Induction of anchorage-independent growth in human fibroblasts by propane sultone.

We have demonstrated a dose-dependent increase in the frequency of diploid human cells capable of anchorage-independent (AI) growth after treatment with the carcinogen propane sultone, followed by exponential growth to allow full expression of this phenotype (8 to 13 population doublings). Exposure to these same concentrations of propane sultone also resulted in a dose-dependent increase in the frequency of 6-thioguanine-resistant cells in the population. Procedures such as synchronization of cells and treatment just after the onset of DNA synthesis or the use of special selective medium were not essential for this induction. A very low frequency of cells with the AI phenotype was found in the control population (background). Cells which exhibited the AI phenotype spontaneously or after carcinogen treatment retained the characteristic over as many generations as tested (greater than 13). The data suggest that AI growth is the result of a mutational event.