Antiviral activity of arabinosylthymine in herpesviral replication: mechanism of action in vivo and in vitro

Linking Antimicrobial Potential of Natural Products Derived from Aquatic Organisms and Microbes Involved in Alzheimer's Disease - A Review

The following review is oriented towards microbes linked to Alzheimer's disease (AD) and antimicrobial effect of compounds and extracts derived from aquatic organisms against specific bacteria, fungi and viruses which were found previously in patients suffering from AD. Major group of microbes linked to AD include bacteria: Chlamydia pneumoniae, Helicobacter pylori, Porphyromonas gingivalis, Fusobacterium nucleatum, Prevotella intermedia, Actinomyces naeslundii, spirochete group; fungi: Candida sp., Cryptococcus sp., Saccharomyces sp., Malassezia sp., Botrytis sp., and viruses: herpes simplex virus type 1 (HSV-1), Human cytomegalovirus (CMV), hepatitis C virus (HCV). In the light of that fact, this review is the first to link antimicrobial potential of aquatic organisms against these sorts of microbes. This literature review might serve as a starting platform to develop novel supportive therapy for patients suffering from AD and to possibly prevent escalation of the disease in patients already having high-risk factors for AD occurrence.

In vitro Anti-Herpesvirus Activities of 5-Substituted 2′-Deoxy-2′-Methylidene Pyrimidine Nucleosides

New pyrimidine deoxyribonucleoside analogues, 2′-deoxy-2′-methylideneuridine (DMDU), 2′-deoxy-2′-methylidenecytidine (DMDC), and their 5-substituted derivatives were tested for the anti-herpesvirus activities and anti-proliferative activity. E-5-(2-Bromovinyl)uracil derivative (BV-DMDU) and its cytosine congener were synthesized from 1-β-D-arabinofuranosyl- E-5-(2-bromovinyl)uracil (BV-araU). 5-Bromo, 5-iodo, 5-methyl, and 5-ethyl derivatives of DMDU and BV-DMDU showed activities against herpes simplex virus type 1 (HSV-1) and varicella-zoster virus (VZV). The corresponding DMDC derivatives had no or only weak antiviral activity. Among the 2′-deoxy-2′-methylidene pyrimidine nucleosides, BV-DMDU showed the most potent and selective anti-VZV activity. BV-DMDU was more potent than acyclovir, but less active than BV-araU. BV-DMDU was inactive against human diploid and tumour cells. DMDC and F-DMDC (5-fluoro derivative) were potent inhibitors of HSV-1, herpes simplex virus type 2, VZV, and human cytomegalovirus (HCMV) and also had significant anti-proliferative activity. Their potency against HCMV was better than that of ganciclovir and araC. Some DMDU derivatives also showed anti-HCMV activity, but they had anti-proliferative activity. The anti-HCMV activity of these DMDC and DMDU compounds was generally more potent than those against HSV-1 and VZV thereof, suggesting the participation of cellular kinase in their antiviral action.

Marine nucleosides: structure, bioactivity, synthesis and biosynthesis

Nucleosides are glycosylamines that structurally form part of nucleotide molecules, the building block of DNA and RNA. Both nucleosides and nucleotides are vital components of all living cells and involved in several key biological processes. Some of these nucleosides have been obtained from a variety of marine resources. Because of the biological importance of these compounds, this review covers 68 marine originated nucleosides and their synthetic analogs published up to June 2014. The review will focus on the structures, bioactivities, synthesis and biosynthetic processes of these compounds.

Chapter 3 Antiviral drugs: general considerations

The development of an antiviral drug as well as of other drugs is a long process. In most programmes the screening and evaluation start using inhibition of virus multiplication in cell cultures, but in some instances the screening starts in animal models of different viral diseases. In these cases, the mechanism of action has to be analyzed after the in vivo effect has been found. It is not possible to specify precisely the time and resources required in a newly started project to find a compound active against a virus infection but 5-10 years is a reasonable estimation. For some viruses such as herpesviruses, where a number of active inhibitors are already known, the task is simpler than it is to find inhibitors of a virus such as influenza against which only a few active inhibitors have been reported. Evaluation of clinical efficacy in humans is a large and difficult part of the development of an antiviral drug. The number of uncontrolled clinical studies claiming efficacy of different drugs against viral diseases is depressingly large. It is essential to perform double-blind, placebo-controlled and statistically well evaluated studies to be able to judge the clinical efficacy of an antiviral drug. As the knowledge of the detailed natural history and molecular biology of viral diseases and viruses themselves increases, one will obviously have better opportunities to find new drugs. Methods such as X-ray diffraction measurement and NMR determinations will probably lead to a detailed understanding of the structures and interactions taking place at the active site of viral enzymes and their cellular counterparts.

Pyrimidine as constituent of natural biologically active compounds

This review describes the various manifestations of the pyrimidine system (alkylated, glycosylated, benzo-annelated.). These comprise pyrimidine nucleosides as well as alkaloids and antibiotics--some of them have been discovered and isolated from natural sources already long time ago, others have been reported very recently. A short overview on pyrimidine syntheses (prebiotic synthesis, biosynthesis, and metabolism) is given. The biological activities of most of the pyrimidine analogs are briefly described, and, in some cases, syntheses are formulated.

Construction of bovine herpesvirus-1 (BHV-1) recombinants which express pseudorabies virus (PRV) glycoproteins gB, gC, gD, and gE

We have improved the method for constructing recombinants of bovine herpesvirus type-1 (BHV-1). Using this method, we constructed three recombinants in which the pseudorabies virus (PRV) thymidine kinase (tk) gene was inserted at three different sites in the unique short region of BHV-1. These three sites are located in the open reading frame of gE, gG and gI genes. Previously, two sites (tk and gC) had been used to insert foreign DNA fragments to BHV-1 genome. Therefore we now have 5 sites in BHV-1 where DNA can be inserted. The gB, gC, gD, gE and gI genes of PRV were successfully inserted at the tk or the gC gene of BHV-1 genome and Western blot analyses confirmed that the recombinants express PRV gB, gC, gD and gE. Anti-PRV gB and gC antibodies as well as anti-PRV polyclonal serum neutralized BHV-1 recombinants which express PRV gB and gC. The latter was neutralized more strongly. However, anti-gD monoclonal antibody and anti-PRV polyclonal serum failed to neutralize gD-expressing recombinants. This suggests that PRV gC and some gB are integrated into the viral envelope of the recombinants, but very little gD is present in the viral envelope.

Effects of phosphonylmethoxyalkyl derivatives studied with a murine model for abortion induced by equine herpesvirus 1

(S)-9-(3-Hydroxy-2-phosphonylmethoxypropyl)adenine (HPMPA) and (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine (HPMPC) were tested in a mouse model for equine herpesvirus 1-induced abortion. HPMPA, given twice daily, reduced virus replication, but the compound was embryotoxic. A single dose of HPMPC, however, reduced the incidence of abortion and transfer of virus to the fetuses while producing no obvious toxic effects.

Prospects for Antiviral Chemotherapy in Veterinary Medicine: 2. Avian, Piscine, Canine, Porcine, Bovine and Equine Virus Diseases

This paper, which is published in two parts, reviews the literature pertaining to antiviral chemotherapy of viruses of veterinary importance. While early reports in the 1970s referred to the chemotherapy of a number of different RNA and DNA viruses, there was considerable focus in the 1980s, initially on herpesviruses and latterly on retroviruses, and particularly in cats. Details are given of the successful treatments of FeLV and FIV, which have been used as animal models for HIV therapy. Therapy of equine, canine, bovine, porcine, avian, and fish diseases is also considered. The high costs of developing and registering a new chemical entity, especially for food species in which extensive toxicity/residue data are required, is the main reason why specific antiviral compounds are not currently available for veterinary use, although some non-specific immune modulators are now emerging. Concurrent availability of appropriate diagnostic tools is a prerequisite for successful veterinary antiviral chemotherapy, as is a greater understanding of the pathogenesis of virus infections in animals and the development of more sophisticated means of drug delivery, appropriate to both food animal species and companion animals (dogs, cats, and horses). Additionally, antiviral agents are valuable as research tools per se, as opposed to solely as chemotherapeutic agents. Part 1 covers the feline virus diseases, while part 2 includes the other viruses of veterinary importance, in dogs, horses, cattle, pigs, birds, and fish.

Viral thymidine kinases and their relatives

Thymidine kinases were described for cellular life long before it was shown that they could also be encoded by viruses, but the viral thymidine kinase genes were the first to be sequenced. These enzymes have been extraordinarily useful to the researcher, serving first to help label DNA, then to get thymidine analogs incorporated into DNA for therapeutic and other purposes and more recently to move genes from one genome to another. Knowledge of the nucleotide and amino acid sequences of these enzymes has allowed some deductions about their possible three-dimensional structure, as well as the location on the polypeptide of various functions; it has also allowed their classification into two main groups: the herpesviral thymidine/eukaryotic deoxycytidine kinases and the poxviral and cellular thymidine kinases; the relationships of the mitochondrial enzyme are still not clear.

Cytopathogenicity, drug susceptibility, and thymidine kinase activity of a retinovirulent herpes simplex virus type 2

We investigated some of the biological and biochemical characteristics of a neuroinvasive, retinovirulent herpes simplex virus type 2 strain SL (HSV-2[SL]) and compared them with those of a neurovirulent, nonretinovirulent HSV-2 (186). HSV-2(SL) was shown to spread rapidly and produce large syncytium in vitro. HSV-2(SL) and HSV-2(186) were equally susceptible to acyclovir (ACV) and thymine arabinoside (Ara-T). However, HSV-2(SL) was fourfold and 44-fold more susceptible than HSV-2(186) to iododeoxyuridine (IUdR) and bromovinyldeoxyuridine (BVDU), respectively. In addition, cytosolic TK from HSV-2(SL)-infected cells phosphorylated 4, 20, and 23,000 times more IUdR, iododeoxycytidine (IdCyD), and Ara-T than the TK of HSV-2(186), respectively. Further, HSV-2(186) TK did not phosphorylate Ara-T, but HSV-2(186) replication was inhibited by Ara-T. These studies indicate that the retinovirulent HSV-2(SL) has a syn phenotype and a TK with broad substrate activity.

Effective chemotherapy of equine herpesvirus 1 by phosphonylmethoxyalkyl derivatives of adenine demonstrated in a novel murine model for the disease

Equine herpesvirus 1 was established in adult mice by means of intranasal inoculation. A disease developed that showed several features closely resembling the infection in the natural host. These included the restriction of virus replication to the respiratory tract and blood, the replication of virus in ciliated mucosa, and development of viremia for several days during the acute phase of the infection. Infected mice were treated with the antiviral agent (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine. A marked effect was observed on virus replication in the respiratory tract when chemotherapy was commenced 1 day before virus inoculation; it also cleared the viremia and reversed the progression of clinical signs. When chemotherapy was commenced 1 day after virus inoculation, a moderate, though less marked effect was observed. The efficacy of this drug in the murine infection correlated with activity of the drug against equine herpesvirus 1 in cell cultures. The prospects for chemotherapy in the natural host are discussed in the light of these findings.

Detection of thymidine kinase activity using an assay based on the precipitation of nucleoside monophosphates with lanthanum chloride

A new assay method for the measurement of thymidine kinase (TK) is described. Cytosols were prepared from TK- and TK+ cells and evaluated for TK activity using an assay which is based on the phosphorylation of [125I]-iododeoxyuridine, [125I]-iododeoxycytidine, or [3H]thymidine and the precipitation of the monophosphates of these nucleosides by lanthanum chloride. The specificity, reproducibility, sensitivity, and convenience of this assay are demonstrated.

Clinical isolate of herpes simplex virus type 2 that induces a thymidine kinase with altered substrate specificity

In vitro and in vivo studies were done on a herpes simplex virus type 2 strain recovered from a patient on acyclovir (ACV) which was ACV resistant but expressed thymidine (dThd) kinase (EC 2.7.1.21) activity. Plaque-purified clones derived from the original clinical sample were heterogeneous with respect to plaque size and drug susceptibility. The heterogeneity of this viral mixture was also evident from varied 125I-labeled 5-iodo-2'-deoxycytidine autoradiographic patterns and from varied expression of dThd kinase-associated phosphorylating activities. Four clones from this mixture were 1-beta-D-arabinofuranosylthymine (ara-T) susceptible and ACV resistant. Extracts of cells infected with these clones catalyzed the phosphorylation of ara-T but little of ACV. The virus-coded dThd kinase was purified from one of these clones to determine whether its substrate specificity was altered. The amount of virus-coded dThd phosphorylating activity with the cell extracts was estimated to be sevenfold lower with the resistant clone than with the MS strain of herpes simplex virus type 2. The dThd kinase eluted from a dThd-agarose affinity column under the same conditions with extracts from both sources and substrate saturations of both enzymes by acyclic nucleoside analog phosphate acceptors were classical hyperbolic functions. However, there were significant differences in the kinetic parameters of substrates between the two enzymes. Apparent Km (Km') values for dThd, deoxycytidine, ara-T, ACV, and the acyclic guanosine analog 9-[[2-hydroxyl-1-(hydroxymethyl)ethoxy]methyl]guaine (BW B759U) were 2- to 60-fold higher with the variant enzyme than with the enzyme from laboratory strain MS. Comparing these two enzymes, relative maximal phosphorylation rates (Vm) were eightfold lower for ACV but unchanged for BW B759U. In contrast, the relative rates for deoxycytidine and ara-T were eight- and twofold higher, respectively. The surprisingly good substrate activity with BW B759U compared with that of ACV (Vm/Km' = 0.39 versus 0.01) coincided with susceptibility of the ACV-resistant virus to BW B759U. This clinical variant retained its pathogenicity for mice and was only moderately less neurovirulent than wild-type virus. Although such mutants have the potential to induce illness less responsive to therapy, the recurrence from which the isolate was obtained was typical for this patient in severity and duration. Since this episode, the patient has been treated successfully with ACV.

Xylotubercidin against herpes simplex virus type 2 in mice

Of a series of newly synthesized derivatives of the pyrrolo[2,3-d]pyrimidine nucleosides tubercidin, toyocamycin, and sangivamycin, the xylosyl analog of tubercidin, xylotubercidin, exhibited the greatest potency and selectivity against herpes simplex virus type 2 (HSV-2) in vitro. At dosage regimens that were not toxic for the host, xylotubercidin proved efficacious in various HSV-2 animal model infections. When applied topically at 0.25, 0.5, or 1% in dimethyl sulfoxide or when administered systemically (intraperitoneally) at 12.5 or 25 mg/kg per day, xylotubercidin suppressed the development of herpetic skin lesions and the paralysis and mortality associated therewith in hairless mice inoculated intracutaneously with HSV-2. In this model, acyclovir was effective only if administered topically at 5 or 10% in dimethyl sulfoxide. When administered intraperitoneally over a dosage range of 10 to 50 mg/kg per day, xylotubercidin achieved a significant reduction in the mortality rate of mice infected intraperitoneally with HSV-2. Under the same conditions, acyclovir did not offer any protection even when administered at doses up to 250 mg/kg per day. Xylotubercidin thus appears to have considerable potential for both topical and systemic treatment of HSV-2 infections.

Enzymology and pathogenicity in mice of a herpes simplex virus type 1 mutant resistant to 2'-fluoro-2'-deoxy-1-beta-D-arabinofuranosyl-5-iodocytosine

The deoxypyrimidine nucleoside analog 2'-fluoro-2'-deoxy-1-beta-D-arabinofuranosyl-5-iodocytosine (FIAC) is a potent and selective inhibitor of herpes simplex virus type 1 in vitro (C. Lopez, K. A. Watanabe, and J. J. Fox, Antimicrob. Agents Chemother. 17:803-806, 1980). Isopycnographic analysis demonstrated that 1 microM FIAC inhibited herpes simplex virus DNA replication by more than 95% but inhibited cellular DNA replication by only 32%. Mutant herpes simplex virus type 1 selected resistant to FIAC displayed linked resistance to other nucleoside analogs, including arabinosylthymine and acyclovir. Lysates derived from Vero cells infected with FIAC-resistant virus showed markedly lower levels of thymidine kinase activity and were unable to phosphorylate selectively arabinosylthymine or FIAC, in contrast to lysates from cells infected with wild-type herpes simplex virus type 1. Finally, drug-resistant virus displayed a 6,000-fold decrease in pathogenicity when inoculated intraperitoneally into genetically susceptible A/J mice. These results indicate that resistance to deoxypyrimidine nucleoside analogs is due, at least in part, to alterations in viral thymidine kinase and is accompanied by decreased pathogenicity in vivo.

Isolation and differentiation of herpes simplex virus and Trichomonas vaginalis in cell culture

During the period January 1982 to January 1985, 2,234 specimens were cultured for isolation of herpes simplex virus (HSV). HSV was isolated from 23% of these, Trichomonas vaginalis was isolated from 1.6%, and 75.3% were negative. In 0.2% of these, HSV and T. vaginalis were isolated from the same specimen. Cytopathic effects produced by HSV were identified by their sensitivity to arabinosylthymine, whereas those produced by T. vaginalis were identified by their lack of sensitivity to arabinosylthymine and by observation of motility. Cytopathic effects produced by T. vaginalis were reproduced by trophozoites from axenic cultures of T. vaginalis as well as by lysates of T. vaginalis added to serum-free BHK cells.

Identification of a herpes simplex virus function that represses late gene expression from parental viral genomes

The expression of herpes simplex virus gamma 2 (late) genes is inhibited before the onset of viral DNA replication. We report that the block in the expression of certain gamma 2 genes is relieved, at least in part, by defects in the beta ICP8 protein. We have examined the expression of the gamma 2 gene encoding glycoprotein C (gC) in cells infected with a temperature-sensitive ICP8 mutant. Under conditions in which viral DNA replication is inhibited, cells infected with the ICP8 mutant overproduce the gC family of mRNAs relative to the level observed in cells infected with a wild-type virus. The gC mRNA synthesized in cells infected with the ICP8 mutant virus is correctly initiated and spliced and is translated with the same relative efficiency as in cells infected with a replicating wild-type virus. These results suggest that ICP8 is involved in the negative regulation of gamma 2 genes expressed from parental viral genomes. The level of gC expression was greatest in cells infected with a replicating wild-type virus. These data suggest that DNA replication and genome amplification are not absolute requirements for gamma 2 gene expression but may facilitate full-level expression of these genes.

Inhibition of human and woodchuck hepatitis virus DNA polymerase by the triphosphates of acyclovir, 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5-iodocytosine and E-5-(2-bromovinyl)-2'-deoxyuridine

The triphosphates of acyclovir (ACV), 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5-iodocytosine (FIAC) and E-5-(2-bromovinyl)-2'-deoxyuridine (BVdU) have been examined for their inhibitory effects on the endogenous DNA polymerase reactions of human hepatitis B virus (HBV) and woodchuck hepatitis virus (WHV). All three triphosphates (ACVTP, FIACTP and BVdUTP) inhibited the HBV and WHV DNA polymerases by competing with the corresponding natural substrates. FIACTP was the most potent inhibitor of HBV and WHV DNA polymerase while ACVTP was the least effective inhibitor. The inhibitory properties of these compounds were compared with those of the 5'-triphosphates of 1-beta-arabinofuranosyl-cytosine (ara-CTP) and 1-beta-arabinofuranosylthymine (ara-TTP). The 50% inhibitory doses for HBV and WHV DNA polymerases were in the following order: FIACTP less than BVdUTP less than ara-TTP less than ACVTP less than ara-CTP. BVdUTP appeared to be an efficient alternate substrate to dTTP for HBV DNA polymerase while FIACTP was much less efficient when substituted for dCTP. ACVTP did not act as an alternate substrate to dGTP and appeared to prevent DNA chain elongation.

Effect of eight antiviral drugs on the reactivation of herpes simplex virus in explant cultures of latently infected mouse trigeminal ganglia

The effect of several antiviral drugs on the reactivation of herpes simplex virus type 1 in explant cultures of latently infected mouse trigeminal ganglia was investigated. Phosphonoacetate and phosphonoformate, which act directly on the virus-induced DNA polymerase, require a drug concentration of 400 micrograms/ml for the inhibition of virus reactivation in latently infected ganglia. Arabinosyladenine and arabinosyladenine monophosphate, which are phosphorylated to triphosphates by cellular enzymes and inhibit virus synthesis either by blocking the DNA polymerase or by incorporation into viral DNA, require a concentration of only 100 micrograms/ml for the inhibition of the reactivation process. Drugs that are phosphorylated by the virus-induced thymidine kinase, such as acyclovir, arabinosylthymine, bromovinyldeoxyuridine, and three fluorinated pyrimidine nucleosides require the lowest drug concentrations for complete inhibition of virus reactivation in latently infected ganglia explant cultures. Our data suggest that the inhibition of virus reactivation is dependent not only on drug concentration, but also on the number of latently infected neurons in the ganglia.

Differential binding affinities of sugar-modified derivatives of (E)-5-(2-bromovinyl)-2'-deoxyuridine for herpes simplex virus-induced and human cellular deoxythymidine kinases

The affinity of a large number of sugar-modified derivatives of (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) was determined towards deoxythymidine (dThd) kinases (TK) of various origin, i.e. human cytosol and mitochondrial TK, as well as herpes simplex virus (HSV) type 1 and type 2 TK. Substitution at the 3'- and 5'-position had differential effects on the interaction of BVDU with TK from different sources. The binding affinity of the nucleoside analogs for these different TKs was also influenced by the nature of the 5-substituent (2-bromovinyl vs 2- chlorovinyl ). The 5'-azido and 5'-amino derivatives of BVDU showed affinity for HSV-1 TK only and may, therefore, be useful to differentiate HSV-1 TK from all other TKs . There was no stringent correlation between the antiviral effects of the compounds and their binding constants for viral TK, suggesting that phosphorylation by viral TK is an essential but not sufficient factor in determining the antiviral activity of these analogs.

Comparison of properties of woodchuck hepatitis virus and human hepatitis B virus endogenous DNA polymerases

The principal properties of the DNA polymerases of woodchuck hepatitis virus and human hepatitis B virus were compared. The enzymes of both viruses exhibited optimal activities in the same range of pH, ionic strength, and MgCl2 concentration. Like human hepatitis B virus DNA polymerase, the woodchuck hepatitis virus DNA polymerase was strongly inhibited by phosphonoformic acid but not by phosphonoacetic acid and aphidicolin. Similar inhibition patterns for both enzymes were observed with arabinofuranosyl nucleotides (9-beta-D-arabinofuranosyladenine-5'-triphosphate, 1-beta-D-arabinofuranosylcytosine-5'-triphosphate, 1-beta-D-arabinofuranosylthymine-5'-triphosphate) and dideoxythymidine triphosphate, whereas no effect was obtained with corresponding nucleosides. The therapeutic significance of these results and the relevance of the woodchuck as an experimental animal model for the study of human hepatitis B virus infections are discussed.

Thymidine kinase (TK) induction after infection of TK-deficient rabbit cell mutants with bovine herpesvirus type 1 (BHV-1): isolation of TK- BHV-1 mutants

Cytosol thymidine kinase (TK) activity is enhanced at 6 hr after bovine embryo tracheal (EBTr) and rabbit skin fibroblast (RAB-9) cells are infected with the Los Angeles and Cooper strains of bovine herpesvirus type 1 (BHV-1). To learn whether this enhancement resulted from the induction of a virus-specific TK activity, biochemical and genetic studies were carried out. The biochemical experiments demonstrated that: (i) the BHV-1-induced TK activity had a relative disc PAGE mobility (Rm) characteristic of other herpesvirus-encoded TKs and distinctly different from the Rm value of the cytosol TK of host cells; and (ii) the BHV-1-induced TK was significantly more sensitive to competitive inhibition by arabinosylthymine (araT) than the cytosol TKs of EBTr and RAB-9 cells. The genetic experiments entailed the isolation of a bromodeoxyuridine (BrdUrd)-resistant rabbit cell line [RAB(BU)] deficient in cytosol TK activity and of BrdUrd- and araT-resistant BHV-1 mutants. RAB(BU) cells acquired TK activity after they were infected by wild-type, TK+ BHV-1, but not drug-resistant BHV-1 mutants. The experiments strongly suggest that wild-type BHV-1 induces a virus-specific TK activity.

Antiherpes activity of (E)-5-(2-bromovinyl)- and 5-vinyl-1-beta-D-arabinofuranosyluracil and some other 5-substituted uracil arabinosyl nucleosides in two different cell lines

Of a series of 5-substituted 1-beta-D-arabinofuranosyluracil (5-X-araU) analogues, (E)-5-(2-bromovinyl)-araU(BrVaraU) and 5-vinyl-araU (VaraU) were the most potent inhibitors of plaque formation by two herpes simplex virus type 1 (HSV-1) strains in human embryonic lung fibroblast (HELF) cell cultures. They were not only more active than 5-methyl-araU (MaraU, araT) and 5-ethyl-araU (EaraU), but even more than 1000 times more potent than the 5-fluoro, 5-iodo, 5-formyl and 5-trifluoromethyl (FaraU, IaraU, faraU, CF3araU) analogues. BrVaraU and VaraU were superior to 9-(2-hydroxyethoxymethyl)guanine (Acyclovir, ACV) and comparable in potency with 2'-fluoro-5-iodoaracytosine (FIAC) and 2'-fluoro-5-methylarauracil (FMAU). Their anti-HSV-1 potency was surpassed only by (E)-5-(2-bromovinyl)-2'-deoxyuridine (BrVUdR). Surprisingly, in a HSV-1 plaque inhibition assay in African green monkey kidney (Vero) cells, BrVaraU and VaraU were nearly 100 times active or even inactive. In contrast, the antiherpes activity of ACV, FIAC, FMAU and BrVUdR differed only marginally in the two cell lines. The following order of (decreasing) activity against HSV-2 in HELF cells was found: FIAC = FMAU greater than MaraU (araT) greater than ACV greater than VaraU greater than BrVUdR greater than CF3araU greater than IaraU greater than FaraU = Eara U greater than BrVaraU greater than araU greater than faraU. When deoxyribose is replaced by arabinose in 5-X-UdR analogues, a slight increase in anti-HSV-1-77 activity was observed for the 5-vinyl or 5-ethyl substituent, whereas the other 5-X-araU nucleosides were two to more than 100 times less active than their deoxyribosyl counterparts. However, the sugar exchange led to a strong reduction in anti-HSV-2 activity regardless of the 5-substituent.

Relative activities of acyclovir and BW759 against Aujeszky's disease and equine rhinopneumonitis viruses

Compound BW759 (9-[2-hydroxy-1-(hydroxymethyl)ethoxymethyl]guanine) was shown to be about 230 times more active than acyclovir (9-[2-hydroxyethoxymethyl]guanine) (ACV) against Equid herpesvirus type 1 infection in Syrian hamsters and was more effective against Aujeszky's disease in mice. The therapeutic superiority of BW759 over ACV was greater than expected from quantitative inhibitory results in tissue culture with these viruses. When administered to hamsters at dose rates sufficient to prevent any Equid herpesvirus type 1-induced mortality (100 mg of ACV per kg per day; 3 mg of BW759 per kg per day), BW759 inhibited viral multiplication, as judged by histopathological observations, clinical chemistry, and liver virus concentrations, to a greater extent than ACV. Compound BW759 was particularly effective when administered via the oral route. The reasons for the superiority of BW759 over ACV remain to be elucidated.

Inhibition of glycosylation of bovine herpesvirus 1 glycoproteins by the thymidine analog (E)-5-(2 Bromovinyl)-2'-deoxyuridine

(E)-5-(2-Bromovinyl)-2'-deoxyuridine (BVdU) was phosphorylated by the bovine herpesvirus 1 (BHV-1)-induced thymidine kinase and subsequently incorporated into viral DNA, resulting in DNA that was more dense than DNA from untreated cells. Incorporation of the drug did not result in the termination of replicating BHV-1 DNA molecules since radioactively labeled DNA synthesized in drug-treated and untreated cells sedimented at similar rates in alkaline sucrose gradients. No differences were observed in the electrophoretic mobility of [35S]methionine-labeled viral polypeptides synthesized in treated and untreated cells, although [3H]glucosamine-labeled viral glycoproteins synthesized in treated cells were of a lower molecular weight than those in untreated cells. In BVdU-treated cells, unlike untreated cells, immature neutral and basic precursors of the mature viral glycoproteins accumulated. Although BVdU-treated and untreated cells contained similar amounts of virus, very little virus was released into the culture supernatant from BVdU-treated cells. Our results suggest that BVdU partially inhibits the glycosylation of BHV-1 glycoproteins. BVdU-sensitive glycosylation, however, is not necessary for expression of these glycoproteins on the surface of infected cells since the glycoproteins could be labeled on intact cells with 125I and because BVdU-treated cells remained sensitive to antibody-dependent, cell-mediated cytotoxity mediated by anti-BHV-1 serum. The phosphorylation of BVdU was a prerequisite for its effect on glycosylation since the glycoproteins of a thymidine kinase-deficient mutant of BHV-1 were not affected.

Susceptibility of phosphonoformic acid-resistant herpes simplex virus variants to arabinosylnucleosides and aphidicolin

A plaque-reduction assay was used to examine the susceptibility of five phosphonoformic acid-resistant variants of herpes simplex virus type 1 to arabinosylnucleosides and aphidicolin. These viruses were cross-resistant to arabinosylhypoxanthine and to arabinosyladenine when tested in the absence of deoxycoformycin, a deaminase inhibitor. In the presence of deoxycoformycin, no cross-resistance between arabinosyladenine and phosphonoformic acid was observed. The two variants tested were cross-resistant to arabinosylthymine, and all five variants were collaterally susceptible to aphidicolin inhibition.

Effect of arabinofuranosylthymine on the replication of Epstein-Barr virus and relationship with a new induced thymidine kinase activity

1-beta-D-Arabinofuranosylthymine (araT) is a selective inhibitor of Epstein-Barr virus replication induced in both thymidine kinase (TK)-negative (TK-) and TK+ variants of the lymphoid cell line P3HR-I. This analog has no effect on the growth of noninduced cells (T. Ooka and A. Calender, Virology 104:219-223, 1980). The synthesis of early antigens is not affected by the analog, whereas that of late viral capsid antigens is completely inhibited, as demonstrated by the indirect immunofluorescence technique; kinetic reassociation experiments have also shown that araT strongly inhibits replication of viral DNA. Phosphorylation of the tritiated form of the analog ([3H]araT) was analyzed by thin-layer chromatography in cultures of control and induced cells, and the results demonstrated that only induced cells can convert the analog to the triphosphate form. These results indicate that the selective effect of araT in induced cells is probably related to a new virally induced TK activity. Preliminary characterization of this new activity has shown that it is able to phosphorylate the analog specifically, whereas cellular TKs cannot. araTTP, a final phosphorylation product of araT, is a potent inhibitor of Epstein-Barr virus-specific DNA polymerase, suggesting a possible inhibitory action of this product on Epstein-Barr virus replication.

Replication of thymidine kinase deficient herpes simplex virus type 1 in neuronal cell culture: infection of the PC 12 cell

Replication of a thymidine kinase deficient (TK-) mutant of herpes simplex virus type 1 (HSV-1) was compared to replication of its parental TK+ strain in the PC 12 cell. This is a cell which ceases cell division and undergoes neuron-like morphological and physiological differentiation in the presence of nerve growth factor (NGF). No difference between mutant and parental strain replication was detected either when these cells were infected in the proliferative state or while maintained under the influence of NGF. Neither viral TK nor enhanced cellular TK activity was detected during TK- HSV-1 replication, which proceeded in the presence of selective antiviral drugs that inhibited TK+ HSV-1 viral replication. Moreover, thymidylate synthetase was inhibited early in TK- infection, and reutilization of thymine nucleotides derived from degraded cellular DNA was not detected. Under the conditions of these in vitro studies, increased production of dTTP as a result of enhanced TK activity did not appear to be rate-limiting, despite the non-dividing "differentiated" state of the PC 12 cell.

Comparison of the in vitro and in vivo anti-herpes activities of 1-beta-D-arabinofuranosylthymine and its 5'-monophosphate

In vitro and in vivo anti-herpes activities of 1-beta-D-arabinofuranosylthymine 5'-monophosphate (ara-TMP) were compared with those of 1-beta-D-arabinofuranosylthymine (ara-T). On a molar basis ara-TMP was almost as active as ara-T against six strains of herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) as monitored by a cytopathogenicity-inhibition and a plaque reduction assay in human embryonic lung fibroblast cells. When tested against experimental encephalitis in mice inoculated intracerebrally with HSV-1, intraperitoneal or intravenous treatment with 150 mg/kg/day of ara-TMP or 100 mg/kg/day of ara-T, for 5 days was effective in increasing in the mean survival time of mice. For a single dose of ara-TMP, intravenous administration was more effective than intraperitoneal or oral administration. However, oral administration of ara-T was the most effective of the treatment regimens used. Substantial plasma levels of ara-T were detected for a longer time after oral administration of ara-T than after intravenous administration of ara-TMP or ara-T, suggesting that the efficacy of oral administration of ara-T may be correlated with the maintenance of the substantial blood drug levels.

Capacity of deoxycytidine to selectively antagonize cytotoxicity of 5-halogenated analogs of deoxycytidine without loss of antiherpetic activity

Enzyme kinetic studies from this laboratory (M. Dobersen and S. Greer, Biochemistry 17:920-928, 1978) suggested that deoxycytidine could antagonize the toxicity of 5-halogenated analogs of deoxycytidine without interfering with their antiviral activity. Antagonism by deoxycytidine of the toxicity of 5-chlorodeoxycytidine without impairing its anti-herpes simplex virus type 2 activity is demonstrated in the present studies. Tetrahydrouridine, an inhibitor of cytidine deaminase, was utilized. The high Km for deoxycytidine (0.6 mM) with respect to the herpes pyrimidine nucleoside kinase as compared with the low Km for 5-chlorodeoxycytidine (1.1 microM) accounts for the absence of antagonism of the antiviral activity. The high Km for 5-chlorodeoxycytidine (56 microM) as compared with the low Km of deoxycytidine (2 microM) with respect to mammalian deoxycytidine kinase accounts, in great part, for the antagonism of toxicity. In addition, antagonism of toxicity by deoxycytidine is the result of factors other than the kinetic parameters of nucleoside kinases, as indicated by its antagonism of the cytotoxicity of 5-chlorodeoxyuridine. This may be attributed to replenishment of low dCTP pools, diminished because of effector inhibition of ribonucleoside diphosphate reductase by Cl-dUTP. Resistance of the herpes-encoded enzymes to effector control may also play a role in the selective antagonism. Cell culture studies with high concentrations of tetrahydrouridine and 2'-deoxytetrahydrouridine suggest that competition by deoxycytidine for deaminases may not play a major role. The fact that deoxycytidine antagonizes the toxicity of chlorodeoxyuridine also argues against competition for the deaminases as a major reason for its effect. Limited studies with a topical herpes simplex virus type 2 infection system indicate heightened efficacy of 5-chlorodeoxycytidine (and tetrahydrouridine) when deoxycytidine is coadministered. The concepts of selective antagonism of a chemotherapeutic agent derived from these studies may be applied to other approaches that extent beyond viral chemotherapy.

Pathogenesis of experimental skin infections induced by drug-resistant herpes simplex virus mutants

The comparative analysis of the pathogenicity of a parental herpes simplex virus type 1 strain and its phosphonoacetic acid (PAA)-resistant and acyclovir (ACV)-resistant mutants showed marked differences among them. After orofacial skin inoculation of hairless mice the parental and PAA-resistant viruses were detected during the first 4 days after infection at high and increasing titers in the trigeminal ganglia; the ACV-resistant mutant was present at low and decreasing titers in the ganglia. Severe and slow-healing skin lesions were produced by the parental and PAA-resistant viruses; mild and rapidly healing lesions were produced by the ACV-resistant mutant. Virus titers in ganglia and the intensity of skin lesions were related to the virus dose used in the primary infection. Latent infections became established in trigeminal ganglia of mice inoculated with 10(6.0) plaque-forming units of the parental or PAA-resistant virus; no latent infections were detected in ganglia of mice inoculated with 10(7.0) plaque-forming units of the ACV-resistant mutant. Serum antibody titers attained similar values 4 weeks after primary infection with both mutants and the parental virus. Mice infected with the ACV-resistant mutant were reinfected with the parental and PAA-resistant viruses; the degree of protection against development of skin lesions, mortality, and latency was related to the dose of ACV-resistant virus used in the primary infection. Mortality was prevented by a dose of 10(6.0) plaque-forming units, skin lesions were prevented by a dose of 10(6.5) plaque-forming units, and latency was prevented by a dose of 10(7.0) plaque-forming units of the ACV-resistant mutant. Protection against reinfection with the PAA-resistant mutant was achieved with lower doses than protection against the parental virus. Serum antibody titers showed a 4- to 15-fold increase after reinfection. The results suggest that the ACV-resistant, latency-negative mutant has many attributes of a live attenuated herpes simplex virus vaccine.

Differential activity of potential antiviral nucleoside analogs on herpes simplex virus-induced and human cellular thymidine kinases

Potential antiviral nucleoside analogs 1-beta-D-arabinofuranosylthymine, the 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-nucleosides of -5-methyluracil, -5-iodouracil, -5-methylcytosine, -5-iodocytosine, and -E-5-(2-bromovinyl)uracil, E-5-(2-bromovinyl)-2'-deoxyuridine, E-5-(2-bromovinyl)-1-beta-D-arabinofuranosyluracil, and 9-(2-hydroxyethyoxymethyl)guanine were studied to compare their phosphorylation rates relative to thymidine by purified thymidine kinases from human and herpes simplex virus sources. Most of these analogs are capable of being phosphorylated by both human and viral enzymes. On the assumption that inhibition constants (Ki) reflect binding affinity, Ki values were determined for these analogs with the same thymidine kinases. In general, these analogs have a greater affinity for the viral enzymes. The amount of the analogs phosphorylated to the monophosphate form, which is presumably necessary to produce cytotoxic effects, was determined by the combined effects of phosphorylation rates and binding affinities. All of these analogs act as preferential substrates for the viral thymidine kinases at low concentrations, which may be one of the main reasons for their selective antiviral action.

On the mechanism of selective inhibition of herpesvirus replication by (E)-5-(2-bromovinyl)-2'-deoxyuridine

Bromovinyldeoxyuridine (BVdUrd) is a potent antiherpesvirus compound with low cytotoxicity. To gain an insight into its selectivity and mechanism of inhibition, we chemically synthesized the 5'-triphosphate of BVdUrd, BVdUTP, and tested its effect on the activities of DNA polymerases [DNA nucleotidyltransferase (DNA directed), EC 2.7.7.7] of two herpesviruses--i.e., herpes simplex virus type 1 (HSV-1) and Epstein-Barr virus (EBV)--as well as cellular DNA polymerases alpha, beta, and gamma. The effects on the DNA polymerases were determined under assay conditions optimal for the individual polymerases. We found that the BVdUTP was considerably more inhibityory to the utilization of dTTP by the HSV-1 DNA polymerase then by the cellular DNA polymerases. For instance, as little as 1 microM BVdUTP inhibited the utilization of dTTP by HSV-1 DNA polymerase 50%, whereas the same concentration inhibited the DNA polymerase alpha and the DNA polymerase beta activities only 9% and 3%, respectively. The BVdUTP inhibited DNA synthesis by competing with the natural substrate, dTTP. The Km for dTTP and the Ki for the BVdUTP of the HSV-1 DNA polymerase were 0.66 and 0.25 microM, respectively. Kinetic analyses with the DNA polymerases alpha and beta and the EBV DNA polymerase also reflected a similar difference in sensitivity between the HSV-1 enzyme and other enzymes. Increasing the concentration of either the DNA template or the enzyme in the reaction mixture did not bring about a significant change in the extent of inhibition. Preincubation of the inhibitor with the enzyme was not necessary for inhibition. Studies on time course of inhibition revealed that the compound is inhibitory even after the initiation of DNA synthesis. These studies indicate that the ability of BVdUTP to preferentially inhibit the HSV-1 DNA polymerase may contribute towards its selective inhibition of the viral DNA replication in infected cells.

Inhibition of mouse LM cell replication by trifluorothymidine: role of cytosolic deoxythymidine kinase

The effects of trifluorothymidine (5-trifluoromethyl-2'-deoxyuridine, F3dThd) on the replication of three mouse cell lines, LM929, Ltk- (and LM929 derivative devoid of cytosolic deoxythymidine [dThd] kinase activity), and Ltk- c139 (a Ltk- derivative which expresses herpes simplex virus type 1-specified dThd kinase subsequent to biochemical transformation with ultraviolet-irradiated herpes simplex virus type 1), have been investigated. Complete inhibition of Ltk- cell growth required a 10,000-fold higher concentration of F3dThd (1.0 mM) than was required to completely inhibit LM929 and Ltk- c139 cell growth. The plating efficiency of exponentially dividing Ltk- cells after exposure to F3dThd (10 microM) for 24 h was 63% as compared to 3% for exponentially dividing LM929 cells. Stationary LM929 cells (confluent cultures held for a 6-day period in serum-reduced medium) with reduced dThd kinase specific activity and deoxyribonucleic acid biosynthesis level exhibited a plating efficiency similar to that of exponentially dividing Ltk- cells after exposure to F3Thd (1.0 mM) for 24 h. In addition, treatment of exponentially dividing LM929 and Ltk- cells with F3dThd (10 microM) for 24 h resulted in approximately an 80% and 25% reduction in deoxyribonucleic acid biosynthesis, respectively. These data indicated a requirement for cytosolic dThd kinase in the expression of F3dThd-induced cytotoxicity. F3dThd was shown to be a linear competitive inhibitor with respect to dThd for affinity-purified LM929 cytosolic dThd kinase. The Km(app) for dThd and Ki(app) for F3dThd with the cytosolic dThd kinase were 2.4 and 3.8 microM, respectively.

Tetrahydrouridine specifically facilitates deoxycytidine incorporation into herpes simplex virus DNA

As reported by Jamieson and Subak-Sharpe (J. Gen. Virol. 31:303-313, 1976), exogenous deoxycytidine is very poorly incorporated into herpes simplex virus DNA. Here it is shown that this incorporation was dramatically increased in the presence of tetrahydrouridine (THU), a specific inhibitor of cytidine-deoxycytidine deaminase. Thus, the exclusion of deoxycytidine from herpes simplex virus DNA probably results from massive degradation by the deaminase, which is consistent with the observation that in the absence of THU, most of the nucleotides formed from exogenous deoxycytidine are dUMP. The effect of tHU upon deoxycytidine incorporation was specific for herpes simplex virus-infected cells; THU did not increase deoxycytidine incorporation into DNA of uninfected cells. Therefore, one might expect THU to enhance the antiviral activity of 1-beta-D-arabinofuranasylcytosine since this analog is also readily deaminated. However, THU increased both the antiviral activity and the cell toxicity only slightly and to about the same extent. Therefore, the metabolism of 1-beta-D-arabnofuranosylcytosine is different from that of deoxycytidine in herpes simplex virus-infected cells.

Experimental skin infection with an acyclovir resistant herpes simplex virus mutant: response to antiviral treatment and protection against reinfection

Skin infections induced in hairless mice with an Acyclovir resistant herpes simplex virus (HSV) mutant were not followed by the death of the animals, and the survivors had no evidence of latent infections in their sensory ganglia. However, mutant virus was detected in the ganglia during the acute phase of the infection. Mice inoculated with the mutant were fully protected against the fatal outcome of the infection when subsequently challenged with the relatively pathogenic parental virus. In addition the frequency of latent infections established after challenge was significantly reduced. Phosphonoacetic acid treatment of the primary mutant-induced infection abolished the protection against reinfection with parental virus. Acyclovir treatment of the primary infection with the mutant virus did not affect the protection against reinfection with parental virus. The results indicate that drug-resistant, latency-negative, HSV mutants are a promising starting point for the development of an attenuated HSV vaccine.

Antiherpesviral activity and inhibitory action on cell growth of 5-alkenyl derivatives of 1-beta D-arabinofuranosyluracil

Antiherpesviral activity of 5-vinyl-1-beta-D-arabinofuranosyluracil was as high as that of 1-beta-D-arabinofuranosylthymine, whereas the former was less inhibitory to cell growth than the latter. 5-Propenyl- and 5-butenyl-1-beta-D-arabinofuranosyluracil were less active than 5-vinyl-1-beta-D-arabinofuranosyluracil.

Biochemical characterization of equine herpesvirus type 3-induced deoxythymidine kinase purified from lytically infected horse embryo dermal fibroblasts

Infection of horse KyED cells with equine herpesvirus type 3 (EHV-3) resulted in a sevenfold increase in cytosol deoxythymidine kinase (dTK) activity. The EHV-3 dTK was purified from KyED cytosol dTK by affinity chromatography on deoxythymidine-Sepharose and characterized with respect to its electrophoretic mobility, molecular weight, substrate specificity, phosphate donor specificity, and immunological specificity. The purified EHV-3 dTK migrated in polyacrylamide gels with an Rf of 0.30 and sedimented in glycerol gradients with an S value of 5.13, corresponding to a molecular weight of 83,000. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis yielded a single band with a molecular weight of 38,000 to 40,000. Antiserum prepared against the EHV-3 dTK induced in KyED cells neutralized the EHV-3-induced enzyme activity but not the dTK purified from uninfected cells. EHV-3 dTK was less sensitive to feedback inhibition to dTTP and had a lower Ki for the antiviral compound 1-beta-D-arabinofuranyosylthymine and a lower Km for the substrate deoxythymidine. These results indicate that infection of cells with EHV-3 results in the induction of a new virus-coded dTK activity which meets the criteria of Jensen for an evolutionary primitive enzyme.