Human and rodent transformed cells are more sensitive to in vitro induction of SCE by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) than normal cells.

The sensitivity to sister chromatid exchange (SCE) induction by N-methyl-nitro-N'-nitrosoguanidine (MNNG) in human, mouse, Chinese hamster, and Syrian hamster normal cell strains and in permanent transformed cell lines of the same species was compared. Exponentially growing or growth-inhibited cultures of permanent cell lines transformed spontaneously or by chemical carcinogen or oncogenic virus responded with a higher SCE frequency after MNNG treatment than did normal diploid cell strains. Compared with the normals, exponentially growing Simian virus 40 transformed human fibroblast GM637 had the highest SCE frequency, followed by mouse cell line alpha L929 and Chinese hamster V79-4; the least sensitive were two Syrian hamster cell lines, OBP, derived from transformation of embryo cells with benzo(a)pyrene, and BHK, a spontaneously transformed baby hamster kidney line. Similar results were obtained with cultures arrested in G1 with glutamine-arginine deficient medium. The SCE response observed with transformed cells to carcinogen probably reflects cellular changes associated with the transformed state, such as shortening of the cell cycle, excision repair deficiency, or an increase in DNA replicon size. The current results demonstrating a difference in SCE induction between normal and malignant cells are important since normal or transformed cultured cells are utilized to assess potentially deleterious environmental agents, particularly carcinogens. In general, SCE induction by a specific direct acting carcinogen may be a useful approach for identifying transformed cells with the ability to produce tumors.