Dynamic fluorescence changes during photodynamic therapy in vivo and in vitro of hydrophilic Al(III) phthalocyanine tetrasulphonate and lipophilic Zn(II) phthalocyanine administered in liposomes

The fluorescence emission of hydrophilic tetrasulphonated aluminium phthalocyanine (AlPcS(4)) and hydrophobic zinc phthalocyanine (ZnPc), bound to the membrane of liposomes, was investigated in vivo in an appropriate tumour model of the rat bladder and in RR 1022 epithelial cells of the rat. The sensitizers were administered systemically to the rats and photodynamic therapy (PDT) was performed 24 h later. During PDT treatment, the fluorescence was measured every 30 s. The fluorescence was excited with 633 nm light from an HeNe laser and the fluorescence spectra were detected with an optical mulichannel analyser system. PDT was performed for both sensitizers using 672 nm light from an Ar+ dye laser. The fluorescence changes during PDT were significantly different for the two phthalocyanines. For AlPcS(4), an initial fluorescence intensity increase, followed by subsequent photobleaching, was observed. In contrast, ZnPc fluorescence showed an exponential decrease and no increase at the start of treatment, Tumour necrosis 24 h after PDT was significant only for ZnPc. RR 1022 cells incubated for 24 h with AlPcS(4) revealed a granular fluorescence pattern, whereas ZnPc was localized diffusely in the cytoplasm of the cells. In agreement with the in vivo measurements, subcellular relocalization and a fluorescence intensity increase were detected exclusively in the case of AlPcS(4). Morphological changes at this time were significant only for ZnPc. The subcellular localization and fluorescence kinetics were obtained using a confocal laser scanning microscope.