Spontaneous sister chromatid exchange in metastatic variants of the murine B16 melanoma and human astrocytomas in culture.

Three metastatic variants, BL6 (high metastasis), F1 (nonmalignant) and F10 (intermediate malignancy) of the B16 murine melanoma, and a pulmonary metastatic line BL6-ML8 of the BL6 primary tumour have been examined for spontaneous sister chromatid exchange (SCE). Two human astrocytoma cell lines were also examined. SCE was encountered in 29 and 13% of second division metaphases of BL6 and F10. In contrast, only 3% of second division metaphases of the F1 showed SCE. In BL6-ML8, 40% of the metaphases showed SCE. Approximately 2-4% of the human astrocytoma second division cells showed SCE. The variant lines were karyotypically heterogeneous. The pattern of cell distribution according to chromosome number showed an overall similar profile in the melanoma variants. However, the metastatic BL6-ML lines showed a marked shift to a hypertriploid state. SCEs occurred with higher frequency in this hypertriploid subpopulation of BL6 and F10 cells than in F1. SCE incidence in the hypertriploid subpopulation was twofold higher in the metastatic line than in the primary BL6 line. The number of SCEs per chromosome was twice as high in F10, BL6 and BL6-ML8 as in the F1 cells. This hypertriploid subpopulation showed a marked increase of SCEs on exposure to mitomycin C and ethyl methane sulphonate, indicating their mutability. It is suggested that the parallelism between SCE and metastatic potential may be relevant in the context of the generation of the metastatic phenotype.