Application of EPR spectroscopy to examination of free radicals in melanins from A-375 and G-361 human melanoma malignum cells

Melanins are polymorphous and multifunctional biopolymers with a relatively high concentration of free radicals. EPR spectroscopy was used to study o-semiquinone free radicals in model eumelanins synthesized from 3,4-dihydroxyphenylalanine (DOPA) and tyrosine in the presence of tyrosinase, and melanins isolated from A-375 and G-361 human melanoma malignum cells exposed to two compounds: 5,7-dimethoxycoumarin (DMC) and valproic acid (VPA). Changes were determined in the concentrations of free radicals in the individual melanins from tumour cells treated with DMC and VPA. A strong decrease in the concentrations of free radicals characterizes melanins isolated from tumour cells treated together with DMC and VPA. Slow spin-lattice relaxation processes were noted in the melanins tested with homogeneous broadened EPR spectra. The EPR technique may be useful not only for the elucidation of free radicals in melanins from A-375 and G-361 cells treated with VPA and DMC but it could also be applied to establish the relationship between melanin type and the malignancy of melanoma malignum.