Cocarcinogenesis in vitro using Balb/3T3 cells and aromatic hydrocarbon cocarcinogens

The mouse skin cocarcinogens fluoranthene, pyrene, and undecane were used with the indirect-acting carcinogen, benzo(a)pyrene (BP), and the direct-acting alkylating carcinogen, ß-propiolactone (BPL), in an in vitro transformation assay. Dose response, cytotoxicity, and transformation studies with these compounds were performed with a subclone (A31-1-1) of the Balb/3T3 cell line. Transformation frequencies were found to increase with increasing concentrations of BP used up to 1.0 µg/ml or when BPL was used up to 4.0 µg/ml. A significant increase (P<0.05) in the transformation frequency over that seen with carcinogen alone was observed when cells were exposed to a combination of fluoranthene (4.0 µg/ml) and BP (0.063 µg/ml) or pyrene (5.0 µg/ml) and BP (0.063 µg/ml). Thus, the transformation frequency obtained with BP + fluoranthene was 3.8 × 10⁻⁴ compared to 1.2 × 10⁻⁴ when BP was tested alone. Similarly, the transformation frequency using BP + pyrene was 2.8 × 10⁻⁴ vs 1.2 × 10⁻⁴ when BP was tested alone. Undecane did not exert any cocarcinogenic effect with BP in the dose range tested. In this in vitro assay, no cocarcinogenic effect was observed when BPL was used with any of the above mouse skin cocarcinogens. All cells isolated from transformed foci showed characteristics of transformed cells including anchorage-independent growth.