Effect of arabinofuranosylthymine on the replication of Epstein-Barr virus and relationship with a new induced thymidine kinase activity

1-beta-D-Arabinofuranosylthymine (araT) is a selective inhibitor of Epstein-Barr virus replication induced in both thymidine kinase (TK)-negative (TK-) and TK+ variants of the lymphoid cell line P3HR-I. This analog has no effect on the growth of noninduced cells (T. Ooka and A. Calender, Virology 104:219-223, 1980). The synthesis of early antigens is not affected by the analog, whereas that of late viral capsid antigens is completely inhibited, as demonstrated by the indirect immunofluorescence technique; kinetic reassociation experiments have also shown that araT strongly inhibits replication of viral DNA. Phosphorylation of the tritiated form of the analog ([3H]araT) was analyzed by thin-layer chromatography in cultures of control and induced cells, and the results demonstrated that only induced cells can convert the analog to the triphosphate form. These results indicate that the selective effect of araT in induced cells is probably related to a new virally induced TK activity. Preliminary characterization of this new activity has shown that it is able to phosphorylate the analog specifically, whereas cellular TKs cannot. araTTP, a final phosphorylation product of araT, is a potent inhibitor of Epstein-Barr virus-specific DNA polymerase, suggesting a possible inhibitory action of this product on Epstein-Barr virus replication.

Effect of acyclovir on the proliferation of human fibroblasts and peripheral blood mononuclear cells

The effect of acyclovir on human cells was measured. A concentration of 50 to 100 microM inhibited the division of fibroblasts to a variable extent, depending on the experimental design and the confluency of the monolayer. The magnitude of this effect was less than that caused by human leukocyte interferon when these antiviral agents were compared at clinically relevant concentrations. Acyclovir also inhibited thymidine incorporation by peripheral blood mononuclear cells stimulated by either phytohemagglutinin or three different herpesvirus antigens. A linear dose-response curve was observed with these cells, and their proliferation was inhibited 50% by 100 microM acyclovir. Inhibition was exerted on T-cell proliferation without apparent effect on the release of lymphokines or on monocyte function.