The degree of pigmentation modulates the radiosensitivity of human melanoma cells

The relationship between cell pigmentation and radiosensitivity was investi gated in two selected human melanoma cell lines with different melanin cont ent (mixed type: eumelanin and pheomelanin, and pheomelanotic phenotypes), The same study was also done after stimulation of melanogenesis (1) by addi tion of the melanin precursor L-tyrosine to each of the cell lines separate ly and (2) by irradiation alone with doses ranging from 0 to 10 Gy, We foun d that a decrease in cell radiosensitivity was correlated with the type of melanin, with a dear involvement of eumelanin rather than pheomelanin, Incr easing the intracellular content of both melanins promoted the growth of ir radiated cells. Moreover, at a dose of 10 Gy, both tyrosinase activity and melanin cell content were significantly increased in the absence of any oth er melanogenesis promoter. Our data suggest that the amount of intracellula r melanin is inversely related to the radiosensitivity of melanoma cells an d may explain at least in part the controversial responses to ionizing radi ations reported for melanoma, (C) 2000 by Radiation Research Society.