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

A Synopsis of Hepatitis C Virus Treatments and Future Perspectives

Hepatitis C virus (HCV) infection is a worldwide public health problem. Chronic infection with HCV can lead to liver cirrhosis or cancer. Although some immune-competent individuals can clear the virus, others develop chronic HCV disease due to viral mutations or an impaired immune response. IFNs type I and III and the signal transduction induced by them are essential for a proper antiviral effect. Research on the viral cycle and immune escape mechanisms has formed the basis of therapeutic strategies to achieve a sustained virological response (SVR). The first therapies were based on IFNα; then, IFNα plus ribavirin (IFN-RBV); and then, pegylated-IFNα-RBV (PEGIFNα-RIV) to improve cytokine pharmacokinetics. However, the maximum SVR was 60%, and several significant side effects were observed, decreasing patients' treatment adherence. The development of direct-acting antivirals (DAAs) significantly enhanced the SVR (>90%), and the compounds were able to inhibit HCV replication without significant side effects, even in paediatric populations. The management of coinfected HBV-HCV and HCV-HIV patients has also improved based on DAA and PEG-IFNα-RBV (HBV-HCV). CD4 cells are crucial for an effective antiviral response. The IFNλ3, IL28B, TNF-α, IL-10, TLR-3, and TLR-9 gene polymorphisms are involved in viral clearance, therapeutic responses, and hepatic pathologies. Future research should focus on searching for strategies to circumvent resistance-associated substitution (RAS) to DAAs, develop new therapeutic schemes for different medical conditions, including organ transplant, and develop vaccines for long-lasting cellular and humoral responses with cross-protection against different HCV genotypes. The goal is to minimise the probability of HCV infection, HCV chronicity and hepatic carcinoma.

Recent Insights into the Role of B Cells in Chronic Hepatitis B and C Infections

Chronic viral hepatitis infections, caused by the hepatitis B or C virus, are a major global health problem causing an estimated one million deaths each year. Immunological studies have classically focused on T cells, while B cells have largely been neglected. Emerging evidence, however, highlights a role for B cells in the immunopathogenesis of chronic hepatitis B and C infections. B cell responses appear to be altered across different clinical phases of chronic HBV infection and across stages of disease in chronic HCV infection. These B cell responses show signs of a more activated state with a simultaneous enrichment of phenotypically exhausted atypical memory B cells. Despite the fact that studies show an activating B cell signature in chronic viral hepatitis infection, antibody responses to HBsAg remain impaired in chronic HBV infection, and glycoprotein E2-specific neutralizing antibody responses remain delayed in the acute phase of HCV infection. At the same time, studies have reported that a subset of HBV- and HCV-specific B cells exhibit an exhausted phenotype. This may, at least in part, explain why antibody responses in chronic HBV and HCV patients are suboptimal. Here, we summarize recent findings and discuss upcoming research questions while looking forward to how new single-cell technologies could provide novel insights into the role of B cells in chronic viral hepatitis infections.

Anti-viral triterpenes: a review

Triterpenes are naturally occurring derivatives biosynthesized following the isoprene rule of Ruzicka. The triterpenes have been reported to possess a wide range of therapeutic applications including anti-viral properties. In this review, the recent studies (2010-2020) concerning the anti-viral activities of triterpenes have been summarized. The structure activity relationship studies have been described as well as brief biosynthesis of these triterpenes is discussed.

Two novel SNPs in the promoter region of PKR gene in hepatitis C patients and their impact on disease outcome and response to treatment

BACKGROUND AND STUDY AIMS

The double-stranded RNA dependent protein kinase (PKR) plays a vital role in the immune system. During HCV infection, PKR has antiviral effect by inhibition of protein synthesis of the HCV. The functional single nucleotide polymorphisms (SNPs) in PKR promoter region might have a relation to HCV disease outcome and response to treatment. The objective of the present work was threefold. First, it proposed an optimized protocol for PCR amplification of PKR promoter. Second, it screened the promoter region of PKR gene in HCV Egyptian patients to detect the possible SNPs' function. Third, to study the association between the detected SNPs and the response to treatment.

PATIENTS AND METHODS

The functional SNPs in PKR promoter region were detected using DNA sequencing in 40 HCV infected patients; 20 sustained virologic response (SVR) patients and 20 nonresponse (NR) patients after combined interferon/ribavirin therapy. Twenty healthy subjects were included as a control.

RESULTS

Two functional SNPs were detected: rs62133148T>G and rs12992188C>T within our target PKR promoter region. In rs62133148 polymorphism, there is a significant difference between patients and control subjects for TT and TG genotypes (p < 0.0001). In addition, the G allele is more predominant in HCV patients. In rs12992188 polymorphism, the CC genotype is significantly different between patients and healthy control subjects (OR/95% CI: 0.033/0.006-0.172, p < 0.0001). The presence of C allele was significantly associated with the NR patients (OR/95%CI: 0.25/0.097-0.643, p = 0.006). The TT genotype is significantly different between SVR and NR (OR/95%CI: 8.5/1.54-46.871, p = 0.014).

CONCLUSION

This study is a pioneer clinical study on these two functional SNPs (rs62133148T>G and rs12992188 C>T). The rs62133148 polymorphism does not show any association with response to treatment. The TT genotype in rs12992188 polymorphism shows association with response to treatment. Therefore, patients with TT genotypes were more likely to achieve SVR.

Combinations of siRNAs against La Autoantigen with NS5B or hVAP-A Have Additive Effect on Inhibition of HCV Replication

Hepatitis C virus is major cause of chronic liver diseases such as chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. Presently available direct-acting antiviral drugs have improved success rate; however, high cost limits their utilization, especially in developing countries like India. In the present study, we evaluated anti-HCV potential of several siRNAs targeted against the HCV RNA-dependent RNA polymerase NS5B and cellular factors, La autoantigen, PSMA7, and human VAMP-associated protein to intercept different steps of viral life cycle. The target genes were downregulated individually as well as in combinations and their impact on viral replication was evaluated. Individual downregulation of La autoantigen, PSMA7, hVAP-A, and NS5B resulted in inhibition of HCV replication by about 67.2%, 50.7%, 39%, and 52%, respectively. However, antiviral effect was more pronounced when multiple genes were downregulated simultaneously. Combinations of siRNAs against La autoantigen with NS5B or hVAP-A resulted in greater inhibition in HCV replication. Our findings indicate that siRNA is a potential therapeutic tool for inhibiting HCV replication and simultaneously targeting multiple viral steps with the combination of siRNAs is more effective than silencing a single target.

Exploring Internal Ribosome Entry Sites as Therapeutic Targets

Initiation of eukaryotic mRNA translation may proceed via several different routes, each requiring a different subset of factors and relying on different and specific interactions between the mRNA and the ribosome. Two modes predominate: (i) so-called cap-dependent initiation, which requires all canonical initiation factors and is responsible for about 95–97% of all initiation events in eukaryotic cells; and (ii) cap-independent internal initiation, which requires a reduced subset of initiation factors and accounts for up to 5% of the remaining initiation events. Internal initiation relies on the presence of so-called internal ribosome entry site (IRES) elements in the 5′ UTRs of some viral and cellular mRNAs. These elements (often possessing complex secondary and tertiary structures) promote efficient interaction of the mRNA with the 40S ribosome and allow for internal ribosome entry. Internal initiation of translation of specific mRNAs may contribute to development of severe disease and pathological states, such as hepatitis C and cancer. Therefore, this cellular mechanism represents an attractive target for pharmacological modulation. The purpose of this review is to provide insight into current strategies used to target viral and cellular IRESs and discuss the physiological consequences (and potential therapeutic implications) of abrogation/modulation of IRES-mediated translation.

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.

Treating hepatitis C: current standard of care and emerging direct-acting antiviral agents

Summary.  During the late 1990s and early 2000s, major advances were made in the treatment of patients with chronic hepatitis C virus (HCV) infection. Interferon, combination interferon plus ribavirin (RBV) and pegylated interferon plus RBV increased sustained virologic response (SVR) rates from ~5% to ~40-80%, depending on the genotype of HCV infection. Advances in molecular biology have allowed investigators to begin to understand the mechanisms of HCV infection and replication. Advances in understanding of viral kinetics have provided tools to identify patients who are most likely to attain SVR. With the advances in the science of HCV infection, the first part of the 21st century has seen the development and early introduction of a number of direct-acting antiviral (DAA) drugs. These novel medications interfere with critical steps in HCV replication and have the potential to significantly increase SVR rates. This article will review the key elements of HCV replication and evaluate the various classes of new and investigational DAA that have the potential to create a revolution in the management of patients with chronic hepatitis C.

Efficient, enantioselective assembly of silanediol protease inhibitors

A five-step assembly of silicon-protected dipeptide mimics from commercially available reagents is described. This methodology makes silanediol protease inhibitors readily available for the first time. The sequence features asymmetric hydrosilylation, a novel reduction of a silyl ether to a silyllithium reagent, and addition of this dianion to a sulfinimine, to produce the complete inhibitor skeleton with full control of stereochemistry. Oxidation of the primary alcohol to an acid completes the synthesis.