Dependence of bleomycin-induced cytotoxicity and DNA damage on the in vitro culture growth phase of mouse tumour cells.

EMT 6/Ca/VJAC cells have been treated with various doses of bleomycin and the effects of these treatments in terms of cell killing and DNA damage have been determined. The experiments have been carried out with exponentially growing and plateau-phase cultures. Dose-response curves have been obtained using a clonogenic cell survival assay. Bleomycin-induced DNA damage was quantitated by a fluorescence procedure, based upon the time-dependent partial unwinding of cellular DNA under alkaline conditions. Although cells in exponential-phase of culture growth were more sensitive to bleomycin than those in plateau-phase, this could only be attributed to enhanced drug-DNA interaction at high (greater than 40 micrograms/ml) drug concentration. Thus factors other than DNA damaging potential and related to culture growth status control drug sensitivity.