Transformation frequency of Syrian golden hamster cells and its modulation by ultraviolet irradiation.

UV (253.7 nm) exposure of Syrian golden hamster cells seeded for colony formation caused an induction of transformation without any other insult. Analysis of the quantitative data demonstrated a lack of a threshold response and a transfomation frequency proportional to UV dose. No transformation occurred in unirradiated colonies. When cells seeded for colony formation are exposed to UV and subsequently treated with AcAAF, a carcinogen known to induce UV-like damage, neither an additive nor a synergistic effect occurred. Caffeine at nontoxic concentrations potentiates lethality caused by AcAAF and also the number od colonies transformed by AcAAF when added post-AcAAF. The addition of a constant amount of caffeine (50 micrograms/ml) for 48 hours at different intervals after carcinogen resulted in maximum enhancement (10- to 17-fold) when added 4 hours post-AcAAF. UV-associated transformation was enhanced by pretreating the cells with a nontransforming dose of X-irradiation 48 hours before UV. The increase in transformation frequency was 6- to 12-fold per colony and 3- to 6-fold per dish.