Analysis of the Process of Malignant Transformation of Human Fibroblasts in Culture by Ionising Radiation and Other Carcinogens

摘要

Carcinogenesis is a multistep process by which normal cells acquire the properties of tumourigenic cells by various genetic and epigenetic changes, i.e. become transformed. Several cell culture assays have been devised for studying various aspects of the transformation process in vitro. The most common use of in vitro cell transformation assays is to detect potentially carcinogenic agents. Typically, the agent being tested is used to treat infinite life-span rodent fibroblasts, such as mouse fibroblasts, or finite life-span Syrian hamster embryo cells. With the C3H 10T1/2 cells, the characteristic that is assayed after treatment with a carcinogen is the induction of distinct foci on a confluent monolayer of nontransformed cells; with the hamster cells, it is the induction of morphologically altered colonies. The frequency of induction of cells exhibiting either of these properties can be quantified, although with the C3H 10T1/2 cells, this is not straightforward. The C3H 10T1/2 cells isolated from Type III foci are highly tumourigenic in athymic mice, whereas with the Syrian hamster embryo cells, the cells isolated from the morphologically altered colonies have the potential to acquire an infinite life span and eventually become tumourigenic . With the latter cells, the ability of an agent to induce morphologically altered colonies has been shown to correlate with its tumourigenic effect in animals. The weakness of both of these types of rodent cell transformation assays is that the mechanisms that underlie the specific characteristic being assayed are not yet well understood. A distinctly different application of mammalian cell transformation assays is their use for investigating the molecular changes required for malignant transformation of cells in culture. Syrian hamster cells have been extensively investigated for this purpose. In this application, known carcinogenic agents are used to induce specific new phenotypic properties in the target cells, and the investigator then seeks to link such new characteristics to the specific genetic or nongenetic change(s) induced in the cells. The use of C3H 10T1/2 fibroblasts for such purposes is not practical, because these sub-tetraploid cells have already acquired many unknown but critical changes that make them readily able to be transformed into malignant cells by carcinogen treatment.