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Inhibition of the host RNA polyadenylating polymerases, PAPD5 and PAPD7 (PAPD5/7), with dihydroquinolizinone, a small orally available, molecule, results in a rapid and selective degradation of hepatitis B virus (HBV) RNA, and hence reduction in the amounts of viral gene products. DHQ, is a first in class investigational agent and could represent an entirely new category of HBV antivirals. PAPD5 and PAPD7 are non-canonical, cell specified, polyadenylating polymerases, also called terminal nucleotidyl transferases 4B and 4A (TENT4B/A), respectively. They are involved in the degradation of poor-quality cell transcripts, mostly non-coding RNAs and in the maturation of a sub-set of transcripts. They also appear to play a role in shielding some mRNA from degradation. The results of studies with DHQ, along with other recent findings, provide evidence that repression of the PAPD5/7 arm of the cell "RNA quality control" pathway, causes a profound (multi-fold) reduction rather than increase, in the amount of HBV pre-genomic, pre-core and HBsAg mRNA levels in tissue culture and animal models, as well. In this review we will briefly discuss the need for new HBV therapeutics and provide background about HBV transcription. We also discuss cellular degradation of host transcripts, as it relates to a new family of anti-HBV drugs that interfere with these processes. Finally, since HBV mRNA maturation appears to be selectively sensitive to PAPD5/7 inhibition in hepatocytes, we discuss the possibility of targeting host RNA "quality control" as an antiviral strategy., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Standard literature procedures for the chemical synthesis of l-threose nucleosides generally employ l-ascorbic acid as starting material. Herein, we have explored two alternative routes that start from either l-arabitol or l-diethyl tartrate, both affording 2- O -methyl-l-threofuranose as a key building block for nucleobase incorporation. The access to multigram quantities of this glycosyl donor in a reproducible fashion allows for the preparation of 2'-deoxy-α-l-threofuranosyl phosphonate nucleosides on a large scale. This methodology was applied to the gram scale synthesis of an aryloxy amidate prodrug of phosphonomethoxydeoxythreosyl adenine. This prodrug exerted potent activity against an entecavir-resistant hepatitis B virus (HBV) strain, while leading to a significant reduction in the levels of HBV covalently closed circular DNA in a cellular assay. Furthermore, its remarkable anti-HBV efficacy was also confirmed in vivo using a hydrodynamic injection-based HBV mouse model, without relevant toxicity and systemic exposure occurring.

Similar to other mammalian viruses, the life cycle of hepatitis B virus (HBV) is heavily dependent upon and regulated by cellular (host) functions. These cellular functions can be generally placed in to two categories: (a) intrinsic host restriction factors and innate defenses, which must be evaded or repressed by the virus; and (b) gene products that provide functions necessary for the virus to complete its life cycle. Some of these functions may apply to all viruses, but some may be specific to HBV. In certain cases, the virus may depend upon the host function much more than does the host itself. Knowing which host functions regulate the different steps of a virus' life cycle, can lead to new antiviral targets and help in developing novel treatment strategies, in addition to improving a fundamental understanding of viral pathogenesis. Therefore, in this review we will discuss known host factors which influence key steps of HBV life cycle, and further elucidate therapeutic interventions targeting host-HBV interactions., (Copyright © 2018. Published by Elsevier B.V.)

Targeting host functions essential for viral replication has been considered as a broad spectrum and resistance-refractory antiviral approach. However, only a few host functions have, thus far, been validated as broad-spectrum antiviral targets in vivo. ER α-glucosidases I and II have been demonstrated to be essential for the morphogenesis of many enveloped viruses, including members from four families of viruses causing hemorrhagic fever. In vivo antiviral efficacy of various iminosugar-based ER α-glucosidase inhibitors has been reported in animals infected with Dengue, Japanese encephalitis, Ebola, Marburg and influenza viruses. Herein, we established Huh7.5-derived cell lines with ER α-glucosidase I or II knockout using CRISPR/Cas9 and demonstrated that the replication of Dengue, Yellow fever and Zika viruses was reduced by only 1-2 logs in the knockout cell lines. The results clearly indicate that only a partial suppression of viral replication can possibly be achieved with a complete inhibition of ER-α-glucosidases I or II by their inhibitors. We therefore explore to improve the antiviral efficacy of a lead iminosugar IHVR-19029 through combination with another broad-spectrum antiviral agent, favipiravir (T-705). Indeed, combination of IHVR-19029 and T-705 synergistically inhibited the replication of Yellow fever and Ebola viruses in cultured cells. Moreover, in a mouse model of Ebola virus infection, combination of sub-optimal doses of IHVR-19029 and T-705 significantly increased the survival rate of infected animals. We have thus proved the concept of combinational therapeutic strategy for the treatment of viral hemorrhagic fevers with broad spectrum host- and viral- targeting antiviral agents., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Systemically administered interferons are rapidly cleared from the circulation thus requiring frequent dosing to maintain the therapeutic levels of circulating interferon. This is particularly problematic for their use in the treatment of chronic diseases. The purpose of this study was to evaluate the potential of proprietary calcium phosphate (CaP) particles to deliver biologically active interferon alpha (IFNα) via the lungs into systemic circulation. Recombinant human IFNα-2a was formulated with proprietary CaP particles. In vitro biological activity of IFNα was assessed for its potential to activate IFN-induced cellular pathways in HEK-Blu-IFN α/β cell cultures. Antiviral activity was evaluated against vesicular stomatitis virus (VSV) infection of HeLa cells. Male BALB/c mice were used to evaluate the absorption of IFNα from CaP-IFNα across the lungs following intratracheal (IT) instillation. Serum IFNα concentrations up to 9 h post-treatment were determined. Data were analyzed to obtain pharmacokinetic (PK) parameters. Data from these studies indicated that IFNα formulated with CaP retains its biological activity, and it is transported into circulation in a dose-dependent manner. PK analysis showed larger than two-fold area under the serum concentration-time curve (AUC) for CaP-IFNα compared to non-formulated IFNα administered IT. The IFNα formulated with CaP had two-fold longer half-life (t1/2) and mean residence time (MRT) relative to IFNα alone administered by injection. Clearance of CaP-IFNα was slower than IFNα administered IM or IT. Relative bioavailability of CaP-IFNα was 1.3-fold of IFNα injection and twofold of IFNα administered IT. Furthermore, inhalation of aerosolized CaP did not indicate any lung toxicity in animals.

In pursuit of novel therapeutics targeting the hepatitis B virus (HBV) infection, we evaluated a dihydroquinolizinone compound (DHQ-1) that in the nanomolar range reduced the production of virion and surface protein (HBsAg) in tissue culture. This compound also showed broad HBV genotype coverage, but was inactive against a panel of DNA and RNA viruses of other species. Oral administration of DHQ-1 in the AAV-HBV mouse model resulted in a significant reduction of serum HBsAg as soon as 4 days following the commencement of treatment. Reduction of HBV markers in both in vitro and in vivo experiments was related to the reduced amount of viral RNA including pre-genomic RNA (pgRNA) and 2.4/2.1 kb HBsAg mRNA. Nuclear run-on and subcellular fractionation experiments indicated that DHQ-1 mediated HBV RNA reduction was the result of accelerated viral RNA degradation in the nucleus, rather than the consequence of inhibition of transcription initiation. Through mutagenesis of HBsAg gene sequences, we found induction of HBsAg mRNA decay by DHQ-1 required the presence of the HBV posttranscriptional regulatory element (HPRE), with a 109 nucleotides sequence within the central region of the HPRE alpha sub-element being the most critical. Taken together, the current study shows that a small molecule can reduce the overall levels of HBV RNA, especially the HBsAg mRNA, and viral surface proteins. This may shed light on the development of a new class of HBV therapeutics., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The aminoglycoside Geneticin (G418) is known to inhibit cell culture proliferation, via virus-specific mechanisms, of two different virus genera from the family Flaviviridae. Here, we tried to determine whether Geneticin can selectively alter the switching of the nucleotide 1 to 570 RNA region of hepatitis C virus (HCV) and, if so, whether this inhibits viral growth. Two structure-dependent RNases known to specifically cleave HCV RNA were tested in the presence or absence of the drug. One was the Synechocystis sp. RNase P ribozyme, which cleaves the tRNA-like domain around the AUG start codon under high-salt buffer conditions; the second was Escherichia coli RNase III, which recognizes a double-helical RNA switch element that changes the internal ribosome entry site (IRES) from a closed (C) conformation to an open (O) one. While the drug did not affect RNase P activity, it did inhibit RNase III in the micromolar range. Kinetic studies indicated that the drug favors the switch from the C to the O conformation of the IRES by stabilizing the distal double-stranded element and inhibiting further processing of the O form. We demonstrate that, because the RNA in this region is highly conserved and essential for virus survival, Geneticin inhibits HCV Jc1 NS3 expression, the release of the viral genomic RNA, and the propagation of HCV in Huh 7.5 cells. Our study highlights the crucial role of riboswitches in HCV replication and suggests the therapeutic potential of viral-RNA-targeted antivirals., (Copyright © 2016 Ariza-Mateos et al.)

This year marks the 50th anniversary of the discovery of the Australia antigen (Blumberg et al., 1965), which in 1967 was identified to be the hepatitis B virus (HBV) surface antigen. Even though several antiviral medications have been in use for the management of chronic HBV infection for more than 20years, sustained clearance of HBsAg, similar to the sustained viral response (SVR) or cure in chronic hepatitis C, occurs in only a minority of treated patients. Moreover, even after 10years of effective suppression of HBV viremia with current therapy, there is only a 40-70% reduction in deaths from liver cancer. Recent success in developing antivirals for hepatitis C that are effective across all genotypes has renewed interest in a similar cure for chronic HBV infection. In this article, we review a wave of newly identified drug targets, investigational compounds and experimental strategies that are now under clinical evaluation or in preclinical development. The paper forms part of a symposium in Antiviral Research on "An unfinished story: From the discovery of the Australia antigen to the development of new curative therapies for hepatitis B.", (Copyright © 2015 Elsevier B.V. All rights reserved.)

Unlabelled: Interferon alpha (IFN-α) is an approved medication for chronic hepatitis B therapy. Besides acting as an immunomodulator, IFN-α elicits a pleiotropic antiviral state in hepatitis B virus (HBV)-infected hepatocytes, but whether or not IFN-α impedes the late steps of the HBV life cycle, such as HBV secretion, remains elusive. Here we report that IFN-α treatment of HepAD38 cells with established HBV replication selectively reduced HBV virion release without altering intracellular viral replication or the secretion of HBV subviral particles and nonenveloped capsids. In search of the interferon-stimulated gene(s) that is responsible for the reduction of HBV virion release, we found that tetherin, a broad-spectrum antiviral transmembrane protein that inhibits the egress of a variety of enveloped viruses, was highly induced by IFN-α in HepAD38 cells and in primary human hepatocytes. We further demonstrated that the expression of full-length tetherin, but not the C-terminal glycosylphosphatidylinositol (GPI) anchor-truncated form, inhibited HBV virion egress from HepAD38 cells. In addition, GPI anchor-truncated tetherin exhibited a dominant-negative effect and was incorporated into the liberated virions. We also found colocalization of tetherin and HBV L protein at the intracellular multivesicular body, where the budding of HBV virions takes place. In line with this, electron microscopy demonstrated that HBV virions were tethered in the lumen of the cisterna membrane under tetherin expression. Finally, knockdown of tetherin or overexpression of dominant negative tetherin attenuated the IFN-α-mediated reduction of HBV virion release. Taken together, our study suggests that IFN-α inhibits HBV virion egress from hepatocytes through the induction of tetherin., Importance: Tetherin is a host restriction factor that blocks the egress of a variety of enveloped viruses through tethering the budding virions on the cell surface with its membrane anchor domains. Here we report that interferon directly and selectively inhibits the secretion of HBV virions, but not subviral particles or nonenveloped capsids, through the induction of tetherin in hepatocyte-derived cells. The antiviral function of tetherin requires the carboxyl-terminal GPI anchor, while the GPI anchor deletion mutant exhibits dominant negative activity and attaches to liberated HBV virions. Consistent with the fact that HBV is an intracellular budding virus, microscopy analyses demonstrated that the tethering of HBV virions occurs in the intracellular cisterna and that tetherin colocalizes with HBV virions on the multivesicular body, which is the HBV virion budding site. Our study not only expands the antiviral spectrum of tetherin but also sheds light on the mechanisms of interferon-elicited anti-HBV responses., (Copyright © 2015, American Society for Microbiology. All Rights Reserved.)

Chronicity of hepatitis B virus (HBV) infection is due to the failure of a host to mount a sufficient immune response to clear the virus. The aim of this study was to identify small-molecular agonists of the pattern recognition receptor (PRR)-mediated innate immune response to control HBV infection. To achieve this goal, a coupled mouse macrophage and hepatocyte culture system mimicking the intrahepatic environment was established and used to screen small-molecular compounds that activate macrophages to produce cytokines, which in turn suppress HBV replication in a hepatocyte-derived stable cell line supporting HBV replication in a tetracycline-inducible manner. An agonist of the mouse stimulator of interferon (IFN) genes (STING), 5,6-dimethylxanthenone-4-acetic acid (DMXAA), was found to induce a robust cytokine response in macrophages that efficiently suppressed HBV replication in mouse hepatocytes by reducing the amount of cytoplasmic viral nucleocapsids. Profiling of cytokines induced by DMXAA and agonists of representative Toll-like receptors (TLRs) in mouse macrophages revealed that, unlike TLR agonists that induced a predominant inflammatory cytokine/chemokine response, the STING agonist induced a cytokine response dominated by type I IFNs. Moreover, as demonstrated in an HBV hydrodynamic mouse model, intraperitoneal administration of DMXAA significantly induced the expression of IFN-stimulated genes and reduced HBV DNA replication intermediates in the livers of mice. This study thus proves the concept that activation of the STING pathway induces an antiviral cytokine response against HBV and that the development of small-molecular human STING agonists as immunotherapeutic agents for treatment of chronic hepatitis B is warranted., (Copyright © 2015, American Society for Microbiology. All Rights Reserved.)

Endoplasmic reticulum (ER)-resident glucosidases I and II sequentially trim the three terminal glucose moieties on the N-linked glycans attached to nascent glycoproteins. These reactions are the first steps of N-linked glycan processing and are essential for proper folding and function of many glycoproteins. Because most of the viral envelope glycoproteins contain N-linked glycans, inhibition of ER glucosidases with derivatives of 1-deoxynojirimycin, i.e., iminosugars, efficiently disrupts the morphogenesis of a broad spectrum of enveloped viruses. However, like viral envelope proteins, the cellular receptors of many viruses are also glycoproteins. It is therefore possible that inhibition of ER glucosidases not only compromises virion production but also disrupts expression and function of viral receptors and thus inhibits virus entry into host cells. Indeed, we demonstrate here that iminosugar treatment altered the N-linked glycan structure of angiotensin I-converting enzyme 2 (ACE2), which did not affect its expression on the cell surface or its binding of the severe acute respiratory syndrome coronavirus (SARS-CoV) spike glycoprotein. However, alteration of N-linked glycans of ACE2 impaired its ability to support the transduction of SARS-CoV and human coronavirus NL63 (HCoV-NL63) spike glycoprotein-pseudotyped lentiviral particles by disruption of the viral envelope protein-triggered membrane fusion. Hence, in addition to reducing the production of infectious virions, inhibition of ER glucosidases also impairs the entry of selected viruses via a post-receptor-binding mechanism., (Copyright © 2015, American Society for Microbiology. All Rights Reserved.)

Virus infection of host cells is sensed by innate pattern recognition receptors (PRRs) and induces production of type I interferons (IFNs) and other inflammatory cytokines. These cytokines orchestrate the elimination of the viruses but are occasionally detrimental to the hosts. The outcomes and pathogenesis of viral infection are largely determined by the specific interaction between the viruses and their host cells. Therefore, compounds that either inhibit viral infection or modulate virus-induced cytokine response should be considered as candidates for managing virus infection. The aim of the study was to identify compounds in both categories, using a single cell-based assay. Our screening platform is a HEK293 cell-based reporter assay where the expression of a firefly luciferase is under the control of a human IFN-β promoter. We have demonstrated that infection of the reporter cell line with a panel of RNA viruses activated the reporter gene expression that correlates quantitatively with the levels of virus replication and progeny virus production, and could be inhibited in a dose-dependent manner by known antiviral compound or inhibitors of PRR signal transduction pathways. Using Dengue virus as an example, a pilot screening of a small molecule library consisting of 26,900 compounds proved the concept that the IFN-β promoter reporter assay can serve as a convenient high throughput screening platform for simultaneous discovery of antiviral and innate immune response modulating compounds. A representative antiviral compound from the pilot screening, 1-(6-ethoxybenzo[d]thiazol-2-yl)-3-(3-methoxyphenyl) urea, was demonstrated to specifically inhibit several viruses belonging to the family of flaviviridae., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Endoplasmic reticulum (ER)-resident α-glucosidases I and II sequentially trim the three terminal glucose moieties on N-linked glycans attached to nascent glycoproteins. These reactions are the first steps of N-linked glycan processing and are essential for proper folding and function of many glycoproteins. Because most viral envelope glycoproteins contain N-linked glycans, inhibition of ER α-glucosidases with derivatives of 1-deoxynojirimycin (DNJ) or castanospermine (CAST), two well-studied pharmacophores of α-glucosidase inhibitors, efficiently disrupts the morphogenesis of a broad spectrum of enveloped viruses. Moreover, both DNJ and CAST derivatives have been demonstrated to prevent the death of mice infected with several distinct flaviviruses and filoviruses and suppress the multiplication of several other species of viruses in infected animals. N-Butyl derivative of DNJ (NB-DNJ) and 6 O-bytanoyl prodrug of CAST (Bu-CAST) have been evaluated in human clinical trials for their antiviral activities against human immunodeficiency virus and hepatitis C virus, and there is an ongoing trial of treating dengue patients with Bu-CAST. This article summarizes the current status of ER α-glucosidase-targeted antiviral therapy and proposes strategies for development of more efficacious and specific ER α-glucosidase inhibitors as broad-spectrum, drug resistance-refractory antiviral therapeutics. These host function-targeted, broad-spectrum antiviral agents do not rely on time-consuming etiologic diagnosis, and should therefore be particularly promising in the management of viral hemorrhagic fever and respiratory tract viral infections, medical conditions that can be caused by many different enveloped RNA viruses, with a short window for medical intervention., (Copyright © 2013. Published by Elsevier B.V.)

Novel N-alkyldeoxynojirimycins (NADNJs) based on our previous lead 3 were designed, synthesized and tested in metabolic assays and in virus cultures. NADNJs containing terminal tertiary benzamide, sulfonamide, urea, and oxazolidinone moieties were discovered to have improved metabolic stability compared to 3, while maintaining submicromolar EC50 against BVDV and Tacaribe virus; and low cytotoxicity., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Chronic hepatitis B virus (HBV) infection, a serious public health problem leading to cirrhosis and hepatocellular carcinoma, is currently treated with either pegylated alpha interferon (pegIFN-α) or one of the five nucleos(t)ide analogue viral DNA polymerase inhibitors. However, neither pegIFN-α nor nucleos(t)ide analogues are capable of reliably curing the viral infection. In order to develop novel antiviral drugs against HBV, we established a cell-based screening assay by using an immortalized mouse hepatocyte-derived stable cell line supporting a high level of HBV replication in a tetracycline-inducible manner. Screening of a library consisting of 26,900 small molecules led to the discovery of a series of sulfamoylbenzamide (SBA) derivatives that significantly reduced the amount of cytoplasmic HBV DNA. Structure-activity relationship studies have thus far identified a group of fluorine-substituted SBAs with submicromolar antiviral activity against HBV in human hepatoma cells. Mechanistic analyses reveal that the compounds dose dependently inhibit the formation of pregenomic RNA (pgRNA)-containing nucleocapsids of HBV but not other animal hepadnaviruses, such as woodchuck hepatitis virus (WHV) and duck hepatitis B virus (DHBV). Moreover, heterologous genetic complementation studies of capsid protein, DNA polymerase, and pgRNA between HBV and WHV suggest that HBV capsid protein confers sensitivity to the SBAs. In summary, SBAs represent a novel chemical entity with superior activity and a unique antiviral mechanism and are thus warranted for further development as novel antiviral therapeutics for the treatment of chronic hepatitis B.

Host cellular endoplasmic reticulum α-glucosidases I and II are essential for the maturation of viral glycosylated envelope proteins that use the calnexin mediated folding pathway. Inhibition of these glycan processing enzymes leads to the misfolding and degradation of these viral glycoproteins and subsequent reduction in virion secretion. We previously reported that, CM-10-18, an imino sugar α-glucosidase inhibitor, efficiently protected the lethality of dengue virus infection of mice. In the current study, through an extensive structure-activity relationship study, we have identified three CM-10-18 derivatives that demonstrated superior in vitro antiviral activity against representative viruses from four viral families causing hemorrhagic fever. Moreover, the three novel imino sugars significantly reduced the mortality of two of the most pathogenic hemorrhagic fever viruses, Marburg virus and Ebola virus, in mice. Our study thus proves the concept that imino sugars are promising drug candidates for the management of viral hemorrhagic fever caused by variety of viruses., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Novel N-alkyldeoxynojirimycins (NADNJs) with two hydrophobic groups attached to a nitrogen linker on the alkyl chain were designed. A novel NADNJ containing a terminal tertiary carboxamide moiety was discovered that was a potent inhibitor against BVDV. Further optimization resulted in a structurally more stable lead compound 24 with a submicromolar EC50 against BVDV, Dengue, and Tacaribe; and low cytotoxicity., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Chronic hepatitis B can currently be medically managed with either pegylated interferon-alpha (pegIFN-α) or one of the five nucleos(t)ide analog Direct Acting Antivirals (DAAs) that inhibit the hepatitis B virus (HBV) DNA polymerase. While pegIFN-α is effective in approximately one-third of the treated patients, the polymerase inhibitors significantly reduce viral load in the vast majority of those treated. However, neither pegIFN-α nor nucleosi(t)de analogs are capable of reliably eliminating the virus and achieving a cure. Moreover, the interferons and polymerase inhibitors are recommended by US, European and Asian professional society practice guidelines for use in only a subset of those infected with HBV. This subset is the population with the greatest levels of circulating viral DNA and abnormal liver function. Although this is the population at the highest risk for cirrhosis and liver cancer, those who fall outside the treatment guidelines, with low levels of viral replication and normal serum ALTs, may also benefit from antiviral therapy. The questions are thus: are new classes of drugs needed to manage chronic hepatitis B? Is a cure possible? Is a cure even necessary? It is therefore important to define the meaning of a cure and determine what the goals of new therapies should be. In this article, we address those questions and propose two operational definitions of medically attainable cures. The first is a "functional cure" based on the clinical outcome, in which the patient's life expectancy becomes the same as that of an individual who has resolved his HBV infection without therapy. Because such an outcome cannot be measured over the short term, we also define an "apparent virological cure," based on the stable off-drug suppression of HBV viremia and antigenemia and the normalization of ALTs and other laboratory tests. We suggest that such a virological cure should be the goal of future therapeutics in all patients with chronic hepatitis B. The extent to which a virological cure predicts a functional cure will only be determined by long-term follow-up., (Copyright © 2013 Elsevier B.V. All rights reserved.)

There are now seven nucleoside/tide analogues, along with interferon-α, that are approved by the FDA for the management of chronic hepatitis B virus (HBV) infection, a disease affecting hundreds of millions of people worldwide. These medications, however, are limited in usefulness, and significant side effects and the emergence of viral escape mutants make the development of novel and updated therapeutics a pressing need in the treatment of HBV. With this in mind, a library containing 2000 compounds already known to be safe in both humans and mice with known mechanisms of action in mammalian cells were tested for the possibility of either antiviral activity against HBV or selective toxicity in HBV producing cell lines. A modified real-time immune-absorbance-polymerase chain reaction (IA-PCR) assay was developed for this screen, utilizing cells that produce and secrete intact HBV virions. In this procedure, viral particles are first captured by an anti-HBs antibody immobilized on a plate. The viral load is subsequently assessed by real-time PCR directly on captured particles. Using this assay, eight compounds were shown to consistently reduce the amount of secreted HBV viral particles in the culture medium under conditions that had no detectable impact on cell viability. Two compounds, proparacaine and chlorophyllide, were shown to reduce HBV levels 4- to 6-fold with an IC₅₀ of 1 and 1.5 μM, respectively, and were selected for further study. The identification of these compounds as promising antiviral drug candidates against HBV, despite a lack of previous recognition of HBV antiviral activity, supports the validity and utility of testing known compounds for "off-pathogen target" activity against HBV, and also validates this IA-PCR assay as an important tool for the detection of anti-viral activity against enveloped viruses., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Hepatitis B virus (HBV) covalently closed circular DNA (cccDNA) plays a central role in viral infection and persistence and is the basis for viral rebound after the cessation of therapy, as well as the elusiveness of a cure even after extended treatment. Therefore, there is an urgent need for the development of novel therapeutic agents that directly target cccDNA formation and maintenance. By employing an innovative cell-based cccDNA assay in which secreted HBV e antigen is a cccDNA-dependent surrogate, we screened an in-house small-molecule library consisting of 85,000 drug-like compounds. Two structurally related disubstituted sulfonamides (DSS), termed CCC-0975 and CCC-0346, emerged and were confirmed as inhibitors of cccDNA production, with low micromolar 50% effective concentrations (EC(50)s) in cell culture. Further mechanistic studies demonstrated that DSS compound treatment neither directly inhibited HBV DNA replication in cell culture nor reduced viral polymerase activity in the in vitro endogenous polymerase assay but synchronously reduced the levels of HBV cccDNA and its putative precursor, deproteinized relaxed circular DNA (DP-rcDNA). However, DSS compounds did not promote the intracellular decay of HBV DP-rcDNA and cccDNA, suggesting that the compounds interfere primarily with rcDNA conversion into cccDNA. In addition, we demonstrated that CCC-0975 was able to reduce cccDNA biosynthesis in duck HBV-infected primary duck hepatocytes. This is the first attempt, to our knowledge, to identify small molecules that target cccDNA formation, and DSS compounds thus potentially serve as proof-of-concept drug candidates for development into therapeutics to eliminate cccDNA from chronic HBV infection.

We recently described the discovery of oxygenated N-alkyl deoxynojirimycin (DNJ) derivative 7 (CM-10-18) with antiviral activity against dengue virus (DENV) infection both in vitro and in vivo. This imino sugar was promising but had an EC(50) against DENV in BHK cells of 6.5 μM, which limited its use in in vivo. Compound 7 presented structural opportunities for activity relationship analysis, which we exploited and report here. These structure-activity relationship studies led to analogues 2h, 2l, 3j, 3l, 3v, and 4b-4c with nanomolar antiviral activity (EC(50) = 0.3-0.5 μM) against DENV infection, while maintaining low cytotoxicity (CC(50) > 500 μM, SI > 1000). In male Sprague-Dawley rats, compound 3l was well tolerated at a dose up to 200 mg/kg and displayed desirable PK profiles, with significantly improved bioavailability (F = 92 ± 4%).

Recognition of virus infection by innate pattern recognition receptors (PRRs), including membrane-associated toll-like receptors (TLR) and cytoplasmic RIG-I-like receptors (RLR), activates cascades of signal transduction pathways leading to production of type I interferons (IFN) and proinflammatory cytokines that orchestrate the elimination of the viruses. Although it has been demonstrated that PRR-mediated innate immunity plays an essential role in defending virus from infection, it also occasionally results in overwhelming production of proinflammatory cytokines that cause severe inflammation, blood vessel leakage and tissue damage. In our efforts to identify small molecules that selectively enhance PRR-mediated antiviral, but not the detrimental inflammatory response, we discovered a compound, RO 90-7501 ('2'-(4-Aminophenyl)-[2,5'-bi-1H-benzimidazol]-5-amine), that significantly promoted both TLR3 and RLR ligand-induced IFN-β gene expression and antiviral response, most likely via selective activation of p38 mitogen-activated protein kinase (MAPK) pathway. Our results thus imply that pharmacological modulation of PRR signal transduction pathways in favor of the induction of a beneficial antiviral response can be a novel therapeutic strategy.

Dengue virus infection causes diseases in people, ranging from the acute febrile illness dengue fever, to life-threatening dengue hemorrhagic fever/dengue shock syndrome. We previously reported that a host cellular α-glucosidases I and II inhibitor, imino sugar CM-10-18, potently inhibited dengue virus replication in cultured cells, and significantly reduced viremia in dengue virus infected AG129 mice. In this report we show that CM-10-18 also significantly protects mice from death and/or disease progress in two mouse models of lethal dengue virus infection. Our results thus provide a strong support for the development of CM-10-18 or its derivatives as antiviral agents to treat servere dengue virus infections., (Copyright © 2011 Elsevier B.V. All rights reserved.)

α-Glucosidases I and II are endoplasmic reticulum-resident enzymes that are essential for N-linked glycan processing and subsequent proper folding of glycoproteins. In this report, we first demonstrate that downregulation of the expression of α-glucosidase I, II, or both in Huh7.5 cells by small hairpin RNA technology inhibited the production of hepatitis C virus (HCV). In agreement with the essential role of α-glucosidases in HCV envelope glycoprotein processing and folding, treatment of HCV-infected cells with a panel of imino sugar derivatives, which are competitive inhibitors of α-glucosidases, did not affect intracellular HCV RNA replication and nonstructural protein expression but resulted in the inhibition of glycan processing and subsequent degradation of HCV E2 glycoprotein. As a consequence, HCV virion assembly and secretion were inhibited. In searching for imino sugars with better antiviral activity, we found that a novel imino sugar, PBDNJ0804, had a superior ability to inhibit HCV virion assembly and secretion. In summary, we demonstrated that glucosidases are important host factor-based antiviral targets for HCV infection. The low likelihood of drug-resistant virus emergence and potent antiviral efficacy of the novel glucosidase inhibitor hold promise for its development as a therapeutic agent for the treatment of chronic hepatitis C.

We screened ∼2,200 compounds known to be safe in people for the ability to reduce the amount of virion-associated hepatitis B virus (HBV) DNA in the culture medium of producer cells. These efforts led to the discovery of an alkylated porphyrin, chlorophyllide, as the compound that achieved the greatest reduction in signal. Here we report that chlorophyllide directly and quantitatively disrupted HBV virions at micromolar concentrations, resulting in the loss of all detectable virion DNA, without detectably affecting cell viability or intracellular viral gene products. Chemophores of chlorophyllide were also tested. Chlorin e6, a metal-free chlorophyllide-like molecule, showed the strongest antiviral activity against HBV as well as profound antiviral effects on other enveloped viruses, such as hepatitis C virus (HCV), human immunodeficiency virus (HIV), dengue virus (DENV), Marburg virus (MARV), Tacaribe virus (TCRV), and Junin viruses (JUNV). Remarkably, chlorin e6 inactivated DENV at subnanomolar-level concentrations. However, the compound had no antiviral effect against encephalomyocarditis virus and adenovirus, suggesting that chlorin e6 may be less active or inactive against nonenveloped viruses. Although other porphyrin derivatives have been previously reported to possess antiviral activity, this is the first analysis of the biochemical impact of chlorophyllide and chlorin e6 against HBV and of the dramatic anti-infectivity impact upon DENV. The possible application of this family of compounds as antiviral agents, as microbicides and systemic virus neutralizing agents, is discussed.

Cellular α-glucosidases I and II are enzymes that sequentially trim the three terminal glucoses in the N-linked oligosaccharides of viral envelope glycoproteins. This process is essential for the proper folding of viral glycoproteins and subsequent assembly of many enveloped viruses, including dengue virus (DENV). Imino sugars are substrate mimics of α-glucosidases I and II. In this report, we show that two oxygenated alkyl imino sugar derivatives, CM-9-78 and CM-10-18, are potent inhibitors of both α-glucosidases I and II in vitro and in treated animals, and efficiently inhibit DENV infection of cultured human cells. Pharmacokinetic studies reveal that both compounds are well tolerated at doses up to 100mg/kg in rats and have favorable pharmacokinetic properties and bioavailability in mice. Moreover, we showed that oral administration of either CM-9-78 or CM-10-18 reduces the peak viremia of DENV in mice. Interestingly, while treatment of DENV infected mice with ribavirin alone did not reduce the viremia, combination therapy of ribavirin with sub-effective dose of CM-10-18 demonstrated a significantly enhanced antiviral activity, as indicated by a profound reduction of the viremia. Our findings thus suggest that combination therapy of two broad-spectrum antiviral agents may provide a practically useful approach for the treatment of DENV infection., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Type III interferons (IFN), IFN-lambda or IL-28/29, are new members of the IFN super-family. Except for using distinct receptors, type I and type III IFNs share the same major post receptor signaling components to activate the transcription of a similar set of IFN-stimulated genes (ISGs). To examine the antiviral effects of the new type IFNs against West Nile virus (WNV), we compared the antiviral effects of IFN-alpha and IFN-lambda on WNV virus-like particle (VLP) infection and replicon replication in Huh7.5 and Hela cells. The results revealed that (i) both types of IFNs could efficiently prevent the WNV infection, but IFN-alpha demonstrated a stronger antiviral efficacy; (ii) WNV genome replication in VLP-infected cells and replicon-containing cell lines could only be inhibited by IFN-alpha, but not IFN-lambda; (iii) in agreement with the observed antiviral effects, only IFN-lambda-induced activation of JAK-STAT signaling pathway and induction of ISG expression were completely inhibited in WNV replicon-containing cell lines, but IFN-alpha signal transduction was either unaffected or only partially inhibited in Huh7.5 or Hela cells by the virus. Hence, the differential inhibition of WNV on IFN-alpha and IFN-lambda signal transduction implies that the receptors of the two types of IFNs, but not the common post receptor signaling components, could be selectively targeted either directly by WNV nonstructural proteins or indirectly by the cellular responses induced by the virus infection to inhibit the signal transduction of the cytokines.

The aminoglycoside, geneticin (G418), was recently shown to have antiviral activity against bovine viral diarrhea virus (BVDV). Since BVDV, dengue virus (DENV) and yellow fever virus (YFV) all belong to the Flaviviridae family, it seemed possible that a common step in their life cycle might be affected by this aminoglycoside. Here it is shown that geneticin prevented the cytopathic effect (CPE) resulting from DENV-2 infection of BHK cells, in a dose-dependent manner with an 50% effective concentration (EC(50)) value of 3+/-0.4microg/ml. Geneticin had no detectable effect on CPE caused by YFV in BHK cells. Geneticin also inhibited DENV-2 viral yield with an EC(50) value of 2+/-0.1microg/ml and an EC(90) value of 20+/-2microg/ml. With a CC(50) value of 165+/-5microg/ml, the selectivity index of anti-DENV activity of geneticin in BHK cells was established to be 66. Furthermore, 25microg/ml of geneticin nearly completely blocked plaque formation induced by DENV-2, but not YFV. In addition, geneticin, inhibited DENV-2 viral RNA replication and viral translation. Gentamicin, kanamycin, and the guanidinylated geneticin showed no anti-DENV activity. Neomycin and paromomycin demonstrated weak antiviral activity at high concentrations. Finally, aminoglycoside-3'-phosphotransferase activity of neomycin-resistant gene abolished antiviral activity of geneticin.

Imino sugars, such as N-butyl-deoxynojirimycin and N-nonyl-deoxynojirimycin (NNDNJ), are glucose analogues that selectively inhibit cellular alpha-glucosidase I and II in the endoplasmic reticulum and exhibit antiviral activities against many types of enveloped viruses. Although these molecules have broad-spectrum antiviral activity, their development has been limited by a lack of efficacy and/or selectivity. We have previously reported that a DNJ derivative with a hydroxylated cyclohexyl side chain, called OSL-95II, has an antiviral efficacy similar to that of NNDNJ but significantly less toxicity. Building upon this observation, a family of imino sugar derivatives containing an oxygenated side chain and terminally restricted ring structures were synthesized and shown to have low cytotoxicity and superior antiviral activity against members of the Flaviviridae family, including bovine viral diarrhea virus, dengue virus (DENV), and West Nile virus. Of particular interest is that several of these novel imino sugar derivatives, such as PBDNJ0801, PBDNJ0803, and PBDNJ0804, potently inhibit DENV infection in vitro, with 90% effective concentration values at submicromolar concentrations and selectivity indices greater than 800. Therefore, these compounds represent the best in their class and may offer realistic candidates for the development of antiviral therapeutics against human DENV infections.

Hepatitis C virus (HCV) infection is a common cause of chronic hepatitis and is currently treated with alpha interferon (IFN-alpha)-based therapies. However, the underlying mechanism of IFN-alpha therapy remains to be elucidated. To identify the cellular proteins that mediate the antiviral effects of IFN-alpha, we created a HEK293-based cell culture system to inducibly express individual interferon-stimulated genes (ISGs) and determined their antiviral effects against HCV. By screening 29 ISGs that are induced in Huh7 cells by IFN-alpha and/or up-regulated in HCV-infected livers, we discovered that viperin, ISG20, and double-stranded RNA-dependent protein kinase (PKR) noncytolytically inhibited the replication of HCV replicons. Mechanistically, inhibition of HCV replication by ISG20 and PKR depends on their 3'-5' exonuclease and protein kinase activities, respectively. Moreover, our work, for the first time, provides strong evidence suggesting that viperin is a putative radical S-adenosyl-l-methionine (SAM) enzyme. In addition to demonstrating that the antiviral activity of viperin depends on its radical SAM domain, which contains conserved motifs to coordinate [4Fe-4S] cluster and cofactor SAM and is essential for its enzymatic activity, mutagenesis studies also revealed that viperin requires an aromatic amino acid residue at its C terminus for proper antiviral function. Furthermore, although the N-terminal 70 amino acid residues of viperin are not absolutely required, deletion of this region significantly compromises its antiviral activity against HCV. Our findings suggest that viperin represents a novel antiviral pathway that works together with other antiviral proteins, such as ISG20 and PKR, to mediate the IFN response against HCV infection.

This article reviews the molecular biology of the hepatitis B virus in an effort to explain its natural history from a molecular perspective. The life cycle of the virus, with special attention to virus replication, polypeptide production, and morphogenesis, is described. The way in which these steps may influence the natural history of viral pathogenesis, as well as the effectiveness of interventions, receives special consideration.

The antiviral activity of iminocyclitol compounds with a deoxynojirimycin (DNJ) head group and either a straight chain alkyl or alkylcycloalkyl group attached to the nitrogen atom have been tested in vitro against multiple-enveloped viruses. Several of these analogues were superior to previously reported DNJ compounds. Iminocyclitols that inhibit the glycan-processing enzyme endoplasmic-reticular glucosidase have been shown to inhibit the morphogenesis of viruses that bud from the endoplasmic reticulum (ER) at non-cytotoxic concentrations. Bovine viral diarrhoea virus (BVDV) has been used as a surrogate system for study of the hepatitis C virus, which belong to the virus family (Flaviviridae) as West Nile virus (WNV) and dengue virus (DV). N-Nonyl-DNJ (NNDNJ) was previously reported to have micromolar antiviral activity against BVDV, but a limiting toxicity profile. N-Butylcyclohexyl-DNJ (SP169) was shown to be as potent as NNDNJ in assays against BVDV and less toxic. However, it was inactive against hepatitis B virus (HBV). The present study reports efforts to improve the performance profiles of these compounds. Introduction of an oxygen atom into the N-alkyl side chain of DNJ, either as an ether or a hydroxyl functionality, reduced toxicity but sacrificed potency. Introduction of a hydroxyl group at the tertiary carbon junction of the cycloalkyl and linear alkyl group, as in N-pentyl-(1-hydroxycyclohexyl)-DNJ (OSL-9511), led to a structure that was as well tolerated as DNJ (CC50>500 microM), but retained micromolar antiviral activity against all ER morphogenesis budding viruses tested: BVDV, WNV, DV and HBV. The implication of this modification to the development of broad-spectrum antiviral agents is discussed.

West Nile virus (WNV) is a positive-sense, single-stranded RNA virus of the family Flaviviridae. WNV persistently infects insect cells, but can causes acute cytopathic infection of mammalian cells and is an etiologic agent of viral encephalitis in humans. By using a cell line expressing a WNV subgenomic replicon [Rossi, S.L., Zhao, Q., O'Donnell, V.K., Mason, P.W., 2005. Adaptation of West Nile virus replicons to cells in culture and use of replicon-bearing cells to probe antiviral action. Virology 331 (2), 457-470], we developed a high-throughput assay and used it to screen a library of small molecule compounds for inhibitors of WNV replication in the absence of live virus. Here we report the identification of novel small molecule inhibitors for WNV replicon replication. We demonstrate that the compounds inhibited WNV replication-dependent luciferase expression in the replicon cells and reduced WNV viral protein accumulation and viral RNA copy number in the replicon cells. Two classes of compounds with multiple hits, parazolotrahydrothophenes and pyrozolopyrimidines, showed preliminary structure-activity relationships. In WNV infection assays, one pyrozolopyrimidine compound was confirmed to have antiviral activity. These compounds should be valuable for developing anti-WNV therapeutic drugs as well as research tools to study the mechanism of WNV replication.

Previous work has shown that the secretion of enveloped hepatitis B virus (HBV) DNA and the HBV middle envelope protein (MHBs) are sensitive to glucosidase inhibition. Here, it is shown that HBV DNA secretion remains depressed after the removal of the glucosidase inhibitor and long after glucosidase function returns to normal. For example, glyco-processing and the secretion of alpha-1 anti-trypsin returned to normal within 3 h of the removal of the glucosidase inhibitor. In contrast, the secretion of HBV did not return to normal for more than 7 days after the removal of the inhibitor. Consistent with the inhibition of HBV virion secretion, the levels of HBV L and HBV M proteins were also reduced by treatment with the glucosidase inhibitor and remained reduced for 7 days after compound withdrawal. The implications of the prolonged antiviral effect against HBV and the use of glucosidase inhibitors as antiviral agents are discussed.

As secretion of the middle (MHBs) glycoprotein of hepatitis B virus is highly dependent upon the action of the host oligosaccharide processing enzymes glucosidase I and II, drugs that inhibit this enzyme have been proposed as potential antiviral agents. To facilitate the identification of new, more effective inhibitors of MHBs secretion, an assay has been developed based on the expression of this glycoprotein alone by transfection of Huh7 hepatoma cells. The data clearly demonstrate that both mono- and di-glycosylated forms of MHBs are produced in this system and both forms are equally dependent upon glucosidase processing for secretion. In addition, inclusion of a co-transfected reporter construct that encodes secreted alkaline phosphatase (SEAP) to permit normalization of transfection revealed that the SEAP gene product was itself sensitive to glucosidase inhibition. This sensitivity also was observed in HepG2 human hepatoma cells. Thus, measuring SEAP secretion may be another method for evaluating glucosidase inhibition. In addition, this finding has important implications for the use of a SEAP reporter in screens of potential antiviral agents.

Chlorination-elimination chemistry coupled with three-component Joullié-Ugi reaction and facile deprotection allowed efficient access to an array of polyhydroxylated pyrrolidines through parallel synthesis that may be considered to be a library of imino (aza) sugars (glycomimetics) and/or dihydroxyprolyl peptides (peptidomimetics). The utility of generating such a library was illustrated by screening against 15 different targets that revealed potent and selective inhibition of the Gaucher's disease glycosyltransferase enzyme glucosylceramide synthase and of primary pathogen model for human hepatitis C virus (HCV) and bovine diarrhoeal virus (BVDV). An observed selectivity for this HCV model over hepatitis B virus and remarkably low toxicity suggest a novel mode of action.

alpha-Galactosylceramide is a glycolipid derived from marine sponges that is currently in human clinical trials as an anticancer agent. It has also been shown to be effective in reducing the amount of hepatitis B virus (HBV) DNA detected in mice that produce HBV constitutively from a transgene. It was assumed that all of the antiviral and antitumor activities associated with alpha-galactosylceramide were mediated through the activation of NK T cells. However, we report here an additional unpredicted activity of alpha-galactosylceramide as a direct antiviral agent and inducer of the innate host defense pathway. To exploit this activity, we have developed a new class of smaller, orally available glycolipids that also induce the innate host defense pathway and have direct activity against HBV and hepatitis C virus.

n-(n-Nonyl)-deoxygalactonojirimycin (n,n-DGJ), an alkylated imino sugar, reduces the amount of HBV DNA produced within the stably transfected HBV-producing HepG2.2.15 line in culture and is under consideration for development as a human therapeutic. n,n-DGJ does not appear to inhibit HBV DNA polymerase activity or envelop antigen production (A. Mehta, S. Carrouee, B. Conyers, R. Jordan, T. Butters, R. A. Dwek, and T. M. Block, Hepatology 33:1488-1495, 2001), and the mechanism of antiviral action is unknown. In this study, the step in the virus life cycle affected by n,n-DGJ was explored. Using Northern analysis and immunoprecipitation with anti-HBc antibody, we found that, under conditions in which cell viability was not affected but viral DNA production was substantially reduced, neither the amount of HBV transcription products nor the core polypeptide was detectably reduced. However, the pregenomic RNA, endogenous polymerase activity, and core polypeptide sedimenting in sucrose gradients with a density consistent with that of assembled nucleocapsids were significantly less in the HepG2.2.15 cells incubated with n,n-DGJ. These data suggest that n,n-DGJ either prevents the maturation of HBV nucleocapsids or destabilizes the formed nucleocapsids. Although the cellular and viral mediators of this inhibition are not known, depletion of nucleocapsid has been attributed to some other compounds as well as interferon's mechanism of anti-HBV action. The similarities and differences between this alkylated imino sugar and these other mediators are discussed.

N-Nonyl-deoxy-galactonojirimycin (N-nonyl-DGJ) has been shown to reduce the amount of hepatitis B virus (HBV) produced by tissue cultures under conditions where cell viability is not affected. We show here that the compound N-nonyl-DGJ was effective against lamivudine-resistant HBV mutants bearing the YMDD motif in the polymerase gene, consistent with the compound's activity being distinct from those of nucleoside inhibitors. To better understand the chemical structures that influence its antiviral activity, a series of imino sugar derivatives were made and tested for their antiviral activity against HBV. This work suggests that the antiviral activity of the alkovirs requires an alkyl chain length of at least eight carbons but that the galactose-based head group can be modified with little or no loss in activity.

Imino sugar glucosidase inhibitors have selective antiviral activity against certain enveloped, mammalian viruses. Deoxynojirimycins (DNJs) modified by N-alkylation to contain a nine carbon atom side chain (N-n-nonyl-deoxynojirimycin; N-nonyl-DNJ, NN-DNJ) were shown to be, for example, at least 20 times more potent in inhibiting hepatitis B virus (HBV) and bovine viral diarrhoea virus (BVDV) in cell based assays than the non-alkylated DNJ. These data suggested that modification of the alkyl side chain could influence antiviral activity. Previous work has focused on varying side chain length. In this report, the influence of side chain branching and cyclization upon toxicity and antiviral activity was explored. Briefly, using a virus secretion assay for HBV and a single step growth (yield reduction) assay for BVDV, 14 different DNJ-based sugars, possessing various N-alkyl substitutions, were tested for antiviral activity. Of the series, N-methoxy-nonyl-DNJ and N-butyl-cyclohexyl DNJ were determined to have the best selectivity index against BVDV and HBV, with the N-methoxy analogue being the most potent with micromolar antiviral activity. The results of this antiviral survey and the implications for the mechanism of action and ultimate therapeutic potential of the DNJ-based imino sugars is provided and discussed.

Interferon alpha-2b (IFN) alone or in combination with Ribavirin is approved in the United States for the treatment of chronic hepatitis C virus (HCV) infection. We have previously reported that the glucosidase inhibitor, n-butyl deoxynojirimycin (nB-DNJ) inhibits the production of infectious bovine diarrhea virus (BVDV) (Proc. Natl. Acad. Sci. 96 (1999) 11878). Since BVDV has been used as a model for HCV and grows productively in tissue culture, and IFN and glucosidase inhibitors are thought to act at different steps in the virus life cycle, it was of interest to determine the antiviral impact of combining nB-DNJ with IFN. Using plaque reduction and single-step growth analyses of the cytopathic BVDV strain NADL, data are presented that shows human IFN inhibited BVDV production in a dose dependent manner, with 3 IU/ml inhibiting 50% of the yield of virus (IC50) when added within 1 h post infection. Under the same conditions, the glucosidase inhibitors nB-DNJ and castanospermine (CST) also prevented BVDV production in a dose dependent manner with IC50s of 226 microM and 47 microM, respectively. In combination with 138 microM nB-DNJ the apparent IC50 for IFN was 0.056 IU/ml. This 54-fold increase in IFN potency suggests that nB-DNJ can synergize with IFN. Two additional independent analyses were performed to measure combination effects which demonstrated that the combined antiviral effect of nB-DNJ and IFN were greater than would be expected for a simple additivity. These data are consistent with an interpretation that glucosidase inhibitors and IFN have a synergistic antiviral effect in tissue culture. The relevance of these finding to treatment of HCV infection is discussed.

Abstract: Pattern recognition receptor (PRR)-mediated innate immune responses play an essential role in defending the host from viral infections. Intriguingly, hepatitis B virus (HBV) has been shown to induce negligible innate immune responses during the early phase of infection. Whether this is due to the failure of the virus to activate PRRs or suppression of PRR signaling pathways by the virus remains controversial. However, a plethora of evidence suggests that HBV is sensitive to PRR ligand-induced antiviral responses. This review summarizes current understanding of the interaction between HBV and PRR-mediated host innate immunity, antiviral mechanisms of PRR responses against HBV and strategies to combat chronic HBV infection via induction of host innate antiviral responses. [Copyright &y& Elsevier]

Recognition of virus infection by innate pattern recognition receptors (PRRs), including membrane-associated toll-like receptors (TLR) and cytoplasmic RIG-I-like receptors (RLR), activates cascades of signal transduction pathways leading to production of type I interferons (IFN) and proinflammatory cytokines that orchestrate the elimination of the viruses. Although it has been demonstrated that PRR-mediated innate immunity plays an essential role in defending virus from infection, it also occasionally results in overwhelming production of proinflammatory cytokines that cause severe inflammation, blood vessel leakage and tissue damage. In our efforts to identify small molecules that selectively enhance PRR-mediated antiviral, but not the detrimental inflammatory response, we discovered a compound, RO 90-7501 ('2'-(4- Aminophenyl)-[2,5'-bi-1H-benzimidazol]-5-amine), that significantly promoted both TLR3 and RLR ligand-induced IFN-β gene expression and antiviral response, most likely via selective activation of p38 mitogen-activated protein kinase (MAPK) pathway. Our results thus imply that pharmacological modulation of PRR signal transduction pathways in favor of the induction of a beneficial antiviral response can be a novel therapeutic strategy. [ABSTRACT FROM AUTHOR]

Chronic hepatitis B virus (HBV) infection is a global public health problem. Although the currently approved medications can reliably reduce the viral load and prevent the progression of liver diseases, they fail to cure the viral infection. In an effort toward discovery of novel antiviral agents against HBV, a group of benzamide (BA) derivatives that significantly reduced the amount of cytoplasmic HBV DNA were discovered. The initial lead optimization efforts identified two BA derivatives with improved antiviral activity for further mechanistic studies. Interestingly, similar to our previously reported sulfamoylbenzamides (SBAs), the BAs promote the formation of empty capsids through specific interaction with HBV core protein but not other viral and host cellular components. Genetic evidence suggested that both SBAs and BAs inhibited HBV nucleocapsid assembly by binding to the heteroaryldihydropyrimidine (HAP) pocket between core protein dimer-dimer interfaces. However, unlike SBAs, BA compounds uniquely induced the formation of empty capsids that migrated more slowly in native agarose gel electrophoresis from A36V mutant than from the wild-type core protein. Moreover, we showed that the assembly of chimeric capsids from wild-type and drug-resistant core proteins was susceptible to multiple capsid assembly modulators. Hence, HBV core protein is a dominant antiviral target that may suppress the selection of drug-resistant viruses during core protein-targeting antiviral therapy. Our studies thus indicate that BAs are a chemically and mechanistically unique type of HBV capsid assembly modulators and warranted for further development as antiviral agents against HBV. IMPORTANCE HBV core protein plays essential roles in many steps of the viral replication cycle. In addition to packaging viral pregenomic RNA (pgRNA) and DNA polymerase complex into nucleocapsids for reverse transcriptional DNA replication to take place, the core protein dimers, existing in several different quaternary structures in infected hepatocytes, participate in and regulate HBV virion assembly, capsid uncoating, and covalently closed circular DNA (cccDNA) formation. It is anticipated that small molecular core protein assembly modulators may disrupt one or multiple steps of HBV replication, depending on their interaction with the distinct quaternary structures of core protein. The discovery of novel core protein-targeting antivirals, such as benzamide derivatives reported here and investigation of their antiviral mechanism may lead to the identification of antiviral therapeutics for the cure of chronic hepatitis B. [ABSTRACT FROM AUTHOR]

Although a highly effective vaccine is available, the number of yellow fever cases has increased over the past 2 decades, which highlights the pressing need for antiviral therapeutics. In a high-throughput screening campaign, we identified an acetic acid benzodiazepine (BDAA) compound which potently inhibits yellow fever virus (YFV). Interestingly, while treatment of YFV-infected cultures with 2 μMBDAA reduced the virion production by greater than 2 logs, the compound was not active against 21 other viruses from 14 different viral families. Selection and genetic analysis of drug-resistant viruses revealed that replacement of the proline at amino acid 219 (P219) of the nonstructural protein 4B (NS4B) with serine, threonine, or alanine conferred YFV with resistance to BDAA without apparent loss of replication fitness in cultured mammalian cells. However, replacement of P219 with glycine conferred BDAA resistance with significant loss of replication ability. Bioinformatics analysis predicts that the P219 amino acid is localized at the endoplasmic reticulum lumen side of the fifth putative transmembrane domain of NS4B, and the mutation may render the viral protein incapable of interacting with BDAA. Our studies thus revealed an important role and the structural basis for the NS4B protein in supporting YFV replication. Moreover, in YFV-infected hamsters, oral administration of BDAA protected 90% of the animals from death, significantly reduced viral load by greater than 2 logs, and attenuated virus infection-induced liver injury and body weight loss. The encouraging preclinical results thus warrant further development of BDAA or its derivatives as antiviral agents to treat yellow fever. [ABSTRACT FROM AUTHOR]

Alpha interferon (IFN-α) is an approved medication for chronic hepatitis B. Gamma interferon (IFN-γ) is a key mediator of host antiviral immunity against hepatitis B virus (HBV) infection in vivo. However, the molecular mechanism by which these antiviral cytokines suppress HBV replication remains elusive. Using an immortalized murine hepatocyte (AML12)-derived cell line supporting tetracycline-inducible HBV replication, we show in this report that both IFN-α and IFN-γ efficiently reduce the amount of intracellular HBV nucleocapsids. Furthermore, we provide evidence suggesting that the IFN-induced cellular antiviral response is able to distinguish and selectively accelerate the decay of HBV replication-competent nucleocapsids but not empty capsids in a proteasome-dependent manner. Our findings thus reveal a novel antiviral mechanism of IFNs and provide a basis for a better understanding of HBV pathobiology. [ABSTRACT FROM AUTHOR]

Hepatitis C virus (HCV) infection is a common cause of chronic hepatitis and is currently treated with alpha interferon (IFN-α)-based therapies. However, the underlying mechanism of IFN-α therapy remains to be elucidated. To identify the cellular proteins that mediate the antiviral effects of IFN-α, we created a HEK293-based cell culture system to inducibly express individual interferon-stimulated genes (ISGs) and determined their antiviral effects against HCV. By screening 29 ISGs that are induced in Huh7 cells by IFN-α and/or up-regulated in HCV-infected livers, we discovered that viperin, ISG20, and double-stranded RNA-dependent protein kinase (PKR) noncytolytically inhibited the replication of HCV replicons. Mechanistically, inhibition of HCV replication by ISG20 and PKR depends on their 3'-5' exonuclease and protein kinase activities, respectively. Moreover, our work, for the first time, provides strong evidence suggesting that viperin is a putative radical S-adenosyl-L-methionine (SAM) enzyme. In addition to demonstrating that the antiviral activity of viperin depends on its radical SAM domain, which contains conserved motifs to coordinate [4Fe-4S] cluster and cofactor SAM and is essential for its enzymatic activity, mutagenesis studies also revealed that viperin requires an aromatic amino acid residue at its C terminus for proper antiviral function. Furthermore, although the N-terminal 70 amino acid residues of viperin are not absolutely required, deletion of this region significantly compromises its antiviral activity against HCV. Our findings suggest that viperin represents a novel antiviral pathway that works together with other antiviral proteins, such as ISG20 and PKR, to mediate the IFN response against HCV infection. [ABSTRACT FROM AUTHOR]