Antiviral effect of N-butyldeoxynojirimycin against bovine viral diarrhea virus correlates with misfolding of E2 envelope proteins and impairment of their association into E1-E2 heterodimers

Exogenous interactome analysis of bovine viral diarrhea virus-host using network based-approach and identification of hub genes and important pathways involved in virus pathogenesis

Bovine viral diarrhea (BVD) is one of the most important diseases in livestock, caused by BVD virus (BVDV). During the pathogenesis of the virus, many interactions occur between host and viral proteins. Studying these interactions can help better understand the pathogenesis of the virus, identify putative functional proteins, and find new treatment and prevention strategies. To this aim, a BVDV-host protein-protein interaction (PPI) network map was constructed using Cytoscape and analyzed with cytoHubba, Kyoto Encyclopedia of Genes and Genomics (KEGG), Gene Ontology (GO), and Protein Analysis Through Evolutionary Relationships (PANTHER). Npro with 125 connections had the greatest number of interactions with host proteins. CD46, EEF-2, and TXN genes were detected as hub genes using different ranking algorithms in cytoHubba. BVDV interactions with its host mainly focus on targeting translation, protein synthesis, and cellular metabolism pathways. Different classes of proteins including translational proteins, nucleic acid metabolism proteins, metabolite interconversion enzymes, and protein-modifying enzymes are affected by BVDV. These findings improve our understanding of the effects of the virus on the cell. Hub genes and key pathways identified in the present study can serve as targets for novel BVDV prevention or treatment strategies.

Glycosylation Modulation Dictates Trafficking and Interaction of SARS-CoV-2 S1 Subunit and ACE2 in Intestinal Epithelial Caco-2 Cells

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mainly targets the upper respiratory tract. It gains entry by interacting with the host cell receptor angiotensin-converting enzyme 2 (ACE2) via its heavily glycosylated spike glycoprotein. SARS-CoV-2 can also affect the gastrointestinal tract. Given the significant role of glycosylation in the life cycle of proteins and the multisystem target of SARS-CoV-2, the role of glycosylation in the interaction of S1 with ACE2 in Caco-2 cells was investigated after modulation of their glycosylation patterns using N-butyldeoxynojirimycin (NB-DNJ) and 1-deoxymannojirimycin (dMM), in addition to mutant CHO cells harboring mutations at different stages of glycosylation. The data show a substantial reduction in the interactions between the altered glycosylation forms of S1 and ACE2 in the presence of NB-DNJ, while varied outcomes resulted from dMM treatment. These results highlight the promising effects of NB-DNJ and its potential use as an off-label drug to treat SARS-CoV-2 infections.

Benzimidazole-2-Phenyl-Carboxamides as Dual-Target Inhibitors of BVDV Entry and Replication

Bovine viral diarrhea virus (BVDV), also known as Pestivirus A, causes severe infection mostly in cattle, but also in pigs, sheep and goats, causing huge economical losses on agricultural farms every year. The infections are actually controlled by isolation of persistently infected animals and vaccination, but no antivirals are currently available to control the spread of BVDV on farms. BVDV binds the host cell using envelope protein E2, which has only recently been targeted in the research of a potent and efficient antiviral. In contrast, RdRp has been successfully inhibited by several classes of compounds in the last few decades. As a part of an enduring antiviral research agenda, we designed a new series of derivatives that emerged from an isosteric substitution of the main scaffold in previously reported anti-BVDV compounds. Here, the new compounds were characterized and tested, where several turned out to be potent and selectively active against BVDV. The mechanism of action was thoroughly studied using a time-of-drug-addition assay and the results were validated using docking simulations.

75 years of bovine viral diarrhea virus: Current status and future applications of the use of directed antivirals

Bovine viral diarrhea virus (BVDV) was first reported 75 years ago and remains a source of major financial and production losses in the North American cattle industry. Currently, control methods in North America primarily center around biosecurity and vaccination programs; however, despite high levels of vaccination, the virus persists in the cattle herd due at least in part to the often-insidious nature of disease and the constant viremia and viral shedding of persistently infected animals which act as a reservoir for the virus. Continued development of targeted antivirals represents an additional tool for the prevention of BVDV-associated losses. Currently, in vivo studies of BVDV antivirals are relatively limited and have primarily been directed at the RNA-dependent RNA polymerase which represents the viral target with the highest potential for commercial development. Additional live animal studies have explored the potential of exogenous interferon treatment. Future research of commercial antivirals must focus on the establishment and validation of in vivo efficacy for compounds with demonstrated antiviral potential. The areas which provide the most viable economic justification for the research and development of antivirals drugs are the fed cattle sector, outbreak control, and wildlife or animals of high genetic value. With further development, targeted antivirals represent an additional tool for the management and control of BVDV in North American cattle herds.

Design and Optimization of Quinazoline Derivatives: New Non-nucleoside Inhibitors of Bovine Viral Diarrhea Virus

Bovine viral diarrhea virus (BVDV) belongs to the Pestivirus genus (Flaviviridae). In spite of the availability of vaccines, the virus is still causing substantial financial losses to the livestock industry. In this context, the use of antiviral agents could be an alternative strategy to control and reduce viral infections. The viral RNA-dependent RNA polymerase (RdRp) is essential for the replication of the viral genome and constitutes an attractive target for the identification of antiviral compounds. In a previous work, we have identified potential molecules that dock into an allosteric binding pocket of BVDV RdRp via a structure-based virtual screening approach. One of them, N-(2-morpholinoethyl)-2-phenylquinazolin-4-amine [1, 50% effective concentration (EC₅₀) = 9.7 ± 0.5 μM], was selected to perform different chemical modifications. Among 24 derivatives synthesized, eight of them showed considerable antiviral activity. Molecular modeling of the most active compounds showed that they bind to a pocket located in the fingers and thumb domains in BVDV RdRp, which is different from that identified for other non-nucleoside inhibitors (NNIs) such as thiosemicarbazone (TSC). We selected compound 2-[4-(2-phenylquinazolin-4-yl)piperazin-1-yl]ethanol (1.9; EC₅₀ = 1.7 ± 0.4 μM) for further analysis. Compound 1.9 was found to inhibit the in vitro replication of TSC-resistant BVDV variants, which carry the N264D mutation in the RdRp. In addition, 1.9 presented adequate solubility in different media and a high-stability profile in murine and bovine plasma.

Iminosugars: A host-targeted approach to combat Flaviviridae infections

N-linked glycosylation is the most common form of protein glycosylation and is required for the proper folding, trafficking, and/or receptor binding of some host and viral proteins. As viruses lack their own glycosylation machinery, they are dependent on the host's machinery for these processes. Certain iminosugars are known to interfere with the N-linked glycosylation pathway by targeting and inhibiting α-glucosidases I and II in the endoplasmic reticulum (ER). Perturbing ER α-glucosidase function can prevent these enzymes from removing terminal glucose residues on N-linked glycans, interrupting the interaction between viral glycoproteins and host chaperone proteins that is necessary for proper folding of the viral protein. Iminosugars have demonstrated broad-spectrum antiviral activity in vitro and in vivo against multiple viruses. This review discusses the broad activity of iminosugars against Flaviviridae. Iminosugars have shown favorable activity against multiple members of the Flaviviridae family in vitro and in murine models of disease, although the activity and mechanism of inhibition can be virus-specfic. While iminosugars are not currently approved for the treatment of viral infections, their potential use as future host-targeted antiviral (HTAV) therapies continues to be investigated.

Anti-BVDV Activity Evaluation of Naphthoimidazole Derivatives Compared with Parental Imidazoquinoline Compounds

Background:

Pestivirus genus includes animal pathogens which are involved in economic impact for the livestock industry. Among others, Bovine Viral Diarrhoea Virus (BVDV) establish a persistent infection in cattle causing a long list of symptoms and a high mortality rate. In the last decades, we synthesised and reported a certain number of anti-BVDV compounds.

Methods:

In them, imidazoquinoline derivatives turned out as the most active. Their mechanism of actions has been deeply investigated, BVDV RNA-dependent RNA polymerase (RpRd) resulted as target and the way of binding was predicted in silico through three main H-bond interaction with the target.

The prediction could be confirmed by target or ligand mutation. The first approach has already been performed and published confirming the in silico prediction.

Results:

Here, we present how the ligand chemical modification affects the anti-BVDV activity. The designed compounds were synthesised and tested against BVDV as in silico assay negative control.

Conclusion:

The antiviral results confirmed the predicted mechanism of action, as the newly synthesised compounds resulted not active in the in vitro BVDV infection inhibition.

Quinolinecarboxamides Inhibit the Replication of the Bovine Viral Diarrhea Virus by Targeting a Hot Spot for the Inhibition of Pestivirus Replication in the RNA-Dependent RNA Polymerase

The bovine viral diarrhea virus (BVDV), a pestivirus from the family of Flaviviridae is ubiquitous and causes a range of clinical manifestations in livestock, mainly cattle. Two quinolinecarboxamide analogues were identified in a CPE-based screening effort, as selective inhibitors of the in vitro bovine viral diarrhea virus (BVDV) replication, i.e., TO505-6180/CSFCI (average EC₅₀ = 0.07 µM, SD = 0.02 µM, CC₅₀ > 100 µM) and TO502-2403/CSFCII (average EC₅₀ = 0.2 µM, SD = 0.06 µM, CC₅₀ > 100 µM). The initial antiviral activity observed for both hits against BVDV was corroborated by measuring the inhibitory effect on viral RNA synthesis and the production of infectious virus. Modification of the substituents on the quinolinecarboxamide scaffold resulted in analogues that proved about 7-fold more potent (average EC₅₀ = 0.03 with a SD = 0.01 µM) and that were devoid of cellular toxicity, for the concentration range tested (SI = 3333). CSFCII resistant BVDV variants were selected and were found to carry the F224P mutation in the viral RNA-dependent RNA polymerase (RdRp), whereas CSFCI resistant BVDV carried two mutations in the same region of the RdRp, i.e., N264D and F224Y. Likewise, molecular modeling revealed that F224P/Y and N264D are located in a small cavity near the fingertip domain of the pestivirus polymerase. CSFC-resistant BVDV proved to be cross-resistant to earlier reported pestivirus inhibitors (BPIP, AG110, LZ37, and BBP) that are known to target the same region of the RdRp. CSFC analogues did not inhibit the in vitro activity of recombinant BVDV RdRp but inhibited the activity of BVDV replication complexes (RCs). CSFC analogues likely interact with the fingertip of the pestivirus RdRp at the same position as BPIP, AG110, LZ37, and BBP. This indicates that this region is a “hot spot” for the inhibition of pestivirus replication.

Assessment of the potential for host-targeted iminosugars UV-4 and UV-5 activity against filovirus infections in vitro and in vivo

Iminosugars are host-directed antivirals with broad-spectrum activity. The iminosugar, N-butyl-deoxynojirimycin (NB-DNJ or Miglustat^®), is used in humans for treatment of Gaucher's disease and has mild antiviral properties. More potent analogs of NB-DNJ have been generated and have demonstrated activity against a variety of viruses including flaviviruses, influenza, herpesviruses and filoviruses. In the current study, a panel of analogs based on NB-DNJ was analyzed for activity against Ebola (EBOV) and Marburg viruses (MARV). The antiviral activity of NB-DNJ (UV-1), UV-2, UV-3, UV-4 and UV-5 against both EBOV and MARV was demonstrated in Vero cells. Subsequent studies to examine the activity of UV-4 and UV-5 using rodent models of EBOV and MARV were performed. In vivo efficacy studies provided inconsistent data following treatment with iminosugars using filovirus mouse models. A tolerability study in nonhuman primates demonstrated that UV-4 could be administered at much higher dose levels than rodents. Since UV-4 was active in vitro, had been demonstrated to be active against influenza and dengue in vivo, and was being tested in a Phase 1 clinical trial, a small proof-of-concept nonhuman primate trial was performed to determine whether this antiviral candidate could provide clinical benefit to EBOV-infected individuals. Administration of UV-4B did not provide a clinical or survival benefit to macaques infected with EBOV-Makona; however, dosing of animals was not optimal in this study. Efficacy may be improved by thrice daily dosing (e.g. by nasogastric tube feeding) to match the efficacious dosing regimens demonstrated against dengue and influenza viruses.

Minimal In Vivo Efficacy of Iminosugars in a Lethal Ebola Virus Guinea Pig Model

The antiviral properties of iminosugars have been reported previously in vitro and in small animal models against Ebola virus (EBOV); however, their effects have not been tested in larger animal models such as guinea pigs. We tested the iminosugars N-butyl-deoxynojirimycin (NB-DNJ) and N-(9-methoxynonyl)-1deoxynojirimycin (MON-DNJ) for safety in uninfected animals, and for antiviral efficacy in animals infected with a lethal dose of guinea pig adapted EBOV. 1850 mg/kg/day NB-DNJ and 120 mg/kg/day MON-DNJ administered intravenously, three times daily, caused no adverse effects and were well tolerated. A pilot study treating infected animals three times within an 8 hour period was promising with 1 of 4 infected NB-DNJ treated animals surviving and the remaining three showing improved clinical signs. MON-DNJ showed no protective effects when EBOV-infected guinea pigs were treated. On histopathological examination, animals treated with NB-DNJ had reduced lesion severity in liver and spleen. However, a second study, in which NB-DNJ was administered at equally-spaced 8 hour intervals, could not confirm drug-associated benefits. Neither was any antiviral effect of iminosugars detected in an EBOV glycoprotein pseudotyped virus assay. Overall, this study provides evidence that NB-DNJ and MON-DNJ do not protect guinea pigs from a lethal EBOV-infection at the dose levels and regimens tested. However, the one surviving animal and signs of improvements in three animals of the NB-DNJ treated cohort could indicate that NB-DNJ at these levels may have a marginal beneficial effect. Future work could be focused on the development of more potent iminosugars.

Synthesis of β-Enantiomers of N4-Hydroxy-3′-Deoxy-Pyrimidine Nucleosides and Their Evaluation against Bovine Viral Diarrhoea Virus and Hepatitis C Virus in Cell Culture

N4-Hydroxycytidine (NHC) was recently reported to have anti-pestivirus and anti-hepacivirus activity. It is thought that this nucleoside acts as a weak alternative substrate for the hepatitis C virus (HCV) polymerase. In addition to NHC, 3′-deoxyuridine (3′-dU) was found to inhibit bovine diarrhoea virus (BVDV) production by 1 log10 at 37.2 μM. These initial findings prompted the synthesis of β-D and β-L analogues of (i) base-modified 3′-deoxy-NHC; (ii) 3′-deoxyuridine; and 3′-deoxycytidine. The antiviral activity of these 42 nucleosides was evaluated against BVDV and HCV bicistronic replicon in cell culture. Among the NHC analogues, the antiviral activity observed for the β-L-3′-deoxy-5-fluoro-derivative 1-(3-deoxy-β-L- erythro-pentofuranosyl)-5-fluoro-4-hydrox-yaminopyrimidin-2( 1H)-one and the β-D-3′-deoxy-5-iodo-derivative 1-(3-deoxy-β-D-erythro-pentofuranosyl)-5-iodocytosine in the replicon system (1 log10 reduction at 100 μM) was due to the concomitant toxicity towards intracellular ribosomal RNA levels (CC90 equal or lower than the EC90). In conclusion, none of the newly synthesized derivatives exhibited enhanced antiviral activity compared to the parent nucleoside NHC.

Action of Celgosivir (6 O-Butanoyl Castanospermine) against the Pestivirus BVDV: Implications for the Treatment of Hepatitis C

α-Glucosidase I inhibitors have been shown to inhibit the replication of a broad range of enveloped viruses by preventing the correct folding of their envelope glycoproteins. This study assesses the potential of 6 O-butanoyl castanospermine (cel-gosivir) as a treatment for hepatitis C virus (HCV). In the absence of an adequate culture system for HCV, the closely related virus, bovine viral diarrhoea virus (BVDV), was used as a surrogate model. Using both a plaque assay and a cytopathic effect assay, celgosivir (IC50 16 and 47 μM respectively) was shown to be more potent than N-nonyl DNJ (105 and 74 μM), castanospermine (110 and 367 μM) and N-butyl DNJ (>250 and 550 μM). Of the α-glucosi-dase inhibitors tested, only N-nonyl DNJ showed evidence of toxicity (CC50 ≥120 μM). Two-way combinations of interferon-α, ribavirin and either celgosivir or castanospermine demonstrated that each could enhance the antiviral efficacy of the others, either additively or synergistically. The observation that the number of viral genomes released from BVDV-infected cells was inhibited by either castanospermine or celgosivir in parallel with the number of infectious units was taken as confirmation that these α-glucosidase I inhibitors block the production or release of flavivirus particles.

3-(imidazo[1,2-a:5,4-b']dipyridin-2-yl)aniline inhibits pestivirus replication by targeting a hot spot drug binding pocket in the RNA-dependent RNA polymerase

The compound 3-(imidazo[1,2-a:5,4-b']dipyridin-2-yl)aniline (CF02334) was identified as a selective inhibitor of the cytopathic effect (CPE) caused by bovine viral diarrhea virus (BVDV) in a virus-cell-based assay. The EC50-values for inhibition of CPE, viral RNA synthesis and the production of infectious virus progeny were 13.0 ± 0.6 μM, 2.6 ± 0.9 μM and 17.8 ± 0.6 μM, respectively. CF02334 was found to be inactive in the hepatitis C subgenomic replicon system. CF02334-resistant BVDV was obtained and was found to carry the N264D mutation in the viral RNA-dependent RNA polymerase (RdRp). Molecular modeling revealed that N264D is located in a small cavity near the fingertip domain of the pestivirus polymerase. CF02334-resistant BVDV was proven to be cross-resistant to BPIP, AG110 and LZ37, inhibitors that have previously been described to target the same region of the BVDV RdRp. CF02334 did not inhibit the in vitro activity of recombinant BVDV RdRp, but did inhibit the activity of BVDV replication complexes. Taken together, these observations indicate that CF02334 likely interacts with the fingertip of the pestivirus RdRp at the same position as BPIP, AG110 and LZ37, which marks this region of the viral polymerase as a "hot spot" for inhibition of pestivirus replication.

Morphology and Molecular Composition of Purified Bovine Viral Diarrhea Virus Envelope

The family Flaviviridae includes viruses that have different virion structures and morphogenesis mechanisms. Most cellular and molecular studies have been so far performed with viruses of the Hepacivirus and Flavivirus genera. Here, we studied bovine viral diarrhea virus (BVDV), a member of the Pestivirus genus. We set up a method to purify BVDV virions and analyzed their morphology by electron microscopy and their protein and lipid composition by mass spectrometry. Cryo-electron microscopy showed near spherical viral particles displaying an electron-dense capsid surrounded by a phospholipid bilayer with no visible spikes. Most particles had a diameter of 50 nm and about 2% were larger with a diameter of up to 65 nm, suggesting some size flexibility during BVDV morphogenesis. Morphological and biochemical data suggested a low envelope glycoprotein content of BVDV particles, E1 and E2 being apparently less abundant than E^rns. Lipid content of BVDV particles displayed a ~2.3 to 3.5-fold enrichment in cholesterol, sphingomyelin and hexosyl-ceramide, concomitant with a 1.5 to 5-fold reduction of all glycerophospholipid classes, as compared to lipid content of MDBK cells. Although BVDV buds in the endoplasmic reticulum, its lipid content differs from a typical endoplasmic reticulum membrane composition. This suggests that BVDV morphogenesis includes a mechanism of lipid sorting. Functional analyses confirmed the importance of cholesterol and sphingomyelin for BVDV entry. Surprisingly, despite a high cholesterol and sphingolipid content of BVDV envelope, E2 was not found in detergent-resistant membranes. Our results indicate that there are differences between the structure and molecular composition of viral particles of Flaviviruses, Pestiviruses and Hepaciviruses within the Flaviviridae family.

Bovine viral diarrhea virus (BVDV) is the etiologic agent of mucosal disease and bovine viral diarrhea, two economically important diseases of the livestock. BVDV is a member of the Pestivirus genus in the Flaviviridae family, which also includes Hepacivirus and Flavivirus genera. Members of this family share similar genome organization and replication strategies, but differ about their mode of transmission and particle structure. Whereas most studies have been so far performed on viruses of the Hepacivirus and Flavivirus genera, little is known about infectious particles of pestiviruses. In this study, we set up a novel purification method of BVDV infectious particles and analyzed their morphology by cryo-electron microscopy and their molecular composition by mass spectrometry. Our results provide new insights into the structure and biochemical composition of a pestivirus infectious particle, and have implications for research on molecular mechanisms of their morphogenesis and entry.

Structures and Functions of Pestivirus Glycoproteins: Not Simply Surface Matters

Pestiviruses, which include economically important animal pathogens such as bovine viral diarrhea virus and classical swine fever virus, possess three envelope glycoproteins, namely E^rns, E1, and E2. This article discusses the structures and functions of these glycoproteins and their effects on viral pathogenicity in cells in culture and in animal hosts. E2 is the most important structural protein as it interacts with cell surface receptors that determine cell tropism and induces neutralizing antibody and cytotoxic T-lymphocyte responses. All three glycoproteins are involved in virus attachment and entry into target cells. E1-E2 heterodimers are essential for viral entry and infectivity. E^rns is unique because it possesses intrinsic ribonuclease (RNase) activity that can inhibit the production of type I interferons and assist in the development of persistent infections. These glycoproteins are localized to the virion surface; however, variations in amino acids and antigenic structures, disulfide bond formation, glycosylation, and RNase activity can ultimately affect the virulence of pestiviruses in animals. Along with mutations that are driven by selection pressure, antigenic differences in glycoproteins influence the efficacy of vaccines and determine the appropriateness of the vaccines that are currently being used in the field.

The Molecular Biology of Pestiviruses

Pestiviruses are among the economically most important pathogens of livestock. The biology of these viruses is characterized by unique and interesting features that are both crucial for their success as pathogens and challenging from a scientific point of view. Elucidation of these features at the molecular level has made striking progress during recent years. The analyses revealed that major aspects of pestivirus biology show significant similarity to the biology of human hepatitis C virus (HCV). The detailed molecular analyses conducted for pestiviruses and HCV supported and complemented each other during the last three decades resulting in elucidation of the functions of viral proteins and RNA elements in replication and virus-host interaction. For pestiviruses, the analyses also helped to shed light on the molecular basis of persistent infection, a special strategy these viruses have evolved to be maintained within their host population. The results of these investigations are summarized in this chapter.

The elusive function of the hepatitis C virus p7 protein

Hepatitis C virus (HCV) is a major global health burden with 2–3% of the world׳s population being chronically infected. Persistent infection can lead to cirrhosis and hepatocellular carcinoma. Recently available treatment options show enhanced efficacy of virus clearance, but are associated with resistance and significant side effects. This warrants further research into the basic understanding of viral proteins and their pathophysiology. The p7 protein of HCV is an integral membrane protein that forms an ion-channel. The role of p7 in the HCV life cycle is presently uncertain, but most of the research performed to date highlights its role in the virus assembly process. The aim of this review is to provide an overview of the literature investigating p7, its structural and functional details, and to summarize the developments to date regarding potential anti-p7 compounds. A better understanding of this protein may lead to development of a new and effective therapy.

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This review paper provides an overview of the literature investigating HCV.

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The content focuses on p7 structural and functional details.

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We summarize the developments to date regarding potential anti-p7 compounds.

Recombinant pestivirus E2 glycoproteins prevent viral attachment to permissive and non permissive cells with different efficiency

Bovine viral diarrhoea virus (BVDV) is an economically important animal pathogen, which like other pestiviruses has similar molecular biological features to hepaciviruses, including human Hepatitis C virus. The pestivirus E2 glycoproteins are the major target for virus-neutralising antibodies, as well as playing a role in receptor binding and host range restriction. In this study, recombinant E2 glycoproteins (rE2) derived from three different pestivirus species were examined for their inhibitory effects on pestivirus infectivity in cell culture. Histidine-tagged rE2 glycoproteins of BVDV type 2 strain 178003, BVDV type 1 strain Oregon C24V and CSFV strain Alfort 187 were produced in Spodoptera frugiperda insect cells and purified under native conditions. The ability of rE2 glycoprotein to inhibit the infection of permissive cells by both homologous and heterologous virus was compared, revealing that the inhibitory effects of rE2 glycoproteins correlated with the predicted similarity of the E2 structures in the recombinant protein and the test virus. This result suggests that the sequence and structure of E2 are likely to be involved in the host specificity of pestiviruses at their point of uptake into cells.

Substituted 2,6-bis(benzimidazol-2-yl)pyridines: a novel chemical class of pestivirus inhibitors that targets a hot spot for inhibition of pestivirus replication in the RNA-dependent RNA polymerase

2,6-Bis(benzimidazol-2-yl)pyridine (BBP/CSFA-0) was identified in a CPE-based screening as a selective inhibitor of the in vitro bovine viral diarrhea virus (BVDV) replication. The EC50-values for the inhibition of BVDV-induced cytopathic (CPE) effect, viral RNA synthesis and the production of infectious virus were 0.3±0.1μM, 0.05±0.01μM and 0.3±0.04μM, respectively. Furthermore, BBP/CSFA-0 inhibits the in vitro replication of the classical swine fever virus (CSFV) with an EC50 of 0.33±0.25μM. BBP/CSFA-0 proved in vitro inactive against the hepatitis C virus, that belongs like BVDV and CSFV to the family of Flaviviridae. Modification of the substituents on the two 1H-benzimidazole groups of BBP resulted in analogues equipotent in anti-BVDV activity (EC50=0.7±0.1μM), devoid of cytotoxicity (S.I.=142). BBP resistant BVDV was selected for and was found to carry the I261M mutation in the viral RNA-dependent RNA polymerase (RdRp). Likewise, BBP-resistant CSFV was selected for; this variant carries either an I261N or a P262A mutation in NS5B. Molecular modeling revealed that I261 and P262 are located in a small cavity near the fingertip domain of the pestivirus polymerase. BBP-resistant BVDV and CSFV proved to be cross-resistant to earlier reported pestivirus inhibitors (BPIP, AG110 and LZ37) that are known to target the same region of the RdRp. BBP did not inhibit the in vitro activity of recombinant BVDV RdRp but inhibited the activity of BVDV replication complexes (RCs). BBP interacts likely with the fingertip of the pestivirus RdRp at the same position as BPIP, AG110 and LZ37. This indicates that this region is a "hot spot" for inhibition of pestivirus replication.

Structural models of the membrane anchors of envelope glycoproteins E1 and E2 from pestiviruses

The membrane anchors of viral envelope proteins play essential roles in cell entry. Recent crystal structures of the ectodomain of envelope protein E2 from a pestivirus suggest that E2 belongs to a novel structural class of membrane fusion machinery. Based on geometric constraints from the E2 structures, we generated atomic models of the E1 and E2 membrane anchors using computational approaches. The E1 anchor contains two amphipathic perimembrane helices and one transmembrane helix; the E2 anchor contains a short helical hairpin stabilized in the membrane by an arginine residue, similar to flaviviruses. A pair of histidine residues in the E2 ectodomain may participate in pH sensing. The proposed atomic models point to Cys987 in E2 as the site of disulfide bond linkage with E1 to form E1-E2 heterodimers. The membrane anchor models provide structural constraints for the disulfide bonding pattern and overall backbone conformation of the E1 ectodomain.

A novel membrane fusion protein family in Flaviviridae?

Enveloped viruses must fuse their lipid membrane to a cellular membrane to deliver their genome into the cytoplasm for replication. Viral envelope proteins catalyze this critical membrane fusion event. They fall into three distinct structural classes. In 2013, envelope proteins from a pestivirus and hepatitis C virus were found to have two distinct novel folds. This was unexpected because these viruses are in the same family as flaviviruses, which have class II fusion proteins. We propose that the membrane fusion machinery of the closely related pestiviruses and hepatitis C virus defines a new structural class. This and other recently identified structural relationships between viral fusion proteins shift the paradigm for how these proteins evolved.

Morphogenesis of pestiviruses: new insights from ultrastructural studies of strain Giraffe-1

Knowledge on the morphogenesis of pestiviruses is limited due to low virus production in infected cells. In order to localize virion morphogenesis and replication sites of pestiviruses and to examine intracellular virion transport, a cell culture model was established to facilitate ultrastructural studies. Based on results of virus growth kinetic analysis and quantification of viral RNA, pestivirus strain Giraffe-1 turned out to be a suitable candidate for studies on virion generation and export from culture cells. Using conventional transmission electron microscopy and single-tilt electron tomography, we found virions located predominately in the lumen of the endoplasmic reticulum (ER) in infected cells and were able to depict the budding process of virions at ER membranes. Colocalization of the viral core protein and the envelope glycoprotein E2 with the ER marker protein disulfide isomerase (PDI) was demonstrated by immunogold labeling of cryosections. Moreover, pestivirions could be shown in transport vesicles and the Golgi complex and during exocytosis. Interestingly, viral capsid protein and double-stranded RNA (dsRNA) were detected in multivesicular bodies (MVBs), which implies that the endosomal compartment plays a role in pestiviral replication. Significant cellular membrane alterations such as those described for members of the Flavivirus and Hepacivirus genera were not found. Based on the gained morphological data, we present a consistent model of pestivirus morphogenesis.

Imino sugar glucosidase inhibitors as broadly active anti-filovirus agents

Ebola virus and Marburg virus are members of the family of Filoviridae and are etiological agents of a deadly hemorrhagic fever disease. The clinical symptoms of Ebola and Marburg hemorrhagic fevers are difficult to distinguish and there are currently no specific antiviral therapies against either of the viruses. Therefore, a drug that is safe and effective against both would be an enormous breakthrough. We and others have shown that the folding of the glycoproteins of many enveloped viruses, including the filoviruses, is far more dependent upon the calnexin pathway of protein folding than are most host glycoproteins. Drugs that inhibit this pathway would be expected to be selectively antiviral. Indeed, as we summarize in this review, imino sugars that are competitive inhibitors of the host endoplasmic reticular α-glucosidases I and II, which are enzymes that process N-glycan on nascent glycoproteins and thereby inhibit calnexin binding to the nascent glycoproteins, have been shown to have antiviral activity against a number of enveloped viruses including filoviruses. In this review, we describe the state of development of imino sugars for use against the filoviruses, and provide an explanation for the basis of their antiviral activity as well as limitations.

Structure of a pestivirus envelope glycoprotein E2 clarifies its role in cell entry

Enveloped viruses have developed various adroit mechanisms to invade their host cells. This process requires one or more viral envelope glycoprotein to achieve cell attachment and membrane fusion. Members of the Flaviviridae such as flaviviruses possess only one envelope glycoprotein, E, whereas pestiviruses and hepacivirus encode two glycoproteins, E1 and E2. Although E2 is involved in cell attachment, it has been unclear which protein is responsible for membrane fusion. We report the crystal structures of the homodimeric glycoprotein E2 from the pestivirus bovine viral diarrhea virus 1 (BVDV1) at both neutral and low pH. Unexpectedly, BVDV1 E2 does not have a class II fusion protein fold, and at low pH the N-terminal domain is disordered, similarly to the intermediate postfusion state of E2 from sindbis virus, an alphavirus. Our results suggest that the pestivirus and possibly the hepacivirus fusion machinery are unlike any previously observed.

Expression, purification and crystallization of the ectodomain of the envelope glycoprotein E2 from Bovine viral diarrhoea virus

Bovine viral diarrhoea virus (BVDV) is an economically important animal pathogen which is closely related to Hepatitis C virus. Of the structural proteins, the envelope glycoprotein E2 of BVDV is the major antigen which induces neutralizing antibodies; thus, BVDV E2 is considered as an ideal target for use in subunit vaccines. Here, the expression, purification of wild-type and mutant forms of the ectodomain of BVDV E2 and subsequent crystallization and data collection of two crystal forms grown at low and neutral pH are reported. Native and multiple-wavelength anomalous dispersion (MAD) data sets have been collected and structure determination is in progress.

Activation of ERAD pathway by human hepatitis B virus modulates viral and subviral particle production

Hepatitis B virus (HBV) belongs to the Hepadnaviridae family of enveloped DNA viruses. It was previously shown that HBV can induce endoplasmic reticulum (ER) stress and activate the IRE1-XBP1 pathway of the unfolded protein response (UPR), through the expression of the viral regulatory protein X (HBx). However, it remained obscure whether or not this activation had any functional consequences on the target genes of the UPR pathway. Of these targets, the ER degradation-enhancing, mannosidase-like proteins (EDEMs) are thought to play an important role in relieving the ER stress during UPR, by recognizing terminally misfolded glycoproteins and delivering them to the ER-associated degradation (ERAD). In this study, we investigated the role of EDEMs in the HBV life-cycle. We found that synthesis of EDEMs (EDEM1 and its homologues, EDEM2 and EDEM3) is significantly up-regulated in cells with persistent or transient HBV replication. Co-expression of the wild-type HBV envelope proteins with EDEM1 resulted in their massive degradation, a process reversed by EDEM1 silencing. Surprisingly, the autophagy/lysosomes, rather than the proteasome were involved in disposal of the HBV envelope proteins. Importantly, inhibition of the endogenous EDEM1 expression in HBV replicating cells significantly increased secretion of both, enveloped virus and subviral particles. This is the first report showing that HBV activates the ERAD pathway, which, in turn, reduces the amount of envelope proteins, possibly as a mechanism to control the level of virus particles in infected cells and facilitate the establishment of chronic infections.

Complementation studies with the novel "Bungowannah" virus provide new insights in the compatibility of pestivirus proteins

In recent years several atypical pestiviruses have been described. Bungowannah virus is the most divergent virus in this group. Therefore, heterologous complementation was used to clarify the phylogenetic relationship and to analyze the exchangeability of genome regions encoding structural proteins. Using a BVDV type 1 backbone, chimeric constructs with substituted envelope proteins E(rns), E1 and E2, were investigated. While all constructs replicated autonomously, infectious high titer chimeric virus could only be observed after exchanging the complete E1-E2 encoding region. The complementation of E1 and E2 alone resulted only in replicons. Complementation of BVDV-E(rns) was only efficient if Bungowannah virus-E(rns) was expressed from a bicistronic construct. Our data provide new insights in the compatibility of pestivirus proteins and demonstrate that heterologous complementation could be useful to characterize new pestiviruses.

Endotoxin-free purification for the isolation of bovine viral diarrhoea virus E2 protein from insoluble inclusion body aggregates

Background

Protein expression in Escherichia coli may result in the recombinant protein being expressed as insoluble inclusion bodies. In addition, proteins purified from E. coli contain endotoxins which need to be removed for in vivo applications. The structural protein, E2, from Bovine Viral Diarrhoea Virus (BVDV) is a major immunogenic determinant, and is an ideal candidate as a subunit vaccine. The E2 protein contains 17 cysteine residues creating difficulties in E. coli expression. In this report we outline a procedure for successfully producing soluble and endotoxin-free BVDV E2 protein from inclusion bodies (IB).

Results

The expression of a truncated form of BVDV-E2 protein (E2-T1) in E. coli resulted in predominantly aggregated insoluble IB. Solubilisation of E2-T1 with high purity and stability from IB aggregates was achieved using a strong reducing buffer containing 100 mM Dithiothreitol. Refolding by dialysis into 50 mM Tris (pH 7.0) containing 0.2% Igepal CA630 resulted in a soluble but aggregated protein solution. The novel application of a two-phase extraction of inclusion body preparations with Triton X-114 reduced endotoxin in solubilised E2-T1 to levels suitable for in vivo use without affecting protein yields. Dynamic light scattering analyses showed 37.5% of the protein was monomeric, the remaining comprised of soluble aggregates. Mice immunised with E2-T1 developed a high titre antibody response by ELISA. Western hybridisation analysis showed E2-T1 was recognised by sera from immunised mice and also by several BVDV-E2 polyclonal and monoclonal antibodies.

Conclusion

We have developed a procedure using E. coli to produce soluble E2-T1 protein from IB, and due to their insoluble nature we utilised a novel approach using Triton X-114 to efficiently remove endotoxin. The resultant protein is immunogenic and detectable by BVDV-E2 specific antibodies indicating its usefulness for diagnostic applications and as a subunit vaccine. The optimised E. coli expression system for E2-T1 combined with methodologies for solubilisation, refolding and integrated endotoxin removal presented in this study should prove useful for other vaccine applications.

Last stop before exit - hepatitis C assembly and release as antiviral drug targets

Chronic Hepatitis C infection is a global health problem. While primary infection is often inapparent, it becomes chronic in most cases. Chronic infection with Hepatitis C virus (HCV) frequently leads to liver cirrhosis or liver cancer. Consequently, HCV infection is one of the leading causes for liver transplantation in industrialized countries. Current treatment is not HCV specific and is only effective in about half of the infected patients. This situation underlines the need for new antivirals against HCV. To develop new and more efficient drugs, it is essential to specifically target the different steps of the viral life cycle. Of those steps, the targeting of HCV assembly has the potential to abolish virus production. This review summarizes the advances in our understanding of HCV particle assembly and the identification of new antiviral targets of potential interest in this late step of the HCV life cycle.

Cellular models for the screening and development of anti-hepatitis C virus agents

Investigations on the biology of hepatitis C virus (HCV) have been hampered by the lack of small animal models. Efforts have therefore been directed to designing practical and robust cellular models of human origin able to support HCV replication and production in a reproducible, reliable and consistent manner. Many different models based on different forms of virions and hepatoma or other cell types have been described including virus-like particles, pseudotyped particles, subgenomic and full length replicons, virion productive replicons, immortalised hepatocytes, fetal and adult primary human hepatocytes. This review focuses on these different cellular models, their advantages and disadvantages at the biological and experimental levels, and their respective use for evaluating the effect of antiviral molecules on different steps of HCV biology including virus entry, replication, particles generation and excretion, as well as on the modulation by the virus of the host cell response to infection.

Genotype-dependent sensitivity of hepatitis C virus to inhibitors of the p7 ion channel

The hepatitis C virus (HCV) p7 protein plays a critical role during particle formation in cell culture and is required for virus replication in chimpanzees. The discovery that it displayed cation channel activity in vitro led to its classification within the "viroporin" family of virus-coded ion channel proteins, which includes the influenza A virus (IAV) M2 protein. Like M2, p7 was proposed as a potential target for much needed new HCV therapies, and this was supported by our finding that the M2 inhibitor, amantadine, blocked its activity in vitro. Since then, further compounds have been shown to inhibit p7 function but the relationship between inhibitory effects in vitro and efficacy against infectious virus is controversial. Here, we have sought to validate multiple p7 inhibitor compounds using a parallel approach combining the HCV infectious culture system and a rapid throughput in vitro assay for p7 function. We identify a genotype-dependent and subtype-dependent sensitivity of HCV to p7 inhibitors, in which results in cell culture largely mirror the sensitivity of recombinant protein in vitro; thus building separate sensitivity profiles for different p7 sequences. Inhibition of virus entry also occurred, suggesting that p7 may be a virion component. Second site effects on both cellular and viral processes were identified for several compounds in addition to their efficacy against p7 in vitro. Nevertheless, for some compounds antiviral effects were specific to a block of ion channel function.

CONCLUSION

These data validate p7 inhibitors as prototype therapies for chronic HCV disease. (HEPATOLOGY 2008;48:1779-1790.).

Virus entry inhibition by chlorite-oxidized oxyamylose versus induction of antiviral interferon by poly(I:C)

Unlike polyribonucleotides, such as poly(I:C), chlorite-oxidized oxyamylose (COAM) has been poorly characterized as a polyanionic antiviral. COAM possesses a controversial interferon (IFN)-inducing capacity and its mechanism of action has not been elucidated. In this study, COAM was biochemically characterized and fractionated according to molecular mass. In comparison with a strong IFN induction and upregulation of the helicase RIG-I and MDA-5 mRNAs by poly(I:C), COAM did not enhance IFN-alpha or -beta and IFN-inducible RNA helicases in mouse fibroblastoid cells. Instead, COAM inhibited virus entry by blocking the attachment to the cells. These results suggest that COAM can alter the outcome of infection, not by IFN induction and in turn modifying the cellular antiviral state, but through inhibition of virus entry into cells.

Design, synthesis and anti flaviviridae activity of N(6)-, 5',3'-O- and 5',2'-O-substituted adenine nucleoside analogs

During a random screening of representative libraries of nucleoside analogues we discovered that the adenine derivatives FEVB28 and FEG118 were Flaviviridae inhibitors endowed with potency comparable, if not superior, to that of ribavirin. Those studies prompted us to design a new class of protected nucleoside analogs, reported herein, which displays interesting anti-bovine viral diarrhea virus (BVDV) activity and low cytotoxicity in cell-based assays (4, 23, 29 EC(50): 14, 11, 26 microM respectively, CC(50)>100 microM) and appreciable activity in enzyme assays against the RNA dependent RNA polymerase (RdRp) of BVDV (4, 23, 29, RdRp inhibition activity 27, 16, 15 microM respectively). A molecular modeling study was also carried out to highlight the possible interactions between this compounds class and the corresponding hepatitis C virus (HCV) enzyme.

Functionality of Chimeric E2 Glycoproteins of BVDV and CSFV in Virus Replication

An intriguing difference between the E2 glycoprotein of CSFV and the other groups of pestiviruses (nonCSFV) is a lack of two cysteine residues on positions cysteine 751 and 798. Other groups of pestivirus are not restricted to one species as swine, whereas CSFV is restricted to swine and wild boar. We constructed chimeric CSFV/BVDV E2 genes based on a 2D model of E2 proposed by van Rijn et al. (van Rijn et al. 1994, J Virol 68, 3934–42) and confirmed their expression by immunostaining of plasmid-transfected SK6 cells. No equivalents for the antigenic units B/C and A were found on E2 of BVDVII. This indicates major structural differences in E2. However, the immunodominant BVDVII domain A, containing epitopes with essential amino acids between position 760–764, showed to be dependent on the presence of the region defined by amino acids 684 to 796. As for the A domain of CSFV, the BVDVII A-like domain seemed to function as a separate unit. These combined domains in E2 proved to be the only combination which was functional in viral background of CSFV C-strain. The fitness of this virus (vflc36BVDVII 684–796) seemed to be reduced compared to vflc9 (with the complete antigenic region of BVDVII).

Iminosugars in combination with interferon and ribavirin permanently eradicate noncytopathic bovine viral diarrhea virus from persistently infected cells

We evaluated interferon (IFN) and ribavirin (RBV) as dual therapy and as part of triple-combination therapies with the iminosugars N-butyl-deoxynojirimycin (NB-DNJ), N-nonyl-deoxynojirimycin, and N-7-oxanonyl-6-deoxymethyl-galactonojirimycin. The ability of these compounds to clear bovine viral diarrhea virus (BVDV), a surrogate model for hepatitis C virus (HCV), from a persistently infected Madin-Darby bovine kidney cells cell line was determined by monitoring the secretion of viral RNA and the infectivity of secreted virions. In the BVDV system, after treatment with IFN-RBV alone, viral rebound was observed immediately after removal of the drugs. In contrast, we demonstrate that a triple drug combination of IFN, RBV, and an iminosugar eradicated the BVDV infection in a time- and a dose-dependent manner, leading to sustained viral clearance. Importantly, in the case of NB-DNJ, the sustained viral clearance was achieved by using physiologically relevant and tolerated drug concentrations. Therefore, the use of a triple-combination therapy that includes an iminosugar may prove to be of greater therapeutic value for the treatment of HCV infection than the use of IFN-RBV alone.

Antiviral activity of geneticin against bovine viral diarrhoea virus

BACKGROUND

Aminoglycoside G418 is commonly used to generate stable replicons for RNA viruses, such as hepatitis C virus, West Nile virus, and bovine viral diarrhoea virus (BVDV). This precludes testing 6418's own antiviral activities against those viruses. Here, we report antiviral activity of 6418 against BVDV.

METHODS

Cell viability and virus yield reduction assays were used to investigate antiviral effects of G418 against BVDV. The expression of viral proteins and RNA were determined by western blot and real-time quantitive PCR, respectively.

RESULTS

We demonstrated that G418 (50% cytotoxicity concentration of 400 microg/ml) improved cell viability of Madin-Darby bovine kidney cells infected with a cytopathic strain of BVDV (NADL) in a dose-dependent manner with 50% effective concentration of 4 microg/ml. Interestingly, close structural analogues with known properties as translation inhibitors similar to G418 - kanamycin and gentamicin - had no antiviral activity against BVDV. In addition, 6418 inhibits virus yield of two different strains of BVDV (NADL and NY-1) without affecting viral RNA replication and translation or viral NS3 protein processing.

CONCLUSION

Our data indicate that antiviral activity of G418 could result from interference with either the assembly or release of active virus, rather than the regulation of viral translation and replication. Thus, we propose the use of chemical analogues of G418 as antiviral therapeutics for treatment of viral diseases associated with the Flaviviridae family, such as hepatitis C virus, dengue virus, yellow fever virus, West Nile virus and others.

exo-Imino to endo-iminocyclitol rearrangement. A general route to five-membered antiviral azasugars

A facile synthesis is reported for five-membered iminocyclitols which allows for variation in stereochemistry at all the chiral centers, diverse C1- and N-substitution, and the potential for a three-component combinatorial process. The key step is inversion at the C4 stereocenter (L-lyxo sugar --> D-ribono azasugar). The exo-imino to endo-iminocyclitol process was extended to the D-lyxo and the D- and L-hexose series. Some analogues were found to be more potent than N-butyl DNJ and N-nonyl DNJ in antiviral activity.

Reduction of the infectivity of hepatitis C virus pseudoparticles by incorporation of misfolded glycoproteins induced by glucosidase inhibitors

Folding and assembly into complexes of some viral glycoproteins are exquisitely sensitive to endoplasmic reticulum (ER) alpha-glucosidase inhibition, which prevents the trimming of glucose from N-linked glycans. Derivatives of deoxynojirimycin (DNJ) iminosugars, which are potent alpha-glucosidase inhibitors, were shown to have antiviral activity against bovine viral diarrhea virus, a pestivirus related to hepatitis C virus (HCV). The aim of this study was to determine whether these inhibitors would affect HCV infectivity and to provide novel insights on their mechanism of action. The overall antiviral activity of glucosidase inhibitors was shown by using the two most relevant models currently available: the cell-culture model enabling complete replication of the HCV JFH1 strain in Huh7.5 cells, and infectious HCV pseudotyped particles (HCVpp) produced in HEK-293T cells that display functional E1-E2 glycoprotein complexes. By using the latter model, it is shown that the inhibition of alpha-glucosidases by iminosugars results in the misfolding and misassembly of HCV glycoprotein pre-budding complexes. This inhibition of the assembly of E1-E2 in the ER of transfected HEK-293T cells leads to a reduction in the incorporation of E1-E2 complexes into HCVpp. More importantly, it is demonstrated that the infectivity of HCVpp that are released under treatment is reduced and that this reduction in infectivity is due to the incorporation of misfolded envelope glycoproteins in secreted particles. These properties suggest the potential usefulness of DNJ derivatives in combating HCV infection.

A novel, highly selective inhibitor of pestivirus replication that targets the viral RNA-dependent RNA polymerase

We report on the highly potent and selective antipestivirus activity of 5-[(4-bromophenyl)methyl]-2-phenyl-5H-imidazo[4,5-c]pyridine (BPIP). The 50% effective concentration (EC50) for inhibition of bovine viral diarrhea virus (BVDV)-induced cytopathic effect formation was 0.04 +/- 0.01 microM. Comparable reduction of viral RNA synthesis (EC50 = 0.12 +/- 0.02 microM) and production of infectious virus (EC50= 0.074 +/- 0.003 microM) were observed. The selectivity index (ratio of 50% cytostatic concentration/EC50) of BPIP was approximately 2,000. BPIP was inactive against the hepatitis C virus subgenomic replicon and yellow fever virus but demonstrated weak activity against GB virus. Drug-resistant mutants were at least 300-fold less susceptible to BPIP than wild-type virus; showed cross-resistance to N-propyl-N-[2-(2H-1,2,4-triazino[5,6-b]indol-3-ylthio)ethyl]-1-propanamine (VP32947), and carried the F224S mutation in the viral RNA-dependent RNA polymerase (RdRp). When the F224S mutation was introduced into an infectious clone, the drug-resistant phenotype was obtained. BPIP did not inhibit the in vitro activity of recombinant BVDV RdRp, but did inhibit the activity of replication complexes (RCs). Computational docking revealed that F224 is located at the top of the finger domain of the polymerase. Docking of BPIP in the crystal structure of the BVDV RdRp revealed aromatic ring stacking, some hydrophobic contacts, and a hydrogen bond. Since two structurally unrelated compounds, i.e., BPIP and VP32947, target the same region of the BVDV RdRp, this position may be expected to be critical in the functioning of the polymerase or assembly of the RC. The potential of BPIP for the treatment of pestivirus and hepacivirus infections is discussed.

Antiviral effects of glycosylation and glucose trimming inhibitors on human parainfluenza virus type 3

Endoplasmic reticulum (ER) alpha-glucosidase inhibitors block the trimming of N-linked glycosylation and thus prevent the production of several viruses. The present study investigates the antiviral effects of the alpha-glucosidase and alpha-mannosidase inhibitors (castanospermine, 1-deoxynojirimycin, bromoconduritol, deoxymannojirimycin and swainsonine) on human parainfluenza virus type 3 (HPIV3). The alpha-glucosidase inhibitors (castanospermine, 1-deoxynojirimycin) in recombinant expression systems reduced the surface and intracellular expression of both HPIV3 F and HN proteins. On the other hand, alpha-mannosidase inhibitors prevented processing of the oligosaccharides on HPIV3 glycoproteins into the complex form. Consequently, alpha-glycosidase inhibitors (castanospermine and 1-deoxynojirimycin) significantly inhibited viral fusion activity. We demonstrated that the alpha-glucosidase inhibitors (castanospermine and 1-deoxynojirimycin) reduced the infectivity of newly released viral particles. We postulate that alpha-glucosidase inhibitors can prevent the first steps of HPIV3 envelope glycoprotein processing and that the inhibition of glucose trimming has antiviral effects.

Brefeldin A inhibits pestivirus release from infected cells, without affecting its assembly and infectivity

The enveloped bovine viral diarrhea virus (BVDV) is a member of the Pestivirus genus within the Flaviviridae family. While considerable information has been gathered on virus entry into the host cell, genome structure and protein function, little is known about pestivirus morphogenesis and release from cells. Here, we analyzed the intracellular localization, N-glycan processing and secretion of BVDV using brefeldin A (BFA), which blocks protein export from the endoplasmic reticulum (ER) and causes disruption of the Golgi complex with subsequent fusion of its cis and medial cisternae with the ER. BFA treatment of infected cells resulted in complete inhibition of BVDV secretion and increased co-localization of the envelope glycoproteins with the cis-Golgi marker GM 130. Processing of the N-linked glycans was affected by BFA, however, virus assembly was not perturbed and intracellular virions were fully infectious, suggesting that trafficking beyond the cis-Golgi is not a prerequisite for pestivirus infectivity.

Antiviral effect of alpha-glucosidase inhibitors on viral morphogenesis and binding properties of hepatitis C virus-like particles

Hepatitis C virus (HCV) infections are a major public-health concern. New antiviral drugs are needed urgently to complement and improve the efficacy of current chemotherapies. The morphogenesis of HCV represents an interesting, and still unexploited, novel molecular target. alpha-Glucosidase inhibitors derived from the glucose analogue deoxynojirimycin (DNJ) inhibit viral morphogenesis in cellulo via perturbation of the N-glycosylation pathway and hence the misfolding of viral glycoproteins that depend on certain N-glycans for correct folding. Due to the heavy N-glycosylation of HCV glycoproteins, it was hypothesized that such inhibitors would also affect HCV morphogenesis. To study the effect of alpha-glucosidase inhibitors on viral morphogenesis and binding properties, HCV virus-like particles (VLPs) were produced by using baculovirus loaded with HCV structural-protein genes. Here, it is demonstrated that, in the presence of these alpha-glucosidase inhibitors, viral glycoproteins synthesized and retained in the endoplasmic reticulum (i) contain unprocessed, triglucosylated N-glycans, (ii) are impaired in their interaction with calnexin and (iii) are at least partially misfolded. Moreover, it is shown that, although the production of VLPs is not affected by alpha-glucosidase inhibitors, these VLPs contain unprocessed, triglucosylated N-glycans and potentially misfolded glycoproteins. Finally, it is demonstrated that VLPs produced in the presence of alpha-glucosidase inhibitors have impaired binding properties to hepatoma cells. The inhibitors of morphogenesis studied here target steps of the HCV viral cycle that may prevent or delay viral resistance. These alpha-glucosidase inhibitors may prove to be useful molecules to fight HCV infection in combination protocols.

Synthesis and Anti-BVDV Activity of Acridones As New Potential Antiviral Agents

In this study we report the design, synthesis, and activity against bovine viral diarrhea virus (BVDV) of a novel series of acridone derivatives. BVDV is responsible for major losses in cattle. The virus is also considered to be a valuable surrogate for the hepatitis C virus (HCV) in antiviral drug studies. Some of the synthesized acridones elicited selective anti-BVDV activity with EC(50) values ranging from 0.4 to 4 microg/mL and were not cytotoxic at concentrations that were 25- to 200-fold higher (CC(50) >100 microg/mL). It was proven that the most potent acridone derivative 10 was able to not only protect cells from virus-induced cytopathic effect but also reduce the production of infectious virus and extracellular viral RNA. Furthermore, compound 10, as well as a number of other analogues, inhibited HCV replication to some extent. However, there was no direct correlation between anti-BVDV and anti-HCV activity. Thus, the acridone scaffold, when appropriately functionalized, can yield compounds with selective activity against pestiviruses and related viruses such as the HCV.

Virus morphogenesis and viral entry as alternative targets for novel hepatitis C antivirals

Hepatitis C virus (HCV) infection is a major public health concern. New antiviral drugs are required urgently to complement and improve the efficacy of current chemotherapies. Molecules specifically targeting viral enzymes are the most attractive in terms of drug development and are, therefore, the most studied. However, an antiviral strategy based uniquely on the utilization of this type of target is expected to encounter problems caused by the emergence of viral escape mutants as has already been widely described for HIV and hepatitis B virus. HCV morphogenesis and viral entry represent interesting, and yet unexploited, novel molecular targets. Inhibitors of morphogenesis have recently been identified and studied in different virus–cell systems. Some of these are currently being evaluated in clinical trials against HCV. This review focuses on HCV morphogenesis, viral entry and inhibition and presents clinical development perspectives of this new generation of antivirals.

Immunization with plasmid DNA encoding a truncated, secreted form of the bovine viral diarrhea virus E2 protein elicits strong humoral and cellular immune responses

The major protective antigen of bovine viral diarrhea virus (BVDV), the E2 protein, is cell-associated and not expressed on the cell surface. In this study we evaluated a DNA vaccine encoding various secreted versions of E2. In vitro analysis demonstrated that deletion of the transmembrane anchor and addition of the signal sequence of bovine herpesvirus-1 (BHV-1) (gDsDeltaE2) resulted in efficient secretion of E2 into the culture medium. In contrast, full-length E2, either without or with gDs (gDsE2), as well as truncated E2 without gDs (DeltaE2), remained entirely cell-associated. Mice immunized with plasmid encoding gDsDeltaE2 developed significantly higher IgG and virus neutralizing antibody titres compared to animals vaccinated with plasmid encoding E2, DeltaE2 or gDsE2. To optimize secretion of E2, the efficiency of gDs was compared with that of the tissue plasminogen activator signal (tPAs) sequence. In addition, the effect of the plasmid backbone was assessed by comparing two vectors. Four plasmids, pMASIA-gDsDeltaE2, pMASIA-tPAsDeltaE2, pSLKIA-gDsDeltaE2 and pSLKIA-tPAsDeltaE2, were constructed and administered intradermally to mice. The mice immunized with pMASIA-tPAsDeltaE2 developed the strongest and most balanced immune responses. Vaccination of cattle confirmed that pMASIA-tPAsDeltaE2 elicited both strong humoral and cellular immune responses and thus could be a candidate DNA vaccine against BVDV.

Cellular effects of deoxynojirimycin analogues: inhibition of N-linked oligosaccharide processing and generation of free glucosylated oligosaccharides

In the accompanying paper [Mellor, Neville, Harvey, Platt, Dwek and Butters (2004) Biochem. J. 381, 861-866] we treated HL60 cells with N-alk(en)yl-deoxynojirimycin (DNJ) compounds to inhibit glucosphingolipid (GSL) biosynthesis and identified a number of non-GSL-derived, small, free oligosaccharides (FOS) most likely produced due to inhibition of the oligosaccharide-processing enzymes a-glucosidases I and II. When HL60 cells were treated with concentrations of N-alk(en)ylated DNJ analogues that inhibited GSL biosynthesis completely, N-butyl- and N-nonyl-DNJ inhibited endoplasmic reticulum (ER) glucosidases I and II, but octadecyl-DNJ did not, probably due to the lack of ER lumen access for this novel, long-chain derivative. Glucosidase inhibition resulted in the appearance of free Glc1-3Man structures, which is evidence of Golgi glycoprotein endomannosidase processing of oligosaccharides with retained glucose residues. Additional large FOS was also detected in cells following a 16 h treatment with N-butyl- and N-nonyl-DNJ. When these FOS structures (>30, including >20 species not present in control cells) were characterized by enzyme digests and MALDI-TOF (matrix-assisted laser-desorption ionization-time-of-flight) MS, all were found to be polymannose-type oligosaccharides, of which the majority were glucosylated and had only one reducing terminal GlcNAc (N-acetylglucosamine) residue (FOS-GlcNAc1), demonstrating a cytosolic location. These results support the proposal that the increase in glucosylated FOS results from enzyme-mediated cytosolic cleavage of oligosaccharides from glycoproteins exported from the ER because of misfolding or excessive retention. Importantly, the present study characterizes the cellular properties of DNJs further and demonstrates that side-chain modifications allow selective inhibition of protein and lipid glycosylation pathways. This represents the most detailed characterization of the FOS structures arising from ER a-glucosidase inhibition to date.