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Quantitation of Chemically Induced Neoplastic Transformation of BALB/3T3 Cloned Cell Lines

National Cancer Institute, Bethesda, Maryland 20014 [J. A. D., N. C. P.], and Meloy Laboratory, Inc.,^,3 Springfield, Virginia 22151 [K. T.]

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.

¹ Present address: Department of Microbiology and Chemotherapy, Nippon Roche Research Center, Kamekura, Japan.

² Visiting Associate. Permanent address: Oncological Institute, Bucharest, Romania.

³ Supported by Contract NIH 70-2201.

Received 7/ 6/72. Accepted 8/31/72.

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