Sister chromatid exchange (SCE) rates in human melanoma cells as an index of mutagenesis

Melanomas are highly clonogenic. Genetic variability and polymorphismof tumour cell populations have been reported. However, no directevidence of imitator activity as a source of genetic polymorphismfor melanoma cells has been described. Some intermediates ofmelanin synthesis are cytotoxic and genotoxic and their mutagenicpower has been described. We show here that the rate of sisterchromatid exchange (SCE) of the line of human melanoma cellsused varies with the concentration of the melanin precursorL-tyrosine, in the culture medium. An increase of melanin synthesisresults in increased SCE rates. The highest values of SCEs arefound in melanotic melanoma cells compared with the amelanoticones. Indeed we present evidence that melanoma cells show higherlevels of SCE when compared with normal human lymphocytes, andto the SCE frequencies derived from the literature on the lymphocytesof familial malignant melanoma, sporadic malignant melanomapatients and the lymphocytes of relatives of familial and sporadicmelanoma patients. ³To whom correspondence should be addressed