. Culture of genotypes 1-6 in PIs induced numerous mutations in the NS3 protease domain, highly variable between genotypes. Introduction of danoprevir and BILN 2061-induced mutations into the original clones by site-directed mutagenesis (n 5 29) all conferred resistant phenotypes, with particularly large increases (1-2 log greater IC 50 values) in the initially susceptible genotypes 1/4/6. Most introduced mutations and showed little or no effect on replicative fitness. Conclusion: Major differences were found between genotypes in their susceptibility and resistance development to PIs. However, equal sensitivities of genotypes 1, 4, and 6 to danoprevir and a broader efficacy range of telaprevir between genotypes than initially conceptualized provide strong evidence that PIs might be effectively used beyond their genotype 1 target group. (HEPATOLOGY 2011;53:1090-1099 I nfections with hepatitis C virus (HCV) are a major cause of chronic liver diseases, such as cirrhosis and hepatocellular carcinoma. 1 Clinical management of HCV and the effectiveness of currently used interferon-a (IFN)/ribavirin (RBV) therapy of infected individuals is greatly influenced by genetic heterogeneity of the virus. There are, for example, major differences between the six genotypes of HCV in response rate to therapy and evidence for some genotype-associated variability in the rate of disease progression and associated liver pathology. 2,3 HCV replication is additionally associated with high mutation rates; this confers on HCV, in common with human immunodeficiency virus 1 (HIV-1), considerable adaptive capacity to escape from immunological or drug-treatment pressure. The effectiveness of newly developed protease and polymerase inhibitors for HCV, at least as monotherapy, is indeed likely to be substantially impaired through the acquisition or selection for preexisting amino acid mutations that confer antiviral resistance.Genetic heterogeneity between HCV genotypes translates into significant molecular and clin...
