Malignant transformation of a cloned, nontumorigenic mouse epidermal keratinocyte cell line, MSK-C3H-NU, by 7,12-dimethylbenz(a)anthracene.

MSK-C3H-NU, a cloned mouse epidermal keratinocyte cell line, was established from the epidermis of C3H/HeN mammary tumor virus-positive nude mice. Although it has lost its diploid chromosome number, the cell line is nontumorigenic, has been stable during serial subcultivations for over 2 years, and has retained some differentiated biological characteristics of normal keratinocytes. MSK-C3H-NU cells were cultured in growth medium containing 7,12-dimethylbenz(a)anthracene. After 2 months, colonies exhibited marked changes in cell morphology, cell arrangement, and keratinization pattern that appeared. The transformation frequency per 10(5) survivors in 7,12-dimethylbenz(a)anthracene-treated (10, 100, and 500 ng/ml) subgroups was 0, 119, and 1370 for Experiment I and 3.9, 238, and 2500 for Experiment II, respectively. Most of these transformed cells became malignant and formed tumors in nude mice. Histologically, the tumors were well-differentiated, keratinizing, squamous cell carcinomas showing papillary growths. In 7,12-dimethylbenz(a)anthracene-treated subgroups, cells from colonies that retained the original morphological characteristics did not form tumors in animals, and in control groups, no cell population showed tumorigenicity. In the MSK-C3H-NU cell system, the morphological alterations seem to be strongly associated with malignant conversion.