X-radiation-induced transformation in a C3H mouse embryo-derived cell line

Reproducible X-ray-induced oncogenic transformation has been demonstrated in an established cell line of mouse embryo fibroblasts. Cells derived from transformed foci formed malignant tumors when injected into syngeneic hosts. An exponential increase in the number of transformants per viable cell occurred with doses of up to 400 rads of X-radiation. The transformation frequency in exponentially growing cultures remained constant at 2.3 x 10(-3) following doses of 400 to 1500 rads. There was little change in survival following X-ray doses up to 300 rads. Doses greater than 300 rads were associated with an exponential decline in survival; the Do for the survival curve was 175 rads. Transformation frequency varied with changes in the number of viable cells seeded per dish. There was about a 10-fold decline in the transformation frequency when the number of cells was increased from 400 to 1000 viable cells/100-mm Petri dish. Below this density range there was little change in transformation frequency. The presence of lethally preir-radiated cells was not associated with an enhancement of transformation in irradiated cells or with the induction of transformation in unirradiated cell cultures. Amphotericin B (Fungizone) inhibited the appearance of transformants when added to the culture medium within 2 to 3 weeks after initiation of the experiment.