Quantitation of chemically induced neoplastic transformation of BALB-3T3 cloned cell lines.

Sublines from a BALB/3T3 line were sensitive to a variety of carcinogens. A quantitative system of chemical transformation resulted in cell lines that caused fibrosarcomas when injected into mice (106 cells/mouse); no tumors developed from control lines (108). Transformation, indicated by criss-crossing of fibroblast-like cells not seen in controls, was scored in discrete colonies at 10 to 11 days or in foci after 3 weeks. Transformation was observed with carcinogenic polycyclic hydrocarbons, aflatoxin B1, N -acetoxy-2-fluorenylacetamide, and N -methyl- N′ -nitro- N -nitrosoguanidine but not with diethylnitrosoamine or noncarcinogens. Transformation rate increased (based on transformed colonies/total colonies or original cell inoculum used), and cloning efficiency decreased as concentration of carcinogen was increased. The dose-response relationship was consistent with a one-hit phenomenon. The Poisson distribution of frequency of transformed colonies per dish indicates that transformation is due to induction. Transformed cell lines from carcinogen-transformed colonies or foci had decreased doubling time and increased saturation densities relative to control lines. Recloned, carcinogen-sensitive, BALB/3T3 cell lines present a reliable in vitro quantitative bioassay model for the study of chemical carcinogenesis.