Evaluation of Oxygen Consumption of Culture Medium andIn VitroPhotodynamic Effect of Talaporfin Sodium in Lung Tumor Cells

Abstract

Successful photodynamic therapy (PDT) requires high production of radical ions and singlet oxygen to kill target cells. However, PDT also induces angiogenesis through production of vascular endothelial growth factor (VEGF), which promotes cell regrowth and vascularization. In this study, we evaluated the importance of oxygen in PDT by measuring oxygen consumption, photosensitizer bleaching, and reactive oxygen species (ROS) production in the culture medium, and VEGF secretion either during or after PDT treatment using mouse Lewis lung carcinoma (LLC) cells. Local hypoxia is induced under a low oxygen environment. Oxygen is consumed when ROS and singlet oxygen are produced during PDT. The effect of oxygen consumption on cytotoxicity and VEGF secretion has not been clarified. Mouse Lewis lung carcinoma (LLC) cells treated with the photosensitizer talaporfin sodium were irradiated by a continuous wave semiconductor laser (wavelength, 664 +/- 1 nm). We used oxygen microelectrode for oxygen measurement, a fluorescent probe to detect ROS, MTT assay to evaluate the PDT efficacy, and enzyme-linked immunosorbent assay to measure VEGF concentration. During PDT, oxygen consumption was higher with high doses of talaporfin sodium solution compared with low doses. In addition, the fluorescence of 2-[6-(4'-amino)phenoxy-3H-xanthen-3-on-9-yl]benzoic acid, a probe for highly reactive oxygen species such as hydroxyl radicals (*OH), dramatically increased when the dose of talaporfin sodium solution was high. Moreover, VEGF concentration increased after PDT due to hypoxia in a manner dependent on photosensitizer concentration. These results indicate that the efficiency of PDT might be improved by sustaining a replete oxygen environment during PDT, not only for ROS and singlet oxygen production, but also for inhibiting neoangiogenesis.