Acyclovir-sensitive Herpes Simplex Virus Research Articles

Therapeutic Nucleic Acids: A Potential Source of Resistance to Cancer, Antiviral and Immunosuppressive Therapy.

According to their unique structural and chemical properties nucleic acids were recognized to provide inherent therapeutic potential beyond sole information storage. In the meantime an increasing number of nucleic acid based drugs achieved FDA approval and entered clinical trails (e.g. “antisense” or “immunosustimulatory CpG” oligodeoxynucletides (ODNs), aptamers, ribozymes, RNA interference or defibrotide). But so far, no or less information is available whether these compounds mightcompete with chemically and structurally related drugs, e.g. nucleoside analogues (NA) widely used in cancer or antiviral therapy, orinterfere with the intracellular nucleic acid metabolism.In the present report we provide evidence, that nucleic-acid based drugs antagonize fludarabine, acyclovir or mycophenolate mofetil (MMF). In presence of defibrotide (DF), a polydisperse mixture of single-stranded oligodeoxyribonucleotides (15 to 30 kD) e.g. used for treatment of hepatic veno-occlusive disease and other endothelial disorders, fludarabine treated lymphocytes or myeloid blasts where rescued from apoptosis. According to nucleic acid degradation the resulting metabolite deoxycytidine turned out to be the key substrate competing with fludarabine for phosphorylation by deoxycitidine kinase (dCK) and suggested interference with nucleic acid metabolism rather than direct competition with the drug for cellular uptake. Moreover, in standard drug resistance assays using acyclovir sensitive herpes simplex virus (HSV) strains (V0631508), 4 mM of DF restored viral replication in presence of 50 mM acyclovir. This was confirmed by quantitative PCR of viral DNA. Here, deoxythymidine turned out to be the main competitor for intracellular phosphorylation mediated by virus thymidine kinase. To further extent our findings, that an increase of the extracellular concentration of nucleic acids directly interfere with the intracellular nucleic acid metabolism, mixed lymphocyte reactions (MLRs) were performed, to test whether the immunosuppressive effects of mycophenolate mofetil (MMF) could be reversed. As control cyclosporine A (CsA) was used. Here, addition of singular ribonucleotides almost completely antagonized the T cell inhibitory effects of mycophenolic acid (MPA), respectively its prodrug MMF, but not of CsA. As MPA is known to be a potent, selective, uncompetitive and reversible inhibitor of inosine monophosphate dehydrogenase, a key enzyme for the de novo pathway of guanosine nucleotide synthesis, addition of guanosine to the MLRs was found to be effective and sufficient to reverse the immunosuppressive effects of MPA. We conclude that treatment with nucleic-acid-based drugs interfere with the intracellular nucleic acid metabolism, thus decreasing the efficacy of NAs used for cancer and antiviral therapy or the immunosuppressive therapy using MMF. Prospective clinical trials are required to confirm these in vitro findings.

Exogenous Nucleic Acids - A Potential Source of Resistance to Nucleoside Analogues in Cancer and Antiviral Therapy.

The metabolism of exogenous nucleic acids is not well defined. Moreover, there is little information whether there might be interference with chemically and structurally related drugs, e.g. nucleoside analogues (NA) widely used in cancer or in antiviral therapy. In the present report we provide evidence, that nucleic-acid based drugs might antagonize fludarabine or acyclovir. In vitro, fludarabine treated lymphocytes or myeloid blasts where rescued from apoptosis when incubated with defibrotide (DF), a polydisperse mixture of single-stranded oligodeoxyribonucleotides (15 to 30 kD) or singular deoxynucleotides. Thereby deoxycytidine (dCTP) turned out to be the key substrate competing with fludarabine for phosphorylation by deoxycitidine kinase (dCK) and suggested interference with nucleic acid metabolism rather than direct competition with the drug. To further prove this hypothesis the influence of defibrotide on HSV replication was evaluated. In standard drug resistance assays performed with acyclovir sensitive herpes simplex virus (HSV) strains (V0631508) 4 mM of DF restored viral replication in presence of 50 mM acyclovir. This was confirmed by quantitative PCR of viral DNA. Moreover, in this case deoxythymidine (dTTP) turned out to be the competitor for intracellular phosphorylation mediated by virus thymidine kinase. We conclude that treatment with DF and other nucleic-acid-based drugs interfere with the efficacy of NA used for cancer and antiviral therapy. Prospective clinical trials are required to confirm these in vitro findings.

Relapse of Herpes Encephalitis after Acyclovir Therapy: Report of Two New Cases and Review of the Literature

Relapse of herpes simplex virus (HSV) encephalitis following acyclovir therapy has been reported infrequently in children beyond the neonatal period. The pathogenic mechanism of the recurrence is not fully understood. We report two new cases that support a mechanism of latent HSV infection with reactivation of the disease. Our patients were 2 years (#1) and 8 months (#2) old at initial infection. Both presented with fever, lethargy, focal seizures, and focal motor abnormalities. Serum HSV antibodies (Abs) were negative. The patients were treated with acyclovir for 14 and 21 days, respectively. They were readmitted at 1 month, and 4 days after discharge, respectively, with recurrent lethargy, seizures, and choreo-athetoid movements. Serum and CSF HSV Abs were significantly increased. CSF PCR was positive. In patient # 2 acyclovir-sensitive HSV was isolated from a brain biopsy. Both patients were re-treated with acyclovir, but progressed to a neurovegetative state. In our cases, latent HSV infection and reactivation is the most likely explanation for recurrent encephalitis. The immuno-pathogenic mechanisms of the infection recurrence are discussed. Based on the reported cases in the literature, patients younger than 2 years of age and with lower total dose of acyclovir treatments have a higher risk of recurrence.

Suppression of generation and replication of acyclovir-resistant herpes simplex virus by a sensitive virus.

The role of acyclovir-sensitive herpes simplex virus (HSV) was analyzed in the process of its replacement by a resistant virus in vitro and in vivo in the aspect of acyclovir therapy. The mode of replacement of acyclovir-sensitive HSV with acyclovir-resistant HSV was examined by the passages of acyclovir-sensitive wild type HSV in Vero cells under acyclovir-treatment. The development of resistance was monitored more adequately by counting the number of acyclovir-resistant viruses in 10,000 plaque forming units than by the conventional susceptibility assay. The resistance increased with the proportion of thymidine kinase-deficient (TK(-)) viruses, when the susceptibilities of acyclovir-treated HSV population to 5'-iodo-2'deoxyuridine and phosphonoacetic acid were examined. The increased resistance was due to the increased proportion of acyclovir-resistant virus but not intermediately resistant virus. Infection with mixtures of TK(-) and acyclovir-sensitive strains rendered TK(-) sensitive to acyclovir, and virus yields were reduced to the levels of acyclovir-sensitive virus in Vero cells. Their yield reduction depended on the proportion of acyclovir-sensitive viruses and induction of TK activity. This reduction in virus yields of the mixture of TK(-) and acyclovir-sensitive strains was confirmed by acyclovir treatment in the skin of mice with cutaneous infection. Acyclovir treatment combined with superinfection of acyclovir-sensitive virus delayed the development of herpetic skin lesions due to acyclovir-resistant virus and reduced virus yields in the infected skin. Acyclovir-sensitive virus plays an important role in suppressing the generation and replication of acyclovir-resistant virus during acyclovir therapy.

Genotypic and phenotypic characterization of the thymidine kinase of ACV-resistant HSV-1 derived from an acyclovir-sensitive herpes simplex virus type 1 strain

Twenty-four strains of acyclovir (ACV)-resistant (ACV r) herpes simplex virus type 1 (HSV-1) were generated from the HSV-1 TAS strain by exposure to ACV, and the genotype and phenotype of the thymidine kinase (TK) from these mutants were analyzed. The TK polypeptide of the ACV r HSV-1 strains was examined by Western blot using an anti-HSV-1 TK rabbit serum. The sensitivity of each strain to ACV, foscarnet and cidofovir (CDV) was also determined. A single guanine (G) insertion or a single cytosine (C) deletion was detected in 12 of the 24 ACV r strains at the G or C homopolymer stretches within the TK gene. Genotypic analysis predicted that two thirds of the ACV r HSV-1 strains expressed truncated TK polypeptides, while one third expressed viral TK polypeptide with a single amino acid substitution at various sites. Western blot abnormalities in the viral TK polypeptides were identified in 21 ACV r strains. There was an inverse correlation between the susceptibility of the HSV-1 mutant strains to ACV and that to CDV. Nucleotide sequencing of the TK gene and Western blot analysis of the viral TK polypeptides are considered to be one of the methods for predicting virus sensitivity to ACV and CDV.

Relapse of Herpes Simplex Encephalitis After Conventional Acyclovir Therapy

Acyclovir sodium is the drug of choice for the treatment of herpes simplex encephalitis. We treated an immunocompetent patient with a ten-day course of intravenous acyclovir sodium at the recommended dosage of 10 mg/kg every eight hours for clinically apparent herpes simplex encephalitis. After marked improvement, his condition deteriorated four days after completing acyclovir therapy. A subsequent brain biopsy specimen disclosed acyclovir-sensitive herpes simplex virus type 1. A longer duration of acyclovir therapy (14 to 21 days) should be considered for treating herpes simplex encephalitis.