Cytotoxic and cytokinetic effects of 1 ^–β^–d–arabinofuranosylcytosine daunorubicin, and 6–thioguanine on hela cells in culture

Exponentially growing HeLa cells were exposed to ^1–β^–d–arabinofuranosylcytosine, daunorubicin, and 6–thioguanine singly and in combination for 21 hr. Survivals were determined by a colony–counting assay, and cytokinetic effects of the drugs were evaluated by flow cytometry. When used in two–drug combinations (concurrent exposures), 1–β–D–arabinofur–anosylcytosine was found to protect cells against both 6–thio–guanine–and daunorubicin–induced lethality, the former to a greater extent than the latter. Protection against 6–thioguanine appeared to be related to the degree of inhibition of DNA synthesis by 1–β–D–arabinofuranosylcytosine, but this was not the case with daunorubicin. When cells were exposed to the three drugs simultaneously, survivals were in agreement with those predicted from the various two–drug combinations. This implies that no additional drug interactions occurred when a third drug was added to the two–drug combinations.