Inhibition of murine sarcoma virus-induced foci formation by cytidine analogues and other drugs chemotherapeutically effective in human malignancies.

The present report describes an in vitro culture system using the Kirsten murine sarcoma virus transformation focus assay to evaluate the antiviral activities of 12 commonly used chemotherapeutically effective drugs. Since these drugs are cytotoxic, the plating efficiencies of the cells treated were monitored simultaneously. Using this procedure, Adriamycin, Daunorubicin, Bleomycin Camptothecin, Mithramycin, hydroxyurea, 5-fluorouracil, thioguanine, 9-beta-D-arabinofuranosyladenine, 1-beta-D-arabinofuranosylcytosine (ara-C), azacytidine and cyclocytidine were tested. Of all these compounds tested only the cytidine analogues - cyclocytidine, ara-C and, to a lesser extent, azacytidine - showed selective effect on inhibition of viral foci over cytotoxicity. Studies on the duration of exposure to ara-C indicated that an exposure time of 10-30 h produced the most pronounced effect on the inhibition of foci formation over that of cytotoxicity.