Radioautographic Analysis of 7,12-Dimethylbenz[a]anthracene-³H Incorporation and Cell Survival of Syrian Hamster Embryo Cells During Exposure to Nucleic Acid Inhibitors

Summary

Radioautographic techniques showed that cell cultures derived from Syrian hamster embryos continuously incorporated 7,12-dimethylbenz[a]anthracene (DMBA-³H) into nuclei during a 7-hour exposure to the carcinogen. The rate at which nuclei incorporated label was affected by the growth rate (doubling time) of the cell culture. Concentrations of nucleic acid inhibitors, selected on the basis of cell survival rather than maximum inhibition attainable, caused a 40–50% decrease in cell number relative to control cultures. Combinations of carcinogen and inhibitor had the same range of growth inhibition. The DNA inhibitors, hydroxyurea and excess thymidine, had no effect on DMBA-³H incorporation. Excess thymidine completely inhibited thymidine-³H incorporation, whereas hydroxyurea caused an incomplete and transient inhibition. Excess thymidine also reduced uridine-³H uptake. Inhibitors of RNA synthesis actinomycin D (act D) and 2-mercapto-1-(β-4-pyridethyl)benzimidazole (MPB) decreased uptake of DMBA-³H. MPB was more effective than act D as an inhibitor of uridine-³H incorporation, and both caused partial inhibition of thymidine-³H incorporation. The effect of act D on altering DMBA binding may be that of a toxic agent, since the concentrations used lethally damaged more than 60% of the population as seen by reduced DNA synthetic ability 24 hours after treatment.