Qualitative Differences in the Generation of Activated Oxygen Species by Photosensitizers Used in PDT

Abstract

Summary The photosensitizers commonly used in PDT represent a chemically inhomogeneous group of compounds. They generate cytotoxic reactive oxygen species (“ROS”), including various oxygen based radicals and the non-radical activated form of oxygen, singlet oxygen 1 O 2 . The various ROS are physically and chemically very different, and this fact may well be expected to have biological importance. Direct measurements of 1 O 2 or radical generation must be performed to answer questions concerning their relative generation by photosensitizers. The aim of these studies was to develop methods using electron spin resonance (ESR) to investigate in vitro the degree to which some commonly used photosensitizers generate the different activated oxygen products in aqueous solution. ESR spectroscopy can be used to effectively distinguish photosensitizers with respect to such products, and can serve to specifically probe biological questions important to PDT.