Electron paramagnetic resonance evidence of the generation of superoxide (O2.-) and hydroxyl (.OH) radicals by irradiation of a new photodynamic therapy photosensitizer, Victoria Blue BO.

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-alpha-dipalmitoylphosphatidylcholine liposomes, photoexcited Victoria Blue BO is unable to generate 1O2, whereas O2.- and .OH are trapped by 5,5-dimethyl-1-pyrroline-N-oxide in the presence or absence of electron donors. The O2.- formed probably leads to the .OH radical, with an efficiency which is increased by electron donors such as FE2+.