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.

We characterized the selective advantage profiles of a panel of hepatitis C virus (HCV) NS3 protease mutants with three HCV protease inhibitors (PIs), BILN-2061, ITMN-191, and VX-950, using a genotype 1b HCV replicon system. Selective advantage curves were generated by a novel mathematical method that factors in the degree of drug susceptibility provided by the mutation, the base-level replication capacity of the mutant in the absence of drugs, and the overall viral replication levels as a function of drug concentration. Most of the mutants showed significantly increased selective advantages over the wild-type species upon drug treatment. Each drug is associated with unique selective advantage profiles that reflect its antiviral activity and mutant susceptibility. Five mutants (R155K/Q, A156T, and D168A/V) showed significant levels of selective advantage after treatment with >10 nM ( approximately 7 times the wild-type 50% effective concentration [EC50]) of BILN-2061. R155K displayed dominant levels of selective advantage over the other mutants upon treatment with ITMN-191 over a broad range of concentrations. Upon VX-950 treatment, various mutants (A156T, A156S, R155K, T54A, V170A, V36M/R155K, and R155Q) exhibited high levels of selective advantage in different drug concentration ranges, with A156T and A156S being the dominant mutants at >3 microM ( approximately 10 times the wild-type EC50) of VX-950. This method provides more accurate estimates of the behavior of various mutants under drug pressure than replication capacity analysis. We noted that the R155K mutant shows reduced susceptibility to all three PIs and significant selective advantage, raising concern over the potential emergence of R155K as a multidrug-resistant, highly fit mutant in HCV patients treated with PIs.