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.

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.

Synthesis and antiviral activity of water-soluble esters of acyclovir [9-[(2-hydroxyethoxy)methyl]guanine]

Several water-soluble ester derivatives of acyclovir [9-[(2-hydroxyethoxy)methyl]guanine], i.e., the 2'-O-glycyl-, 2'-O-alpha-alanyl-, 2'-O-beta-alanyl- and 2'-O-3-carboxypropionyl esters, were synthesized and evaluated for their antiviral activity in cell culture. The compounds were all prepared directly from acyclovir by application of the usual esterification methods with the appropriate acyl precursors and isolated as their hydrochloride or sodium salts. When assayed in primary rabbit kidney cell cultures against various herpes simplex virus type 1 and type 2 strains, the four acyclovir esters proved almost as active as acyclovir itself, suggesting that they were readily hydrolyzed to release the parent compound.

Synergism among BIOLF-62, phosphonoformate, and other antiherpetic compounds

9-[[2-Hydroxy-1-(hydroxymethyl)ethoxy]methyl]guanine (BIOLF-62) is highly synergistic with either phosphonoformate or phosphonoacetate when used in combination against herpes simplex virus types 1 and 2 in vitro. Acycloguanosine did not show significant synergism with these two compounds. Bromovinyldeoxyuridine and phosphonoformate were highly synergistic against herpes simplex virus type 2, but not against type 1.

Acyclovir in the treatment of herpetic keratitis

Fourty-three eyes with active dendritic keratitis, nearly one third of which had failed to respond to other antiviral agents, were treated with acyclovir with or without preceding debridement. The patients were randomly selected. No statistical difference could be demonstrated between the 2 groups in terms of rate of healing or in efficacy of cure. Acyclovir also seemed to be effective in stromal corneal lesions. There were only minor side effects.

Mode of action of acyclovir triphosphate on herpesviral and cellular DNA polymerases

The effect of 5'-triphosphate of acyclovir (ACV) on DNA polymerases of two human herpes-viruses, herpes simplex virus type-1 (HSV-1) and Epstein-Barr virus (EBV) as well as human cellular DNA polymerases alpha and beta has been examined. Of the enzymes tested, HSV-1 DNA polymerase was the most sensitive to inhibition by acyclovir triphosphate (ACVTP). The EBV DNA polymerase and DNA polymerase beta were less sensitive. ACVTP inhibition was competitive with dGTP with Ki values of 0.03, 0.15, 9.8 and 11.9 microM for HSV-1 DNA polymerase, DNA polymerase alpha, EBV DNA polymerase and DNA polymerase beta, respectively. Substituting a synthetic primer template (dG) approximately 15 x (dC)n for activated DNA template did not alter the pattern of inhibition. In a time course experiment, addition of ACVTP instead of dGTP did not increase DNA synthesis and it appeared to act as a chain terminator in DNA replication catalyzed by either HSV-1 DNA polymerase or DNA polymerase alpha. Although EBV DNA polymerase was less sensitive to ACVTP inhibition, the nucleoside analog itself was inhibitory to EB virus production by P3HR1 cell line as determined by a reduction in the percentage of cells expressing virus capsid antigen (VCA). On day 4, ACV at 10 and 25 micrograms/ml reduced the cell growth by 10% and 32%, respectively, while it reduced the VCA-positive cells by 80% and 84%, respectively. These results indicate that inhibition of EBV DNA polymerase activity by ACVTP may not be the primary mechanism responsible for ACV inhibition of EBV replication.

Purine acyclic nucleosides. Nitrogen isosteres of 9-[(2-hydroxyethoxy)methyl]guanine as candidate antivirals

A number of nitrogen analogues of 9-[(2-hydroxyethoxy)methyl]guanine [acylovir, Zovirax] containing amine functions in the side chain were synthesized and tested for antiviral activity. These purine acyclic nucleosides were prepared by reaction of tris(trimethylsilyl)guanine or 2,6-diaminopurine sodium salt with the chloromethyl ethers prepared from N-(2-hydroxyethyl)phthalimide, N-[2-(2-hydroxyethoxy)ethyl]phthalimide, or N-(2-hydroxyethyl)oxazolidin-2-one to give the N-blocked intermediates 5-8. Deprotection with hydrazine or by alkaline hydrolysis gave 9-[(2-aminoethoxy)methyl]guanine (9), 9-[(2-aminoethoxy)methyl]-2,6-diaminopurine (10), 9-[2(2-aminoethoxy]ethoxymethyl]guanine (11), and 9-[[2-[(2-hydroxyethyl)amino]ethoxy]methyl]guanine (12). When tested against herpes simplex virus type 1, only 9 was active with an IC50 = 8 microM. Little or no activity was observed against a range of other DNA and RNA viruses.

Inhibition of purified human and herpes simplex virus-induced DNA polymerases by 9-(2-hydroxyethoxymethyl)guanine triphosphate. Effects on primer-template function

The inhibition of highly purified herpes simplex virus (HSV)-induced and host cell DNA polymerases by the triphosphate form of 9-(2-hydroxyethoxymethyl)guanine (acyclovir; acycloguanosine) was examined. Acyclovir triphosphate (acyclo-GTP) competitively inhibited the incorporation of dGMP into DNA, catalyzed by HSV DNA polymerase; apparent Km and Ki values of dGTP and acyclo-GTP were 0.15 microM and 0.003 microM, respectively. HeLa DNA polymerase alpha was also competitively inhibited; Km and Ki values of dGTP and acyclo-GTP were 1.2 microM and 0.18 microM, respectively. In contrast, HeLa DNA polymerase beta was insensitive to the analogue. The "limited" DNA synthesis observed when dGTP was omitted from HSV or alpha DNA polymerase reactions was inhibited by acyclo-GTP in a concentration-dependent manner. Prior incubation of activated DNA, acyclo-GTP, and DNA polymerase (alpha or HSV resulted in a marked decrease in the utilization of the primer-template in subsequent DNA polymerase reactions. This decreased ability of preincubated primer-templates to support DNA synthesis was dependent on acyclo-GTP, enzyme concentration, and the time of prior incubation. Acyclo-GMP-terminated DNA was found to inhibit HSV DNA polymerase-catalyzed DNA synthesis. Kinetic experiments with variable concentrations of activated DNA and fixed concentrations of acyclo-GMP-terminated DNA revealed a noncompetitive inhibition of HSV-1 DNA polymerase. The apparent Km of 3'-hydroxyl termini was 1.1 X 10(-7) M, the Kii and Kis of acyclo-GMP termini in activated DNA were 8.8 X 10(-8) M and 2.1 X 10(-9) M, respectively. Finally, 14C-labeled acyclo-GMP residues incorporated into activated DNA by HSV-1 DNA polymerase could not be excised by the polymerase-associated 3',5'-exonuclease activity.

Inhibition of cellular alpha and virally induced deoxyribonucleic acid polymerases by the triphosphate of acyclovir

The effect of the triphosphate of 9-(2-hydroxyethoxymethyl)guanine (acyclovir, acycloguanosine) on cellular alpha deoxyribonucleic acid (DNA) polymerases (DNA nucleotidyltransferases), DNA polymerases of several members of the herpes group, vaccinia virus DNA polymerase, and Friend leukemia virus ribonucleic acid-dependent DNA polymerase was examined. Several viruses, which were found to be susceptible to acyclovir, were found to induce DNA polymerases which were sensitive to acyclovir triphosphate (acyclo-GTP). Human cytomegalovirus and the H29R strain of herpes simplex virus type 1, however, were found to be relatively insusceptible to acyclovir, even though their induced DNA polymerases were inhibited by low concentrations of acyclo-GTP. The amount of acyclovir anabolized to acyclo-GTP was significantly lower for human cytomegalovirus and H29R than for the more susceptible viruses. Vaccinia virus and Friend leukemia virus induced DNA polymerases which were insensitive to inhibition by low concentrations of acyclo-GTP, anabolized little acyclovir to acyclo-GTP, and were found to be insensitive to inhibition by acyclovir. Uninfected WI-38 cells were not susceptible to inhibition by acyclovir, anabolized little acyclovir to acyclo-GTP, and had an alpha DNA polymerase which was insensitive to inhibition by low concentrations of acyclo-GTP.

Induction of Epstein-Barr virus-associated DNA polymerase by 12-O-tetradecanoylphorbol-13-acetate. Purification and characterization

The diterpene ester promoter of mouse skin tumors, 12-O-tetradecanoylphorbol-13-acetate (TPA), efficiently induces Epstein-Barr virus (EBV)-associated DNA polymerase (DNA nucleotidyltransferase) activity in the EBV-producing lymphoblastoid cell line, P3HR-1. With the use of intervent dilution chromatography followed by sequential DEAE-cellulose and phosphocellulose column chromatography, the virus-associated enzyme has been isolated and purified 300-fold. The partially purified EBV DNA polymerase activity could be distinguished from cellular polymerases by its activation with salt and its degree of sensitivity to N-ethylmaleimide and phosphonoacetic acid. The enzyme showed maximum activity for copying activated calf thymus DNA in the presence of 100 mM ammonium sulfate. In the absence of salt, the enzyme utilized with high efficiency deoxyoligomer-homopolymer templates, but failed to copy poly(rA) . oligo(dT)10 and oligo(dT)10, showing that the enzyme had properties distinct from DNA polymerase gamma, reverse transcriptase, and terminal deoxynucleotidyltransferase. The partially purified enzyme is strongly inhibited by acyclovir triphosphate and thus has properties similar to herpes simplex virus DNA polymerase.