Hepatitis C Virus Nonstructural Protein 5B Research Articles

Atypical activation of the RNA sensor MDA5 by hepatitis C virus.

Hepatitis C virus (HCV) is a significant human pathogen that can cause a number of serious diseases including chronic inflammation of the liver, cirrhosis, and hepatocellular carcinoma. A key enzyme in the HCV life cycle is the nonstructural protein 5B (NS5B), which functions as an RNA-dependent RNA polymerase (RdRp) responsible for replicating the viral RNA genome. In their recent study, Dansako and colleagues showed that HCV NS5B induces type I interferon via activation of the RNA receptor MDA5, an activity that was dependent on the RdRp enzymatic activity but independent of viral RNA replication. Their data further indicated that the NS5B enzymes of HCV and the related GB virus-B produce cellular double-stranded RNA (dsRNA) species with potential immunostimulatory activity. These findings unveil an unconventional mechanism of activation of MDA5-mediated host immunity by viral RdRp enzymes, which is expected to spur new research directions in viral immunology.

Characterization of Acute HCV Infection and Transmission Networks in People Who Currently Inject Drugs in Catalonia: Usefulness of Dried Blood Spots.

Accurate identification of recent HCV infections is critical for tracing the extent and mechanisms of ongoing transmission. We aimed to validate dried blood spot (DBS) samples for the assessment of Hepatitis C virus (HCV) genetic diversity and to determine epidemiological parameters including incidence, determinants of acute infection, and phylogenetic clustering in people who inject drugs (PWID). HCV nonstructural protein 5B next-generation sequencing was performed from plasma and/or DBS in 220 viremic PWID from the HepCdetect II study. No significant differences were found in consensus sequences or Shannon entropy (SE) intrahost diversity estimate between paired plasma/DBS specimens. SE values were used to identify acute infections with 93.3% sensitivity (95% CI, 0.81-1.06) and 95.0% specificity (95% CI, 0.88-1.02) in a set of well-defined controls. An acute HCV infection (either primary infection or reinfection) was detected in 13.5% of viremic participants and was associated with age ≤30years (OR,8.09), injecting less than daily (OR,4.35), ≤5years of injected drug use (OR,3.43), sharing cocaine snorting straws (OR,2.89), and being unaware of their HCV status (OR,3.62). Annualized HCV incidence was estimated between 31 and 59/100 person-years. On phylogenetic analysis, 46.8% of viremic cases were part of a transmission pair or cluster; age ≤30years (OR,6.16), acute infection (OR,5.73), and infection with subtype 1a (OR,4.78) were independently associated with this condition. The results obtained from plasma and DBS characterize PWID with acute infection and those involved in ongoing HCV transmission and allow estimating incidence from cross-sectional data. This information is critical for the design and assessment of targeted harm reduction programs and test-and-treat interventions and to facilitate monitoring of HCV elimination in this key population.

Follow-up Results of HCV GT2 Patients After Sofosbuvir/Ribavirin Therapy: Careful Attention to Occurrence of HCC.

We examined treatment the efficacy and data on long-term outcomes in real-world Japanese patients infected with hepatitis C virus (HCV) genotype 2 treated with 12-week sofosbuvir/ribavirin combination therapy. In a total of 86 patients who were treated with sofosbuvir/ribavirin, sustained virological response (SVR) rates and long-term-outcomes were retrospectively analyzed. The adherence to this combination therapy was 98.8%. The rates of SVR at week 24 (SVR24) achieved with this treatment according to the 'intention-to-treat' and 'per-protocol' analyses were 89.5% and 96.2%, respectively. Two patients who experienced relapse did not have any previously reported resistance-associated substitutions in the HCV non-structural protein 5B (NS5B) polymerase region. We did not observe any patients who experienced late relapse but did observe that 50% and 1.3% of patients with and without a previous history of hepatocellular carcinoma (HCC), respectively, developed HCC after achieving SVR24 (with a mean follow-up period of 2.7±0.8 years). Patients with SVR should be carefully followed-up to screen for the occurrence of HCC, although it is infrequent.

NMR reveals the intrinsically disordered domain 2 of NS5A protein as an allosteric regulator of the hepatitis C virus RNA polymerase NS5B

Non-structural protein 5B (NS5B) is the RNA-dependent RNA polymerase that catalyzes replication of the hepatitis C virus (HCV) RNA genome and therefore is central for its life cycle. NS5B interacts with the intrinsically disordered domain 2 of NS5A (NS5A-D2), another essential multifunctional HCV protein that is required for RNA replication. As a result, these two proteins represent important targets for anti-HCV chemotherapies. Despite this importance and the existence of NS5B crystal structures, our understanding of the conformational and dynamic behavior of NS5B in solution and its relationship with NS5A-D2 remains incomplete. To address these points, we report the first detailed NMR spectroscopic study of HCV NS5B lacking its membrane anchor (NS5BΔ21). Analysis of constructs with selective isotope labeling of the δ1 methyl groups of isoleucine side chains demonstrates that, in solution, NS5BΔ21 is highly dynamic but predominantly adopts a closed conformation. The addition of NS5A-D2 leads to spectral changes indicative of binding to both allosteric thumb sites I and II of NS5BΔ21 and induces long-range perturbations that affect the RNA-binding properties of the polymerase. We compared these modifications with the short- and long-range effects triggered in NS5BΔ21 upon binding of filibuvir, an allosteric inhibitor. We demonstrate that filibuvir-bound NS5BΔ21 is strongly impaired in the binding of both NS5A-D2 and RNA. NS5A-D2 induces conformational and functional perturbations in NS5B similar to those triggered by filibuvir. Thus, our work highlights NS5A-D2 as an allosteric regulator of the HCV polymerase and provides new insight into the dynamics of NS5B in solution.

Limited overlap between phylogenetic HIV and hepatitis C virus clusters illustrates the dynamic sexual network structure of Dutch HIV-infected MSM.

MSM are at increased risk for infection with HIV-1 and hepatitis C virus (HCV). Is HIV/HCV coinfection confined to specific HIV transmission networks? A HIV phylogenetic tree was constructed for 5038 HIV-1 subtype B polymerase (pol) sequences obtained from MSM in the AIDS therapy evaluation in the Netherlands cohort. We investigated the existence of HIV clusters with increased HCV prevalence, the HIV phylogenetic density (i.e. the number of potential HIV transmission partners) of HIV/HCV-coinfected MSM compared with HIV-infected MSM without HCV, and the overlap in HIV and HCV phylogenies using HCV nonstructural protein 5B sequences from 183 HIV-infected MSM with acute HCV infection. Five hundred and sixty-three of 5038 (11.2%) HIV-infected MSM tested HCV positive. Phylogenetic analysis revealed 93 large HIV clusters (≥10 MSM), 370 small HIV clusters (2-9 MSM), and 867 singletons with a median HCV prevalence of 11.5, 11.6, and 9.3%, respectively. We identified six large HIV clusters with elevated HCV prevalence (range 23.5-46.2%). Median HIV phylogenetic densities for MSM with HCV (3, interquartile range 1-7) and without HCV (3, interquartile range 1-8) were similar. HCV phylogeny showed 12 MSM-specific HCV clusters (clustersize: 2-39 HCV sequences); 12.7% of HCV infections were part of the same HIV and HCV cluster. We observed few HIV clusters with elevated HCV prevalence, no increase in the HIV phylogenetic density of HIV/HCV-coinfected MSM compared to HIV-infected MSM without HCV, and limited overlap between HIV and HCV phylogenies among HIV/HCV-coinfected MSM. Our data do not support the existence of MSM-specific sexual networks that fuel both the HIV and HCV epidemic.

151 - RNA-Dependent RNA Polymerase Activity of HCV NS5B Protein Is Modulated by Glutathionylation

Hepatitis C virus (HCV) is a human blood-borne pathogen that causes chronic liver disease. Chronic hepatitis C often leads to development of liver fibrosis, cirrhosis and hepatocellular carcinoma as well as other hepatic and extrahepatic pathologies. HCV genome is presented by a short positive strand RNA encoding ten structural and non-structural proteins. Among these non-structural protein 5B (NS5B) exhibits RNA-dependent RNA-polymerase activity capable of replicating genomic RNA de novo thus acting as a key component of HCV replicase. Investigation of mechanisms of regulation of HCV replication was focused mostly on search for NS5B-interacting viral and cellular proteins. Much less attention was given to metabolic alterations in the infected cells. It was already shown that HCV triggers massive reactive oxygen species (ROS) production, and virus replication can be inhibited by extracellular H 2 O 2 . Our aim was to explore possible redox modifications of NS5B protein as a link between these events. Using antibodies against glutathionylated proteins we showed that the recombinant NS5B protein of 1b or 2a genotypes, expressed in E.coli , contain glytathione residues. Treatment of NS5B with oxidized glutathione increases degree of glutathionylation, whereas reduced glutathione causes opposite effect. Increase of NS5B glutathionylation degree was accompanied by inhibition of its enzymatic activity both in primer-dependent and primer-independent ( de novo ) systems. MALDI MS analysis revealed that glutathionylation of the recombinant protein of 2a genotype occurs at cysteine residues at positions 89, 146, 274, and 279/295, and GSSG treatment affected residues 170, 223, and 521. Construction of a panel of NS5B mutants with substitution of any single cysteine by serine demonstrated that C279S mutant lost its enzymatic activity, whereas other mutant forms retained sensitivity to glutathione and reducing agents. Currently these data are being verified in HCV cellular replicon system. Acknowledgements This study was supported by Russian Science Foundation (grant #14-14-01021).

Computational study on the binding and unbinding mechanism of HCV NS5B with the inhibitor GS-461203 and substrate using conventional and steered molecular dynamics simulations

The active metabolite GS-461203 of hepatitis C virus (HCV) non-structural protein 5B (NS5B) inhibitor sofosbuvir can stall RNA synthesis or replication by competitively inhibiting the natural substrate nucleoside triphosphate like UTP. Unfortunately, S282T mutant can lead to the resistance to sofosbuvir. Here, the detailed binding mechanism and unbinding process of GS-461203 and UTP to HCV NS5B were unraveled by using conventional molecular dynamics (MD) simulation and steered molecular dynamics (SMD) simulation. Our simulation results demonstrate that both polar and nonpolar interactions are favorable for GS-461203 and UTP binding. Meanwhile, we also identified the key residues responsible for GS-461203 and UTP binding in NS5B-RNA together with the three unbinding process steps including translation, reversal of base and ribose and complete divorce. The 2′-fluoro-2′-C-methyl ribose of GS-461203 can form stronger polar and nonpolar interactions with residues S282 and I160 than UTP. The results can also explain the reason why GS-461203 can effectively be incorporated into RNA synthesis or replication. In the S282T mutant system, the binding affinity attenuation of UTP relative to wild type HCV NS5B is less than that of GS-461203. The obtained binding and unbinding mechanism of HCV NS5B with the inhibitor GS-461203 and substrate in our work will provide useful guidance for the development of new and effective HCV NS5B inhibitors with low resistance.

Allosteric mechanism of cyclopropylindolobenzazepine inhibitors for HCV NS5B RdRp via dynamic correlation network analysis.

HCV RNA dependent RNA polymerase (RdRp) nonstructural protein 5B (NS5B) is a major target against hepatitis C virus (HCV) for antiviral therapy. Recently discovered cyclopropylindolobenzazepine derivatives have been considered as the most potent for their ability to bind the thumb site 1 domain and allosterically inhibit HCV NS5B RdRp activity. However, the allosteric mechanism for these derivatives has not been clarified at the molecular level. In this study, fluctuation correlation networks were constructed based on all-atom molecular dynamics simulations to elucidate the allosteric mechanism. The fluctuation correlation networks between free and M2 bound NS5B are significantly different. Information can better transfer from the allosteric site to the catalytic site for bound NS5B than for free NS5B. Thus, the hypothesis of "binding induced allosteric regulation" is proposed to link the enzyme activation and inhibitor binding and then confirmed by the mutant network. Finally, one possible allosteric pathway was identified with the shortest path and evaluated by the perturbation of the network. These methods will be helpful to identify the allosteric pathway of other proteins and to design new drugs targeting the pathway.

On the Origins of Hepatitis C Virus NS5B Polymerase Inhibitory Activity Using Machine Learning Approaches.

Inhibition of non-structural protein 5B (NS5B) represents an attractive strategy for the therapeutic treatment of hepatitis C virus (HCV). In this study, machine learning classifiers such as artificial neural network (ANN), support vector machine (SVM), random forest (RF) and decision tree (DT) analyses were used to classify 970 compounds based on their physicochemical properties, including quantum chemical descriptors, constitutional descriptors, functional groups and molecular properties. Good predictive performance was obtained from all classifiers, providing accuracies ranging from 82.47-89.61% for external validation set. SVM was noted as the best classifier, indicated by its highest accuracy of 89.61%. The analyses were performed on data sets stratified by structural scaffolds (nucleoside and non-nucleoside) and bioactivities (active and inactive properties). In addition, a molecular fragment analysis was performed to investigate molecular substructures corresponding to biological activities. Furthermore, common substructures and potential functional groups governing the activities of active and inactive inhibitors were noted for the benefit of rational design and high-throughput screening towards potential HCV NS5B inhibitors.

Pharmacokinetics of a Cholesterol-conjugated Aptamer Against the Hepatitis C Virus (HCV) NS5B Protein.

Hepatitis C virus (HCV) is the major cause of progressive liver disease such as chronic hepatitis, cirrhosis, and hepatocellular carcinoma. Previously, we reported that a 29 nucleotide-long 2'-F pyrimidine modified RNA aptamer against the HCV nonstructural protein 5B efficiently inhibited HCV replication and suppressed HCV infectious virus particle formation in a cell culture system. In this study, we modified this aptamer through conjugation of cholesterol for in vivo availability. This cholesterol-conjugated aptamer (chol-aptamer) efficiently entered the cell and inhibited HCV RNA replication, without any alteration in gene expression profiling including innate immune response-related genes. Moreover, systemic administration of the chol-aptamer was well tolerated without any abnormalities in mice. To evaluate the pharmacokinetics of the chol-aptamer in vivo, dose proportionality, bioavailability, and pharmacokinetic parameters were evaluated by noncompartmental analyses in normal BALB/c mice. Population analysis was performed using nonlinear mixed effects modeling. Moreover, the pharmacokinetics of two different routes (intravenous, IV, versus intraperitoneal, IP) were compared. Cholesterol conjugation showed dose proportionality, extended the time that the aptamer was in the plasma, and enhanced aptamer exposure to the body. Noticeably, the IV route was more suitable than the IP route due to the chol-aptamer remaining in the plasma for a longer period of time.

Phosphorylation of hepatitis C virus RNA polymerases ser29 and ser42 by protein kinase C-related kinase 2 regulates viral RNA replication.

Hepatitis C virus (HCV) nonstructural protein 5B (NS5B), an RNA-dependent RNA polymerase (RdRp), is the key enzyme for HCV RNA replication. We previously showed that HCV RdRp is phosphorylated by protein kinase C-related kinase 2 (PRK2). In the present study, we used biochemical and reverse-genetics approaches to demonstrate that HCV NS5B phosphorylation is crucial for viral RNA replication in cell culture. Two-dimensional phosphoamino acid analysis revealed that PRK2 phosphorylates NS5B exclusively at its serine residues in vitro and in vivo. Using in vitro kinase assays and mass spectrometry, we identified two phosphorylation sites, Ser29 and Ser42, in the Δ1 finger loop region that interacts with the thumb subdomain of NS5B. Colony-forming assays using drug-selectable HCV subgenomic RNA replicons revealed that preventing phosphorylation by Ala substitution at either Ser29 or Ser42 impairs HCV RNA replication. Furthermore, reverse-genetics studies using HCV infectious clones encoding phosphorylation-defective NS5B confirmed the crucial role of these PRK2 phosphorylation sites in viral RNA replication. Molecular-modeling studies predicted that the phosphorylation of NS5B stabilizes the interactions between its Δ1 loop and thumb subdomain, which are required for the formation of the closed conformation of NS5B known to be important for de novo RNA synthesis. Collectively, our results provide evidence that HCV NS5B phosphorylation has a positive regulatory role in HCV RNA replication. While the role of RNA-dependent RNA polymerases (RdRps) in viral RNA replication is clear, little is known about their functional regulation by phosphorylation. In this study, we addressed several important questions about the function and structure of phosphorylated hepatitis C virus (HCV) nonstructural protein 5B (NS5B). Reverse-genetics studies with HCV replicons encoding phosphorylation-defective NS5B mutants and analysis of their RdRp activities revealed previously unidentified NS5B protein features related to HCV replication and NS5B phosphorylation. These attributes most likely reflect potential structural changes induced by phosphorylation in the Δ1 finger loop region of NS5B with two identified phosphate acceptor sites, Ser29 and Ser42, which may transiently affect the closed conformation of NS5B. Elucidating the effects of dynamic changes in NS5B phosphorylation status during viral replication and their impacts on RNA synthesis will improve our understanding of the molecular mechanisms of NS5B phosphorylation-mediated regulation of HCV replication.

Dynamics of Hepatitis C Virus (HCV) RNA-dependent RNA Polymerase NS5B in Complex with RNA

The hepatitis C virus (HCV) non-structural protein 5B (NS5B) is an RNA-dependent RNA polymerase that is essentially required for viral replication. Although previous studies revealed important properties of static NS5B-RNA complexes, the nature and relevance of dynamic interactions have yet to be elucidated. Here, we devised a single molecule Förster Resonance Energy Transfer (SM-FRET) assay to monitor temporal changes upon binding of NS5B to surface immobilized RNA templates. The data show enzyme association-dissociation events that occur within the time resolution of our setup as well as FRET-fluctuations in association with stable binary complexes that extend over prolonged periods of time. Fluctuations are shown to be dependent on the length of the RNA substrate, and enzyme concentration. Mutations in close proximity to the template entrance (K98E, K100E), and in the center of the RNA binding channel (R394E), reduce both the population of RNA-bound enzyme and the fluctuations associated to the binary complex. Similar observations are reported with an allosteric nonnucleoside NS5B inhibitor. Our assay enables for the first time the visualization of association-dissociation events of HCV-NS5B with RNA, and also the direct monitoring of the interaction between HCV NS5B, its RNA template, and finger loop inhibitors. We observe both a remarkably low dissociation rate for wild type HCV NS5B, and a highly dynamic enzyme-RNA binary complex. These results provide a plausible mechanism for formation of a productive binary NS5B-RNA complex, here NS5B slides along the RNA template facilitating positioning of its 3' terminus at the enzyme active site.

Sofosbuvir in the treatment of chronic hepatitis C: new dog, new tricks.

The existing standard of care for chronic hepatitis C virus (HCV) infection includes the use of pegylated interferon and ribavirin as primary components of treatment, with the addition of a direct-acting antiviral for genotype 1 infection. Sofosbuvir, an oral nucleotide inhibitor of the HCV nonstructural protein 5B RNA-dependent RNA polymerase enzyme, was recently approved for use in combination with ribavirin and/or pegylated interferon for chronic HCV infection, depending on the genotype. Sofosbuvir is orally administered, and peak plasma concentrations are not affected by food. The drug is renally eliminated and does not require adjustment in mild to moderate renal insufficiency or in any degree of hepatic impairment. Sofosbuvir is not metabolized by cytochrome P450 isoenzymes, nor does it induce or inhibit the metabolism of agents that are substrates of these enzymes. Sofosbuvir demonstrates a high barrier to resistance and was well tolerated by patients in clinical trials. Overall efficacy rates vary between 70% and 90%.

Inhibition of Hepatitis C Virus Replication by GS-6620, a Potent C -Nucleoside Monophosphate Prodrug

As a class, nucleotide inhibitors (NIs) of the hepatitis C virus (HCV) nonstructural protein 5B (NS5B) RNA-dependent RNA polymerase offer advantages over other direct-acting antivirals, including properties, such as pangenotype activity, a high barrier to resistance, and reduced potential for drug-drug interactions. We studied the in vitro pharmacology of a novel C-nucleoside adenosine analog monophosphate prodrug, GS-6620. It was found to be a potent and selective HCV inhibitor against HCV replicons of genotypes 1 to 6 and against an infectious genotype 2a virus (50% effective concentration [EC50], 0.048 to 0.68 μM). GS-6620 showed limited activities against other viruses, maintaining only some of its activity against the closely related bovine viral diarrhea virus (EC50, 1.5 μM). The active 5'-triphosphate metabolite of GS-6620 is a chain terminator of viral RNA synthesis and a competitive inhibitor of NS5B-catalyzed ATP incorporation, with Ki/Km values of 0.23 and 0.18 for HCV NS5B genotypes 1b and 2a, respectively. With its unique dual substitutions of 1'-CN and 2'-C-Me on the ribose ring, the active triphosphate metabolite was found to have enhanced selectivity for the HCV NS5B polymerase over host RNA polymerases. GS-6620 demonstrated a high barrier to resistance in vitro. Prolonged passaging resulted in the selection of the S282T mutation in NS5B that was found to be resistant in both cellular and enzymatic assays (>30-fold). Consistent with its in vitro profile, GS-6620 exhibited the potential for potent anti-HCV activity in a proof-of-concept clinical trial, but its utility was limited by the requirement of high dose levels and pharmacokinetic and pharmacodynamic variability.

In vitro selection of the 3′-untranslated regions of the human liver mRNA that bind to the HCV nonstructural protein 5B

Hepatitis C virus (HCV) nonstructural protein 5B (NS5B) has RNA-dependent RNA polymerase (RdRp) activity. Because NS5B recognizes various RNA motifs besides the HCV genome, NS5B has the potential of interacting with host RNA molecules. In this study, an RNA pool enriched with the 3′-UTR sequences was generated and mRNA molecules with high affinity binding to NS5B were selected by iterative selection. Among the high binding mRNA 3′-UTR segments, we analyzed the housekeeping ribosomal protein S4, X-linked [RPS4X] mRNA 3′-UTR and the 3′-UTR of galectin-1 (GAL-1) mRNA, which is known to be one of the genes upregulated in HCV-infected liver cells and to have a wide spectrum of biological properties. By means of IP-RT-PCR, it was demonstrated that both of the mRNA molecules bind to NS5B in the cytoplasm. Interestingly, GAL-1 and RPS4X mRNA can serve as templates for NS5B RdRp, suggesting these RNA molecules are regulated in vivo by NS5B.

Hepatitis C Virus NS5B and Host Cyclophilin A Share a Common Binding Site on NS5A

Nonstructural protein 5B (NS5B) is essential for hepatitis C virus (HCV) replication as it carries the viral RNA-dependent RNA polymerase enzymatic activity. HCV replication occurs in a membrane-associated multiprotein complex in which HCV NS5A and host cyclophilin A (CypA) have been shown to be present together with the viral polymerase. We used NMR spectroscopy to perform a per residue level characterization of the molecular interactions between the unfolded domains 2 and 3 of NS5A (NS5A-D2 and NS5A-D3), CypA, and NS5B(Δ21). We show that three regions of NS5A-D2 (residues 250-262 (region A), 274-287 (region B), and 306-333 (region C)) interact with NS5B(Δ21), whereas NS5A-D3 does not. We show that both NS5B(Δ21) and CypA share a common binding site on NS5A that contains residues Pro-306 to Glu-323. No direct molecular interaction has been detected by NMR spectroscopy between HCV NS5B(Δ21) and host CypA. We show that cyclosporine A added to a sample containing NS5B(Δ21), NS5A-D2, and CypA specifically inhibits the interaction between CypA and NS5A-D2 without altering the one between NS5A-D2 and NS5B(Δ21). A high quality heteronuclear NMR spectrum of HCV NS5B(Δ21) has been obtained and was used to characterize the binding site on the polymerase of NS5A-D2. Moreover these data highlight the potential of using NMR of NS5B(Δ21) as a powerful tool to characterize in solution the interactions of the HCV polymerase with all kinds of molecules (proteins, inhibitors, RNA). This work brings new insights into the comprehension of the molecular interplay between NS5B, NS5A, and CypA, three essentials proteins for HCV replication.

The conserved lysine 151 of HCV NS5B modulates viral genome replication and infectious virus production

Hepatitis C virus (HCV) nonstructural protein 5B (NS5B) is an RNA-dependent RNA polymerase (RdRp) that is involved in genome replication and virus assembly. NS5B contains a distinct loop (loop Λ2) at the beginning of the nucleoside triphosphate tunnel with a highly conserved lysine (K151). In this study, reverse genetic analysis revealed that substitution of Jc1 NS5B K151 for alanine (K151A) and aspartic acid (K151D) affected genome replication and infectious virus production. However, genome replication and virus production by Jc1 containing NS5B K151R remained unaltered. A major deletion in loop Λ2 abolished RNA replication, suggesting a role for this structural domain in NS5B polymerase activity. In conclusion, this study demonstrated that the conserved K151 modulates infectious virus production; and loop Λ2 is essential for the polymerase activity of NS5B.

Hepatitis C Virus Replication-Specific Inhibition of MicroRNA Activity with Self-Cleavable Allosteric Ribozyme

Functional sequestration of microRNA 122 (miR-122) by treatment with an oligonucleotide complementary to the miRNA results in long-lasting suppression of hepatitis C virus (HCV) viremia in primates. However, the safety of the constitutive miR-122 silencing approach to HCV inhibition is unclear, since miR-122 can modulate the expression of many host genes. In this study, a regulation system capable of specifically inhibiting miR-122 activity only upon HCV infection was developed. To this end, an allosteric self-cleavable ribozyme capable of releasing antisense sequence to miR-122 only in the presence of HCV nonstructural protein 5B was developed using in vitro selection method. The activity of the reporter construct with miR-122 target sequences at its 3' untranslated region and the expression of endogenous miR-122 target proteins were specifically stimulated through sequestration of miR-122 only in HCV replicon Huh-7 cells, but not in naïve Huh-7 cells, when transfected with expression vector encoding the specific allosteric ribozyme. These findings indicate that miR-122 function can be specifically inhibited by the allosteric ribozyme only in HCV-replicating cells. Importantly, HCV replicon replication was efficiently inhibited by the allosteric ribozyme. This ribozyme could be useful for the specific, safe, and efficacious anti-HCV modulation.

Current Perspective of HCV NS5B Inhibitors: A Review

Hepatitis C virus (HCV) infection has emerged as one of the most significant disease to affect humans. Despite its large medical and economical impact, there are no vaccines or efficient therapies without major side effects. The HCV non-structural protein 5B (NS5B) is the RNA-dependent RNA polymerase responsible for the complete copy of the RNA viral genome and is a target of choice for the development of anti-HCV drugs. Although many small molecules have been identified as allosteric inhibitors of NS5B, very few are active in clinical applications. Developments in the field have prompted us to review the research work on HCV NS5B polymerase inhibitors, especially their structure activity relationships and molecular modeling studies. This review will focus on the journey of drug discovery of HCV NS5B inhibitors covering both nucleoside and non-nucleosides.

Ligand and Structure Based Virtual Screening Strategies for Hit-Finding and Optimization of Hepatitis C Virus (HCV) Inhibitors

Virtual Screening (VS) has experienced increased attention into the recent years due to the large datasets made available, the development of advanced VS techniques and the encouraging fact that VS has contributed to the discovery of several compounds that have either reached the market or entered clinical trials. Hepatitis C Virus (HCV) nonstructural protein 5B (NS5B) has become an attractive target for the development of antiviral drugs and many small molecules have been explored as possible HCV NS5B inhibitors. In parallel with experimental practices, VS can serve as a valuable tool in the identification of novel effective inhibitors. Different techniques and workflows have been reported in literature with the goal to prioritize possible potent hits. In this context, different virtual screening strategies have been deployed for the identification of novel Hepatitis C Virus (HCV) inhibitors. This work reviews recent applications of virtual screening in an effort to identify novel potent HCV inhibitors.