Inhibition of the replication of hepatitis B virus in vitro by 2',3'-dideoxy-3'-thiacytidine and related analogues

Making new drugs the hard way

A new drug can have its origin in either pharma, biotech or academia. In general, discovery scientists working in pharma and biotech are advantaged over their academic counterparts and the relative advantages and disadvantages associated are discussed in depth. Against all odds, an increasing number of important drugs have had their origins in academia. This article reports three case studies from the Liotta Research Group (LRG), which explores the special circumstances that allowed these drug development campaigns to be successful. The first involves the antiretroviral agent, emtricitabine. In this case efficient synthetic methodology, developed in the LRG, coupled with some key university and commercial sector partnerships, enabled a group of academic collaborators to discover and develop a highly effective HIV reverse transcriptase inhibitor. The second case study involves the discovery and development of the breakthrough hepatitis C drug, sofosbuvir. Based on key input from Professors Schinazi and Liotta at Emory University, scientists at the Emory startup, Pharmasset, identified the nucleoside core of the drug that would become sofosbuvir. Subsequent analysis of its phosphorylation profile by Pharmasset scientists suggested that converting it to its corresponding monophosphate prodrug would circumvent a kinase block and enable it to be an effective hepatitis C polymerase inhibitor. The third case study describes the formation of DRIVE (Drug Innovation Ventures at Emory)/EIDD (Emory Institute for Drug Development), which were created to circumvent unintended impediments for carrying out academic drug discovery and development. Although DRIVE/EIDD is a wholly-owned, not-for-profit subsidiary of Emory University, it contains many attributes that enables it to operate much more nimbly than a typical academic laboratory. With an experienced drug development team and no shareholders to distract them, DRIVE/EIDD was able to focus its attention of the development of drugs to address viral diseases of global concern. In particular, their strategy to identify and develop an antiviral agent active against multiple single-stranded RNA viruses led to molnupiravir, a broadly active, oral drug that received Emergency Use Authorization for the treatment of SARS-CoV-2 infections (i.e., COVID-19).

Isolation and Characterization of Two Chalcone Derivatives with Anti-Hepatitis B Virus Activity from the Endemic Socotraen Dracaena cinnabari (Dragon’s Blood Tree)

Hepatitis B virus (HBV) infection is prevalent and continues to be a global health concern. In this study, we determined the anti-hepatitis B virus (HBV) potential of the Socotra-endemic medicinal plant Dracaena cinnabari and isolated and characterized the responsible constituents. A bioassay-guided fractionation using different chromatographic techniques of the methanolic extract of D. cinnabari led to the isolation of two chalcone derivatives. Using a variety of spectroscopic techniques, including ¹H-, ¹³C-, and 2D-NMR, these derivatives were identified as 2,4’-dihydroxy-4-methoxydihydrochalcone (compound 1) and 2,4’-dihydroxy-4-methoxyhydrochalcone (compound 2). Both compounds were isolated for the first time from the red resin (dragon’s blood) of D. cinnabari. The compounds were first evaluated for cytotoxicity on HepG2.2.15 cells and 50% cytotoxicity concentration (CC50) values were determined. They were then evaluated for anti-HBV activity against HepG2.2.15 cells by assessing the suppression of HBsAg and HBeAg production in the culture supernatants and their half maximum inhibitory concentration (IC₅₀) and therapeutic index (TI) values were determined. Compounds 1 and 2 indicated inhibition of HBsAg production in a dose- and time-dependent manner with IC₅₀ values of 20.56 and 6.36 μg/mL, respectively.

Microbial α-L-Rhamnosidases of Glycosyl Hydrolase Families GH78 and GH106 Have Broad Substrate Specificities toward α-L-Rhamnosyl- and α-L-Mannosyl-Linkages

α-L-Rhamnosidases (α-L-Rha-ases, EC 3.2.1.40) are glycosyl hydrolases (GHs) that hydrolyze a terminal α-linked L-rhamnose residue from a wide spectrum of substrates such as heteropolysaccharides, glycosylated proteins, and natural flavonoids. As a result, they are considered catalysts of interest for various biotechnological applications. α-L-rhamnose (6-deoxy-L-mannose) is structurally similar to the rare sugar α-L-mannose. Here we have examined whether microbial α-L-Rha-ases possess α-L-mannosidase activity by synthesizing the substrate 4-nitrophenyl α-L-mannopyranoside. Four α-L-Rha-ases from GH78 and GH106 families were expressed and purified from Escherichia coli cells. All four enzymes exhibited both α-L-rhamnosyl-hydrolyzing activity and weak α-L-mannosyl-hydrolyzing activity. SpRhaM, a GH106 family α-L-Rha-ase from Sphingomonas paucimobilis FP2001, was found to have relatively higher α-L-mannosidase activity as compared with three GH78 α-L-Rha-ases. The α-L-mannosidase activity of SpRhaM showed pH dependence, with highest activity observed at pH 7.0. In summary, we have shown that α-L-Rha-ases also have α-L-mannosidase activity. Our findings will be useful in the identification and structural determination of α-L-mannose-containing polysaccharides from natural sources for use in the pharmaceutical and food industries.

In Vitro and In Vivo Renoprotective Effects of Telbivudine in Chronic Hepatitis B Patients Receiving Nucleotide Analogue

AIM

Renal toxicity of adefovir disoproxil (ADV) and tenofovir disoproxil fumarate (TDF) is a significant concern in chronic hepatitis B (CHB) patients. Early observational clinical data suggested that telbivudine (LdT) might have renoprotective effects.

METHODS

In this prospective study, consecutive CHB patients on combined lamivudine (LAM) + ADV/TDF were switched to LdT + ADV/TDF at recruitment and were followed up for 24 months. Estimated glomerular filtration rate (eGFR) was calculated with the modification of diet in renal disease equation. The effects of LdT on cell viability and expression of kidney injury or apoptotic biomarkers were investigated in cultured renal tubular epithelial cell line HK-2.

RESULTS

Thirty-one patients (median age 55 years, 90.3% male) were recruited (54.8% TDF: 45.2% ADV). Serum HBV DNA was undetectable at all time points. Median eGFR was 70.2 (IQR 62.6-77.9) and 81.5 (IQR 63.6-99.1) mL/min/1.73 m² at baseline and 24 months, respectively (p < 0.001). Downstaging of chronic kidney disease was observed in eight (25.8%) patients and was more common in ADV-treated compared to TDF-treated patients (7/8 vs. 1/17, p = 0.011; OR 16, 95% CI 1.643-155.766, p = 0.017). In vitro data showed that adding LdT to ADV or TDF was associated with improved cell viability and lower expression of injury and apoptotic biomarkers compared with ADV or TDF alone. Treatment was prematurely discontinued in four(12.9%) patients due to myalgia.

CONCLUSIONS

Clinical and in vitro data suggest that LdT has renoprotective effects in patients on long-term ADV/TDF treatment. LdT may be considered as an adjuvant therapy in this special group of patients with renal impairment (NCT03778567).

hNTCP‑expressing primary pig hepatocytes are a valuable tool for investigating hepatitis B virus infection and antiviral drugs

Primary human hepatocytes (PHHs) are the 'gold standard' for investigating hepatitis B virus (HBV) infection and antiviral drugs. However, poor availability, variation between batches and ethical issues regarding PHHs limit their applications. The discovery of human sodium taurocholate co‑transporting polypeptide (hNTCP) as a functional HBV receptor has enabled the development of a surrogate model to supplement the use of PHHs. In the present study, the evolutionary distance of seven species was assessed based on single‑copy homologous genes. Based on the evolutionary distance and availability, PHHs and primary rabbit hepatocytes (PRHs) were isolated and infected with hNTCP‑recombinant lentivirus, and susceptibility to HBV infection in the two cell types was tested and compared. In addition, HBV infection efficiency of hNTCP‑expressing PPHs with pooled HBV‑positive serum and purified particles was determined. The potential use of HBV‑infected hNTCP‑expressing PPHs for drug screening was assessed. The results demonstrated that pigs and rabbits are closer to humans in the divergence tree compared with mice and rats, indicating that pigs and rabbits were more likely to facilitate the HBV post‑entry lifecycle. Following hNTCP complementation and HBV infection, PPHs and Huh7D human hepatocellular carcinoma cells, but not PRHs, exhibited increased hepatitis B surface antigen and hepatitis B e‑antigen secretion, covalently closed circular DNA formation and infectious particle secretion. hNTCP‑expressing PPHs were susceptible to infection with HBV particles purified from pooled HBV‑positive sera, but were poisoned by raw HBV‑positive sera. The use of HBV‑infected hNTCP‑expressing PPHs for viral entry inhibitor screening was revealed to be applicable and reproducible. In conclusion, hNTCP‑expressing PPHs may be valuable tool for investigating HBV infection and antiviral drugs.

Antiretroviral Effects on HBV/HIV Co-infection and the Natural History of Liver Disease

Hepatitis B virus (HBV) coinfection is common in persons with human immunodeficiency virus (HIV) infection, contributing significantly to morbidity and mortality. Many currently used HIV antiretroviral therapy (ART) regimens provide potent anti-HBV activity and it is recommended that HBV-HIV coinfected persons be treated with ART regimens containing tenofovir. ART has multiple benefits, including increasing rates of HBV clearance after initial infection and potent suppression of HBV DNA in chronic infection. Nevertheless, long-term studies have yet to demonstrate a profound positive impact of ART on HBV-related fibrosis progression and development of endstage liver disease.

Twenty-Five Years of Lamivudine: Current and Future Use for the Treatment of HIV-1 Infection

Supplemental Digital Content is Available in the Text.

Innovation in medicine is a dynamic, complex, and continuous process that cannot be isolated to a single moment in time. Anniversaries offer opportunities to commemorate crucial discoveries of modern medicine, such as penicillin (1928), polio vaccination (inactivated, 1955; oral, 1961), the surface antigen of the hepatitis B virus (1967), monoclonal antibodies (1975), and the first HIV antiretroviral drugs (zidovudine, 1987). The advent of antiretroviral drugs has had a profound effect on the progress of the epidemiology of HIV infection, transforming a terminal, irreversible disease that caused a global health crisis into a treatable but chronic disease. This result has been driven by the success of antiretroviral drug combinations that include nucleoside reverse transcriptase inhibitors such as lamivudine. Lamivudine, an L-enantiomeric analog of cytosine, potently affects HIV replication by inhibiting viral reverse transcriptase enzymes at concentrations without toxicity against human polymerases. Although lamivudine was approved more than 2 decades ago, it remains a key component of first-line therapy for HIV because of its virological efficacy and ability to be partnered with other antiretroviral agents in traditional and novel combination therapies. The prominence of lamivudine in HIV therapy is highlighted by its incorporation in recent innovative treatment strategies, such as single-tablet regimens that address challenges associated with regimen complexity and treatment adherence and 2-drug regimens being developed to mitigate cumulative drug exposure and toxicities. This review summarizes how the pharmacologic and virologic properties of lamivudine have solidified its role in contemporary HIV therapy and continue to support its use in emerging therapies.

Genetic Factors That Affect Spontaneous Clearance of Hepatitis C or B Virus, Response to Treatment, and Disease Progression

Hepatitis C virus (HCV) and hepatitis B virus (HBV) infections can lead to cirrhosis, end-stage liver disease, and hepatocellular carcinoma. Over the past decade, studies of individuals infected with these viruses have established genetic associations with the probability of developing a chronic infection, risk of disease progression, and likelihood of treatment response. We review genetic and genomic methods that have been used to study risk of HBV and HCV infection and patient outcomes. For example, genome-wide association studies have linked a region containing the interferon lambda genes to spontaneous and treatment-induced clearance of HCV. We review the genetic variants associated with HCV and HBV infection, and how these variants affect specific expression or activities of their products. Further studies of these variants could provide insights into risk factors for and mechanisms of chronic infection and disease progression, as well as new strategies for treatment.

Sirtuin 2 Isoform 1 Enhances Hepatitis B Virus RNA Transcription and DNA Synthesis through the AKT/GSK-3β/β-Catenin Signaling Pathway

Sirtuin 2 (Sirt2), a NAD⁺-dependent protein deacetylase, is overexpressed in many hepatocellular carcinomas (HCCs) and can deacetylate many proteins, including tubulins and AKT, prior to AKT activation. Here, we found that endogenous Sirt2 was upregulated in wild-type hepatitis B virus (HBV WT)-replicating cells, leading to tubulin deacetylation; however, this was not the case in HBV replication-deficient-mutant-transfected cells and 1.3-mer HBV WT-transfected and reverse transcriptase inhibitor (entecavir or lamivudine)-treated cells, but all HBV proteins were expressed. In HBV WT-replicating cells, upregulation of Sirt2 induced AKT activation, which consequently downregulated glycogen synthase kinase 3β (GSK-3β) and increased β-catenin levels; however, downregulation of Sirt2 in HBV-nonreplicating cells impaired AKT/GSK-3β/β-catenin signaling. Overexpression of Sirt2 isoform 1 stimulated HBV transcription and consequently HBV DNA synthesis, which in turn activated AKT and consequently increased β-catenin levels, possibly through physical interactions with Sirt2 and AKT. Knockdown of Sirt2 by short hairpin RNAs (shRNAs), inhibition by 2-cyano-3-[5-(2,5-dichlorophenyl)-2-furanyl]-N-5-quinolinyl-2-propenamide (AGK2), or dominant negative mutant expression inhibited HBV replication, reduced AKT activation, and decreased β-catenin levels. Through HBV infection, we demonstrated that Sirt2 knockdown inhibited HBV replication from transcription. Although HBx itself activates AKT and upregulates β-catenin, Sirt2-mediated signaling and upregulated HBV replication were HBx independent. Since constitutively active AKT inhibits HBV replication, the results suggest that upregulated Sirt2 and activated AKT may balance HBV replication to prolong viral replication, eventually leading to the development of HCC. Also, the results indicate that Sirt2 inhibition may be a new therapeutic option for controlling HBV infection and preventing HCC.IMPORTANCE Even though Sirt2, a NAD⁺-dependent protein deacetylase, is overexpressed in many HCCs, and overexpressed Sirt2 promotes hepatic fibrosis and associates positively with vascular invasion by primary HCCs through AKT/GSK-3β/β-catenin signaling, the relationship between Sirt2, HBV, HBx, and/or HBV-associated hepatocarcinogenesis is unclear. Here, we show that HBV DNA replication, not HBV expression, correlates positively with Sirt2 upregulation and AKT activation. We demonstrate that overexpression of Sirt2 further increases HBV replication, increases AKT activation, downregulates GSK-3β, and increases β-catenin levels. Conversely, inhibiting Sirt2 decreases HBV replication, reduces AKT activation, and decreases β-catenin levels. Although HBx activates AKT to upregulate β-catenin, Sirt2-mediated effects were not dependent on HBx. The results also indicate that a Sirt2 inhibitor may control HBV infection and prevent the development of hepatic fibrosis and HCC.

Heat shock protein 70 and heat shock protein 90 synergistically increase hepatitis B viral capsid assembly

Hepatitis B virus (HBV) infection can cause chronic liver diseases, cirrhosis, and hepatocellular carcinoma (HCC). Heat shock proteins (Hsps) are important factors in the formation of the HBV capsid and in genome replication during the viral life cycle. Hsp90 is known to promote capsid assembly. However, the functional roles of Hsp70 in HBV capsid assembly with Hsp90 have not been studied so far. Using microscale thermophoresis analyses and in vitro nucleocapsid formation assays, we found that Hsp70 bound to a HBV core protein dimer and facilitated HBV capsid assembly. Inhibition of Hsp70 by methylene blue (MB) led to a decrease in capsid assembly. Moreover, Hsp70 inhibition reduced intracellular capsid formation and HBV virus particle number in HepG2.2.15 cells. Furthermore, we examined synergism between Hsp70 and Hsp90 on HBV capsid formation in vitro. Our results clarify the role of Hsp70 in HBV capsid formation via an interaction with core dimers and in synergistically promoting capsid assembly with Hsp90.

The evolution of nucleoside analogue antivirals: A review for chemists and non-chemists. Part 1: Early structural modifications to the nucleoside scaffold

This is the first of two invited articles reviewing the development of nucleoside-analogue antiviral drugs, written for a target audience of virologists and other non-chemists, as well as chemists who may not be familiar with the field. Rather than providing a simple chronological account, we have examined and attempted to explain the thought processes, advances in synthetic chemistry and lessons learned from antiviral testing that led to a few molecules being moved forward to eventual approval for human therapies, while others were discarded. The present paper focuses on early, relatively simplistic changes made to the nucleoside scaffold, beginning with modifications of the nucleoside sugars of Ara-C and other arabinose-derived nucleoside analogues in the 1960's. A future paper will review more recent developments, focusing especially on more complex modifications, particularly those involving multiple changes to the nucleoside scaffold. We hope that these articles will help virologists and others outside the field of medicinal chemistry to understand why certain drugs were successfully developed, while the majority of candidate compounds encountered barriers due to low-yielding synthetic routes, toxicity or other problems that led to their abandonment.

WITHDRAWN: Cetylpyridinium chloride as a novel inhibitor of hepatitis B viral capsid assembly

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New and bioactive natural products from an endophyte of Panax notoginseng

Secondary metabolites with cytotoxic activity, antiviral activity and antimicrobial activity from the endophytic fungi of Panax notoginseng.

Strategies for Antiviral Drug Discovery

The need for antiviral drugs is growing rapidly as more viral diseases are recognized. The methods used to discover these drugs have evolved considerably over the past 40 years and the overall process of discovery can be broken down into sub-processes which include lead generation, lead optimization and lead development. Various methods are now employed to ensure these processes are carried out efficiently. For lead generation, screening methodologies have developed to the extent where hundreds of thousands of compounds can be screened against a particular target. An alternative approach is to use the structures of enzyme substrates as a starting point for drug discovery. Much use is now made of X-ray crystallographic data of target–inhibitor complexes for the optimization of lead structures, and methods for preparing libraries of compounds to assist both generation and optimization of leads are welldeveloped. The methods used to predict and improve the pharmacokinetic properties of compounds are also changing rapidly. Finally, novel approaches to antiviral therapy using oligonucleotide-based compounds or modulating the host immune response are also being explored. This review discusses these approaches, provides examples of where their application has been successful and sets them against a historical background.

Discovery and Development of the Anti-Human Immunodeficiency Virus Drug, Emtricitabine (Emtriva, FTC)

The HIV/AIDS epidemic, which was first reported on in 1981, progressed in just 10 years to a disease afflicting 10 million people worldwide including 1 million in the US. In 1987, AZT was approved for treating HIV/AIDS. Unfortunately, its clinical usefullness was severly limited by associated toxicities and the emergence of resistance. Three other drugs that were approved in the early 1990s suffered from similar liabilities. In 1990, the Liotta group at Emory University developed a highly diastereoselective synthesis of racemic 3'-thia-2',3'-dideoxycytidine and 3'-thia-2',3'-5-fluorodideoxycytidine and demonstrated that these compounds exhibited excellent anti-HIV activity with no apparent cytotoxicity. Subsequently, the enantiomers of these compounds were separated using enzyme-mediated kinetic resolutions and their (-)-enantiomers (3TC and FTC, respectively) were found to have exceptionally attractive preclinical profiles. In addition to their anti-HIV activity, 3TC and FTC potently inhibit the replication of hepatitis B virus. The development of FTC, which was being carried out by Burroughs Wellcome, had many remarkable starts and stops. For example, passage studies indicated that the compound rapidly selected for a single resistant mutant, M184V, and that this strain was 500-1000-fold less sensitive to FTC than was wild-type virus. Fortunately, it was found that combinations of AZT with either 3TC or FTC were synergistic. The effectiveness of AZT-3TC combination therapy was subsequently demonstrated in four independent clinical trials, and in 1997, the FDA approved Combivir, a fixed dose combination of AZT and 3TC. In phase 1 clinical trials, FTC was well tolerated by all subjects with no adverse events observed. However, the development of FTC was halted by the aquistition of Wellcome PLC by Glaxo PLC in January 1995. In 1996, Triangle Pharmaceuticals licensed FTC from Emory and initiated a series of phase I/II clinical studies that demonstrated the safety and efficacy of the drug. In August 1998, FTC was granted "Fast Track" status, based primarily on its potential for once daily dosing. While the outcomes of two subsequent phase III trials were positive, a third phase III clinical trial involving combinations of 3TC or FTC with stavudine and neviripine had to be terminated due to serious liver-related adverse events. Although analysis of the data suggested that the liver toxicity was due to neviripine, the FDA decided that the study could not be used for drug registration. Ultimately, in January 2003, Gilead Sciences acquired Triangle Pharmaceuticals and completed the development of FTC (emtricitabine), which was approved for once a day, oral administration in July 2003. A year later, Truvada, a once a day, oral, fixed dose combination of emtricitabine and tenofovir disoproxyl fumarate received FDA approval and quickly became the accepted first line therapy when used with a third antiretroviral agent. In July 2006, the FDA approved Atripla, a once a day, oral, fixed dose combination of emtricitabine, tenofovir disoproxyl fumarate, and efavirenz, which represented the culmination of two decades of research that had transformed AIDS from a death sentence to a manageable chronic disease.

Therapy of HIV Infection: Current Approaches and Prospects

The human immunodeficiency virus type 1 (HIV-1) is the causative agent of one of the most dangerous human diseases - the acquired immune deficiency syndrome (AIDS). Over the past 30 years since the discovery of HIV-1, a number of antiviral drugs have been developed to suppress various stages of the HIV-1 life cycle. This approach has enables the suppression of virus replication in the body, which significantly prolongs the life of HIV patients. The main downside of the method is the development of viral resistance to many anti-HIV drugs, which requires the creation of new drugs effective against drug-resistant viral forms. Currently, several fundamentally new approaches to HIV-1 treatment are under development, including the use of neutralizing antibodies, genome editing, and blocking an integrated latent provirus. This review describes a traditional approach involving HIV-1 inhibitors as well as the prospects of other treatment options.

Absolute Configuration of the Antiviral Agent (−)-cis-5-Fluoro-1-[2-Hydroxymethyl)-1,3-Oxathiolan-5-yl]Cytosine

The structure and absolute configuration of (−)- cis-5-fluoro-1-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl]cytosine (FTC), has been determined by X-ray crystallographic analysis. The results confirm that the L-isomer of the nucleoside analogue is the most active enantiomer and that the correct absolute configuration of (−)-FTC is 5-fluoro-(2′R,5′S)-(−)-1-[2-hydroxymethyl)oxathiolan-5-yl]-fluorocytosine. The two molecules in the asymmetric unit show conformations that combine conformational features of two other classes of potent antiviral nucleosides. Both oxathiolane rings have the 3′-sulphur atom in nearly perfect S3′- exo envelope conformations, similar to what is observed for 3′-azido-3′-deoxythymidine (AZT) and 2′,3′-dideoxycytidine. One of the two molecules has a glycosylic link conformation in which the base is eclipsed with the C5′-O1′ bond. This mimics the high- anti conformation that has been observed in the structures of several 2′,3′-didehydro-2′,3′-dideoxypyrimidine nucleosides but is inaccessible for saturated pyrimidine nucleosides. However, the observed conformations cannot be superimposed adequately with other active antiviral nucleosides to suggest a common ‘active site’ conformation.

Comparative Pharmacokinetics of Racivir®, (±)-β-2′,3′-Dideoxy-5-Fluoro-3′-Thiacytidine in Rats, Rabbits, Dogs, Monkeys and HIV-Infected Humans

Racivir® is a 50:50 racemic mixture of the (–)- and (+)-β-enantiomers of 2′-deoxy-3′-thia-5-fluorocytosine (FTC), which is being developed for the treatment of HIV and hepatitis B virus (HBV). The (+)-enantiomer of FTC is approximately 10–20-fold less potent than (–)-FTC, but it selects for a different HIV mutation in human lymphocytes. Plasma concentrations from a group of 54 rats, 12 pregnant rabbits and 60 dogs enrolled in large toxicity studies using a wide variety of oral doses, were compared using non-compartment pharmacokinetic modelling versus dose, treatment duration, species and gender. The pharmacokinetics of Racivir® were also compared with those of a previously published pharmacokinetic study in rhesus monkeys and with data from HIV-infected human male volunteers. The (+)-FTC, but not the (–)-enantiomer, can be deaminated to the non-toxic inactive metabolite (+)-FTU. Therefore, the plasma exposure to (+)-FTU was also determined. The order of relative plasma exposure to (+)-FTU was rhesus monkeys > humans > pregnant rabbits > dogs > rats. Allometric scaling was performed to relate systemic clearance/fraction of drug absorbed (Cl/F) and terminal phase volume of distribution (Vβ/F) versus species body weights. No individual animal species mimicked the Cl/F values in humans. However, allometric scaling using a combination of rats, pregnant rabbits and monkeys predicted the mean human Cl/F value better than a combination of rats and rabbits only (within 0.24 and SD of mean vs 0.81 SD of the observed mean value). Similarly, human Vβ/F values were best predicted using a combination of rat and monkey data (within 0.64 SD of mean value). Species demonstrating greater deamination to (+)-FTU tended to have greater than predicted Cl/F values. The Cmax values of dogs were the closest to humans, but were statistically different. This study highlights the importance of selecting animal species that demonstrate similar cytidine deaminase activity to humans when performing preclinical dosing studies on Racivir® other antiviral agents that are substrates for mammalian cytidine deaminases.

The Effect of Absolute Configuration on the Anti-HIV and Anti-HBV Activity of Nucleoside Analogues

This review concerns the effect of stereoisomerism on the selective activity of anti-HIV and anti-HBV nucleoside analogues.

The synthesis of a number of nucleoside analogues with anti-HIV and anti-HBV activity yields mixtures of 1-β-D and 1-β-L stereoisomers. Anti-HIV and anti-HBV activity is associated primarily with one of the two enantiomers and the more potent activity does not always reside with the 1-β-D configuration characteristic of natural nucleosides. In the case of HIV, the origin of this stereoselectivity appears to be the result of differential metabolism of the analogues and not due to differential inhibition of the target enzyme; the HIV reverse transcriptase. However, mutations at position 184 of the HIV-RT does result in stereoselective inhibition of the enzyme. On the other hand, with HBV, there is also a stereoselective inhibition of the HBV DNA polymerase, where the 5′-triphosphate of the 1-β-L enantiomer is the more potent inhibitor.

Synthesis and anti-HIV-1 Activity of [1-[2′,5′-Bis-O-(Tert-Butyldimethylsilyl)-β-L-Ribofuranosyl]Thymine]-3′-Spiro-5″-(4″-Amino-1″,2″-Oxathiole-2″,2″-Dioxide) (L-TSAO-T), the L-enantiomer of the Highly Specific HIV-1 Reverse Transcriptase Inhibitor TSAO-T

The L-isomer of the potent HIV-1-RT inhibitor TSAO-T has been stereospecifically synthesized and tested for its ‘ in vitro’ antiretroviral activity against HIV-1. Unlike the D-isomer, the L-isomer did not show appreciable inhibition of HIV-1 replication. The cytotoxicity was comparable with the cytotoxicity of the D-enantiomer.

Preventive effects of a major component of green tea, epigallocathechin-3-gallate, on hepatitis-B virus DNA replication

BACKGROUND

Hepatitis B virus infection is one of the major world health problems. Epigallocatechin-3 gallate is the major component of the polyphenolic fraction of green tea and it has an anti-viral, anti-mutagenic, anti- tumorigenic, anti-angiogenic, anti-proliferative, and/or pro-apoptotic effects on mammalian cells. In this study, our aim was to investigate the inhibition of HBV replication by epigallocatechin-3 gallate in the Hep3B2.1-7 hepatocellular carcinoma cell line.

MATERIALS AND METHODS

HBV-replicating Hep3B2.1-7 cells were used to investigate the preventive effects of epigallocatechin-3 gallate on HBV DNA replication. The expression levels of HBsAg and HBeAg were determined using ELISA. Quantitative real-time-PCR was applied for the determination of the expression level of HBV DNA.

RESULTS

Cytotoxicity of epigallocathechin-3-gallate was not observed in the hepatic carcinoma cell line when the dose was lower than 100 μM. The ELISA method demonstrated that epigallocatechin-3 gallate have strong effects on HBsAg and HBeAg levels. Also it was detected by real-time PCR that epigallocatechin-3 gallate could prevent HBV DNA replication.

CONCLUSIONS

The obtained data pointed out that although the exact mechanism of HBV DNA replication and related diseases remains unclear, epigallocatechin-3 gallate has a potential as an effective anti-HBV agent with low toxicity.

Hepatitis B virus therapy: What’s the future holding for us?

Hepatitis B is one of the leading causes of liver cancer worldwide and unfortunately the number of people affected with hepatitis B virus (HBV) infection is still on the rise. Although the HBV has been known to cause fatal illness since decades but the population effected by this lethal virus have still only a few options for its management. The major treatment strategies include interferons and nucleos(t)ide analogues. These agents have so far produced unsatisfactory results in terms of complete virus eradication. Interferons cannot be used for long term therapy because of their potential side effects. Prolong treatment with nucleos(t)ide analogues has also been reported to cause serious side effects besides the increasing resistance by the virus. The need for new innovative solutions for treatment of HBV has been realized by global research institutes and pharmaceutical industry. Present review focuses in detail on the new ideas that are being transformed into therapeutic tools for use as future therapies in HBV infection. Modern drug designing and screening methods have made the drug discovery process shorter and more reliable. HBV therapeutics will take a new turn in coming years owing to these intelligent drug designing and screening methods. Future therapy of HBV is aiming to include the use of vaccines (both prophylactic and therapeutic), immunomodulators such as antibodies, non-nucleoside antivirals such as RNAi and inhibitors of viral life cycle.

Detectability and clinical significance of serum hepatitis B virus ribonucleic acid

Serum hepatitis B virus (HBV) RNA is detected during treatment with nucleoside analogue as a consequence of interrupted reverse transcription (RT) and unaffected replicative intermediates. The presence of serum HBV RNA in chronic HBV patients is confirmed by using ribonuclease digestion. Serum HBV RNA is differentially inhibited by interferon, but not by nucleoside analogue. The inhibitory effect of interferon on HBV RNA replicative intermediates may potentiate the suppression of HBV replication. Clinical significance of serum HBV RNA includes: (I) reflect the antiviral potency of nucleoside analogue; (II) predictor of early emergence of viral mutation during lamivudine therapy; (III) independently predict initial virologic response or earlier HBV suppression during nucleoside analogue therapy; (IV) predict HBV reactivation after discontinuation of nucleoside analogue. Thus, serum HBV RNA might be useful to optimize treatment efficacy in patients with chronic HBV, including shifting of oral antivirals or conversion to immunomodulatory agent i.e., interferon. Furthermore, serum HBV RNA levels correlate better with serum quantitative HBsAg (qHBsAg) than with serum HBV DNA levels. The predictive role of serum HBV RNA in long-term treatment effects of nucleoside analogue needs further study.

Modulation of the unfolded protein response by the human hepatitis B virus

During productive viral infection the host cell is confronted with synthesis of a vast amount of viral proteins which must be folded, quality controlled, assembled and secreted, perturbing the normal function of the endoplasmic reticulum (ER). To counteract the ER stress, cells activate specific signaling pathways, designated as the unfolded proteins response (UPR), which essentially increase their folding capacity, arrest protein translation, and degrade the excess of misfolded proteins. This cellular defense mechanism may, in turn, affect significantly the virus life-cycle. This review highlights the current understanding of the mechanisms of the ER stress activation by Human Hepatitis B virus (HBV), a deadly pathogen affecting more than 350 million people worldwide. Further discussion addresses the latest discoveries regarding the adaptive strategies developed by HBV to manipulate the UPR for its own benefits, the controversies in the field and future perspectives.

Molecular virology of hepatitis B virus and targets for antiviral intervention

The members of the viral family Hepadnaviridae comprise one of the smallest enveloped DNA viruses and cause acute and chronic infections in mammals and birds, leading to large virus and antigen loads in the blood. They have a restricted host range and depend on differentiated hepatocytes for replication. Hepatitis B virus (HBV) is the prototype of the Hepadnaviridae. HBV can persist in infected hepatocytes and has evolved elaborate strategies to evade the immune system. HBV replicates like HIV (family of Retroviridae) via reverse transcription. Drugs licensed for inhibition of HIV reverse transcriptase lower the viral load of chronic HBV patients, but they do not cure the infection. HBV genomes are archived in the nucleus of hepatocytes as episomal DNA before reverse transcription. In contrast, the RNA genome of HIV first needs reverse transcription before proviral integration within the host genome. Wild-type HBV remains relatively stable in chronic HBV patients during the immunotolerant state, but is able to evolve mutants rapidly upon selective pressure due to therapy or immune reactions. Current therapies for chronic hepatitis B are far from optimal. To extend therapeutic options, further studies on HBV and its interaction with the host are urgently needed.

On-treatment low serum HBV RNA level predicts initial virological response in chronic hepatitis B patients receiving nucleoside analogue therapy

BACKGROUND

Serum HBV RNA is detectable during nucleoside/nucleotide analogue therapy as a result of unaffected RNA replicative intermediates or interrupted reverse transcription. We studied the predictive value of serum HBV RNA for initial virological response during nucleoside analogue therapy.

METHODS

Serum HBV RNA was quantified before and at 12 and 24 weeks of lamivudine or entecavir therapy. Serum HBV DNA was measured every 4-12 weeks during treatment to define initial virological response.

RESULTS

Serum HBV RNA was detectable in 21 of 52 (40%) consecutive patients with a mean of 5.2 log copies/ml (male/female 35/17, mean age of 60 years with a range of 31-82, 44% HBeAg-positive, and 26 with lamivudine and 26 with entecavir) before treatment. Serum HBV RNA level at week 12 in patients with an interval from detectable to undetectable serum HBV DNA level <16 weeks was significantly lower than those with an interval ≥16 weeks (3.8 ±3.8 versus 6.6 ±3.5 log copies/ml, P=0.013). After adjustment for serum HBV DNA level at week 12, serum quantatitive HBsAg level at week 12 and pretreatment ALT level, low serum HBV RNA level at week 12 predicted a shorter interval to undetectable serum HBV DNA level (adjusted hazard ratio =0.908, 95% CI 0.829, 0.993, P=0.035).

CONCLUSIONS

Low serum HBV RNA level at week 12 of nucleoside analogue therapy independently predicts initial virological response in treated chronic hepatitis B patients. Serum HBV RNA levels may thus be useful for optimizing treatment of chronic hepatitis B.

Anti-viral therapy to reduce recurrence and improve survival in hepatitis B virus-related hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common malignancy and the third leading cause of cancer death worldwide. Chronic infection with hepatitis B virus (HBV) and hepatitis C virus accounts for approximately 75%-80% of HCC cases worldwide. In particular, chronic HBV infection is a predominant risk factor for HCC in Asia and Africa. Hepatic resection and radiofrequency ablation are increasingly used for the curative treatment of HCC, and good local control can be achieved. However, the high rate of recurrence is a major obstacle to improving prognosis. A high viral load of HBV DNA is the most important correctable risk factor for recurrence. Furthermore, interferon and/or nucleotide analogues may decrease HBV DNA. Therefore, these drugs may decrease recurrence. In this article, treatment strategies for HBV-related HCC are described in order to reduce recurrence and improve survival.

Anti-hepatitis B activity of isoquinoline alkaloids of plant origin

Hepatitis B virus (HBV) is the causative agent of B-type hepatitis in humans, a vaccine-preventable disease. Despite the availability of effective vaccines, globally, 2 billion people show evidence of past or current HBV infection, of which 350 million people are persistently infected, with an estimated annual increase of 1 million. There is no cure for chronic HBV infections, which are associated with cirrhotic liver failure and with an increased risk of developing hepatocellular carcinoma. Hepatitis antiviral research has focused primarily on the development of inhibitors of viral polymerase through the use of nucleoside analogues. Therefore, there is an urgent need for the development of non-nucleoside compounds to be used as an alternative or to complement the current therapy. To address this need, 18 isoquinoline alkaloids were evaluated for their potential antiviral activity against HBV in vitro.

How academic labs can approach the drug discovery process as a way to synergize with big pharma

While the pharmaceutical industry is facing highly challenging times, the academic drug discovery sector has the potential to contribute meaningfully to the discovery of novel drug targets and to the development of new mode-of-action therapeutics against a range of diseases, including rare and neglected diseases.

Effects of substitutions at the 4' and 2 positions on the bioactivity of 4'-ethynyl-2-fluoro-2'-deoxyadenosine

Nucleos(t)ide reverse transcriptase inhibitors (NRTIs) form the backbone of most anti-HIV therapies. We have shown that 4'-ethynyl-2-fluoro-2'-deoxyadenosine (EFdA) is a highly effective NRTI; however, the reasons for the potent antiviral activity of EFdA are not well understood. Here, we use a combination of structural, computational, and biochemical approaches to examine how substitutions in the sugar or adenine rings affect the incorporation of dA-based NRTIs like EFdA into DNA by HIV RT and their susceptibility to deamination by adenosine deaminase (ADA). Nuclear magnetic resonance (NMR) spectroscopy studies of 4'-substituted NRTIs show that ethynyl or cyano groups stabilize the sugar ring in the C-2'-exo/C-3'-endo (north) conformation. Steady-state kinetic analysis of the incorporation of 4'-substituted NRTIs by RT reveals a correlation between the north conformation of the NRTI sugar ring and efficiency of incorporation into the nascent DNA strand. Structural analysis and the kinetics of deamination by ADA demonstrate that 4'-ethynyl and cyano substitutions decrease the susceptibility of adenosine-based compounds to ADA through steric interactions at the active site. However, the major determinant for decreased susceptibility to ADA is the 2-halo substitution, which alters the pKa of N1 on the adenine base. These results provide insight into how NRTI structural attributes affect their antiviral activities through their interactions with the RT and ADA active sites.

An efficient antiviral strategy for targeting hepatitis B virus genome using transcription activator-like effector nucleases

The hepatitis B virus (HBV) is a DNA virus that can cause chronic hepatitis B (CHB) in humans. Current therapies for CHB infection are limited in efficacy and do not target the pre-existing viral genomic DNA, which are present in the nucleus as a covalently closed circular DNA (cccDNA) form. The transcription activator-like (TAL) effector nucleases (TALENs) are newly developed enzymes that can cleave sequence-specific DNA targets. Here, TALENs targeting the conserved regions of the viral genomic DNA among different HBV genotypes were constructed. The expression of TALENs in Huh7 cells transfected with monomeric linear full-length HBV DNA significantly reduced the viral production of HBeAg, HBsAg, HBcAg, and pgRNA, resulted in a decreased cccDNA level and misrepaired cccDNAs without apparent cytotoxic effects. The anti-HBV effect of TALENs was further demonstrated in a hydrodynamic injection-based mouse model. In addition, an enhanced antiviral effect with combinations of TALENs and interferon-α (IFN-α) treatment was observed and expression of TALENs restored HBV suppressed IFN-stimulated response element-directed transcription. Taken together, these data indicate that TALENs can specifically target and successfully inactivate the HBV genome and are potently synergistic with IFN-α, thus providing a potential therapeutic strategy for treating CHB infection.

Medical virology of hepatitis B: how it began and where we are now

Infection with hepatitis B virus (HBV) may lead to acute or chronic hepatitis. HBV infections were previously much more frequent but there are still 240 million chronic HBV carriers today and ca. 620,000 die per year from the late sequelae liver cirrhosis or hepatocellular carcinoma. Hepatitis B was recognized as a disease in ancient times, but its etiologic agent was only recently identified. The first clue in unraveling this mystery was the discovery of an enigmatic serum protein named Australia antigen 50 years ago by Baruch Blumberg. Some years later this was recognized to be the HBV surface antigen (HBsAg). Detection of HBsAg allowed for the first time screening of inapparently infected blood donors for a dangerous pathogen. The need to diagnose clinically silent HBV infections was a strong driving force in the development of modern virus diagnostics. HBsAg was the first infection marker to be assayed with a highly sensitive radio immune assay. HBV itself was among the first viruses to be detected by assay of its DNA genome and IgM antibodies against the HBV core antigen were the first to be selectively detected by the anti-μ capture assay. The cloning and sequencing of the HBV genome in 1978 paved the way to understand the viral life cycle, and allowed development of efficient vaccines and drugs. Today’s hepatitis B vaccine was the first vaccine produced by gene technology. Among the problems that still remain today are the inability to achieve a complete cure of chronic HBV infections, the recognition of occult HBV infections, their potential reactivation and the incomplete protection against escape mutants and heterologous HBV genotypes by HBV vaccines.

Efficient asymmetric synthesis of lamivudine via enzymatic dynamic kinetic resolution

The anti-HIV nucleoside lamivudine was asymmetrically synthesized in only three steps via a novel surfactant-treated subtilisin Carlsberg-catalyzed dynamic kinetic resolution protocol.

Effects of OCT2 c.602C > T genetic variant on the pharmacokinetics of lamivudine

1. The renal excretion of organic cation drugs, including lamivudine, is mostly mediated by OCT2 in vitro. To date, three putatively relevant single nucleotide polymorphisms (SNPs), including c.596C > T (p.Thr199Ile), c.602C > T (p.Thr201Met), and c.808G > T (p.Ala270Ser) have been observed in Asians. The effects of the SLC22A2 c.602C > T genetic variant on the pharmacokinetics of lamivudine were studied with healthy Korean subjects. 2. Nineteen healthy subjects carrying either the SLC22A2 c.602CC (n = 12) or c.602CT (n = 7) genotype volunteered for this study. A single 100 mg dose of lamivudine was orally administered to each subject. Blood samples were collected for up to 24 h and the plasma concentrations of lamivudine were measured using liquid chromatography-tandem mass spectrometry. 3. The mean plasma concentration-time profiles of lamivudine in the c.602CC and c.602CT genotype groups were similar. There was no significant difference in the overall pharmacokinetic parameters of lamivudine between the c.602CC and c.602CT genotype groups. Differences in renal clearance and tubular secretion clearance were also not statistically significant between the two genotype groups. 4. The SLC22A2 c.602C > T genotype did not affect the pharmacokinetics of lamivudine in humans in vivo. Dose adjustment of lamivudine is not required between individuals with c.602CC and c.602CT genotypes.

Development of novel sugar isomerases by optimization of active sites in phosphosugar isomerases for monosaccharides

Phosphosugar isomerases can catalyze the isomerization of not only phosphosugar but also of monosaccharides, suggesting that the phosphosugar isomerases can be used as sugar isomerases that do not exist in nature. Determination of active-site residues of phosphosugar isomerases, including ribose-5-phosphate isomerase from Clostridium difficile (CDRPI), mannose-6-phosphate isomerase from Bacillus subtilis (BSMPI), and glucose-6-phosphate isomerase from Pyrococcus furiosus (PFGPI), was accomplished by docking of monosaccharides onto the structure models of the isomerases. The determinant residues, including Arg133 of CDRPI, Arg192 of BSMPI, and Thr85 of PFGPI, were subjected to alanine substitutions and found to act as phosphate-binding sites. R133D of CDRPI, R192 of BSMPI, and T85Q of PFGPI displayed the highest catalytic efficiencies for monosaccharides at each position. These residues exhibited 1.8-, 3.5-, and 4.9-fold higher catalytic efficiencies, respectively, for the monosaccharides than the wild-type enzyme. However, the activities of these 3 variant enzymes for phosphosugars as the original substrates disappeared. Thus, R133D of CDRPI, R192 of BSMPI, and T85Q of PFGPI are no longer phosphosugar isomerases; instead, they are changed to a d-ribose isomerase, an l-ribose isomerase, and an l-talose isomerase, respectively. In this study, we used substrate-tailored optimization to develop novel sugar isomerases which are not found in nature based on phosphosugar isomerases.

Direct acting antivirals for the treatment of chronic viral hepatitis

The development and evaluation of antiviral agents through carefully designed clinical trials over the last 25 years have heralded a new dawn in the treatment of patients chronically infected with the hepatitis B and C viruses, but not so for the D virus (HBV, HCV, and HDV). The introduction of direct acting antivirals (DDAs) for the treatment of HBV carriers has permitted the long-term use of these compounds for the continuous suppression of viral replication, whilst in the case of HCV in combination with the standard of care [SOC, pegylated interferon (PegIFN), and ribavirin] sustained virological responses (SVRs) have been achieved with increasing frequency. Progress in the case of HDV has been slow and lacking in significant breakthroughs.This paper aims to summarise the current state of play in treatment approaches for chonic viral hepatitis patients and future perspectives.

Durability of viral response after off-treatment in HBeAg positive chronic hepatitis B

AIM: To evaluate the durability in hepatitis B e antigen (HBeAg) positive chronic hepatitis B patients who discontinued antiviral treatment.

METHODS: A total of 48 HBeAg positive chronic hepatitis B patients who were administered nucleoside analogues and maintained virological response for ≥ 6 mo [hepatitis B virus (HBV) DNA < 300 copies/mL and HBeAg seroconversion] before cessation of treatment were enrolled between February 2007 and January 2010. The criteria for the cessation of the antiviral treatment were defined as follows: (1) achievement of virological response; and (2) duration of consolidation therapy (≥ 6 mo). After treatment cessation, the patients were followed up at 3-6 mo intervals. The primary endpoint was serologic and virologic recurrence rates after withdrawal of antiviral treatment. Serologic recurrence was defined as reappearance of HBeAg positivity after HBeAg seroconversion. Virologic recurrence was defined as an increase in HBV-DNA level > 10⁴ copies/mL after HBeAg seroconversion with previously undetectable HBV-DNA level.

RESULTS: During the median follow-up period of 18.2 mo (range: 5.1-47.5 mo) after cessation of antiviral treatment, the cumulative serological recurrence rate was 15 % at 12 mo. The median duration between the cessation of antiviral treatment and serologic recurrence was 7.2 mo (range: 1.2-10.9 mo). Of the 48 patients with HBeAg positive chronic hepatitis, 20 (41.6%) showed virological recurrence. The cumulative virologic recurrence rates at 12 mo after discontinuing the antiviral agent were 41%. The median duration between off-treatment and virologic recurrence was 7.6 mo (range: 4.3-27.1 mo). The mean age of the virological recurrence group was older than that of the non-recurrence group (46.7 ± 12.1 years vs 38.8 ± 12.7 years, respectively; P = 0.022). Age (> 40 years) and the duration of consolidation treatment (≥ 15 mo) were significant predictive factors for offtreatment durability in the multivariate analysis [P = 0.049, relative risk (RR) 0.31, 95% CI (0.096-0.998) and P = 0.005, RR 11.29, 95% CI (2.054-65.12), respectively]. Patients with age (≤ 40 years) who received consolidation treatment (≥ 15 mo) significantly showed durability in HBeAg positive chronic hepatitis B patients (P = 0.014). These results suggest that additional treatment for more than 15 mo after HBeAg seroconversion in patients who are ≤ 40 years old may be beneficial in providing a sustained virological response.

CONCLUSION: Our data suggest that HBeAg seroconversion is an imperfect end point in antiviral treatment. Long-term consolidation treatment (≥ 15 mo) in younger patients is important for producing better prognosis in HBeAg positive chronic hepatitis B.