The transformation of a rat cell line induced by a tumor promoter occurs without affecting sister chromatid exchange.

Malignant transformation of cells of an established rat cell line, FR3T3, can be achieved by the exclusive treatment of the cells with the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) over a stationary growth period. In the course of the transformation process, sister chromatid exchange (SCE) rates of treated cells were examined at various key-points and compared to control cells. It was found that neither a single TPA treatment nor repeated TPA application during 16-22 consecutive cell-doubling times (which induces substantial alterations of the phenotypes) increased SCE rates in the rat cells. Furthermore, transformed cell clones, which were selected from low-serum cultures and which were found to be tumorigenic in vivo, had SCE rates in the same range as the parental nontransformed FR3T3 cells. It is, therefore, concluded that malignant transformation of the rat cells - induced by TPA - occurs without affecting such large-scale DNA rearrangements as are detectable by means of the SCE method.