Free radicals in melanotic human melanoma and human colon adenocarcinoma cells after photodynamic therapy

Changes of free radical system in two different types of tumor cells after photodynamic therapy (PDT) were compared. Melanotic human melanoma cells (SK-MEL) and human colon adenocarcinoma cells (Caco-2) were tested. Melanin pigment does not exist in Caco-2, while is present in SK-MEL cells. Tumor cells were treated using 5-8-aminolevulinic acid (ALA) and irradiated with 635nm light. Changes in paramagnetic centers were examined in SK-MEL and Caco-2 6 hours after PDT treatment. The EPR spectra were recorded using an electron paramagnetic resonance spectrometer at X-band (9.3 GHz) with magnetic modulation of 100 kHz. Relatively stronger EPR lines were measured for control SK-MEL cells than for Caco-2 cells. The content of o-semiquinone in melanin in SK-MEL cells is responsible for this effect. Free radicals in Caco-2 cells, resulted from broken bounds in unsaturated fatty acids revealed relatively lower EPR lines. irradiation of both melanotic (SK-MEL) and non melanotic (Caco-2) cells with 635 nm light was accompanied by the increase of free radical content. After light irradiation, the decrease of free radical concentration was observed in SK-MEL and Caco-2 cells, first treated with ALA. The effects were stronger for SK-MEL than for Caco-2 cells.