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Effects of Acyclovir, Foscarnet, and Ribonucleotides on Herpes Simplex Virus-1 DNA Polymerase: Mechanistic Insights and a Novel Mechanism for Preventing Stable Incorporation of Ribonucleotides into DNA.

ABSTRACT: We examined the impact of two clinically approved anti-herpes drugs, acyclovir and Forscarnet (phosphonoformate), on the exonuclease activity of the herpes simplex virus-1 DNA polymerase, UL30. Acyclovir triphosphate and Foscarnet, along with the closely related phosphonoacetic acid, did not affect exonuclease activity on single-stranded DNA. Furthermore, blocking the polymerase active site due to either binding of Foscarnet or phosphonoacetic acid to the E-DNA complex or polymerization of acyclovir onto the DNA also had a minimal effect on exonuclease activity. The inability of the exonuclease to excise acyclovir from the primer 3'-terminus results from the altered sugar structure directly impeding phosphodiester bond hydrolysis as opposed to inhibiting binding, unwinding of the DNA by the exonuclease, or transfer of the DNA from the polymerase to the exonuclease. Removing the 3'-hydroxyl or the 2'-carbon from the nucleotide at the 3'-terminus of the primer strongly inhibited exonuclease activity, although addition of a 2'-hydroxyl did not affect exonuclease activity. The biological consequences of these results are twofold. First, the ability of acyclovir and Foscarnet to block dNTP polymerization without impacting exonuclease activity raises the possibility that their effects on herpes replication may involve both direct inhibition of dNTP polymerization and exonuclease-mediated destruction of herpes DNA. Second, the ability of the exonuclease to rapidly remove a ribonucleotide at the primer 3'-terminus in combination with the polymerase not efficiently adding dNTPs onto this primer provides a novel mechanism by which the herpes replication machinery can prevent incorporation of ribonucleotides into newly synthesized DNA.

SUBMITTER: Vashishtha AK

PROVIDER: S-EPMC5551684 | biostudies-literature | 2016 Feb

REPOSITORIES: biostudies-literature

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Effects of Acyclovir, Foscarnet, and Ribonucleotides on Herpes Simplex Virus-1 DNA Polymerase: Mechanistic Insights and a Novel Mechanism for Preventing Stable Incorporation of Ribonucleotides into DNA.

Vashishtha Ashwani Kumar AK Kuchta Robert D RD

Biochemistry 20160211 7

We examined the impact of two clinically approved anti-herpes drugs, acyclovir and Forscarnet (phosphonoformate), on the exonuclease activity of the herpes simplex virus-1 DNA polymerase, UL30. Acyclovir triphosphate and Foscarnet, along with the closely related phosphonoacetic acid, did not affect exonuclease activity on single-stranded DNA. Furthermore, blocking the polymerase active site due to either binding of Foscarnet or phosphonoacetic acid to the E-DNA complex or polymerization of acycl ...[more]

PMID: 26836009

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Project description:Importance:The role of herpes simplex virus (HSV) reactivation on morbidity and mortality in patients in the intensive care unit requiring mechanical ventilation remains unknown. Objective:To determine whether preemptive treatment with intravenous acyclovir reduces the duration of mechanical ventilation in patients with HSV oropharyngeal reactivation. Design, Setting, and Participants:A double-blind, placebo-controlled randomized clinical trial was conducted in 16 intensive care units in France. Participants included 239 adults (age, >18 years) who received mechanical ventilation for at least 96 hours and continued to receive mechanical ventilation for 48 hours or more, with HSV oropharyngeal reactivation. Patients were enrolled between February 2, 2014, and February 22, 2018. Interventions:Participants were randomized to receive intravenous acyclovir, 5 mg/kg, 3 times daily for 14 days or a matching placebo. Main Outcomes and Measures:The primary end point was ventilator-free days from randomization to day 60. Prespecified secondary outcomes included mortality at 60 days. Main analyses were conducted on an intention-to-treat basis. Results:Of 239 patients enrolled and randomized, 1 patient withdrew consent, leaving 238 patients, with 119 patients in both the acyclovir and placebo (control) groups (median [IQR] age, 61 [50-70] years; 76 [32%] women) available for primary outcome measurement. On day 60, the median (IQR) numbers of ventilator-free days were 35 (0-53) for acyclovir recipients and 36 (0-50]) for controls (P?=?.17 for between-group comparison). Among secondary outcomes, 26 patients (22%) and 39 patients (33%) had died at day 60 (risk difference, 0.11, 95% CI, -0.004 to 0.22, P?=?.06). The adverse event frequency was similar for both groups (28% in the acyclovir group and 23% in the placebo group, P?=?.40), particularly acute renal failure post randomization affecting 3 acyclovir recipients (3%) and 2 controls (2%). Four patients (3%) in the acyclovir group vs none in the placebo group stopped the study drug for treatment-related adverse events. Conclusions and Relevance:In patients receiving mechanical ventilation for 96 hours or more with HSV reactivation in the throat, use of acyclovir, 5 mg/kg, 3 times daily for 14 days, did not increase the number of ventilator-free days at day 60, compared with placebo. These findings do not appear to support routine preemptive use of acyclovir in this setting. Trial Registration:ClinicalTrials.gov identifier: NCT02152358.

Dataset Information

Effects of Acyclovir, Foscarnet, and Ribonucleotides on Herpes Simplex Virus-1 DNA Polymerase: Mechanistic Insights and a Novel Mechanism for Preventing Stable Incorporation of Ribonucleotides into DNA.

Publications

Effects of Acyclovir, Foscarnet, and Ribonucleotides on Herpes Simplex Virus-1 DNA Polymerase: Mechanistic Insights and a Novel Mechanism for Preventing Stable Incorporation of Ribonucleotides into DNA.

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