The Binding Characteristics and Intracellular Localization of Temoporfin (mTHPC) in Myeloid Leukemia Cells: Phototoxicity and Mitochondrial Damage¶

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Abstract
The state of aggregation of the photosensitizer meso-tetrahydroxyphenylchlorin (mTHPC) in both cell free and intracellular environment was elucidated by comparing its absorption and excitation spectra. In methanol, mTHPC existed as monomers and strongly fluoresced. In aqueous solutions such as phosphate-buffered saline (PBS), mTHPC formed nonfluorescent aggregates. Some portion of mTHPC monomerized in the presence of 10% fetal calf serum PBS. In murine myeloid leukemia M1 and WEHI-3B (JCS) cells, cytoplasmic mTHPC were monomeric. By using organelle-specific fluorescent probes, it was found that mTHPC localized preferentially at the mitochondria and the perinuclear region. Photodynamic treatment of mTHPC-sensitized leukemia cells caused rapid appearance of the apoptogenic protein cytochrome c in the cytosol. Results from flow cytometric analysis showed that the release of cytochrome c was especially pronounced in JCS cells, and well correlated with the extent of apoptotic cell death as reported ea...