Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.7.7 (DNA polymerase)
17,007 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Acyclovir [9-(2-hydroxyethoxymethyl)guanine] triphosphate inhibits Epstein-Barr virus (EBV)-associated DNA polymerase (DNA nucleotidyltransferase; EC 2.7.7.7) to a greater extent than it inhibits host alpha and beta DNA polymerases. The affinity of the compound for viral polymerase is 100-fold higher than for alpha-polymerase. The extent of inhibition is dependent upon the base composition of the template-primer. The inhibition is prevented by increasing concentrations of deoxyguanosine triphosphate. The EBV-associated DNA polymerase reaction in the presence of the inhibitor, although depressed, proceeds at a linear rate over a long period of time. In contrast, the reaction of Escherichia coli DNA polymerase I in the presence of 2',3'-dideoxythymidine 5'-triphosphate, a DNA chain terminator, levels off after initial linearity. Preincubation of acyclovir triphosphate with DNA and enzyme does not increase its inhibitory activity. The virus-producing cell line P3HRF-1 consistently shows reduced viral genome numbers and viral capsid antigen on prolonged exposure to acyclovir. The number of EBV genomes returns to the control level when the cells are grown in drug-free medium. The results suggest that a competitive mechanism is the major mode of acyclovir inhibition of EBV replication.
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PMID:Acyclovir inhibition of Epstein-Barr virus replication. 625 61

Acyclovir (9-[2-hydroxyethoxymethyl]guanine or ACV) is a nucleoside analogue with considerable potential for the treatment of herpes simplex virus (HSV) infections in man. Two virus-coded enzymes are important in the mechanism of action of this drug: thymidine kinase (TK) which initiates its activation by converting it to the monophosphate and DNA polymerase whose action is inhibited by ACV triphosphate. Changes in either gene may confer resistance, but all reported mutations in the TK gene have resulted in failure of the resistant virus to induce appreciable levels of the enzyme. Such TK- mutants arise readily in tissue culture systems where the enzyme is non-essential for virus replication, but in animals they show considerably reduced pathogenicity and neurovirulence. We now describe the isolation of a resistant mutant which induces a TK of altered substrate specificity and we show that this virus retains pathogenicity for mice with only a slight attenuation of neurovirulence.
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PMID:Altered substrate specificity of herpes simplex virus thymidine kinase confers acyclovir-resistance. 625 50

Previous studies of herpesvirus infections have indicated that a virus-specified thymidine kinase is required for the initial phosphorylation of acyclovir [acycloguanosine or 9-(2-hydroxyethoxymethyl)guanine] in the formation of acycloguanosine triphosphate. The latter compound accumulates in infected cells and competitively inhibits the viral DNA polymerase. We found that mouse cytomegalovirus, which does not express a thymidine kinase, was sensitive to the antiviral effects of acyclovir at a 50% inhibitory dose of approximately 0.23 microM. Acyclovir was equally effective against mouse cytomegalovirus in normal 3T3 cells and in 3T3 cells deficient in cellular thymidine kinase. Furthermore, the activity of acyclovir could not be reversed by excess thymidine, which easily reversed the antiviral activity of acyclovir against herpes simplex virus. Using a high-pressure liquid chromatography technique that easily detected acycloguanosine triphosphate in cells infected with herpes simplex virus, we could not detect acycloguanosine triphosphate in mouse cytomegalovirus-infected cells. These experiments demonstrated that the activity of acyclovir against mouse cytomegalovirus is not dependent on a thymidine phosphorylation pathway. Additional experiments are underway to determine whether acycloguanosine triphosphate is produced by another pathway in concentrations sufficient to inhibit mouse cytomegalovirus DNA polymerase.
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PMID:Thymidine kinase not required for antiviral activity of acyclovir against mouse cytomegalovirus. 627 Mar 57

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.
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PMID:Inhibition of purified human and herpes simplex virus-induced DNA polymerases by 9-(2-hydroxyethoxymethyl)guanine triphosphate. Effects on primer-template function. 627 50

Acyclovir [9-(2-hydroxyethoxymethyl)guanine] inhibits Epstein-Barr virus (EBV) replication in lymphoblastoid cells at concentrations nontoxic to cellular growth. The mode of action of the drug against EBV differs from the mechanism described in herpes simplex virus systems. Due to the absence of virus-specified thymidine kinase, the drug is poorly phosphorylated in EBV-infected cells. The extent of monophosphorylation is similar both in mock-infected and EBV-infected cells. Despite weak phosphorylation of the drug, the replication of linear EBV DNA is inhibited due to exquisite sensitivity of the viral DNA polymerase. Activation of acyclovir does not require phosphorylation by virus-specified thymidine kinase, inhibition of different herpes-group viruses depends on three variable factors: degree of phosphorylation, cellular metabolism of the drug, and degree of sensitivity of the viral polymerase. Interaction of acyclovir-triphosphate with EBV DNA polymerase is reversible. Cells infected with EBV and treated with acyclovir resume virus replication following removal of the drug even after long exposure. Acyclovir inhibits replication of linear genomes and stops production of virus, but has no effect on latent cellular infection. These results lead us to predict that acyclovir will suppress, but not cure, EBV infection.
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PMID:Perspectives on interactions of acyclovir with Epstein-Barr and other herpes viruses. 628 10

Acyclovir, an acrylic purine nucleoside analog, is a highly potent inhibitor of herpes simplex virus (HSV), types 1 and 2, and varicella zoster virus, and has extremely low toxicity for the normal host cells. This selectivity is due to the ability of these viruses to code for a viral thymidine kinase capable of phosphorylating acyclovir to a monophosphate; this capability is essentially absent in uninfected cells. The acyclovir monophosphate (acyclo-GMP) is subsequently converted to acyclovir triphosphate (acyclo-GTP) by cellular enzymes. Acyclo-GTP persists in HSV-infected cells for many hours after acyclovir is removed from the medium. The amounts of acyclo-GTP formed in HSV-infected cells are 40 to 100 times greater than in uninfected Vero cells. Acyclo-GTP acts as a more potent inhibitor of the viral DNA polymerases than of the cellular polymerases. The DNA polymerases of HSV-1 and HSV-2 also use acyclo-GTP as a substrate and incorporate acyclo-GMP into the DNA primer-template to a much greater extent than do the cellular enzymes. The viral DNA polymerase binds strongly to the acyclo-GMP-terminated template, and in thereby inactivated.
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PMID:Mechanism of action and selectivity of acyclovir. 628 36

Acyclovir (ACV) has been shown to inhibit the replication of herpes simplex virus (HSV) in vitro. We examined a wide variety of HSV clinical isolates for the presence of naturally occurring ACV-resistant (ACVr) variants. Although the ACV doses that inhibited 50% of these isolates were within the range of doses inhibiting 50% of the ACV-susceptible wild-type strains, we successfully isolated variants resistant to high ACV concentrations (25 to 75 microM) from each virion population even in the absence of prior drug exposure. Furthermore, we demonstrated, by fluctuation analysis of two encephalitis strains, that the ACVr variants were clonally distributed in the virus populations before exposure to ACV and did not result from rapid adaptation to ACV. All variants isolated after a single exposure to a high dose of ACV were true ACVr variants, as demonstrated by their plating efficiencies in the presence of ACV. We found that 36 and 50% of the ACVr variants of the two strains examined in detail displayed plating efficiencies in phosphonoacetic acid of greater than 0.1, possibly indicating that many of the ACVr variants contained alterations in the DNA polymerase gene locus. Because the distribution of ACVr variants in natural populations is relatively high (10(-4), these results suggest that selection of ACVr strains during ACV therapy is possible.
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PMID:Herpes simplex virus variants restraint to high concentrations of acyclovir exist in clinical isolates. 628 42

Acyclovir, the new virucidal drug recently approved by the Food and Drug Administration for the treatment of herpes simplex virus (HSV), is the first available effective drug to treat such infections. Acyclovir boasts activity against four of the five major herpes-group viruses, including herpes simplex (types 1 and 2), varicella-zoster, and Epstein-Barr. The drug, phosphorylated preferentially in viral cells, exclusively attacks infected cells possessing virus-specific DNA polymerase, giving acyclovir low toxicity coupled with high efficacy. Problems of renal toxicity and viral resistance now dampen some of the initial expectations. Present-day research continues to reveal insights into the mechanism and action of acyclovir.
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PMID:Acyclovir. 630 47

Acyclovir (acycloguanosine) is a new antiviral compound with activity against certain herpes viruses. Acyclovir is phosphorylated preferentially in virus-infected cells into its active form, acyclovir triphosphate, an inhibitor of viral-induced DNA polymerase. Acyclovir, which possesses an acyclic carbohydrate moiety, also causes premature DNA chain termination. Acyclovir has shown clinical activity against herpes simplex virus (HSV) types 1 and 2 and varicella zoster virus (VZV), but its usefulness in cytomegalovirus, Epstein-Barr virus, and chronic hepatitis B infections requires further study. In randomized clinical trials of infections caused by HSV and VZV, intravenous acyclovir has been shown to shorten the duration of viral shedding and lesion pain and hasten the resolution of skin lesions, with minimal toxicity.
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PMID:The clinical use of intravenous acyclovir. 631 3

Acyclovir, 9-(2-hydroxyethoxymethyl)guanine, is an acyclic nucleoside analogue which has a high activity and selectivity for herpes viruses, particularly herpes simplex viruses types 1 and 2 and varicella zoster virus. This selectivity is due to the initial activation of the drug by phosphorylation by a herpes virus-specified thymidine kinase. Normal cellular enzymes do not phosphorylate acyclovir to any significant degree. Acyclovir monophosphate is subsequently converted to a triphosphate which is a more potent inhibitor of herpes virus DNA polymerases than of cellular DNA polymerases. The relationship between the amount of acyclovir triphosphate formed and its inhibition constant (Ki) for the particular viral or cellular DNA polymerase is predictive of the inhibitory activity of acyclovir on DNA replication.
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PMID:The biochemistry and mechanism of action of acyclovir. 631


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