Suppression of viral RNA binding and the assembly of infectious hepatitis C virus particles in vitro by cyclophilin inhibitors. J Virol. 2012;86:12616-12624. [PMID: 22973029 DOI: 10.1128/jvi.01351-12]

Mechanisms of Action of the Host-Targeting Agent Cyclosporin A and Direct-Acting Antiviral Agents against Hepatitis C Virus

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

Cyclophilins and Their Roles in Hepatitis C Virus and Flavivirus Infections: Perspectives for Novel Antiviral Approaches

Cyclophilins are cellular peptidyl-prolyl isomerases that play an important role in viral infections, with demonstrated roles in the replication of hepatitis C virus (HCV) and other viruses in the Flaviviridae family, such as dengue virus (DENV) and yellow fever virus (YFV). Here, we discuss the roles of cyclophilins in HCV infection and provide a comprehensive overview of the mechanisms underlying the requirement for cyclophilins during HCV replication. Notably, cyclophilin inhibitor therapy has been demonstrated to be effective in reducing HCV replication in chronically infected patients. While the roles of cyclophilins are relatively well-understood for HCV infection, cyclophilins are more recently emerging as host factors for flavivirus infection as well, providing potential new therapeutic avenues for these viral infections which currently lack antiviral therapies. However, further studies are required to elucidate the roles of cyclophilins in flavivirus replication. Here, we review the current knowledge of the role of cyclophilins in HCV infection to provide a conceptual framework to understand how cyclophilins may contribute to other viral infections, such as DENV and YFV. Improved understanding of the roles of cyclophilins in viral infection may open perspectives for the development of cyclophilin inhibitors as effective antiviral therapeutics for HCV and related viruses.

The Role of Cyclophilins in Inflammatory Bowel Disease and Colorectal Cancer

Cyclophilins (Cyps) is a kind of ubiquitous protein family in organisms, which has biological functions such as promoting intracellular protein folding and participating in the pathological processes of inflammation and tumor. Inflammatory bowel disease (IBD) and colorectal cancer (CRC) are two common intestinal diseases, but the etiology and pathogenesis of these two diseases are still unclear. IBD and CRC are closely associated, IBD has always been considered as one of the main risks of CRC. However, the role of Cyps in these two related intestinal diseases is rarely studied and reported. In this review, the expression of CypA, CypB and CypD in IBD, especially ulcerative colitis (UC), and CRC, their relationship with the development of these two intestinal diseases, as well as the possible pathogenesis, were briefly summarized, so as to provide modest reference for clinical researches and treatments in future.

The Antiviral Properties of Cyclosporine. Focus on Coronavirus, Hepatitis C Virus, Influenza Virus, and Human Immunodeficiency Virus Infections

This review updates current knowledge regarding the risk of viral infections, including COVID-19, in patients treated with cyclosporine. We also shortly refer to bacterial infections and parasitic infestations in patients treated with cyclosporin. Cyclosporine is an immunosuppressive drug, which is widely used in medicine, including in the treatment of autoimmune skin diseases in dermatology, rheumatology, ophthalmology and nephrology, and in organ transplantation. A usual concern associated with immunosuppressive treatment is the potential risk of infections. Interestingly, several data indicate a relatively low risk of infections, especially viral infections, in patients receiving cyclosporine. It was shown that cyclosporine exerts an inhibitory effect on the replication of some viruses, or may have a potentially beneficial effect on the disease course in infections. These include hepatitis C, influenza virus, rotavirus, human immunodeficiency virus and coronavirus infections. Available data indicate that cyclosporine may have a beneficial effect on COVID-19, which is caused by the coronavirus SARS-COV2.

Hepatitis C virus exploits cyclophilin A to evade PKR

Counteracting innate immunity is essential for successful viral replication. Host cyclophilins (Cyps) have been implicated in viral evasion of host antiviral responses, although the mechanisms are still unclear. Here, we show that hepatitis C virus (HCV) co-opts the host protein CypA to aid evasion of antiviral responses dependent on the effector protein kinase R (PKR). Pharmacological inhibition of CypA rescues PKR from antagonism by HCV NS5A, leading to activation of an interferon regulatory factor-1 (IRF1)-driven cell intrinsic antiviral program that inhibits viral replication. These findings further the understanding of the complexity of Cyp-virus interactions, provide mechanistic insight into the remarkably broad antiviral spectrum of Cyp inhibitors, and uncover novel aspects of PKR activity and regulation. Collectively, our study identifies a novel antiviral mechanism that harnesses cellular antiviral immunity to suppress viral replication.

Proteostasis in Viral Infection: Unfolding the Complex Virus-Chaperone Interplay

Viruses are obligate intracellular parasites that rely on their hosts for protein synthesis, genome replication, and viral particle production. As such, they have evolved mechanisms to divert host resources, including molecular chaperones, facilitate folding and assembly of viral proteins, stabilize complex structures under constant mutational pressure, and modulate signaling pathways to dampen antiviral responses and prevent premature host death. Biogenesis of viral proteins often presents unique challenges to the proteostasis network, as it requires the rapid and orchestrated production of high levels of a limited number of multifunctional, multidomain, and aggregation-prone proteins. To overcome such challenges, viruses interact with the folding machinery not only as clients but also as regulators of chaperone expression, function, and subcellular localization. In this review, we summarize the main types of interactions between viral proteins and chaperones during infection, examine evolutionary aspects of this relationship, and discuss the potential of using chaperone inhibitors as broad-spectrum antivirals.

Differences across cyclophilin A orthologs contribute to the host range restriction of hepatitis C virus

The restricted host tropism of hepatitis C virus (HCV) remains incompletely understood, especially post-entry, and has hindered developing an immunocompetent, small animal model. HCV replication in non-permissive species may be limited by incompatibilities between the viral replication machinery and orthologs of essential host factors, like cyclophilin A (CypA). We thus compared the ability of CypA from mouse, tree shrew, and seven non-human primate species to support HCV replication, finding that murine CypA only partially rescued viral replication in Huh7.5-shRNA CypA cells. We determined the specific amino acid differences responsible and generated mutants able to fully rescue replication. We expressed these mutants in engineered murine hepatoma cells and although we observed increases in HCV replication following infection, they remained far lower than those in highly permissive human hepatoma cells, and minimal infectious particle release was observed. Together, these data suggest additional co-factors remain unidentified. Future work to determine such factors will be critical for developing an immunocompetent mouse model supporting HCV replication.

Proprotein convertase subtilisin/kexin type 9 inhibits hepatitis C virus replication through interacting with NS5A

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a serine protease actively involved in regulating lipid homeostasis. Although PCSK9 has been shown to inhibit hepatitis C virus (HCV) entry and replication, the underlying mechanisms have not been thoroughly characterized. Moreover, whether PCSK9 regulates HCV translation and assembly/secretion has not been determined. We therefore further studied the effects of PCSK9 on the HCV life cycle. We showed that PCSK9 did not affect HCV translation or assembly/secretion. Overexpression of PCSK9 inhibited HCV replication in HCV genomic replicon cells in a dose-dependent manner and after cell culture-derived HCV (HCVcc) infection. Knocking down PCSK9 increased HCV replication. The gain-of-function (D374Y) or loss-of-function (Δaa. 31-52) PCSK9 mutants for low-density lipoprotein receptor (LDLR) degradation had no effect on HCV replication, suggesting that HCV replication inhibition by PCSK9 was not due to LDLR degradation. The uncleaved ProPCSK9, but not cleaved PCSK9, down-regulated HCV replication, suggesting that the auto-cleavage of PCSK9 affected HCV replication. We also found that PCSK9 interacted with NS5A through NS5A aa. 95-215, and this region played an important role in NS5A dimerization, NS5A-RNA binding and was essential for HCV replication. More importantly, NS5A dimerization and NS5A-RNA binding were suppressed by PCSK9 upon interaction. These results suggested that PCSK9 inhibited HCV replication through interaction with NS5A. Our study should help optimize anti-HCV treatment regimen in patients with abnormal lipid profiles.

A CRISPR toolbox to study virus-host interactions

Viruses are obligate intracellular pathogens that depend on host cellular components for replication.

Genetic screens are an unbiased and comprehensive method to uncover host cellular components that are critical for the infection with viruses.

Loss-of-function screens result in the genome-wide disruption of gene expression, whereas gain-of-function screens rely on large-scale overexpression of host genes.

Genetic knockout screens can be conducted using haploid insertional mutagenesis or the CRISPR–Cas system.

Genetic screens using the CRISPR–Cas system have provided crucial insights in the host determinants of infections with important human pathogens such as dengue virus, West Nile virus, Zika virus and hepatitis C virus.

CRISPR–Cas-based techniques additionally provide ways to generate both in vitro and in vivo models to study viral pathogenesis, to manipulate viral genomes, to eradicate viral disease vectors using gene drive systems and to advance the development of antiviral therapeutics.

In this Review, Puschnik and colleagues discuss the technical aspects of using CRISPR–Cas technology in genome-scale knockout screens to study virus–host interactions, and they compare these screens with alternative genetic screening technologies.

Viruses depend on their hosts to complete their replication cycles; they exploit cellular receptors for entry and hijack cellular functions to replicate their genome, assemble progeny virions and spread. Recently, genome-scale CRISPR–Cas screens have been used to identify host factors that are required for virus replication, including the replication of clinically relevant viruses such as Zika virus, West Nile virus, dengue virus and hepatitis C virus. In this Review, we discuss the technical aspects of genome-scale knockout screens using CRISPR–Cas technology, and we compare these screens with alternative genetic screening technologies. The relative ease of use and reproducibility of CRISPR–Cas make it a powerful tool for probing virus–host interactions and for identifying new antiviral targets.

Systems Biology Reveals NS4B-Cyclophilin A Interaction: A New Target to Inhibit YFV Replication

Yellow fever virus (YFV) replication is highly dependent on host cell factors. YFV NS4B is reported to be involved in viral replication and immune evasion. Here interactions between NS4B and human proteins were determined using a GST pull-down assay and analyzed using 1-DE and LC-MS/MS. We present a total of 207 proteins confirmed using Scaffold 3 Software. Cyclophilin A (CypA), a protein that has been shown to be necessary for the positive regulation of flavivirus replication, was identified as a possible NS4B partner. 59 proteins were found to be significantly increased when compared with a negative control, and CypA exhibited the greatest difference, with a 22-fold change. Fisher's exact test was significant for 58 proteins, and the p value of CypA was the most significant (0.000000019). The Ingenuity Systems software identified 16 pathways, and this analysis indicated sirolimus, an mTOR pathway inhibitor, as a potential inhibitor of CypA. Immunofluorescence and viral plaque assays showed a significant reduction in YFV replication using sirolimus and cyclosporine A (CsA) as inhibitors. Furthermore, YFV replication was strongly inhibited in cells treated with both inhibitors using reporter BHK-21-rep-YFV17D-LucNeoIres cells. Taken together, these data suggest that CypA-NS4B interaction regulates YFV replication. Finally, we present the first evidence that YFV inhibition may depend on NS4B-CypA interaction.

Daclatasvir Prevents Hepatitis C Virus Infectivity by Blocking Transfer of the Viral Genome to Assembly Sites

BACKGROUND & AIMS

Daclatasvir is a direct-acting antiviral agent and potent inhibitor of NS5A, which is involved in replication of the hepatitis C virus (HCV) genome, presumably via membranous web shaping, and assembly of new virions, likely via transfer of the HCV RNA genome to viral particle assembly sites. Daclatasvir inhibits the formation of new membranous web structures and, ultimately, of replication complex vesicles, but also inhibits an early assembly step. We investigated the relationship between daclatasvir-induced clustering of HCV proteins, intracellular localization of viral RNAs, and inhibition of viral particle assembly.

METHODS

Cell-culture-derived HCV particles were produced from Huh7.5 hepatocarcinoma cells in presence of daclatasvir for short time periods. Infectivity and production of physical particles were quantified and producer cells were subjected to subcellular fractionation. Intracellular colocalization between core, E2, NS5A, NS4B proteins, and viral RNAs was quantitatively analyzed by confocal microscopy and by structured illumination microscopy.

RESULTS

Short exposure of HCV-infected cells to daclatasvir reduced viral assembly and induced clustering of structural proteins with non-structural HCV proteins, including core, E2, NS4B, and NS5A. These clustered structures appeared to be inactive assembly platforms, likely owing to loss of functional connection with replication complexes. Daclatasvir greatly reduced delivery of viral genomes to these core clusters without altering HCV RNA colocalization with NS5A. In contrast, daclatasvir neither induced clustered structures nor inhibited HCV assembly in cells infected with a daclatasvir-resistant mutant (NS5A-Y93H), indicating that daclatasvir targets a mutual, specific function of NS5A inhibiting both processes.

CONCLUSIONS

In addition to inhibiting replication complex biogenesis, daclatasvir prevents viral assembly by blocking transfer of the viral genome to assembly sites. This leads to clustering of HCV proteins because viral particles and replication complex vesicles cannot form or egress. This dual mode of action of daclatasvir could explain its efficacy in blocking HCV replication in cultured cells and in treatment of patients with HCV infection.

Alisporivir inhibits MERS- and SARS-coronavirus replication in cell culture, but not SARS-coronavirus infection in a mouse model

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In cell culture models, low-micromolar doses of alisporivir block SARS-CoV and MERS-CoV replication.

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Combination treatment with alisporivir and ribavirin increases the anti-MERS-CoV activity in cell culture.

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Combination treatment with alisporivir and ribavirin does not protect against SARS-CoV infection in a mouse model.

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Cyclophilin-binding drugs should be explored further in the context of host-directed anti-coronaviral strategies.

Currently, there is no registered treatment for infections with emerging zoonotic coronaviruses like SARS- and MERS-coronavirus. We here report that in cultured cells low-micromolar concentrations of alisporivir, a non-immunosuppressive cyclosporin A-analog, inhibit the replication of four different coronaviruses, including MERS- and SARS-coronavirus. Ribavirin was found to further potentiate the antiviral effect of alisporivir in these cell culture-based infection models, but this combination treatment was unable to improve the outcome of SARS-CoV infection in a mouse model. Nevertheless, our data provide a basis to further explore the potential of Cyp inhibitors as host-directed, broad-spectrum inhibitors of coronavirus replication.

HCV1b genome evolution under selective pressure of the cyclophilin inhibitor alisporivir during the DEB-025-HCV-203 phase II clinical trial

Major advances have revolutionized the HCV antiviral treatment field, with interferon-free combinations of direct-acting antivirals (DAAs) resulting into success rates of >90% for all HCV genotypes. Nevertheless, viral eradication at a global level stills remains challenging, stimulating the continued search for new affordable pan-genotypic drugs. To overcome selection of drug resistant variants, targeting host proteins can be an attractive mechanism of action. Alisporivir (Debio 025) is a potent pan-genotypic host-targeting antiviral agent, acting on cyclophilin A, which is necessary for HCV replication. The efficacy and safety of three different oral doses of alisporivir in combination with pegylated interferon-α2a given over a period of four weeks, was investigated in a randomized, double-blind and placebo-controlled phase IIa clinical trial, in 90 treatment-naïve subjects infected with chronic hepatitis C, wherefrom 58 HCV1b samples were selected for genetic sequencing purposes. Sequencing results were used to study the HCV genome for amino acid changes potentially related with selective pressure and resistance to alisporivir. By comparing baseline and on-treatment sequences, a large variation in proportion of amino acid changes was detected in all treatment arms. The NS5A variant D320E, which was previously identified during in vitro resistance selection and resulted in 3.6-fold reduced alisporivir susceptibility, emerged in two subjects in the alisporivir monotherapy arm. However, emergence of D320E appeared to be associated only with concurrent viral load rebound in one subject with 0.8log10IU/ml increase in HCV RNA. In general, for all datasets, low numbers of positions under positive selective pressure were observed, with no significant differences between naïve and treated sequences. Additionally, incomplete sequence information for some of the 22 patients and the low number of individuals per treatment arm, is limiting the power to assess the association of alisporivir or interferon treatment with the observed amino acid changes.

Chaperones in hepatitis C virus infection

The hepatitis C virus (HCV) infects approximately 3% of the world population or more than 185 million people worldwide. Each year, an estimated 350000-500000 deaths occur worldwide due to HCV-associated diseases including cirrhosis and hepatocellular carcinoma. HCV is the most common indication for liver transplantation in patients with cirrhosis worldwide. HCV is an enveloped RNA virus classified in the genus Hepacivirus in the Flaviviridae family. The HCV viral life cycle in a cell can be divided into six phases: (1) binding and internalization; (2) cytoplasmic release and uncoating; (3) viral polyprotein translation and processing; (4) RNA genome replication; (5) encapsidation (packaging) and assembly; and (6) virus morphogenesis (maturation) and secretion. Many host factors are involved in the HCV life cycle. Chaperones are an important group of host cytoprotective molecules that coordinate numerous cellular processes including protein folding, multimeric protein assembly, protein trafficking, and protein degradation. All phases of the viral life cycle require chaperone activity and the interaction of viral proteins with chaperones. This review will present our current knowledge and understanding of the role of chaperones in the HCV life cycle. Analysis of chaperones in HCV infection will provide further insights into viral/host interactions and potential therapeutic targets for both HCV and other viruses.

The role of immunophilins in viral infection

BACKGROUND

Tremendous progress has been made in the past 20 years in understanding the roles played by immunophilins, and in particular the cyclophilins, in supporting the replication cycles of human viruses. A growing body of genetic and biochemical evidence and data from clinical trials confirm that cyclophilins are essential cofactors that contribute to establishing a permissive environment within the host cell that supports the replication of HIV-1 and HCV. Cyclophilin A regulates HIV-1 replication kinetics and infectivity, modulates sensitivity to host restriction factors, and cooperates in the transit of the pre-integration complex into the nucleus of infected cells. Cyclophilin A is an essential cofactor whose expression supports HCV-specific RNA replication in human hepatocytes.

GENERAL SIGNIFICANCE

Peptidyl-prolyl isomerase inhibitors have been used in clinical trials to validate cyclophilins as antiviral targets for the treatment of HIV-1 and Chronic Hepatitis C virus infection and as molecular probes to identify the roles played by immunophilins in supporting the replication cycles of human viruses.

SCOPE OF REVIEW

This review summarizes emerging research that defines the functions of immunophilins in supporting the replication cycles of HIV-1, HCV, HBV, coronaviruses, and other viral pathogens and describes new information that suggests a role for immunophilins in regulating innate immune responses against chronic viral infection.

MAJOR CONCLUSIONS

The dependence on cyclophilins by evolutionarily distinct viruses for accomplishing various steps in replication such as viral entry, initiation of genomic nucleic acid replication, viral genome uncoating, nuclear import and nuclear entry, emphasizes the potential of cyclophilin inhibitors as therapeutic agents. This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.

Discovery of Novel Small Molecule Anti-HCV Agents via the CypA Inhibitory Mechanism Using O-Acylation-Directed Lead Optimization

In this work, the relationship between cyclophilin A (CypA) and HCV prompted us to screen a series of small molecule CypA inhibitors which were previously reported by our group. Among them, compound 1, discovered as a non-immunosuppressive anti-HCV agent with an EC₅₀ value of 0.67 μM in a virus assay, was selected for further study. Subsequent chemical modification by O-acylation led to a novel class of molecules, among which compound 25 demonstrated the most potent anti-HCV activity in the virus assay (EC₅₀ = 0.19 μM), but low cytotoxicity and hERG cardiac toxicity. The following studies (a solution stability assay and a simple pharmacokinetic test together with a CypA enzyme inhibition assay) preliminarily indicated that 25 was a prodrug of 1. To the best of our knowledge, 25 is probably the most potent currently reported small molecule anti-HCV agent acting via the CypA inhibitory mechanism. Consequently, our study has provided a new potential small molecule for curing HCV infection.

Advances in experimental systems to study hepatitis C virus in vitro and in vivo

Hepatitis C virus (HCV) represents a global health concern affecting over 185 million people worldwide. Chronic HCV infection causes liver fibrosis and cirrhosis and is the leading indication for liver transplantation. Recent advances in the field of direct-acting antiviral drugs (DAAs) promise a cure for HCV in over 90% of cases that will get access to these expensive treatments. Nevertheless, the lack of a protective vaccine and likely emergence of drug-resistant viral variants call for further studies of HCV biology. With chimpanzees being for a long time the only non-human in vivo model of HCV infection, strong efforts were put into establishing in vitro experimental systems. The initial models only enabled to study specific aspects of the HCV life cycle, such as viral replication with the subgenomic replicon and entry using HCV pseudotyped particles (HCVpp). Subsequent development of protocols to grow infectious HCV particles in cell-culture (HCVcc) ignited investigations on the full cycle of HCV infection and the virus-host interactions required for virus propagation. More recently, small animal models permissive to HCV were generated that allowed in vivo testing of novel antiviral therapies as well as vaccine candidates. This review provides an overview of the currently available in vitro and in vivo experimental systems to study HCV biology. Particular emphasis is given to how these model systems furthered our understanding of virus-host interactions, viral pathogenesis and immunological responses to HCV infection, as well as drug and vaccine development.

Cyclophilin and NS5A inhibitors, but not other anti-hepatitis C virus (HCV) agents, preclude HCV-mediated formation of double-membrane-vesicle viral factories

Although the mechanisms of action (MoA) of nonstructural protein 3 inhibitors (NS3i) and NS5B inhibitors (NS5Bi) are well understood, the MoA of cyclophilin inhibitors (CypI) and NS5A inhibitors (NS5Ai) are not fully defined. In this study, we examined whether CypI and NS5Ai interfere with hepatitis C virus (HCV) RNA synthesis of replication complexes (RCs) or with an earlier step of HCV RNA replication, the creation of double-membrane vesicles (DMVs) essential for HCV RNA replication. In contrast to NS5Bi, both CypI and NS5Ai do not block HCV RNA synthesis by way of RCs, suggesting that they exert their antiviral activity prior to the establishment of enzymatically active RCs. We found that viral replication is not a precondition for DMV formation, since the NS3-NS5B polyprotein or NS5A suffices to create DMVs. Importantly, only CypI and NS5Ai, but not NS5Bi, mir-122, or phosphatidylinositol-4 kinase IIIα (PI4KIIIα) inhibitors, prevent NS3-NS5B-mediated DMV formation. NS3-NS5B was unable to create DMVs in cyclophilin A (CypA) knockdown (KD) cells. We also found that the isomerase activity of CypA is absolutely required for DMV formation. This not only suggests that NS5A and CypA act in concert to build membranous viral factories but that CypI and NS5Ai mediate their early anti-HCV effects by preventing the formation of organelles, where HCV replication is normally initiated. This is the first investigation to examine the effect of a large panel of anti-HCV agents on DMV formation, and the results reveal that CypI and NS5Ai act at the same membranous web biogenesis step of HCV RNA replication, thus indicating a new therapeutic target of chronic hepatitis C.

Cyclosporin A, but not tacrolimus, negatively affects the hepatic extraction fraction of hepatobiliary scintigraphy in liver transplant recipients

Background

Hepatobiliary scintigraphy using ^99mTc-mebrofenin has been used as an investigation to study liver function after liver transplantation (LTx). Hepatic extraction fraction (HEF) is a measurement of the hepatic extraction efficiency and hepatic extraction rate. With the purpose of evaluating a possible diverging effect of cyclosporin A (CSA) and tacrolimus (TAC) on the HEF, we compared the HEF with biochemical and histological parameters in LTx patients receiving either CSA or TAC.

Methods

Thirty-nine adult patients who underwent LTx due to hepatitis C virus (HCV) cirrhosis were evaluated. All patients underwent a 3-month and 1-year follow-up that included hepatobiliary scintigraphy and biochemistry tests. Liver biopsy was performed at 1 year. These clinical parameters were compared between the two groups, TAC (n = 15) and CSA (n = 24).

Results

The average HEF was significantly lower in the CSA group compared to the TAC group both at 3 months and 1 year after LTx. The liver biochemistry tests, average donor and recipient age, average cold ischemia time (CIT), and a clearance were comparable in the two groups. The TAC group had more inflammation than the CSA group. Moreover, three patients who converted from CSA to TAC increased their HEF values.

Conclusions

CSA-treated patients presented a lower HEF value on hepatobiliary scintigraphy in spite of comparable liver function by traditional measurements indicating a decrease on HEF values by CSA.

An update on the management of hepatitis C virus-related arthritis

INTRODUCTION

Hepatitis C virus (HCV)-related arthritis is an uncommon disease belonging to the autoimmune disorders due to the chronic stimulus exerted by the virus on the immune system. It shows two clinical subsets: a symmetrical polyarthritis resembling rheumatoid arthritis but less aggressive and an intermittent mono-oligoarthritis involving the lower limbs.

AREAS COVERED

We extensively review the current literature using the largest electronic databases (MEDLINE, EMBASE and COCHRANE) with regard to HCV-related arthritis (HCVrA) and studies focusing on the co-existence of HCV and other kinds of arthritides.

EXPERT OPINION

The therapeutic approach to HCVrA remains largely empirical, because few studies have been published on this topic. Mainstream treatment based on the administration of hydroxychloroquine and low doses of corticosteroid is still largely preferred. Cyclosporine represents a useful alternative due to its antiviral properties. Anti-TNF agents are safe, but their hypothetic use appears excessive for a mild disorder such as HCVrA. IFN-α (and more recently pegylated IFN-α) when administered as a component of the combined (IFN-α + ribavirin) anti-HCV therapy can promote the appearance or the worsening of several autoimmune HCV-related disorders, including arthritis. New and forthcoming antiviral molecules will be used in the near future for a revolutionary IFN-free treatment.

The HCV life cycle: in vitro tissue culture systems and therapeutic targets

Hepatitis C virus (HCV) is a highly variable plus-strand RNA virus of the family Flaviviridae. Viral strains are grouped into six epidemiologically relevant genotypes that differ from each other by more than 30% at the nucleotide level. The variability of HCV allows immune evasion and facilitates persistence. It is also a substantial challenge for the development of specific antiviral therapies effective across all HCV genotypes and for prevention of drug resistance. Novel HCV cell culture models were instrumental for identification and profiling of therapeutic strategies. Concurrently, these models revealed numerous host factors critical for HCV propagation, some of which have emerged as targets for antiviral therapy. It is generally assumed that the use of host factors is conserved among HCV isolates and genotypes. Additionally, the barrier to viral resistance is thought to be high when interfering with host factors. Therefore, current drug development includes both targeting of viral factors but also of host factors essential for virus replication. In fact, some of these host-targeting agents, for instance inhibitors of cyclophilin A, have advanced to late stage clinical trials. Here, we highlight currently available cell culture systems for HCV, review the most prominent host-targeting strategies against hepatitis C and critically discuss opportunities and risks associated with host-targeting antiviral strategies.

Inhibition of HCV replication by cyclophilin antagonists is linked to replication fitness and occurs by inhibition of membranous web formation

BACKGROUND & AIMS

Replication of hepatitis C virus (HCV) requires host cell factors, such as cyclophilin A (CypA). CypA binds to HCV's nonstructural protein (NS)5A to promote replication of viral RNA. CypA antagonists, such as cyclosporines, are potent inhibitors of HCV replication. NS2 modulates sensitivity of HCV to cyclosporines. We investigated why cyclosporines require NS2 to increase their inhibitory effect and how they block HCV replication.

METHODS

We determined replication fitness and sensitivity of various HCV replicons, containing or lacking NS2, to cyclosporine and other direct-acting antiviral agents. We also analyzed the effects of cyclosporine on membranous web formation by electron microscopy.

RESULTS

NS2-5B replicons of genotype 2a (JFH1), but not genotype 1b, had increased sensitivity to cyclosporine. This difference was lost with replication-attenuated NS3-5B JFH1 RNAs, showing that cyclosporine sensitivity is linked to reduced replication fitness of NS2-containing HCV RNAs. Fitness also determined sensitivity to a nucleoside analogue and an NS5A inhibitor, but not to telaprevir. Cyclosporine blocked de novo formation of the membranous web, but had little effect on established membranous replication factories. This block was prevented by cyclosporine resistance mutations in NS5A.

CONCLUSIONS

Cleavage at the NS2/3 junction is a rate-limiting step in replication of particular HCV isolates and determines their sensitivity to CypA inhibitors. These drugs target de novo formation of the membranous web and RNA replication.

A new stochastic model for subgenomic hepatitis C virus replication considers drug resistant mutants

As an RNA virus, hepatitis C virus (HCV) is able to rapidly acquire drug resistance, and for this reason the design of effective anti-HCV drugs is a real challenge. The HCV subgenomic replicon-containing cells are widely used for experimental studies of the HCV genome replication mechanisms, for drug testing in vitro and in studies of HCV drug resistance. The NS3/4A protease is essential for virus replication and, therefore, it is one of the most attractive targets for developing specific antiviral agents against HCV. We have developed a stochastic model of subgenomic HCV replicon replication, in which the emergence and selection of drug resistant mutant viral RNAs in replicon cells is taken into account. Incorporation into the model of key NS3 protease mutations leading to resistance to BILN-2061 (A156T, D168V, R155Q), VX-950 (A156S, A156T, T54A) and SCH 503034 (A156T, A156S, T54A) inhibitors allows us to describe the long term dynamics of the viral RNA suppression for various inhibitor concentrations. We theoretically showed that the observable difference between the viral RNA kinetics for different inhibitor concentrations can be explained by differences in the replication rate and inhibitor sensitivity of the mutant RNAs. The pre-existing mutants of the NS3 protease contribute more significantly to appearance of new resistant mutants during treatment with inhibitors than wild-type replicon. The model can be used to interpret the results of anti-HCV drug testing on replicon systems, as well as to estimate the efficacy of potential drugs and predict optimal schemes of their usage.

Genetic complementation of hepatitis C virus nonstructural protein functions associated with replication exhibits requirements that differ from those for virion assembly

Within the polyprotein encoded by hepatitis C virus (HCV), the minimum components required for viral RNA replication lie in the NS3-5B region, while virion assembly requires expression of all virus components. Here, we have employed complementation systems to examine the role that HCV polyprotein precursors play in RNA replication and virion assembly. In a trans-complementation assay, an HCV NS3-5A polyprotein precursor was required to facilitate efficient complementation of a replication-defective mutation in NS5A. However, this requirement for precursor expression was partially alleviated when a second functional copy of NS5A was expressed from an additional upstream cistron within the RNA to be rescued. In contrast, rescue of a virion assembly mutation in NS5A was more limited but exhibited little or no requirement for expression of functional NS5A as a precursor, even when produced in the context of a second replicating helper RNA. Furthermore, expression of NS5A alone from an additional cistron within a replicon construct gave greater rescue of virion assembly in cis than in trans. Combined with the findings of confocal microscope analysis examining the extent to which the two copies of NS5A from the various expression systems colocalize, the results point to NS3-5A playing a role in facilitating the integration of nonstructural (NS) proteins into viral membrane-associated foci, with this representing an early stage in the steps leading to replication complex formation. The data further imply that HCV employs a minor virion assembly pathway that is independent of replication.

IMPORTANCE

In hepatitis C virus-infected cells, replication is generally considered an absolute prerequisite for virus particle formation. Here we investigated the role that the viral protein NS5A has in both replication and particle assembly using complementation assays and microscopy. We found that efficient rescue of replication required NS5A to be expressed as part of a larger polyprotein, and this correlated with detection of NS5A at sites where replication occurred. In contrast, rescue of particle assembly did not require expression of NS5A within the context of a polyprotein. Interestingly, although only partial restoration of particle assembly was possible by complementation, that proportion that could be rescued benefitted from expressing NS5A from the same RNA being packaged. Collectively, these findings provide new insight into aspects of polyprotein function. They also support the existence of a minor virion assembly pathway that bypasses replication.

Interaction between calcineurin inhibitors and IL-28B rs12979860 C>T polymorphism and response to treatment for post-transplant recurrent hepatitis C

BACKGROUND

The impact of calcineurin inhibitors on achievement of sustained virological response to antiviral therapy for post-transplant recurrent hepatitis C is controversial. This study aimed at investigating the interactions between calcineurin inhibitors and interleukin-28B (IL-28B) gene polymorphisms and sustained virological response.

METHODS

Retrospective study of 147 liver transplant recipients with recurrent hepatitis C, who received 48 weeks of peg-interferon-α (N=113) or standard interferon (N=34), in association with ribavirin. Cyclosporine and tacrolimus were administered in 68 and 79 patients, respectively. IL-28B rs12979860 allele frequency was assessed in both donors and recipients.

RESULTS

Overall, 57 patients (38.8%) obtained sustained virological response; no difference was found between cyclosporine and tacrolimus-treated patients (42.6% vs. 35.4%, p=0.371). Recipient and donor IL-28B genotypic frequencies were C/C=30.6%, C/T=51.7%, T/T=17.7% and C/C=44.9%, C/T=50.3%, T/T=4.8%, respectively. Combining donor and recipient alleles, response rates decreased from cyclosporine-treated patients carrying ≤ 1 T allele (56.1%) to tacrolimus-treated patients carrying ≤ 1 T allele (44.7%) to patients carrying ≥ 2 T alleles (25.0%, p=0.0009).

CONCLUSIONS

Donor and recipient rs12979860 alleles synergistically influence sustained virological response rate to antiviral treatment for recurrent hepatitis C. In patients carrying <2 T alleles cyclosporine favours a better response than tacrolimus, while no difference was found in the presence of ≥ 2 T alleles.

Opportunities and Risks of Host-targeting Antiviral Strategies for Hepatitis C

Hepatitis C virus (HCV) infects more than 2 % of the world population with highest prevalence in parts of Africa and Asia. Past standard of care using interferon α and ribavirin had adverse effects and showed modest efficacy for some HCV genotypes spurring the development of direct acting antivirals (DAAs). Such DAAs target viral proteins and are thus better tolerated but they suffer from emergence of vial resistance. Furthermore, DAAs are often HCV genotype specific. Novel drug candidates targeting host factors required for HCV propagation, so called host-targeting antivirals (HTAs), promise to overcome both caveats. The genetic barrier to resistance is usually considered to be high for HTAs and all HCV genotypes presumably use the same host factors. Recent data, however, challenge these assumptions, at least for some HTAs. Here, we highlight the most important host-targeting strategies against hepatitis C and critically discuss their opportunities and risks.

Cyclophilins as modulators of viral replication

Cyclophilins are peptidyl‐prolyl cis/trans isomerases important in the proper folding of certain proteins. Mounting evidence supports varied roles of cyclophilins, either positive or negative, in the life cycles of diverse viruses, but the nature and mechanisms of these roles are yet to be defined. The potential for cyclophilins to serve as a drug target for antiviral therapy is evidenced by the success of non-immunosuppressive cyclophilin inhibitors (CPIs), including Alisporivir, in clinical trials targeting hepatitis C virus infection. In addition, as cyclophilins are implicated in the predisposition to, or severity of, various diseases, the ability to specifically and effectively modulate their function will prove increasingly useful for disease intervention. In this review, we will summarize the evidence of cyclophilins as key mediators of viral infection and prospective drug targets.

Management of the transplant recipient with chronic hepatitis C

More than one-third of listed potential liver recipients in the US are infected with the hepatitis C virus (HCV). Recurrence of infection with HCV after liver transplantation is associated with accelerated graft loss and diminished patient survival. Current HCV treatments using peginterferon and ribavirin either alone or with first generation protease inhibitors (telaprevir, boceprevir) are limited by suboptimal viral response, drug-drug interaction, and side effects, some of which may be graft- or life-threatening. Rapid advances in new drug therapy for HCV promise to improve outcomes, reduce side effects and drug-drug interaction, shorten treatment duration, and simplify treatment regimens.