Evaluation of tumour promoters by the hamster embryo cell transformation assay.

Morphological transformation of hamster embryo cells has been used to study the effect of exposure to different combinations of compounds. Combined exposure to benzo[a]pyrene and cigarette smoke extract, to benzo[a]pyrene and nickel sulphate, and to cigarette smoke extract and nickel sulphate resulted in a synergistic increase in the formation of morphologically transformed colonies. This synergistic effect can be accounted for mainly by the finding that cigarette smoke extract and nickel sulphate promote or increase the number of transformed colonies following exposure to benzo[a]pyrene. Different tumour promoters and non-promoting analogues possess a potency for enhancing the transformation frequency similar to that of tumour promoters in experimental systems in vivo. Thus, our modification of the hamster embryo cell transformation assay may be a simple and quick method for studying modifiers of carcinogenesis.