Identification of the NS5B S282T resistant variant and two novel amino acid substitutions that affect replication capacity in hepatitis C virus-infected patients treated with mericitabine and danoprevir

Direct-acting antiviral resistance of Hepatitis C virus is promoted by epistasis

Direct-acting antiviral agents (DAAs) provide efficacious therapeutic treatments for chronic Hepatitis C virus (HCV) infection. However, emergence of drug resistance mutations (DRMs) can greatly affect treatment outcomes and impede virological cure. While multiple DRMs have been observed for all currently used DAAs, the evolutionary determinants of such mutations are not currently well understood. Here, by considering DAAs targeting the nonstructural 3 (NS3) protein of HCV, we present results suggesting that epistasis plays an important role in the evolution of DRMs. Employing a sequence-based fitness landscape model whose predictions correlate highly with experimental data, we identify specific DRMs that are associated with strong epistatic interactions, and these are found to be enriched in multiple NS3-specific DAAs. Evolutionary modelling further supports that the identified DRMs involve compensatory mutational interactions that facilitate relatively easy escape from drug-induced selection pressures. Our results indicate that accounting for epistasis is important for designing future HCV NS3-targeting DAAs.

Hepatitis C Resistance-Associated Substitutions Among People Who Inject Drugs Treated With Direct-Acting Antiviral-Containing Regimens

BACKGROUND

Resistance-associated substitutions (RASs) to HCV direct-acting antivirals (DAAs) can contribute to virologic failure and limit retreatment options. People who inject drugs (PWID) are at highest risk for transmission of resistant virus. We report on RASs at baseline and after virologic failure in DAA-naive and protease inhibitor-experienced PWID.

METHODS

We sequenced the NS3/4A, NS5A, and NS5B regions from 150 PWID with genotype 1 (GT1) viruses; 128 (85.3%) GT1a, 22 (14.7%) GT1b.

RESULTS

Among the 139 (92.7%) DAA-naive PWID, 85 of 139 (61.2%) had baseline RASs-67 of 139 (48.2%) in NS3 (predominantly Q80K/L); 25 of 139 (18.0%) in NS5A; and 8 of 139 (5.8%) in NS5B. Of the 11 protease inhibitor-experienced participants, 9 had baseline NS3 RASs (V36L N = 1, Q80K N = 9) and 4 had baseline NS5A RASs (M28V N = 2, H58P N = 1, A92T N = 1). Among the 11 participants who had posttreatment samples with detectable virus (7 treatment failures, 1 late relapse, 3 reinfections), 1 sofosbuvir/ledipasvir failure had a baseline H58P. Two sofosbuvir/ledipasvir-treated participants developed new NS5A mutations (Q30H, Y93H, L31M/V). Otherwise, no RASs were detected.

CONCLUSIONS

Our results demonstrate RAS prevalence among DAA-naive PWID is comparable to that in the general population. Only 2 of 150 (1.3%) in our longitudinal cohort developed treatment-emergent RASs. Concern for transmission of resistant virus may therefore be minimal.

Danoprevir: First Global Approval

Ascletis has developed danoprevir (Ganovo^®), an orally-administered hepatitis C virus NS3 protease inhibitor, as a treatment for hepatitis C. Based on positive results in phase II and phase III trials in patients with hepatitis C, danoprevir, in combination with ritonavir, peginterferon alfa and ribavirin was recently approved for marketing in China for the treatment of treatment-naive patients with non-cirrhotic genotype 1b chronic hepatitis C. This article summarizes the milestones in the development of danoprevir leading to this first approval.

Prevalence and Factors Related to Natural Resistance-Associated Substitutions to Direct-Acting Antivirals in Patients with Genotype 1 Hepatitis C Virus Infection

This study aimed to assess the prevalence of natural resistance-associated substitutions (RASs) to NS3, NS5A and NS5B inhibitors in 86 genotype 1 Hepatitis C Virus (HCV)-infected patients from Buenos Aires, Argentina, and to determine their effect on therapy outcome. Additionally, virological, clinical and host genetic factors were explored as predictors of the presence of baseline RASs. NS3 RASs (39.2%) were more prevalent than NS5A RASs (25%) and NS5B RASs (8.9%). In the three regions, the frequencies of RASs were significantly higher in HCV-1b than in HCV-1a. The prevalence of Y93H, L159F and Q80K were 1.3%, 6.3% and 2.5%, respectively. IFNL3 CC genotype was identified as an independent predictor of the presence of baseline RASs in NS5A and NS3 genes (p = 0.0005 and p = 0.01, respectively). Sustained virologic response was achieved by 93.3% of the patients after receiving direct-acting antivirals (DAAs), although 48.7% of them showed baseline RASs related to the DAA-regimen. Notably, the prevalence of clinically relevant RASs in the three genes was lower than that observed around the world. The baseline presence of RASs in both subtypes did not appear to affect therapy outcome. These results support the need to evaluate resistance patterns in each particular country since RASs´ prevalence significantly vary worldwide.

In vitro selection of resistance to sofosbuvir in HCV replicons of genotype-1 to -6

BACKGROUND

Sofosbuvir is a nucleoside analogue inhibitor of the HCV NS5B polymerase approved for treatment of HCV-infected patients in combination with ribavirin or with other antivirals. It has activity against all genotypes of HCV. Resistance to sofosbuvir in genotype-1 and -2 HCV is conferred by the S282T substitution in NS5B.

METHODS

To begin to define the correlates of resistance to sofosbuvir in other genotypes, we performed selection experiments in cell culture using cell lines containing subgenomic replicons derived from genotypes-1b, -2a, -3a and -4a, or chimeric replicons in a genotype-1b background but encoding genotype-2b, -5a and -6a NS5B polymerase.

RESULTS

In every case, S282T was selected following passage in the presence of increasing concentrations of sofosbuvir for 10 to 15 weeks. When introduced as a site-directed mutant, S282T conferred reductions in sofosbuvir susceptibility of between 2.4 and 19.4-fold. Other substitutions observed during the selections had relatively less impact on susceptibility, such as N237S in genotype-6a (2.5-fold). Replication capacity was affected by the introduction of S282T in all genotypes to variable extents (3.2% to 22% of wild type).

CONCLUSIONS

These results confirm that S282T is the primary sofosbuvir resistance-associated substitution and that replication capacity is reduced when it is present in all genotypes of HCV.

Prevalence of resistant associated variants (RAVs) in the naïve HCV patient candidate for direct acting antiviral (DAA) therapy

BACKGROUND

Viral hepatitis C is an important global health problem that affects about 2.2% of humans. Strategies on the control of this hepatotropic virus focused on chemotherapy and surveillance of emerging HCV drug resistant mutants, respectively. HCV genotype 1 response to therapy is one of major interests. The aim of this research was to study the prevalence of resistant associated variants (RAVs) in the naïve HCV patient candidate for direct acting antiviral (DAA) therapy.

METHODS

A total of 70 HCV confirmed patients which referred to hospitals affiliated to Iran University of Medial Sciences, Tehran, Iran from May 2014 to March 2015 were enrolled in this cross sectional study. After RNA extraction, RFLP-RT-Nested-PCR was performed for HCV genotyping, then some genotypes 1 and 3 strains were used for further amplification of NS5B gene S282T mutation site and purified products were sequenced. Bioinformatics software was used for analysis of sequences.

RESULTS

From a total of 70 HCV patients, 54 were male (mean age (y)±SD 35.1 ± 8.2) and 16 were female (mean age (y)±SD 43.4 ± 10.1); 26 isolates from 1a, 1b and 3a showed that there were no S282T resistant mutants. Moreover, 2 (4.8%) had a synonymous point mutation (C to T). Statistical analysis didn't found any significant correlation between age, sex and genotype variables.

CONCLUSION

Finally, it can be concluded that there were no resistant mutants in our HCV genotypes 1 and 3 infected patients and broader scale of studies are required in this area using larger specimens, genotype groups and stages of treatment.

Antiviral response and resistance analysis of treatment-naïve HCV infected patients receiving multiple doses of the NS3 protease inhibitor GS-9256

The NS3 protease inhibitor (PI) GS-9256 has demonstrated antiviral activity in a monotherapy study and in combination with other DAAs for treatment of chronic hepatitis C virus (HCV) infection. The resistance profile of GS-9256 was investigated in a phase 1 monotherapy study of patients with HCV genotype (GT) 1 infection. No PI resistance associated substitutions (RASs) at positions 36, 155, 156, 168 and 170 were observed at baseline by population sequencing (15% cutoff) in the 54 patients enrolled in the study, however the PI RAS Q80K were detected in 41% of patients at baseline. In patients who received 75 mg of the investigational protease inhibitor (PI) GS-9256 BID, 300 mg of GS-9256 QD and 200 mg of GS-9256 BID for three days, NS3 RASs (A156V, R155K, D168G/E/N/V) were observed in 9/21, 3/7 and 8/8 post-treatment, respectively. Q80K was not selected in any patients post-treatment. The mean maximal viral load response was -3.0 ± 0.42 log₁₀ IU/mL HCV RNA in the 200 mg BID cohort. In more than 50% of the patients with RASs detected at Day 4, mutations were no longer detectable by population sequencing at Day 14. One patient had the R155K mutation persist to Week 24. Phenotypic analyses showed that substitutions at R155, A156 and D168 significantly reduced susceptibility to GS-9256. In conclusion, NS3 PI RASs were rapidly selected in the majority of patients receiving GS-9256 as monotherapy, despite undetectable levels at baseline. The R155, A156 and D168 substitutions identified in patients confer reduced susceptibility to GS-9256 and other PIs in vitro.

Comprehensive Screening for Naturally Occurring Hepatitis C Virus Resistance to Direct-Acting Antivirals in the NS3, NS5A, and NS5B Genes in Worldwide Isolates of Viral Genotypes 1 to 6

There is no comprehensive study available on the natural hepatitis C virus (HCV) polymorphism in sites associated with resistance including all viral genotypes which may present variable susceptibilities to particular direct-acting antivirals (DAAs). This study aimed to analyze the frequencies, genetic barriers, and evolutionary histories of naturally occurring resistance-associated variants (RAVs) in the six main HCV genotypes. A comprehensive analysis of up to 103 RAVs was performed in 2,901, 2,216, and 1,344 HCV isolates for the NS3, NS5A, and NS5B genes, respectively. We report significant intergenotypic differences in the frequencies of natural RAVs for these three HCV genes. In addition, we found a low genetic barrier for the generation of new RAVs, irrespective of the viral genotype. Furthermore, in 1,126 HCV genomes, including sequences spanning the three genes, haplotype analysis revealed a remarkably high frequency of viruses carrying more than one natural RAV to DAAs (53% of HCV-1a, 28.5% of HCV-1b, 67.1% of HCV-6, and 100% of genotype 2, 3, 4, and 5 haplotypes). With the exception of HCV-1a, the most prevalent haplotypes showed RAVs in at least two different viral genes. Finally, evolutionary analyses revealed that, while most natural RAVs appeared recently, others have been efficiently transmitted over time and cluster in well-supported clades. In summary, and despite the observed high efficacy of DAA-based regimens, we show that naturally occurring RAVs are common in all HCV genotypes and that there is an overall low genetic barrier for the selection of resistance mutations. There is a need for natural DAA resistance profiling specific for each HCV genotype.

Interferon-free regimens containing setrobuvir for patients with genotype 1 chronic hepatitis C: a randomized, multicenter study

BACKGROUND & AIMS

Setrobuvir is a direct-acting antiviral (DAA) non-nucleoside inhibitor of hepatitis C virus (HCV) polymerase. This study examined interferon-free combinations containing setrobuvir, a ritonavir-boosted protease inhibitor (danoprevir/r) and ribavirin, with/without the nucleoside inhibitor mericitabine in HCV genotype (G)1 patients.

METHODS

Non-cirrhotic treatment-naïve patients (N = 110) were randomized to five groups. Three groups received a 14-day mericitabine/ribavirin lead-in followed by treatment with 3 DAAs (setrobuvir, danoprevir/r, mericitabine) plus ribavirin for 12 weeks (Group A: G1a; D: G1b) or 24 weeks (B: G1a), and two groups received 2 DAAs (setrobuvir, danoprevir/r) plus ribavirin for 12 weeks (E: G1b) or 24 weeks (C: G1a). Efficacy was defined as sustained virological response (HCV RNA <25 IU/ml after 12 weeks' follow-up, SVR12).

RESULTS

Two groups met predefined futility criteria for breakthrough (C) or relapse (A) and were discontinued. SVR12 rates were 42.9% (3/7) and 74.1% (20/27) in G1a patients in Groups A and B, respectively, and 95.7% (22/23) and 68.2% (15/22) in G1b patients in Groups D and E respectively. All G1a patients assigned to 24 weeks of treatment who experienced a decrease in HCV RNA of ≥2.3 log10 IU by the end of the lead-in period (n = 28) achieved SVR12. Overall, treatment was well tolerated and most adverse events were mild to moderate. No major safety signals were identified.

CONCLUSIONS

An interferon-free setrobuvir-based regimen (3 DAAs plus ribavirin) is safe and effective in treatment-naïve G1 patients.

Identification of a Pyridoxine-Derived Small-Molecule Inhibitor Targeting Dengue Virus RNA-Dependent RNA Polymerase

The viral RNA-dependent RNA polymerase (RdRp) activity of the dengue virus (DENV) NS5 protein is an attractive target for drug design. Here, we report the identification of a novel class of inhibitor (i.e., an active-site metal ion chelator) that acts against DENV RdRp activity. DENV RdRp utilizes a two-metal-ion mechanism of catalysis; therefore, we constructed a small library of compounds, through mechanism-based drug design, aimed at chelating divalent metal ions in the catalytic site of DENV RdRp. We now describe a pyridoxine-derived small-molecule inhibitor that targets DENV RdRp and show that 5-benzenesulfonylmethyl-3-hydroxy-4-hydroxymethyl-pyridine-2-carboxylic acid hydroxyamide (termed DMB220) inhibited the RdRp activity of DENV serotypes 1 to 4 at low micromolar 50% inhibitory concentrations (IC50s of 5 to 6.7 μM) in an enzymatic assay. The antiviral activity of DMB220 against DENV infection was also verified in a cell-based assay and showed a 50% effective concentration (EC50) of <3 μM. Enzyme assays proved that DMB220 was competitive with nucleotide incorporation. DMB220 did not inhibit the enzymatic activity of recombinant HIV-1 reverse transcriptase and showed only weak inhibition of HIV-1 integrase strand transfer activity, indicating high specificity for DENV RdRp. S600T substitution in the DENV RdRp, which was previously shown to confer resistance to nucleoside analogue inhibitors (NI), conferred 3-fold hypersusceptibility to DMB220, and enzymatic analyses showed that this hypersusceptibility may arise from the decreased binding/incorporation efficiency of the natural NTP substrate without significantly impacting inhibitor binding. Thus, metal ion chelation at the active site of DENV RdRp represents a viable anti-DENV strategy, and DMB220 is the first of a new class of DENV inhibitor.

Evolution of the HCV viral population from a patient with S282T detected at relapse after sofosbuvir monotherapy

Clinical phase II/III studies of the nucleotide analogue HCV NS5B inhibitor sofosbuvir (SOF) have demonstrated high efficacy in HCV-infected patients in combination therapy. To date, resistance to SOF (S282T in NS5B) has rarely been detected in patients. In this study, we investigated the evolution of S282T viral variants detected in one HCV genotype 2b-infected patient who relapsed following 12 weeks of SOF monotherapy. Deep sequencing of the NS5B gene was performed on longitudinal plasma samples at baseline, days 2 and 3 on SOF, and longitudinal samples post-SOF treatment through week 48. Intrapatient HCV evolution was analysed by maximum-likelihood phylogenetic analysis. Deep sequencing analysis revealed a low level pre-existence of S282T at 0.05% of viral sequences (4/7755 reads) at baseline and 0.03% (6/23 415 reads) at day 2 on SOF. Viral relapse was detected at week 4 post-treatment where 99.8% of the viral population harboured S282T. Follow-up analysis determined that S282T levels diminished post-treatment reaching undetectable levels 24-48 weeks post-SOF. Phylogenetic analysis together with the persistence of unique post-treatment mutations in all post-SOF samples suggested that growth of wild type resulted from reversion of the S282T mutant to a wild type and not outgrowth of the baseline wild-type population. Our data suggest that a very low level of pre-existing S282T at baseline in this patient was enriched and transiently detected following SOF monotherapy. Despite relapse with drug resistance to SOF, this patient was successfully retreated with SOF plus ribavirin for 12 weeks and is now cured from HCV infection.

Similar prevalence of low-abundance drug-resistant variants in treatment-naive patients with genotype 1a and 1b hepatitis C virus infections as determined by ultradeep pyrosequencing

Background and Objectives

Hepatitis C virus (HCV) variants that confer resistance to direct-acting-antiviral agents (DAA) have been detected by standard sequencing technology in genotype (G) 1 viruses from DAA-naive patients. It has recently been shown that virological response rates are higher and breakthrough rates are lower in G1b infected patients than in G1a infected patients treated with certain classes of HCV DAAs. It is not known whether this corresponds to a difference in the composition of G1a and G1b HCV quasispecies in regards to the proportion of naturally occurring DAA-resistant variants before treatment.

Methods

We used ultradeep pyrosequencing to determine the prevalence of low-abundance (<25% of the sequence reads) DAA-resistant variants in 191 NS3 and 116 NS5B isolates from 208 DAA-naive G1-infected patients.

Results

A total of 3.5 million high-quality reads of ≥200 nucleotides were generated. The median coverage depth was 4150x and 4470x per NS3 and NS5B amplicon, respectively. Both G1a and G1b populations showed Shannon entropy distributions, with no difference between G1a and G1b in NS3 or NS5B region at the nucleotide level. A higher number of substitutions that confer resistance to protease inhibitors were observed in G1a isolates (mainly at amino acid 80 of the NS3 region). The prevalence of amino acid substitutions that confer resistance to NS5B non-nucleoside inhibitors was similar in G1a and G1b isolates. The NS5B S282T variant, which confers resistance to the polymerase inhibitors mericitabine and sofosbuvir, was not detected in any sample.

Conclusion

The quasispecies genetic diversity and prevalence of DAA-resistant variants was similar in G1a and G1b isolates and in both NS3 and NS5B regions, suggesting that this is not a determinant for the higher level of DAA resistance observed across G1a HCV infected patients upon treatment.

Resistance to nucleotide analogue inhibitors of hepatitis C virus NS5B: mechanisms and clinical relevance

The high barrier to the development of resistance to nucleotide analogue inhibitors of the hepatitis C virus (HCV) RNA-dependent RNA polymerase is an intriguing property of this class of drugs. The S282T substitution in the viral polymerase confers resistance to 2'-C-methylated nucleotide analogues. Although this mutation can be selected in HCV replicons, it has only been identified in very few cases in the clinic. Alternative resistance pathways are likewise rarely seen in vivo. Possible underlying mechanisms that are associated with the selection and establishment of a resistant genotype are discussed in this review.