Electron paramagnetic resonance evidence of the generation of superoxide (O 2.− and hydroxyl ( .OH) radicals by irradiation of a new photodynamic therapy photosensitizer, Victoria Blue BO

Abstract

Electron paramagnetic resonance (EPR) experiments were performed on Victoria Blue BO, a cationic dye whose photocytotoxicity has been studied against the human leukaemic cell lines K-562 and TF-1. EPR experiments with 2,2,6,6-tetramethyl-4-piperidone and spin trapping with 5,5-dimethyl-1-pyrroline- N-oxide showed that, on illumination in aerated aqueous solution or dl-α-dipalmitoylphosphatidylcholine liposomes, photoexcited Victoria Blue BO is unable to generate 1O 2, whereas O 2 .− and ·;OH are trapped by 5,5-dimethyl-1-pyrroline- N-oxide in the presence or absence of electron donors. The O 2 .− formed probably leads to the ·OH radical, with an efficiency which is increased by electron donors such as Fe 2+.