Recent development of therapeutics for chronic HCV infection

Novel 6-Aminoquinazolinone Derivatives as Potential Cross GT1-4 HCV NS5B Inhibitors

Chronic hepatitis C virus (HCV) infections are a worldwide medical problem responsible for diverse types of liver diseases. The NS5B polymerase enzyme has become a very interesting target for the development of anti-HCV drugs owing to its fundamental role in viral replication. Here we report the synthesis of a novel series of 1-substituted phenyl-4(1H)-quinazolinone and 2-methyl-1-substituted phenyl-4(1H)-quinazolinone derivatives and evaluate their activity against HCV in HCV subgenomic replicon assays. The biological data revealed that compound 11a showed the highest activity against HCV GT1b at a micromolar concentration (EC₅₀ = 0.984 µM) followed by compound 11b (EC₅₀ = 1.38 µM). Both compounds 11a and 11b had high selectivity indices (SI = CC₅₀/EC₅₀), 160.71 and 71.75, respectively, which make them very interesting candidates for further development of more potent and selective anti-HCV agents.

The Importance of Rhodanine Scaffold in Medicinal Chemistry: A Comprehensive Overview

After the clinical use of epalrestat that contains a rhodanine ring, in type II diabetes mellitus and diabetic complications, rhodanin-based compounds have become an important class of heterocyclic in the field of medicinal chemistry. Various modifications to the rhodanine ring have led to a broad spectrum of biological activity of these compounds. Synthesis of rhodanine derivatives, depended on advenced throughput scanning hits, frequently causes potent and selective modulators of targeted enzymes or receptors, which apply their pharmacological activities through different mechanisms of action. Rhodanine-based compounds will likely stay a privileged scaffold in drug discovery because of different probability of chemical modifications of the rhodanine ring. We have, therefore reviewed their biological activities and structure activity relationship.

MicroRNA-let-7c suppresses hepatitis C virus replication by targeting Bach1 for induction of haem oxygenase-1 expression

MicroRNAs are small noncoding RNAs that are central factors between hepatitis C virus (HCV) and host cellular factors for viral replication and liver disease progression, including liver fibrosis, cirrhosis and hepatocellular carcinoma. In the present study, we found that overexpressing miR-let-7c markedly reduced HCV replication because it induced haem oxygenase-1 (HO-1) expression by targeting HO-1 transcriptional repressor Bach1, ultimately leading to stimulating an antiviral interferon response and blockade of HCV viral protease activity. In contrast, the antiviral actions of miR-let-7c were attenuated by miR-let-7c inhibitor treatment, exogenously expressing Bach1 or suppressing HO-1 activity and expression. A proposed model indicates a key role for miR-let-7c targeting Bach1 to transactivate HO-1-mediated antiviral actions against HCV. miR-let-7c may serve as an attractive target for antiviral development.

Los Alamos Hepatitis C Virus Sequence and Human Immunology Databases: An Expanding Resource for Antiviral Research

The hepatitis C virus (HCV) resource at Los Alamos (hcv.lanl.gov) provides access to multiple databases: one containing annotated sequences and the other a repository of immunogenic epitopes. They are derived from databases originally developed for HIV research (hiv.lanl.gov). HCV and HIV are RNA viruses with relatively compact genomes (around 10 kb) that are extraordinarily variable, both within and between hosts. This diversity requires methods to track and exclude variants from an individual infection or from epidemiologically related infections, and tools to analyse the variation. The HCV immunology database contains a curated inventory of immunogenic epitopes and information about their interaction with the host immune system, with associated retrieval and analysis tools. This interactive resource provides flexible retrieval tools for sequences, epitopes, clinical information, and metadata, as well as utilities for scientific data analysis, to investigators with internet access and a web browser. This paper describes the types of data and the services that these databases offer, the tools they provide, and their configuration and use. Examples of applications to clonal analysis for drug-resistance mutations are shown.

Lycorine-derived phenanthridine downregulators of host Hsc70 as potential hepatitis C virus inhibitors

BACKGROUND

A new series of potential phenanthridine hepatitis C virus (HCV) inhibitors which work by suppressing Hsc70 expression in the host cell was designed and synthesized from lycorine.

RESULTS

Thirty-one new potential phenanthridine HCV inhibitors were synthesized and five of these compounds exhibited good anti-HCV activity and these inhibitors probably inhibit HCV by downregulating the host Hsc70 expression. Structure-activity analysis of these compounds revealed that the double bond between C-11 and C-12 and the substituents at C-8 and C-9 are important for their activity against HCV.

CONCLUSION

Suppression of Hsc70 expression in the host cell to limit HCV replication is a potential anti-HCV strategy. Phenanthridines are probably the HCV inhibitors with this mode of action.

Design, Synthesis and Structure-Activity Relationship Optimization of Lycorine Derivatives for HCV Inhibition

Lycorine is reported to be a multifunctional compound. We previously showed that lycorine is an HCV inhibitor with strong activity. Further research on the antivirus mechanism indicated that lycorine does not affect the enzymes that are indispensable to HCV replication but suppresses the expression of Hsc70 in the host cell to limit HCV replication. However, due to the cytotoxicity and apoptosis induction of lycorine, lycorine is unsafe to be a anti-HCV agent for clinical application. As a result of increasing interest, its structure was optimized for the first time and a novel series of lycorine derivatives was synthesized, all of which lost their cytotoxicity to different degrees. Structure-activity analysis of these compounds revealed that disubstitution on the free hydroxyl groups at C1 and C2 and/or degradation of the benzodioxole group would markedly reduce the cytotoxicity. Furthermore, an α, β-unsaturated ketone would improve the HCV inhibitory activity of lycorine. The C3-C4 double bond is crucial to the anti-HCV activity because hydrogenation of this double bond clearly weakened HCV inhibition.

Resistance to cyclosporin A derives from mutations in hepatitis C virus nonstructural proteins

Cyclosporine A (CsA) is an immunosuppressive drug that targets cyclophilins, cellular cofactors that regulate the immune system. Replication of hepatitis C virus (HCV) is suppressed by CsA, but the molecular basis of this suppression is still not fully understood. To investigate this suppression, we cultured HCV replicon cells (Con1, HCV genotype 1b, FLR-N cell) in the presence of CsA and obtained nine CsA-resistant FLR-N cell lines. We determined full-length HCV sequences for all nine clones, and chose two (clones #6 and #7) of the nine clones that have high replication activity in the presence of CsA for further analysis. Both clones showed two consensus mutations, one in NS3 (T1280V) and the other in NS5A (D2292E). Characterization of various mutants indicated that the D2292E mutation conferred resistance to high concentrations of CsA (up to 2 μM). In addition, the missense mutation T1280V contributed to the recovery of colony formation activity. The effects of these mutations are also evident in two established HCV replicon cell lines-HCV-RMT ([1], genotype 1a) and JFH1 (genotype 2a). Moreover, three other missense mutations in NS5A-D2303H, S2362G, and E2414K-enhanced the resistance to CsA conferred by D2292E; these double or all quadruple mutants could resist approximately 8- to 25-fold higher concentrations of CsA than could wild-type Con1. These four mutations, either as single or combinations, also made Con1 strain resistant to two other cyclophilin inhibitors, N-methyl-4-isoleucine-cyclosporin (NIM811) or Debio-025. Interestingly, the changes in IC50 values that resulted from each of these mutations were the lowest in the Debio-025-treated cells, indicating its highest resistant activity against the adaptive mutation.

Understanding the interaction of hepatitis C virus with host DEAD-box RNA helicases

The current therapeutic regimen to combat chronic hepatitis C is not optimal due to substantial side effects and the failure of a significant proportion of patients to achieve a sustained virological response. Recently developed direct-acting antivirals targeting hepatitis C virus (HCV) enzymes reportedly increase the virologic response to therapy but may lead to a selection of drug-resistant variants. Besides direct-acting antivirals, another promising class of HCV drugs in development include host targeting agents that are responsible for interfering with the host factors crucial for the viral life cycle. A family of host proteins known as DEAD-box RNA helicases, characterized by nine conserved motifs, is known to play an important role in RNA metabolism. Several members of this family such as DDX3, DDX5 and DDX6 have been shown to play a role in HCV replication and this review will summarize our current knowledge on their interaction with HCV. As chronic hepatitis C is one of the leading causes of hepatocellular carcinoma, the involvement of DEAD-box RNA helicases in the development of HCC will also be highlighted. Continuing research on the interaction of host DEAD-box proteins with HCV and the contribution to viral replication and pathogenesis could be the panacea for the development of novel therapeutics against HCV.

Chutes and ladders in hepatitis C nucleoside drug development

Chutes and Ladders is an exciting up-and-down-again game in which players race to be the first to the top of the board. Along the way, they will find ladders to help them advance, and chutes that will cause them to move backwards. The development of nucleoside analogs for clinical treatment of hepatitis C presents a similar scenario in which taking shortcuts may help quickly advance a program, but there is always a tremendous risk of being sent backwards as one competes for the finish line. In recent years the treatment options for chronic hepatitis C virus (HCV) infection have expand due to the development of a replicon based in vitro evaluation system, allowing for the identification of multiple drugable viral targets along with a concerted and substantial drug discovery effort. Three major drug targets have reached clinical study for chronic HCV infection: the NS3/4A serine protease, the large phosphoprotein NS5A, and the NS5B RNA-dependent RNA polymerase. Recently, two oral HCV protease inhibitors were approved by the FDA and were the first direct acting anti-HCV agents to result from the substantial research in this area. There are currently many new chemical entities from several different target classes that are being evaluated worldwide in clinical trials for their effectiveness at achieving a sustained virologic response (SVR) (Pham et al., 2004; Radkowski et al., 2005). Clearly the goal is to develop therapies leading to a cure that are safe, widely accessible and available, and effective against all HCV genotypes (GT), and all stages of the disease. Nucleoside analogs that target the HCV NS5B polymerase that have reached human clinical trials is the focus of this review as they have demonstrated significant advantages in the clinic with broader activity against the various HCV GT and a higher barrier to the development of resistant viruses when compared to all other classes of HCV inhibitors.

Conformation-based restrictions and scaffold replacements in the design of hepatitis C virus polymerase inhibitors: discovery of deleobuvir (BI 207127)

Conformational restrictions of flexible torsion angles were used to guide the identification of new chemotypes of HCV NS5B inhibitors. Sites for rigidification were based on an acquired conformational understanding of compound binding requirements and the roles of substituents in the free and bound states. Chemical bioisosteres of amide bonds were explored to improve cell-based potency. Examples are shown, including the design concept that led to the discovery of the phase III clinical candidate deleobuvir (BI 207127). The structure-based strategies employed have general utility in drug design.

Combined 3D-QSAR, molecular docking, molecular dynamics simulation, and binding free energy calculation studies on the 5-hydroxy-2H-pyridazin-3-one derivatives as HCV NS5B polymerase inhibitors

The NS5B RNA-dependent RNA polymerase (RdRP) is a promising therapeutic target for developing novel anti-hepatitis C virus (HCV) drugs. In this work, a combined molecular modeling study was performed on a series of 193 5-hydroxy-2H-pyridazin-3-one derivatives as inhibitors of HCV NS5B Polymerase. The best 3D-QSAR models, including CoMFA and CoMSIA, are based on receptor (or docking). Furthermore, a 40-ns molecular dynamics (MD) simulation and binding free energy calculations using docked structures of NS5B with ten compounds, which have diverse structures and pIC50 values, were employed to determine the detailed binding process and to compare the binding modes of the inhibitors with different activities. On one side, the stability and rationality of molecular docking and 3D-QSAR results were validated by MD simulation. The binding free energies calculated by the MM-PBSA method gave a good correlation with the experimental biological activity. On the other side, by analyzing some differences between the molecular docking and the MD simulation results, we can find that the MD simulation could also remedy the defects of molecular docking. The analyses of the combined molecular modeling results have identified that Tyr448, Ser556, and Asp318 are the key amino acid residues in the NS5B binding pocket. The results from this study can provide some insights into the development of novel potent NS5B inhibitors.

Molecular modeling comparison of the performance of NS5b polymerase inhibitor (PSI-7977) on prevalent HCV genotypes

The current available treatment for hepatitis C virus (HCV)-the causative of liver cirrhosis and development of liver cancer-is a dual therapy using modified interferon and ribavirin. While this regimen increases the sustained viral response rate up to 40-80 % in different genotypes, unfortunately, it is poorly tolerated by patients. PSI-7977, a prodrug for PSI-7409, is a Non-Structural 5b (NS5b) polymerase nucleoside inhibitor that is currently in phase III clinical trials. The activated PSI-7977 is a direct acting antiviral (DAA) drug that acts on NS5b polymerase of HCV through a coordination bond with the two Mg(+2) present at the GDD active site motif. The present work utilizes a molecular modeling approach for studying the interaction between the activated PSI-7977 and the 12 amino acids constituting a 5 Å region surrounding the GDD active triad motif for HCV genotypes 1a, 2b, 3b and 4a. The analysis of the interaction parameters suggests that PSI-7977 is probably a better DAA drug for HCV genotypes 1a and 3b rather than genotypes 2b and 4a.

Evaluation of anti-HCV activity and SAR study of (+)-lycoricidine through targeting of host heat-stress cognate 70 (Hsc70)

The anti hepatitis C virus (HCV) activity of (+)-lycoricidine (1) was evaluated for the first time in this letter, yielding an EC50 value of 0.55 nmol/mL and an selection index (SI) value of 12.72. Further studies indicated that 1 induced this effect by down-regulating host heat-stress cognate 70 (Hsc70) expression. In addition, 20 derivatives were designed and synthesised to investigate the basic structure-activity relationship (SAR) of the title compound. Several of these derivatives exhibit a good inhibition of HCV, such as compound 3 (EC50=0.68 nmol/mL, SI=33.86), compound 2d (EC50=15 nmol/mL, SI=12) and compound 5 (EC50=33 nmol/mL, SI >10.91). Meanwhile, the experimental data suggest that the modification of certain groups of (+)-lycoricidine can reduce the cytotoxicity of the compounds.

Inhibitory effects of polyphenols toward HCV from the mangrove plant Excoecaria agallocha L

Four new polyphenols namely excoecariphenols A-D (1-4) were isolated from the Chinese mangrove plant Excoecaria agallocha L. together with 23 known phenolic compounds. The structures of new compounds were elucidated on the basis of extensive spectroscopic analyses including IR, MS, NMR, and CD data. Excoecariphenols A and B presented as the unusual flavane-based 1-thioglycosides. Part of the isolated polyphenols were tested against hepatitis C NS3-4A protease and HCV RNA in huh 7.5 cells. Excoecariphenol D, corilagin, geraniin, and chebulagic acid showed potential inhibition toward HCV NS3-4A protease with IC(50) values in a range of 3.45-9.03μM, while excoecariphenol D and corilagin inhibited HCV RNA in huh 7.5 cells significantly. A primary structure-activity relationship (SAR) is discussed.

Synthesis and SAR optimization of diketo acid pharmacophore for HCV NS5B polymerase inhibition

Hepatitis C virus (HCV) NS5B polymerase is a key target for anti-HCV therapeutics development. Here we report the synthesis and biological evaluation of a new series of α,γ-diketo acids (DKAs) as NS5B polymerase inhibitors. We initiated structure-activity relationship (SAR) optimization around the furan moiety of compound 1a [IC(50) = 21.8 μM] to achieve more active NS5B inhibitors. This yielded compound 3a [IC(50) = 8.2 μM] bearing the 5-bromobenzofuran-2-yl moiety, the first promising lead compound of the series. Varying the furan moiety with thiophene, thiazole and indazole moieties resulted in compound 11a [IC(50) = 7.5 μM] bearing 3-methylthiophen-2-yl moiety. Finally replacement of the thiophene ring with a bioisosteric phenyl ring further improved the inhibitory activity as seen in compounds 21a [IC(50) = 5.2 μM] and 24a [IC(50) = 2.4 μM]. Binding mode of compound 24a using glide docking within the active site of NS5B polymerase will form the basis for future SAR optimization.

Recent advances in drug discovery of benzothiadiazine and related analogs as HCV NS5B polymerase inhibitors

Hepatitis C virus (HCV) is a major health burden, with an estimated 170 million chronically infected individuals worldwide, and a leading cause of liver transplantation. Patients are at increased risk of developing liver cirrhosis, hepatocellular carcinoma and even liver failure. In the past two decades, several approaches have been adopted to inhibit non-structural viral proteins. The RNA-dependent RNA polymerase (NS5B) of HCV is one of the attractive validated targets for development of new drugs to block HCV infection. In this review, we report the recent progress made towards identifying and developing benzothiadiazines as HCV NS5B polymerase inhibitors. The substituted benzothiadiazine class was identified by HTS in 2002 as an NS5B inhibitor. Further optimization and modification of the core has improved the potency and pharmacokinetic properties of substituted benzothiadiazines. Research on palm site-binding benzothiadiazine analogs and related derivatives and analogs is discussed in this article.

Importance of ligand bioactive conformation in the discovery of potent indole-diamide inhibitors of the hepatitis C virus NS5B

Significant advances have led to receptor induced-fit and conformational selection models for describing bimolecular recognition, but a more comprehensive view must evolve to also include ligand shape and conformational changes. Here, we describe an example where a ligand's "structural hinge" influences potency by inducing an "L-shape" bioactive conformation, and due to its solvent exposure in the complex, reasonable conformation-activity-relationships can be qualitatively attributed. From a ligand design perspective, this feature was exploited by successful linker hopping to an alternate "structural hinge" that led to a new and promising chemical series which matched the ligand bioactive conformation and the pocket bioactive space. Using a combination of X-ray crystallography, NMR and modeling with support from binding-site resistance mutant studies and photoaffinity labeling experiments, we were able to derive inhibitor-polymerase complexes for various chemical series.

Advances in nucleoside monophosphate prodrugs as anti-HCV agents

Nucleoside monophosphate prodrugs that are eventually bioconverted to the active nucleoside triphosphate (NTP) offer the potential to deliver increased intracellular NTP levels and/or organ-specific NTP enhancement. There are several classes of monophosphate prodrugs that have been applied to HCV drug discovery, and some of these approaches are currently being evaluated in humans. This review discusses recent advances in monophosphate prodrug approaches to improve oral absorption, stability and pharmacokinetic profile, including their advantages and potential pitfalls.

Synthesis and biological evaluation of [D-lysine]8cyclosporin A analogs as potential anti-HCV agents

An efficient synthesis of [D-lysine](8)cyclosporin A has been developed. Several analogs of [D-lysine](8)cyclosporin A have been synthesized and show promising anti-HCV activity, particularly compounds 39 and 43, which each exhibit an anti-HCV EC(50)<200 nM, and are each ≥50-fold less immunosuppressive than cyclosporin A.

Structure-based virtual screening, synthesis and SAR of novel inhibitors of hepatitis C virus NS5B polymerase

Hepatitis C virus (HCV) NS5B polymerase is a key target for the development of therapeutic agents aimed at the treatment of HCV infections. Here we report on the identification of novel allosteric inhibitors of HCV NS5B through a combination of structure-based virtual screening, synthesis and structure-activity relationship (SAR) optimization approach. Virtual screening of 260,000 compounds from the ChemBridge database against the tetracyclic indole inhibitor binding pocket of NS5B (allosteric pocket-1, AP-1), sequentially down-sized the library by 4 orders of magnitude to yield 23 candidates. In vitro evaluation of the NS5B inhibitory activity of the in-silico selected compounds resulted in 17% hit rate, identifying two novel chemotypes. Of these, compound 3, bearing the rhodanine scaffold, proved amenable for productive SAR exploration and synthetic modification. As a result, 25 derivatives that exhibited IC₅₀ values ranging from 7.7 to 68.0 μM were developed. Docking analysis of lead compound 28 within the tetracyclic indole- and benzylidene-binding allosteric pockets (AP-1 and AP-3, respectively) of NS5B revealed topological similarities between these two pockets. Compound 28, a novel rhodanine analog with NS5B inhibitory potency in the low micromolar level range may be a promising lead for future development of more potent NS5B inhibitors.

Synergistic experimental/computational studies on arylazoenamine derivatives that target the bovine viral diarrhea virus RNA-dependent RNA polymerase

Starting from a series of arylazoenamine derivatives, shown to be selectively and potently active against the bovine viral diarrhea virus (BVDV), we developed a hierarchical combined experimental/molecular modeling strategy to explore the drug leads for the BVDV RNA-dependent RNA polymerase. Accordingly, BVDV mutants resistant to lead compounds in our series were isolated, and the mutant residues on the viral molecular target, the RNA-dependent RNA polymerase, were identified. Docking procedures upon previously identified pharmacophoric constraints and actual mutational data were carried out, and the binding affinity of all active compounds for the RdRp was estimated. Given the excellent agreement between in silico and in vitro data, this procedure is currently being employed in the design a new series of more selective and potent BVDV inhibitors.

Novel hepatitis C virus reporter replicon cell lines enable efficient antiviral screening against genotype 1a

The hepatitis C virus (HCV) subgenomic replicon is the primary tool for evaluating the activity of anti-HCV compounds in drug discovery research. Despite the prevalence of HCV genotype 1a (approximately 70% of U.S. HCV patients), few genotype 1a reporter replicon cell lines have been described; this is presumably due to the low replication capacity of such constructs in available Huh-7 cells. In this report, we describe the selection of highly permissive Huh-7 cell lines that support robust replication of genotype 1a subgenomic replicons harboring luciferase reporter genes. These novel cell lines support the replication of multiple genotype 1a replicons (including the H77 and SF9 strains), are significantly more permissive to genotype 1a HCV replication than parental Huh7-Lunet cells, and maintain stable genotype 1a replication levels suitable for antiviral screening. We found that the sensitivity of genotype 1a luciferase replicons to known antivirals was highly consistent between individual genotype 1a clonal cell lines but could vary significantly between genotypes 1a and 1b. Sequencing of the nonstructural region of 12 stable replicon cell clones suggested that the enhanced permissivity is likely due to cellular component(s) in these new cell lines rather than the evolution of novel adaptive mutations in the replicons. These new reagents will enhance drug discovery efforts targeting genotype 1a and facilitate the profiling of compound activity among different HCV genotypes and subtypes.

Pharmacophore modeling, resistant mutant isolation, docking, and MM-PBSA analysis: Combined experimental/computer-assisted approaches to identify new inhibitors of the bovine viral diarrhea virus (BVDV)

Starting from a series of our new 2-phenylbenzimidazole derivatives, shown to be selectively and potently active against the bovine viral diarrhea virus (BVDV), we developed a hierarchical combined experimental/molecular modeling strategy to explore the drug leads for the BVDV RNA-dependent RNA-polymerase. Accordingly, a successful 3D pharmacophore model was developed, characterized by distinct chemical features that may be responsible for the activity of the inhibitors. BVDV mutants resistant to lead compounds in our series were then isolated, and the mutant residues on the viral molecular target, the RNA-dependent RNA-polymerase, were identified. Docking procedures upon pharmacophoric constraints and mutational data were carried out, and the binding affinity of all active compounds for the RdRp were estimated. Given the excellent agreement between in silico and in vitro data, this procedure is currently being employed in the design a new series of more selective and potent BVDV inhibitors.

Diastereoselective synthesis of (+/-)-1',4'-dimethyluridine

The de novo synthesis of racemic 1',4'-dimethyluridine was accomplished in 12 steps starting from 2,5-dimethylfuran and vinylene carbonate. Key steps of the sequence include the stereoconvergent preparation of a meso diacid, and a stereoselective glycosylation without neighboring group participation. Such 1',4'-disubstituted ribonucleoside analogues are undisclosed compounds, which may present interesting biological activities.

N-Acetamideindolecarboxylic acid allosteric 'finger-loop' inhibitors of the hepatitis C virus NS5B polymerase: discovery and initial optimization studies

SAR studies at the N(1)-position of allosteric indole-based HCV NS5B inhibitors has led to the discovery of acetamide derivatives with good cellular potency in subgenomic replicons (EC(50) <200 nM). This class of inhibitors displayed improved physicochemical properties and favorable ADME-PK profiles over previously described analogs in this class.

Pyrazolo[1,5-a]pyrimidine-based inhibitors of HCV polymerase

The present paper describes a novel series of HCV RNA polymerase inhibitors based on a pyrazolo[1,5-a]pyrimidine scaffold bearing hydrophobic groups and an acidic functionality. Several compounds were optimized to low nanomolar potencies in a biochemical RdRp assay. SAR trends clearly reveal a stringent preference for a cyclohexyl group as one of the hydrophobes, and improved activities for carboxylic acid derivatives.

Characterization of aurintricarboxylic acid as a potent hepatitis C virus replicase inhibitor

BACKGROUND

Hepatitis C virus (HCV) NS5B is an essential component of the viral replication machinery and an important target for antiviral intervention. Aurintricarboxylic acid (ATA), a broad-spectrum antiviral agent, was evaluated and characterized for its anti-NS5B activity in vitro and in HCV replicon cells.

METHODS

Recombinant NS5B, HCV replicase and Huh-7 cells harbouring the subgenomic HCV replicon of genotype 1b were employed for biochemical and mechanistic investigations.

RESULTS

Analysis of ATA activity in vitro yielded equipotent inhibition of recombinant NS5B and HCV replicase in the submicromolar range (50% inhibition concentration [IC(50)] approximately 150 nM). Biochemical and mechanistic studies revealed a bimodal mechanism of ATA inhibition with characteristics of pyrophosphate mimics and non-nucleoside inhibitors. Molecular modelling and competition displacement studies were consistent with these parameters, suggesting that ATA might bind to the benzothiadiazine allosteric pocket 3 of NS5B or at its catalytic centre. Kinetic studies revealed a mixed mode of ATA inhibition with respect to both RNA and UTP substrates. Under single-cycle assay conditions, ATA inhibited HCV NS5B initiation and elongation from pre-bound RNA, but with > or =fivefold decreased potency compared with continuous polymerization conditions. The IC(50) value of ATA for the native replicase complex was 145 nM. In HCV replicon cells, ATA treatment ablated HCV RNA replication (50% effective concentration =75 nM) with concomitant decrease in NS5B expression and no apparent cytotoxic effects.

CONCLUSIONS

This study identified ATA as a potent anti-NS5B inhibitor and suggests that its unique mode of action might be exploited for structural refinement and development of novel anti-NS5B agents.

Comparison of HCV NS3 protease and NS5B polymerase inhibitor activity in 1a, 1b and 2a replicons and 2a infectious virus

The hepatitis C virus infection system represents an important new tool for drug discovery. In this study, we compared the in vitro antiviral efficacy of several NS3 and NS5B inhibitors in genotype 1a, 1b, and 2a replicons and in the 2a infectious virus system. The nucleoside inhibitor 2'-C-methyl adenosine showed similar efficacy in each system tested. Three non-nucleoside inhibitors had small differences in potency between genotype 1a and 1b. In contrast, there was a dramatic loss of potency for these non-nucleoside inhibitors in the genotype 2a replicon, 2a infectious virus, and 2a NS5B biochemical assays. The protease inhibitor BILN-2061 had similar efficacy against 1a and 1b replicons but was 61-109-fold less potent against the 2a replicon and virus, respectively. VX-950, a covalent protease inhibitor, had similar efficacy (<3-fold changes in EC(50)) regardless of genotype or subtype. Importantly, we observed a significant correlation (p<0.0001) in antiviral potency between the 2a replicon and 2a infectious virus for all classes of compounds tested.

Development of novel treatments for hepatitis C

Hepatitis C virus (HCV) infection is a major and growing global health problem, affecting about 170 million people worldwide, and is a leading cause of liver cirrhosis and hepatocellular carcinoma. Currently, treatment is restricted to interferon alfa and ribavirin, which leads to a successful outcome in only about 50% of individuals. New effective treatments with tolerable side-effect profiles are needed urgently, but development has been hindered by an inability to culture HCV and a scarcity of animal models. Herein, we review progress in HCV biology, including cell culture and new animal models, and the contribution of this work to our understanding of the virus' life-cycle and pathogenesis and development of specifically targeted antiviral treatment. We also discuss changes in our understanding of HCV epidemiology, clinical manifestations, and diagnostics.

Trends in the Treatment of Chronic Hepatitis C Virus Infection

Despite reductions in the incidence of new hepatitis C virus infections, infections from previous decades continue to place a substantial burden on our health care system. Although the course of the disease is highly variable, approximately 20% to 30% of patients develop cirrhosis, end-stage liver disease, or hepatocellular carcinoma. Fortunately, treatment with our current standard of care, peginterferon a and ribavirin, can reduce the complications of chronic liver disease. However, these drugs are associated with significant adverse effects, many patients are ineligible for treatment, and only 50% are cured. Thus, there is a tremendous need to improve our current therapies and develop new compounds for this disease. This review highlights the transmission, pathophysiology, and course of illness; the pharmacokinetics, proposed mechanisms of action, adverse events, and potential drug interactions with peginterferon a and ribavirin; current treatment trends; the role of the pharmacist in the treatment of this disease; and investigational drugs in later stages of clinical development. Despite the initial hope that these new drugs would replace our current standard of care, it has become clear that ribavirin and peginterferon a will continue to play an important role in the treatment of chronic hepatitis C virus in the years to come.

Approaches for the development of antiviral compounds: the case of hepatitis C virus

Traditional methods for general drug discovery typically include evaluating random compound libraries for activity in relevant cell-free or cell-based assays. Success in antiviral development has emerged from the discovery of more focused libraries that provide clues about structure activity relationships. Combining these with more recent approaches including structural biology and computational modeling can work efficiently to hasten discovery of active molecules, but that is not enough. There are issues related to biology, toxicology, pharmacology, and metabolism that have to be addressed before a hit compound becomes nominated for clinical development. The objective of gaining early preclinical knowledge is to reduce the risk of failure in Phases 1, 2, and 3, leading to the goal of approved drugs that benefit the infected individual. This review uses hepatitis C virus (HCV), for which we still do not have an ideal therapeutic modality, as an example of the multidisciplinary efforts needed to discover new antiviral drugs for the benefit of humanity.

Structural determinant of human La protein critical for internal initiation of translation of hepatitis C virus RNA

Human La protein has been implicated in facilitating internal ribosome entry site (IRES)-mediated translation of hepatitis C virus (HCV). Earlier, we demonstrated that the RNA recognition motif (RRM) encompassing residues 112 to 184 of La protein [La (112-184)] interacts with the HCV IRES near the initiator AUG codon. A synthetic peptide, LaR2C (24-mer), derived from La RRM (112-184), retains RNA binding ability, competes with La protein binding to the HCV IRES, and inhibits translation. The peptide interferes with the assembly of 48S complexes, resulting in the accumulation of preinitiation complexes that are incompetent for the 60S ribosomal subunit joining. Here, nuclear magnetic resonance spectroscopy of the HCV IRES-bound peptide complex revealed putative contact points, mutations that showed reduced RNA binding and translation inhibitory activity. The residues responsible for RNA recognition were found to form a turn in the RRM (112-184) structure. A 7-mer peptide comprising this turn showed significant translation inhibitory activity. The bound structure of the peptide inferred from transferred nuclear Overhauser effect experiments suggests that it is a beta turn. This conformation is significantly different from that observed in the free RRM (112-184) NMR structure, suggesting paths toward a better-stabilized mimetic peptide. Interestingly, addition of hexa-arginine tag enabled the peptide to enter Huh7 cells and showed inhibition of HCV IRES function. More importantly, the peptide significantly inhibited replication of the HCV monocistronic replicon. Elucidation of the structural determinant of the peptide provides a basis for developing small peptidomimetic structures as potent anti-HCV therapeutics.

Production and characterization of monoclonal antibody specific for NS3 helicase of hepatitis C virus

Hepatitis C virus (HCV) infection is the major etiological agent of chronic hepatitis, which leads to liver cirrhosis and hepatocellular carcinomas. HCV NS3 helicase is a promising target of anti-virus therapy. In this report, we discuss a strategy to generate monoclonal antibodies (MAbs) of the HCV NS3 helicase, and investigate its potential characteristic. Our results showed the production of MAbs against NS3 helicase, which could specifically recognize the native NS3 helicase in transiently transfected cells in the immunofluorescence experiment. The resultant MAbs were used as the first antibody in Western blot analyses, and observed the specific band that defines the NS3 helicase. Likewise, one MAb could inhibit the NS3 helicase enzymatic activity distinctly in the NS3 helicase-mediated DNA-unwinding assay. To conclude, these antibodies may be useful to generate specific diagnostic tools for HCV infection and may also be developed for potential therapeutics.

Review article: novel therapeutic options for chronic hepatitis C

BACKGROUND

The efficacy of treatment against hepatitis C virus has improved, but it is still far from ideal. Thus, new antihepatitis C virus therapies are required.

AIM

To evaluate the data on antihepatitis C virus approaches beyond the current standard combination of pegylated interferon-alpha and ribavirin.

METHOD

We reviewed the available literature regarding novel antihepatitis C virus options, given alone or in combination with existing agents.

RESULTS

New interferons and ribavirin alternatives have been tried aiming to improve the efficacy and the safety/tolerability profile of standard agents. The hepatitis C virus polymerase and NS3/4A protease have been rather popular targets for new antihepatitis C virus agents. The combination of such inhibitors with pegylated interferon-alpha and ribavirin seems to act synergistically and to prevent viral resistance, compared to monotherapies. Several novel immunomodulators are currently evaluated and may be useful in combination therapies. Alternative strategies (inhibition of hepatitis C virus protein translation, assembly/release or binding) or agents with different modes of action (statins, S-adenosylmethionine and herbs) need further evaluation.

CONCLUSIONS

Many novel promising antihepatitis C virus agents are being developed, offering hope for future therapies that may target multiple points of the viral life cycle and/or host immune response. Newer approaches should ideally provide safe, effective and more tolerable therapy to all chronic hepatitis C virus patients.

Intrahepatic status of regulatory T cells in autoimmune liver diseases and chronic viral hepatitis

AIM

Regulatory T cells (Tregs) maintain immunological tolerance and suppress autoreactive immune responses. We evaluated the intrahepatic status of Tregs in patients with autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC), chronic hepatitis C (CH-C), or chronic hepatitis B (CH-B).

METHODS

We analyzed 85 patients (20 AIH, 22 PBC, 27 CH-C, and 16 CH-B) and 14 controls. Using liver tissue samples obtained by needle biopsy or from marginal parts of resected metastatic liver tumors in the controls, immunohistochemical analyses of forkhead box P3(+), which is a specific marker for Tregs, CD4(+), and CD8(+) cells were performed.

RESULTS

Intrahepatic Tregs were significantly more infiltrated in patients with liver diseases than in the controls. There were significantly fewer intrahepatic Tregs in the AIH patients than in the PBC patients (P = 0.037). Patients with alow frequency of intrahepatic Tregs were detected significantly more in the AIH and CH-B groups than in the PBC and CH-C groups (P < 0.05). In addition, the frequency of Tregs decreased in the liver of PBC patients as the pathological stage of the disease advanced. We found significantly less infiltration of CD4(+) T cells in AIH than in other diseases (P < 0.05). Liver-infiltrating CD8(+) T cells were detected more frequently in the CH-B group than in other groups (P < 0.003).

CONCLUSION

Intrahepatic Tregs were increased in both patients with autoimmune liver diseases and those with viral hepatitis. In autoimmune liver diseases, intrahepatic Tregs were fewer in the AIH patients than in the PBC patients.

A vector-based minigene vaccine approach results in strong induction of T-cell responses specific of hepatitis C virus

Multiepitope-based vaccines against hepatitis C virus (HCV) were designed in the form of three minigenes encompassing four domains of the NS3, NS4 and NS5B proteins that contain multiple class I/II restricted epitopes. The polyEp-WT minigene encodes all four domains in fusion, the polyEp-C minigene encodes the same fusion but optimised for mammalian translation and the polyEp-E3 minigene has an additional endoplasmic reticulum targeting sequence. Whereas the minigenes vectorised by DNA were poorly immunogenic, adenovirus vectorisation induced strong and broader IFNgamma-ELISpot and CTL responses in HLA-A2 transgenic mice. In addition, polyEp-WT and polyEp-E3 responses were found cross-reactive in a recombinant Listeria-NS3-based surrogate challenge. This study illustrates the potency of vectorised minigenes in the field of HCV vaccine development.

Enhancing therapeutic vaccination by blocking PD-1-mediated inhibitory signals during chronic infection

Therapeutic vaccination is a potentially promising strategy to enhance T cell immunity and viral control in chronically infected individuals. However, therapeutic vaccination approaches have fallen short of expectations, and effective boosting of antiviral T cell responses has not always been observed. One of the principal reasons for the limited success of therapeutic vaccination is that virus-specific T cells become functionally exhausted during chronic infections. We now provide a novel strategy for enhancing the efficacy of therapeutic vaccines. In this study, we show that blocking programmed death (PD)-1/PD-L1 inhibitory signals on exhausted CD8⁺ T cells, in combination with therapeutic vaccination, synergistically enhances functional CD8⁺ T cell responses and improves viral control in mice chronically infected with lymphocytic choriomeningitis virus. This combinatorial therapeutic vaccination was effective even in the absence of CD4⁺ T cell help. Thus, our study defines a potent new approach to augment the efficacy of therapeutic vaccination by blocking negative signals. Such an approach may have broad applications in developing treatment strategies for chronic infections in general, and perhaps also for tumors.

Hepatitis B virus precore protein augments genetic immunizations of the truncated hepatitis C virus core in BALB/c mice

DNA immunization has been used to induce either humoral or cellular immune responses against many antigens, including hepatitis C virus (HCV). In addition, DNA immunizations can be enhanced or modulated at the nucleotide level. Genetic immunizations were examined in BALB/c mice through the use of plasmids and chimeric DNA constructs encoding HCV core proteins and hepatitis B virus (HBV) precore (preC) regions. Plasmids encoding the truncated HCV core induced potent humoral and cellular responses to HCV; pcDNA3.0A-C154 produced a stronger antibody response than pcDNA3.0A-C191 (P < 0.01) and pcDNA3.0A-C69 (P < 0.05). HBV preC enhanced the humoral and cellular immune responses of BALB/c mice to HCV; however, pcDNA3.0A-C69preC resulted in a weak cytotoxic T lymphocyte (CTL) response. In addition, the humoral and cellular immune responses to HCV of groups immunized with pcDNA3.0A-C154preC and pcDNA3.0A-C191preC plasmids were higher than those of groups immunized with pcDNA3.0A-C154 and pcDNA3.0A-C191. In vivo CTL responses verified that mice immunized with preC core fused DNAs showed significantly high specific lysis compared with mice immunized with HCV cores only (P < 0.01). In our study, pcDNA3.0A-C154preC led to the highest immune response among all DNA constructs.

CONCLUSION

DNA that encodes truncated HCV core proteins may lead to increased immune responses in vivo, and these responses may be enhanced by HBV preC.

Evaluation systems for anti-HCV drugs

Development of therapeutics for chronic hepatitis C has been hampered by the lack of an efficient cell culture system and a small animal model for the hepatitis C virus (HCV). An RNA replicon system, in which the HCV genome replicates autonomously in cells, and replication competent viruses derived from an HCV genotype 2a JFH1 strain efficiently propagating in Huh7 cells have been developed, and these systems have contributed to the evaluation of anti-HCV drugs targeted to viral and host proteins involved in the replication of HCV. Several compounds counteracting the viral enzymes, such as RNA polymerase and proteases, and host proteins involved in the lipid synthesis and protein folding are reported to have anti-HCV activities based on assessments using these in vitro systems. Furthermore, a mouse model transplanted with human liver fragments was shown to be capable of replicating HCV and has been used to evaluate the efficacy of antiviral drugs in vivo. In this review, we summarize information regarding systems for studying the HCV life cycle and potential new targets for therapeutic intervention for chronic hepatitis C.

First Example of Phosphoramidate Approach Applied to a 4‘-Substituted Purine Nucleoside (4‘-Azidoadenosine): Conversion of an Inactive Nucleoside to a Submicromolar Compound versus Hepatitis C Virus

We report on the synthesis of the anti hepatitis C virus (HCV) agent 4'-azidoadenosine (1) and the application of the phosphoramidate ProTide technology to this nucleoside. The synthesis of 1 was achieved through an epoxide intermediate followed by regio- and stereoselective ring opening by azidotrimethylsilane in the presence of a Lewis acid. Compound 1 did not inhibit HCV replication in cell culture at concentrations up to 0.1 mM. However, a submicromolar active agent could be derived from 1 by the application of the ProTide technology. All the phosphoramidates prepared were L-alanine derivatives with variations in the aryl moiety and in the ester part of the amino acid. The benzyl ester and the l-naphthyl phosphate (18) had the best activity in replicon assay. Phosphoramidates (18-21) achieved a significant improvement in antiviral potency over the parent nucleoside (1) with no increase in cytotoxicity.

Small molecule and novel treatments for chronic hepatitis C virus infection

The development of molecular-based therapies for the treatment of chronic hepatitis C virus (HCV) infection is an area of intense clinical research, driven by the inability of the current standard of care, combination therapy with pegylated interferon alfa (PEG-IFNalpha) and ribavirin (RBV), to achieve a sustained virologic response (SVR) in a large proportion of patients and by the lack of approved alternative therapies for PEG-IFNalpha/RBV nonresponders and relapsers. Agents being developed against specific HCV viral proteins have recently been termed Specifically Targeted Antiviral Therapy for HCV (STAT-C). Preliminary data for several agents show they have high antiviral activity, especially when used in combination with PEG-IFNalpha, and are tolerable, but resistance mutations have been identified. Further study is needed to clarify the safety, tolerability, and efficacy of these compounds. Once established, the potential for shorter treatment strategies could then be evaluated. Other novel therapies in development that may improve both outcomes and tolerability include a prodrug of RBV and an albumin-modified IFNalpha. In conclusion, small molecule and novel therapies for HCV infection are showing promise in clinical trials, and research to develop new agents and optimize treatment regimens is ongoing.

Allosteric inhibitors of hepatitis C polymerase: discovery of potent and orally bioavailable carbon-linked dihydropyrones

The discovery and optimization of a novel class of carbon-linked dihydropyrones as allosteric HCV NS5B polymerase inhibitors are presented. Replacement of the sulfur linker atom with carbon reduced compound acidity and greatly increased cell permeation. Further structure-activity relationship (SAR) studies led to the identification of compounds, exemplified by 23 and 24, with significantly improved antiviral activities in the cell-based replicon assay and favorable pharmacokinetic profiles.