NS5A inhibitors for the treatment of hepatitis C infection

N-Heterocycles as Promising Antiviral Agents: A Comprehensive Overview

Viruses are a real threat to every organism at any stage of life leading to extensive infections and casualties. N-heterocycles can affect the viral life cycle at many points, including viral entrance into host cells, viral genome replication, and the production of novel viral species. Certain N-heterocycles can also stimulate the host's immune system, producing antiviral cytokines and chemokines that can stop the reproduction of viruses. This review focused on recent five- or six-membered synthetic N-heterocyclic molecules showing antiviral activity through SAR analyses. The review will assist in identifying robust scaffolds that might be utilized to create effective antiviral drugs with either no or few side effects.

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.

Horner-Wadsworth-Emmons reaction as an excellent tool in the synthesis of fluoro-containing biologically important compounds

Selective introduction of a double bond motif into a multifunctional organic compound is always a big challenge. The Horner-Wadsworth-Emmons reaction is one of the most reliable, simple, and stereoselective olefination methods, widely used in organic chemistry. To the best of our knowledge, no review article on the application of HWE reaction in the synthesis of fluoroorganic compounds with direct biological interest has been published in recent years. The importance of the HWE reaction should be emphasised due to its simplicity and stereoselectivity. Under mild conditions and in one step, valuable compounds can be obtained. The HWE reaction is primarily a great tool in the synthesis of fluoroolefins that are, among others, peptide bond mimetics. Therefore, it can serve as an indispensable approach to access peptide bioisosteres and, consequently, analogues of numerous enzyme inhibitors. The protocol may be utilized to obtain florinated vinylphosphonate, vinylsulfone or sulfonate derivatives, which exhibit biological activity. In this review article, we would like to summarize the HWE reaction output of the last 12 years (since 2010).

Chronic Hepatitis C

Hepatitis C virus (HCV) infection contributes significantly to liver cirrhosis and hepatocellular carcinoma (HCC), often requiring liver transplantation. Introducing direct-acting antiviral agents (DAAs) has radically changed HCV treatment. DAAs achieve high rates of sustained virological response (>98%). Even then, resistant-associated substitution and HCC during or after treatment have become prominent clinical concerns. Further, several clinically significant issues remain unresolved after successful HCV eradication by DAAs, including treating patients with chronic kidney disease or decompensated liver cirrhosis. Extensive and large-scale screening and treatment implementation programs are needed to make DAA therapies effective at the population level.

Identifying Structural Features of Nucleotide Analogues to Overcome SARS-CoV-2 Exonuclease Activity

With the recent global spread of new SARS-CoV-2 variants, there remains an urgent need to develop effective and variant-resistant oral drugs. Recently, we reported in vitro results validating the use of combination drugs targeting both the SARS-CoV-2 RNA-dependent RNA polymerase (RdRp) and proofreading exonuclease (ExoN) as potential COVID-19 therapeutics. For the nucleotide analogues to be efficient SARS-CoV-2 inhibitors, two properties are required: efficient incorporation by RdRp and substantial resistance to excision by ExoN. Here, we have selected and evaluated nucleotide analogues with a variety of structural features for resistance to ExoN removal when they are attached at the 3' RNA terminus. We found that dideoxynucleotides and other nucleotides lacking both 2'- and 3'-OH groups were most resistant to ExoN excision, whereas those possessing both 2'- and 3'-OH groups were efficiently removed. We also found that the 3'-OH group in the nucleotide analogues was more critical than the 2'-OH for excision by ExoN. Since the functionally important sequences in Nsp14/10 are highly conserved among all SARS-CoV-2 variants, these identified structural features of nucleotide analogues offer invaluable insights for designing effective RdRp inhibitors that can be simultaneously efficiently incorporated by the RdRp and substantially resist ExoN excision. Such newly developed RdRp terminators would be good candidates to evaluate their ability to inhibit SARS-CoV-2 in cell culture and animal models, perhaps combined with additional exonuclease inhibitors to increase their overall effectiveness.

Leveraging structural and 2D-QSAR to investigate the role of functional group substitutions, conserved surface residues and desolvation in triggering the small molecule-induced dimerization of hPD-L1

Small molecules are rising as a new generation of immune checkpoints’ inhibitors, with compounds targeting the human Programmed death-ligand 1 (hPD-L1) protein are pioneering this area of research. Promising examples include the recently disclosed compounds from Bristol-Myers-Squibb (BMS). These molecules bind specifically to hPD-L1 through a unique mode of action. They induce dimerization between two hPD-L1 monomers through the hPD-1 binding interface in each monomer, thereby inhibiting the PD-1/PD-L1 axis. While the recently reported crystal structures of such small molecules bound to hPD-L1 reveal valuable insights regarding their molecular interactions, there is still limited information about the dynamics driving this unusual complex formation. The current study provides an in-depth computational structural analysis to study the interactions of five small molecule compounds in complex with hPD-L1. By employing a combination of molecular dynamic simulations, binding energy calculations and computational solvent mapping techniques, our analyses quantified the dynamic roles of different hydrophilic and lipophilic residues at the surface of hPD-L1 in mediating these interactions. Furthermore, ligand-based analyses, including Free-Wilson 2D-QSAR was conducted to quantify the impact of R-group substitutions at different sites of the phenoxy-methyl biphenyl core. Our results emphasize the importance of a terminal phenyl ring that must be present in any hPD-L1 small molecule inhibitor. This phenyl moiety overlaps with a very unfavorable hydration site, which can explain the ability of such small molecules to trigger hPD-L1 dimerization.

Analysis of Clinical Trials of New Drugs for Liver Diseases in China

Background

Liver diseases are a major public health concern worldwide, and the development of novel therapeutic drugs is an important research focus. But no overview has been conducted so far on the current research and development for liver-specific drugs in China, and the actual situation regarding the development and evaluation of new drugs in clinical trials.

Methods

The information of all clinical trials on liver diseases were obtained through the "Pharmaceutical Clinical Trial Registration and Information Disclosure Platform" before December 31, 2020.

Results

A total of 751 clinical trials on liver disease-related drugs were published on the above platform, including 574 chemical drugs, 128 biological products, and 49 traditional Chinese medicine (TCM)/natural drugs. The number of annual registrations has increased on an annual basis. The main indications for these clinical trials are viral hepatitis, liver malignancies, liver abscess, liver transplantation, congenital liver metabolic disease, and other hepatitis-related diseases. Hepatitis B, hepatitis C and liver cancer accounted for 72.4% of the total clinical trials, and the majority are related to generic drug research. There are 103 innovative drugs currently in clinical testing, mainly for hepatitis B, hepatitis C and hepatocellular carcinoma.

Conclusion

The stronger macro-control is required for the clinical trials conducted in China, and it is necessary to identify new therapeutic targets and develop novel drugs for the key liver diseases, as well as preventive hepatitis C vaccines, and targeted therapy, TCM/natural drugs and immunotherapy for liver cancer.

Update on the management and treatment of viral hepatitis

This review aims to summarize the current evidence on the treatment of viral hepatitis, focusing on its clinical management. Also, future treatment options and areas of potential research interest are detailed. PubMed and Scopus databases were searched for primary studies published within the last ten years. Keywords included hepatitis A virus, hepatitis B virus (HBV), hepatitis C virus, hepatitis D virus (HDV), hepatitis E virus, and treatment. Outcomes reported in the studies were summarized, tabulated, and synthesized. Significant advances in viral hepatitis treatment were accomplished, such as the advent of curative therapies for hepatitis C and the development and improvement of hepatitis A, hepatitis B, and hepatitis E vaccination. Drugs that cure hepatitis B, going beyond viral suppression, are so far unavailable; however, targeted antiviral drugs against HBV (immunomodulatory therapies and gene silencing technologies) are promising approaches to eradicating the virus. Ultimately, high vaccination coverage and large-scale test-and-treat programmes with high screening rates may eliminate viral hepatitis and mitigate their burden on health systems. The development of curative hepatitis C treatment renewed the enthusiasm for curing hepatitis B, albeit further investigation is required. Novel therapeutic options targeting HDV life cycle are currently under clinical investigation.

Recent studies of nitrogen containing heterocyclic compounds as novel antiviral agents: A review

N-heterocycles are important, not only because of their abundance, but above all because of their chemical, biological and technical significance. They play an important role in biological investigation such as anticancer, antiinflammatory, antibacterial, antiviral, anti-tumor, antidiabetic, etc. In this study, we focused on examining synthesized some 5- or 6-ring N-heterocyclic compounds that showed the antiviral activity in last 5 years, and investigation of these compounds structure-activity relationship studies. This review will be useful to scientists in research fields of organic synthesis, medicinal chemistry, and pharmacology.

Determination and structural characterization of ravidasvir metabolites by LC coupled to triple quadrupole linear ion trap MS: Application to pharmacokinetics and phase I metabolism in rats

Hepatitis C virus (HCV) is an infectious disease that has become a global clinical issue because of its significant morbidity and mortality. Novel anti-hepatitis C drugs are continuously developed to decrease the pervasiveness of the infection globally. A synthetic ravidasvir, benzimidazole-naphthylene-imidazole derivatives, has been used as an anti-HCV drug. This study determined the metabolites of ravidasvir and its pharmacokinetics in rats using information-dependent acquisition and multiple reaction monitoring scanning modes in linear ion trap LC-MS/MS instrument, respectively. Two time-programming linear-gradient chromatographic methods were employed using a Kinetex C₁₈ column (50 × 3 mm, 2.6 μm) and a Luna HILIC column (100 × 4.6 mm, 3 μm) for the qualitative and quantitative determination of ravidasvir and its metabolites, respectively. In silico prediction where sites in a molecule are susceptible to metabolism by cytochrome P₄₅₀ was implemented, which helped in proposing the metabolic pathway of ravidasvir. The most dominant metabolite in rat liver microsomal samples was oxidative ravidasvir, where one O-demethylated metabolite and eight isomers of the oxidative ravidasvir metabolites were identified. The study provides essential data for proposing the metabolic pathway and successfully applied it to determine the pharmacokinetics of ravidasvir in rat plasma.

Nucleotide analogues as inhibitors of SARS-CoV Polymerase

SARS-CoV-2, a member of the coronavirus family, has caused a global public health emergency. Based on our analysis of hepatitis C virus and coronavirus replication, and the molecular structures and activities of viral inhibitors, we previously reasoned that the FDA-approved hepatitis C drug EPCLUSA (Sofosbuvir/Velpatasvir) should inhibit coronaviruses, including SARS-CoV-2. Here, using model polymerase extension experiments, we demonstrate that the active triphosphate form of Sofosbuvir is incorporated by low-fidelity polymerases and SARS-CoV RNA-dependent RNA polymerase (RdRp), and blocks further incorporation by these polymerases; the active triphosphate form of Sofosbuvir is not incorporated by a host-like high-fidelity DNA polymerase. Using the same molecular insight, we selected 3'-fluoro-3'-deoxythymidine triphosphate and 3'-azido-3'-deoxythymidine triphosphate, which are the active forms of two other anti-viral agents, Alovudine and AZT (an FDA-approved HIV/AIDS drug) for evaluation as inhibitors of SARS-CoV RdRp. We demonstrate the ability of two of these HIV reverse transcriptase inhibitors to be incorporated by SARS-CoV RdRp where they also terminate further polymerase extension. Given the 98% amino acid similarity of the SARS-CoV and SARS-CoV-2 RdRps, we expect these nucleotide analogues would also inhibit the SARS-CoV-2 polymerase. These results offer guidance to further modify these nucleotide analogues to generate more potent broad-spectrum anti-coronavirus agents.

Sofosbuvir terminated RNA is more resistant to SARS-CoV-2 proofreader than RNA terminated by Remdesivir

SARS-CoV-2 is responsible for COVID-19, resulting in the largest pandemic in over a hundred years. After examining the molecular structures and activities of hepatitis C viral inhibitors and comparing hepatitis C virus and coronavirus replication, we previously postulated that the FDA-approved hepatitis C drug EPCLUSA (Sofosbuvir/Velpatasvir) might inhibit SARS-CoV-2. We subsequently demonstrated that Sofosbuvir triphosphate is incorporated by the relatively low fidelity SARS-CoV and SARS-CoV-2 RNA-dependent RNA polymerases (RdRps), serving as an immediate polymerase reaction terminator, but not by a host-like high fidelity DNA polymerase. Other investigators have since demonstrated the ability of Sofosbuvir to inhibit SARS-CoV-2 replication in lung and brain cells; additionally, COVID-19 clinical trials with EPCLUSA and with Sofosbuvir plus Daclatasvir have been initiated in several countries. SARS-CoV-2 has an exonuclease-based proofreader to maintain the viral genome integrity. Any effective antiviral targeting the SARS-CoV-2 RdRp must display a certain level of resistance to this proofreading activity. We report here that Sofosbuvir terminated RNA resists removal by the exonuclease to a substantially higher extent than RNA terminated by Remdesivir, another drug being used as a COVID-19 therapeutic. These results offer a molecular basis supporting the current use of Sofosbuvir in combination with other drugs in COVID-19 clinical trials.

Orally bioavailable HCV NS5A inhibitors of unsymmetrical structural class

A novel unsymmetrical structural class of orally bioavailable hepatitis C virus (HCV) nonstructural 5A protein (NS5A) inhibitors has been generated by improving both the solubility and membrane permeability of the lead compound found in our previous work. The representative compound 14, with a 5-hydroxymethylpyrazine group and a 3-t-butylpropargyl group on each side of the molecule, exhibited the best oral bioavailability in this study, inhibiting not only the HCV genotype 1a, 1b, 2a, and 3a replicons with EC₅₀ values in the picomolar range, but also inhibited 1a Q30 mutants induced by launched symmetrical inhibitors with EC₅₀ values in the low nanomolar range.

Nonstructural NS5A Protein Regulates LIM and SH3 Domain Protein 1 to Promote Hepatitis C Virus Propagation

Hepatitis C virus (HCV) propagation is highly dependent on cellular proteins. To identify the host factors involved in HCV propagation, we previously performed protein microarray assays and identified the LIM and SH3 domain protein 1 (LASP-1) as an HCV NS5A-interacting partner. LASP-1 plays an important role in the regulation of cell proliferation, migration, and protein-protein interactions. Alteration of LASP-1 expression has been implicated in hepatocellular carcinoma. However, the functional involvement of LASP1 in HCV propagation and HCV-induced pathogenesis has not been elucidated. Here, we first verified the protein interaction of NS5A and LASP-1 by both in vitro pulldown and coimmunoprecipitation assays. We further showed that NS5A and LASP-1 were colocalized in the cytoplasm of HCV infected cells. NS5A interacted with LASP-1 through the proline motif in domain I of NS5A and the tryptophan residue in the SH3 domain of LASP-1. Knockdown of LASP-1 increased HCV replication in both HCV-infected cells and HCV subgenomic replicon cells. LASP-1 negatively regulated viral propagation and thereby overexpression of LASP-1 decreased HCV replication. Moreover, HCV propagation was decreased by wild-type LASP-1 but not by an NS5A binding-defective mutant of LASP-1. We further demonstrated that LASP-1 was involved in the replication stage of the HCV life cycle. Importantly, LASP-1 expression levels were increased in persistently infected cells with HCV. These data suggest that HCV modulates LASP-1 via NS5A in order to regulate virion levels and maintain a persistent infection.

HCV NS5A hyperphosphorylation is involved in viral translation modulation

Hepatitis C virus (HCV) non-structural (NS) 5A protein is a multifunctional phosphoprotein. NS5A exists as hypo- and hyper-phosphorylated forms and the dynamic transitions between these two states are involved in the functions of NS5A. Hyperphosphorylation occurs primarily at six serine residues within the low complexity sequence I of NS5A. We previously showed that NS5A downregulates viral translation. In this study, we investigated the role of NS5A hyperphosphorylation in translation modulation. By analyzing the effects of phospho-ablative and phospho-mimetic mutants of the six serine residues on translation, we showed that NS5A hyperphospho-ablative mutation at all six serine residues can no longer downregulate viral translation. We then studied the effects of phospho-mutations at each of the six serine residues on translation. We found that phosphorylation of S222, S225, S235 is not involved in translation downregulation by NS5A. In contrast, NS5A with alanine mutations at S229 or S238 can no longer downregulate translation, whereas S229D or S238D mutations have no effect. Interestingly, S232D NS5A, but not S232A, abrogates translation downregulation by NS5A. Since dimerization of NS5A plays an important role in its functions, we also studied the effects of phospho-mutants of S229, S232, and S238 on dimerization in a protein-protein interaction assay. We showed that phopho-mimetic S229D or S238D mutations enhances NS5A dimerization, whereas the phospho-ablative mutations of these two residues have no effect. Neither phospho-ablative nor phopho-mimetic mutations of S232 affect dimerization. These results indicate that phosphorylation of NS5A at S229, S232, and S238 is involved in viral translation regulation and NS5A dimerization.

Overview of HCV Life Cycle with a Special Focus on Current and Possible Future Antiviral Targets

Hepatitis C infection is the leading cause of liver diseases worldwide and a major health concern that affects an estimated 3% of the global population. Novel therapies available since 2014 and 2017 are very efficient and the WHO considers HCV eradication possible by the year 2030. These treatments are based on the so-called direct acting antivirals (DAAs) that have been developed through research efforts by academia and industry since the 1990s. After a brief overview of the HCV life cycle, we describe here the functions of the different targets of current DAAs, the mode of action of these DAAs and potential future inhibitors.

Viral resistance in HCV infection

The introduction of new multi-genotypic direct acting antivirals (DAA) in clinical practice has revolutionized HCV treatment, permitting the achievement of >95% rates of sustained virological response in many patients. However, virological failures can occur particularly if the treatments are sub optimal and/or with too short duration. Failure is often associated with development of resistance. The wide genetic variability in terms of different genotypes and subtypes, together with the natural presence and/or easy development of resistance during treatment, are intrinsic characteristics of HCV that may affect the treatment outcome and the chances of achieving a virological cure. This review explores in detail the aspects of HCV innate and treatment-induced resistance to new interferon-free DAA regimens.

HCV Detection, Discrimination, and Genotyping Technologies

According to the World Health Organization (WHO), 71 million people were living with Hepatitis C virus (HCV) infection worldwide in 2015. Each year, about 399,000 HCV-infected people succumb to cirrhosis, hepatocellular carcinoma, and liver failure. Therefore, screening of HCV infection with simple, rapid, but highly sensitive and specific methods can help to curb the global burden on HCV healthcare. Apart from the determination of viral load/viral clearance, the identification of specific HCV genotype is also critical for successful treatment of hepatitis C. This critical review focuses on the technologies used for the detection, discrimination, and genotyping of HCV in clinical samples. This article also focuses on advantages and disadvantages of the reported methods used for HCV detection, quantification, and genotyping.

Performance of 6 HCV genotyping 9G test for HCV genotyping in clinical samples

Background

A treatment of HCV infection depends on the genotype and sub-genotype. Therefore, accurate HCV genotyping is critical for selecting the appropriate treatment regimen.

Method

This study included 280 plasma samples to evaluate the performance of 6 HCV Genotyping 9G test. The performance of 6 HCV Genotyping 9G test for accurate detection of HCV 1a, 1b, 2, 3, 4, and 6 genotypes was evaluated by comparing it with LiPA 2.0 assay and sequencing.

Results

6 HCV Genotyping 9G test and LiPA 2.0 assay demonstrated 83.9% (n = 235) agreement. 39/45 samples that showed discrepant results between the two tests were analyzed by sequencing. Sequencing genotyped 39 discrepant samples as 0 (HCV 1a), 24 (HCV 1b), 1 (HCV 6f), 12 (HCV 6i), and 2 (HCV-negative). Results of 6 HCV Genotyping 9G test were very similar to the sequencing as it detected 1, 23, 1, 12, and 2 samples as HCV 1a, 1b, 3 & 6a or 6f, 6i or 6n, and negative, respectively. However, LiPA 2.0 assay showed complete disagreement with sequencing, as it did not detect any of these 39 samples correctly. These results indicate that LiPA 2.0 assay has limitations in identifying HCV genotypes 1b, and 6. The sensitivity, specificity, PPV, and NPV of 6 HCV Genotyping 9G test were 99.5, 98.8, 99.5, and 98.8%, respectively. It is important to note that HCV Genotyping 9G test showed 98.3 and 100% sensitivity for HCV 1b and 6 genotyping, respectively. However, LiPA 2.0 assay demonstrated 57.9 and 71.7% sensitivity for these genotypes.

Conclusions

6 HCV Genotyping 9G test identifies HCV 1a, 1b, 2, 3, and 6 with good agreement with sequencing. Hence, 6 HCV Genotyping 9G test has a high clinical value because it can provide critical information to physicians and assist them to use the correct drug for efficient hepatitis C treatment.

Electronic supplementary material

The online version of this article (10.1186/s12985-018-1017-4) contains supplementary material, which is available to authorized users.

Epistatic Interactions in NS5A of Hepatitis C Virus Suggest Drug Resistance Mechanisms

Hepatitis C virus (HCV) causes a major health burden and can be effectively treated by direct-acting antivirals (DAAs). The non-structural protein 5A (NS5A), which plays a role in the viral genome replication, is one of the DAAs’ targets. Resistance-associated viruses (RAVs) harbouring NS5A resistance-associated mutations (RAMs) have been described at baseline and after therapy failure. A mutation from glutamine to arginine at position 30 (Q30R) is a characteristic RAM for the HCV sub/genotype (GT) 1a, but arginine corresponds to the wild type in the GT-1b; still, GT-1b strains are susceptible to NS5A-inhibitors. In this study, we show that GT-1b strains with R30Q often display other specific NS5A substitutions, particularly in positions 24 and 34. We demonstrate that in GT-1b secondary substitutions usually happen after initial R30Q development in the phylogeny, and that the chemical properties of the corresponding amino acids serve to restore the positive charge in this region, acting as compensatory mutations. These findings may have implications for RAVs treatment.

Highlights of the Structure-Activity Relationships of Benzimidazole Linked Pyrrolidines Leading to the Discovery of the Hepatitis C Virus NS5A Inhibitor Pibrentasvir (ABT-530)

Curative interferon and ribavirin sparing treatments for hepatitis C virus (HCV)-infected patients require a combination of mechanistically orthogonal direct acting antivirals. A shared component of these treatments is usually an HCV NS5A inhibitor. First generation FDA approved treatments, including the component NS5A inhibitors, do not exhibit equivalent efficacy against HCV virus genotypes 1-6. In particular, these first generation NS5A inhibitors tend to select for viral drug resistance. Ombitasvir is a first generation HCV NS5A inhibitor included as a key component of Viekira Pak for the treatment of patients with HCV genotype 1 infection. Since the launch of next generation HCV treatments, functional cure for genotype 1-6 HCV infections has been achieved, as well as shortened treatment duration across a wider spectrum of genotypes. In this paper, we show how we have modified the anchor, linker, and end-cap architecture of our NS5A inhibitor design template to discover a next generation NS5A inhibitor pibrentasvir (ABT-530), which exhibits potent inhibition of the replication of wild-type genotype 1-6 HCV replicons, as well as improved activity against replicon variants demonstrating resistance against first generation NS5A inhibitors.

Design, synthesis and identification of silicon-containing HCV NS5A inhibitors with pan-genotype activity

Modification of a HCV NS5A inhibitor, ombitasvir, led to the identification of 10d with improved pan-genotype NS5A inhibition and better pharmacokinetic properties. The key structural changes to ombitasvir include bioisosteric replacement of carbon with silicon atom. Compared with ombitasvir, the activity of anti-HCV genotypes (GT 1 to 6) of 10d is increased to some extent, especially the inhibitory activity against genotype 3a and 6a is increased by more than seven times, and the dog's in vivo pharmacokinetics properties were also superior to ombitasvir. Further drug evaluation showed that 10d was similar to ombitasvir on plasma protein binding and liver distribution profiles, with no cytotoxicity and no inhibitory effect on both CYP 450 and hERG ligand binding. However, permeability assay results indicated that 10d was not the substrate of P-gp or BCRP transporter, which is different from that of ombitasvir. The results of a 14-day repeat-dose toxicity study identified no toxicity with 10d. Our findings in preclinical tests suggest that the silicon-containing compound 10d could be worthy of continued study as a potential drug candidate.

Natural NS5A inhibitor resistance associated substitutions in hepatitis C virus genotype 1 infected patients from Italy

OBJECTIVES

Genetic variability in NS5A is associated with different levels of resistance to the currently licensed NS5A inhibitors. The aim of this study was to detect NS5A inhibitor resistance associated substitutions (RASs) in hepatitis C virus (HCV) genotype 1 (GT1) patients who are naive to direct-acting HCV antivirals.

METHODS

Amplification, Sanger sequencing and phylogenetic analysis of the HCV NS5A region were performed on plasma obtained from 122 consecutive patients with HCV chronic infection attending four different clinics in Italy.

RESULTS

NS5A inhibitor RASs were detected in 14/61 (23.0%) HCV GT1b and 3/61 (4.9%) HCV GT1a infected patients (p 0.007). The pan-genotypic RAS Y93H was detected in 1 (1.6%) GT1a and 4 (6.6%) GT1b patients. GT1a sequences clustered into two different clades with RASs detected in 1/34 (2.9%) clade I and 2/27 (7.4%) clade II sequences.

CONCLUSIONS

Although the impact of naturally occurring NS5A RASs might be limited with upcoming pan-genotypic treatment regimens, this information is still useful to map naturally occurring HCV variants in different geographic areas in the context of current HCV therapy.