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Keywords:

Animals, Antiviral Agents, Cell Line, Cercopithecus aethiops, Drug Synergism, Guanine, Guanosine Triphosphate, Herpesviridae, Herpesvirus 1, Human, Herpesvirus 2, Human, Herpesvirus 3, Human, Humans, Immunosuppressive Agents, Mycophenolic Acid, Plaque Assay, Ribavirin, Thymidine Kinase, Vero Cells, Science & Technology, Life Sciences & Biomedicine, Microbiology, Pharmacology & Pharmacy, HUMAN-IMMUNODEFICIENCY-VIRUS, MOLECULAR MECHANISMS, RIBAVIRIN, 2',3'-DIDEOXYINOSINE, DEHYDROGENASE, REPLICATION, INHIBITION, EFFICACY, PHOSPHORYLATION, HERPESVIRUSES, Chlorocebus aethiops, Viral Plaque Assay, 0605 Microbiology, 1108 Medical Microbiology, 1115 Pharmacology and Pharmaceutical Sciences, 3107 Microbiology, 3207 Medical microbiology, 3214 Pharmacology and pharmaceutical sciences

Abstract:

Mycophenolate mofetil (MMF) has been approved as an immunosuppressive agent in kidney transplant recipients and may thus be used concomitantly with antiherpetic agents, which are used for the treatment of intercurrent herpesvirus infections. We have recently demonstrated that MMF and its parent compound mycophenolic acid (MPA), which is a potent inhibitor of IMP dehydrogenase, potentiate the antiherpesvirus activity of acyclovir, ganciclovir, and penciclovir. We have now evaluated the antiviral efficacy of the combination of MPA and the novel antiherpesvirus agent H2G [(R)-9-[4-hydroxy-2-(hydroxymethyl)butyl]guanine]. When combined with H2G, MPA (at concentrations ranging from 0.25 to 10 microgram/ml, which are readily attainable in human plasma) markedly potentiated the antiviral efficacy of H2G against herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2), as reflected by a 10- to 150-fold decrease in the 50% effective concentration. Moreover, the activity of H2G against a thymidine kinase-deficient strain of HSV-1 (TK- HSV-1) was increased more than 2,500-fold when combined with MPA. MPA by itself had little or no effect on the replication of these viruses. Similar observations were made for varicella-zoster virus. Also, ribavirin (another inhibitor of IMP dehydrogenase) caused a marked enhancement of the activity of H2G against HSV-1 (10-fold), HSV-2 (10-fold), and TK- HSV-1 (>185-fold). Exogenously added guanosine reversed the potentiating effects of MPA on the antiviral activity of H2G, indicating that this potentiating effect resulted from a depletion of the endogenous dGTP pools, thus favoring the inhibitory action of the H2G triphosphate on the viral DNA polymerase.