Cloudman S91 mouse
melanoma cells vary in constitutive and inducible
melanin levels. Survival, mutation induction and DNA damage were quantitated after exposure to UVB, UVA and FS20 lamps. Assuming that the observed differences are related to
melanin, induced pigment is photo-protective for survival and mutation after UVB and FS20 exposure, and is photosensitizing for survival after UVA exposure. No changes in
pyrimidine dimers could be measured. DNA damage in pigmented mouse melanocytes (
melan-a and melan-b) was greater than that in albino melanocytes (melan-c) after UVB and FS20, and the pigmented cells were more sensitive to killing. Pigment appears to be protective for killing by UVA in these melanocytes. Human melanocytes from different skin types vary in both
melanin amount and composition (eu- and
pheomelanin). Effects of pigmentation on UVB responses are unclear. In UVA, heavily pigmented cells have more DNA damage than lightly pigmented cells, but are resistant to killing. Increased
pheomelanin photosensitizes DNA damage in lightly pigmented cells. Since
eumelanin predominates in the mouse
melanoma cells and melanocytes, they are less likely than human cells to provide a satisfactory model for human solar melanomagenesis. In order to understand the mechanism of photocarcinogenesis of
melanoma,
melanins in human melanocytes from different pigment types should be carefully quantitated and characterized. Mutations induced in them by solar wavelength-emitting lamps with well-characterized spectra should be measured, and mutant
DNA should be sequenced to determine the nature of the solar-induced lesions. Research should focus on UVA and
pheomelanin.