Subcellular localization of meta-tetra(hydroxyphenyl) chlorin in human tumor cells subjected to photodynamic treatment

Subcellular localization of meta-tetra(hydroxyphenyl)chlorin (mTHPC) in HT2 9 human colon adenocarcinoma cells has been studied by means of fluorescenc e microscopy. The observed diffuse intracellular distribution of mTHPC fluo rescence outside the nucleus indicates general staining of cellular organel les. No changes in dye fluorescence pattern are evident during and immediat ely after cell illumination. Alternatively, the changes in mTHPC fluorescen ce pattern are observed upon subsequent cell incubation, and are characteri zed by the appearance of distinct bright fluorescence zones. Reaching a max imum 1 h after illumination, modifications of the fluorescence pattern then gradually disappear in parallel with the formation of plasma membrane bleb s, suggesting that cell necrotic lysis is taking place. Photosensitized dam age to mitochondria and the Golgi apparatus has been studied using fluoresc ent probes 1 h after irradiation, the stage of extensive cytoplasm vacuoliz ation, and reveal alterations of these organelles. Changes in the mTHPC flu orescence pattern and mTHPC photocytotoxicity, as measured by the MTT test 24 h after illumination, are inhibited by sodium azide, a singlet oxygen qu encher. (C) 1999 Elsevier Science S.A. All rights reserved.