Enhancement and inhibition of transformation of Syrian hamster embryo cells.

Diploid Syrian hamster embryo cells are particularly appropriate for the study of the transformation phenomenon in target cells. In vitro morphologic transformation occurs in a dose-dependent manner and is characterized by random crisscrossing and piling of cells; it correlates with tumorigenicity because individually transformed cell colonies can be isolated, cell lines can be developed, and the formation of tumors can be demonstrated after the injection of the transformed cells into either Syrian hamsters or athymic nude mice. HEC can also be used to investigate stages of carcinogenesis, initiation, and promotion. The susceptibility of normal HEC to transformation by environmental carcinogens including asbestos, bisulfite, nitrated non-carcinogenic polycyclic hydrocarbons, and X- or ultraviolet irradiation has made possible the determination of a variety of cell responses as they proceed to the neoplastic state. The initiation is usually a hereditary process involving single-hit kinetics and the transformation data indicate there is no measurable threshold response to carcinogens. The promotional aspects of transformation are readily modulated by environmental factors and have a threshold, as well as a maximal effect. The results of transformation studies using hamster cells indicate that in vitro studies are relevant to carcinogenesis and indicate that the various steps involved can be identified. Therefore, it should be possible to intervene with the various stages or steps leading to neoplasia so that cancer can be prevented.