Chemical Carcinogenesis In Vitro: Limitations and Possibilities in the Use of Rat Liver Epithelial Cells for Screening Carcinogens
We have developed assays based on the in vitro properties of malignant liver epithelial cells in which the qualitative changes of the carcinogen-treated cell population, and the quantitative changes of individual cells within such a population, can be studied. Even with these improved methods, it is not possible to identify the transformed epithelial cells when the percentage of transformed cells is low. We have examined several conditions under which the untransformed cells are either killed or maintained, without cell division, while the viability or proliferation of the transformed cells is not affected. Using the selective methods and the improved techniques for the identification of transformed cells, it should be possible to investigate the mechanisms of chemical carcinogenesis and to use the liver epithelial cells for assessing the possible hepatocarcinogenic potency of environmental agents.
Concurrently, we are attempting to develop a cell system which can be used exclusively for carcinogen screening. In many existing fibroblastic cell systems, hepatocytes are added to metabolize chemical carcinogens to active metabolites which, in turn, induce the altered characteristic in the “target” cells. However, the metabolites excreted by the hepatocytes are mostly detoxified (conjugated) products. Experiments are going on to produce hybrid cells by fusing hepatocytes with fibroblasts. If the hybrids retain the capacity to metabolize carcinogens and the ability to form “piled-up” colonies after carcinogen-treatment, such cells should prove better than the co-cultivated mixture for carcinogen screening since the active metabolites formed de novo within the cell can induce transformation of the same cell.
KeywordsToxicity Magnesium Glycerol DMSO Trypsin
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