Bhas42 cell transformation assay as a predictor of carcinogenicity

The Bhas-system was established by using the reference carcinogen 3-methylcholanthrene as an initiator and TPA and Insulin as promoters. Increasing concentrations led to a dose-dependent increase in transformed foci. By selective trypsinization separate cultures could be established from foci cells and from normal cells. Micronucleus frequencies turned out to be 1.7 fold higher in cultures of transformed cells. More surprisingly, no significant differences in mitotic rates and cell cycle distribution between cultures of transformed and normal cells exist. Nevertheless, parallel staining of microfilaments and nuclei clearly displayed a dense and multilayered piling-up of cells in foci. Thus alterations in adhesion protein profiles and enzyme activities modulating cellular adhesion and migration seem to be involved in the process of focus formation. These may be promising candidates for the identification of molecular markers leading to a more objective scoring of foci and a greater acceptance of cell transformation tests in general.