Mechanism and mode of action of 5-iodo-2-pyrimidinone 2'-deoxyribonucleoside, a potent anti-herpes simplex virus compound, in herpes simplex virus-infected cells.

The anti-herpes simplex virus type 2 (-HSV-2) action of 5-iodo-2-pyrimidinone deoxyribonucleoside (IPdR) was found to be exerted through inhibition of HSV DNA synthesis. The inhibition of viral DNA synthesis was not caused by inhibition of the synthesis of HSV-2-specified proteins or HSV-2 mRNA species involved with viral DNA synthesis or by depletion of deoxynucleotides. The inhibition of viral DNA synthesis may be due to damage to the DNA template in the nuclei or to an action at the DNA replication complex, because nuclei isolated from HSV-2-infected cells treated with IPdR could not support DNA synthesis in vitro. Moreover, the addition of exogenous template to the reaction enabled nuclear DNA synthesis to occur at the level of control. The major cellular metabolite of IPdR in HeLa S3 cells infected with HSV-2 was IPdR monophosphate, which was formed through virally specified kinase. Attempts to either identify or synthesize IPdR diphosphate and triphosphate were unsuccessful. The accumulation of IPdR monophosphate was dependent on the extracellular concentration of IPdR. IPdR monophosphate did not have any inhibitory effect on nuclear DNA synthesis, even at 200 microM. Thus, the action of IPdR could be due to an unidentified metabolite of IPdR or the depletion of a cellular metabolite that is essential for viral DNA synthesis.