Clonal Analysis of Tumorigenicity and Paratumorigenic Phenotypes in Rat Liver Epithelial Cells Chemically Transformed in V/fro1

Clonal subpopulations of a chemically induced tumorigenic rat liver epithelial cell line were analyzed for their cellular, biochemi cal, and in vitro growth properties and their tumorigenicity after injection into day-old newborn isogeneic rats. The phenotypic properties studied included DMA content; growth rate in culture; activities of 7-glutamyl transpeptidase, NADH diaphorase, pyruvate kinase, glucose-6-phosphate dehydrogenase, and lactate dehydrogenase; ability to grow in calcium-poor medium; and ability to form colonies in soft agar. The results show that none of these phenotypes cosegregates with tumorigenicity and there fore is not reliable as a "marker" phenotype for neoplastic trans formation in cultured rat liver epithelial cells. The poor correla tions, either qualitatively or quantitatively, between paratumorigenic phenotypes and tumorigenicity suggest that neoplastic transformation in these cells involves a specific transforming gene locus or loci and that in vitro paratumorigenic phenotypes are merely epiphenomena of neoplastic transformation and pro gression. This study further reveals that the efficiency of the tumorigenicity assay of cultured rat liver epithelial cells in isoge neic newborn rats can be considerably improved by incubating the cells in medium containing only trace amounts of serum prior to transplantation into the host animals.