Synergy of a hepatitis C virus (HCV) NS4A antagonist in combination with HCV protease and polymerase inhibitors

Competitive Intramolecular Hydrogen Bonding: Offering Molecules a Choice

The conformational preferences of N-((6-methylpyridin-2-yl)carbamothioyl)benzamide were studied in solution, the gas phase and the solid state via a combination of NMR, density functional theory (DFT) and single crystal X-ray techniques. This acyl thiourea derivative can adopt two classes of low energy conformation, each stabilized by a different 6-membered intramolecular hydrogen bond (IHB) pseudoring. Analysis in different solvents revealed that the conformational preference of this molecule is polarity dependent, with increasingly polar environments yielding a higher proportion of the minor conformer containing an NH⋅⋅⋅N IHB. The calculated barrier to interconversion is consistent with dynamic behaviour at room temperature, despite the propensity of 6-membered IHB pseudorings to be static. This work demonstrates that introducing competitive IHB pathways can render static IHBs more dynamic and that such systems could have potential as chameleons in drug design.

Synergistic inhibition of hepatitis C virus infection by a novel microtubule inhibitor in combination with daclatasvir

Even though substantial progress has been made in the treatment of hepatitis C virus (HCV) infection, viral resistance and relapse still occur in some patients and additional therapeutic approaches may ultimately be needed should viral resistance become more prevalent. Microtubules play important roles in several HCV life cycle events, including cell attachment, entry, cellular transportation, morphogenesis and progeny secretion steps. Therefore, it was hypothesized that microtubular inhibition might be a novel approach for the treatment of HCV infection. Here, the inhibitory effects of our recently developed microtubule inhibitors were studied in the HCV replicon luciferase reporter system and the infectious system. In addition, the combination responses of microtubule inhibitors with daclatasvir, which is a clinically used HCV NS5A inhibitor, were also evaluated. Our results indicated that microtubule targeting had activity against HCV replication and showed synergistic effect with a current clinical drug.

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Microtubule inhibition affects HCV replication.

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Compound 9f displays time and concentration dependent inhibitory activities against HCV production.

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Combination of compound 9f with Daclatasvir shows modest synergistic effects against HCV replication.

Design, synthesis, characterization, and biological evaluation of nicotinoyl thioureas as antimicrobial and antioxidant agents

Addressed herein a series of thioureas starting from various amines and nicotinic acid have been synthesized. Notably, thiourea based scaffolds are increasingly employed in medicinal chemistry owing to their tunable physicochemical and structural properties. As well-known from the literature, the pyridine ring contains various biological properties, especially antimicrobial activity. Therefore, we performed the synthesis of biologically important thiourea derivatives containing pyridine ring. The structures of the synthesized compounds were characterized by ¹H NMR, ¹³C NMR and FT-IR. In the second part of the study, newly synthesized compounds were also tested in order to demonstrate their antimicrobial and antioxidant properties. All compounds exhibited moderate activity against all tested bacteria known to cause nosocomial infections, which have acquired resistance to many antibiotics, as compared to the standard antibiotics and also strong antioxidant properties. Therefore, they can be evaluated as possible seeds of agents in the treatment of bacterial infections and many health problems related to aging such as cancer, and neurodegenerative diseases.

New Substituted Benzoylthiourea Derivatives: From Design to Antimicrobial Applications

The increasing threat of antimicrobial resistance to all currently available therapeutic agents has urged the development of novel antimicrobials. In this context, a series of new benzoylthiourea derivatives substituted with one or more fluorine atoms and with the trifluoromethyl group have been tested, synthesized, and characterized by IR, NMR, CHNS and crystal X-ray diffraction. The molecular docking has provided information regarding the binding affinity and the orientation of the new compounds to Escherichia coli DNA gyrase B. The docking score predicted the antimicrobial activity of the studied compounds, especially against E. coli, which was further demonstrated experimentally against planktonic and biofilm embedded bacterial and fungal cells. The compounds bearing one fluorine atom on the phenyl ring have shown the best antibacterial effect, while those with three fluorine atoms exhibited the most intensive antifungal activity. All tested compounds exhibited antibiofilm activity, correlated with the trifluoromethyl substituent, most favorable in para position.

Discovery of New Inhibitors of Hepatitis C Virus NS3/4A Protease and Its D168A Mutant

Hepatitis C virus (HCV) is a human pathogen with high morbidity. The HCV NS3/4A protease is essential for viral replication and is one of the top three drug targets. Several drugs targeting the protease have been developed, but drug-resistant mutant strains emerged. Here, we screened a library and synthesized a novel class of small molecules based on a tryptophan derivative scaffold identified as HCV NS3/4A protease inhibitors that are active against both wild type and mutant form of the protease. Only the compounds with predicted binding poses not affected by the most frequent mutations in the active site were selected for experimental validation. The antiviral activities were evaluated by replicon and enzymatic assays. Twenty-two compounds were found to inhibit HCV with EC50 values ranging between 0.64 and 63 μM with compound 22 being the most active. In protease assays, 22 had a comparable inhibition profile for the common mutant HCV GT1b D168A and the wild-type enzyme. However, in the same assay, the potency of the approved drug, simeprevir, decreased 5.7-fold for the mutant enzyme relative to the wild type. The top three inhibitors were also tested against four human serine proteases and were shown to be specific to the viral protease. The fluorescence-based cell viability assay demonstrated a sufficient therapeutic range for the top three candidates.

A review on HCV inhibitors: Significance of non-structural polyproteins

Hepatitis C virus (HCV) mortality and morbidity is a world health misery with an approximate 130–150 million chronically HCV tainted and suffering individuals and it initiate critical liver malfunction like cirrhosis, hepatocellular carcinoma or liver HCV cancer. HCV NS5B protein one of the best studied therapeutic target for the identification of new drug candidates to be added to the combination or multiple combination medication recently approved. During the past few years, NS5B has thus been an important object of attractive medicinal chemistry endeavors, which induced to the surfacing of betrothal preclinical drug molecules. In this scenario, the current review set limit to discuss research published on NS5B and few other therapeutic functional inhibitors concentrating on hit investigation, hit to lead optimization, ADME parameters evaluation, and the SAR data which was out for each compound type and similarity taken into consideration. The discussion outlined in this specific review will surly helpful and vital tool for those medicinal chemists investigators working with HCV research programs mainly pointing on NS5B and set broad spectrum identification of creative anti HCV compounds. This mini review also tells each and every individual compound ability related how much they are active against NS5B and few other targets.

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Hepatitis C infection causes severe liver cirrhosis and carcinoma.

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The new acute HCV infections are raising every year and mortality rate become serious concern.

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The plausible list of anti-HCV drugs and clinical agents were listed in this review.

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The divergent medicinal scaffolds as anti-HCV agents were presented as per their targets.

Modeling Suggests a Mechanism of Synergy Between Hepatitis C Virus Entry Inhibitors and Drugs of Other Classes

Hepatitis C virus (HCV) entry inhibitors (EIs) act synergistically with drugs targeting other stages of the HCV lifecycle. The origin of this synergy remains unknown. Here, we argue that the synergy may arise from the complementary activities of the drugs across cell subpopulations expressing different levels of HCV entry receptors. We employ mathematical modeling of viral kinetics in vitro, where cells with a distribution of entry receptor expression levels are exposed to HCV with or without drugs. The drugs act independently in each cell, as expected in the absence of underlying interactions. Yet, at the cell population level our model predicts that the drugs exhibit synergy. EIs effectively block infection of cells with low receptor levels. With high receptor levels, where EIs are compromised, other drugs are potent. This novel mechanism of synergy, arising at the cell population level may facilitate interpretation of drug activity and treatment optimization.

Adapted J6/JFH1-based Hepatitis C virus recombinants with genotype-specific NS4A show similar efficacies against lead protease inhibitors, alpha interferon, and a putative NS4A inhibitor

To facilitate studies of hepatitis C virus (HCV) NS4A, we aimed at developing J6/JFH1-based recombinants with genotype 1- to 7-specific NS4A proteins. We developed efficient culture systems expressing NS4A proteins of genotypes (isolates) 1a (H77 and TN), 1b (J4), 2a (J6), 4a (ED43), 5a (SA13), 6a (HK6a), and 7a (QC69), with peak infectivity titers of ∼3.5 to 4.5 log10 focus-forming units per ml. Except for genotype 2a (J6), growth depended on adaptive mutations identified in long-term culture. Genotype 1a, 1b, and 4a recombinants were adapted by amino acid substitutions F772S (p7) and V1663A (NS4A), while 5a, 6a, and 7a recombinants required additional substitutions in the NS3 protease and/or NS4A. We demonstrated applicability of the developed recombinants for study of antivirals. Genotype 1 to 7 NS4A recombinants showed similar responses to the protease inhibitors telaprevir (VX-950), boceprevir (Sch503034), simeprevir (TMC435350), danoprevir (ITMN-191), and vaniprevir (MK-7009), to alpha interferon 2b, and to the putative NS4A inhibitor ACH-806. The efficacy of ACH-806 was lower than that of protease inhibitors and was not influenced by changes at amino acids 1042 and 1065 (in the NS3 protease), which have been suggested to mediate resistance to ACH-806 in replicons. Genotype 1a, 1b, and 2a recombinants showed viral spread under long-term treatment with ACH-806, without acquisition of resistance mutations in the NS3-NS4A region. Relatively high concentrations of ACH-806 inhibited viral assembly, but not replication, in a single-cycle production assay. The developed HCV culture systems will facilitate studies benefitting from expression of genotype-specific NS4A in a constant backbone in the context of the complete viral replication cycle, including functional studies and evaluations of the efficacy of antivirals.

A phase 2B study of MK-7009 (vaniprevir) in patients with genotype 1 HCV infection who have failed previous pegylated interferon and ribavirin treatment

BACKGROUND & AIMS

MK-7009 (vaniprevir) is a non-covalent competitive inhibitor of the hepatitis C virus (HCV) NS3/4A protease. This report presents the primary analysis results (safety and sustained viral response) of a phase 2b study of MK-7009 given in combination with peginterferon (PegIFN) alfa2a 180 μg weekly and ribavirin (RBV) 1000-1200 mg/day, for 24-48 weeks to non-cirrhotic patients who have failed previous PegIFN and RBV treatment.

METHODS

We present results of a randomized, placebo-controlled, double-blind study of MK-7009 administered for 24-48 weeks in combination with PegIFN and RBV in 4 regimens to at least 40 patients per arm. Stratification by prior response to PegIFN and RBV was as follows: null response, partial response, breakthrough and relapse. HCV RNA was determined by Roche Cobas Taqman with a lower limit of detection (LLoD) of 10 IU/ml and a lower limit of quantification (LLoQ) of 25 IU/ml.

RESULTS

SVR24 in patients on MK-7009+PegIFN and ribavirin (P/R) was statistically superior to placebo+P/R in all treatment groups (p<0.001). MK-7009 at 300 mg b.i.d. and 600 mg b.i.d. is generally well tolerated for use for up to 48 weeks of therapy. Patients in MK-7009 regimens had higher rates of gastrointestinal adverse events as compared to control (mostly mild to moderate). There were no significant differences in rates of anemia and rash between the MK-7009 regimens and control.

CONCLUSIONS

In conclusion, patients treated with MK-7009 plus P/R experienced significant improvement in SVR compared to P/R control in a population of GT 1 experienced patients.

Targeting the non-structural proteins of hepatitis C virus: beyond hepatitis C virus protease and polymerase

BACKGROUND

Chronic hepatitis C virus (HCV) infection is a main cause of cirrhosis of the liver and hepatocellular carcinoma. The standard of care is a combination of pegylated interferon with ribavirin, a regimen that has undesirable side effects and is frequently ineffective. Compounds targeting HCV protease and polymerase are in late-stage clinical trials and have been extensively reviewed elsewhere.

OBJECTIVE

To review and evaluate the progress towards finding novel HCV antivirals targeting HCV proteins beyond the already precedented NS3 protease and NS5B polymerase.

METHODS

Searches of CAplus and Medline databases were combined with information from key conferences. This review focuses on NS2/3 serine protease, NS3 helicase activity and the non-structural proteins 4A, 4B and 5A.

CONCLUSIONS

Use of the replicon model of HCV replication and biochemical assays of specific targets has allowed screening of vast libraries of compounds, but resulted in clinical candidates from only NS4A and NS5A. The field is hindered by a lack of good chemical matter that inhibits the remaining enzymes from HCV, and a lack of understanding of the functions of non-structural proteins 4A, 4B and 5A in the replication of HCV.

Modeling quasispecies and drug resistance in hepatitis C patients treated with a protease inhibitor

Telaprevir, a novel hepatitis C virus (HCV) NS3-4A serine protease inhibitor, has demonstrated substantial antiviral activity in patients infected with HCV. However, drug-resistant HCV variants were detected in vivo at relatively high frequency a few days after drug administration. Here we use a two-strain mathematical model to explain the rapid emergence of drug resistance in HCV patients treated with telaprevir monotherapy. We examine the effects of backward mutation and liver cell proliferation on the preexistence of the mutant virus and the competition between wild-type and drug-resistant virus during therapy. We also extend the two-strain model to a general model with multiple viral strains. Mutations during therapy only have a minor effect on the dynamics of various viral strains, although they are capable of generating low levels of HCV variants that would otherwise be completely suppressed because of fitness disadvantages. Liver cell proliferation may not affect the pretreatment frequency of mutant variants, but is able to influence the quasispecies dynamics during therapy. It is the relative fitness of each mutant strain compared with wild-type that determines which strain(s) will dominate the virus population. This study provides a theoretical framework for exploring the prevalence of preexisting mutant variants and the evolution of drug resistance during treatment with other HCV protease inhibitors or polymerase inhibitors.

SAR analysis of a series of acylthiourea derivatives possessing broad-spectrum antiviral activity

A series of acylthiourea derivatives were designed, synthesized, and evaluated for broad-spectrum antiviral activity with selected viruses from Poxviridae (vaccinia virus) and two different genera of the family Bunyaviridae (Rift Valley fever and La Crosse viruses). A compound selected from a library screen, compound 1, displayed submicromolar antiviral activity against both vaccinia virus (EC(50)=0.25 μM) and La Crosse virus (EC(50)=0.27 μM) in cytopathic effect (CPE) assays. SAR analysis was performed to further improve antiviral potency and to optimize drug-like properties of the initial hits. During our analysis, we identified 26, which was found to be nearly fourfold more potent than 1 against both vaccinia and La Crosse viruses. Selected compounds were further tested to more fully characterize the spectrum of antiviral activity. Many of these possessed single digit micromolar and sub-micromolar antiviral activity against a diverse array of targets, including influenza virus (Orthomyxoviridae), Tacaribe virus (Arenaviridae), and dengue virus (Flaviviridae).

Evaluation of ITX 5061, a scavenger receptor B1 antagonist: resistance selection and activity in combination with other hepatitis C virus antivirals

ITX 5061 is a scavenger receptor B1 antagonist that has entered phase 1 clinical trials in hepatitis C virus (HCV)-infected humans. We evaluated ITX 5061 in combination with interferon-α, ribavirin, and HCV protease and polymerase inhibitors in a genotype 2a infectious virus system. ITX 5061 is a potent inhibitor of HCV replication and is additive to synergistic with interferon-α, ribavirin, BILN2061, VX950, VX1, and 2'-C-methyladenosine. Resistance selection experiments were performed using a Jc1-FEO virus co-culture system and intermittent ITX 5061 exposure under neomycin selection. We identified a mutant virus with a substitution of aspartic acid for asparagine at the highly conserved position 415 in E2 (N415D). Introduction of this mutation into wild-type virus conferred high-level resistance to ITX 5061. There was no cross-resistance between ITX 5061 and HCV protease inhibitors or interferon-α. These results suggest that ITX 5061 is a promising compound for study in combination with other HCV inhibitors.

Resistance analysis and characterization of a thiazole analogue, BP008, as a potent hepatitis C virus NS5A inhibitor

Hepatitis C virus (HCV) is a global health problem, affecting approximately 3% of the world's population. The standard treatment for HCV infection is often poorly tolerated and ineffective. Therefore, the development of novel or more effective treatment strategies to treat chronic HCV infection is urgently needed. In this report, BP008, a potent small-molecule inhibitor of HCV replication, was developed from a class of compounds with thiazol core structures by means of utilizing a cell-based HCV replicon system. The compound reduced the reporter expression of the HCV1b replicon with a 50% effective concentration (EC(50)) and selective index value of 4.1 ± 0.7 nM and >12,195, respectively. Sequencing analyses of several individual clones derived from BP008-resistant RNAs purified from cells harboring HCV1b replicon revealed that amino acid substitutions mainly within the N-terminal region (domain I) of NS5A were associated with decreased inhibitor susceptibility. Q24L, P58S, and Y93H are the key substitutions for resistance selection; F149L and V153M play the compensatory role in the replication and drug resistance processes. Moreover, BP008 displayed synergistic effects with alpha interferon (IFN-α), NS3 protease inhibitor, and NS5B polymerase inhibitor, as well as good oral bioavailability in SD rats and favorable exposure in rat liver. In summary, our results pointed to an effective small-molecule inhibitor, BP008, that potentially targets HCV NS5A. BP008 can be considered a part of a more effective therapeutic strategy for HCV in the future.

A new method for induced fit docking (GENIUS) and its application to virtual screening of novel HCV NS3-4A protease inhibitors

Hepatitis C virus (HCV) is an etiologic agent of chronic liver disease, and approximately 170 million people worldwide are infected with the virus. HCV NS3-4A serine protease is essential for the replication of this virus, and thus has been investigated as an attractive target for anti-HCV drugs. In this study, we developed our new induced-fit docking program (genius), and applied it to the discovery of a new class of NS3-4A protease inhibitors (IC(50)=1-10 μM including high selectivity index). The new inhibitors thus identified were modified, based on the docking models, and revealed preliminary structure-activity relationships. Moreover, the genius in silico screening performance was validated by using an enrichment factor. We believe our designed scaffold could contribute to the improvement of HCV chemotherapy.

Current drug discovery strategies for treatment of hepatitis C virus infection

OBJECTIVES

Hepatitis C virus (HCV) infection represents a major worldwide-health problem. The current standard of care is combination therapy with pegylated interferon and ribavirin, which achieves a successful response in only approximately 40% of genotype I patients.

KEY FINDINGS

The biology of HCV infection has been under intensive research and important progress has been made in understanding the replication cycle of the virus. Several therapeutic targets have been under investigation, such as NS3 protease, NS4A replicase and NS5B polymerase. New potential targets, such as NS2 protease, as well as CD-81 and claudin-1 entry co-receptors, have also been identified.

SUMMARY

Clinical evaluations of drug candidates targeting NS3 protease, NS4A cofactor, and NS5B polymerase have demonstrated the potential of developing small molecules that interfere with the replication of the virus. Additional issues, including genotype coverage, resistant mutations, and combination therapy represent major challenges for future drug discovery efforts.

Structural and functional parameters of the flaviviral protease: a promising antiviral drug target

Flaviviruses have a single-strand, positive-polarity RNA genome that encodes a single polyprotein. The polyprotein is comprised of seven nonstructural (NS) and three structural proteins. The N- and C-terminal parts of NS3 represent the serine protease and the RNA helicase, respectively. The cleavage of the polyprotein by the protease is required to produce the individual viral proteins, which assemble a new viral progeny. Conversely, inactivation of the protease blocks viral infection. Both the protease and the helicase are conserved among flaviviruses. As a result, NS3 is a promising drug target in flaviviral infections. This article examines the West Nile virus NS3 with an emphasis on the structural and functional parameters of the protease, the helicase and their cofactors.

Synthesis, activity, and pharmacokinetic properties of a series of conformationally-restricted thiourea analogs as novel hepatitis C virus inhibitors

A series of novel conformationally-restricted thiourea analogs were designed, synthesized, and evaluated for their anti-HCV activity. Herein we report the synthesis, structure-activity relationships (SARs), and pharmacokinetic properties of this new class of thiourea compounds that showed potent inhibitory activities against HCV in the cell-based subgenomic HCV replicon assay. Among compounds tested, the fluorene compound 4b was found to possess the most potent activity (EC(50)=0.3 microM), lower cytotoxicity (CC(50)>50 microM), and significantly better pharmacokinetic properties compared to its corresponding fluorenone compound 4c.

Review article: specifically targeted anti-viral therapy for hepatitis C - a new era in therapy

BACKGROUND

Novel, directly acting anti-viral agents, also named 'specifically targeted anti-viral therapy for hepatitis C' (STAT-C) compounds, are currently under development.

AIM

To review the potential of STAT-C agents which are currently under clinical development, with a focus on agents that target HCV proteins.

METHODS

Studies evaluating STAT-C compounds were identified by systematic literature search using PubMed as well as databases of abstracts presented in English at recent liver and gastroenterology congresses.

RESULTS

Numerous directly-acting anti-viral agents are currently under clinical phase I-III evaluation. Final results of phase II clinical trials evaluating the most advanced compounds telaprevir and boceprevir indicate that the addition of these NS3/4A protease inhibitors to pegylated interferon-alfa and ribavirin strongly improves the chance to achieve a SVR in treatment-naive HCV genotype 1 patient as well as in prior nonresponders and relapsers to standard therapy. Monotherapy with directly acting anti-virals is not suitable. NS5B polymerase inhibitors in general have a lower anti-viral efficacy than protease inhibitors.

CONCLUSIONS

STAT-C compounds in addition to pegylated interferon-alfa and ribavirin can improve SVR rates at least in HCV genotype 1 patients. Future research needs to evaluate whether a SVR can be achieved by combination therapies of STAT-C compounds in interferon-free regimens.

Antiviral therapy for hepatitis C virus: beyond the standard of care

Hepatitis C virus (HCV) represents a major health burden, with an estimated 180 million chronically infected individuals worldwide. These patients are at increased risk of developing liver cirrhosis and hepatocellular carcinoma. Infection with HCV is the leading cause of liver transplantation in the Western world. Currently, the standard of care (SoC) consists of pegylated interferon alpha (pegIFN-α) and ribavirin (RBV). However this therapy has a limited efficacy and is associated with serious side effects. Therefore more tolerable, highly potent inhibitors of HCV replication are urgently needed. Both Specifically Targeted Antiviral Therapy for HCV (STAT-C) and inhibitors that are believed to interfere with the host-viral interaction are discussed.

[Evaluation and application of natural products for viral infections]

The limited efficacy and significant clinical toxicity of combination interferone and ribavirin therapy have generated strong interest in developing novel inhibitors of hepatitis C virus (HCV) replication. Recently, a growing understanding of the structure and function of critical viral enzymes and the development of HCV replicons have accelerated the development of highly specific candidate antiviral agents. In the life cycle of HCV, enveloped virions bind and penetrate into host cell using viral envelope glycoproteins. In the cytoplasm, the viral RNA genome serves as mRNA, and produces viral protein as a long polyprotein that is cleaved by both host and viral proteases. Progeny virions assemble by budding into ER/Golgi apparatus, where the glycoproteins maturate, and are released at the cell surface. All stages of replication cycle from the attachment of virus to the release of progeny should be antiviral targets. We have searched for antiviral candidates from natural resources for about 20 years. So far, we have found several classes of compounds with unique antiviral action. Among them, anionic substances interfere with virus attachment and/or entry, several substances inhibit the maturation of virus-specific glycoproteins, low molecules can inhibit the virus release from infected cells, glycerol derivatives reduce the pathogenicity of virus, and some compounds exert virucidal action that impairs the ability of virus to infect host cells. These substances might be worthy to be evaluated as novel anti-HCV agents by using HCV replication systems in cultured cell lines.

Hepatitis C virus replication and potential targets for direct-acting agents

We finally stand at the brink of novel, oral, direct-acting antivirals for the treatment of hepatitis C virus (HCV) infection. Basic science research has lead to a greater understanding of the viral life cycle and identified numerous potential targets for therapy. Early compounds were plagued by inconsistent in vivo activity and side effects that led to discontinuation of investigational efforts. However, several agents have now progressed to phase 2 human studies and two protease inhibitors have completed enrolment for their phase 3 clinical trials and look promising. Thus, while it appears that protease inhibitors will likely be the next available drugs for the treatment of HCV infection, the quest for additional therapeutic agents will continue. The future of HCV therapy lies in multidrug cocktails of several agents targeted against a variety of targets. In the near future these agents will be added to the current standard therapy consisting of pegylated interferon and ribavirin; however, the ultimate and probably realistic goal will be to develop multidrug oral regiments to replace the need for interferon.

MK-7009, a potent and selective inhibitor of hepatitis C virus NS3/4A protease

The administration of hepatitis C virus (HCV) NS3/4A protease inhibitors to patients with chronic HCV infections has demonstrated that they have dramatic antiviral effects and that compounds acting via this mechanism are likely to form a key component of future anti-HCV therapy. We report here on the preclinical profile of MK-7009, an inhibitor of genotype 1a and 1b proteases at subnanomolar concentrations with modestly shifted potency against genotype 2a and 2b proteases at low nanomolar concentrations. Potent activity was also observed in a cell-based HCV replicon assay in the presence of added human serum (50%). In multiple species evaluated in preclinical studies, the MK-7009 concentrations in the liver were maintained at a significant multiple of the cell-based replicon 50% effective concentration over 12 to 24 h following the administration of moderate oral doses (5 to 10 mg per kg of body weight). MK-7009 also had excellent selectivity against both a range of human proteases and a broad panel of pharmacologically relevant ion channels, receptors, and enzymes. On the basis of this favorable profile, MK-7009 was selected for clinical development and is currently being evaluated in controlled clinical trials with both healthy volunteers and HCV-infected patients.

HCV NS2/3 protease: a future antiviral drug target?

Current HCV therapy presents many side effects, is inadequate in treating all patients infected with the disease, and it is likely that future therapy will involve the specific targeting of multiple viral enzymes. The HCV NS2/3 protease is a dimeric autocatalytic protease that cleaves the viral polyprotein between NS2 and NS3. NS2/3 cleavage has been shown to be absolutely required for genome replication and viral infectivity in a chimpanzee and, therefore, NS2/3 has been suggested to be a promising target for future HCV drug development. This article focuses on the characterization of NS2/3 processing, the methods developed and progress achieved towards the generation of NS2/3 cleavage inhibitors. The challenges involved in developing active site inhibitors of this enzyme, as well as alternative approaches to inhibiting HCV replication through the NS2/3 and NS2 proteins, are also discussed.

Design and synthesis of indole, 2,3-dihydro-indole, and 3,4-dihydro-2H-quinoline-1-carbothioic acid amide derivatives as novel HCV inhibitors

An efficient synthetic methodology to provide indole, 2,3-dihydro-indole, and 3,4-dihydro-2H-quinoline-1-carbothioic acid amide derivatives is described. These conformationally restricted heterobicyclic scaffolds were evaluated as a novel class of HCV inhibitors. Introduction of an acyl group at the NH(2) of the thiourea moiety has been found to enhance inhibitory activity. The chain length and the position of the alkyl group on the indoline aromatic ring markedly influenced anti-HCV activity. The indoline scaffold was more potent than the corresponding indole and tetrahydroquinoline scaffolds and analogue 31 displayed excellent activity (EC(50)=510nM) against HCV without significant cytotoxicity (CC(50) >50microM).

Cellular models for the screening and development of anti-hepatitis C virus agents

Investigations on the biology of hepatitis C virus (HCV) have been hampered by the lack of small animal models. Efforts have therefore been directed to designing practical and robust cellular models of human origin able to support HCV replication and production in a reproducible, reliable and consistent manner. Many different models based on different forms of virions and hepatoma or other cell types have been described including virus-like particles, pseudotyped particles, subgenomic and full length replicons, virion productive replicons, immortalised hepatocytes, fetal and adult primary human hepatocytes. This review focuses on these different cellular models, their advantages and disadvantages at the biological and experimental levels, and their respective use for evaluating the effect of antiviral molecules on different steps of HCV biology including virus entry, replication, particles generation and excretion, as well as on the modulation by the virus of the host cell response to infection.

Design, synthesis, and anti-HCV activity of thiourea compounds

A series of thiourea derivatives were synthesized and their antiviral activity was evaluated in a cell-based HCV subgenomic replicon assay. SAR studies revealed that the chain length and the position of the alkyl linker largely influenced the in vitro anti-HCV activity of this class of potent antiviral agents. Among this series of compounds synthesized, the thiourea derivative with a six-carbon alkyl linker at the meta-position of the central phenyl ring (10) was identified as the most potent anti-HCV inhibitor (EC(50) = 0.047 microM) with a selectivity index of 596.

Perspectives on antiviral drug development

The 21st International Conference on Antiviral Research provided novel insights and approaches to drug discovery across a wide array of virologic fields. Topics ranged from the chemical synthesis of new compounds against the human immunodeficiency virus (HIV) to the long-term use of established drugs against influenza. A session on novel targets for HIV therapy focused on the importance of Apobec3G, LEDGF/p75 and other cellular factors as innovative ways to control infection. New targets for hepatitis B and C viruses were surveyed. There were also discussions as to how the development of new antiviral compounds might lead to novel mechanisms of drug resistance by HIV, herpesviruses and hepatitis viruses. These covered such issues as transmission dynamics, viral fitness, the acquisition of differential resistance patterns depending on viral subtype, and clinical outcomes. Drug efficacy, toxicity, patient adherence, treatment interruption and the importance of generic drugs in resource-poor settings were also extensively discussed. These topics will all play a pivotal role in drug development and the management of viral infections in the years to come.