titutions F43L, R155K, A156T, and D168A/F/H/V/Y in HCV NS3 reduced susceptibility to paritaprevir. In the genotype 1a replicon, the activity of paritaprevir was reduced 20-, 37-, and 17-fold by the F43L, R155K and A156T substitutions, respectively. The activity of paritaprevir was reduced 96-fold by D168V, and 50- to 219-fold by each of the other D168 substitutions. The activity of paritaprevir in genotype 1a was not significantly affected (less than or equal to 3-fold) by single substitutions V36A/M, V55I, Y56H, Q80K or E357K. Double variants including combinations of V36LM, F43L, Y56H, Q80K or E357K with R155K or with a D168 substitution reduced the activity of paritaprevir by an additional 2 to 3-fold relative to the single R155K or D168 substitution. In the genotype 1b replicon, the activity of paritaprevir was reduced 76- and 159-and 337- fold by D168A, D168H, D168V, and D168Y respectively. Y56H alone could not be eva luated due to poor replication capacity, however, the combination of Y56H and D168A/V/Y reduced the activity of paritaprevir by 700- to 4118-fold.
In genotype 1a, substitutions M28T/V, Q30E/R, L31V, H58D, Y93C/H/N, and M28V + Q30R in HCV NS5A reduced susceptibility to ombitasvir. In the genotype 1a replicon, the activity of ombitasvir was reduced by 896-, 58- and 243-fold against the M28T/V and H58D substitutions, respectively, and 1326-, 800-, 155-foldand 1675- to 66740- fold by the Q30E/R, L31V and Y93C/H/N substitutions, respectively. Y93H, Y93N or M28V in combination with Q30R reduced the activity of ombitasvir by more than 42,802-fold. In genotype 1b, substitutions L28T, L31F/V, as well as Y93H alone or in combination with L28M, R30Q, L31F/M/V or P58S in HCV NS5A reduced susceptibility to ombitasvir. In the genotype 1b replicon, the activity of ombitasvir was reduced by less than 10-fold by variants at amino acid positions 30 and 31. The activity of ombitasvir was reduced by 661-, 77-, 284- and 142-fold against the genotype 1b substitutions L28T, Y93H, R30Q in combination with Y93H, and L31M in combination with Y93H, respectively. All other double substitutions of Y93H in combination with substitutions at positions 28, 31, or 58 reduced the activity of ombitasvir by more than 400-fold.
Genotype 4
In genotype 4a, resistance to paritaprevir or ombitasvir by variants in NS3 or NS5A, respectively, selected in cell culture were phenotypically characterised. Substitutions R155C, A156T/V, and D168H/V in HCV NS3 reduced susceptibility to paritaprevir by 40- to 323-fold. Substitution L28V in HCV NS5A reduced the susceptibility to ombitasvir by 21-fold.
Effect of baseline HCV substitutions/polymorphisms on treatment outcome
A pooled analysis of subjects with genotype 1 HCV infection, who were treated with ombitasvir, paritaprevir, and dasabuvir (a non-nucleotide NS5B inhibitor) with or without ribavirin in the Phase 2b and 3 clinical trials was conducted to explore the association between baseline NS3/4A, NS5A or NS5B substitutions/polymorphisms and treatment outcome in recommended regimens.
In the greater than 500 genotype 1a baseline samples in this analysis, the most frequently observed resistance-associated variants were M28V (7.4%) in NS5A and S556G (2.9%) in NS5B. Q80K, although a highly preva lent polymorphism in NS3 (41.2% of samples), confers minimal resistance to paritaprevir. Resistance-associated variants at amino acid positions R155 and D168 in NS3 were rarely observed (less than 1%) at baseline. I
