[Experimental studies on the hyperthermia-photodynamic effect of tumor cells photosensitized with Y-HpD]

Experimental studies were made on the hyperthermia-photodynamic effect of tumor cells photosensitized with Y-HpD (China-made). Fluorescence spectra were determined in different animal and human cancer tissues before and after treatment. The results showed: Hyperthermia (42-44 degrees C) significantly increased the efficacy of photodynamic therapy (PDT) with a prolongation of survival time of mice and significant difference between PDT groups with and without hyperthermia (P less than 0.05). However, this difference was not present with mild hyperthermia (39-40 degrees C); A new fluorescence band was first observed in animal and human cancer cells after PDT treatment (with or without hyperthermia), with a maximum emission wave-length of 460 nm (excitation wave-length, 370 nm). The intensity of the band being correlated with cancer cell destruction, and the highest fluorescence intensity together with the strongest cytocidal effect were seen in the PDT-plus-heat group. Most Y-HpD was found the cytoplasm after treatment, with little Y-HpD left in the nucleus. The amount of Y-HpD in the cells decreased with the formation of fluorophores in the cytoplasm as a product of photochemical reactions. The authors suggest that hyperthermia may activate Y-HpD, and the increase of cellular Y-HpD then enhances the photochemical reaction.