ELECTRON-PARAMAGNETIC-RESONANCE EVIDENCE OF THE GENERATION OF SUPEROXIDE (O-2(CENTER-DOT-)) AND HYDROXYL ((OH)-O-CENTER-DOT) RADICALS BY IRRADIATION OF A NEW PHOTODYNAMIC THERAPY PHOTOSENSITIZER, VICTORIA-BLUE-BO

Electron paramagnetic resonance (EPR) experiments were performed on Vi ctoria Blue BO, a cationic dye whose photocytotoxicity has been studie d against the human leukaemic cell lines K-562 and TF-1. EPR experimen ts with 2,2,6,6-tetramethyl-4-piperidone and spin trapping with 5,5-di methyl-1-pyrroline-N-oxide showed that, on illumination in aerated aqu eous solution or DL-alpha-dipalmitoylphosphatidylcholine liposomes, ph otoexcited Victoria Blue BO is unable to generate O-1(2), whereas O-2( .-) and (OH)-O-. are trapped by 5,5-dimethyl-1-pyrroline-N-oxide in th e presence or absence of electron donors. The O-2(.-) formed probably leads to the (OH)-O-. radical, with an efficiency which is increased b y electron donors such as Fe2+.