Baseline and mitomycin-C-induced sister chromatic exchanges ina melanoma and a colon tumor cell line

Baseline and mitomycin C (MMC)-induced sister chromatid exchanges (SCEs) in two human tumor cell lines (a colon tumor and a melanoma) and in a normal fibroblast cell line were analyzed and compared. The tumor cells showed numerical and structural chromosomal abnormalities. Their baseline SCE rate was slightly, but not significantly, higher than that of the control. Each tumor cell line showed a dose-dependent increase in SCE frequency above the spontaneous level in its own specific manner. The response in the malanoma cell was consistently below that of the control, but only the response to the highest dose of MMC (10(-9) M) was significantly lower than that of the control. The response of the colon tumor cells varied with respect to that of the control. Thus, it appears that karyotypic instability in tumor cells is not necessarily associated with elevated baseline or induced SCE/chromosome rates. In addition, within each cell line dose group, the SCE frequency was proportional to the number of chromosomes. thus, the SCE/chromosome is a better expression of genetic damage than SCE/metaphase in analyses involving heteroploid cells.