Inhibition Of Herpes Simplex Virus Replication Research Articles

Therapeutic Nucleic Acids against Herpes Simplex Viruses

The Herpes simplex virus (HSV) causes a wide range of diseases, ranging from relatively mild primary skin lesions to severe and often fatal episodes of encephalitis. Currently, the most effective drugs for HSV-infected people are nucleoside analogs (e.g., acyclovir) targeting enzymes encoded by viral DNA. The effectiveness of nucleoside analogs is reduced because of poor solubility in water, rapid intracellular catabolism, high cellular toxicity, and the appearance of resistant viral strains. Antisense technology that exploits nucleic acid fragments (NA-based agents) is a promising alternative to antiviral therapy due to the high affinity of these agents to target nucleic acids, their high solubility in water, and lower cellular toxicity. In the last decade, antisense oligonucleotides have been investigated as potential drugs for various diseases associated with “harmful” nucleic acids. Oligonucleotides with different chemical modifications targeted at specific regions of the HSV genome have shown effectiveness in suppressing the virus. siRNA-based agents have demonstrated prolonged and effective (up to 99%) inhibition of HSV replication. Based on the publications reviewed in the review over the past 30 years, it can be concluded about the prospects of using NA-based agents to combat herpes viral infections.

The Exonuclease Activity of Herpes Simplex Virus 1 UL12 Is Required for Production of Viral DNA That Can Be Packaged To Produce Infectious Virus.

The herpes simplex virus (HSV) type I alkaline nuclease, UL12, has 5'-to-3' exonuclease activity and shares homology with nucleases from other members of the Herpesviridae family. We previously reported that a UL12-null virus exhibits a severe defect in viral growth. To determine whether the growth defect was a result of loss of nuclease activity or another function of UL12, we introduced an exonuclease-inactivating mutation into the viral genome. The recombinant virus, UL12 D340E (the D340E mutant), behaved identically to the null virus (AN-1) in virus yield experiments, exhibiting a 4-log decrease in the production of infectious virus. Furthermore, both viruses were severely defective in cell-to-cell spread and produced fewer DNA-containing capsids and more empty capsids than wild-type virus. In addition, DNA packaged by the viral mutants was aberrant, as determined by infectivity assays and pulsed-field gel electrophoresis. We conclude that UL12 exonuclease activity is essential for the production of viral DNA that can be packaged to produce infectious virus. This conclusion was bolstered by experiments showing that a series of natural and synthetic α-hydroxytropolones recently reported to inhibit HSV replication also inhibit the nuclease activity of UL12. Taken together, our results demonstrate that the exonuclease activity of UL12 is essential for the production of infectious virus and may be considered a target for development of antiviral agents.IMPORTANCE Herpes simplex virus is a major pathogen, and although nucleoside analogs such as acyclovir are highly effective in controlling HSV-1 or -2 infections in immunocompetent individuals, their use in immunocompromised patients is complicated by the development of resistance. Identification of additional proteins essential for viral replication is necessary to develop improved therapies. In this communication, we confirm that the exonuclease activity of UL12 is essential for viral replication through the analysis of a nuclease-deficient viral mutant. We demonstrate that the exonuclease activity of UL12 is essential for the production of viral progeny and thus provides an attractive, druggable enzymatic target.

Inhibition of clinical pathogenic herpes simplex virus 1 strains with enzymatically created siRNA pools.

Herpes simplex virus (HSV) is a common human pathogen causing severe diseases such as encephalitis, keratitis, and neonatal herpes. There is no vaccine against HSV and the current antiviral chemotherapy fails to treat certain forms of the disease. Here, we evaluated the antiviral activity of enzymatically created small interfering (si)RNA pools against various pathogenic HSV strains as potential candidates for antiviral therapies. Pools of siRNA targeting 0.5-0.8 kbp of essential HSV genes UL54, UL29, or UL27 were enzymatically synthesized. Efficacy of inhibition of each siRNA pool was evaluated against multiple clinical isolates and laboratory wild type HSV-1 strains using three cell lines representing host tissues that support HSV-1 replication: epithelial, ocular, and cells that originated from the nervous system. The siRNA pools targeting UL54, UL29, and UL27, as well as their equimolar mixture, inhibited HSV replication, with the pool targeting UL29 having the most prominent antiviral effect. In contrast, the non-specific control siRNA pool did not have such an effect. Moreover, the UL29 pool elicited only a minimal innate immune response in the HSV-infected cells, thus evidencing the safety of its potential clinical use. These results are promising for the development of a topical RNA interference approach for clinical treatment of HSV infection. J. Med. Virol. 88:2196-2205, 2016. © 2016 Wiley Periodicals, Inc.

Upstream binding factor inhibits herpes simplex virus replication

Herpes simplex virus 1 (HSV-1) infection induces changes to the host cell nucleus including relocalization of the cellular protein Upstream Binding Factor (UBF) from the nucleolus to viral replication compartments (VRCs). Herein, we tested the hypothesis that UBF is recruited to VRCs to promote viral DNA replication. Surprisingly, infection of UBF-depleted HeLa cells with HSV-1 or HSV-2 produced higher viral titers compared to controls. Reduced expression of UBF also led to a progressive increase in the relative amount of HSV-1 DNA versus controls, and increased levels of HSV-1 ICP27 and TK mRNA and protein, regardless of whether viral DNA replication was inhibited or not. Our results suggest that UBF can inhibit gene expression from viral DNA prior to its replication. A similar but smaller effect on viral titers was observed in human foreskin fibroblasts. This is the first report of UBF having a restrictive effect on replication of a virus.

HIV integrase inhibitors block replication of alpha-, beta-, and gammaherpesviruses.

ABSTRACTThe catalytic site of the HIV integrase is contained within an RNase H-like fold, and numerous drugs have been developed that bind to this site and inhibit its activity. Herpes simplex virus (HSV) encodes two proteins with potential RNase H-like folds, the infected cell protein 8 (ICP8) DNA-binding protein, which is necessary for viral DNA replication and exhibits recombinase activity in vitro, and the viral terminase, which is essential for viral DNA cleavage and packaging. Therefore, we hypothesized that HIV integrase inhibitors might also inhibit HSV replication by targeting ICP8 and/or the terminase. To test this, we evaluated the effect of 118-D-24, a potent HIV integrase inhibitor, on HSV replication. We found that 118-D-24 inhibited HSV-1 replication in cell culture at submillimolar concentrations. To identify more potent inhibitors of HSV replication, we screened a panel of integrase inhibitors, and one compound with greater anti-HSV-1 activity, XZ45, was chosen for further analysis. XZ45 significantly inhibited HSV-1 and HSV-2 replication in different cell types, with 50% inhibitory concentrations that were approximately 1 µM, but exhibited low cytotoxicity, with a 50% cytotoxic concentration greater than 500 µM. XZ45 blocked HSV viral DNA replication and late gene expression. XZ45 also inhibited viral recombination in infected cells and ICP8 recombinase activity in vitro. Furthermore, XZ45 inhibited human cytomegalovirus replication and induction of Kaposi’s sarcoma herpesvirus from latent infection. Our results argue that inhibitors of enzymes with RNase H-like folds may represent a general antiviral strategy, which is useful not only against HIV but also against herpesviruses.

Zinc ionophores pyrithione inhibits herpes simplex virus replication through interfering with proteasome function and NF-κB activation

Pyrithione (PT), known as a zinc ionophore, is effective against several pathogens from the Streptococcus and Staphylococcus genera. The antiviral activity of PT was also reported against a number of RNA viruses. In this paper, we showed that PT could effectively inhibit herpes simplex virus types 1 and 2 (HSV-1 and HSV-2). PT inhibited HSV late gene (Glycoprotein D, gD) expression and the production of viral progeny, and this action was dependent on Zn2+. Further studies showed that PT suppressed the expression of HSV immediate early (IE) gene, the infected cell polypeptide 4 (ICP4), but had less effect on another regulatory IE protein, ICP0. It was found that PT treatment could interfere with cellular ubiquitin-proteasome system (UPS), leading to the inhibition of HSV-2-induced IκB-α degradation to inhibit NF-κB activation and enhanced promyelocytic leukemia protein (PML) stability in nucleus. However, PT did not show direct inhibition of 26S proteasome activity. Instead, it induced Zn2+ influx, which facilitated the dysregulation of UPS and the accumulation of intracellular ubiquitin-conjugates. UPS inhibition by PT caused disruption of IκB-α degradation and NF-κB activation thus leading to marked reduction of viral titer.

Inhibitory effect and structure–activity relationship of some Biginelli-type pyrimidines against HSV-1

Inevitable emergence of multi-drug resistant strains to current available drugs makes an impetus for finding new therapeutic agents against herpes simplex virus (HSV). In this study, a series of novel derivatives of Biginelli-type pyrimidines were evaluated as potential anti-HSV-1 compounds by plaque reduction method. The cellular toxicity was assessed by XTT proliferation assay. The time course of anti-HSV activity of the most active compound was studied to show the anti-viral effect in various intervals of replication cycle. Compounds 2, 6, 8, 11, 12, 17, 18, 20, and 40 had the highest activity for inhibition of HSV. Compound 40 inhibited HSV replication with IC50 of 0.9 μmol/l and had CC50 of up to 100 μmol/l. This compound was a noteworthy inhibitor against HSV with TI value of 111. Compound 20 also showed considerable inhibitory activity with IC50 of 1.8 μmol/l. Result of time-of-addition study showed that compound 40 inhibits HSV replication at a stage after entry of virions to the target cells. Analysis of structure of the studied compounds demonstrated clear relationships with their anti-HSV effects. Some of the compounds seem to be promising candidates for future anti-HSV drug discovery researches. Structural manipulation based on the obtained structure–activity relationships would propose some new leads for anti-HSV drug discovery programs.

New Acridone Inhibitors of Human Herpes Virus Replication

Modern biomedicinal research with acridones began with plant secondary metabolites but the successful development of these alkaloids into drugs has yet to be realized. However, there are synthetic acridones unrelated to the natural products now emerging as promising bioactive compounds. The purpose of this mini-review is to highlight the renewed interest in acridones for antiviral drug research, with the emphasis placed on several derivatives in early stage development for treating herpes virus infection. Novel anti-herpes acridones developed using a ligand-based approach have much simpler structure and generally have higher selectivity than the corresponding alkaloids. Three sub-types are currently classified on the basis of activity against Herpes Simplex Virus (HSV) and, or Human Cytomegalovirus (HCMV) and all of them inhibit viral replication post-adsorption. In terms of mode/mechanism of action, this "second wave" of early generation lead molecules appears unique in comparison to the natural products and to drugs derived from more traditional templates. Inhibition of HSV replication by these agents is best understood and it occurs after viral DNA synthesis. The mechanism for one prototype inhibitor (5-chloro-1,3-dihydroxy acridone), involves a blockade of viral DNA maturation (cleavage/packaging) and viral capsids accumulate abnormally. Interestingly, the 7-Chloro regioisomer blocks a later stage of viral assembly. At this time it is unclear whether atypical target-interaction or unusual polypharmacology is responsible for the antiviral activities observed and this key issue will hamper future drug development until it is resolved.

Robust expression of TNF-alpha, IL-1beta, RANTES, and IP-10 by human microglial cells during nonproductive infection with herpes simplex virus.

Cytokine (TNF-alpha/beta, IL-1beta, IL-6, IL-18, IL-10, and IFN-alpha/beta/gamma) and chemokine (IL-8, IP-10, MCP-1, MIP-1alpha/beta, and RANTES) production during herpes simplex virus (HSV) 1 infection of human brain cells was examined. Primary astrocytes as well as neurons were found to support HSV replication, but neither of these fully permissive cell types produced cytokines or chemokines in response to HSV. In contrast, microglia did not support extensive viral replication; however, ICP4 was detected by immunochemical staining, demonstrating these cells were infected. Late viral protein (nucleocapsid antigen) was detected in <10% of infected microglial cells. Microglia responded to nonpermissive viral infection by producing considerable amounts of TNF-alpha, IL-1beta, IP-10, and RANTES, together with smaller amounts of IL-6, IL-8, and MIP-1alpha as detected by RPA and ELISA. Surprisingly, no interferons (alpha, beta, or gamma) were detected in response to viral infection. Pretreatment of fully permissive astrocytes with TNF-alpha prior to infection with HSV was found to dramatically inhibit replication, resulting in a 14-fold reduction of viral titer. In contrast, pretreatment of astrocytes with IL-1beta had little effect on viral replication. When added to neuronal cultures, exogenous TNF-alpha or IL-1beta did not suppress subsequent HSV replication. Exogenously added IP-10 inhibited HSV replication in neurons (with a 32-fold reduction in viral titer), however, similar IP-10 treatment did not affect viral replication in astrocytes. These results suggest that IP-10 possesses direct antiviral activity in neurons and support a role for microglia in both antiviral defense of the brain as well as amplification of immune responses during neuroinflammation.

Roscovitine, a specific inhibitor of cellular cyclin-dependent kinases, inhibits herpes simplex virus DNA synthesis in the presence of viral early proteins.

We have previously shown that two inhibitors specific for cellular cyclin-dependent kinases (cdks), Roscovitine (Rosco) and Olomoucine (Olo), block the replication of herpes simplex virus (HSV). Based on these results, we demonstrated that HSV replication requires cellular cdks that are sensitive to these drugs (L. M. Schang, J. Phillips, and P. A. Schaffer. J. Virol. 72:5626-5637, 1998). We further established that at least two distinct steps in the viral replication cycle require cdks: transcription of immediate-early (IE) genes and transcription of early (E) genes (L. M. Schang, A. Rosenberg, and P. A. Schaffer, J. Virol. 73:2161-2172, 1999). Since Rosco inhibits HSV replication efficiently even when added to infected cells at 6 h postinfection, we postulated that cdks may also be required for viral functions that occur after E gene expression. In the study presented herein, we tested this hypothesis directly by measuring the efficiency of viral replication, viral DNA synthesis, and expression of several viral genes during infections in which Rosco was added after E proteins had already been synthesized. Rosco inhibited HSV replication, and specifically viral DNA synthesis, when the drug was added at the time of release from a 12-h phosphonoacetic acid (PAA)-induced block in viral DNA synthesis. Inhibition of DNA synthesis was not a consequence of inhibition of expression of IE or E genes in that Rosco had no effect on steady-state levels of two E transcripts under the same conditions in which it inhibited viral DNA synthesis. Moreover, viral DNA synthesis was inhibited by Rosco even in the absence of protein synthesis. In a second series of experiments, the replication of four HSV mutants harboring temperature-sensitive mutations in genes essential for viral DNA replication was inhibited when Rosco was added at the time of shift-down from the nonpermissive to the permissive temperature. Viral DNA synthesis was inhibited by Rosco under these conditions, whereas expression of viral E genes was not affected. We conclude that cellular Rosco-sensitive cdks are required for replication of viral DNA in the presence of viral E proteins. This requirement may indicate that HSV DNA synthesis is functionally linked to transcription, which requires cdks, or that both viral transcription and DNA replication, independently, require viral or cellular factors activated by Rosco-sensitive cdks.

Transcription of herpes simplex virus immediate-early and early genes is inhibited by roscovitine, an inhibitor specific for cellular cyclin-dependent kinases.

Although herpes simplex virus (HSV) replicates in noncycling as well as cycling cells, including terminally differentiated neurons, it has recently been shown that viral replication requires the activities of cellular cyclin-dependent kinases (cdks) (L. M. Schang, J. Phillips, and P. A. Schaffer, J. Virol. 72:5626-5637, 1998). Since we were unable to isolate HSV mutants resistant to two cdk inhibitors, Olomoucine and Roscovitine (Rosco), we hypothesized that cdks may be required for more than one viral function during HSV replication. In the experiments presented here, we tested this hypothesis by measuring the efficiency of (i) viral replication; (ii) expression of selected immediate-early (IE) (ICP0 and ICP4), early (E) (ICP8 and TK), and late (L) (gC) genes; and (iii) viral DNA synthesis in infected cultures to which Rosco was added after IE or IE and E proteins had already been synthesized. Rosco inhibited HSV replication, transcription of IE and E genes, and viral DNA synthesis when added at 1, 2, or 6 h postinfection or after release from a 6-h cycloheximide block. Transcription of a representative L gene, gC, was also inhibited by Rosco under all conditions examined. We conclude from these studies that cellular cdks are required for transcription of E as well as IE genes. In contrast, steady-state levels of at least one cellular housekeeping gene were not affected by Rosco. The requirement of viral IE and E transcription for cellular cdks may reflect either a requirement for specific cdk-activated cellular and/or viral transcription factors or a more global requirement for cdks in the transcriptional activation of the viral genome.

Herpes Simplex Virus Latency after Direct Ganglion Virus Inoculation

Herpes simplex virus (HSV) latent infection of ganglion neurons follows axoplasmic transport of HSV, probably in the form of nucleocapsid from peripheral sites of infection (e.g. footpad). This raises the possibility that latency is dependent on this particular means of presenting HSV to ganglion neurons. To investigate this, we directly infected ganglia of mice with HSV and evaluated latency. Initially, ganglia were surgically exposed in intact mice, infected with HSV and after 4 weeks evaluated for HSV latency-associated transcript (LAT) expression. LAT expression suggested latency. To more fully evaluate latency after direct ganglion inoculation, a transplant model was developed. In this model, ganglia were removed from mice, inoculated with HSV, transplanted into syngeneic recipients and evaluated for latency after several weeks. Latency was evident in transplanted ganglia by (1) the presence of LAT in neurons; (2) the lack of HSV ICP4 RNA or viral antigen, and (3) the isolation of HSV from explants of transplants but not from direct homogenates. The transplant model was then used to evaluate the effect of inhibition of HSV replication on latency. Antivirals which inhibited HSV replication markedly decreased the number of LAT-positive neurons in transplants, suggesting a role for HSV replication mechanisms and latency. It is thought that direct ganglion inoculation and ganglion transplant methods will permit unique investigations of mechanisms of latency.

Transinhibition of herpes simplex virus replication by an inducible cell-resident gene encoding a dysfunctional VP19c capsid protein

This study demonstrates that cells expressing a dysfunctional analog of a herpes simplex virus (HSV) capsid protein inhibits HSV replication. Vero cell lines expressing HSV-1 capsid protein VP19c/β-galactosidase fusion proteins were constructed and tested for their kinetics of expression, intracellular location, and ability to interfere with HSV replication. Two chimeric genes were constructed for these studies. The larger chimeric gene encodes the amino terminal 327 amino acids (aa) of VP19c fused to the carboxy terminal 1026 aa of β-galactosidase, and the shorter chimeric gene encodes VP19c aa 1–30 and 302–327 fused to the carboxy-terminal 1026 aa of β-galactosidase. Cell lines V32G-1 and V32G-2 containing the larger and the shorter chimeric genes, respectively, were isolated after cotransfection with plasmid pSV2-neo DNA, cell selection, and limiting-dilution cloning. The chimeric VP19c/β-galactosidase genes resident in V32G-1 and V32G-2 cell lines were induced by early gene products of superinfecting wild-type HSV-1 and HSV-2, but were not constitutively expressed. The hybrid proteins expressed in infected V32G-1 and V32G-2 cells both colocalized with infected cell protein 8 (ICP8) into virus-replicative compartments in the cell nuclei. HSV-1 and HSV-2 growth in V32G-1 cells (which express the larger chimeric gene) was significantly reduced compared to growth in V32G-2 and control Vero cells. The data suggest that the larger VP19c/β-galactosidase hybrid protein interferes with virus capsid assembly or morphogenesis in a competitive manner. Results also demonstrate that a small portion of VP19c containing the predicted endoplasmic reticulum signal sequence for this capsid protein (aa 1–30) promotes incorporation of the VP19c/β-galactosidase fusion proteins into nuclear viral replication compartments.

Treatment of oro-facial herpes simplex infections with acyclovir: A review

The treatment of herpes simplex virus (HSV) infections in the past has been largely unsuccessful. Introduction of the drug acyclovir has been a positive development. Acyclovir has been extensively studied in the treatment of a variety of HSV infections in immunocompromised patients and in otherwise healthy patients. The results have shown it to effectively inhibit HSV replication but to have no effect in preventing or eliminating the latent state of the virus. It has been shown to be very effective in certain instance and not so effective in others.

Inhibition of herpes simplex virus replication by anthracycline compounds

The replication of type 1 and type 2 strains of herpes simplex virus (HSV) was inhibited >99.9% by low concentrations (0.1-0.2 μM) of anthracycline compounds. The degree of viral inhibition was dependent upon the host cell. N,N-dimethyl daunomycin (NDMD), a non-mutagenic compound, was more potent as an inhibitor of HSV synthesis than either daunomycin (DM) or adriamycin (AD). The depression of viral yield by DM or AD was attributable, in part, to a temperature-dependent direct effect on infectious virions. Tritium-labeled DM bound tightly to HSV particles. NDMD did not directly inactivate virions in spite of superior potency in reducing viral yields. All three anthracyclines could be added late in the infectious cycle (6–8 h p.i.) and retain effectiveness. Cesium chloride density gradient analysis verified that viral DNA synthesis was blocked by addition of all three anthracyclines early in the infectious cycle. The inhibition of HSV replication was not a simple consequence of the suppression of host DNA synthesis since treatment of cells with compounds for 24 h before infection did not reduce virus yields even though host DNA synthesis was inhibited by 90%. Further, the kinetics of inhibition of cellular DNA synthesis by anthracyclines was similar in HFF or Vero cells but the degree of inhibition of virus replication was markedly different. The data suggest that anthracyclines with substitutions on the sugar moiety may be useful anti-herpes agents.

Impaired neonatal natural killer-cell activity to herpes simplex virus: decreased inhibition of viral replication and altered response to lymphokines.

Human adult natural killer (NK) cells were recently demonstrated to inhibit herpes simplex virus (HSV) replication in vitro. In this study we compared the ability of newborn and adult NK cells to inhibit HSV replication. Cord blood mononuclear cells (MNCs) from healthy, term newborns and MNCs from adults were analyzed for their percentage of Leu-11+ cells and compared in vitro for their NK-cell activity against HSV-infected fibroblasts and the tumor cell line K562. Cord blood MNCs, compared with adult MNCs, had significantly lower percentages of Leu-11+ cells (5 vs 11%; P less than 0.01), less anti-K562 NK activity (6 vs 54 lytic units/10(7) cells; P less than 0.001), and less anti-HSV NK activity (5 vs 52% HSV plaque inhibition; P less than 0.02). Comparing individual neonates and adults with equal percentages of Leu-11+ cells, neonatal MNCs still had less NK activity against either target. When Leu-11+ MNCs were isolated using the fluorescence-activated cell sorter, neonatal Leu-11+ MNCs still inhibited HSV replication less than adult Leu-11+ MNCs (P less than 0.01). MNCs from some neonates had significant anti-K562 NK activity but poor anti-HSV NK activity, suggesting either nonidentical NK-cell subpopulations or specific suppression. Whereas neonatal NK activity against K562 was always augmented by prior exposure to either interferon (IFN) or interleukin-2 (IL-2), the neonatal NK activity against HSV-infected cells was only augmented for half of the neonates tested. Endogenous production of alpha-IFN and gamma-IFN by MNCs exposed to HSV-infected fibroblasts was the same for cells from neonates or from HSV-seronegative adults.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of Replication of Herpes Simplex Virus in Mouse Macrophages by Interferons

The replication of herpes simplex virus (HSV) type 1 in macrophages grown from spleen cells of mouse strains susceptible to HSV infection in vivo was very sensitive to interferon (IFN). Different types of mouse IFN (alpha, beta, gamma) exhibited similar antiviral activities. However, treatment of cells with IFN-gamma in combination with IFN-alpha or IFN-beta resulted in a synergistic inhibition of virus growth. As shown by assaying HSV DNA polymerase, IFN inhibited expression of the beta-genes. Inhibition of enzyme induction correlated well with the reduction of viral yield. Induction of HSV DNA polymerase was delayed by IFN in a dose-dependent manner. These results show that IFN inhibits HSV replication at an early step prior to or during the synthesis of beta-proteins.

Synthesis of herpes simplex virus proteins in interferon-treated human cells.

Pretreatment of HeLa cells with human interferon (IFN) resulted in the inhibition of herpes simplex virus (HSV) replication. We examined the stages in the replication of HSV type 1 and type 2 that were affected by IFN. The rate of synthesis of the HSV immediate-early (alpha) proteins was inhibited in IFN-pretreated HeLa cells. The subsequent inductions of HSV early (beta) genes, determined by measuring the levels of cytoplasmic mRNA specific for the thymidine kinase, as well as the DNA polymerase enzyme activity, were also suppressed in the IFN-pretreated cells. These results indicate that IFN inhibits HSV replication primarily at a very early step, either prior to, or during the synthesis of alpha-proteins.

Anti-herpesvirus activity of the acyclic nucleoside 9-(1,3-dihydroxy-2-propoxymethyl)guanine.

The antiherpetic effects of a novel purine acyclic nucleoside, 9-(1,3-dihydroxy-2-propoxymethyl)guanine (DHPG), were compared with those of acyclovir in cell cultures and in mice. The modes of action of DHPG and acyclovir were similar in that herpes thymidine kinase phosphorylated each compound, and both agents selectively inhibited viral over host cell DNA synthesis. In 50% plaque reduction assays in Vero cells, the drugs inhibited herpes simplex virus types 1 and 2 thymidine kinase-positive strains at 0.2 to 2.4 microM. DHPG was markedly more active than acyclovir against human cytomegalovirus (50% inhibitory doses were 7 and 95 microM, respectively). Each nucleoside inhibited uninfected cell macromolecule synthesis and cell proliferation at concentrations far above those required to inhibit herpes simplex virus replication. Although the two compounds had many similarities in their behavior in vitro, the important difference was the superior performance of DHPG against herpesvirus-induced encephalitis and vaginitis in vivo. Thus, mortality in mice infected with herpesvirus type 2 was reduced 50% by daily doses of 7 to 10 mg of DHPG/kg, whereas an equally effective daily dose of acyclovir was approximately 500 mg/kg. DHPG at a daily dose of 50 mg/kg was also superior to acyclovir at 100 mg/kg per day in its inhibition of herpetic vaginal lesions in mice.

In vitro acquisition of resistance against herpes simplex virus by permissive murine macrophages

This study has documented that peritoneal macrophages (PM) from adult mice of strains DBA/2J, BALB/c and AKR can support productive replication of herpes simplex virus (HSV) strains Thea and Haase. Simian virus 40 transformed PM of C57 BL/6J origin yielded high titers of Thea and Haase, whereas normal PM from adult mice of the same genetic background were infected abortively. The evidence obtained suggested that multiplication of PM per se is insufficient to allow HSV replication. PM from DBA/2J mice, immune to HSV or Listeria monocytogenes lacked the capacity to support productive replication of HSV. PM from nonimmune, adult DBA/2J or suckling C57BL/6J mice acquired the potential to effectively restrict HSV replication when preincubated for 24 hours with 72 hours old MLC supernatant. These macrophages could also inhibit HSV replication if pretreated with supernatant from cultures of specific antigen stimulated, HSV or Listeria immune spleen lymphocytes (SL). Likewise, supernatant from concanavalin A stimulated SL also possessed the capacity to confer resistance against HSV replication in otherwise permissive PM. Sensitized T cells proved to be essential for the generation of active supernatants. Active supernatants had the potential to confer resistance against HSV replication within mouse but not chick or hamster embryo cells. The other characteristics of the soluble mediator included: instability at pH 2, inactivation by trypsin but not by DNase or RNase and persistence of activity when exposed to 56° C for 20 minutes.