Mechanism of Action
TECHNIVIE combines two direct-acting antiviral agents with distinct mechanisms of action and non-overlapping resistance profiles to target HCV at multiple steps in the viral lifecycle.
Ombitasvir
Ombitasvir is an inhibitor of HCV NS5A, which is essential for viral RNA replication and virion assembly. The mechanism of action of ombitasvir has been characterized based on cell culture antiviral activity and drug resistance mapping studies.
Paritaprevir
Paritaprevir is an inhibitor of HCV NS3/4A protease which is necessary for the proteolytic cleavage of the HCV encoded polyprotein (into mature forms of the NS3, NS4A, NS4B, NS5A, and NS5B proteins) and is essential for viral replication. In a biochemical assay, paritaprevir inhibited the proteolytic activity of a recombinant HCV genotype 4a NS3/4A protease enzyme with an IC50 value of 0.16 nM.
Antiviral Activity
Ombitasvir
The EC50 values of ombitasvir against HCV replicons containing NS5A from a single isolate each of genotype 4a and genotype 4d were 1.7 pM and 0.38 pM, respectively. Ombitasvir had median EC50 values of 0.21 pM (range 0.10 pM to 0.36 pM; n=9) and 35.6 pM (range 0.14 pM to 71 pM; n=2) against transient HCV replicons containing NS5A genes from a panel of genotype 4a and genotype 4b clinical isolates, respectively, from treatment-naïve subjects.
Paritaprevir
The EC50 values of paritaprevir against HCV replicons containing NS3 from a single isolate each of genotype 4a and genotype 4d were 0.09 nM and 0.015 nM, respectively.
Ritonavir
In HCV replicon cell culture assays, ritonavir did not exhibit a direct antiviral effect and the presence of ritonavir did not affect the antiviral activity of paritaprevir.
Resistance
In Cell Culture
Exposure of HCV genotype 4a replicons to ombitasvir or paritaprevir resulted in the emergence of drug resistant replicons carrying amino acid substitutions in NS5A or NS3, respectively. Amino acid substitutions in NS5A or NS3 selected in cell culture or identified in clinical study PEARL-I were phenotypically characterized in genotype 4 replicons.
For ombitasvir, in an HCV genotype 4a replicon, NS5A substitution L28V reduced ombitasvir antiviral activity by 21-fold. In an HCV genotype 4d replicon, substitutions L28V alone and L28V in combination with T58S reduced ombitasvir antiviral activity by 310- and 760-fold, respectively. Ombitasvir activity against an HCV genotype 4d replicon was not reduced by a T58P polymorphism, which represents the consensus sequence observed at this position for HCV genotype 4a and 4d subjects in PEARL-I. The presence of NS5A L30S and Y93H polymorphisms in a genotype 4b clinical isolate was associated with approximately 200-fold reduced activity of ombitasvir.
For paritaprevir, in an HCV genotype 4a replicon, NS3 substitutions R155C, A156T/V, and D168H/V reduced paritaprevir antiviral activity by 40- to 323-fold. In an HCV genotype 4d replicon, NS3 substitutions Y56H and D168V reduced paritaprevir antiviral activity by 8- and 313-fold, respectively, while a combination of Y56H and D168V reduced the activity of paritaprevir by 12,533-fold.
In Clinical Studies
In the clinical study PEARL-I, three subjects experienced virologic failure (2 post-treatment relapse, 1 on-treatment failure). All 3 virologic failures were observed in a regimen containing paritaprevir/ritonavir and ombitasvir without ribavirin. Treatment-emergent, resistance-associated substitutions were detected at the time of failure in all 3 subjects and included D168V (with or without Y56H) in NS3, and L28S and L28V (with or without M31I or T58S) in NS5A.
In the clinical study AGATE-I, one subject experienced on-treatment virologic failure and a second subject experienced virologic relapse at the Post-Treatment Week 24 timepoint. Treatment-emergent resistance-associated substitutions detected in these subjects included NS3 substitutions A156K or D168V, and NS5A substitutions K24Q, L28I/M, M31I or Y93H.
Persistence of Resistance-Associated Substitutions
The persistence of ombitasvir and paritaprevir treatment-emergent amino acid substitutions in NS5A and NS3, respectively, was assessed in subjects in clinical study PEARL-I whose virus had at least 1 treatment-emergent resistance-associated substitution in the drug target, and with available data through at least 24 weeks post-treatment. Population and clonal nucleotide sequence analyses (assay sensitivity approximately 5-10%) were conducted to detect the persistence of viral populations with treatment-emergent substitutions. Available data were from 3 subjects with genotype 4d infection.
For ombitasvir, viral populations with 1 or more resistance-associated treatment-emergent substitutions in NS5A persisted at detectable levels in 3/3 (100%) subjects at Post-Treatment Week 24 and in 2/3 (67%) subjects through Post-Treatment Week 48. For paritaprevir, viral populations with 1 or more resistance-associated treatment-emergent substitutions in NS3 were detected through Post-Treatment Week 24 in 2/3 (67%) subjects, and in 0/3 (0%) subjects through Post-Treatment Week 48.
Effect of Baseline HCV Polymorphisms on Treatment Response
Phylogenetic analysis of HCV nucleotide sequences from subjects in the clinical study PEARL-I, identified 7 HCV genotype 4 subtypes (4a, 4b, 4c, 4d, 4f, 4g/4k, 4o). Most subjects were infected with either subtype 4a (38%) or 4d (52%); 1 to 7 subjects were infected with each of the other genotype 4 subtypes. Among subjects enrolled at U.S. study sites, 16/18 (89%) were infected with HCV subtype 4a; one subject each was infected with subtype 4c or 4d. Three subjects who experienced virologic failure with the regimen containing paritaprevir/ritonavir and ombitasvir without ribavirin were infected with HCV subtype 4d.
Phylogenetic analysis of HCV nucleotide sequences from subjects who received ombitasvir/paritaprevir/ritonavir plus ribavirin for 12 weeks in the clinical study AGATE-I, identified 11 HCV genotype 4 subtypes (4a, 4c, 4d, 4e, 4f, 4k, 4n, 4p, 4q, 4r, 4t). Most subjects were infected with either subtype 4a (58%) or 4d (20%); 1 to 2 subjects were infected with each of the other genotype 4 subtypes. Two subjects who experienced virologic failure in AGATE-I were infected with HCV subtype 4a or 4d.
Baseline HCV polymorphisms are not expected to impact the likelihood of achieving SVR when TECHNIVIE is used as recommended to treat HCV genotype 4 infected patients, based on the low virologic failure rates observed in PEARL-I and AGATE-I, although limited data are available for genotype 4 subtypes other than 4a and 4d.
Cross-resistance
Cross-resistance may occur among NS5A inhibitors and among NS3/4A protease inhibitors within each individual class. The impact of prior ombitasvir or paritaprevir treatment experience on the efficacy of other NS5A inhibitors or NS3/4A protease inhibitors has not been studied. Similarly, the efficacy of TECHNIVIE has not been studied in subjects who have failed prior treatment with another NS5A inhibitor, NS3/4A protease inhibitor, or NS5B inhibitor.