Anti-heparan sulfate peptides that block herpes simplex virus infection in vivo

Construction of Various γ34.5 Deleted Fluorescent-Expressing Oncolytic herpes Simplex type 1 (oHSV) for Generation and Isolation of HSV-Based Vectors

Background

Oncolytic herpes simplex virus (oHSV)-based vectors lacking γ34.5 gene, are considered as ideal templates to construct efficient vectors for (targeted) cancer gene therapy. Herein, we reported the construction of three single/dually-flourescence labeled and γ34.5-deleted, recombinant HSV-1 vectors for rapid generation and easy selection/isolation of different HSV-Based vectors.

Methods

Generation of recombinant viruses was performed with conventional homologous recombination methods using green fluorescent protein (GFP) and BleCherry harboring shuttle vectors. Viruses were isolated by direct fluorescence observation and standard plaque purifying methods and confirmed by PCR and sequencing and flow cytometry. XTT and plaque assay titration were performed on Vero, U87MG, and T98 GBM cell lines.

Results

We generated three recombinant viruses, HSV-GFP, HSV-GR (Green-Red), and HSV-Red. The HSV-GFP showed two log higher titer (1010 PFU) than wild type (108 PFU). In contrast, HSV-GR and HSV-Red showed one log lower titer (107 PFU) than parental HSV. Cytotoxicity analysis showed that HSV-GR and HSV-Red can lyse target tumor cells at multiplicity of infection of 10 and 1 (P<0.001). Moreover, HSV-GFP showed higher infection potency (98%) in comparison with HSV-GR (82%).

Conclusion

Our oHSVs provide a simple and an efficient platform for construction and rapid isolation of 2nd and 3rd generation oHSVs by replacing the inserted dyes with transgenes and also for rapid identification via fluorescence activated cell sorting. These vectors can also be used for tracing the efficacy of therapeutic agents on target cells, imaging of neural or tumoral cells in vitro/in vivo and as oncolytic agents in cancer therapy.

A novel peptide specifically binding to VEGF receptor suppresses angiogenesis in vitro and in vivo

Vascular endothelial growth factor (VEGF), one of the most important angiogenic factors, plays an essential role in both physiological and pathological angiogenesis through binding to VEGF receptors (VEGFRs). Here we report a novel peptide designated HRHTKQRHTALH (peptide HRH), which was isolated from the Ph.D. -12 phage display library using VEGFR-Fc fusion protein as the bait. This peptide was found to dose-dependently inhibit the proliferation of human umbilical vein endothelial cells stimulated by VEGF. The anti-angiogenesis effect of the HRH peptide was further confirmed in vivo using the chick chorioallantoic membrane assay, which was also dose-dependent. Besides, peptide HRH was proved to inhibit corneal neovascularization in an alkali-burnt rat corneal model and a suture-induced rat corneal model. Taken together, these findings suggest that the HRH peptide can inhibit angiogenesis both in vitro and in vivo. Consequently, the HRHTKQRHTALH peptide might be a promising lead peptide for the development of potential angiogenic inhibitors.

HSV-1 interaction to 3-O-sulfated heparan sulfate in mouse-derived DRG explant and profiles of inflammatory markers during virus infection

The molecular mechanism of herpes simplex virus (HSV) entry and the associated inflammatory response in the nervous system remain poorly understood. Using mouse-derived ex vivo dorsal root ganglia (DRG) explant model and single cell neurons (SCNs), in this study, we provided a visual evidence for the expression of heparan sulfate (HS) and 3-O-sulfated heparan sulfate (3-OS HS) followed by their interactions with HSV-1 glycoprotein B (gB) and glycoprotein D (gD) during cell entry. Upon heparanase treatment of DRG-derived SCN, a significant inhibition of HSV-1 entry was observed suggesting the involvement of HS role during viral entry. Finally, a cytokine array profile generated during HSV-1 infection in DRG explant indicated an enhanced expression of chemokines (LIX, TIMP-2, and M-CSF)—known regulators of HS. Taken together, these results highlight the significance of HS during HSV-1 entry in DRG explant. Further investigation is needed to understand which isoforms of 3-O-sulfotransferase (3-OST)-generated HS contributed during HSV-1 infection and associated cell damage.

Cultured corneas show dendritic spread and restrict herpes simplex virus infection that is not observed with cultured corneal cells

Herpes simplex virus-1 (HSV-1) causes life-long morbidities in humans. While fever blisters are more common, occasionally the cornea is infected resulting in vision loss. A very intriguing aspect of HSV-1 corneal infection is that the virus spread is normally restricted to only a small fraction of cells on the corneal surface that connect with each other in a dendritic fashion. Here, to develop a comprehensive understanding of the susceptibility of human corneal epithelial (HCE) cells to HSV-1 infection, we infected HCE cells at three different dosages of HSV-1 and measured the outcomes in terms of viral entry, gene and protein expression, viral replication and cytokine induction. In cultured cells, infectivity and cytokine induction were observed even at the minimum viral dosage tested, while a more pronounced dose-restricted infectivity was seen in ex vivo cultures of porcine corneas. Use of fluorescent HSV-1 virions demonstrated a pattern of viral spread ex vivo that mimics clinical findings. We conclude that HCE cell cultures are highly susceptible to infection whereas the cultured corneas demonstrate a higher ability to restrict the infection even in the absence of systemic immune system. The restriction is helped in part by local interferon response and the unique cellular architecture of the cornea.

Rapid Screening by Cell-Based Fusion Assay for Identifying Novel Antivirals of Glycoprotein B-Mediated Herpes Simplex Virus Type 1 Infection

Herpes simplex virus type 1 (HSV-1) is a causative agent for a variety of diseases. Although antiherpetic drugs such as acyclovir have been developed to inhibit virus replication through interaction with DNA kinases, their continuous administration leads to an increase in the frequency of drug-resistant HSV-1, which is an important clinical issue that requires urgent solution. Recently, we reported that the sialylated O-linked sugar T antigen (sTn) and its attached peptide region (O-glycosylated sTn peptide) derived from the HSV-1 glycoprotein B (gB) protein inhibited HSV-1 infection by specifically targeting paired immunoglobulin-like type 2 receptor alpha (PILRα) in vitro. In this study, to further identify novel inhibitors of gB-mediated HSV-1 infection in vitro, we established a cell-based fusion assay for rapid drug screening. Chinese hamster ovary (CHO) cells were transfected with expression plasmids for HSV-1 gB, gD, gH, and gL, and T7 RNA polymerase, and were designated as the effector cells. The CHO-K1 cells stably expressing PILRα were transfected with the expression plasmid for firefly luciferase under the T7 promoter, and were designated as the target cells. The effector and target cells were co-cultured, and luminescence was measured when both cells were successfully fused. Importantly, we found that cell-to-cell fusion was specifically inhibited by O-glycosylated sTn peptide in a dose dependent manner. Our results suggested that this virus-free cell-based fusion assay system could be a useful and promising approach to identify novel inhibitors of gB-mediated HSV-1 infection, and will aid in the development of antiviral therapeutic strategies for HSV-1-associated diseases.

Nanoparticles in Antiviral Therapy

In addition to general unavailability of specific antiviral therapeutics for a variety of viral diseases, usage of most antiviral drugs is linked to their limited solubility in aqueous media, short half-life time, and inadequate penetration to specified anatomic compartments. Accordingly, there is continuous effort to improve physicochemical characteristics of existing antiviral drugs. Since nanomaterials display remarkable physical and chemical properties, high surface area to volume ratio, and increased reactivity, new approaches for antiviral therapies include combinations of nanomaterials and current antiviral agents. Multivalent nanostructures, polymers, dendrimers, and liposomes can establish multivalent binding interactions with many biological systems and thus can target pathogenic interactions. There are reports about anitiviral activities of different metal nanoparticles, especially silver nanoparticles and their potential for treatment, prophylaxis, and control of viral infections. Integration of classic antiviral drugs, in the form of multiple ligands, onto nanostructures provides the advantages by creating a high local concentration of active molecules. This article will summarize the antiviral activity of different nanoparticle-based approaches currently available for the treatment of viral infections, and it will discuss metal nanoparticles as possible future antiviral drugs.

Participation of 3-O-sulfated heparan sulfates in the protection of macrophages by herpes simplex virus-1 glycoprotein D and cyclophilin B against apoptosis

Heparan sulfates (HS) are involved in numerous biological processes, which rely on their ability to interact with a large panel of proteins. Although the reaction of 3‐O‐sulfation can be catalysed by the largest family of HS sulfotransferases, very few mechanisms have been associated with this modification and to date, only glycoprotein D (gD) of herpes simplex virus‐1 (HSV‐1 gD) and cyclophilin B (CyPB) have been well‐described as ligands for 3‐O‐sulfated HS. Here, we hypothesized that both ligands could induce the same responses via a mechanism dependent on 3‐O‐sulfated HS. First, we checked that HSV‐1 gD was as efficient as CyPB to induce the activation of the same signalling events in primary macrophages. We then demonstrated that both ligands efficiently reduced staurosporin‐induced apoptosis and modulated the expression of apoptotic genes. In addition to 3‐O‐sulfated HS, HSV‐1 gD was reported to interact with other receptors, including herpes virus entry mediator (HVEM), nectin‐1 and ‐2. Thus, we decided to identify the contribution of each binding site in the responses triggered by HSV‐1 gD and CyPB. We found that knock‐down of 3‐O‐sulfotransferase 2, which is the main 3‐O‐sulfated HS‐generating enzyme in macrophages, strongly reduced the responses induced by both ligands. Moreover, silencing the expression of HVEM rendered macrophages unresponsive to either HSV‐1 gD and CyPB, thus indicating that both proteins induced the same responses by interacting with a complex formed by 3‐O‐sulfated HS and HVEM. Collectively, our results suggest that HSV‐1 might hijack the binding sites for CyPB in order to protect macrophages against apoptosis for efficient infection.

The D-form of a novel heparan binding peptide decreases cytomegalovirus infection in vivo and in vitro

Human cytomegalovirus (HCMV) infection in utero can lead to congenital sensory neural hearing loss and mental retardation. Reactivation or primary infection can increase the morbidity and mortality in immune suppressed transplant recipients and AIDS patients. The current standard of care for HCMV disease is nucleoside analogs, which can be nephrotoxic. In addition resistance to current treatments is becoming increasingly common. In an effort to develop novel CMV treatments, we tested the effectiveness of the D-form of a novel heparan sulfate binding peptide, p5R_D, at reducing infection of ganciclovir (GCV) resistant HCMVs in vitro and MCMV in vivo. HCMV infection was reduced by greater than 90% when cells were pretreated with p5R_D. Because p5R_D acts by a mechanism unrelated to those used by current antivirals, it was effective at reducing GCV resistant HCMVs by 85%. We show that p5R_D is resistant to common proteases and serum inactivation, which likely contributed to its ability to significantly reduced infection of peritoneal exudate cells and viral loads in the spleen and the lungs in vivo. The ability of p5R_D to reduce HCMV infectivity in vitro including GCV resistant HCMVs and MCMV infection in vivo suggests that this peptide could be a novel anti-CMV therapeutic.

Extended Release of an Anti-Heparan Sulfate Peptide From a Contact Lens Suppresses Corneal Herpes Simplex Virus-1 Infection

PURPOSE

To prolong the release of a heparan sulfate binding peptide, G2-C, using a commercially available contact lens as a delivery vehicle and to demonstrate the ability of the released peptide to block herpes simplex virus-1 (HSV-1) infection using in vitro, ex vivo, and in vivo models of corneal HSV-1 infection.

METHODS

Commercially available contact lenses were immersed in peptide solution for 5 days prior to determining the release of the peptide at various time points. Cytotoxicity of the released samples was determined by MTT and cell cycle analysis, and the functional activity of the released samples were assessed by viral entry, and viral spread assay using human corneal epithelial cells (HCE). The ability to suppress infection in human and pig cornea ex vivo and mouse in vivo models were also assessed.

RESULTS

Peptide G2-C was released through the contact lens. Following release for 3 days, the peptide showed significant activity by inhibiting HSV-1 viral entry and spread in HCE cells. Significant suppression of infection was also observed in the ex vivo and in vivo experiments involving corneas.

CONCLUSIONS

Extended release of an anti-HS peptide through a commercially available contact lens can generate significant anti-HSV-1 activity and provides a new and effective way to control corneal herpes.

Novel therapeutic investigational strategies to treat severe and disseminated HSV infections suggested by a deeper understanding of in vitro virus entry processes

The global burden of herpes simplex virus (HSV) legitimates the critical need to develop new prevention strategies, such as drugs and vaccines that are able to fight either primary HSV infections or reactivations. Moreover, the ever-growing number of patients receiving transplants increases the number of severe HSV infections that are unresponsive to current therapies. Finally, the high global incidence of genital HSV-2 infection increases the risk of perinatal transmission to newborns, in which disseminated infection or central nervous system (CNS) involvement is frequent, with associated high morbidity and mortality rates. There are several key features shared by novel anti-HSV drugs, from currently available optimized drugs to small molecules able to interfere with various virus replication steps. However, several virological aspects of the disease and associated clinical needs highlight why an ideal anti-HSV drug has yet to be developed.

Role of Heparan Sulfate in Cellular Infection of Integrin-Binding Coxsackievirus A9 and Human Parechovirus 1 Isolates

Heparan sulfate/heparin class of proteoglycans (HSPG) have been shown to function in cellular attachment and infection of numerous viruses including picornaviruses. Coxsackievirus A9 (CV-A9) and human parechovirus 1 (HPeV-1) are integrin-binding members in the family Picornaviridae. CV-A9 Griggs and HPeV-1 Harris (prototype) strains have been reported not to bind to heparin, but it was recently shown that some CV-A9 isolates interact with heparin in vitro via VP1 protein with a specific T132R/K mutation. We found that the infectivity of both CV-A9 Griggs and HPeV-1 Harris was reduced by sodium chlorate and heparinase suggestive of HSPG interactions. We analyzed the T132 site in fifty-four (54) CV-A9 clinical isolates and found that only one of them possessed T132/R mutation while the other nine (9) had T132K. We then treated CV-A9 Griggs and HPeV-1 Harris and eight CV-A9 and six HPeV-1 clinical isolates with heparin and protamine. Although infectivity of Griggs strain was slightly reduced (by 25%), heparin treatment did not affect the infectivity of the CV-A9 isolates that do not possess the T132R/K mutation, which is in line with the previous findings. Some of the HPeV-1 isolates were also affected by heparin treatment, which suggested that there may be a specific heparin binding site in HPeV-1. In contrast, protamine (a specific inhibitor of heparin) completely inhibited the infection of both prototypes and clinical CV-A9 and HPeV-1 isolates. We conclude that T132R/K mutation has a role in heparin binding of CV-A9, but we also show data, which suggest that there are other HSPG binding sites in CV-A9. In all, we suggest that HSPGs play a general role in both CV-A9 and HPeV-1 infections.

Herpes Simplex Virus (HSV) Modulation of Staphylococcus aureus and Candida albicans Initiation of HeLa 299 Cell-Associated Biofilm

Although herpes simplex virus type-1 (HSV-1), and type-2 (HSV-2), Staphylococcus aureus and Candida albicans co-habit the oral and genital mucosa, their interaction is poorly understood. We determined the effect HSV has on bacterial and/or fungal adherence, the initial step in biofilm formation. HeLa229 cells were infected with HSV-1 (KOS) gL86 or HSV-2 (KOS) 333gJ⁻ at a multiplicity of infection (MOI) of 50 and 10. S. aureus (ATCC 25923) and/or C. albicans (yeast forms or germ tube forms) were co-incubated for 30 min (37 °C; 5 % CO₂; 5:1 organism: HeLa cell ratio; n = 16) with virus-infected HeLa cells or uninfected HeLa cell controls. Post-incubation, the monolayers were washed (3x; PBS), lysed (RIPA), and the lysate plated onto Fungisel and/or mannitol salts agar for standard colony count. The level of HeLa-associated S. aureus was significantly decreased (P < 0.05) for both HSV-1- and HSV-2-infected cells, as compared to virus-free HeLa cell controls (38 and 59 % of control, respectively). In contrast, HSV-1 and HSV-2 significantly (P < 0.05) enhanced HeLa cell association of C. albicans yeast forms and germ tube approximately two-fold, respectively. The effect of S. aureus on germ tube and yeast form adherence to HSV-1- and HSV-2-infected cells was specific for the Candida phenotype tested. Our study suggests that HSV, while antagonist towards S. aureus adherence enhances Candida adherence. Furthermore, the combination of the three pathogens results in S. aureus adherence that is either unaffected, or partially restored depending on both the herpes viral species and the fungal phenotype present.

A Haploid Genetic Screen Identifies Heparan Sulfate Proteoglycans Supporting Rift Valley Fever Virus Infection

Rift Valley fever virus (RVFV) causes recurrent insect-borne epizootics throughout the African continent, and infection of humans can lead to a lethal hemorrhagic fever syndrome. Deep mutagenesis of haploid human cells was used to identify host factors required for RVFV infection. This screen identified a suite of enzymes involved in glycosaminoglycan (GAG) biogenesis and transport, including several components of the cis-oligomeric Golgi (COG) complex, one of the central components of Golgi complex trafficking. In addition, disruption of PTAR1 led to RVFV resistance as well as reduced heparan sulfate surface levels, consistent with recent observations that PTAR1-deficient cells exhibit altered Golgi complex morphology and glycosylation defects. A variety of biochemical and genetic approaches were utilized to show that both pathogenic and attenuated RVFV strains require GAGs for efficient infection on some, but not all, cell types, with the block to infection being at the level of virion attachment. Examination of other members of the Bunyaviridae family for GAG-dependent infection suggested that the interaction with GAGs is not universal among bunyaviruses, indicating that these viruses, as well as RVFV on certain cell types, employ additional unidentified virion attachment factors and/or receptors.

IMPORTANCE

Rift Valley fever virus (RVFV) is an emerging pathogen that can cause severe disease in humans and animals. Epizootics among livestock populations lead to high mortality rates and can be economically devastating. Human epidemics of Rift Valley fever, often initiated by contact with infected animals, are characterized by a febrile disease that sometimes leads to encephalitis or hemorrhagic fever. The global burden of the pathogen is increasing because it has recently disseminated beyond Africa, which is of particular concern because the virus can be transmitted by widely distributed mosquito species. There are no FDA-licensed vaccines or antiviral agents with activity against RVFV, and details of its life cycle and interaction with host cells are not well characterized. We used the power of genetic screening in human cells and found that RVFV utilizes glycosaminoglycans to attach to host cells. This furthers our understanding of the virus and informs the development of antiviral therapeutics.

Cell entry mechanisms of HSV: what we have learned in recent years

HSV type-1 and -2 are widespread pathogens producing lifelong infection with multiple sequelae, including oral, ocular and genital disease. The process of herpesvirus entry is a highly complex process involving numerous viral and cellular factors. Entry begins with attachment of virus to the cell surface followed by interactions between viral glycoproteins and cellular receptors to facilitate capsid penetration. The nucleocapsid is then transported along microtubules to the nuclear membrane, where viral DNA is released for replication in the nucleus. The work reviewed here comprises the most recent advancements in our understanding of the mechanism involved in the herpesvirus entry process.

Nanostructures for the Inhibition of Viral Infections

Multivalent interactions are omnipresent in biology and confer biological systems with dramatically enhanced affinities towards different receptors. Such multivalent binding interactions have lately been considered for the development of new therapeutic strategies against bacterial and viral infections. Multivalent polymers, dendrimers, and liposomes have successfully targeted pathogenic interactions. While a high synthetic effort was often needed for the development of such therapeutics, the integration of multiple ligands onto nanostructures turned to be a viable alternative. Particles modified with multiple ligands have the additional advantage of creating a high local concentration of binding molecules. This review article will summarize the different nanoparticle-based approaches currently available for the treatment of viral infections.

Novel heparan sulfate-binding peptides for blocking herpesvirus entry

Human cytomegalovirus (HCMV) infection can lead to congenital hearing loss and mental retardation. Upon immune suppression, reactivation of latent HCMV or primary infection increases morbidity in cancer, transplantation, and late stage AIDS patients. Current treatments include nucleoside analogues, which have significant toxicities limiting their usefulness. In this study we screened a panel of synthetic heparin-binding peptides for their ability to prevent CMV infection in vitro. A peptide designated, p5+14 exhibited ~ 90% reduction in murine CMV (MCMV) infection. Because negatively charged, cell-surface heparan sulfate proteoglycans (HSPGs), serve as the attachment receptor during the adsorption phase of the CMV infection cycle, we hypothesized that p5+14 effectively competes for CMV adsorption to the cell surface resulting in the reduction in infection. Positively charged Lys residues were required for peptide binding to cell-surface HSPGs and reducing viral infection. We show that this inhibition was not due to a direct neutralizing effect on the virus itself and that the peptide blocked adsorption of the virus. The peptide also inhibited infection of other herpesviruses: HCMV and herpes simplex virus 1 and 2 in vitro, demonstrating it has broad-spectrum antiviral activity. Therefore, this peptide may offer an adjunct therapy for the treatment of herpes viral infections and other viruses that use HSPGs for entry.

Heparanase is a host enzyme required for herpes simplex virus-1 release from cells

Herpesviruses exemplified by herpes simplex virus-1 (HSV-1) attach to cell surface heparan sulfate (HS) for entry into host cells. However, during a productive infection the HS moieties on parent cells can trap newly exiting viral progenies and inhibit their release. Here, we demonstrate that a HS-degrading enzyme of the host, heparanase (HPSE), is upregulated through NF-kB and translocated to the cell surface upon HSV-1 infection for the removal of HS to facilitate viral release. We also find a significant increase in HPSE release in vivo during infection of murine corneas and that knockdown of HPSE in vivo inhibits virus shedding. Overall, we propose that HPSE acts as a molecular switch for turning a virus-permissive “attachment mode” of host cells to a virus-deterring “detachment mode”. Since many human viruses use HS as an attachment receptor, the HPSE-HS interplay may delineate a common mechanism for virus release.

A role for 3-O-sulfated heparan sulfate in promoting human cytomegalovirus infection in human iris cells

Human cytomegalovirus (HCMV) has emerged as a clinically opportunistic pathogen that targets multiple types of ocular cells and tissues, including the iris region of the uveal tract during anterior uveitis. In this report, we used primary cultures of human iris stroma (HIS) cells derived from human eye donors to investigate HCMV entry. The following lines of evidence suggested the role of 3-O-sulfated heparan sulfate (3-OS HS) during HCMV-mediated entry and cell-to-cell fusion in HIS cells. First, 3-O-sulfotransferase-3 (3-OST-3) expression in HIS cells promoted HCMV internalization, while pretreatment of HIS cells with heparinase enzyme or with anti-3-OS HS (G2) peptide significantly reduced the HCMV-mediated formation of plaques/foci. Second, coculture of the HCMV-infected HIS cells with CHO-K1 cells expressing 3-OS HS significantly enhanced cell fusion. Finally, a similar trend of enhanced fusion was observed with cells expressing HCMV glycoproteins (gB, gO, and gH-gL) cocultured with 3-OS HS cells. Taken together, these results highlight the role of 3-OS HS during HCMV plaque formation and cell-to-cell fusion and identify a novel target for future therapeutic interventions.

Diversity of heparan sulfate and HSV entry: basic understanding and treatment strategies

A modified form of heparan sulfate (HS) known as 3-O-sulfated heparan sulfate (3-OS HS) generates fusion receptor for herpes simplex virus (HSV) entry and spread. Primary cultures of corneal fibroblasts derived from human eye donors have shown the clinical significance of this receptor during HSV corneal infection. 3-OS HS- is a product of a rare enzymatic modification at C3 position of glucosamine residue which is catalyzed by 3-O-sulfotransferases (3-OSTs) enzymes. From humans to zebrafish, the 3-OST enzymes are highly conserved and widely expressed in cells and tissues. There are multiple forms of 3-OSTs each producing unique subset of sulfated HS making it chemically diverse and heterogeneous. HSV infection of cells or zebrafish can be used as a unique tool to understand the structural-functional activities of HS and 3-OS HS and likewise, the infection can be used as a functional assay to screen phage display libraries for identifying HS and 3-OS HS binding peptides or small molecule inhibitors. Using this approach over 200 unique 12-mer HS and 3-OS HS recognizing peptides were isolated and characterized against HSV corneal infection where 3-OS HS is known to be a key receptor. In this review we discuss emerging role of 3-OS HS based therapeutic strategies in preventing viral infection and tissue damage.

Protein and oligonucleotide delivery systems for vaginal microbicides against viral STIs

Intravaginal delivery offers an effective option for localized, targeted, and potent microbicide delivery. However, an understanding of the physiological factors that impact intravaginal delivery must be considered to develop the next generation of microbicides. In this review, a comprehensive discussion of the opportunities and challenges of intravaginal delivery are highlighted, in the context of the intravaginal environment and currently utilized dosage forms. After a subsequent discussion of the stages of microbicide development, the intravaginal delivery of proteins and oligonucleotides is addressed, with specific application to HSV and HIV. Future directions may include the integration of more targeted delivery modalities to virus and host cells, in addition to the use of biological agents to affect specific genes and proteins involved in infection. More versatile and multipurpose solutions are envisioned that integrate new biologicals and materials into potentially synergistic combinations to achieve these goals.

The Antimicrobial and Antiviral Applications of Cell-Penetrating Peptides

Over the past two decades, cell-penetrating peptides (CPPs) have become increasingly popular both in research and in application. There have been numerous studies on the physiochemical characteristics and behavior of CPPs in various environments; likewise, the mechanisms of entry and delivery capabilities of these peptides have also been extensively researched. Besides the fundamental issues, there is an enormous interest in the delivery capabilities of the peptides as the family of CPPs is a promising and mostly non-toxic delivery vector candidate for numerous medical applications such as gene silencing, transgene delivery, and splice correction. Lately, however, there has been an emerging field of study besides the high-profile gene therapy applications-the use of peptides and CPPs to combat various infections caused by harmful bacteria, fungi, and viruses.In this chapter, we aim to provide a short overview of the history and properties of CPPs which is followed by more thorough descriptions of antimicrobial and antiviral peptides. To achieve this, we analyze the origin of such peptides, give an overview of the mechanisms of action and discuss the various practical applications which are ongoing or have been suggested based on research.

Characterization of a proteolytically stable D-peptide that suppresses herpes simplex virus 1 infection: implications for the development of entry-based antiviral therapy

Uncontrolled herpes simplex virus 1 (HSV-1) infection can advance to serious conditions, including corneal blindness or fatal encephalitis. Here, we describe a highly potent anti-HSV-1 peptide (DG2) that inhibits HSV-1 entry into host cells and blocks all aspects of infection. Importantly, DG2 is highly resistant to proteases and shows minimal toxicity, paving the way for prophylactic or therapeutic application of the peptide in vivo.

Peptide therapeutics for treating ocular surface infections

Microbial pathogens-bacteria, viruses, fungi, and parasites-are significant causes of blindness, particularly in developing countries. For bacterial and some viral infections a number of antimicrobial drugs are available for therapy but there are fewer available for use in treating fungal and parasitic keratitis. There are also problems with current antimicrobials, such as limited efficacy and the presence of drug-resistant microbes. Thus, there is a need to develop additional drugs. Nature has given us an example of 1 potential source of new antimicrobials: antimicrobial peptides and proteins that are either present in bodily fluids and tissues constitutively or are induced upon infection. Given the nature of peptides, topical applications are the most likely use to be successful and this is ideal for treating keratitis. Such peptides would also be active against drug-resistant pathogens and might act synergistically if used in combination therapy. Hundreds of peptides with antimicrobial properties have been isolated or synthesized but only a handful have been tested against ocular pathogens and even fewer have been tested in animal models. This review summarizes the currently available information on the use of peptides to treat keratitis, outlines some of the problems that have been identified, and discusses future studies that will be needed. Most of the peptides that have been tested have shown activity at concentrations that do not warrant further development, but 1 or 2 have promising activity raising the possibility that peptides can be developed to treat keratitis.

Overexpression of herpes simplex virus glycoprotein K (gK) alters expression of HSV receptors in ocularly-infected mice

PURPOSE

We have shown previously that HSV-1 glycoprotein K (gK) exacerbates corneal scarring (CS) in mice and rabbits. Here, we investigated the relative impact of gK overexpression on host responses during primary corneal infection and latency in trigeminal ganglia (TG) of infected mice.

METHODS

Mice were infected ocularly with HSV-gK(3) (expressing two extra copies of gK replacing latency associated transcript [LAT]), HSV-gK(3) revertant (HSV-gK(3)R), or wild-type HSV-1 strain McKrae. Individual corneas on day 5 post infection (PI) and TG on day 28 PI were isolated and used for detection of gB DNA in the TG, HSV-1 receptors in the cornea and TG, and inflammatory infiltrates in TG.

RESULTS

During primary HSV-1 infection, gK overexpression resulted in altered expression of herpesvirus entry mediator (HVEM), 3-O-sulfated heparin sulfate (3-OS-HS), paired immunoglobulin-like type 2 receptor-α (PILR-α), nectin-1, and nectin-2 in cornea of BALB/c, but not C57BL/6 mice. However, gK overexpression did have an effect on 3-OS-HS, PILR-α, nectin-1, and nectin-2 expression (but not HVEM expression) in TG of C57BL/6 mice during latency. These differences did not affect the level of latency, but instead were correlated with the presence of CS. The presence of LAT increased HVEM expression and this effect was enhanced further by the presence of CS in latently-infected mice. Finally, the presence of LAT, but not overexpression of gK, affected CD4, CD8, TNF-α, Tim-3, PD-1, IL-21, IL-2, and IFN-γ expression in TG.

CONCLUSIONS

We demonstrate a novel link between gK exacerbation of CS and HSV-1 receptors, suggesting a gK-induced molecular route for the pathogenesis as well as selective advantage of these entry routes for the pathogen during latency-reactivation cycle.

Recent developments in antiviral agents against enterovirus 71 infection

Enterovirus 71 (EV-71) is the main etiological agent of hand, foot and mouth disease (HFMD). Recent EV-71 outbreaks in Asia-Pacific were not limited to mild HFMD, but were associated with severe neurological complications such as aseptic meningitis and brainstem encephalitis, which may lead to cardiopulmonary failure and death. The absence of licensed therapeutics for clinical use has intensified research into anti-EV-71 development. This review highlights the potential antiviral agents targeting EV-71 attachment, entry, uncoating, translation, polyprotein processing, virus-induced formation of membranous RNA replication complexes, and RNA-dependent RNA polymerase. The strategies for antiviral development include target-based synthetic compounds, anti-rhinovirus and poliovirus libraries screening, and natural compound libraries screening. Growing knowledge of the EV-71 life cycle will lead to successful development of antivirals. The continued effort to develop antiviral agents for treatment is crucial in the absence of a vaccine. The coupling of antivirals with an effective vaccine will accelerate eradication of the disease.

Zebrafish 3-O-sulfotransferase-4 generated heparan sulfate mediates HSV-1 entry and spread

Rare modification of heparan sulfate (HS) by glucosaminyl 3-O sulfotransferase (3-OST) isforms generates an entry receptor for herpes simplex virus type-1 (HSV-1). In the zebrafish (ZF) model multiple 3-OST isoforms are differentially expressed. One such isoform is 3-OST-4 which is widely expressed in the central nervous system of ZF. In this report we characterize the role of ZF encoded 3-OST-4 isoform for HSV-1 entry. Expression of ZF 3-OST-4 into resistant Chinese hamster ovary (CHO-K1) cells promoted susceptibility to HSV-1 infection. This entry was 3-O sulfated HS (3-OS HS) dependent as pre-treatment of ZF 3-OST-4 cells with enzyme HS lyases (heparinase II/III) significantly reduced HSV-1 entry. Interestingly, co-expression of ZF 3-OST-4 along with ZF 3-OST-2 which is also expressed in brain rendered cells more susceptible to HSV-1 than 3-OST-4 alone. The role of ZF-3-OST-4 in the spread of HSV-1 was also evaluated as CHO-K1 cells that expressed HSV-1 glycoproteins fused with ZF 3-OST-4 expressing effector CHO-K1 cells. Finally, adding further evidence ZF 3-OST-4 mediated HSV-1 entry was inhibited by anti-3O HS G2 peptide. Taken together our results demonstrate a role for ZF 3-OST-4 in HSV-1 pathogenesis and support the use of ZF as a model to study it.

Zebrafish: modeling for herpes simplex virus infections

For many years, zebrafish have been the prototypical model for studies in developmental biology. In recent years, zebrafish has emerged as a powerful model system to study infectious diseases, including viral infections. Experiments conducted with herpes simplex virus type-1 in adult zebrafish or in embryo models are encouraging as they establish proof of concept with viral-host tropism and possible screening of antiviral compounds. In addition, the presence of human homologs of viral entry receptors in zebrafish such as 3-O sulfated heparan sulfate, nectins, and tumor necrosis factor receptor superfamily member 14-like receptor bring strong rationale for virologists to test their in vivo significance in viral entry in a zebrafish model and compare the structure-function basis of virus zebrafish receptor interaction for viral entry. On the other end, a zebrafish model is already being used for studying inflammation and angiogenesis, with or without genetic manipulations, and therefore can be exploited to study viral infection-associated pathologies. The major advantage with zebrafish is low cost, easy breeding and maintenance, rapid lifecycle, and a transparent nature, which allows visualizing dissemination of fluorescently labeled virus infection in real time either at a localized region or the whole body. Further, the availability of multiple transgenic lines that express fluorescently tagged immune cells for in vivo imaging of virus infected animals is extremely attractive. In addition, a fully developed immune system and potential for receptor-specific knockouts further advocate the use of zebrafish as a new tool to study viral infections. In this review, we focus on expanding the potential of zebrafish model system in understanding human infectious diseases and future benefits.

An investigative peptide-acyclovir combination to control herpes simplex virus type 1 ocular infection

PURPOSE

To investigate the efficacy of a combination treatment composed of the cationic, membrane-penetrating peptide G2, and acyclovir (ACV) in both in vitro and ex vivo models of herpes simplex virus 1 (HSV-1) ocular infection.

METHODS

The antiviral activity of a combined G2 peptide and ACV therapy (G2-ACV) was assessed in various treatment models. Viral entry, spread, and plaque assays were performed in vitro to assess the prophylactic efficacy of G2, G2-ACV, and ACV treatments. In the ex vivo model of HSV-1 infection, the level of viral inhibition was also compared among the three treatment groups via Western blot analysis and immunohistochemistry. The potential change in expression of the target receptor for G2 was also assessed using immunohistochemistry and RT-PCR.

RESULTS

Statistically significant effects against HSV-1 infection were seen in all treatment groups in the viral entry, spread, and plaque assays. The greatest effects against HSV-1 infection in vitro were seen in the G2-ACV group. In the ex vivo model, statistically significant anti-HSV-1 effects were also noted in all control groups. At 24 hours, the greatest inhibitory effect against HSV-1 infection was seen in the ACV group. At 48 hours, however, the G2-ACV-treated group demonstrated the greatest antiviral activity. Syndecan-1, a target of G2, was found to be upregulated at 12-hours postinfection.

CONCLUSIONS

This study shows that G2-ACV may be an effective antiviral against HSV-1 (KOS) strain when applied as single prophylactic applications with or without continuous doses postinfection.

Inhibition of myosin light chain kinase can be targeted for the development of new therapies against herpes simplex virus type-1 infection

BACKGROUND

Herpes simplex virus type-1 (HSV-1) is the leading cause of infectious blindness worldwide. Through a multistep process, HSV-1 enters into naturally susceptible human corneal epithelial (HCE) cells where it establishes an optimal environment for viral replication and spread. HSV-1 employment of cytoskeletal proteins, kinases, and cell signalling pathways is crucial for the entry process.

METHODS

Here we demonstrate that non-muscle myosin IIA (NM-IIA) and/or a myosin activating kinase, myosin light chain kinase (MLCK), can be targeted for the development of new and effective therapies against HSV-1. HCE cells were incubated with MLCK inhibitors ML-7 and ML-9 and NM-IIA inhibitor blebbistatin. Following the application of inhibitors, HSV-1 entry and spread to neighbouring HCE cells was evaluated.

RESULTS

Upon application of MLCK inhibitors ML-7 and ML-9 and NM-IIA inhibitor blebbistatin, HSV-1 entry into HCE cells was significantly decreased. Furthermore, dramatic impairment of glycoprotein-mediated membrane fusion was seen in cells treated with MLCK inhibitors, thus establishing a role for MLCK activation in cell-to-cell fusion and multinucleated syncytial cell formation. These results also indicate that the activation of motor protein NM-IIA by MLCK is crucial for cytoskeletal changes required for HSV-1 infection of corneal cells.

CONCLUSIONS

We provide new evidence that NM-IIA and MLCK can be used as effective antiviral targets against ocular herpes.

Glycoprotein targeted therapeutics: a new era of anti-herpes simplex virus-1 therapeutics

Herpes simplex virus type-1 (HSV-1) is among the most common human pathogens worldwide. Its entry into host cells is an intricate process that relies heavily on the ability of the viral glycoproteins to bind host cellular proteins and to efficiently mediate fusion of the virus envelope with the cell membrane. Acquisition of HSV-1 results in a lifelong latent infection. Because of the cycles of reactivation from a latent state, much emphasis has been placed on the management of infection through the use of DNA synthesis inhibitors. However, new methods are needed to provide more effective treatment at earlier phases of the viral infection and to prevent the development of drug resistance by the virus. This review outlines the infection process and the common therapeutics currently used against the fundamental stages of HSV-1 replication and fusion. The remainder of this article will focus on a new approach for HSV-1 infection control and management, the concept of glycoprotein-receptor targeting.

Role of heparan sulfate in ocular diseases

Heparan sulfate (HS), a ubiquitous and structurally diverse cell surface polysaccharide and extracellular matrix component, is a factor common to several major eye pathologies. Its multitude of functions and variable distribution among the different ocular tissues makes it an important contributor to a variety of disease states. Although HS facilitates the pathogenesis of many disorders, its role in each varies. Unique functions of HS have been particularly noted in viral and bacterial keratitis and age-related macular degeneration. Combined, these pathologies comprise a large portion of conditions leading to visual impairment worldwide. Given this prevalence of diseases facilitated by HS, it is prudent to take an in-depth look at this compound in the context of these pathologic states. While the initial part of the review will discuss the pathogenic aspects of HS, it is also important to consider the wider implications of such roles for HS. The remainder of the article will specifically address one such implication, the possibility for future use of novel HS-based therapeutics to combat these eye pathologies.

Susceptibility of human iris stromal cells to herpes simplex virus 1 entry

Ocular herpes simplex virus 1 (HSV-1) infection can lead to multiple complications, including iritis, an inflammation of the iris. Here, we use human iris stroma cells as a novel in vitro model to demonstrate HSV-1 entry and the inflammatory mediators that can damage the iris. The upregulated cytokines observed in this study provide a new understanding of the intrinsic immune mechanisms that can contribute to the onset of iritis.

Members of 3-O-Sulfotransferases (3-OST) Family: A Valuable Tool from Zebrafish to Humans for Understanding Herpes Simplex Virus Entry

The journey of many viruses to infect cells begins when the virus first binds to cell surface heparan sulfate (HS). The initial step of cell attachment or binding during herpes simplex virus type-1 (HSV-1) entry is mediated by envelope glycoprotein B (gB) and C (gC). The binding is followed by fusion between virus envelope and cell membrane during which HSV-1 glycoprotein D (gD) interacts with a modified form of HS know as 3-O-sulfated heparan sulfate (3-OS HS). The rare modification of 3-O-sulfation on HS chain is governed by enzymes known as 3-O-sulfotransferase (3-OST). Currently, there are seven isoforms of human 3-OSTs that have been identified, and with the exception of 3-OST-1, all other 3-OST isoforms allow HSV-1 entry and spread. Recently, the product of the zebrafish (ZF)-encoded 3-OST-3 was also recognized as a gD receptor, which mediates HSV-1 entry and cell-cell fusion similar to human 3-OST-3. Interestingly, the ZF system expresses multiple isoforms of 3-OST which could be very useful for studying the involvement of HS and 3-OS HS in virus tropism and virus-induced inflammation. In addition, therapeutic targeting of 3-OST generated HS is likely to bring about novel interventions against HSV-1. In this review we have taken a closer look at the potential of both human and ZF encoded 3-OSTs as valuable tools in HSV entry and inflammation studies.

Role of heparan sulfate in sexually transmitted infections

Cell surface heparan sulfate (HS), a polysaccharide composed of alternating uronic acid and glucosamine residues, represents a common link that many sexually transmitted infections (STIs) require for infection. Variable modifications within the monomeric units of HS chains together with their unique structural conformations generate heterogeneity, which expands the ability of HS to bind a diverse array of host and microbial proteins. Recent advances made in the field of glycobiology have critically enhanced our understanding of HS and its interactions with microbes and their significance in important human diseases. The role of HS has been elaborated for several STIs to include those caused by herpes simplex virus, human immunodeficiency virus, human papillomavirus, and Chlamydia. In addition, gonorrhea, syphilis, and yeast infections are also dependent on the presence of HS on human target cells. Critical steps such as pathogen adhesion or binding to host cells followed by internalization to enhance intracellular survival and possible spread to other cells are mediated by HS. In addition, HS guided cell signaling plays a role in the development of angiogenesis and inflammation associated with many STIs. Past and ongoing investigations are providing new push for the development of HS-mimetics and analogs as novel prevention strategies against many different STIs. This review article summarizes the significance of HS in STIs and describes how emerging new products that target HS can be used to control the spread of STIs.

Enterovirus 71 uses cell surface heparan sulfate glycosaminoglycan as an attachment receptor

Enterovirus 71 (EV-71) infections are usually associated with mild hand, foot, and mouth disease in young children but have been reported to cause severe neurological complications with high mortality rates. To date, four EV-71 receptors have been identified, but inhibition of these receptors by antagonists did not completely abolish EV-71 infection, implying that there is an as yet undiscovered receptor(s). Since EV-71 has a wide range of tissue tropisms, we hypothesize that EV-71 infections may be facilitated by using receptors that are widely expressed in all cell types, such as heparan sulfate. In this study, heparin, polysulfated dextran sulfate, and suramin were found to significantly prevent EV-71 infection. Heparin inhibited infection by all the EV-71 strains tested, including those with a single-passage history. Neutralization of the cell surface anionic charge by polycationic poly-d-lysine and blockage of heparan sulfate by an anti-heparan sulfate peptide also inhibited EV-71 infection. Interference with heparan sulfate biosynthesis either by sodium chlorate treatment or through transient knockdown of N-deacetylase/N-sulfotransferase-1 and exostosin-1 expression reduced EV-71 infection in RD cells. Enzymatic removal of cell surface heparan sulfate by heparinase I/II/III inhibited EV-71 infection. Furthermore, the level of EV-71 attachment to CHO cell lines that are variably deficient in cell surface glycosaminoglycans was significantly lower than that to wild-type CHO cells. Direct binding of EV-71 particles to heparin-Sepharose columns under physiological salt conditions was demonstrated. We conclude that EV-71 infection requires initial binding to heparan sulfate as an attachment receptor.

Identifying targets in the hunt for effective respiratory syncytial virus interventions

Respiratory syncytial virus (RSV) is a major cause of human infections worldwide. There is currently no effective vaccine or antiviral therapy available for widespread clinical use; prophylaxis with anti-RSV antibodies is used in only a small percentage of potential recipients. New targets for effective RSV interventions are needed. Previous anti-RSV intervention strategies have focused on targeting aspects of the virus, an approach that can lead to the emergence of resistant RSV strains. Increased understanding of the biology of RSV-host interactions provides an alternative approach for identifying novel targets for RSV interventions that focus on host factors, and exploiting them with the aim to limit the incidence and severity of RSV infections.

Inhibition of enterovirus 71 (EV-71) infections by a novel antiviral peptide derived from EV-71 capsid protein VP1

Enterovirus 71 (EV-71) is the main causative agent of hand, foot and mouth disease (HFMD). In recent years, EV-71 infections were reported to cause high fatalities and severe neurological complications in Asia. Currently, no effective antiviral or vaccine is available to treat or prevent EV-71 infection. In this study, we have discovered a synthetic peptide which could be developed as a potential antiviral for inhibition of EV-71. Ninety five synthetic peptides (15-mers) overlapping the entire EV-71 capsid protein, VP1, were chemically synthesized and tested for antiviral properties against EV-71 in human Rhabdomyosarcoma (RD) cells. One peptide, SP40, was found to significantly reduce cytopathic effects of all representative EV-71 strains from genotypes A, B and C tested, with IC₅₀ values ranging from 6–9.3 µM in RD cells. The in vitro inhibitory effect of SP40 exhibited a dose dependent concentration corresponding to a decrease in infectious viral particles, total viral RNA and the levels of VP1 protein. The antiviral activity of SP40 peptide was not restricted to a specific cell line as inhibition of EV-71 was observed in RD, HeLa, HT-29 and Vero cells. Besides inhibition of EV-71, it also had antiviral activities against CV-A16 and poliovirus type 1 in cell culture. Mechanism of action studies suggested that the SP40 peptide was not virucidal but was able to block viral attachment to the RD cells. Substitutions of arginine and lysine residues with alanine in the SP40 peptide at positions R3A, R4A, K5A and R13A were found to significantly decrease antiviral activities, implying the importance of positively charged amino acids for the antiviral activities. The data demonstrated the potential and feasibility of SP40 as a broad spectrum antiviral agent against EV-71.

A 3-O-sulfated heparan sulfate binding peptide preferentially targets herpes simplex virus 2-infected cells

Herpes simplex virus 2 (HSV-2) is the primary cause of genital herpes, which is one of the most common sexually transmitted viral infections worldwide and a major cofactor for human immunodeficiency virus infection. The lack of an effective vaccine or treatment and the emergence of drug-resistant strains highlight the need for developing new antivirals for HSV-2. Here, we demonstrate that a low-molecular-weight peptide isolated against 3-O-sulfated heparan sulfate (3-OS HS) can efficiently block HSV-2 infection. Treatment with the peptide inhibited viral entry and cell-to-cell spread both in vitro and in vivo using a mouse model of genital HSV-2 infection. Quite interestingly, the peptide showed a preferential binding to HSV-2-infected cells, with more than 200% increased binding compared to uninfected cells. Our additional results show that heparan sulfate expression is upregulated by 25% upon HSV-2 infection, which is a significant new finding that could be exploited for designing new diagnostic tests and treatment strategies against HSV-2-infected cells. In addition, our results also raise the possibility that 3-OS HS modifications within HS may be upregulated even more to accommodate for a significantly higher increase in the peptide binding to the infected cells.

Phage display against corneal epithelial cells produced bioactive peptides that inhibit Aspergillus adhesion to the corneas

Dissection of host-pathogen interactions is important for both understanding the pathogenesis of infectious diseases and developing therapeutics for the infectious diseases like various infectious keratitis. To enhance the knowledge about pathogenesis infectious keratitis, a random 12-mer peptide phage display library was screened against cultured human corneal epithelial cells (HCEC). Fourteen sequences were obtained and BLASTp analysis showed that most of their homologue counterparts in GenBank were for defined or putative proteins in various pathogens. Based on known or predicted functions of the homologue proteins, ten synthetic peptides (Pc-A to Pc-J) were measured for their affinity to bind cells and their potential efficacy to interfere with pathogen adhesion to the cells. Besides binding to HCEC, most of them also bound to human corneal stromal cells and umbilical endothelial cells to different extents. When added to HCEC culture, the peptides induced expression of MyD88 and IL-17 in HCEC, and the stimulated cell culture medium showed fungicidal potency to various extents. While peptides Pc-C and Pc-E inhibited Aspergillus fumigatus (A.f) adhesion to HCEC in a dose-dependent manner, the similar inhibition ability of peptides Pc-A and Pc-B required presence of their homologue ligand Alb1p on A.f. When utilized in an eyeball organ culture model and an in vivo A.f keratitis model established in mouse, Pc-C and Pc-E inhibited fungal adhesion to corneas, hence decreased corneal disruption caused by inflammatory infiltration. Affinity pull-down of HCEC membrane proteins with peptide Pc-C revealed several molecules as potential receptors for this peptide. In conclusion, besides proving that phage display-selected peptides could be utilized to interfere with adhesion of pathogens to host cells, hence could be exploited for managing infectious diseases including infectious keratitis, we also proposed that the phage display technique and the resultant peptides could be used to explore host-pathogen interactions at molecular levels.

Human metapneumovirus (HMPV) binding and infection are mediated by interactions between the HMPV fusion protein and heparan sulfate

Human metapneumovirus (HMPV) is a major worldwide respiratory pathogen that causes acute upper and lower respiratory tract disease. The mechanism by which this virus recognizes and gains access to its target cell is still largely unknown. In this study, we addressed the initial steps in virus binding and infection and found that the first binding partner for HMPV is heparan sulfate (HS). While wild-type CHO-K1 cells are permissive to HMPV infection, mutant cell lines lacking the ability to synthesize glycosaminoglycans (GAGs), specifically, heparan sulfate proteoglycans (HSPGs), were resistant to binding and infection by HMPV. The permissiveness to HMPV infection was also abolished when CHO-K1 cells were treated with heparinases. Importantly, using recombinant HMPV lacking both the G and small hydrophobic (SH) proteins, we report that this first virus-cell binding interaction is driven primarily by the fusion protein (HMPV F) and that this interaction is needed to establish a productive infection. Finally, HMPV binding to cells did not require β1 integrin expression, and RGD-mediated interactions were not essential in promoting HMPV F-mediated cell-to-cell membrane fusion. Cells lacking β1 integrin, however, were less permissive to HMPV infection, indicating that while β1 integrins play an important role in promoting HMPV infection, the interaction between integrins and HMPV occurs after the initial binding of HMPV F to heparan sulfate proteoglycans.

Herpes simplex virus infects most cell types in vitro: clues to its success

Herpes simplex virus (HSV) type-1 and type-2 have evolved numerous strategies to infect a wide range of hosts and cell types. The result is a very successful prevalence of the virus in the human population infecting 40-80% of people worldwide. HSV entry into host cell is a multistep process that involves the interaction of the viral glycoproteins with various cell surface receptors. Based on the cell type, HSV enter into host cell using different modes of entry. The combination of various receptors and entry modes has resulted in a virus that is capable of infecting virtually all cell types. Identifying the common rate limiting steps of the infection may help the development of antiviral agents that are capable of preventing the virus entry into host cell. In this review we describe the major features of HSV entry that have contributed to the wide susceptibility of cells to HSV infection.

An important role for syndecan-1 in herpes simplex virus type-1 induced cell-to-cell fusion and virus spread

Herpes simplex virus type-1 (HSV-1) is a common human pathogen that relies heavily on cell-to-cell spread for establishing a lifelong latent infection. Molecular aspects of HSV-1 entry into host cells have been well studied; however, the molecular details of the spread of the virus from cell-to-cell remain poorly understood. In the past, the role of heparan sulfate proteoglycans (HSPG) during HSV-1 infection has focused solely on the role of HS chains as an attachment receptor for the virus, while the core protein has been assumed to perform a passive role of only carrying the HS chains. Likewise, very little is known about the involvement of any specific HSPGs in HSV-1 lifecycle. Here we demonstrate that a HSPG, syndecan-1, plays an important role in HSV-1 induced membrane fusion and cell-to-cell spread. Interestingly, the functions of syndecan-1 in fusion and spread are independent of the presence of HS on the core protein. Using a mutant CHO-K1 cell line that lacks all glycosaminoglycans (GAGs) on its surface (CHO-745) we demonstrate that the core protein of syndecan-1 possesses the ability to modulate membrane fusion and viral spread. Altogether, we identify a new role for syndecan-1 in HSV-1 pathogenesis and demonstrate HS-independent functions of its core protein in viral spread.

Virostatic potential of micro-nano filopodia-like ZnO structures against herpes simplex virus-1

Herpes simplex virus type-1 (HSV-1) entry into target cell is initiated by the ionic interactions between positively charged viral envelop glycoproteins and a negatively charged cell surface heparan sulfate (HS). This first step involves the induction of HS-rich filopodia-like structures on the cell surface that facilitate viral transport during cell entry. Targeting this initial first step in HSV-1 pathogenesis, we generated different zinc oxide (ZnO) micro-nano structures (MNSs) that were capped with multiple nanoscopic spikes mimicking cell induced filopodia. These MNSs were predicted to target the virus to compete for its binding to cellular HS through their partially negatively charged oxygen vacancies on their nanoscopic spikes, to affect viral entry and subsequent spread. Our results demonstrate that the partially negatively charged ZnO-MNSs efficiently trap the virions via a novel virostatic mechanism rendering them unable to enter into human corneal fibroblasts - a natural target cell for HSV-1 infection. The anti-HSV-1 activity of ZnO MNSs was drastically enhanced after creating additional oxygen vacancies under UV-light illumination. Our results provide a novel insight into the significance of ZnO MNSs as the potent HSV-1 inhibitor and rationalize their development as a novel topical agent for the prevention of HSV-1 infection.