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Hepatitis C virus (HCV) presents a significant global health issue due to its widespread prevalence and the absence of a reliable vaccine for prevention. While significant progress has been achieved in therapeutic interventions since the disease was first identified, its resurgence underscores the need for innovative strategies to combat it. The nonstructural protein NS5A is crucial in the life cycle of the HCV, serving as a significant factor in both viral replication and assembly processes. This significance is highlighted by its inclusion in all existing approved HCV combination therapies. In this study, a quantitative structure–activity relationship (QSAR) was conducted to design new compounds with enhanced inhibitory activity against HCV. In this context, a set of 82 phenylthiazole derivatives was employed to construct a QSAR model using the Monte Carlo optimization technique. This model offers valuable insights into the specific structural characteristics that either enhance or reduce the inhibitory activity. These findings were used to design novel NS5A inhibitors. Moreover, molecular docking was used to predict the binding affinity of the newly designed inhibitors within the NS5A protein, followed by molecular dynamics simulations to investigate the dynamic interactions over time. Additionally, molecular mechanics generalized born surface area calculations were carried out to estimate the binding free energies of the inhibitor candidates, providing additional insights into their binding affinities and stabilities. Finally, the absorption, distribution, metabolism, excretion, and toxicity analysis were performed to assess the pharmacokinetic and toxicity profiles of the inhibitor candidates. This comprehensive approach provides a detailed understanding of the potential efficacy, stability, and safety of the screened drug candidates, offering valuable insights for their further development as potent therapeutic agents against HCV. [ABSTRACT FROM AUTHOR]

HCV NS5A is a dimeric phosphoprotein involved in HCV replication. NS5A inhibitors are among direct‐acting antivirals (DAA) for HCV therapy. The Y93H mutant of NS5A is resistant to NS5A inhibitors, but the precise mechanism remains unclear. In this report, we proposed a Ser38‐His93‐Asn91 triad to dissect the mechanism. Using pymol 1.3 software, the homology structure of JFH1 NS5A was determined based on the dimer structure of genotype 1b extracted from the database Protein DataBank (www.ebi.ac.uk/pdbsum) with codes 1ZH1 and 3FQM/3FQQ. FLAG‐NS5A‐WT failed to form dimer in the absence of nonstructural proteins from subgenomic replicon (NS3‐5A); however, FLAG‐NS5A‐Y93H was able to form dimer without the aid of NS3‐5A. The Ser38‐His93‐Asn91 triad in the dimer of the Y93H variant predicts a structural crash of the cleft receiving the NS5A inhibitor daclatasvir. The dimerization assay revealed that the existence of JFH1‐NS5A‐1ZH1 and ‐3FQM homology dimers depended on each other for existence and that both NS5A‐WT 1ZH1 and 3FQM dimers cooperated to facilitate RNA replication. However, NS5A‐Y93H 1ZH1 alone could form dimer and conduct RNA replication in the absence of the 3FQM structure. In conclusion, this study provides novel insight into the functional significance of the Ser38‐His93‐Asn91 triad in resistance of the Y93H variant to NS5A inhibitors. [ABSTRACT FROM AUTHOR]

Classical swine fever (CSF) has been eradicated from Western and Central Europe but remains endemic in parts of Central and South America, Asia, and the Caribbean. CSF virus (CSFV) has been endemic in Cuba since 1993, most likely following an escape of the highly virulent Margarita/1958 strain. In recent years, chronic and persistent infections with low-virulent CSFV have been observed. Amino acid substitutions located in immunodominant epitopes of the envelope glycoprotein E2 of the attenuated isolates were attributed to positive selection due to suboptimal vaccination and control. To obtain a complete picture of the mutations involved in attenuation, we applied forward and reverse genetics using the evolutionary-related low-virulent CSFV/Pinar del Rio (CSF1058)/2010 (PdR) and highly virulent Margarita/1958 isolates. Sequence comparison of the two viruses recovered from experimental infections in pigs revealed 40 amino acid differences. Interestingly, the amino acid substitutions clustered in E2 and the NS5A and NS5B proteins. A long poly-uridine sequence was identified previously in the 3′ untranslated region (UTR) of PdR. We constructed functional cDNA clones of the PdR and Margarita strains and generated eight recombinant viruses by introducing single or multiple gene fragments from Margarita into the PdR backbone. All chimeric viruses had comparable replication characteristics in porcine monocyte-derived macrophages. Recombinant PdR viruses carrying either E2 or NS5A/NS5B of Margarita, with 36 or 5 uridines in the 3′UTR, remained low virulent in 3-month-old pigs. The combination of these elements recovered the high-virulent Margarita phenotype. These results show that CSFV evolution towards attenuated variants in the field involved mutations in both structural and non-structural proteins and the UTRs, which act synergistically to determine virulence. [ABSTRACT FROM AUTHOR]

Classical swine fever virus nonstructural protein NS5A is essential for viral genome replication, protein translation, virus assembly, and autophagy. In the present paper, the interaction of cellular PPP2R1A, PP2Ac, and DAPK3 with NS5A has been confirmed. These interactions mediate the dissociation of PP2A from Beclin 1 and its association with DAPK3. Downregulation of DAPK3 or PPP2R1A inhibits CSFV replication. NS5A induced phosphorylation of Ser88 (PK-15 cells) or Ser90 (HEK293T cells) on Beclin 1. Knockdown of Beclin 1 inhibited NS5A-induced autophagy, indicating that NS5A induces Beclin 1-dependent autophagy. Downregulation of DAPK3, PPP2R1A, or PP2Ac by siRNA reduced Beclin 1 phosphorylation and autophagy mediated by NS5A, showing a critical role of PP2A and DAPK3 in Beclin 1 phosphorylation and autophagy triggered by NS5A. In vitro analysis of Beclin 1 phosphorylation revealed PP2A as being essential for DAPK3-mediated phosphorylation of Beclin 1, indicating that PP2A may dephosphorylate DAPK3 to activate its protein kinase activity, with activated DAPK3 phosphorylated Beclin 1, and then triggering autophagy. These data show for the first time that DAPK3 can be activated through dephosphorylation by PP2A. These findings reveal a novel mechanism whereby CSFV NS5A protein activates autophagy via PP2A-DAPK3-Beclin 1 axis to favor viral replication. [ABSTRACT FROM AUTHOR]

Hepatitis C virus (HCV) is a hepatotropic virus that affects millions of human lives worldwide. Direct-acting antiviral (DAA) regimens are the most effective HCV treatment option. However, amino acid substitution-dependent resistance to DAAs has been a major challenge. This study aimed to determine the increasing risk of DAA resistance due to substitutions in DAA target non-structural proteins (NS3/4A, NS5A, and NS5B). Using a Sequence Retrieval System (SRS) at the virus pathogen resource (ViPR/BV-BRC), n = 32763 target protein sequences were retrieved and analyzed for resistance-associated amino acid substitutions (RAASs) by the Sequence Feature Variant Type (SFVT) antiviral-resistance assessment modeling tool. Reference target protein sequences with 100% identity were retried from UniProt following NCBI BLAST. The types and locations of RAASs were identified and visualized by AlphaFold and PyMol. Linux-r-base/R-studio was used for the data presentation. Multi-drug-resistant variants of NS3/4A in genotype 1 (n = 9) and genotype 5 (n = 5) along with DAA-specific NS3/4A, NS5A, and NS5B variants were identified pan-genotypically. A total of 27 variants (RAASs) of all the targets were identified. Fourteen genotype 1-specific substitutions: V1196A, V1158I, D1194A/T/G, R1181K, T1080S, Q1106R, V1062A, S1148G, A1182V, Y2065N, M2000T, and L2003V were identified. The most frequent substitutions were V1062L and L2003M, followed by Q2002H. L2003V, Q2002H, M2000T, Y2065N, and NL2003M of NS5A and L2003M of NS5B conferred resistance to daclatasvir. S2702T NS5B was the sofosbuvir-resistant variant. D1194A NS3/4A was triple DAA (simeprevir, faldaprevir, and asunaprevir) resistant. The double-drug resistant variants R1181K (faldaprevir and asunaprevir), A1182V and Q1106K/R (faldaprevir and simeprevir), T1080S (faldaprevir and telaprevir), and single drug-resistant variants V1062L (telaprevir), D1194E/T (simeprevir), D1194G (asunaprevir), S1148A/G (simeprevir), and Q1106L (Boceprevir) of NS3/4A were determined. The molecular phenomenon of DAA resistance is paramount in the development of HCV drug candidates. RAASs in NS3, NS5A, and NS5B reduce the susceptibility to DAAs; therefore, continuous RAAS-dependent resistance profiling in HCV is recommended to minimize the probability of DAA therapeutic failure. [ABSTRACT FROM AUTHOR]

Vimentin (VIM), an indispensable protein, is responsible for the formation of intermediate filament structures within cells and plays a crucial role in viral infections. However, the precise role of VIM in classical swine fever virus (CSFV) infection remains unclear. Herein, we systematically investigated the function of VIM in CSFV replication. We demonstrated that both knockdown and overexpression of VIM affected CSFV replication. Furthermore, we observed by confocal microscopy the rearrangement of cellular VIM into a cage-like structure during CSFV infection. Threedimensional (3D) imaging indicated that the cage-like structures were localized in the endoplasmic reticulum (ER) and ringed around the double-stranded RNA (dsRNA), thereby suggesting that VIM was associated with the formation of the viral replication complex (VRC). Mechanistically, phosphorylation of VIM at serine 72 (Ser72), regulated by the RhoA/ROCK signaling pathway, induced VIM rearrangement upon CSFV infection. Confocal microscopy and coimmunoprecipitation assays revealed that VIM colocalized and interacted with CSFV NS5A. Structurally, it was determined that amino acids 96 to 407 of VIM and amino acids 251 to 416 of NS5A were the respective important domains for this interaction. Importantly, both VIM knockdown and disruption of VIM rearrangement inhibited the localization of NS5A in the ER, implying that VIM rearrangement recruited NS5A to the ER for VRC formation. Collectively, our results suggest that VIM recruits NS5A to form a stable VRC that is protected by the cage-like structure formed by VIM rearrangement, ultimately leading to enhanced virus replication. These findings highlight the critical role of VIM in the formation and stabilization of VRC, which provides alternative strategies for the development of antiviral drugs. IMPORTANCE Classical swine fever (CSF), caused by classical swine fever virus (CSFV), is a highly infectious disease that poses a significant threat to the global pig industry. Therefore, gaining insights into the virus and its interaction with host cells is crucial for developing effective antiviral measures and controlling the spread of CSF. Previous studies have shown that CSFV infection induces rearrangement of the endoplasmic reticulum, leading to the formation of small vesicular organelles containing nonstructural protein and double-stranded RNA of CSFV, as well as some host factors. These organelles then assemble into viral replication complexes (VRCs). In this study, we have discovered that VIM recruited CSFV NS5A to form a stable VRC that was protected by a cage-like structure formed by rearranged VIM. This enhanced viral replication. Our findings not only shed light on the molecular mechanism of CSFV replication but also offer new insights into the development of antiviral strategies for controlling CSFV. [ABSTRACT FROM AUTHOR]

Several direct-acting antivirals (DAAs) are available, providing interferon-free strategies for a hepatitis C cure. In contrast to DAAs, host-targeting agents (HTAs) interfere with host cellular factors that are essential in the viral replication cycle; as host genes, they are less likely to rapidly mutate under drug pressure, thus potentially exhibiting a high barrier to resistance, in addition to distinct mechanisms of action. We compared the effects of cyclosporin A (CsA), a HTA that targets cyclophilin A (CypA), to DAAs, including inhibitors of nonstructural protein 5A (NS5A), NS3/4A, and NS5B, in Huh7.5.1 cells. Our data show that CsA suppressed HCV infection as rapidly as the fastest-acting DAAs. CsA and inhibitors of NS5A and NS3/4A, but not of NS5B, suppressed the production and release of infectious HCV particles. Intriguingly, while CsA rapidly suppressed infectious extracellular virus levels, it had no significant effect on the intracellular infectious virus, suggesting that, unlike the DAAs tested here, it may block a post-assembly step in the viral replication cycle. Hence, our findings shed light on the biological processes involved in HCV replication and the role of CypA. [ABSTRACT FROM AUTHOR]

Hepatitis C virus (HCV) is a serious disease that threatens human health. Despite consistent efforts to inhibit the virus, it has infected more than 58 million people, with 300,000 deaths per year. The HCV nonstructural protein NS5A plays a critical role in the viral life cycle, as it is a major contributor to the viral replication and assembly processes. Therefore, its importance is evident in all currently approved HCV combination treatments. The present study identifies new potential compounds for possible medical use against HCV using the quantitative structure–activity relationship (QSAR). In this context, a set of 36 NS5A inhibitors was used to build QSAR models using genetic algorithm multiple linear regression (GA-MLR) and Monte Carlo optimization and were implemented in the software CORAL. The Monte Carlo method was used to build QSAR models using SMILES-based optimal descriptors. Four splits were performed and 24 QSAR models were developed and verified through internal and external validation. The model created for split 3 produced a higher value of the determination coefficients using the validation set (R2 = 0.991 and Q2 = 0.943). In addition, this model provides interesting information about the structural features responsible for the increase and decrease of inhibitory activity, which were used to develop eight novel NS5A inhibitors. The constructed GA-MLR model with satisfactory statistical parameters (R2 = 0.915 and Q2 = 0.941) confirmed the predicted inhibitory activity for these compounds. The Absorption, Distribution, Metabolism, Elimination, and Toxicity (ADMET) predictions showed that the newly designed compounds were nontoxic and exhibited acceptable pharmacological properties. These results could accelerate the process of discovering new drugs against HCV. [ABSTRACT FROM AUTHOR]

Background: NS5A and NS5B proteins of hepatitis C virus (HCV) are the main targets of compounds that directly inhibit HCV infections. However, the emergence of resistance-associated substitutions (RASs) may cause substantial reductions in susceptibility to inhibitors.Methods: Viral load and genotyping were determined in eighty-seven naïve HCV-infected patients, and the amplified NS5A and NS5B regions were sequenced by Sanger sequencing. In addition, physicochemical properties, structural features, immune epitopes, and inhibitors-protein interactions of sequences were analyzed using several bioinformatics tools.Results: Several amino acid residue changes were found in NS5A and NS5B proteins; however, we did not find any mutations related to resistance to the treatment in NS5B. Different phosphorylation and few glycosylation sites were assessed. Disulfide bonds were identified in both proteins that had a significant effect on the function and structure of HCV proteins. Applying reliable software to predict B-cell epitopes, 3 and 5 regions were found for NS5A and NS5B, respectively, representing a considerable potential to induce the humoral immune system. Docking analysis determined amino acids involved in the interaction of inhibitors and mentioned proteins may not decrease the drug efficiency.Conclusions: Strong interactions between inhibitors, NS5A and NS5B proteins and the lack of efficient drug resistance mutations in the analyzed sequences may confirm the remarkable ability of NS5A and NS5B inhibitors to control HCV infection amongst Iranian patients. The results of bioinformatics analysis could unveil all features of both proteins, which can be beneficial for further investigations on HCV drug resistance and designing novel vaccines. [ABSTRACT FROM AUTHOR]

In Guangdong Province, hepatitis C virus (HCV) had been found to confer resistance to direct-acting antivirals (DAAs). There were few studies of HCV subtypes and resistance-associated substitutions (RASs) of HCV in different high-risk populations. In this study, we aimed to determine the subtype distribution and the RASs in high-risk population groups, including drug users (DU), men who have sex with men (MSM), female sex workers (FSW), and male patients with sexually transmitted diseases (STD) in Guangdong Province (a highly developed province with a large population). Using a city-based sampling strategy,1356 samples were obtained from different population groups. Phylogenetic analyses determined subtypes based on Core, NS5B, or NS5A sequences. HCV subtype distribution and RASs in various risk groups and regions were analyzed. Ten subtypes, of which 6 h and 6 k were novel in Guangdong, were identified. The primary subtype among all risk groups was 6a. RASs in 1b and 3a were different from those observed in other studie s. Subtype 3b in western Guangdong was higher than the other three regions. No RASs were found in 6a or any other genotype 6. The HCV subtypes are expanding in high-risk populations in Guangdong. Drug use by other risk groups and commercial sex by DU may bridge the dissemination of 6a from DU to other populations. The RAS profiles of 1b and 3a differed from those reported in studies conducted in southwestern China. Further research is required to determine the reason for this discrepancy. Moreover, the combination of RASs was high in subtype 3b. To guide HCV treatment of subtype 3b, pretreatment subtyping of HCV genotype 3 should be considered in western cities in the near future. • Ten HCV subtypes were detected among high-risk population groups in Guangdong, China. • Commercial sex and drug use may bridge the epidemic of 6a. • RAS profiles of 1b and 3a in Guangdong differed from those in southwestern China. • RAS combination of A30K + L31M was high among study participants with 3b. [ABSTRACT FROM AUTHOR]

The Hepatitis C virus nonstructural protein 5A (NS5A) is a membrane‐associated protein involved in multiple steps of the viral life cycle. Direct‐acting antivirals (DAAs) targeting NS5A are a cornerstone of antiviral therapy, but the mode‐of‐action of these drugs is poorly understood. This is due to the lack of information on the membrane‐bound NS5A structure. Herein, we present the structural model of an NS5A AH‐linker‐D1 protein reconstituted as proteoliposomes. We use highly sensitive proton‐detected solid‐state NMR methods suitable to study samples generated through synthetic biology approaches. Spectra analyses disclose that both the AH membrane anchor and the linker are highly flexible. Paramagnetic relaxation enhancements (PRE) reveal that the dimer organization in lipids requires a new type of NS5A self‐interaction not reflected in previous crystal structures. In conclusion, we provide the first characterization of NS5A AH‐linker‐D1 in a lipidic environment shedding light onto the mode‐of‐action of clinically used NS5A inhibitors. [ABSTRACT FROM AUTHOR]

The Hepatitis C virus nonstructural protein 5A (NS5A) is a membrane‐associated protein involved in multiple steps of the viral life cycle. Direct‐acting antivirals (DAAs) targeting NS5A are a cornerstone of antiviral therapy, but the mode‐of‐action of these drugs is poorly understood. This is due to the lack of information on the membrane‐bound NS5A structure. Herein, we present the structural model of an NS5A AH‐linker‐D1 protein reconstituted as proteoliposomes. We use highly sensitive proton‐detected solid‐state NMR methods suitable to study samples generated through synthetic biology approaches. Spectra analyses disclose that both the AH membrane anchor and the linker are highly flexible. Paramagnetic relaxation enhancements (PRE) reveal that the dimer organization in lipids requires a new type of NS5A self‐interaction not reflected in previous crystal structures. In conclusion, we provide the first characterization of NS5A AH‐linker‐D1 in a lipidic environment shedding light onto the mode‐of‐action of clinically used NS5A inhibitors. [ABSTRACT FROM AUTHOR]

Background & Aims: The presence of baseline resistance‐associated substitutions (RASs) reduced sustained virologic response (SVR) rates in chronic hepatitis C virus (HCV) genotype 1a infected patients treated with Elbasvir/Grazoprevir (EBR/GZR). This study aimed to evaluate the frequency of NS5A RASs and treatment outcomes in patients for whom EBR/GZR was intended. Methods: We sequenced NS5A in 832 samples from German genotype1a‐infected DAA‐naïve patients population‐based, which were collected in the European Resistance Database. Treatment outcomes and clinical parameters were evaluated in 519 of such patients retrospectively. Results: Overall, 6.5% of patients harboured EBR‐specific NS5A RASs at baseline, including Q30H/R (3.3%), L31M (1.8%), Y93H (1.6%) and other individual variants. Antiviral treatment, including EBR/GZR, was initiated in 88% of the patients. In the absence of RASs, the majority of patients received EBR/GZR for 12 weeks (57%) and the SVR rate was 97% compared to 99% SVR achieved using other DAA regimens (LDV/SOF ± RBV, G/P, PrOD + RBV, VEL/SOF). Various regimens were used in the presence of RASs and SVR rates were high following treatment with LDV/SOF (100%), G/P (83%), PrOD/RBV (100%), VEL/SOF (100%), SMV/SOF (100%) and EBR/GZR + RBV for 16 weeks (100%). However, two patients received EBR/GZR for 16 weeks without RBV and one relapsed. Conclusions: EBR/GZR treatment with or without RBV for 12 or 16 weeks according to a baseline RAS analysis was highly effective with ≥97% SVR in patients with genotype 1a. EBR/GZR without RBV should be avoided in patients with RASs. High SVR rates were also achieved using other 8‐ or 12‐week DAA regimens. [ABSTRACT FROM AUTHOR]

Replication of the genotype 2 hepatitis C virus (HCV) requires hyperphosphorylation of the nonstructural protein NS5A. It has been known that NS5A hyperphosphorylation results from the phosphorylation of a cluster of highly conserved serine residues (S2201, S2208, S2211, and S2214) in a sequential manner. It has also been known that NS5A hyperphosphorylation requires an NS3 protease encoded on one single NS3-5A polyprotein. It was unknown whether NS3 protease participates in this sequential phosphorylation process. Using an inventory of antibodies specific to S2201, S2208, S2211, and S2214 phosphorylation, we found that protease-dead S1169A mutation abrogated NS5A hyperphosphorylation and phosphorylation at all serine residues measured, consistent with the role of NS3 in NS5A sequential phosphorylation. These effects were not rescued by a wild-type NS3 protease provided in trans by another molecule. Mutations (T1661R, T1661Y, or T1661D) that prohibited proper cleavage at the NS3-4A junction also abolished NS5A hyperphosphorylation and phosphorylation at all serine residues, whereas mutations at the other cleavage sites, NS4A-4B (C1715S) or NS4B-5A (C1976F), did not. In fact, any combinatory mutations that prohibited NS3-4A cleavage (T1661Y/C1715S or T1661Y/C1976F) abrogated NS5A hyperphosphorylation and phosphorylation at all serine residues. In the C1715S/C1976F double mutant, which resulted in an NS4A-NS4BNS5A fusion polyprotein, a hyperphosphorylated band was observed and was phosphorylated at all serine residues. We conclude that NS3-mediated autocleavage at the NS3-4A junction is critical to NS5A hyperphosphorylation at S2201, S2208, S2211, and S2214 and that NS5A hyperphosphorylation could occur in an NS4A-NS4B-NS5A polyprotein. [ABSTRACT FROM AUTHOR]

Classical swine fever is a world organization for animal health listed disease and is caused by classical swine fever virus (CSFV). CSFV can induced unfolded protein response (UPR) and whether NS5A protein plays a role in this process remains unknown. Here, we demonstrate that CSFV induced all the three signal pathways ATF6, IRE1 and PERK of UPR. Furthermore, this phenomenon may be mediated by the NS5A protein since expression of NS5A alone can achieve the same effect. In the current study, we show that NS5A can interact with GRP78 as measured by using the CO-IP and GST pulldown assays. This interaction plays a positive role in the promotion of CSFV replication. Overexpression or knockdown of GRP78 mediated by lentivirus can enhance or decrease viral replication, respectively. Our findings provide the evidence that CSFV infection can activate the cellular UPRs, in which NS5A and GRP78 play key roles in the process. [ABSTRACT FROM AUTHOR]

Using direct-acting antiviral agents (DAAs) against hepatitis C virus (HCV) infection results in a high treatment response rate. However, several factors can significantly alter this outcome such as resistance-associated substitutions (RASs) in HCV NS5A gene. This study aimed to evaluate the prevalence of naturally occurring RASs of NS5A in HCV genotype 3 (HCV-3) sequences isolated from individuals with chronic HCV-3 infection. All the registered sequences in the GenBank under "NS5A" AND "Hepacivirus C" query were evaluated and screened, those which followed our inclusion criteria were enrolled in our pooled analysis. The retrieved sequences of included studies were evaluated for substitutions, RASs, and RASs conferring >100 resistance fold change (RASs >100 × ) in NS5A amino acid positions 24, 28, 30, 31, 62, 92, and 93. From 7 enrolled studies, a total of 370 HCV-3a isolates were retrieved and investigated. Forty-eight (13.0%, 95% CI = 9.9–16.8%) isolates harbored NS5A RASs. Moreover, Y93H was the only NS5A RAS >100 × observed in 13 (3.5%, 95% CI = 2.0–5.9%) retrieved sequences. The low frequency of naturally occurring NS5A RASs, especially those with clinical relevance (RASs >100 × ), among individuals with HCV-3 infection and the high rate of treatment response to DAAs suggest not to investigate every individual with HCV-3 infection for NS5A RASs before treatment. [ABSTRACT FROM AUTHOR]

Assembling a viral replicase on host intracellular membranes is a common strategy for viral replication of almost all of the positive-strand RNA viruses. Understanding how the key modules of the replicase are involved in the replicase assembly may provide insights into the pathway of the replicase assembly. Herein, by using HCV as a model, we dissect the roles of the amphipathic helix (AH) of NS5A, a key repilcase component, in the viral replicase assembly. The results show that the AH is dispensable for membrane anchoring of NS5A. Instead, AH plays a dual role in the viral replicase assembly: positions a replicase module properly for efficient polyprotein processing and participates in protein-protein interactions within the replicase. This property of AH may serve as an attractive direct anti-viral target. [ABSTRACT FROM AUTHOR]

Direct-acting antiviral inhibitors have revolutionized the treatment of hepatitis C virus (HCV) infected patients. Herein is described the discovery of velpatasvir (VEL, GS-5816), a potent pan-genotypic HCV NS5A inhibitor that is a component of the only approved pan-genotypic single-tablet regimens (STRs) for the cure of HCV infection. VEL combined with sofosbuvir (SOF) is Epclusa®, an STR with 98% cure-rates for genotype 1–6 HCV infected patients. Addition of the pan-genotypic HCV NS3/4A protease inhibitor voxilaprevir to SOF/VEL is the STR Vosevi®, which affords 97% cure-rates for genotype 1–6 HCV patients who have previously failed another treatment regimen. [ABSTRACT FROM AUTHOR]

Background: The NS5A resistance-associated substitution (RAS) Y93H is found quite frequently (5–10%) at baseline in direct-acting antiviral agents (DAA) treatment-naïve genotype (GT) 3a patients when studied by the population-sequencing method (cut-off 20%). This RAS may impair HCV DAA treatment response, since it possesses a high fold in vitro resistance to daclatasvir (DCV) and velpatasvir (VEL) in GT 3. We investigated the effect of baseline Y93H in patients with GT 3a infection on treatment outcome, with or without resistance-based DAA-treatment during 2014–2017. Patients/Methods: Treatment in the intervention group (n = 130) was tailored to baseline resistance-findings by population-sequencing method. Detection of baseline Y93H above 20% prompted a prolonged treatment duration of NS5A-inhibitor and sofosbuvir (SOF) and/or addition of ribavirin (RBV). Patients without baseline Y93H in the intervention group and all patients in the control group (n = 78) received recommended standard DAA-treatment. Results: A higher sustained virologic response rate (SVR) in the intervention group was shown compared to the control group at 95.4% (124/130) and 88.5% (69/78), respectively (p =.06). All five patients with baseline Y93H in the intervention group achieved SVR with personalised treatment based on results from resistance testing; either with the addition of RBV or prolonged treatment duration (24w). In the control group, 2/4 patients with Y93H at baseline treated with ledipasvir/SOF/RBV or DCV/SOF without RBV, failed treatment. Conclusion: The results from this real-life study are in accordance with the findings of the randomised controlled trials in 2015 and the EASL-guidelines of 2016, thus, baseline Y93H impacts on DCV and VEL treatment outcome. [ABSTRACT FROM AUTHOR]

Sofosbuvir/velpatasvir/voxilaprevir (SOF/VEL/VOX) provides a needed hepatitis C virus (HCV) antiviral option for direct‐acting antiviral (DAA)‐experienced patients. We evaluated the effectiveness of SOF/VEL/VOX for 12 weeks in DAA‐experienced patients with genotype 1‐4 treated in clinical practice. In this observational cohort analysis from the Veterans Affairs' Clinical Case Registry, 573 DAA‐experienced patients initiating SOF/VEL/VOX were included: 490 genotype 1, 20 genotype 2, 51 genotype 3 and 12 genotype 4. Rates of cirrhosis were 32.7%, 30.0%, 49.0% and 58.3%; rates of prior NS5A‐experience were 100.0%, 95.0%, 90.2% and 100.0% for genotypes 1‐4, respectively. Overall SVR rates were 90.7% (429/473), 90.0% (18/20), 91.3% (42/46) and 100.0% (12/12) for genotypes 1‐4, respectively, and were 91.3% (274/300), 88.9% (16/18), 90.2% (37/41) and 100.0% (11/11) for those with prior NS5A + NS5B experience. For genotype 1, SVR rates were similar in patients with prior regimens of ledipasvir/SOF (90.6%, 298/329), elbasvir/grazoprevir (91.2%, 73/80) and ombitasvir/paritaprevir/ritonavir/dasabuvir (90.9%, 70/77). SVR rates in genotype 1, 2 and 3 patients with prior SOF/VEL experience were 78.9% (15/19), 86.7% (13/15) and 84.6% (11/13). In genotype 1‐4 patients completing 12 weeks of SOF/VEL/VOX, overall SVR rates were 95.1% (409/430), 89.5% (17/19), 93.3% (42/45) and 100% (12/12). In this diverse real‐world cohort of heavily NS5A pretreated patients, SOF/VEL/VOX SVR rates in DAA‐experienced patients were high across all genotypes. Genotype 1 patients who had prior experience with the most commonly prescribed NS5A regimens achieved similarly high SVR rates when retreated with SOF/VEL/VOX. For genotypes 1, 2 and 3, patients with prior SOF/VEL experience had lower SVR rates. [ABSTRACT FROM AUTHOR]

Aims: The presence of pre-existing hepatitis C virus (HCV) resistance-associated substitutions (RASs) could attenuate viral susceptibility to direct-acting antiviral agents. The aim of this study was to better understand the differences among HCV RASs over time. We compared the prevalence and characteristics of naturally occurring HCV RASs in the NS3, NS5A, and NS5B genes between 2008 and 2016 in Chinese patients chronically infected with HCV genotypes (GT) 1b, 2a, 3a, 3b, and 6a. Methods: HCV RNA was extracted after serum samples were collected from 242 patients at treatment baseline, including 120 samples in 2008 and 122 samples in 2016. Reverse transcription and nested PCR were performed, and the PCR products of the NS3, NS5A, and NS5B regions were sequenced using the Sanger sequencing method. Finally, RASs were identified from the different viral strains. Results: In GT1b, the overall frequency of NS5A RASs in 2016 was significantly higher than that in 2008 (42.0% vs. 18.4%; p = 0.002). Among NS5A RASs, the most frequently detected RAS was Y93H (5.3% in 2008 vs. 15.9% in 2016; p = 0.035), which confers medium- to high-level resistance to the NS5A inhibitors: daclatasvir (DCV), ledipasvir (LDV), ombitasvir (OMV), and elbasvir. The frequency of NS5A L28 (low-level resistance to DCV/LDV/OMV) in 2016 was also higher than that in 2008 (11.6% vs. 1.3%; p = 0.027). In addition, the highest frequency of clinically relevant NS3 RASs was S122G/A/T (69.7% in 2008 and 72.5% in 2016) in HCV GT1b isolates, which had medium-level resistance to simeprevir and asunaprevir, followed by Y56F (7.9% in 2008 and 14.5% in 2016), which confers resistance to paritaprevir. Although NS5B C316N had the highest substitution rate in GT1b (80.2% in 2008 and 91.3% in 2016), it was associated with low-level resistance to sofosbuvir and dasabuvir. However, HCV RASs were rarely detectable at baseline in other genotypes or subtypes except GT1b in this study. Conclusion: The frequency of NS5A RASs in 2016 was significantly higher than that in 2008, especially at the L28 and Y93 substitution positions, which may be due to their better fitness compared with wild-type viruses. [ABSTRACT FROM AUTHOR]

Highlights • Determination of the HCV genotype is still recommended before initiating HCV therapy. • Resistance-associated substitutions (RAS) in NS5A can limit the efficacy of therapy. • A pan-genotypic NS5A amplification protocol was established. • It successfully amplified 98.1% of GT1–7 samples including samples <1000 IU/ml. • Genotyping by NS5A is reliable and simultaneously allows resistance testing. Abstract Background Chronic infection with the Hepatitis C Virus (HCV) is associated with the risk of progressive liver disease. Although, HCV treatment options and viral cure rates have tremendously increased over the last decade, all currently licensed combination therapies contain inhibitors of the replication complex NS5A. Resistance-associated substitutions (RAS) in NS5A can limit the efficacy of therapy; however, resistance testing is routinely not recommended for all patients. Notably, pan-genotypic combinations have been approved, however the correct identification of the HCV genotype is still required for treatment decisions and is a good predictor for treatment success. Objective The aim of this study was the establishment of a pan-genotypic NS5A amplification method for reliable genotyping and simultaneous resistance testing in a fast and cheap routine diagnostic setup. Study design Pan-genotypic degenerated nested PCR primer were designed and tested in 262 HCV-patients. The collection included samples from genotypes 1–7 and the median viral load was 1.07 × 106 IU/ml (range 248-21 × 106 IU/ml). Results Amplification of the expected 747bp fragment was successful in 257 of 262 (98.1%) samples including samples <1000 IU/ml. The direct comparison of the genotype information obtained with core sequencing to those obtained by NS5A prediction showed high concordance (97.3%) and discrepancies occurred only for relatively rare subtypes. Resistance analysis using Geno2Pheno [HCV] showed NS5A-RAS in 23 of 257 (8.9%) of samples. Conclusions We successfully developed a routine diagnostic method for pan-genotypic amplification of NS5A. This amplicon can be used for simultaneous genotyping and resistance testing for enhancing and improving routine HCV diagnostic. [ABSTRACT FROM AUTHOR]

Highlights • The substitutions in amino acids 24, 26, 28, 29, 30, 31, 32, 38, 58, 62, 92 and 93 of HCV-1 NS5A were prevalent (23.6%). • The naturally-occurring pre-treatment HCV-1 NS5A RASs were observed in a portion (16.0%) of patients. • The naturally-occurring pre-treatment HCV-1 NS5A RASs >100X were observed in a small (4.7%) number of patients. • The amino acid substitutions in HCV-1 NS5A including RASs were more frequently observed in HCV-1b than in HCV-1a. Abstract Introduction Resistance-associated substitutions (RASs) in the NS5A gene of hepatitis C virus (HCV) has been studied as one of the predictors of response to NS5A inhibitor-containing regimens. This study aimed to evaluate the prevalence of pre-treatment naturally-occurring NS5A RASs in HCV isolates from patients with chronic HCV genotype 1 (HCV-1) infection retrieved from GenBank. Methods In the search procedure, the studies with published HCV-1 NS5A sequence in GenBank were screened and evaluated for inclusion in the pooled analysis. The sequences of the included studies were retrieved from GenBank and evaluated for substitutions in amino acid positions24, 26, 28, 29, 30, 31, 32, 38, 58, 62, 92 and 93 of HCV NS5A including RASs and RASs conferring >100 resistance fold change (RASs >100X). Results In the pooled analysis, 2409 isolates from patients with HCV-1 infection were included, consisting 1305 (54.2%) HCV-1a and 1104 (45.8%) HCV-1b isolates. The prevalence of NS5A RASs and RASs >100X were 16.0% (95%CI = 14.6%–17.5%) and 4.7% (95%CI = 3.9%–5.6%), respectively. The NS5A RASs were more frequently observed in HCV-1b isolates than in HCV-1a isolates (P < 0.001). Conclusion The naturally-occurring HCV NS5A RASs especially those with clinical relevance (RASs >100X) are observed in a small (4.7%) number of patients with HCV-1 infection. [ABSTRACT FROM AUTHOR]

Type I interferon (IFN) inhibits viruses by inducing the expression of antiviral proteins. The IFN-induced myxovirus resistance B (MxB) protein has been reported to inhibit a limited number of viruses, including HIV-1 and herpesviruses, but its antiviral coverage remains to be explored further. Here we show that MxB interferes with RNA replication of hepatitis C virus (HCV) and significantly inhibits viral replication in a cyclophilin A (CypA)-dependent manner. Our data further show that MxB interacts with the HCV protein NS5A, thereby impairing NS5A interaction with CypA and NS5A localization to the endoplasmic reticulum, two events essential for HCV RNA replication. Interestingly, we found that MxB significantly inhibits two additional CypA-dependent viruses of the Flaviviridae family, namely, Japanese encephalitis virus and dengue virus, suggesting a potential link between virus dependence on CypA and virus susceptibility to MxB inhibition. Collectively, these data have identified MxB as a key factor behind IFN-mediated suppression of HCV infection, and they suggest that other CypA-dependent viruses may also be subjected to MxB restriction. IMPORTANCE Viruses of the Flaviviridae family cause major illness and death around the world and thus pose a great threat to human health. Here we show that IFNinducible MxB restricts several members of the Flaviviridae, including HCV, Japanese encephalitis virus, and dengue virus. This finding not only suggests an active role of MxB in combating these major pathogenic human viruses but also significantly expands the antiviral spectrum of MxB. Our study further strengthens the link between virus dependence on CypA and susceptibility to MxB restriction and also suggests that MxB may employ a common mechanism to inhibit different viruses. Elucidating the antiviral functions of MxB advances our understanding of IFN-mediated host antiviral defense and may open new avenues to the development of novel antiviral therapeutics. [ABSTRACT FROM AUTHOR]

Hepatitis C virus (HCV) nonstructural protein 5A (NS5A) is a phosphoprotein with key functions in regulating viral RNA replication and assembly. Two phosphoisoforms are discriminated by their different apparent molecular weights: a basally phosphorylated (p56) and a hyperphosphorylated (p58) variant. The precise mechanisms governing p58 synthesis and specific functions of the isoforms are poorly understood. Our study aimed at a deeper understanding of determinants involved in p58 synthesis. We analyzed two variants of p56 and p58 of isolate JFH-1 separately by mass spectrometry using an expression model and thereby identified a threonine-rich phosphopeptide exclusively found in the hyperphosphorylated variant. Individual exchange of possible phosphoacceptor sites to phosphoablatant or -mimetic residues had little impact on HCV replication or assembly in cell culture. A phosphospecific antibody recognizing pT242 revealed that this position was indeed phosphorylated only in p58 and depended on casein kinase Iα. Importantly, phosphoablative mutations at positions T244 and S247 abrogated pT242 detection without substantial effects on global p58 levels, whereas mutations in the preceding serine-rich cluster dramatically reduced total p58 levels but had minor impact on pT242 levels, suggesting the existence of distinct subspecies of hyperphosphorylated NS5A. Mass spectrometry analyses of different genotypes showed variable phosphorylation patterns across NS5A and suggested that the threonine-rich region is also phosphorylated at T242 in gt4a and at S249 in gt1a, gt1b, and gt4a. Our data therefore indicate that p58 is not a single homogenously phosphorylated protein species but rather a population of various phosphoisoforms, with high variability between genotypes. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • SOF/VEL/VOX for 12 weeks resulted in a 96% SVR12 rate in NS5A inhibitor-experienced patients. • SOF/VEL/VOX for 12 weeks resulted in a 98% SVR12 rate in DAA-experienced patients naïve to NS5A inhibitors. • 83% of DAA-experienced patients had baseline NS3 and/or NS5A RASs. • 79% of NS5A inhibitor-experienced patients had baseline NS5A RASs. • Baseline RASs had no impact on virologic response in DAA-experienced patients following 12 weeks SOF/VEL/VOX. Background & Aims In phase III studies, the fixed dose combination of sofosbuvir/velpatasvir/voxilaprevir (SOF/VEL/VOX) administered for 12 weeks led to a sustained virologic response at 12 weeks (SVR12) in 96% of NS5A inhibitor-experienced patients, and an SVR12 rate of 98% in DAA-experienced patients who had not previously received an NS5A inhibitor. Herein, we evaluate the relationship between the presence of detectable resistance-associated substitutions (RASs) at baseline and treatment outcome, and whether RASs were selected for in cases of virologic failure. Methods NS3, NS5A, and NS5B deep sequencing analyses were performed at baseline for all patients and at the time of virologic failure. Results are reported using a 15% cut-off. Results A total of 82.7% of NS5A inhibitor-experienced patients (205/248) had baseline NS3 and/or NS5A RASs; 79% had baseline NS5A RASs. SVR12 rates were similar in patients with or without NS3 and/or NS5A RASs, and with or without VOX- or VEL-specific RASs. RASs at NS5A position Y93 were present in 37.3% of patients and 95% achieved SVR12. All patients with ≥2 NS5A RASs achieved SVR12. Baseline NS3 and/or NS5A RASs were present in 46.6% (83/178) of non-NS5A inhibitor DAA-experienced patients, all of whom achieved SVR12. All patients with baseline NS5B nucleoside inhibitor RASs, including two patients with S282T, achieved SVR12. Treatment-selected resistance was seen in one of seven patients who relapsed. Conclusions Baseline RASs had no impact on virologic response in DAA-experienced patients following treatment with SOF/VEL/VOX for 12 weeks. Selection of viral resistance with virologic relapse was uncommon. Lay summary In phase III studies, 12 weeks of treatment with the combination of sofosbuvir, velpatasvir and voxilaprevir (SOF/VEL/VOX) cured 97% of patients with hepatitis C virus who failed prior treatment with direct-acting antiviral drugs. Herein, we show that the presence of pretreatment drug resistance did not affect treatment outcome in these patients who had previously received direct-acting antivirals. We also showed that new drug resistance was rare in patients who failed treatment with SOF/VEL/VOX for 12 weeks. This has important implications for the selection of best retreatment strategies for these patients. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Exploited a metallocene to gain access to a biplanar pharmacophoric arrangement. • Leveraged this organometallic architecture in the design of potent anti-HCV agents. • These efforts informed the design of the clinical candidate odalasvir (ACH-3102). Abstract An unprecedented series of organometallic HCV (hepatitis C virus) NS5A (nonstructural 5A protein) replication complex inhibitors that incorporates a 1,1′-ferrocenediyl scaffold was explored. This scaffold introduces the elements of linear flexibility and non-planar topology that are unconventional for this class of inhibitors. Data from 2-D NMR spectroscopic analyses of these complexes in solution support an anti (unstacked) arrangement of the pharmacophoric groups. Several complexes demonstrate single-digit picomolar in vitro activity in an HCV genotype-1b replicon system. One complex to arise from this investigation (10a) exhibits exceptional picomolar activity against HCV genotype 1a and 1b replicons, low hepatocellular cytotoxicity, and good pharmacokinetic properties in rat. [ABSTRACT FROM AUTHOR]

Objectives: Resistance-associated substitutions (RASs) may impair treatment response to direct-acting antivirals (DAA) in hepatitis C virus (HCV) treatment. We investigated the effects of baseline NS3-RASs (Q80K and R155K) and clinically relevant NS5A-RASs in patients with HCV genotype (GT) 1a infection on treatment outcome, with or without resistance-based DAA-treatment. This multi-center study was carried out between 2014 and 2016. Patients/methods: Treatment in the intervention group (n = 92) was tailored to baseline resistance. Detection of NS3-RAS led to an NS5A-inhibitor-based regimen and detection of NS5A-RAS to a protease-inhibitor regimen. Patients without baseline RAS in the intervention group and all patients in the control group (n = 101) received recommended standard DAA-treatment. Results: The sustained virologic response rates (SVR) in the intervention and control groups were 97.8% (90/92) and 93.1% (94/101), respectively (p = .174). A trend toward higher SVR-rate in cirrhotic patients (p = .058) was noticed in the intervention group compared to the control group with SVR-rates 97.5% (39/40) and 83.3% (35/42), respectively. All patients with baseline NS3 (Q80K/R155K) or NS5A-RASs in the intervention group achieved SVR with personalized resistance-based treatment. In the control group, five patients with Q80K or R155K at baseline were treated with simeprevir + sofosbuvir and treatment failed in two of them. Furthermore, one of three patients who failed ledipasvir + sofosbuvir treatment had NS5A-RASs at baseline. Conclusions: In line with the findings of the OPTIMIST-2 trial for Q80K and the EASL-guidelines 2016 for NS5A-RASs, baseline RASs appeared to have an impact on treatment outcome albeit a statistical significance was not observed in this low-prevalence population. [ABSTRACT FROM AUTHOR]

Summary: Hepatitis C virus (HCV) genotype 4 (GT4) is genetically diverse with 17 confirmed and 4 provisional subtypes. In this report, HCV GT4‐infected patient samples from Phase 2/3 clinical studies were analysed to characterize global demographics and genetic diversity of GT4 infection among patients treated with ombitasvir (OBV, NS5A inhibitor) plus paritaprevir/r (NS3/4A inhibitor codosed with ritonavir). Among 17 subtypes isolated from GT4‐infected patients in the PEARL‐I and AGATE‐I studies, subtype prevalence by country of enrolment and country of origin suggested that subtypes 4a and 4d were likely circulating in Europe, while heterogeneous GT4 subtypes and a portion of GT4a detected in European and North American countries were likely due to immigration of HCV‐infected patients from Africa. The distributions of birth cohort and race were also significantly different across GT4 subtypes 4a, 4d, and non‐4a/4d. In addition, phylogenetic analyses of NS5A sequences revealed clustering within subtype 4a which segregated by the patient‐reported country of origin and the presence of the L30R/S polymorphism. HCV NS5A sequences derived from GT4a‐infected patients who originated from Europe and the United States clustered separately from sequences derived from patients who originated from Egypt, suggesting that genetically distinct strains of subtype 4a may be circulating globally. Finally, NS5A baseline polymorphisms were frequently detected at amino acid positions of interest for the inhibitor‐class and OBV retained activity against 37 of 39 NS5A GT4 clinical isolates, with no impact on treatment outcome in the PEARL‐I and AGATE‐I studies. [ABSTRACT FROM AUTHOR]

Hepatitis C virus (HCV) infection is closely associated with type 2 diabetes. We reported that HCV infection induces the lysosomal degradation of hepatocyte nuclear factor 1 alpha (HNF-1α) via interaction with HCV nonstructural protein 5A (NS5A) protein, thereby suppressing GLUT2 gene expression. The molecular mechanisms of selective degradation of HNF-1α caused by NS5A are largely unknown. Chaperonemediated autophagy (CMA) is a selective lysosomal degradation pathway. Here, we investigated whether CMA is involved in the selective degradation of HNF-1α in HCVinfected cells and observed that the pentapeptide spanning from amino acid (aa) 130 to aa 134 of HNF-1α matches the rule for the CMA-targeting motif, also known as KFERQ motif. A cytosolic chaperone protein, heat shock cognate protein of 70 kDa (HSC70), and a lysosomal membrane protein, lysosome-associated membrane protein type 2A (LAMP- 2A), are key components of CMA. Immunoprecipitation analysis revealed that HNF-1α was coimmunoprecipitated with HSC70, whereas the Q130A mutation (mutation of Q to A at position 130) of HNF-1α disrupted the interaction with HSC70, indicating that the CMA-targeting motif of HNF-1α is important for the association with HSC70. Immunoprecipitation analysis revealed that increasing amounts of NS5A enhanced the association of HNF-1α with HSC70. To determine whether LAMP-2A plays a role in the degradation of HNF-1α protein, we knocked down LAMP-2A mRNA by RNA interference; this knockdown by small interfering RNA (siRNA) recovered the level of HNF-1α protein in HCV J6/JFH1-infected cells. This result suggests that LAMP-2A is required for the degradation of HNF-1α. Immunofluorescence study revealed colocalization of NS5A and HNF-1α in the lysosome. Based on our findings, we propose that HCV NS5A interacts with HSC70 and recruits HSC70 to HNF-1α, thereby promoting the lysosomal degradation of HNF-1α via CMA. IMPORTANCE Many viruses use a protein degradation system, such as the ubiquitinproteasome pathway or the autophagy pathway, for facilitating viral propagation and viral pathogenesis. We investigated the mechanistic details of the selective lysosomal degradation of hepatocyte nuclear factor 1 alpha (HNF-1α) induced by hepatitis C virus (HCV) NS5A protein. Using site-directed mutagenesis, we demonstrated that HNF-1α contains a pentapeptide chaperone-mediated autophagy (CMA)-targeting motif within the POU-specific domain of HNF-1α. The CMA-targeting motif is important for the association with HSC70. LAMP-2A is required for degradation of HNF-1α caused by NS5A. We propose that HCV NS5A interacts with HSC70, a key component of the CMA machinery, and recruits HSC70 to HNF-1α to target HNF-1α for CMA-mediated lysosomal degradation, thereby facilitating HCV pathogenesis. We discovered a role of HCV NS5A in CMA-dependent degradation of HNF-1α. Our results may lead to a better understanding of the role of CMA in the pathogenesis of HCV. [ABSTRACT FROM AUTHOR]

RAD51-associated protein 1 (RAD51AP1) is a member of the multiprotein complexes postulated to carry out RAD51-mediated homologous recombination and DNA repair in mammalian cells. In the present study, we showed that hepatitis C virus (HCV) NS5A directly bound RAD51AP1 and increased the protein level of RAD51AP1 through modulation of the ubiquitin-proteasome pathway. We also demonstrated that RAD51AP1 protein levels were increased in the liver tissues of HCV-infected patients and NS5A-transgenic mice. Importantly, NS5A impaired DNA repair by disrupting the RAD51/RAD51AP1/UAF1 complex and rendered HCV-infected cells more sensitive to DNA damage. Silencing of RAD51AP1 expression resulted in a decrease of viral propagation. We further demonstrated that RAD51AP1 was involved in the assembly step of the HCV life cycle by protecting viral RNA. These data suggest that HCV exploits RAD51AP1 to promote viral propagation and thus that host DNA repair is compromised in HCV-infected cells. Overall, our findings provide mechanistic insight into the pathogenesis of HCV infection. IMPORTANCE Chronic infection with HCV is the leading cause of hepatocellular carcinoma (HCC). However, the molecular mechanisms underlying HCV-induced HCC are not fully understood. Here we demonstrate that the HCV NS5A protein physically interacts with RAD51AP1 and increases the RAD51AP1 protein level through modulation of the ubiquitin-proteasome pathway. HCV coopts host RAD51AP1 to protect viral RNA at an assembly step of the HCV life cycle. Note that the RAD51 protein accumulates in the cytoplasm of HCV-infected cells, and thus the RAD51/RAD51AP1/ UAF1-mediated DNA damage repair system in the nucleus is compromised in HCV-infected cells. Our data may provide new insight into the molecular mechanisms of HCV-induced pathogenesis. [ABSTRACT FROM AUTHOR]

HCV NS5A inhibitors have shown impressive in vitro potency profiles in HCV replicon assays thus making them attractive components for inclusion in an all oral fixed dose combination regimen. Herein, we describe the discovery and characterization of silyl proline-containing HCV NS5A inhibitor MK-8325 with good pan-genotype activity and acceptable pharmacokinetic properties. [ABSTRACT FROM AUTHOR]

Classical swine fever virus (CSFV) NS5A protein is a multifunctional protein, playing critical roles in viral RNA replication, translation and assembly. To further explore its functions in viral replication, interaction of NS5A with host factors was assayed using a his-tag “pull down” assay coupled with shotgun LC-MS/MS. Host protein translation initiation factor 3 subunit E was identified as a binding partner of NS5A, and confirmed by co-immunoprecipitation and co-localization analysis. Overexpression of eIF3E markedly enhanced CSFV genomic replication, viral protein expression and production of progeny virus, and downregulation of eIF3E by siRNA significantly decreased viral proliferation in PK-15 cells. Luciferase reporter assay showed an enhancement of translational activity of the internal ribosome entry site of CSFV by eIF3E and a decrease in cellular translation by NS5A. These data indicate that eIF3E plays an important role in CSFV replication, thereby identifying it as a potential target for inhibition of the virus. [ABSTRACT FROM AUTHOR]

Rab1A belongs to the small Rab GTPase family and is involved in the lifecycle of numerous viruses. Here, knockdown of Rab1A inhibited CSFV growth. Further study revealed that Rab1A depletion decreased intracellular and extracellular CSFV titers, but did not affect intracellular virus genome copies and E2 protein expression within a virus lifecycle, which suggested that Rab1A is required for CSFV particle assembly rather than for genome replication or virion release. This was proofed by blocking the spread of virus using neutralizing antibodies, through which the negative effects of Rab1A knockdown on multi-cycle replication of CSFV were eliminated. Moreover, co-immunoprecipitation and confocal microscopy assays showed that Rab1A bound to CSFV NS5A protein, indicating that Rab1A and viral NS5A proteins may work cooperatively during CSFV particle assembly. In conclusion, this study demonstrated for the first time that Rab1A is required for CSFV particle assembly and binds to viral particle assembly-related NS5A protein. [ABSTRACT FROM AUTHOR]

Background and Aim This multinational (Taiwan, South Korea, Russia) phase 3 study evaluated the all-oral, ribavirin-free, fixed-dose combination (DCV-TRIO) of daclatasvir (NS5A inhibitor) 30 mg, asunaprevir (NS3 inhibitor) 200 mg, and beclabuvir (NS5B inhibitor) 75 mg, in patients with chronic hepatitis C virus genotype-1 infection, with or without compensated cirrhosis. Methods UNITY-4 (NCT02170727) was an open-label, two-cohort study in which 169 patients, treatment-naive ( n = 138) or treatment-experienced ( n = 31), received twice-daily DCV-TRIO for 12 weeks with 24 weeks of post-treatment follow-up. The primary efficacy end point was sustained virologic response at post-treatment week 12 (SVR12) in treatment-naive patients. Results Eighty-eight (52%) patients were men, 81 (48%) Taiwanese, 78 (46%) Korean, and 10 (6%) Russian; 23 (14%) had compensated cirrhosis, and 52 (31%) were IL28B (rs1297860) non-CC genotype. Baseline resistance-associated NS5A polymorphisms (L31 and/or Y93) were detected in 25/165 (15%) patients with available genotype-1 sequencing data. SVR12 was achieved by 98.6% (136/138; 95% confidence interval: 94.9-99.8%) of treatment-naive and 100% (31/31; 95% confidence interval: 88.8-100%) of treatment-experienced patients. Both virologic failures were found to be infected with hepatitis C virus genotype-6g; 100% SVR12 was observed for genotype-1a ( n = 8) and genotype-1b ( n = 157). Two patients experienced serious adverse events. Eight (5%) patients experienced reversible grade 3/4 alanine aminotransferase or aspartate aminotransferase elevations, leading to discontinuation in four (2%); all achieved SVR12. There were no grade 3/4 total bilirubin increases and no deaths. Conclusions Twelve weeks of DCV-TRIO was well tolerated and provided 100% SVR12 in treatment-naive and treatment-experienced patients with genotype-1 infection, with or without cirrhosis, including those with baseline NS5A-L31 or NS5A-Y93 resistance-associated substitutions. [ABSTRACT FROM AUTHOR]

Background: Non-structural 5A protein (NS5A) resistance-associated substitutions (RASs) have been identified in patients infected with hepatitis C virus (HCV), even prior to exposure to direct-acting antiviral agents (DAAs). Selection for these variants occurs rapidly during treatment and, in some cases, leads to antiviral treatment failure. DAAs are currently the standard of care for hepatitis C treatment in many parts of the world. Nevertheless, in Brazil, the prevalence of pre-existing NS5A RASs is largely unknown. In this study, we evaluated the frequency of naturally occurring NS5A RASs in Brazilian patients infected with HCV as either a monoinfection or coinfection with human immunodeficiency virus (HIV).Methods: Direct Sanger sequencing of the NS5A region was performed in 257 DAA-naïve patients chronically infected with HCV (156 monoinfected with HCV and 101 coinfected with HIV/HCV).Results: The frequencies of specific RASs in monoinfected patients were 14.6% for HCV GT-1a (M28 V and Q30H/R), 6.0% for GT-1b (L31F/V and Y93H), and 22.6% for GT-3a (A30K and Y93H). For HIV/HCV-coinfected patients, the frequencies of RAS were 3.9% for GT-1a (M28 T and Q30H/R), and 11.1% for GT-1b (Y93H); no RASs were found in GT-3a sequences.Conclusions: Substitutions that may confer resistance to NS5A inhibitors exist at baseline in Brazilian DAA-naïve patients infected with HCV GT-1a, -1b, and -3a. Standardization of RAS definitions is needed to improve resistance analyses and to facilitate comparisons of substitutions reported across studies worldwide. Therapeutic strategies should be optimized to efficiently prevent DAA treatment failure due to selection for RASs, especially in difficult-to-cure patients. [ABSTRACT FROM AUTHOR]

Hepatitis C virus (HCV) nonstructural protein 5A (NS5A) is a phosphoprotein that plays key, yet poorly defined, roles in both virus genome replication and virion assembly/release. It has been proposed that differential phosphorylation could act as a switch to regulate the various functions of NS5A; however, the mechanistic details of the role of this posttranslational modification in the virus life cycle remain obscure. We previously reported (D. Ross-Thriepland, J. Mankouri, and M. Harris, J Virol 89:3123-3135, 2015, doi:10.1128/JVI.02995-14) a role for phosphorylation at serine 225 (S225) of NS5A in the regulation of JFH-1 (genotype 2a) genome replication. A phosphoablatant (S225A) mutation resulted in a 10-fold reduction in replication and a perinuclear restricted distribution of NS5A, whereas the corresponding phosphomimetic mutation (S225D) had no phenotype. To determine the molecular mechanisms underpinning this phenotype we conducted a label-free proteomics approach to identify cellular NS5A interaction partners. This analysis revealed that the S225A mutation disrupted the interactions of NS5A with a number of cellular proteins, in particular the nucleosome assembly protein 1-like protein 1 (NAP1L1), bridging integrator 1 (Bin1, also known as amphiphysin II), and vesicle-associated membrane protein-associated protein A (VAP-A). These interactions were validated by immunoprecipitation/Western blotting, immunofluorescence, and proximity ligation assay. Importantly, small interfering RNA (siRNA)-mediated knockdown of NAP1L1, Bin1 or VAP-A impaired viral genome replication and recapitulated the perinuclear redistribution of NS5A seen in the S225A mutant. These results demonstrate that S225 phosphorylation regulates the interactions of NS5A with a defined subset of cellular proteins. Furthermore, these interactions regulate both HCV genome replication and the subcellular localization of replication complexes. IMPORTANCE Hepatitis C virus is an important human pathogen. The viral nonstructural 5A protein (NS5A) is the target for new antiviral drugs. NS5A has multiple functions during the virus life cycle, but the biochemical details of these roles remain obscure. NS5A is known to be phosphorylated by cellular protein kinases, and in this study, we set out to determine whether this modification is required for the binding of NS5A to other cellular proteins. We identified 3 such proteins and show that they interacted only with NS5A that was phosphorylated on a specific residue. Furthermore, these proteins were required for efficient virus replication and the ability of NS5A to spread throughout the cytoplasm of the cell. Our results help to define the function of NS5A and may contribute to an understanding of the mode of action of the highly potent antiviral drugs that are targeted to NS5A. [ABSTRACT FROM AUTHOR]

Objective: Mutations in HCV nonstructural protein 5A (NS5A) play a vital role in virus resistance. The aim of this study was to develop a correlation between NS5A mutations (genotype 3a) and virological response towards interferon alpha (IFN-α) plus ribavirin therapy. Methods: In this study, which was conducted from 09-02-2013 to 25-11-2015 in the rural area of Province Sindh - Pakistan, total patients' responses to peg-IFN therapy were investigated. Patients were given peg- IFN therapy for 24 to 48 weeks and categorized as sustained virologic responders (SVR) or non-responders (NR) to HCV infection. HCV NS5A region (2215-2335) of genotype 3a was identified in both responders and non-responders. Results: Twenty-four NR with 24 SVR isolates showed significant mutations within the nonstructural protein 5A region in HCV genotype 3a. The New Zealand (NZL1) (GenBank D17763) differences were observed by using gene. The ISDR mutations for nonstructural protein 5A in non-responders have been reported as a possible explanation of HCV interferon resistance. Conclusion: Based on these results, it is suggested that decreased SVR is caused by the increased mutations in nonstructural protein 5A sequences. When the sequence outside the Protein kinases R binding domain (PKRBD) (2281-2335) was examined, significant differentiations were observed among the SVR and NR classes at few amino acid strains. [ABSTRACT FROM AUTHOR]

In this study, we elucidated the mechanism by which human choline kinase-α (hCKα) interacts with nonstructural protein 5A (NS5A) and phosphatidylinositol-4-kinase IIIα (PI4KIIIα), the lipid kinase crucial for maintaining the integrity of virus-induced membranous webs and modulates hepatitis C virus (HCV) replication. hCKα activity positively modulated phosphatidylinositol-4-phosphate (PI4P) levels in HCV-expressing cells, and hCKα-mediated PI4P accumulation was abolished by AL-9, a PI4KIIIα- specific inhibitor. hCKα colocalized with NS5A and PI4KIIIα or PI4P; NS5A expression increased hCKα and PI4KIIIα colocalization; and hCKα formed a ternary complex with PI4KIIIα and NS5A, supporting the functional interplay of hCKα with PI4KIIIα and NS5A. PI4KIIIα inactivation by AL-9 or hCKα inactivation by CK37, a specific hCKα inhibitor, impaired the endoplasmic reticulum (ER) localization and colocalization of these three molecules. Interestingly, hCKα knockdown or inactivation inhibited PI4KIIIα- NS5A binding. In an in vitro PI4KIIIα activity assay, hCKα activity slightly increased PI4KIIIα basal activity but greatly augmented NS5A-induced PI4KIIIα activity, supporting the essential role of ternary complex formation in robust PI4KIIIα activation. Concurring with the upregulation of PI4P production and viral replication, overexpression of active hCKα-R (but not the D288A mutant) restored PI4KIIIα and NS5A translocation to the ER in hCKα stable knockdown cells. Furthermore, active PI4KIIIα overexpression restored PI4P production, PI4KIIIα and NS5A translocation to the ER, and viral replication in CK37-treated cells. Based on our results, hCKα functions as an indispensable regulator that bridges PI4KIIIα and NS5A and potentiates NS5Astimulated PI4KIIIα activity, which then facilitates the targeting of the ternary complex to the ER for viral replication.α IMPORTANCE The mechanisms by which hCKα activity modulates the transport of the hCKα-NS5A complex to the ER are not understood. In the present study, we investigated how hCKα interacts with PI4KIIIα (a key element that maintains the integrity of the "membranous web" structure) and NS5A to regulate viral replication. We demonstrated that HCV hijacks hCKα to bridge PI4KIIIα and NS5A, forming a ternary complex, which then stimulates PI4KIIIα activity to produce PI4P. Pronounced PI4P synthesis then redirects the translocation of the ternary complex to the ER-derived, PI4P-enriched membrane for assembly of the viral replication complex and viral replication. Our study provides novel insights into the indispensable modulatory role of hCKα in the recruitment of PI4KIIIα to NS5A and in NS5A-stimulated PI4P production and reveals a new perspective for understanding the impact of profound PI4KIIIα activation on the targeting of PI4KIIIα and NS5A to the PI4P-enriched membrane for viral replication complex formation. [ABSTRACT FROM AUTHOR]

Hepatitis C virus (HCV) genotype (GT)3 is associated with increased risk of steatosis, development of cirrhosis and hepatocellular carcinoma. Limited data are available regarding genetic variability and use of direct-acting antiviral agents in these patients. non-structural protein 5A (NS5A) and non-structural protein 5B (NS5B) sequencing was performed on 45 HCV GT3-infected Italian patients subsequently treated with sofosbuvir ± daclatasvir (SOF ± DCV). Novel GT3a polymorphisms were observed by Sanger sequencing in three NS5A (T79S, T107K, and T107S) and three NS5B (G166R, Q180K, and C274W) baseline sequences in patients who achieved sustained virological response (SVR). Baseline NS5A resistance-associated substitutions (RASs) A30K and Y93H were detected in 9.5% of patients; one patient with A30K did not achieve SVR. Phylogenetic analyses of sequences showed no distinct clustering. Genetic heterogeneity of NS5A and NS5B was evaluated using ultra-deep pyrosequencing (UDPS) in samples longitudinally collected in patients not achieving SVR. Some novel NS5A and NS5B polymorphisms detected at baseline may not impact treatment outcome, as they were not enriched in post-failure samples. In contrast, the clinically novel GT3 NS5A-L31F RAS emerged in one treatment failure, and I184T, G188D and N310S, located on the same NS5B haplotype, became predominant after failure. These findings suggest a potential impact of these novel substitutions on the treatment outcome; however, their significance requires further investigation. [ABSTRACT FROM AUTHOR]

The nonstructural protein 5A (NS5A) of the hepatitis C virus (HCV) is a phosphoprotein with two phosphorylation states: hypo- and hyperphosphorylation. Genetic mutation studies have demonstrated a cluster of serine residues responsible for NS5A hyperphosphorylation and functions in viral replication and assembly; how-ever, the phosphorylation levels and potential interactions among the serine residues are unclear. We used three specific antibodies to measure NS5A phosphorylation at S222, S235, and S238 that were identified in our previous proteomics study. In the HCV (J6/JFH-1)-infected Huh7.5.1 cells, S222 phosphorylation was barely detected, whereas S235 phosphorylation and S238 phosphorylation were always detected in parallel in time and intracellular spaces. S235A mutation eliminated S238 phosphorylation whereas S238A mutation did not affect S235 phosphorylation, indicating that S235 phosphorylation occurs independently of S238 phosphorylation while S238 phosphorylation depends on S235 phosphorylation. In line with this, immunoprecipitation coupled with immunoblotting showed that S235 phosphorylation existed alone without S238 phosphorylation, whereas S238 phosphorylation existed only when S235 was phosphorylated on the same NS5A molecule. S235-phosphorylated NS5A constituted the primary hyperphosphorylated NS5A species. S235A mutation blunted viral replication, whereas S238A mutation did not affect replication. We concluded that S235 is the primary NS5A hyperphosphorylation site required for HCV replication. S238 is likely phosphorylated by casein kinase Iα, which requires a priming phosphorylation at S235. [ABSTRACT FROM AUTHOR]

The HCV NS5A protein is essential for viral RNA replication and virus particle assembly. To study the viral replication cycle and NS5A biology we generated an infectious HCV construct with a NanoLuciferase (NLuc) insertion within NS5A. Surprisingly, beyond its utility as a sensitive reporter of cytoplasmic viral RNA replication, we also observed strong luminescence in cell culture fluids. Further analysis using assembly-defective viruses and subgenomic replicons revealed that infectious virus production was not required for extracellular NS5A-NLuc activity but was associated with enrichment of extracellular NS5A-NLuc in intermediate-density fractions similar to those of exosomes and virus particles. Additionally, BRET analysis indicated that intracellular and extracellular forms of NS5A may adopt differing conformations. Importantly, infection studies using a human liver chimeric mouse model confirmed robust infection in vivo and ready detection of NLuc activity in serum. We hypothesise that the presence of NS5A in extracellular fluids contributes to HCV pathogenesis. [ABSTRACT FROM AUTHOR]

Background. Patients chronically infected with genotype 3 hepatitis C virus (HCV) have faster disease progression and are less responsive to current direct-acting antiviral regimens than patients infected with other genotypes. We conducted an open-label trial to evaluate the safety, tolerability, and efficacy of ledipasvir and sofosbuvir plus ribavirin in patients with genotype 3 HCV infection. Methods. We enrolled treatment-naive patients with and without compensated cirrhosis at 15 sites in Canada. All patients were treated with ledipasvir-sofosbuvir (90 mg and 400 mg) plus weight-based ribavirin for 12 weeks. The primary endpoint was sustained virologic response 12 weeks after treatment (SVR12). Secondary endpoints included evaluation of baseline and treatment-emergent drug resistance. Results. Of the 111 patients enrolled, 105 (95%) had subtype 3a HCV and 39 (35%) had compensated cirrhosis. SVR12 was achieved by 99 of 111 patients (89%; 95% confidence interval, 82%-94%). Of the 39 patients with cirrhosis, 31 (79%) achieved SVR12, compared with 68 of 72 (94%) patients without cirrhosis. No treatment-emergent resistance mutations occurred in those who failed treatment. One patient discontinued treatment due to liver cancer and died 22 days after treatment discontinuation. The most common adverse events were fatigue (51%), headache (36%), and nausea (23%). Conclusions. In this multicenter trial involving treatment-naive patients with genotype 3 HCV, 12 weeks of ledipasvir-sofosbuvir provided a high level of SVR in those without cirrhosis. [ABSTRACT FROM AUTHOR]

Aim Although interferon-free therapy with direct-acting antivirals has developed as a standard of care for chronic hepatitis C, the existence of resistance-associated variants (RAVs) has a negative impact on treatment results. Recently, several studies indicated a relationship between chronic hepatitis C and serum vitamin D levels. However, the relationship between RAVs at the hepatitis C virus non-structure 5A (NS5A) region and serum vitamin D level has not yet been examined. Methods Among patients with genotype 1 chronic hepatitis C who were enrolled in a multicenter cooperative study, our subjects comprised 247 patients in whom it was possible to measure RAVs at the NS5A region. These RAVs were measured using a direct sequencing method. Results The median age of patients was 70 years (range, 24-87 years), and the number of female patients was 135 (54.7%). The median serum 25(OH) D3 level was 22 ng/mL (range, 6-64 ng/mL). L31 and Y93 RAVs at the NS5A region were detected in 3.7% (9/247) and 13.4% (33/247) of patients, respectively. Multivariate analysis identified vitamin D deficiency (serum 25(OH) D3 ≤ 20 ng/mL) ( P = 5.91 × 10⁻5, odds ratio = 5.015) and elderly age (>70 years) ( P = 1.85 × 10−3, odds ratio = 3.364) as contributing independent factors associated with the presence of the L31 and/or Y93 RAVs. The Y93H RAV was detected in 25.9% (29/112) of patients with a vitamin D deficiency, and in 8.9% (12/135) of those with a serum 25(OH) D3 level >20 ng/mL ( P = 4.90 × 10−3). Conclusion We showed that RAVs at the NS5A region are associated with vitamin D deficiency and elderly age, which may have a negative influence on innate/adaptive immune responses to hepatitis C virus infection. [ABSTRACT FROM AUTHOR]

Background HCV treatment options and cure rates have tremendously increased in the last decade. Although a pan-genotype HCV treatment has recently been approved, most DAA therapies are still genotype specific. Resistance-associated variants (RAVs) can limit the efficacy of DAA therapy and are associated with increased risk for therapy failure. With the approval of DAA regimens that recommend resistance testing prior to therapy, correct assessment of the genotype and testing for viruses with RAVs is clinically relevant. However, genotyping and resistance testing is generally done in costly and laborious separate reactions. Objective The aim of the study was to establish a genotype-independent full-genome reverse transcription protocol to generate a template for both genotyping and resistance testing and to implement it into our routine diagnostic setup. Study design The complete HCV genome was reverse transcribed with a pan-genotype primer binding at the 3′end of the viral RNA. This cDNA served as template for transcription of the genotyping amplicon in the core region as well as for the resistance testing of NS3, NS5A, and NS5B. Results With the established RT-protocol the HCV core region was successfully amplified and genotyped from 124 out of 125 (99.2%) HCV-positive samples. The amplification efficiency of RAV containing regions in NS3, NS5A, NS5B was 96.2%, 96.6% and 94.4%, respectively. Conclusions We developed a method for HCV full-genome cDNA synthesis and implemented it into a routine diagnostic setup. This cDNA can be used as template for genotyping amplicons covering the core or NS5B region as well as for resistance testing amplicons in NS3, NS5A and NS5B. [ABSTRACT FROM AUTHOR]

We evaluated the transition of dominant resistance-associated substitutions (RASs) in hepatitis C virus during long-term follow-up after the failure of DAAs (direct acting antivirals)-based therapy. RASs in non-structure (NS)3/4A, NS5A, NS5B, and deletions in NS5A from 20 patients who failed simeprevir/pegylated-interferon/ribavirin (SMV/PEG-IFN/RBV) and 25 patients who failed daclatasvir/asunaprevir (DCV/ASV) treatment were examined by direct sequencing. With respect to SMV/PEG-IFN/RBV treatment, RAS was detected at D168 in NS3/4A but not detected in NS5A and NS5B at treatment failure in 16 of 20 patients. During the median follow-up period of 64 weeks, the RAS at D168 became less dominant in 9 of 16 patients. Among 25 DCV/ASV failures, RASs at D168, L31, and Y93 were found in 57.1%, 72.2%, and 76.9%, respectively. NS5A deletions were detected in 3 of 10 patients treated previously with SMV/PEG-IFN/RBV. The number of RASs in the breakthrough patients exceeded that in relapsers (mean 3.9 vs. 2.7, p < 0.05). RAS at D168 in NS3/4A became less dominant in 6 of 15 patients within 80 weeks. Y93H emerged at the time of relapse, then decreased gradually by 99% at 130 weeks post-treatment. Emerged RASs were associated with the clinical course of treatment and could not be detected during longer follow-up. [ABSTRACT FROM AUTHOR]

Background & Aims Ledipasvir/sofosbuvir combination treatment in phase III clinical trials resulted in sustained viral suppression in 94–99% of patients. This study characterized drug resistance in treatment failures, which may help to inform retreatment options. Methods We performed NS5A and NS5B deep sequencing of hepatitis C virus (HCV) from patients infected with genotype (GT) 1 who participated in ledipasvir/sofosbuvir phase II and III clinical trials. Results Fifty-one of 2144 (2.4%) (42 GT1a and 9 GT1b) treated patients met the criteria for resistance analysis due to virologic failure following the end of treatment. The majority of patients with virologic failure (38 of 51; 74.5%) had detectable ledipasvir-specific resistance-associated substitutions (RASs) at the time of virologic failure (1% deep sequencing cut-off). The percent of patients with NS5A RASs at virologic failure were 37.5%, 66.7%, 94.7% and 100% in patients treated for 6, 8, 12 and 24 weeks, respectively. The common substitutions detected at failure were Q30R/H, and/or Y93H/N in GT1a and Y93H in GT1b. At failure, 35.3% (18/51) of virologic failure patients’ viruses had two or more NS5A RASs and the majority of patients harbored NS5A RASs conferring a 100–1000-fold (n = 10) or >1000-fold (n = 23) reduced susceptibility to ledipasvir. One patient in a phase II study with a known ledipasvir RAS at baseline (L31M) developed the S282T sofosbuvir (NS5B) RAS at failure. Conclusions In GT1 HCV-infected patients treated with ledipasvir/sofosbuvir ± ribavirin, virologic failure was rare. Ledipasvir resistance in NS5A was selected or enhanced in most patients with virologic failure, one of whom also developed resistance to sofosbuvir. Lay summary Clinical studies have shown that combination treatment with ledipasvir/sofosbuvir efficiently cures most patients with genotype 1 hepatitis C infection. For the few patients failing treatment, we show that resistance to ledipasvir was observed in most patients, whereas resistance to sofosbuvir was less common. This has important implications for the selection of optimal retreatment strategies for these patients. [ABSTRACT FROM AUTHOR]

Hepatitis C, caused by the hepatitis C virus (HCV) that attacks the liver and leads to inflammation, is a severe threat to human health. Pegylated interferon α (INF-α) and ribavirin based therapy was once the standard therapy for HCV infection. However, it is suboptimal in efficacy and poorly tolerated in some patients. In the last five years, four classes of direct antiviral drugs (NAAs) that target non-structural proteins (NS) of the virus including NS3/NS4A, NS5A, and NS5B have been developed and opened a new era in HCV treatment as they are more effective and tolerable than the INF-α and ribavirin combination regimen. Importantly, the newly introduced multiple NAAs combination therapy makes it possible to eradicate all genotypes of HCV. We review recent progress on the research and development of DAAs in the present article. [ABSTRACT FROM AUTHOR]

Hepatitis C virus (HCV) infection is one of the leading causes of chronic liver diseases and hepatocellular carcinoma (HCC). Golgi protein 73 (GP73), a resident Golgi membrane protein, is a novel serum biomarker for the diagnosis of liver diseases and HCC. Although previous studies have demonstrated that HCV upregulates GP73 expression and GP73 promotes HCV secretion through its interaction with apolipoprotein E (ApoE), the exact mechanism underlying GP73 regulates HCV secretion remains unclear. In this study, we demonstrated that GP73 mediates the interaction of ApoE with HCV NS5A protein to promote HCV secretion. We revealed that GP73 is colocalized with HCV replication complex in infected-Huh7.5.1 cells. Further studies demonstrated that GP73 interacted with both NS5A and ApoE proteins. Furthermore, knockdown of GP73 significantly reduced the binding of NS5A with ApoE, and the production of virus particles in culture supernatant. Taken together, our studies revealed that GP73 promotes HCV secretion by directly mediating the interaction of ApoE with HCV replication complex through binding with HCV NS5A. [ABSTRACT FROM AUTHOR]