New Target For Antiviral Therapy Research Articles

Viral Hijacking of Host RNA-binding Proteins: Implications for Viral Replication and Pathogenesis

In the intricate dance between viruses and host cells, RNA-binding proteins (RBPs) serve as crucial orchestrators of gene expression and cellular processes. We will delve into the riveting realm of viral hijacking, where viruses deftly exploit host RBPs to manipulate cellular machinery for their replication and pathogenesis. Through a masterstroke of molecular subterfuge, viruses co-opt RBPs involved in various facets of RNA metabolism - from transcription to degradation - to promote viral gene expression and evade host immune defenses. This manipulation leads to global alterations in cellular RNA metabolism, impacting essential host genes vital for immune responses and homeostasis. Unveiling this clandestine alliance between viruses and RBPs is not just a scientific pursuit, but a critical imperative for devising innovative antiviral strategies to disrupt these interactions. By unraveling the intricate interplay between viral proteins and host RBPs throughout the viral life cycle - from entry to assembly - researchers aim to identify vulnerabilities that can be targeted for therapeutic intervention. Strategies such as disrupting viral protein-RBP interactions hold promise for inhibiting viral replication and curbing pathogenesis, offering a beacon of hope in the battle against viral infections. Our manuscript elucidates the indispensable roles played by RBPs in viral replication, translation, and pathogenesis, shedding light on the molecular mechanisms driving viral success. Delving deeper, it explores how viruses intricately entwine with host RBPs, manipulating cellular signaling pathways to create a hospitable environment for viral spread. By dissecting these manipulative tactics, researchers uncover new targets for antiviral therapy, envisioning a future where tailored interventions disrupt viral-host RBP interactions with precision and efficacy. As the narrative unfolds, the therapeutic implications of targeting RBPs or their interactions with viral proteins emerge as a promising frontier in the fight against viral infections. From small molecule inhibitors to RNA-based therapeutics, innovative approaches are on the horizon, offering new avenues for combating viral diseases. We set the stage for future research, beckoning researchers to delve deeper into the molecular intricacies of viral hijacking of RBPs and charting a course towards novel therapeutic interventions that promise to reshape the landscape of antiviral therapy.\ Ultimately, it beckons the scientific community to embark on a voyage of discovery, unraveling the secrets of viral hijacking of RBPs and paving the way for transformative advances in antiviral therapeutics. The stage is set for a new chapter in the battle against viral infections, where knowledge becomes the sword and innovation the shield against the pernicious machinations of viral pathogens.

Dual RNA-seq Analysis of Patients' Cells and Viral Genome After Measles Infection.

During the infection of a host cell by an infectious agent, a series of gene expression changes occurs as a consequence of host-pathogen interactions. Unraveling this complex interplay is the key for understanding of microbial virulence and host response pathways, thus providing the basis for new molecular insights into the mechanisms of pathogenesis and the corresponding immune response. Dual RNA sequencing (dual RNA-seq) has been developed to simultaneously determine pathogen and host transcriptomes enabling both differential and coexpression analyses between the two partners as well as genome characterization in the case of RNA viruses. Here, we provide a detailed laboratory protocol and bioinformatics analysis guidelines for dual RNA-seq experiments focusing on - but not restricted to - measles virus (MeV) as a pathogen of interest. The application of dual RNA-seq technologies in MeV-infected patients can potentially provide valuable information on the structure of the viral RNA genome and on cellular innate immune responses and drive the discovery of new targets for antiviral therapy.

New Targets for Antiviral Therapy: Inhibitory Receptors and Immune Checkpoints on Myeloid Cells.

Immune homeostasis is achieved by balancing the activating and inhibitory signal transduction pathways mediated via cell surface receptors. Activation allows the host to mount an immune response to endogenous and exogenous antigens; suppressive modulation via inhibitory signaling protects the host from excessive inflammatory damage. The checkpoint regulation of myeloid cells during immune homeostasis raised their profile as important cellular targets for treating allergy, cancer and infectious disease. This review focuses on the structure and signaling of inhibitory receptors on myeloid cells, with particular attention placed on how the interplay between viruses and these receptors regulates antiviral immunity. The status of targeting inhibitory receptors on myeloid cells as a new therapeutic approach for antiviral treatment will be analyzed.

Cyclic peptides with a distinct arginine-fork motif recognize the HIV trans-activation response RNA in vitro and in cells

RNA represents a potential target for new antiviral therapies, which are urgently needed to address public health threats such as the human immunodeficiency virus (HIV). We showed previously that the interaction between the viral Tat protein and the HIV-1 trans-activation response (TAR) RNA was blocked by TB-CP-6.9a. This cyclic peptide was derived from a TAR-binding loop that emerged during lab evolution of a TAR-binding protein (TBP) family. Here we synthesized and characterized a next-generation, cyclic-peptide library based on the TBP scaffold. We sought to identify conserved RNA-binding interactions and the influence of cyclization linkers on RNA binding and antiviral activity. A diverse group of cyclization linkers, encompassing disulfide bonds to bicyclic aromatic staples, was used to restrain the cyclic peptide geometry. Thermodynamic profiling revealed specific arginine-rich sequences with low to submicromolar affinity driven by enthalpic and entropic contributions. The best compounds exhibited no appreciable off-target binding to related molecules, such as BIV TAR and human 7SK RNAs. A specific arginine-to-lysine change in the highest affinity cyclic peptide reduced TAR binding by tenfold, suggesting that TBP-derived cyclic peptides use an arginine-fork motif to recognize the TAR major groove while differentiating the mode of binding from other TAR-targeting molecules. Finally, we showed that HIV infectivity in cell culture was reduced in the presence of cyclic peptides constrained by methylene or naphthalene-based linkers. Our findings provide insight into the molecular determinants required for HIV-1 TAR recognition and antiviral activity. These findings are broadly relevant to the development of antivirals that target RNA molecules.

Discovery and optimization of new 6, 7-dihydroxy-1, 2, 3, 4-tetrahydroisoquinoline derivatives as potent influenza virus PAN inhibitors

Annual unpredictable efficacy of vaccines, coupled with emerging drug resistance, underlines the development of new antiviral drugs to treat influenza infections. The N-terminal domain of the PA (PAN) endonuclease is both highly conserved across influenza strains and serotypes and is indispensable for the viral lifecycle, making it an attractive target for new antiviral therapies. Here, we describe the discovery of a new class of PAN inhibitors derived from recently identified, highly active hits for PAN endonuclease inhibition. By use of structure-guided design and systematic SAR exploration, the hits were elaborated through a fragment growing strategy, giving rise to a series of 1, 3-cis-2-substituted-1-(3, 4-dihydroxybenzyl)-6, 7-dihydroxy-1, 2, 3, 4-tetrahydroisoquinoline-3-carboxylic acid derivatives as potent PAN inhibitors. This approach ultimately resulted in the development of a new lead compound 13e, which exhibited an EC50 value of 4.50 μM against H1N1 influenza virus in MDCK cells.

Dual RNA-Seq Enables Full-Genome Assembly of Measles Virus and Characterization of Host-Pathogen Interactions.

Measles virus (MeV) has a negative-sense 15 kb long RNA genome, which is generally conserved. Recent advances in high-throughput sequencing (HTS) and Dual RNA-seq allow the analysis of viral RNA genomes and the discovery of viral infection biomarkers, via the simultaneous characterization of the host transcriptome. However, these host–pathogen interactions remain largely unexplored in MeV infections. We performed untargeted Dual RNA-seq in 6 pharyngeal and 6 peripheral blood mononuclear cell (PBMCs) specimens from patients with MeV infection, as confirmed via routine real-time PCR testing. Following optimised DNase treatment of total nucleic acids, we used the pharyngeal samples to build poly-A-enriched NGS libraries. We reconstructed the viral genomes using the pharyngeal datasets and we further conducted differential expression, gene-ontology and pathways enrichment analysis to compare both the pharyngeal and the peripheral blood transcriptomes of the MeV-infected patients vs. control groups of healthy individuals. We obtained 6 MeV genotype-B3 full-genome sequences. We minutely analyzed the transcriptome of the MeV-infected pharyngeal epithelium, detecting all known viral infection biomarkers, but also revealing a functional cluster of local antiviral and inflammatory immune responses, which differ substantially from those observed in the PBMCs transcriptome. The application of Dual RNA-seq technologies in MeV-infected patients can potentially provide valuable information on the virus genome structure and the cellular innate immune responses and drive the discovery of new targets for antiviral therapy.

Development of a cellular high-content, immunofluorescent HBV core assay to identify novel capsid assembly modulators that induce the formation of aberrant HBV core structures

Hepatitis B Virus (HBV) core protein has multiple functions in the viral life cycle and is an attractive target for new anti-viral therapies. Capsid assembly modulators (CAMs) target the core protein and induce the formation of either morphologically normal (CAM-N) or aberrant structures (CAM-A), both devoid of genomic material. To date a diverse family of CAM-N chemotypes has been identified, but in contrast, described CAM-As are based on the heteroaryldihydropyrimidine (HAP) scaffold. We used the HBV-inducible HepG2.117 cell line with immunofluorescent labeling of HBV core to develop and validate a cellular high-content image-based assay where aggregated core structures are identified using image analysis spot texture features. Treatment with HAPs led to a dose- and time-dependent formation of aggregated core appearing as dot-like structures in the cytoplasm and nucleus. By combining a biochemical and cellular screening approach, a compound was identified as a novel non-HAP scaffold able to induce dose-dependent formation of aberrant core structures, which was confirmed by electron microscopy and native gel electrophoresis. This compound displayed anti-HBV activity in HepG2.117 cells, providing proof-of-concept for our screening approach. We believe our combined biochemical and cellular high-content screening method will aid in expanding the range of CAM-A chemotypes.

Generation of an HBV core phenotyping assay for evaluating HBV capsid compounds

Hepatitis B virus (HBV) capsids are assembled from HBV core protein and assembly is a critical step in the propagation of the virus. Due to its multiple functions in the viral life cycle, core is an attractive target for new antiviral therapies. For HBV capsid assembly modulators (CAMs), several resistance mutants have been identified, both from the clinic and in vitro. However, currently there is no convenient in vitro assay to monitor resistance to CAMs in the clinic. Here, we developed a facile, cassette-based phenotyping assay to assess the antiviral activity of CAMs on a panel of clinical isolates. Using this system, the core genes from 13 patients infected with HBV genotypes A–H were expressed as chimeric virus and tested for sensitivity to CAMs. No substantial differences in antiviral activity were observed across genotypes due to the conservation of the drug binding pocket. In addition, we tested a panel of constructs encoding 13 single amino acid polymorphs in the CAM binding site, including some polymorphs with previously-described resistance to CAMs. Overall, 11 of 13 constructs replicated in vitro, 6 constructs showed reduced susceptibility to CAMs. The 11 polymorphs which could replicate in vitro remained sensitive to the nucleotide analog tenofovir alafenamide (TAF), indicating that there is no cross-resistance.

Downregulation of SOCS gene expression can inhibit the formation of acute and persistent BDV infections.

High expression of suppressors of cytokine signalling (SOCS) has been detected during various viral infections. As a negative feedback regulator, SOCS participates in the regulation of multiple signalling pathways. In this study, to study the related mechanism between SOCS and BDV and to explore the effect of SOCS on IFN pathways in nerve cells, downregulated of SOCS1/3 in oligodendroglial (OL) cells and OL cells persistently infected with BDV (OL/BDV) were constructed with RNA interference technology. An interferon inducer (poly I:C, PIC) and an IFN-α/β R1 antibody were used as stimulation in the SOCS1/3 low-expression cell models, qRT-PCR was used to detect type I IFN and BDV nucleic acid expression, Western blot was used to detect the expression of BDV P40 protein. After BDV acute infection with OL cells which with downregulated SOCS expression, the virus accounting was not detected, and the viral protein expression was lower than that of OL/BDV cells; the OL/BDV cells with downregulated SOCS expression had lower virus nucleic acid and protein expression than OL/BDV cells. Stimulated by IFN-α/β R1 antibody, the expression of type I interferon in OL/BDV cells decreased, and the content of BDV nucleic acid and protein increased, which was higher than that of OL/BDV cells. From the results, it was concluded that downregulating SOCS1/3 can inhibit the formation of acute BDV infection and virus replication in persistent BDV infection by promoting the expression of IFN-α/β and that SOCS can be used as a new target for antiviral therapy.

Discovery of Phthalazinone Derivatives as Novel Hepatitis B Virus Capsid Inhibitors.

HBV capsid assembly has been viewed as an attractive target for new antiviral therapies against HBV. On the basis of a lead compound 4r, we further investigated this target to identify novel active compounds with appropriate anti-HBV potencies and improved pharmacokinetic (PK) properties. Structure-activity relationship studies based on metabolic pathways of 4r led to the identification of a phthalazinone derivative 19f with appropriate anti-HBV potencies (IC50 = 0.014 ± 0.004 μM in vitro), which demonstrated high oral bioavailability and liver exposure. In the AAV-HBV/mouse model, administration of 19f resulted in a 2.67 log reduction of the HBV DNA viral load during a 4-week treatment with 150 mg/kg dosing twice daily.

Antiviral Properties and Mechanism of Action Studies of the Hepatitis B Virus Capsid Assembly Modulator JNJ-56136379.

Capsid assembly is a critical step in the hepatitis B virus (HBV) life cycle, mediated by the core protein. Core is a potential target for new antiviral therapies, the capsid assembly modulators (CAMs). JNJ-56136379 (JNJ-6379) is a novel and potent CAM currently in phase II trials. We evaluated the mechanisms of action (MOAs) and antiviral properties of JNJ-6379 in vitro Size exclusion chromatography and electron microscopy studies demonstrated that JNJ-6379 induced the formation of morphologically intact viral capsids devoid of genomic material (primary MOA). JNJ-6379 accelerated the rate and extent of HBV capsid assembly in vitro JNJ-6379 specifically and potently inhibited HBV replication; its median 50% effective concentration (EC50) was 54 nM (HepG2.117 cells). In HBV-infected primary human hepatocytes (PHHs), JNJ-6379, when added with the viral inoculum, dose-dependently reduced extracellular HBV DNA levels (median EC50 of 93 nM) and prevented covalently closed circular DNA (cccDNA) formation, leading to a dose-dependent reduction of intracellular HBV RNA levels (median EC50 of 876 nM) and reduced antigen levels (secondary MOA). Adding JNJ-6379 to PHHs 4 or 5 days postinfection reduced extracellular HBV DNA and did not prevent cccDNA formation. Time-of-addition PHH studies revealed that JNJ-6379 most likely interfered with postentry processes. Collectively, these data demonstrate that JNJ-6379 has dual MOAs in the early and late steps of the HBV life cycle, which is different from the MOA of nucleos(t)ide analogues. JNJ-6379 is in development for chronic hepatitis B treatment and may translate into higher HBV functional cure rates.

A Tyrosine-Based Trafficking Motif of the Tegument Protein pUL71 Is Crucial for Human Cytomegalovirus Secondary Envelopment.

The human cytomegalovirus (HCMV) tegument protein pUL71 is required for efficient secondary envelopment and accumulates at the Golgi compartment-derived viral assembly complex (vAC) during infection. Analysis of various C-terminally truncated pUL71 proteins fused to enhanced green fluorescent protein (eGFP) identified amino acids 23 to 34 as important determinants for its Golgi complex localization. Sequence analysis and mutational verification revealed the presence of an N-terminal tyrosine-based trafficking motif (YXXΦ) in pUL71. This led us to hypothesize a requirement of the YXXΦ motif for the function of pUL71 in infection. Mutation of both the tyrosine residue and the entire YXXΦ motif resulted in an altered distribution of mutant pUL71 at the plasma membrane and in the cytoplasm during infection. Both YXXΦ mutant viruses exhibited similarly decreased focal growth and reduced virus yields in supernatants. Ultrastructurally, mutant-virus-infected cells exhibited impaired secondary envelopment manifested by accumulations of capsids undergoing an envelopment process. Additionally, clusters of capsid accumulations surrounding the vAC were observed, similar to the ultrastructural phenotype of a UL71-deficient mutant. The importance of endocytosis and thus the YXXΦ motif for targeting pUL71 to the Golgi complex was further demonstrated when clathrin-mediated endocytosis was inhibited either by coexpression of the C-terminal part of cellular AP180 (AP180-C) or by treatment with methyl-β-cyclodextrin. Both conditions resulted in a plasma membrane accumulation of pUL71. Altogether, these data reveal the presence of a functional N-terminal endocytosis motif that is an important determinant for intracellular localization of pUL71 and that is furthermore required for the function of pUL71 during secondary envelopment of HCMV capsids at the vAC.IMPORTANCE Human cytomegalovirus (HCMV) is the leading cause of birth defects among congenital virus infections and can lead to life-threatening infections in immunocompromised hosts. Current antiviral treatments target viral genome replication and are increasingly overcome by viral mutations. Therefore, identifying new targets for antiviral therapy is important for future development of novel treatment options. A detailed molecular understanding of the complex virus morphogenesis will identify potential viral as well as cellular targets for antiviral intervention. Secondary envelopment is an important viral process through which infectious virus particles are generated and which involves the action of several viral proteins, such as tegument protein pUL71. Targeting of pUL71 to the site of secondary envelopment appears to be crucial for its function during this process and is regulated by utilizing host trafficking mechanisms that are commonly exploited by viral glycoproteins. Thus, intracellular trafficking, if targeted, might present a novel target for antiviral therapy.

Pharmacophoric characteristics of dengue virus NS2B/NS3pro inhibitors: a systematic review of the most promising compounds.

Dengue virus (DENV) infection can lead to a wide range of clinical manifestations, including fatal hemorrhagic complications. There is a need to find effective pharmacotherapies to treat this disease due to the lack of specific immunotherapies and antiviral drugs. That said, the DENV NS2B/NS3pro protease complex is essential in both the viral multiplication cycle and in disease pathogenesis, and is considered a promising target for new antiviral therapies. Here, we performed a systematic review to evaluate the pharmacophoric characteristics of promising compounds against NS2B/NS3pro reported in the past 10years. Online searches in the PUBMED/MEDLINE and SCOPUS databases resulted in 165 articles. Eight studies, which evaluated 3,384,268 molecules exhibiting protease inhibition activity, were included in this review. These studies evaluated anti-dengue activity in vitro and the IC50 and EC50 values were provided. Most compounds exhibited non-competitive inhibition. Cytotoxicity was evaluated in BHK-21, Vero, and LLC-MK2 cells, and the CC50 values obtained ranged from <1.0 to 780.5µM. Several groups were associated with biological activity against dengue, including nitro, catechol, halogen and ammonium quaternaries. Thus, these groups seem to be potential pharmacophores that can be further investigated to treat dengue infections.

Capsid Assembly Modulators Have a Dual Mechanism of Action in Primary Human Hepatocytes Infected with Hepatitis B Virus.

Hepatitis B virus (HBV) capsid assembly is a critical step in the propagation of the virus and is mediated by the core protein. Due to its multiple functions in the viral life cycle, core became an attractive target for new antiviral therapies. Capsid assembly modulators (CAMs) accelerate the kinetics of capsid assembly and prevent encapsidation of the polymerase-pregenomic RNA (Pol-pgRNA) complex, thereby blocking viral replication. CAM JNJ-632 is a novel and potent inhibitor of HBV replication in vitro across genotypes A to D. It induces the formation of morphologically intact viral capsids, as demonstrated by size exclusion chromatography and electron microscopy studies. Antiviral profiling in primary human hepatocytes revealed that CAMs prevented formation of covalently closed circular DNA in a dose-dependent fashion when the compound was added together with the viral inoculum, whereas nucleos(t)ide analogues (NAs) did not. This protective effect translated into a dose-dependent reduction of intracellular HBV RNA levels as well as reduced HBe/cAg and HBsAg levels in the cell culture supernatant. The same observation was made with another CAM (BAY41-4109), suggesting that mechanistic rather than compound-specific effects play a role. Our data show that CAMs have a dual mechanism of action, inhibiting early and late steps of the viral life cycle. These effects clearly differentiate CAMs from NAs and may translate into higher functional cure rates in a clinical setting when given alone or in combination with the current standard of care.

Antiviral profiling of the capsid assembly modulator BAY41-4109 on full-length HBV genotype A-H clinical isolates and core site-directed mutants in vitro

The HBV core protein represents an attractive target for new antiviral therapies due to its multiple functions within the viral life-cycle. Here, we report the antiviral activity of the capsid assembly modulator (CAM) BAY41-4109 and two nucleos(t)ide analogues (NAs) on a diverse panel of 54 HBV clinical isolates from genotype (GT) A-H and assessed the impact of core amino acid (aa) substitutions using site-directed mutants (SDMs).The median EC50 values of BAY41-4109 across genotypes ranged from 26 nM in GT G to 215 nM in GT F irrespective of the presence of NA resistance mutations compared to 43 nM for the GT D reference construct. Combined analyses of clinical isolates and SDMs identified aa changes at positions 29, 33 and 118 led to reduced antiviral activity of BAY41-4109 with fold changes in EC50 values of 6, 46, and 9 for D29G, T33N, and Y118F, respectively. These aa substitutions are located within the CAM binding pocket, and are expected to have an effect on CAM binding based on structural modeling. Importantly aa variations at these positions were rarely (<0.3%) observed as naturally occurring in public sequence databases. NA's remained fully active against these variants.Our study demonstrated that BAY41-4109 generally remained fully active across GT A-H clinical isolates. In addition, core aa substitutions within the CAM-binding pocket replicated in vitro and variants at positions 29, 33, and 118 were identified to reduce antiviral activity.

AXL-Mediated Productive Infection of Human Endothelial Cells by Zika Virus.

The mosquito-borne Zika virus (ZIKV) is now recognized as a blood-borne pathogen, raising an important question about how the virus gets into human bloodstream. The imminent threat of the ZIKV epidemic to the global blood supply also demands novel therapeutics to stop virus transmission though transfusion. We intend to characterize ZIKV tropism for human endothelial cells (ECs) and provide potential targets for intervention. We conducted immunostaining, plaque assay, and quantitative reverse transcription-polymerase chain reaction of ZIKV RNA to evaluate the possible infection of ECs by ZIKV. Both the African and the South American ZIKV strains readily infect human umbilical vein endothelial cells and human ECs derived from aortic and coronary artery, as well as the saphenous vein. Infected ECs released infectious progeny virus. Compared with the African strains, South American ZIKV isolates replicate faster in ECs and are partially cytopathic, suggesting enhanced virulence of these isolates. Flow cytometric analyses showed that the susceptibility of ECs positively correlated with the cell surface levels of tyrosine-protein kinase receptor UFO (AXL) receptor tyrosine kinase. Gain- and loss-of-function studies further revealed that AXL is required for ZIKV entry at a postbinding step. Finally, small-molecule inhibitors of the AXL kinase significantly reduced ZIKA infection of ECs. We identified EC as a key cell type for ZIKV infection. These data support the view of hematogenous dissemination of ZIKV and implicate AXL as a new target for antiviral therapy.

A Cell-Free Assembly System for Generating Infectious Human Papillomavirus 16 Capsids Implicates a Size Discrimination Mechanism for Preferential Viral Genome Packaging.

We have established a cell-free in vitro system to study human papillomavirus type 16 (HPV16) assembly, a poorly understood process. L1/L2 capsomers, obtained from the disassembly of virus-like particles (VLPs), were incubated with nuclear extracts to provide access to the range of cellular proteins that would be available during assembly within the host cell. Incorporation of a reporter plasmid "pseudogenome" was dependent on the presence of both nuclear extract and ATP. Unexpectedly, L1/L2 VLPs that were not disassembled prior to incubation with a reassembly mixture containing nuclear extract also encapsidated a reporter plasmid. As with HPV pseudoviruses (PsV) generated intracellularly, infection by cell-free particles assembled in vitro required the presence of L2 and was susceptible to the same biochemical inhibitors, implying the cell-free assembled particles use the infectious pathway previously described for HPV16 produced in cell culture. Using biochemical and electron microscopy analyses, we observed that, in the presence of nuclear extract, intact VLPs partially disassemble, providing a mechanistic explanation to how the exogenous plasmid was packaged by these particles. Further, we provide evidence that capsids containing an <8-kb pseudogenome are resistant to the disassembly/reassembly reaction. Our results suggest a novel size discrimination mechanism for papillomavirus genome packaging in which particles undergo iterative rounds of disassembly/reassembly, seemingly sampling DNA until a suitably sized DNA is encountered, resulting in the formation of a stable virion structure. Little is known about papillomavirus assembly biology due to the difficulties in propagating virus in vitro. The cell-free assembly method established in this paper reveals a new mechanism for viral genome packaging and will provide a tractable system for further dissecting papillomavirus assembly. The knowledge gained will increase our understanding of virus-host interactions, help to identify new targets for antiviral therapy, and allow for the development of new gene delivery systems based on in vitro-generated papillomavirus vectors.

Dynasore disrupts trafficking of herpes simplex virus proteins.

Dynasore, a small-molecule inhibitor of the GTPase activity of dynamin, inhibits the entry of several viruses, including herpes simplex virus (HSV), but its impact on other steps in the viral life cycle has not been delineated. The current study was designed to test the hypothesis that dynamin is required for viral protein trafficking and thus has pleiotropic inhibitory effects on HSV infection. Dynasore inhibited HSV-1 and HSV-2 infection of human epithelial and neuronal cells, including primary genital tract cells and human fetal neurons and astrocytes. Similar results were obtained when cells were transfected with a plasmid expressing dominant negative dynamin. Kinetic studies demonstrated that dynasore reduced the number of viral capsids reaching the nuclear pore if added at the time of viral entry and that, when added as late as 8 h postentry, dynasore blocked the transport of newly synthesized viral proteins from the nucleus to the cytosol. Proximity ligation assays demonstrated that treatment with dynasore prevented the colocalization of VP5 and dynamin. This resulted in a reduction in the number of viral capsids isolated from sucrose gradients. Fewer capsids were observed by electron microscopy in dynasore-treated cells than in control-treated cells. There were also reductions in infectious progeny released into culture supernatants and in cell-to-cell spread. Together, these findings suggest that targeting dynamin-HSV interactions may provide a new strategy for HSV treatment and prevention. HSV infections remain a global health problem associated with significant morbidity, particularly in neonates and immunocompromised hosts, highlighting the need for novel approaches to treatment and prevention. The current studies indicate that dynamin plays a role in multiple steps in the viral life cycle and provides a new target for antiviral therapy. Dynasore, a small-molecule inhibitor of dynamin, has pleiotropic effects on HSV-1 and HSV-2 infection and impedes viral entry, trafficking of viral proteins, and capsid formation.

Calcium-signal facilitates herpes simplex virus type 1 nuclear transport through slingshot 1 and calpain-1 activation

Herpes simplex virus type 1 (HSV-1) can establish its latency in neurons and is associated with virus-induced pathological neurodegeneration in the nervous system. Here we show that viral penetration-induced calcium release facilitated HSV-1 intracellular trafficking through activating slingshot 1 (SSH), a phosphatase regulating actin filament dynamics. More detailed studies revealed that phospholipase C gamma 1, and the inositol 1,4,5-trisphosphate receptor isoform 1 were required for SSH activation. Besides, calpain-1, a calcium-dependent cysteine protease, was involved in viral intracellular migration. These results may lead to new targets for antiviral therapy.

Assembly-Directed Antivirals Differentially Bind Quasiequivalent Pockets to Modify Hepatitis B Virus Capsid Tertiary and Quaternary Structure

Hepatitis B virus (HBV) is a major cause of liver disease. Assembly of the HBV capsid is a critical step in virus production and an attractive target for new antiviral therapies. We determined the structure of HBV capsid in complex with AT-130, a member of the phenylpropenamide family of assembly effectors. AT-130 causes tertiary and quaternary structural changes but does not disrupt capsid structure. AT-130 binds a hydrophobic pocket that also accommodates the previously characterized heteroaryldihydropyrimidine compounds but favors a unique quasiequivalent location on the capsid surface. Thus, this pocket is a promiscuous drug-binding site and a likely target for different assembly effectors with a broad range of mechanisms of activity. That AT-130 successfully decreases virus production by increasing capsid assembly rate without disrupting capsid structure delineates a paradigm in antiviral design, that disrupting reaction timing is a viable strategy for assembly effectors of HBV and other viruses.