Pheophorbides as photosensitizers for the photodynamic therapy of tumors

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Quantum yields for formation of singlet molecular oxygen have been measured for sodium pheophorbides (Na-Phdes) a and b in aqueous and non-aqueous media. Measurements have been made for both steady-state and pulsed laser excitation with the resultant singlet molecular oxygen being detected by photo-oxygenation reactions or time-resolved luminescence spectroscopy, respectively. Singlet oxygen production sensitized by Na-Phdes a or b is insignificant in aqueous media but occurs with a good efficiency in organic solvents. Plasmid DNA is efficiently photocleaved by Na-Phdes a and b in the absence of oxygen as well as in the presence of oxygen. Fluorescence microscopic observation shows a rapid incorporation of Na-Phde a into nuclei, mitochondria, and lysosome of human oral mucosa cells. In contrast Na-Phde b is incorporated only into the plasma membrane. The photodynamic activity of these pigments in living tissues is probably determined by the monomeric pigment molecules formed in hydrophobic cellular structures.

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