Use of epithelial cell cultures for studies on the mechanism of transformation by chemical carcinogens.

Evidence is reviewed for and against four major theories of chemical carcinogenesis. The development of several normal and transformed epithelial cell lines which should be useful for the analysis of this problem is described. The detection of RNA viral particles in cells transformed with chemical carcinogens is a recurrent finding in studies from our own and other laboratories, but the significance of these particles in terms of the mechanism of chemical carcinogenesis remains to be determined. Finally, we have described the first mutants of chemically transformed epithelial cells which are temperature sensitive in the maintenance of the transformed phenotype. These mutants should be particularly useful for detecting the critical biochemical changes that distinguish a chemically induced tumor cell from its normal counterpart.