N-NITROSODIETHYLAMINE AND 4-(METHYLNITROSAMINO)-1-(3-PYRIDYL)-1-BUTANONE INDUCED MORPHOLOGICAL TRANSFORMATION OF C3H 10T1/2CL8 CELLS EXPRESSING HUMAN CYTOCHROME-P450 2A6/

Transfection of specific genes into cells capable of expressing chemic ally induced morphological cell transformation provides a valuable app roach to study the mechanisms of action of carcinogens. A human cytoch rome P450 isozyme, CYP2A6, has been successfully expressed from a retr oviral vector in transformable C3H/10T1/2 (10T1/2) mouse embryo fibrob lasts and these resulting 10T1/2 clones were evaluated for the cytotox ic and transforming activities of two nitrosamines, 4-(methylnitrosami no)-1-(3-pyridyl)-1-butanone (NNK) and N-nitrosodiethylamine (DEN). 10 T1/2 clone 29 cells, which expressed high levels of CYP2A6 activity, w ere responsive to the cytotoxic and morphological transforming effects of DEN or NNK on a concentration-related basis. In 10T1/2 clone 29 ce lls, DEN at 600 mu g/ml decreased cell survival to 67%, and induced 0. 5 type II&III foci/dish. NNK at 400 mu g/ml administered to 10T1/2 clo ne 29 cells decreased survival to 57% and induced 0.43 type II&III foc i/dish. Wild-type 10T1/2 cells and 10T1/2 clone 4 cells (infected with the vector but not expressing the CYP2A6 activity) were unresponsive. These results indicate that expression of a cDNA coding for cytochrom e P450 in 10T1/2 cells can provide information about the role of the e nzyme in the activities of chemical carcinogens and also increase the sensitivity of 10T1/2 cells to a larger number of classes of chemical carcinogens.