Initiation and promotion in cultures of C3H10T1/2 mouse embryo fibroblasts.

Studies conducted in numerous laboratories have demonstrated that the transformation of C3H10T1/2 cells can proceed through discrete stages of initiation and promotion. Indeed, multiple operational aspects of initiation and promotion in this system closely mimic the essential characteristics of initiation and promotion on mouse skin. The sensitivity of this system to the effects of different tumor promoters also appears to parallel that of mouse skin, and there is evidence to suggest that the C3H10T1/2 system is most sensitive to agents acting as stage II tumor promoters on mouse skin. Sensitivity to compounds active at other tissue sites in rodents and perhaps man has also been observed. At this time it is difficult to assess the relevance of the C3H10T1/2 system for the study of agents capable of modulating respiratory carcinogenesis. The process of promotion can possess extreme tissue and species specificity and effects observed in murine fibroblasts of embryonic origin may have little practical bearing upon effects to be anticipated in the tracheal epithelium of the rat or the bronchial epithelium of man. This is not to say that the C3H10T1/2 system is irrelevant to respiratory carcinogenesis. However, due recognition must be taken of the probable natural limitations of this system for the study of promoters of respiratory carcinogenesis. As the data base for the use of this system is expanded, the relationship between promotion in C3H10T1/2 cells and the respiratory tract of man and rodents will become better defined. Until such time as this relationship is firmly established, it is perhaps best to regard the C3H10T1/2 system as an interesting model with which results obtained using respiratory tissue can be compared or contrasted.