In vitro transformation of rat tracheal epithelial cells: a model for the study of multistage carcinogenesis.

A multistage transformation assay has been developed using normal primary rat tracheal epithelial cells as targets for measuring the transforming activity of a variety of test substances. The assay is suited for quantitation of cell transformation and allows the study of effects of promoters as well as inhibitors of transformation at various stages of this multiphasic process. Studies with TPA and retinoic acid have shown that the first stage of neoplastic transformation of RTE cells cannot be enhanced by TPA but is inhibited by retinoic acid. However, TPA can enhance a later stage of transformation, the conversion of the ag- to the ag+ phenotype. The cellular and biochemical mechanism of the inhibitory effects of RA are under investigation.