Comparison of the therapeutic effects of five antiviral agents on cutaneous herpesvirus infection in guinea pigs

Antiviral activity of arbidol hydrochloride against herpes simplex virus I in vitro and in vivo

Herpes simplex virus type 1 (HSV-1) causes significant human diseases ranging from skin lesions to encephalitis, especially in neonates and immunocompromised hosts. The discovery of novel anti-HSV-1 drugs with low toxicity is required for public health. Arbidol hydrochloride (ARB) is an indole derivative molecule with broad-spectrum antiviral activity. In this study, the antiviral effects of ARB against HSV-1 infection were evaluated in vitro and in vivo. The results showed that ARB presents significant inhibitory effect on HSV-1 plaque formation and generation of progeny virus, with EC50 values (50% effective concentration) of 5.39 µg/mL (10.49 µM) and 2.26 µg/mL (4.40 µM), respectively. Moreover, time-of-addition and time-of-removal assays further suggested that ARB has viral inhibitory effects when added up to 12 h post-infection (p.i.), which could be further corroborated by determining the expression of viral immediate-early (ICP4, ICP22 and ICP27), early (ICP8 and UL42) and late (gB, gD, gH, VP1/2 and VP16) genes by real-time quantitative PCR as well as the expression of viral protein ICP4 and ICP8 at 6 h and 12 h p.i. Results of the in vivo study showed that ARB could reduce guinea pig skin lesions caused by HSV-1 infection. Conclusively, this report offers new perspectives in the search for therapeutic measures in the treatment of HSV-1 infection.

ME-609: A Treatment for Recurrent Herpes Simplex Virus Infections

Studies in conventional murine models of HSV infection use immunologically naive animals. These models thus mimic primary infections rather than recurrent infections in humans. We have, therefore, used a newly developed mouse model that more closely mimics recurrent HSV infection in humans. In this model, the mice are infected, and zosteriform HSV-1 infection develops in the presence of a primed immune response using adoptive transfer of immunity (ATI) as we have described previously. Using the ATI mouse model, it has been shown that a more beneficial therapy for recurrent mucocutaneous HSV infection could be achieved by controlling both the viral replication and the inflammatory response to the virus. Topical treatment was initiated in this model at the time of first occurrence of symptoms and was given three times daily for 4 days. Topical treatment with ME-609 (which contains 5% acyclovir and 1% hydrocortisone) in the ATI mouse model was substantially more efficacious than 5% Zovirax® cream, 1% hydrocortisone or no treatment, respectively. The beneficial properties of ME-609 were also found to be superior to those of Zovirax cream when tested in the standard guinea pig model, representing a primary HSV infection. ME-609 represents a novel treatment principle of recurrent HSV infections and the present paper summarizes the preclinical and early clinical experience of ME-609.

Immunization with a dominant-negative recombinant HSV type 1 protects against HSV-1 skin disease in guinea pigs

CJ9-gD belongs to a new class of replication-defective recombinant herpes simplex viruses (HSVs) type 1 that can function in trans to prevent the replication of wild-type HSV in co-infected cells. Furthermore, CJ9-gD cannot establish latent infection in vivo and it expresses high levels of the major HSV-1 antigen glycoprotein D immediately following infection. In this study we show that guinea pigs immunized with CJ9-gD developed at least 9,600-fold higher titers of HSV-1-specific neutralization antibodies than mock-immunized controls. After challenge with wild-type HSV-1, all 10 mock-immunized guinea pigs developed multiple skin lesions with an average of 53.3 lesions per animal, whereas only 2 minor lesions were found in 1 of 10 CJ9-gD-immunized animals, representing a 267-fold reduction on the incidence of primary herpetic skin lesions in immunized animals. Quantitative PCR analysis revealed that the amount and frequency of wild-type HSV-1 viral DNA present in dorsal root ganglia of immunized animals was significantly lower than that in mock-immunized controls. Collectively, we demonstrate that vaccination with CJ9-gD elicits strong and protective immune responses against primary HSV-1 skin disease and reduces the extent of latent infection by challenge virus.

Phosphonoformate (foscarnet, PFA) versus trifluorthymidine in the treatment of keratitis dendritica in the human. A double-blind, randomized, preliminary trial

Twenty patients with dendritic keratitis were treated in a double-blind analysis study with either phosphonoformate 3% or trifluorthymidine 1% drops. Nineteen cases were virologically confirmed. Follow-up was performed until closure of the corneal lesion was registered and a pair comparison between both substances was made. Healing time was longer for phosphonoformate (7.16 days) than for trifluorthymidine (5.83 days). There was no significant difference between phosphonoformate and trifluorthymidine. One drug failure was registered in each series. No side effects were observed.

Herpes simplex virus type 1 ribonucleotide reductase null mutants induce lesions in guinea pigs

Two herpes simplex virus type 1 ribonucleotide reductase null mutants, hrR3 and ICP6 delta, produced cutaneous lesions in guinea pigs as severe as those of wild-type strains. The lesions induced by hrR3 resulted from in vivo replication of the mutant virus, suggesting that this virus-encoded enzyme is nonessential for virus replication in guinea pigs.

Animal models for antiviral chemotherapy

Traditionally animal models have formed a vital part of the preclinical evaluation of new forms of antiviral therapy. A variety of models used in the past or potentially useful in the future are considered in this short review. Several valuable and complex questions concerning virus-drug interactions in vivo have been successfully addressed by means of animal models. Better understanding of drug modes of action and virus pathogenesis in the models enable even more accurate predictions to be made for the outcome of antiviral therapy in man. The complexity of virus infections in man is such that animals are likely to remain an important part in drug evaluation for many years. To this end, new developments such as improved techniques in the production of transgenic animals are opening up a variety of completely novel methods for studying inhibitors of a wider group of viruses in vivo including the human immunodeficiency virus. However, the correct interpretation of animal data requires the critical evaluation of animal models. This review will identify several important difficulties which confront those working on antiviral chemotherapy in animals and which must continue to be addressed if confidence in animal data is to be maintained.

Topical delivery of liposomally encapsulated interferon evaluated in a cutaneous herpes guinea pig model

The topical delivery of liposomally encapsulated interferon was evaluated in the cutaneous herpes simplex virus guinea pig model. Application of liposomally entrapped interferon caused a reduction of lesion scores, whereas application of interferon formulated as a solution or as an emulsion was ineffective. The method of liposomal preparation rather than the lipid composition of the bilayers appeared to be the most important factor for reducing lesion scores. Only liposomes prepared by the dehydration-rehydration method were effective. This finding implied that the dehydration and subsequent rehydration of the liposomes facilitate partitioning of the interferon into liposomal bilayers, where the drug is positioned for transfer into the lipid compartment of the stratum corneum. Liposomes do not appear to function as permeation enhancers but seem to provide the needed physicochemical environment for transfer of interferon into the skin.

Effect of L-lysine monohydrochloride on cutaneous herpes simplex virus in the guinea pig

The effect of topical applications of crystalline lysine therapy on cutaneous herpes simplex virus (HSV) inoculations and subsequent dorsal root ganglia (DRG) infection was studied in male Hartley guinea pigs. Although HSV-I was recovered from the inoculated sites from all animals, the L-lysine-treated skin remained clinically normal, whereas untreated controls manifested clinical symptoms up to 3 days postinoculation (p.i.). However, cocultivation of DRG (C1-S1) indicated a selective tropism of infective particles to specific DRG in the groups treated with amino acids. In lysine-treated animals, HSV was recovered from a few DRG (T-12, T-13, and L-1) at 3 days p.i. and from DRG T-10 in leucine-treated controls; yet no HSV was recovered from DRG of untreated controls. These results suggest an immunomodulatory effect of L-lysine on inoculation site infections and the possible potentiation of subsequent DRG manifestation in amino-acid-treated animals.

Antiviral effects of phosphonoformate (PFA, foscarnet sodium)

This article describes the antiviral properties of foscarnet (trisodium phosphonoformate) at the enzyme level as well as in cell cultures and in vivo. The mechanism of action against herpesvirus DNA polymerases and reverse transcriptases is outlined. Clinical studies using topical foscarnet against mucocutaneous herpes simplex virus infections are presented. The clinical use of intravenous foscarnet against severe viral infections caused by cytomegalovirus, hepatitis B virus and human immunodeficiency virus is discussed.

Rapid and accurate viral diagnosis

In recent years, there has been increased recognition of the importance of viral infections. In addition, new antiviral agents have become available. These factors have led to a marked increase in utilization of viral diagnostic services. In this review, both conventional and rapid methods for viral diagnosis are presented, with emphasis on recent advances. The antiviral agents currently available and the major drugs under investigation are also briefly discussed. It is hoped that this review will serve as a useful adjunct for the management of patients with virus infections.

Therapeutic effect of pyrophosphate analogues on cutaneous herpes simplex virus type 1 infection in guinea pigs

We investigated the influence of disodium phosphonic formate (PFA-Na2) and trisodium thiophosphonic formate (TPFA-Na3), in comparison with acyclovir (Zovirax) and trisodium phosphonic formate (PFA-Na3) (Triapten) ointment, on the course of primary cutaneous herpes simplex virus infection in a guinea pig skin model. PFA-Na2 at 3.0%, TPFA-Na3 at 0.5% and PFA-Na3 at 0.5% as well as Triapten ointment (2.0% PFA-Na3) completely inhibited virus infection. Zovirax cream (5.0% acyclovir), applied five times (15 min., 4, 20, 24, and 28 h) after virus inoculation did not prevent virus infection. Similarly, application of Zovirax cream 5 times daily for 5 days did not prevent a vesicle formation following cutaneous herpes simplex virus infection of the guinea pig.

Evaluation of antiviral treatments for recurrent herpes simplex labialis in the dorsal cutaneous guinea pig model

Recurrent herpes simplex labialis has proved to be a difficult disease to treat. Despite 25 years of clinical research with established antiviral substances, only small benefits from experimental therapies have been demonstrated. Progress has been slow, in part, because of the time-consuming nature of large, patient-initiated clinical trials. The dorsal cutaneous guinea pig model is a rapid and efficient means to identify topical antiviral formulations with clinical promise. The cumulative results of our studies with 19 different test treatments show that 8 were equal in efficacy to 5% acyclovir ointment, one was worse and ten were better. Two of the treatments found to be better than 5% acyclovir ointment have been studied clinically, with limited but encouraging results. Differences between the guinea pig model and the human illness mandate caution in predicting the degree of clinical efficacy from experimental outcomes. An effective and conservative use of the model is to optimize the topical formulation of a single antiviral substance.

Antiherpesvirus activity of 9-(4-hydroxy-3-hydroxymethylbut-1-yl) guanine (BRL 39123) in animals

The antiviral activity of 9-(4-hydroxy-3-hydroxymethylbut-1-yl)guanine (BRL 39123) was assessed in several animal models of herpes simplex virus (HSV) infection. BRL 39123 was as active as acyclovir (ACV) when applied topically to guinea pigs with a cutaneous HSV type 1 (HSV-1) infection and was also active topically in an HSV-2 genital infection. Before systemic administration to infected animals, BRL 39123 and ACV were administered orally and subcutaneously to mice, and the blood was assayed for each compound by high-pressure liquid chromatography. When given systemically to mice infected cutaneously with HSV-1, BRL 39123 was as active as ACV. In mice infected intranasally with HSV-1 or HSV-2, single daily subcutaneous doses of BRL 39123 were more effective than equivalent treatment with ACV, reflecting the more persistent activity seen in cell culture and a more stable triphosphate within the infected cell. When the compounds were supplied in drinking water for this infection, BRL 39123 and ACV had similar potencies against HSV-1, although ACV was more active against an HSV-2 infection than BRL 39123 was. In mice infected intraperitoneally with HSV-1, BRL 39123 was 10-fold more potent than ACV and a single dose of BRL 39123 reduced virus replication within the peritoneal cavity more effectively than 3 doses of ACV given 1, 5, and 20 h after infection. Although BRL 39123 failed to eradicate the virus from mice latently infected with HSV-1, treatment initiated 5 h after infection of the ear pinna reduced the numbers of mice that developed latent infections.

Therapeutic effect of (E)-5-(2-bromovinyl)-2'-deoxyuridine, caffeic acid oxidation product, and trisodiumphosphonoformate on cutaneous herpes simplex virus type 1 infection in guinea pigs

The influence of (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU), caffeic acid oxidation product (KOP), and trisodiumphosphonoformate (TPF) on the course of the primary cutaneous herpes simplex virus infection was investigated by means of a guinea pig test model. The antiviral substances were applied in an ointment with 10% urea as a penetration mediator. When the treatment was initiated 15 minutes after virus inoculation, 3% BVDU effectively inhibited the development of herpetic vesicles and 0.1% BVDU prevented the appearance of herpetic satellites. Under the same conditions 1% and 3% KOP ointments inhibited the appearance of satellites; and 0.5% TPF ointment completely inhibited the development of cutaneous herpes lesions. Prophylactic drug administration given 24, 20, and 4 hours before virus inoculation was without any protective effect.

Evaluation of triacontanol-containing compounds as anti-inflammatory agents using guinea pig models

A mixture of the aliphatic alcohol, triacontanol, and other chemically associated naturally occurring alcohols was applied to the denuded dorsal cutaneous surface of guinea pigs to evaluate anti-inflammatory activity. In the setting of a chemical irritation with 2% croton oil and in an allergic dermatitis created with dinitrochlorobenzene sensitization and challenge, the triacontanol-containing preparation was significantly more effective than vehicle alone (DHL skin cream) but not as effective as 0.05% Diprolene ointment. Lymphocyte stimulation was studied by tritiated thymidine uptake and morphologic examination for blast transformation. When triacontanol-containing compounds were solubilized in aqueous media, effects on lymphocytes were insignificant. When solubilized in ethanol, there was a marked effect on thymidine uptake but not on blast transformation when compared to parallel controls.

Mode of action, toxicity, pharmacokinetics, and efficacy of some new antiherpesvirus guanosine analogs related to buciclovir

9-[4-Hydroxy-3-(hydroxymethyl)butyl]guanine (3HM-HBG), (RS)-9-[4-hydroxy-2-(hydroxymethyl)butyl]guanine ([+/-]2HM-HBG), and cis-9-(4-hydroxy-2-butenyl)guanine (2EN-HBG), new acyclic guanosine analogs structurally related to buciclovir (BCV [(R)-9-(3,4-dihydroxybutyl)guanine]), were evaluated in parallel with buciclovir as anti-herpes simplex virus (HSV) agents. In cell cultures, replication of different strains of HSV type 1 (HSV-1) and HSV-2 was inhibited at nontoxic drug concentrations. The concentrations giving 50% inhibition of plaque formation were, however, dependent on virus strain and cell type. In most cell types, the order of activity against HSV-1 strains was 3HM-HBG greater than (+/-)2HM-HBG greater than BCV greater than 2EN-HBG, whereas the drugs showed an approximately equivalent activity against HSV-2 strains in different cells. The cytotoxic effects of the drugs were also cell type dependent, the order of activity being BCV greater than 3HM-HBG = (+/-)2HM-HBG greater than 2EN-HBG. At growth-inhibitory concentrations, the guanosine analogs BCV, 3HM-HBG, and (+/-)2HM-HBG showed clastogenic effects in human lymphocytes, mainly because of the induction of chromatid breaks. When evaluated for their anti-HSV effects in systemic HSV-1 infections in mice, the order of activity was BCV = 3HM-HBG greater than (+/-)2HM-HBG greater than 2EN-HBG, and in mice infected systemically with HSV-2, only BCV and 3HM-HBG showed efficacy. The differences between efficacy in vitro and in vivo could be explained in part by differences in kinetics of the drugs in mouse plasma, as the more efficacious drugs, BCV and 3HM-HBG, showed lower clearances and longer half-lives than the less efficacious ones, (+/-)2HM-HBG and 2EN-HBG. When used topically against a cutaneous HSV-1 infection in guinea pigs, 3HM-HBG showed an effect equivalent to that of BCV, whereas (+/-)2HM-HBG and 2EN-HBG were inactive. Mechanistically, the guanosine analogs were characterized by a high affinity for the viral thymidine kinase and a low affinity fo a cellular thymidine kinase and by their inhibition of viral DNA synthesis in infected cells.

Thiosemicarbazones of 2-acetylpyridine, 2-acetylquinoline, 1-acetylisoquinoline, and related compounds as inhibitors of herpes simplex virus in vitro and in a cutaneous herpes guinea pig model

A series of 111 thiosemicarbazones of 2-acetylpyridine, 2-acetylquinoline, 1-acetylisoquinoline, and related compounds were evaluated as inhibitors of herpes simplex virus in vitro and in a cutaneous herpes guinea pig model. All derivatives tested were potent inhibitors of virus replication with mean 50% inhibitory concentrations of 1.1 micrograms/ml for both type 1 and 2 herpes simplex virus. Inhibitory concentrations for cellular protein and DNA synthesis were considerably higher for many compounds resulting in in vitro therapeutic indices ranging from greater than 100 (highly selective) to less than 1 (negatively selective). All compounds were tested for dermal toxicity following topical administration of saturated solutions in 1,3-butanediol to the shaved, depilated skin of guinea pigs. Approximately 50% of the compounds produced slight to no dermal toxicity whereas the remaining compounds produced moderate to severe dermal toxicity. 28 compounds were evaluated in the cutaneous herpes guinea pig model against herpes simplex virus type 1. A number of N4-monosubstituted 2-acetylpyridine thiosemicarbazones produced highly significant reductions in days to healing and lesion score without producing untoward dermal toxicity. Structure-activity relationships revealed that a reduction of the azomethine bond in the molecule (i.e., conversion of a thiosemicarbazone to a thiosemicarbazide) greatly diminished dermal toxicity apparently without producing a proportional decrease in antiviral activity.

Antiherpes effects and pharmacokinetic properties of 9-(4-hydroxybutyl) guanine and the (R) and (S) enantiomers of 9-(3,4-dihydroxybutyl)guanine

Three acyclic guanosine analogs with similar structures, the (R) and (S) forms of 9-(3,4-dihydroxybutyl)guanine and 9-(4-hydroxybutyl)guanine, were compared for antiherpes activity in vivo and in vitro. The three guanosine analogs were viral thymidine kinase-dependent inhibitors of virus multiplication. In cell cultures, (S)-9-(3,4-dihydroxybutyl)guanine was the least active of these three drugs against a variety of herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) strains. This was also the case for a certain HSV-1 or HSV-2 strain in different cell lines. In cell cultures, (R)-9-(3,4-dihydroxybutyl)guanine and 9-(4-hydroxybutyl)guanine had similar antiherpes activities. However, in vivo in cutaneous HSV-1 infections in guinea pigs treated topically and in systemic HSV-2 infections in mice treated orally or intraperitoneally, only (R)-9-(3,4-dihydroxybutyl)guanine had a therapeutic effect. The extremely short half-life in plasma and the high clearance of 9-(4-hydroxybutyl)guanine as compared with those of (R)-9-(3,4-dihydroxybutyl)guanine probably made 9-(4-hydroxybutyl)guanine inefficacious when given intraperitoneally or orally to mice infected with herpesvirus. On the other hand, no kinetic differences between (R)-9-(3,4-dihydroxybutyl)guanine and 9-(4-hydroxybutyl)guanine were observed in penetration through guinea pig skin ex vivo, and no preferential metabolism of 9-(4-hydroxybutyl)guanine in skin was noted. We deduced that high thymidine levels in guinea pig skin preferentially antagonize the antiviral effect of 9-(4-hydroxybutyl) guanine in cutaneous HSV-1 infections.

Cutaneous herpes simplex virus infection of the guinea pig: lack of resistance to acyclovir and phosphonoformic acid after topical treatment

Guinea pigs were infected cutaneously with HSV1 and treated topically with acyclovir or phosphonoformic acid (0.1% to 0.5% solution), or with a combination of both. The therapy was clinically effective and the virus content in the skin diminished. Virus harvests from skin areas in no case showed increased drug resistance, as tested by plaque reduction.

Topical treatment of cutaneous herpes simplex virus infection in hairless mice with (E)-5-(2-bromovinyl)-2'-deoxyuridine and related compounds

(E)-5-(2-Bromovinyl)-2'-deoxyuridine (bromovinyldeoxyuridine) was found to suppress the development of herpetic skin lesions and the paralysis and mortality associated therewith in hairless mice inoculated intracutaneously with herpes simplex virus type 1. This protective effect was achieved with bromovinyldeoxyuridine applied topically at 1, 3, or 10% in either dimethylsulfoxide (DMSO), Beeler base, Tween-glycerol-water, 5% Azone (1-dodecylazacycloheptan-2-one) in water, or 5% Azone in DMSO. The optimal vehicle was 5% Azone in DMSO, in which bromovinyldeoxyuridine was effective even at a concentration as low as 0.3%. In its protective activity against cutaneous herpes simplex virus type 1 infection in hairless mice, bromovinyldeoxyuridine was clearly superior to other established antiherpes compounds such as 5-iodo-2'-deoxyuridine, 5-ethyl-2'-deoxyuridine, arabinosyl thymine, and arabinosyl (E)-5-(2-bromovinyl) uracil when formulated at 10% in DMSO or Azone-DMSO. However, no activity was noted with any of these drug formulations against cutaneous herpes simplex virus type 2 infection. In contrast, acycloguanosine (acyclovir) proved quite effective in the topical treatment of cutaneous herpes simplex virus type 2 infection when used at 10% in DMSO or at 5% in propylene glycol.

Penetration of guinea pig skin by acyclovir in different vehicles and correlation with the efficacy of topical therapy of experimental cutaneous herpes simplex virus infection

Inadequate penetration of antiviral agents through the stratum corneum of the skin may be one of the limiting factors in the topical therapy of recurrent cutaneous herpes simplex virus infections in humans. In vitro studies of the penetration of the nucleoside analog acyclovir (ACV) through guinea pig skin demonstrated a marked increase in drug flux when ACV was formulated in dimethyl sulfoxide (DMSO), compared with water or polyethylene glycol (PEG) as the vehicle. To examine whether the increased transcutaneous flux of ACV effected by DMSO was meaningful in vivo, topical 5% ACV in DMSO was evaluated for the treatment of cutaneous herpes simplex virus infection in guinea pigs and compared with topical 5% ACV in PEG. When compared with infection sites treated with the vehicle alone, ACV in DMSO produced a greater percent reduction than did ACV in PEG in median lesion number (8 versus 58%; P less than 0.001), median lesion area (35 versus 73%; P = 0.001), and median lesion virus titer (21 versus 84%; P = 0.08). We conclude that DMSO is a highly effective vehicle for topical administration of ACV and is superior to PEG in our model. Careful choice of vehicle and consideration of transcutaneous penetration may be important for realization of the full potential of topical antiviral therapy in humans.

Carbocyclic arabinofuranosyladenine (cyclaradine): efficacy against genital herpes in guinea pigs

Carbocyclic arabinofuranosyladenine (cyclaradine), a novel nucleoside analog with such desired features as hydrolytic and enzymatic stability, adenosine deaminase resistance, and low systemic toxicity, inhibited the replication of herpes simplex virus types 1 and 2. The 5'-methoxyacetate prodrug form exhibited significant efficacy in the topical treatment of genital infections by herpes simplex virus type 2.

Antiherpetic activity and mechanism of action of 9-(4-hydroxybutyl)guanine

9-(4-Hydroxybutyl)guanine was synthesized and tested for antiherpes activity. In cell cultures, different strains of herpes simplex virus type 1 (HSV-1) and type 2(HSV-2) were inhibited by 50% at 2-14 microM of 9-(4-hydroxybutyl)guanine, while a HSV-1 mutant lacking thymidine kinase (HSV-1 TK-) was resistant. Linear competitive inhibition of purified HSV-1-induced thymidine kinase (TK) with thymidine as a variable substrate was observed for 9-(4-hydroxybutyl)guanine with an apparent Ki value of 2.06 microM while the corresponding Ki value for the cellular TK was greater than 250 microM. By using high performance liquid chromatography, the formation of 9-(4-hydroxybutyl)guanine monophosphate by HSV-1 TK was measured and the rate of product formation was found to be about 10% of that found by using thymidine as a substrate. A selective inhibition of HSV-1 DNA synthesis by 9-(4-hydroxybutyl)guanine was observed in infected Vero cells. 9-(4-Hydroxybutyl)guanine had a low cellular toxicity. A weak therapeutic effect on herpes keratitis in rabbits was observed whereas cutaneous HSV-1 infection in guinea pigs and systemic HSV-2 infection in mice were not affected by this compound.

9-(3,4-dihydroxybutyl)guanine, a new inhibitor of herpesvirus multiplication

A new compound, 9-(3,4-dihydroxybutyl)guanine, has been synthesized and its antiherpes activity determined. 9-(3,4-Dihydroxybutyl)guanine was selectively phosphorylated by herpes simplex virus thymidine kinase and had a high affinity for this enzyme, with an inhibition constant of 1.5 microM. In cell culture, replication of different strains of herpes simplex virus types 1 and 2 was inhibited to the extent of 50% by 4 to 18 microM (RS)-9-(3,4-dihydroxybutyl)guanine. The (R)-enantiomer of this compound was more inhibitory than the (S)-enantiomer. Herpesvirus DNA synthesis was selectively inhibited by (RS)-9-(3,4-dihydroxybutyl)guanine in infected cells, and a low cellular toxicity was observed. (RS)-9-(3,4-Dihydroxybutyl)guanine had a therapeutic effect when applied topically to guinea pigs with cutaneous herpes simplex type 1 infections and to rabbits with herpes keratitis. Oral treatment of a generalized herpes simplex type 2 infection in mice had a therapeutic effect.

Combined chemotherapy of cutaneous herpes simplex infection of the guinea pig

Cutaneous infection of guinea pigs with HSV1 was topically treated from 2 to 6 days post infection with 7 antiherpetic substances. Phosphonoformic acid and acyclovir were found to be highly effective; trifluorothymidine, thymine arabinoside, ethyldeoxyuridine, and adenine arabinoside monophosphate all had some therapeutic effect in decreasing order, whereas iododeoxyuridine was ineffective. The efficacy of treatment was evaluated from cutaneous lesion scores by the Wilcoxon rank test. The substances were combined in marginally effective concentrations. From the 21 combinations, acyclovir + phosphonoformic acid, acyclovir + thymine arabinoside, and phosphonoformic acid + thymine arabinoside suggested a synergistic interaction, which appeared significant for acyclovir + phosphonoformic acid.

Anti-herpesvirus activity of adenine arabinoside analogues in tissue culture and a genital infection of mice and guinea pigs

Four analogues of adenine arabinoside (ara-A) were compared for activity against herpes simplex virus (HSV) in tissue culture and in a genital infection of mice and guinea pigs. These analogues, 5'-monophosphate (ara-AMP), 5'-valerate ester (ara-AV), 2'3'-diacetate ester (ara-ADA), and 2',3',5'- triacetate ester (ara-ATA) have greater water and lipid solubility and resistance to deamination than ara-A. In mouse embryo fibroblast cells, similar viral inhibitory levels were noted with ara-A, AMP, and ara-Av, while ara-ADA and ara-ATA were 6-10 time less active. In mice infected intravaginally with HSV type 2 (HSV-2), intravaginal treatment with 10% concentrations of each of the compounds beginning 3 h after viral challenge, had no effect on infection rates, titers of virus in vaginal secretions, mortality rates or the mean day of death as compared with placebo-treated controls. In the HSV-2 genital infection of guinea pigs, treatment with 10% vaginal creams or placebo vehicle was initiated 6 or 24 h after viral inoculation. In animals treated at 6 h with ara-A, ara-AMP and ara-AV, there was complete inhibition of viral replication in the vaginal tract and development of external genital lesions. When treatment with these three drugs was delayed 24 h after infection, there was no effect on vaginal virus titers, but lesions severity was reduced by ara-A or ara-AMP therapy. Ara-ATA was ineffective whether begun at 6 or 24 h. The greater solubility in water and lipid as well as the resistance to deamination of ara-AMP and ara-AV did not appear to enhance their antiviral activity over that of ara-A. Additionally, ara-ADA and ara-ATA exhibited less activity both in tissue culture and in the experimental genital infections.

Pyrophosphate analogues as inhibitors of DNA polymerases of cytomegalovirus, herpes simplex virus and cellular origin

Several pyrophosphate analogues have been compared for their ability to inhibit the activities of isolated cytomegalovirus (CMV) DNA polymerase, herpes simplex virus type 1 (HSV 1) DNA polymerase and calf thymus DNA polymerase alpha. The most effective inhibitors were phosphonoformate and phosphonoacetate. Although not identical, the structural requirements for compounds inhibitory to CMV and HSV-1 DNA polymerase were specific, with two negatively charged groups in close vicinity. The CMV DNA polymerase was more susceptible to certain phosphonoacetates containing bulky hydrophobic alpha-substituents than was the HSV-1 DNA polymerase. No example of the converse preference was found. The inhibition of CMV DNA polymerase by phosphonoformate, hypophosphate, alpha-hydroxyphosphonoacetate and alpha-nonylphosphonoacetate was linear non-competitive with the deoxyribonucleoside triphosphates as variable substrates. Phosphonoformate, phosphonoacetate, and to a lesser extent alpha-hydroxyphosphonoacetate, carbonyldiphosphonate and alpha-nonylphosphonoacetate also inhibited the focus formation by CMV in cell-culture.

Ineffectiveness of adenine arabinoside and adenine arabinoside 5'-monophosphate in simian varicella infection

Adenine arabinoside and adenine arabinoside 5'-monophosphate (ara-AMP) have been evaluated for antiviral activity against simian varicella virus infection in monkeys. In a preliminary study for toxicity, intramuscular injection of ara-AMP at 15 mg/kg per day as a single injection for 5 days to two normal patas monkeys caused no detectable local reaction, no weight loss or changes in serum transaminase levels, and no hematological abnormalities. When this dose was given in the treatment of four simian varicella virus-infected patas monkeys, no effect was observed on the clinical course of infection, as compared with four infected monkeys which received phosphate-buffered saline. Treatment was begun 43 h after virus inoculation and was continued for 16 days. Toxicity of intravenously administered ara-AMP at 100 to 50 mg/kg per day for 5 days to pairs of uninfected patas monkeys was evident by hematological and hepatic histological alterations, as well as the death of one monkey in each pair. No gross evidence of toxicity occurred in two monkeys which received 20 mg of ara-AMP per kg per day. The antiviral efficacy of intravenous treatment was studied in groups of four African green monkeys which received adenine arabinoside at 15 mg/kg per day or ara-AMP at 18.4 mg/kg per day. Drug administration began 48 h after inoculation with simian varicella virus and continued for 10 days. The monkeys that received treatment did not respond to infection differently from four infected control monkeys similarly treated with phosphate-buffered saline.

Inhibition of herpesvirus multiplication in guinea pig skin by antiviral compounds

The effects of adenine arabinoside, cytosine arabinoside, iododeoxyuridine, ribavirin, phosphonoacetate and phosphonoformate on virus titers in cutaneous herpesvirus infections of guinea pigs have been determined and compared to their effects on lesion score. Only phosphonoacetate and phosphonoformate caused a reduction in virus titer and lesion score when the drugs were applied topically after symptoms had developed. However, unlike phosphonoacetate, phosphonoformate did not cause local skin irritation. A herpesvirus mutant, inducing a DNA polymerase resistent to phosphonoformate gave rise to an infection in which the virus titer was not reduced by phsophonoformate.

Effect of trisodium phosphonoformate and idoxuridine on experimental herpes simplex keratitis in immunized and non-immunized rabbits

The effect of trisodium phosphonoformate (PFA) has been compared to that of idoxuridine (IDU) when applied topically in both liquid and ointment preparations on herpetic keratitis in rabbits. Trisodium phosphonoformate had a therapeutic effect but was not as effective as idoxuridine in the vehicles tested. This was seen with both herpes-immunized and non-immunized rabbits. A herpesvirus mutant inducing a PFA restant DNA polymerase was used to infect rabbit corneas. A comparison of the effect of PFA on the keratitis caused by this resistant mutant and the wild type herpesvirus indicates that the therapeutic effect of PFA on the herpes keratitis was due to an inhibition of herpesvirus DNA polymerase.

Pyrophosphate analogues as inhibitors of herpes simplex virus type 1 DNA polymerase

Twenty nine pyrophosphate analogues have been tested for their ability to inhibit herpes simplex virus type 1 (HSV-1) DNA polymerase activity. The structural requirements for active inhibitors and their mechanism of action have been investigated. Active compounds had two negatively charged groups at close proximity. The most active compounds contained free phosphono and/or carboxyl groups. Apart from phosphonoformate and phosphonoacetate, which were strong inhibitors, some other analogues, 2-phosphonopropionate, 2-phenylphosphonoacetate, oxalate, carbonyldiphosphate, methanehydroxy-diphosphonate and hypophosphate also inhibited the HSV-1 DNA polymerase activity. With the exception of hypophosphate the tested compounds inhibited the activity of calf thymus DNA polymerase alpha to a lesser extent than the activity of the HSV-1 DNA polymerase. All inhibitors gave linear uncompetitive inhibition of HSV-1 DNA polymerase with activated DNA as variable substrate. With the four deoxynucleoside triphosphates as variable substrates all inhibitors except hypophosphate gave linear non-competitive inhibition patterns. Hypophosphate caused a more competitive type of inhibition. The inhibition constants for the active compounds have been determined. Phosphonoformate, phosphonoacetate, methanehydroxydiphosphonate and hypophosphate also inhibited HSV-1 plaque formation in cell culture.

Effect of trisodium phosphonoformate in genital infection of female guinea pigs with herpes simplex virus type 2

A genital herpesvirus type 2 infection in guinea pigs has been used to evaluate the inhibitory effect of phosphonoformate on the infection. An early topical treatment prevented the appearance of vesicles and histopathological changes and no virus could be recovered. When treatment, either topical or both systemic and topical, was delayed to 24 hours post infection no therapeutic effect was observed.

Trisodium phosphonoformate, a new antiviral compound

Trisodium phosphonoformate selectively inhibits cell-free DNA polymerase activity induced by herpesvirus. The new inhibitor has an antiviral effect on herpes simplex virus types 1 and 2, pseudorables virus, and infectious bovine rhinotracheitis virus in cell culture. It has a good therapeutic activity against cutaneous herpes simplex virus infection in guinea pigs.