Two-stage carcinogenesis in vitro: transformation of 3-methylcholanthrene-initiated Rauscher murine leukemia virus-infected rat embryo cells by diverse tumor promoters.

A modified in vitro transformation assay demonstrated potential for use in the identification and study of tumor promoters. Rauscher murine leukemia virus-infected F344 rat embryo cells were transformable by various chemical carcinogens when they were administered at appropriate doses. Cells treated with subeffective doses of 3-methylcholanthrene did not transform. However, when these cells were regularly treated with 12-O-tetradecanoylphorbol 13-acetate, sodium phenobarbital, limonene, oleic acid, lauric acid, or saccharin, transformation was observed. Thus several dhemically diverse in vivo tumor promoters behaved as promoters in this in vitro system. This assay appeared to be useful for in vitro efforts to identify promoters and may be of value in studies on the mechanisms of action of these cocarcinogens.