Frequencies of sister chromatid exchanges in heteroploid cell lines of human melanoma origin.

Sister chromatid exchange(s) (SCE) per cell and chromosome in five heteroploid cell lines and sublines of human melanoma origin were distinctly more numerous than those in the normal diploid control. The SCE per unit chromosome length was higher in stable heteroploid C32 (0.041-0.047) and C9 (0.056) than in normal diploid control. The SCE per unit chromosome length was higher in stable heteroploid C32 (0.041-0.047) and C9 (0.056) than in normal diploid control C182 (0.036), which suggested that the longer the total chromosome length of the cell genome, the higher the SCE per cell as well as per unit chromosome length. These malignant heteroploid lines had karyotypes ranging from hypodiploidy to hypotriploidy and were extremely heterogeneous in one cell line but unusually homogenous and stable in others. However, none of these properties could be correlated to the increase in SCE frequency. As compared to C32-r7, the subline C32-RO had more SCE per cell, chromosome, and unit chromosome length for the genome as well as for 9 of 11 individual chromosomes and chromosome groups. In contrast, the C32-RO specific ring marker chromosome had only 40% of the SCE of its nonring homologue in C32-r7 cells. Interestingly, C32-RO and its ring marker were less stable than C32-r7 and the nonring marker during in vitro growth. There was no noticeable difference between C32-r7 and its derivative C32-r7-nu-1, which implied that transplantation into nude mice did not alter the expression of SCE in this subline.