Carcinogen-induced changes in tracheal epithelium cultured in serum-free, chemically defined medium

Rat tracheal tissue was cultured for periods up to 2 months in medium containing benzo[a]pyrene, and the epithelium was studied for the histologic effects of deletion of serum from the medium. Nodular hyperplasia occurred in 3 days in the absence of serum, but was not seen until several weeks of culture in media containing the same concentrations of carcinogen with 10% calf serum. In serum-free culture, hyperplasia was induced in 2 weeks with one-tenth of the smallest concentration of benzo[a]pyrene that yielded this change in serum-containing medium. The cells of the hyperplastic epithelium in both serum-containing and serum-free culture exhibited ultrastructural changes described in carcinogenesis in vivo. In the absence of serum, squamous hyperplasia was uniformly seen, a feature that distinguished serum-free culture from culture in the presence of calf serum. No frank intraepithelial or invasive malignant lesions were produced in either medium. It was concluded that exposure of organ cultures to carcinogen in the absence of serum is the more promising method for bioassay because the response to carcinogen was more rapid, more sensitive, and more reproducible than that seen during exposure in media that contained serum.