Does melanin affect the low LET radiation response of Cloudman S91 mouse melanoma cell lines?
Melanin contains melanin-free radicals and can both absorb and produce additional free radicals and active oxygen species on exposure to various stimuli. Yet its role in the radiation responses of malignant melanoma has been little studied. In this report, three subclones of Cloudman S91 mouse melanoma clone PC1A varying in constitutive melanin content were compared with respect to killing by gamma irradiation. Radiation responses correlated with melanin content. The least melanotic line, S91/amel, was most sensitive and the most melanotic line, S91/I3, was most resistant. Curve fitting using the linear-quadratic model suggests that S91/amel is killed only by single event inactivations; S91/I3, only by double event inactivations; and S91/M1B, with intermediate melanin and radiation response, by both types of inactivations. Split dose experiments confirmed a lack of immediate split dose recovery in S91/amel and its existence in S91/I3. Potentially lethal damage and its repair could be d
