Neoplastic Conversion and Chromosomal Characteristics of Rat Embryo Cells In Vitro

Abstract

ALB/N rat-embryo cells, presumably free of murine leukemia virus and grown in a chemically defined medium (CDM) supplemented with serum, underwent “spontaneous” neoplastic conversions in vitro. Cell lines in CDM with horse serum (HS) supplement converted after 9-30 months in vitro, a period significantly longer than that reported for mouse embryo cells in this type medium. From the same embryo cell pool, 1 of 2 lines on CDM with fetal calf serum supplement underwent neoplastic conversion as compared with 3 of 3 lines on HS medium within a period of 412 days, and the cells grown in HS medium produced tumors with shorter latent periods. Cells derived from frozen-thawed cultures converted earlier than those not frozen. Tumor production from the tissue culture cells tended to vary directly with period of culture in vitro. Cells grown on un-supplemented CDM did not convert during the same period (11–38 months) in which the more rapidly dividing lines in serum-supplemented medium did. Cells in HS medium carried with limited or no subculturing, which continued to grow as dense, multilayered cell sheets, did not convert. In the subcultured lines, after an initial period of karyotypic stability (61–110 days), extensive chromosomal alterations occurred. We found no chromosomal alteration or pattern of chromosome change that could be correlated with the neoplastic conversion of the cells.