X-irradiation enhancement of transformation by benzo(a)pyrene in hamster embryo cells

The addition of benzo(a)pyrene to cells obtained from Syrian hamster embryo cultures that had been plated to produce discrete colonies resulted in transformation. Altered colonies were not seen in controls. Prior irradiation of hamster embryo cells increased the transformation by benzo(a)pyrene, both per cell and per total colony. Maximum enhancement occurred when benzo(a)pyrene was added 48 hr after irradiation. Enhancement was greatest after 250-500 R, and decreased with higher doses of radiation. The addition of benzo(a)pyrene 72 hr after irradiation resulted in very little enhancement. Although transformation increased with benzo(a)pyrene concentration, enhancement was independent of concentration within the range used. No colony with transformed morphology was recognized among the colonies of normal cells that survived irradiation.