Neoplastic Transformation of Guinea Pig Fetal Cells in Culture Induced by Chemical Carcinogens

Twenty-four cell strains derived from freshly isolated diploid strain 2 guinea pig fetal cells exposed in utero or directly in culture to a carcinogenic or noncarcinogenic chemical were evaluated during 4 to 24 months of continuous cultivation. Morphological alterations in carcinogen, i.e., benzo(a)pyrene-, 7,12-dimethylbenz(a)anthracene-, 3-methylcholanthrene-, N-methyl-N'-nitro-N-nitrosoguanidine-, diethylnitrosamine-, aflatoxin B1-, or N-acetoxyacetylaminofluorene-treated cultures were seen shortly after treatment; transformation, a loss of cell orientation, did not occur for 4 or more months, was not seen in controls and did not uniformly appear simultaneously with the capacity of transformed cells to grow as tumors in irradiated syngeneic newborn guinea pigs. Changes in plating efficiency, saturation density, doubling time, and chromosome alterations of transformed cells also did not correlate with progressive tumor growth. Formation of colonies in 0.35% agar appeared subsequent to or concomitantly with morphological transformation, and in every case they developed concurrently with the potential for neoplastic growth. Controls originally treated with a noncarcinogen (acetone, polycyclic hydocarbon, or aromatic amide) did not form agar colonies or tumors after inoculation of 108 cells. Studies with guinea pig cells indicate that persistent alterations in some growth parameters occur prior to expression of tumor growth. The ability of cells to form colonies in agar and to produce tumors may require 4 to 18 months of culturing. Of the cell properties examined, colony formation in agar was the best indication of the neoplastic state.