SISTER-CHROMATID EXCHANGE (SCE) RATES IN HUMAN-MELANOMA CELLS AS AN INDEX OF MUTAGENESIS

Melanomas are highly clonogenic. Genetic variability and polymorphism of tumour cell populations have been reported. However, no direct evid ence of mutator activity as a source of genetic polymorphism for melan oma cells has been described. Some intermediates of melanin synthesis are cytotoxic and genotoxic and their mutagenic power has been describ ed. We show here that the rate of sister chromatid exchange (SCE) of t he line of human melanoma cells used varies with the concentration of the melanin precursor L-tyrosine, in the culture medium, An increase o f melanin synthesis results in increased SCE rates. The highest values of SCEs are found in melanotic melanoma cells compared with the amela notic ones, Indeed we present evidence that melanoma cells show higher levels of SCE when compared with normal human lymphocytes, and to the SCE frequencies derived from the literature on the lymphocytes of fam ilial malignant melanoma, sporadic malignant melanoma patients and the lymphocytes of relatives of familial and sporadic melanoma patients.