In vivo and in vitro characteristics of early carcinogen-induced premalignant phenotypes in cultured rat tracheal epithelial cells.

The initial stages of neoplastic transformation in respiratory tract epithelial cells were defined and studied by characterizing a series of morphologically transformed cell colonies from carcinogen-exposed rat tracheal epithelial (RTE) cell cultures both in vivo and in vitro. RTE cells were isolated from Fischer 344 rats, plated on collagen-coated dishes, and exposed to 7,12-dimethylbenz[a]anthracene on day 1 for 24 h. Between days 26 and 30, single colonies of morphologically altered cells were isolated and classified into three major classes based on cell density. Following replating, the cells were tested for their ability to grow on various substrates and in various culture media. Generally, Class II and III cells exhibited a higher colony forming efficiency when replated on various substrates. Class III cells appeared to grow better than Class I or II cells in complete medium, while Class I cells grew better in medium without 3T3 conditioning factors. At early passage levels, the population doubling times were longer for Class I cells than for Class II cells. Class III cells had the shortest population doubling times. The various cell lines were also placed into denuded tracheal grafts. Untreated cells produced a normal mucociliary epithelium, while Class I cells produced a simple cuboidal epithelium. Class II and III cells formed a highly atypical and usually malignant epithelia. Inoculation of the three classes of cells into nude mice provided confirming evidence of the benign nature of Class I cell lines and the malignant nature of some Class II cell lines and all of the Class III cell lines.