Future therapy of hepatitis C

Hepatocellular carcinoma in patients with chronic hepatitis C virus infection in the Asia-Pacific region

Hepatocellular carcinoma (HCC) is the third-leading cause of cancer-related mortality worldwide. Although hepatitis B still remains the most common risk factor worldwide, chronic hepatitis C virus (HCV) infection is the driving force for the increased incidence of HCC especially in Western countries and Japan. In hepatitis B virus (HBV)-endemic areas, after successful vaccination programs against HBV, chronic HCV infection is now emerging as an important cause of chronic liver diseases. Unlike patients with chronic hepatitis B, those with chronic hepatitis C (CHC) develop HCC in the presence of established cirrhosis in most cases. However, a significant minority of CHC develops HCC in the absence of cirrhosis. Although HCV is a RNA virus with little potential for integrating its genetic material into host genome, various HCV proteins, including core, envelope, and nonstructural proteins, have oncogenic properties by inducing oxidative stress, disturbing cellular regulatory pathways associated with proliferation and apoptosis, and suppressing host immune responses. Overall, a combination of virus-specific, host genetic, environmental, and immune-related factors are likely to determine progression to HCC. Strategies aimed at eliminating the virus may provide opportunities for effective prevention of the development of HCC. Pegylated interferon plus ribavirin therapy appears to be effective at reducing the risk of HCC in patients who achieve sustained virologic responses. In summary, with the emerging importance of CHC, mechanisms of HCV-associated hepatocellular carcinogenesis should be clarified to provide insight into advanced therapeutic and preventive approaches, which eventually decrease the incidence and mortality of HCC.

Divergent antiviral effects of bioflavonoids on the hepatitis C virus life cycle

We have previously demonstrated that quercetin, a bioflavonoid, blocks hepatitis C virus (HCV) proliferation by inhibiting NS5A-driven internal ribosomal entry site (IRES)-mediated translation of the viral genome. Here, we investigate the mechanisms of antiviral activity of quercetin and six additional bioflavonoids. We demonstrate that catechin, naringenin, and quercetin possess significant antiviral activity, with no associated cytotoxicity. Infectious virion secretion was not significantly altered by these bioflavonoids. Catechin and naringenin demonstrated stronger inhibition of infectious virion assembly compared to quercetin. Quercetin markedly blocked viral translation whereas catechin and naringenin demonstrated mild activity. Similarly quercetin completely blocked NS5A-augmented IRES-mediated translation in an IRES reporter assay, whereas catechin and naringenin had only a mild effect. Moreover, quercetin differentially inhibited HSP70 induction compared to catechin and naringenin. Thus, the antiviral activity of these bioflavonoids is mediated through different mechanisms. Therefore combination of these bioflavonoids may act synergistically against HCV.

Intramolecular regulation of the sequence-specific mRNA interferase activity of MazF fused to a MazE fragment with a linker cleavable by specific proteases

The genomes of human immunodeficiency virus type 1 (HIV-1) and hepatitis C virus (HCV) consist of single-stranded RNA encoding polyproteins, which are processed to individual functional proteins by virus-encoded specific proteases. These proteases have been used as targets for drug development. Here, instead of targeting these proteases to inhibit viral infection, we utilized the protease activity to activate a toxic protein to prevent viral infection. We engineered the MazE-MazF antitoxin-toxin system of Escherichia coli to fuse a C-terminal 41-residue fragment of antitoxin MazE to the N-terminal end of toxin MazF with a linker having a specific protease cleavage site for either HIV PR (HIV-1 protease), NS3 protease (HCV protease), or factor Xa. These fusion proteins formed a stable dimer (instead of the MazF(2)-MazE(2)-MazF(2) heterohexamer in nature) to inactivate the ACA (sequence)-specific mRNA interferase activity of MazF. When the fusion proteins were incubated with the corresponding proteases, the MazE fragment was cleaved from the fusion proteins, releasing active MazF, which then acted as an ACA-specific mRNA interferase cleaving single-stranded MS2 phage RNA. The intramolecular regulation of MazF toxicity by proteases as demonstrated may provide a novel approach for preventive and therapeutic treatments of infection by HIV-1, HCV, and other single-stranded RNA viruses.

Effects of host and virus related factors on interferon-α+ribavirin and pegylated-interferon+ribavirin treatment outcomes in chronic Hepatitis C patients

Background

Current standard therapy commonly followed for chronic Hepatitis C Virus (HCV) in Pakistan is interferon alpha plus ribavirin combination therapy (IFN α/ribavirin) and pegylated interferon plus ribavirin (PegIFN/ribavirin). PegIFN/ribavirin has increased rate of sustained virological response than standard IFN α/ribavirin therapy. Objective of current study was to analyze rate of early and delayed response to antiviral treatment as well as rate of relapse response in patients following standard treatment IFN α/ribavirin and in patients following pegylated interferon treatment.

Methods

Baseline serum samples of 153 patients enrolled for IFN α/ribavirin and 50 patients for PegIFN/ribavirin were collected. After total RNA extraction, genotyping was and HCV RNA viral load was done. Subsequently HCV RNA viral load was estimated at 4 weeks of treatment, at 12 weeks, at 24 or 48 weeks and finally after 6 months follow up period. All the data was statistically analyzed using fisher's exact test.

Results

Total 86 patients out of 153 patients following conventional IFN α/ribavirin therapy completed treatment and 69% of them showed Rapid Virological Response (RVR). Whereas 50 patients following PegIFN/ribavirin treatment completed treatment and 80% of them achieved RVR. Total 64 out of 86 patients following IFN α/ribavirin therapy completed follow up period and 53.5% of them achieved Sustainded Virologcal Response (SVR). Forty-five out of total 50 patients who received PegIFN/ribavirin treatment completed 6 months follow up period and among these 70% achieved SVR. SVR rates were significantly associated with RVR (p < 0.001), age (p < 0.001) and gender (p < 0.01)

Conclusions

Rate of sustained virological response can be determined by factors like rapid virological response and age since they share significant association with one another. More over rate of SVR was more prominent in males than in females.

Mutations in the E2-PePHD region of hepatitis C virus genotype-3a and correlation with response to interferon and ribavirin combination therapy in Pakistani patients

Hepatitis C is a major health problem affecting more than 200 million individuals in the world. Current treatment regimen consisting of interferon alpha and ribavirin does not always succeed in eliminating the virus completely from patient's body. One of the mechanisms by which virus evades the antiviral effect of interferon alpha involves protein kinase (PKR) eukaryotic initiation factor 2 alpha (eIF2a) phosphorylation homology domain (PePHD). This domain in genotype 1 strains is reportedly homologous to PKR and its target eIF2a. By binding to PKR, PePHD inhibits its activity and therefore cause virus to evade antiviral activity of interferon (IFN). Many studies have correlated substitutions in this domain to the treatment response and lead to inconclusive results. Some studies suggested that substitutions favor response while others emphasized that no correlation exists. In the present study we therefore compared sequences of PePHD domain of thirty one variants of six hepatitis C virus patients of genotype 3. Three of our HCV 3a infected patients showed rapid virological response to interferon alpha and ribavirin combination therapy whereas the remaining three had breakthrough to the same combination therapy. It is found that PePHD domain is not entirely conserved and has substitutions in some isolates irrespective of the treatment response. However substitution of glutamine (Q) with Leucine (L) in one of the breakthrough responders made it more identical to HCV genotype 1a. These substitutions in the breakthrough responders also tended to increase average hydrophilic activity thus making binding of PePHD to PKR and inhibition of PKR more favorable.

Anti-hepatitis C virus activity of novel beta-d-2'-C-methyl-4'-azido pyrimidine nucleoside phosphoramidate prodrugs

BACKGROUND

2'-C-methyl and 4'-azido nucleosides have previously demonstrated inhibition of hepatitis C virus (HCV) replication by targeting the RNA-dependent RNA polymerase NS5B. In an effort to discover new and more potent anti-HCV agents, we envisioned synthesizing nucleoside analogues by combining the 2'-C-methyl-moiety with the 4'-azido-moiety into one molecule.

METHODS

2'-C-methyl-4'-azido pyrimidine nucleosides were synthesized by first converting 2'-C-methyl ribonucleosides to the corresponding 4'-exocyclic methylene nucleosides. Treatment with iodine azide, benzoylation of the 2'- and 3'-hydroxy groups, oxidative displacement of the 5'-iodo group with meta-chloroperoxybenzoic acid, and debenzoylation gave the desired 2'-C-methyl-4'-azido uridine and thymidine analogues in good yield. Standard conversion of uridine to cytidine via the 4-triazole yielded 2'-C-methyl-4'-azido cytidine. In addition, 5'-phosphoramidate derivatives of 2'-C-methyl-4'-azido uridine and cytidine were synthesized to bypass the initial phosphorylation step.

RESULTS

The prepared nucleosides and their 5'-monophosphate prodrugs were evaluated for their ability to inhibit replication of the hepatitis C virus in a subgenomic replicon cell based assay. Cytotoxicity in Huh7 cells was determined simultaneously with anti-HCV activity by extraction and amplification of both HCV RNA and ribosomal RNA. Among the newly synthesized compounds, only the 5'-monophosphate nucleoside prodrugs had modest and selective anti-HCV activity. All prepared pyrimidine nucleosides and 5'-monophosphate nucleoside prodrugs displayed no evidence of cytotoxicity at high concentrations.

CONCLUSIONS

This work is the first example of both inactive uridine and cytidine analogues of a nucleoside being converted to active anti-HCV nucleosides via 5'-monophosphate prodrugs.

Refractoriness of hepatitis C virus internal ribosome entry site to processing by Dicer in vivo

Background

Hepatitis C virus (HCV) is a positive-strand RNA virus harboring a highly structured internal ribosome entry site (IRES) in the 5' nontranslated region of its genome. Important for initiating translation of viral RNAs into proteins, the HCV IRES is composed of RNA structures reminiscent of microRNA precursors that may be targeted by the host RNA silencing machinery.

Results

We report that HCV IRES can be recognized and processed into small RNAs by the human ribonuclease Dicer in vitro. Furthermore, we identify domains II, III and VI of HCV IRES as potential substrates for Dicer in vitro. However, maintenance of the functional integrity of the HCV IRES in response to Dicer overexpression suggests that the structure of the HCV IRES abrogates its processing by Dicer in vivo.

Conclusion

Our results suggest that the HCV IRES may have evolved to adopt a structure or a cellular context that is refractory to Dicer processing, which may contribute to viral escape of the host RNA silencing machinery.

New therapeutic opportunities for Hepatitis C based on small RNA

Hepatitis C virus (HCV) infection is one of the major causes of chronic liver disease, including cirrhosis and liver cancer and is therefore, the most common indication for liver transplantation. Conventional antiviral drugs such as pegylated interferon-alpha, taken in combination with ribavirin, represent a milestone in the therapy of this disease. However, due to different viral and host factors, clinical success can be achieved only in approximately half of patients, making urgent the requirement of exploiting alternative approaches for HCV therapy. Fortunately, recent advances in the understanding of HCV viral replication and host cell interactions have opened new possibilities for therapeutic intervention. The most recent technologies, such as small interference RNA mediated gene-silencing, anti-sense oligonucleotides (ASO), or viral vector based gene delivery systems, have paved the way to develop novel therapeutic modalities for HCV. In this review, we outline the application of these technologies in the context of HCV therapy. In particular, we will focus on the newly defined role of cellular microRNA (miR-122) in viral replication and discuss its potential for HCV molecular therapy.

Antisense oligonucleotide inhibition of hepatitis C virus genotype 4 replication in HepG2 cells

BACKGROUND

Hepatitis C (HCV) viral infection is a serious medical problem in Egypt and it has a devastating impact on the Egyptian economy. It is estimated that over 15% of Egyptians are infected by the virus and thus finding a cure for this disease is of utmost importance. Current therapies for hepatitis C virus (HCV) genotype 4 with interferon/ribavirin have not been successful and thus the development of alternative therapy for this genotype is desperately needed.

RESULTS

Although previous studies utilizing viral subgenomic or full cDNA fragments linked to reporter genes transfected into adhered cells or in a cell free system showed promise, demonstration of efficient viral replication was lacking. Thus, we utilized HepG2 cells infected with native HCV RNA genomes in a replication competent system and used antisense phosphorothioate Oligonucleotides (S-ODN) against stem loop IIId and the AUG translation start site of the viral polyprotein precursor to monitor viral replication. We were able to show complete arrest of intracellular replication of HCV-4 at 1 uM S-ODN, thus providing a proof of concept for the potential antiviral activity of S-ODN on native genomic replication of HCV genotype 4.

CONCLUSION

We have successfully demonstrated that by using two S-ODNs [(S-ODN1 (nt 326-348) and S-ODN-2 (nt 264-282)], we were able to completely inhibit viral replication in culture, thus confirming earlier reports on subgenomic constructs and suggesting a potential therapeutic value in HCV type 4.

VX-950, a novel hepatitis C virus (HCV) NS3-4A protease inhibitor, exhibits potent antiviral activities in HCv replicon cells

The NS3-4A serine protease of hepatitis C virus (HCV) is essential for viral replication and therefore has been one of the most attractive targets for developing specific antiviral agents against HCV. VX-950, a highly selective, reversible, and potent peptidomimetic inhibitor of the HCV NS3-4A protease, is currently in clinical development for the treatment of hepatitis C. In this report, we describe the in vitro characterization of anti-HCV activities of VX-950 in subgenomic HCV replicon cells. Incubation with VX-950 resulted in a time- and dose-dependent reduction of HCV RNA and proteins in replicon cells. Moreover, following a 2-week incubation with VX-950, a reduction in HCV RNA levels of 4.7 log(10) was observed, and this reduction resulted in elimination of HCV RNA from replicon cells, since there was no rebound in replicon RNA after withdrawal of the inhibitor. The combination of VX-950 and alpha interferon was additive to moderately synergistic in reducing HCV RNA in replicon cells with no significant increase in cytotoxicity. The benefit of the combination was sustained over time: a 4-log(10) reduction in HCV RNA level was achieved following a 9-day incubation with VX-950 and alpha interferon at lower concentrations than when either VX-950 or alpha interferon was used alone. The combination of VX-950 and alpha interferon also suppressed the emergence of in vitro resistance mutations against VX-950 in replicon cells.

The Oncogenic Potential of Hepatitis C Virus NS5A Sequence Variants Is Associated with PKR Regulation

The NS5A protein of hepatitis C virus (HCV) confers cell growth regulation and has been implicated in viral oncogenesis. Here, we investigated whether highly divergent NS5A proteins obtained from HCV-infected patients presented an oncogenic potential when expressed in mammalian cells. In general, NS5A expression was associated with increased rates of cell growth and culture proliferation. Immortalized primary hepatocyte and immortalized fibroblast cell lines expressing a subset of these sequences exhibited a significant increase in protein synthetic rate, culture saturation density, and a transformed cellular phenotype, as shown by anchorage-independent cell growth and colony formation in soft agar assays. Oncogenic transformation correlated with inhibition of protein kinase R (PKR) activity and concomitant reduction of eukaryotic initiation factor 2alpha (elF2alpha) phosphorylation levels that caused stimulation of mRNA translation. The extent of sequence variation throughout NS5A or within the previously characterized PKR-binding domain was not a predictive indicator of this cellular phenotype, suggesting that sequences outside this region contribute to PKR regulation. Our data indicate that NS5A oncogenic potential is conditional through viral sequence variation. These results provide further evidence to define the PKR pathway as a mediator of cell growth control and suggest that viral regulation of PKR may contribute to hepatocyte growth deregulation during chronic HCV infection.

Chronic hepatitis C and no response to antiviral therapy: potential current and future therapeutic options

A significant proportion of chronic hepatitis C patients fails to achieve sustained virologic response even after treatment with the current, more potent, combination of pegylated interferon-alpha (IFNa) plus ribavirin. Such patients represent a rather heterogeneous group and may be divided initially into relapsers and nonresponders. Both the type of previous therapy and of previous response are very important factors for the indication and the type of re-treatment. The combination of pegylated IFNa and ribavirin seems to be a rational approach for patients who failed to respond to IFNa monotherapy. Pegylated IFNa-based regimens appear to induce sustained responses in 40-68% of relapsers but in only 11% of nonresponders to previous therapy with standard IFNa plus ribavirin. Thus, new therapeutic approaches are needed for the latter subgroup of patients as well as those who fail to respond to pegylated IFNa-based regimens. Such new approaches currently under evaluation include the triple combination of pegylated IFNa, ribavirin, and amantadine, alternative types of IFN, use of agents with ribavirin like activity but lesser degrees of side-effects, inhibitors of hepatitis C virus (HCV) replication, mainly inhibitors of NS3 protease or helicase, antisense oligonucleotides, and ribozymes, and several immunomodulators. Moreover, maintenance antifibrotic therapy, mostly with low doses of pegylated IFNa, are under evaluation in patients with advanced fibrosis. Thus, even in the current era of the potent pegylated IFNa-based regimens, the management of these difficult-to-treat patients represents an increasingly frequent problem and perhaps the most challenging therapeutic task in chronic hepatitis C.

Mechanism of action and antiviral activity of benzimidazole-based allosteric inhibitors of the hepatitis C virus RNA-dependent RNA polymerase

The RNA-dependent RNA polymerase of hepatitis C virus (HCV) is the catalytic subunit of the viral RNA amplification machinery and is an appealing target for the development of new therapeutic agents against HCV infection. Nonnucleoside inhibitors based on a benzimidazole scaffold have been recently reported. Compounds of this class are efficient inhibitors of HCV RNA replication in cell culture, thus providing attractive candidates for further development. Here we report the detailed analysis of the mechanism of action of selected benzimidazole inhibitors. Kinetic data and binding experiments indicated that these compounds act as allosteric inhibitors that block the activity of the polymerase prior to the elongation step. Escape mutations that confer resistance to these compounds map to proline 495, a residue located on the surface of the polymerase thumb domain and away from the active site. Substitution of this residue is sufficient to make the HCV enzyme and replicons resistant to the inhibitors. Interestingly, proline 495 lies in a recently identified noncatalytic GTP-binding site, thus validating it as a potential allosteric site that can be targeted by small-molecule inhibitors of HCV polymerase.

Disruption of hepatitis C virus RNA replication through inhibition of host protein geranylgeranylation

Hepatitis C virus (HCV) RNA replication depends on viral protein association with intracellular membranes, but the influence of membrane composition on viral replication is unclear. We report that HCV RNA replication and assembly of the viral replication complex require geranylgeranylation of one or more host proteins. In cultured hepatoma cells, HCV RNA replication was disrupted by treatment with lovastatin, an inhibitor of 3-hydroxy-3-methyglutaryl CoA reductase, or with an inhibitor of protein geranylgeranyl transferase I, each of which induced the dissolution of the HCV replication complex. Viral replication was not affected by treatment of cells with an inhibitor of farnesyl transferase. When added to lovastatin-treated cells, geranylgeraniol, but not farnesol, restored replication complex assembly and viral replication. Inasmuch as the HCV genome does not encode a canonical geranylgeranylated protein, the data suggest the involvement of a geranylgeranylated host protein in HCV replication. Inhibition of its geranylgeranylation affords a therapeutic strategy for treatment of HCV infection.

Managing occupational risks for hepatitis C transmission in the health care setting

Hepatitis C virus (HCV) infection is a significant contemporary health problem in the United States and elsewhere. Because it is primarily transmitted via blood, hepatitis C infection presents risks for both nosocomial transmission to patients and occupational spread to health care workers. Recent insights into the pathogenesis, immunopathogenesis, natural history, and treatment of infection caused by this unique flavivirus provide a rationale for the use of new strategies for managing occupational hepatitis C infections when they occur. This article reviews this developing information. Recently published data demonstrate success rates in the treatment of "acute hepatitis C syndrome" that approach 100\%, and although these studies are not directly applicable to all occupational infections, they may provide important clues to optimal management strategies. In addition, the article delineates approaches to the prevention of occupational exposures and also addresses the difficult issue of managing HCV-infected health care providers. The article summarizes currently available data about the nosocomial epidemiology of HCV infection and the magnitude of risk and discusses several alternatives for managing exposure and infection. No evidence supports the use of immediate postexposure prophylaxis with immunoglobulin, immunomodulators, or antiviral agents. Based on the very limited data available, the watchful waiting and preemptive therapy strategies described in detail in this article represent reasonable interim approaches to the complex problem of managing occupational HCV infections, at least until more definitive data are obtained.