An acyclovir-resistant strain of herpes simplex virus type 2 which is highly virulent for mice

Comparison of the antiviral potential among soluble forms of herpes simplex virus type-2 glycoprotein D receptors, herpes virus entry mediator A, nectin-1 and nectin-2, in transgenic mice

Herpesvirus entry mediator A (HVEM), nectin-1 and nectin-2 are cellular receptors of glycoprotein D (gD) of herpes simplex virus type-2 (HSV-2). It has been shown that soluble forms of HSV gD receptors have the antiviral potential in cultured cells and transgenic mice. Here, to compare antiviral potential of soluble forms of HVEM, nectin-1 and nectin-2 against HSV-2 infections in vivo, transgenic mice expressing fusion proteins consisting of the entire ectodomain of HVEM, nectin-1 or nectin-2 and the Fc portion of human IgG (HVEMIg, nectin-1Ig and nectin-2Ig, respectively) were intraperitoneally infected with HSV-2. In the infection with 3 MLD50 (50 % mouse lethal dose), effective resistance was not observed in transgenic mice expressing nectin-2Ig. In a transgenic mouse line with high expression of nectin-1Ig, significant protection from the infection with 30 and 300 MLD50 was observed (survival rate of 100 and 71 %, respectively). On the other hand, transgenic mice expressing HVEMIg showed a complete resistance to the lethal infection even with 300 MLD50 (survival rate of 100 %). These results demonstrated that HVEMIg could exert effective antiviral activities against HSV-2 infections in vivo as compared with other soluble forms of HSV gD receptors.

Enhanced acyclovir delivery using w/o type microemulsion: preclinical assessment of antiviral activity using murine model of zosteriform cutaneous HSV-1 infection

The present study was aimed to develop and evaluate a microemulsion-based dermal drug delivery of an antiviral agent, acyclovir. A water-in-oil microemulsion was prepared using isopropyl myristate, Tween 20, Span 20, water and dimethylsulphoxide. It was characterized for drug content, stability, globule size, pH, viscosity and ex vivo permeation through mice skin. In vivo antiviral efficacy of optimized formulation was assessed in female Balb/c mice against herpes simplex virus-I (HSV-I)-induced infection. It was observed that optimized formulation when applied 24-h post-infection could completely inhibit the development of cutaneous herpetic lesions vis-à-vis marketed cream.

Antiviral agents for herpes simplex virus

This review starts with a brief description of herpes simplex virus types 1 and 2 (HSV-1 and HSV-2), the clinical diseases they cause, and the continuing clinical need for antiviral chemotherapy. A historical overview describes the progress from the early, rather toxic antivirals to acyclovir (ACV) which led the way for its prodrug, valacyclovir, to penciclovir and its prodrug, famciclovir (FCV). These compounds have been the mainstay of HSV therapy for two decades and have established a remarkable safety record. This review focuses on these compounds, the preclinical studies which reveal potentially important differences, the clinical trials, and the clinical experience through two decades. Some possible areas for further investigation are suggested. The focus shifts to new approaches and novel compounds, in particular, the combination of ACV with hydrocortisone, known as ME609 or zovirax duo, an HSV helicase-primase inhibitor, pritelivir (AIC316), and CMX001, the cidofovir prodrug for treating resistant HSV infection in immunocompromised patients. Letermovir has established that the human cytomegalovirus terminase enzyme is a valid target and that similar compounds could be sought for HSV. We discuss the difficulties facing the progression of new compounds. In our concluding remarks, we summarize the present situation including a discussion on the reclassification of FCV from prescription-only to pharmacist-controlled for herpes labialis in New Zealand in 2010; should this be repeated more widely? We conclude that HSV research is emerging from a quiescent phase.

Prevention of the interaction between HVEM, herpes virus entry mediator, and gD, HSV envelope protein, by a Keggin polyoxotungstate, PM-19

One of the Keggin-type heteropolyoxotungstates (K7[PTi2W10O40]6H2O:PM-19) is a potent inhibitor of the replication of herpes simplex virus (HSV) both standard strain 169 and the thymidine kinase-defective strain YS-4C-1 in vitro and in vivo. HSV envelope protein, gD, is necessary for virus entry into the cells. Some cellular molecules, such as HVEM, were reported to act as cofactors during the viral entry step. We determined whether PM-19 prevents these interactions between HSV-gD and HVEM. These activities were investigated using the Ciphergen and BIACORE system. Using a protein chip, many kinds of gD-specific binding proteins were captured, but these proteins could not be identified. Several proteins in these gD-binding proteins were inhibited its interaction with gD due to the presence of PM-19. Using the BIACORE system, the affinity of PM-19 to gD was low, because PM-19 has no direct inactivation activity against the virion. The specific binding of HVEM to the gD was shown as KD of 1.1e-9. The affinity of PM-19 for HVEM was high (KD:2e-9). To determine the competitive binding, the PM-19 (10 microg/ml) and several concentrations of HVEM solution mixtures were injected over the gD-fixed sensor surface. Each binding signal was stable in the range of approximately 270-300 RU. In the case of the addition of PM-19 to HVEM solution, the binding signals were elevated by PM-19 dose dependently. These results suggest that the bindings of PM-19 to gD are not disturbed by the presence of HVEM. PM-19 prevents the interaction between HVEM and gD.

Phenotypic and genotypic characterization of clinical isolates of herpes simplex virus resistant to aciclovir

A panel of 10 clinical isolates of herpes simplex virus (HSV) deficient in the expression of thymidine kinase (TK) and phenotypically resistant to aciclovir was characterized. Sequence analysis revealed a variety of mutations in TK (nucleotide substitutions, insertions and deletions), most of which resulted in truncated TK polypeptides. In line with previous reports, the most common mutation was a single G insertion in the 'G-string' motif. One HSV-1 isolate and two HSV-2 isolates appeared to encode full-length polypeptides and, in each case, an amino acid substitution likely to be responsible for the phenotype was identified. Pathogenicity was determined using a zosteriform model of HSV infection in BALB/c mice. The majority of isolates appeared to show impaired growth at the inoculation site compared with wild-type virus. They also showed poor replication in the peripheral nervous system and little evidence of zosteriform spread. One exception was isolate 4, which had a double G insertion in the G-string but, nevertheless, exhibited zosteriform spread. These studies confirmed that TK-deficient viruses display a range of neurovirulence with respect to latency and zosteriform spread. These results are discussed in the light of previous experience with TK-deficient viruses.

Characterization of a neurovirulent aciclovir-resistant variant of herpes simplex virus

A clinical isolate of herpes simplex virus type 1 that is aciclovir resistant but neurovirulent in mice was described previously. The mutation in this virus is a double G insertion in a run of seven G residues that has been shown previously to be a mutational hotspot. Using a sensitive assay, it has been demonstrated that preparations of this virus are able to induce low but consistent levels of thymidine kinase (TK) activity. However, this activity results from a high frequency mutational event that inserts a further G into the 'G-string' motif and thus restores the TK open reading frame. Passage of this virus through the nervous system of mice results in the rapid selection of the TK-positive variant. Thus, this variant is the major component in virus reactivated from latently infected ganglia. Mutation frequency appears to be influenced by the genetic background of the virus.

Rapid phenotypic characterization method for herpes simplex virus and Varicella-Zoster virus thymidine kinases to screen for acyclovir-resistant viral infection

A rapid phenotypic screening method for herpes simplex virus (HSV) and varicella-zoster virus (VZV) thymidine kinase (TK) genes was developed for monitoring acyclovir-resistant viruses. This method determines the biochemical phenotype of the TK polypeptide, which is synthesized in vitro from viral DNA using a procedure as follows. The TK gene of each sample virus strain is amplified and isolated under the control of a T7 promoter by PCR. The PCR products are transcribed with T7 RNA polymerase and translated in a rabbit reticulocyte lysate. Using this method, enzymatic characteristics and the size of the TK polypeptides encoding HSV and VZV DNA were defined in less than 2 days without virus isolation. The assay should be a powerful tool in monitoring drug-resistant viruses, especially in cases in which virus isolation is difficult.

Pathogenicity of glycoprotein C-deficient herpes simplex virus 1 strain TN-1 which encodes truncated glycoprotein C

A clinical isolate of herpes simplex virus 1 (TN-1) from a stromal keratitis patient was found to be defective in the glycoprotein C (gC) gene (UL44), thus resulting in the production of truncated gC upon infection. To study the pathogenetic role of truncated gC, we prepared a recombinant LTN-8 derived from TN-1 with deletions of the 1.5 kilobase pairs of the gC gene including the initiation codon. A penetration assay revealed LTN-8 to be less efficient in its penetration ability than TN-1, the laboratory strain KOS and RTN-1-20-3, a recombinant derived from TN-1 with the KOS gC gene. The penetration of LTN-8 was facilitated by the addition of TN-1-infected culture medium. TN-1 virus preparations had no hemagglutinating activity. However, the animals infected with TN-1 did develop hemagglutination inhibition (HI) antibodies. The LTN-8-infected animals did not develop HI antibodies. The pathogenicity in BALB/c mice following either corneal, intraperitoneal or intracerebral inoculation did not significantly differ among TN-1, RTN-1-20-3 or LTN-8. Our results indicate that truncated gC was sufficient for the induction of HI antibodies and was also able to facilitate penetration in vitro. Although truncated gC might be a virulence factor acting as a decoy, both truncated gC and intact gC had little effect on the outcome following intracerebral, intraperitoneal or corneal inoculation.

Suppression of infectious virus spread to the liver by foscarnet following lethal infection of acyclovir-resistant herpes simplex virus type 2 in mice

Patients with the acquired immune deficiency syndrome (AIDS) occasionally develop hepatitis, pneumonia or esophagitis due to herpes simplex virus type 2 (HSV-2) infection. HSV hepatitis is a rare but serious complication in liver transplantation. Acyclovir-resistant HSV strains may emerge in immunocompromised patients. Following intraperitoneal inoculation, HSV-2 induces necrotizing hepatitis in mice. We studied the virus spread and mortality following intraperitoneal inoculation of HSV-2 RK (an acyclovir-resistant recombinant virus with altered thymidine kinase activity) as compared to its parent virus 8620K. Neither the 50% lethal dose (LD50) nor the average survival time was significantly different between the two strains. Parenteral acyclovir treatment was found to be effective against 8620K but not RK infection. Parenteral foscarnet treatment was effective against both RK and 8620K, and also inhibited the spread of either virus to the liver, spinal cord and brain. Peroral foscarnet administration was found to prevent the virus growth in the liver.

Gastrointestinal invasion by herpes simplex virus type 1 inoculated cutaneously into the immunosuppressed mice

The pathogenesis of infection in mice with herpes simplex virus type 1 (HSV-1) strain 7401H was studied. Mice immunosuppressed by intraperitoneal injection of cyclophosphamide were inoculated cutaneously into the flank with the virus and developed severe zosteriform skin lesions. All of them died within 2 weeks after the infection, while most of the normal mice survived the viral infection with healing of the lesions. In the gastrointestinal tract of the immunosuppressed mice, macroscopic abnormalities were frequently observed, and infectious viruses were detected on days 7 to 9. The viruses were also detectable in the dorsal root ganglia and the spinal cord of thoracolumbar area on days 5 to 7, and in the celiac plexus on day 7. However, no viruses were detected in the blood. Immunohistological examination of the gastrointestinal tract revealed that the viral antigens were localized in Auerbach's myenteric plexus. These results suggest that HSV-1 inoculated into the flank skin invaded the gastrointestinal tract via the nervous system, which gastrointestinal involvement might possibly have caused the death of the mice.

Molecular analysis of a neurovirulent herpes simplex virus type 2 strain with reduced thymidine kinase activity

Thymidine kinase (TK) of herpes simplex virus (HSV) has been identified as one of the factors responsible for its virulence. We have previously isolated acyclovir (ACV)-resistant HSV type 2 (HSV-2), strain YS-4 C-1, by simple plaque cloning from a clinical isolate. Although YS-4 C-1 had extremely low TK activity, it retained high virulence in mice. To determine the mechanism of the reduction of TK activity, a molecular analysis of the YS-4 C-1 TK gene was performed. YS-4 C-1 produced TK mRNA, which was indistinguishable both in size and amount from that of wild-type strains. However, the YS-4 C-1 TK had a single amino acid change from serine to asparagine at amino acid residue 182 of the TK polypeptide, which was caused by a single nucleotide mutation. It was situated within a highly conserved region (162-194) and close to the putative nucleoside-binding site (169-177), one of the three active centers of TK. In order to confirm the effect of this missense mutation on both the TK activity and neurovirulence, the mutation was introduced into the TK genes of wild-type strains. Although all the recombinants were altered to ACV-resistant viruses with reduced TK activity, they retained high neurovirulence for mice. Our study thus suggested that this mutant TK, in spite of low activity, might play a role in the neurovirulence of HSV-2.

Nucleotide sequence of the major DNA-binding protein gene of herpes simplex virus type 2 and a comparison with the type 1

The nucleotide sequence of a region encompassing about 5,200 base pairs (bp) of the left side of the origin of replication in the long unique region of the herpes simplex virus type 2 (HSV-2) has been determined. This region contained the major DNA-binding protein or the infected-cell protein 8 (ICP 8) gene and 5'-part of the counterpart of HSV-1 ICP 18.5 gene. A comparison of the nucleotide sequence of the ICP8 gene between HSV-1 and HSV-2 showed an 89.8% homology. A primer extension analysis for the HSV-2 ICP 8 mRNA showed that the major transcriptional start site was mapped at 315 bp upstream of the initiation codon. A comparison of the predicted functional amino acid sequence of the ICP 8 between HSV-1 and HSV-2 revealed a striking homology (97.2%), the value of which was the highest among those of the other polypeptides encoded by HSV-1 and HSV-2. Some domains, which were shown to be required for the nuclear function, the binding to single-stranded DNA and the nuclear localization were well conserved. In addition, the nucleotide and the functional amino acid sequences of a part of the HSV-2 counterpart of the HSV-1 ICP 18.5 gene were also compared, demonstrating an 88.4% and 95.9% homology, respectively.

Latent infection of SCID mice with herpes simplex virus 1 and lethal cutaneous lesions in pregnancy

Some SCID mice survived primary infection with herpes simplex virus 1 without the development of peripheral lesions but established coculture-positive ganglionic latency when a low dose of a wild-type strain was inoculated intracutaneously. The latency was also evidenced by the development of the fatal zosteriform skin lesions and the isolation of the virus during pregnancy. We consider that the viral entry into neurons without successive replication, rather than the arrest of the lytic infection within the cells, is an important mechanism in the establishment of latency.

Variants selected by treatment of human immunodeficiency virus-infected cells with an immunotoxin

An immunotoxin has been made by coupling anti-human immunodeficiency virus (HIV) envelope antibody 907 to ricin A chain (907-RAC). 907 recognizes an epitope within the immunodominant PB-1 loop of gp120. Variant cells were selected by cloning persistently infected H9/human T lymphocyte virus IIIB cells in the presence of the immunotoxin. Clones resistant to 907-RAC arose at a frequency of 0.1-1.0%. Seven clones were selected for intensive analysis. When studied, these clones fell into two distinct groups, members of which appeared to be identical, suggesting that the variation arose before the selection process. In contrast to the parent cells, none of the cloned variants produced infectious HIV. The first set of clones, designated the "E" variants, expressed decreased levels of the HIV envelope on the cell surface. However, levels of intracellular HIV antigens and reverse transcriptase were equal to or greater than that of the parental cell line. Radioimmunoprecipitation demonstrated that the gp160 was truncated to 145 kD (gp120 was normal length), capable of binding to CD4, and, unlike normal gp160, was released in its unprocessed form into the cellular supernatant. Sequence analysis demonstrated that a deletion at codon 687 of the envelope gene resulted in the production of this truncated protein. Ultrastructural analysis of E variants demonstrated some budding forms of virus, but also large numbers of HIV within intracellular vesicles. The second set of variants, the "F" series, produced no HIV antigens, reverse transcriptase, nor was there ultrastructural evidence of virus. However, proviral DNA was present. Virus could not be induced with agents known to activate latent HIV. These cells also lacked cell surface CD4 and could not be infected with HIV. These studies demonstrate that variation in HIV can affect the phenotype of the cells carrying the altered virus, allowing for escape from immunologic destruction. The E variants may serve as prototypes for attenuated HIV, which could be used as a vaccine. We have reconstructed the mutation found in the E variants within the infectious HIV clone HXB-2 and demonstrated that the resulting virus retains its noninfectious phenotype.

Characterization of glycoprotein C-negative mutants of herpes simplex virus type 1 isolated from a patient with keratitis

Recently three strains of herpes simplex virus type 1 (HSV-1), which did not react with Micro Trak Herpes (Syva Co.), were isolated by us from a patient with recurrent herpetic keratitis. In this study we characterized these strains of HSV-1 and found them to be HSV-1 gC- mutants which are very rare isolates from humans. The properties of the HSV-1 strains regarding plaque morphology on Vero cells and chick embryo fibroblasts and viral DNA analysis were the same as those of the usual HSV-1 strains. An immunofluorescence study using anti-gC-1 monoclonal antibody and SDS-PAGE analysis of radiolabeled viral glycoproteins showed that these strains are deficient in gC-1. They were virulent for mice and sensitive to acyclovir and bromovinyldeoxyuridine. Furthermore the infectivity of the strains was inactivated by complement though the phenomenon was not observed in the usual HSV-1 strains. This finding suggests that protection from damages by complement is an important function of gC. In keratitis the effects of complement are thought to be minimal because of the scanty blood supply and this may be the reason why these strains were isolated from the cornea.