Infrequent development of resistance in genotype 1-6 hepatitis C virus-infected subjects treated with sofosbuvir in phase 2 and 3 clinical trials

Abstract

Background: Sofosbuvir is a chain-terminating nucleotide analogue inhibitor of the hepatitis C virus (HCV) NS5B RNA polymerase that is efficacious in subjects with HCV genotype 1-6 infection. Sofosbuvir resistance is primarily conferred by the S282T substitution in NS5B.

Methods: NS5B sequencing and susceptibility testing of HCV from subjects infected with genotypes 1-6 who participated in phase 2 and 3 sofosbuvir clinical trials was performed.

Results: No NS5B variants present at baseline among 1645 sofosbuvir-treated subjects were associated with treatment failure; sofosbuvir susceptibility was within 2-fold of reference. Among 282 subjects who did not achieve sustained virologic response, no novel sofosbuvir resistance-associated variants were identified, and the NS5B changes observed did not confer significant reductions in sofosbuvir susceptibility. In 1 subject with S282T observed at relapse 4 weeks after sofosbuvir monotherapy, the resistant variant (13.5-fold reduced sofosbuvir susceptibility, replication capacity <2% of control) became undetectable by deep sequencing 12 weeks after treatment. L159F and V321A were identified as treatment-emergent variants but did not confer resistance to sofosbuvir in the replicon system.

Conclusions: These data demonstrate a uniform susceptibility of subject-derived HCV to sofosbuvir, and also show that selection of sofosbuvir-resistant HCV is exceedingly rare and is associated with a significant reduction in viral fitness.

Keywords: GS-7977; HCV; NS5B polymerase; antiviral resistance; sofosbuvir.

Figure 1.

Sofosbuvir susceptibility at baseline (BL) and posttreatment (PT). Susceptibility is presented as fold change (FC) in half maximal effective concentration (FCEC₅₀) vs reference (Ref), fold-change in 90% or 95% effective concentration (FCEC_90/95) vs reference (Ref), fold-change in EC₅₀ PT vs BL, and FCEC_90/95 PT vs BL. Horizontal bars represent the mean for each group. The data for the subject with the S282T-containing virus is not included.

Figure 2.

Evolution of sofosbuvir resistance in the subject with S282T. The viral load profile for the subject who received sofosbuvir monotherapy for 12 weeks (treatment period depicted as a gray box) and developed S282T is shown. The percentage of the wild-type serine (S) or resistance-associated threonine (T) at position 282 as determined by deep sequencing and the sofosbuvir fold change in the 50% effective concentration (FCEC₅₀) from the baseline and replication capacity (RC) at each time point tested is shown in boxes. The dotted line at 15 IU/mL represents the limit of detection (LOD) of the viral load assay. Abbreviation: HCV, hepatitis C virus.