guanosine-triphosphate and acyclovir-triphosphate

The triphosphates of the antiherpesvirus acyclic guanosine analogs 9-[4-hydroxy-2(hydroxymethyl)butyl] guanine (2HM-HBG), 9-(2-hydroxyethoxymethyl)guanine (acyclovir [ACV]), and 9-(3,4-dihydroxybutyl)guanine (buciclovir) were examined for their effects on partially purified varicella-zoster virus (VZV) DNA polymerase as well as cellular DNA polymerase alpha. The triphosphate of 2HM-HBG competitively inhibited the incorporation of dGMP into DNA catalyzed by the VZV DNA polymerase. 2HM-HBG-triphosphate (2HM-HBG-TP) had a higher affinity for the dGTP-binding site on the VZV DNA polymerase than did dGTP; apparent Km and Ki values of dGTP and 2HM-HBG-TP were 0.64 and 0.034 microM, respectively. ACV-triphosphate (ACV-TP) was found to be the most potent inhibitor of VZV DNA polymerase. ACV-TP had a 14 and 464 times better direct inhibitory effect than 2HM-HBG-TP and buciclovir-triphosphate, respectively. The cellular (human embryonic lung fibroblast) DNA polymerase alpha inhibition was related to viral polymerase inhibition as efficacy ratios: 2HM-HBG-TP had a ratio of more than 1,000, which appeared to be similar to that of ACV-TP.

Topics: Acyclovir; Animals; Antiviral Agents; Cells, Cultured; Chromatography; DNA Polymerase II; DNA-Directed DNA Polymerase; Fibroblasts; Guanosine Triphosphate; Herpesvirus 3, Human; Humans; Kinetics; Nucleic Acid Synthesis Inhibitors; Vero Cells

The triphosphates of 9-(2-hydroxyethoxymethyl)guanine and 9-(1,3-dihydroxy-2-propoxymethyl)guanine were examined for their inhibitory effect on highly purified cellular DNA polymerase alpha and human cytomegalovirus (Towne strain)-induced DNA polymerase. These two nucleoside triphosphates competitively inhibited the incorporation of dGMP into DNA catalyzed by the DNA polymerases. The virus-induced DNA polymerase had greater binding affinity for the triphosphate of 9-(2-hydroxyethoxymethyl)guanine (Ki, 8 nM) than for the triphosphate of 9-(1,3-dihydroxy-2-propoxymethyl)guanine (Ki, 22 nM), although the nucleoside of the latter compound was strikingly more effective against human cytomegalovirus replication in cell cultures than the nucleoside of the former. The Ki values of these two nucleoside triphosphates for alpha polymerase were 96 and 146 nM, respectively, and were 7- to 12-fold higher than those for the virus-induced enzyme. These data indicated that virus-induced DNA polymerase was more sensitive to inhibition by these two nucleoside triphosphates than was the cellular alpha enzyme.

Topics: Acyclovir; Cytomegalovirus; DNA; DNA Polymerase II; Guanosine Triphosphate; Humans; Nucleic Acid Synthesis Inhibitors; Substrate Specificity

The antiherpes agent 9-(1,3-dihydroxy-2-propoxymethyl)guanine (DHPG) is a much more potent inhibitor of herpes simplex viruses in vivo than acyclovir, yet both are equally active in vitro against these viruses. To explain this difference, studies were conducted to compare the intracellular metabolism and enzymatic phosphorylation of the two compounds. In herpes type 1 and type 2 infected cells, the levels of DHPG triphosphate were only about 2-fold greater than levels of acyclovir triphosphate at virus-inhibitory concentrations (less than or equal to microM). At concentrations greater than 2.5 microM in herpes type 1 but not in type 2 infected cells, acyclovir phosphorylation was inhibited relative to that of DHPG. When drug was removed after 6 hr from infected cells, acyclovir triphosphate rapidly degraded to acyclovir and was excreted into the culture medium. In contrast, DHPG triphosphate persisted at 60-70% of the original level for 18 hr after drug removal, and DHPG excretion from cells was very slow. This finding could be a key factor to the superior potency of DHPG in animals, despite the fact that blood levels of both compounds fall rapidly after dosing. In uninfected cells, low levels of DHPG and acyclovir triphosphates were produced at 100 microM concentrations. Phosphorylation of DHPG to mono-, di- and triphosphates by purified viral and cell enzymes was more rapid than that of acyclovir. However, acyclovir triphosphate was a much more potent inhibitor of herpes virus and cell DNA polymerases.

Topics: Acyclovir; Animals; Antiviral Agents; Cells, Cultured; Chlorocebus aethiops; Dose-Response Relationship, Drug; Ganciclovir; Guanosine Triphosphate; Herpes Simplex; Humans; Kinetics; Nucleic Acid Synthesis Inhibitors; Phosphorylation; Time Factors