Interaction between radiation and drug damage in mammalian cells. II. The effect of actinomycin-D on the repair of sublethal radiation damage in plateau phase cells

The effect of actinomycin-D (AMD) on radiation damage repair was studied in plateau phase V79 Chinese hamster cells. Sublethal radiation damage repair, as demonstrated by survival fluctuations following two x-ray exposures separated by time was observed in our plateau phase cells. Plateau phase cells exposed to 0.01 to 0.04 μg/ml AMD (a nontoxic regimen to 8 hours) between x-ray exposures were less able to repair sublethal damage. If plateau phase cells were plated at low dilutions into fresh medium (conditions for resuming exponential growth) immediately after the first x-ray dose, and exposed to 0.01 to 0.04 μg/ml AMD until the second dose, inhibition of sublethal damage repair and additional cell killing were observed particularly at 0.04 μg/ml AMD. It is suggested that radiation-drug damage interactions should be studied in plateau phase cells and in cells resuming exponential growth after plateau phase (possibly analogous to ''recruitment''), as well as in exponential phase cultures