Nutritional and hormonal factors in the prevention of carcinogen-induced neoplastic development in vitro.

Cell cultures and in vitro oncogenic transformation offer a powerful tool for exploring conditions and compounds that may inhibit malignant transformation following exposure to environmental or therapeutic agents. We find, using rodent cell cultures, that retinoids inhibit radiation-induced transformation and eradicate the enhancing effect of tumor promotors. These protective effects of the retinoids are not mediated at a chromosomal level but are reflected at the cell membrane level via the membrane-associated transport enzyme Na/K-ATPase. Using these systems, we also find that hypothyroid condition is protective and that thyroid hormone T3 is essential for the induction of both radiation-induced and chemically induced carcinogenesis, and thus may also play a crucial role in cancer induction in vivo.