Abstract

An overview of the field of photodynamic therapy (PDT) will be presented. PDT is based on the concept that (a) certain photoactivatable compounds, called photosensitizers, can be localized (somewhat preferentially) in neoplastic tissue and (b) subsequently, these photosensitizers can be photoactivated with the appropriate wavelength of light to generate active molecular species such as free radicals and singlet oxygen that are toxic to cells and tissues. A potential advantage of PDT is its inherent dual selectivity. First, selectivity is achieved by an increased concentration of the photosensitizer in target tissue, and second, the irradiation can be limited to a specified volume. Provided that the photosensitizer is nontoxic, only the irradiated areas will be affected, even if the photosensitizer does bind to normal tissues. Selectivity can be further enhanced by binding photosensitizers to molecular delivery systems that have high affinity for target tissue. For photoactivation, the wavelength of light is matched to the electronic absorption spectrum of the photosensitizer so that photons are absorbed by the photosensitizer and the desired photochemistry can occur. Although the initial focus of PDT was cancer, today there is a great deal of interest in the non-cancer applications of PDT. Current status and future directions for applications of PDT and an overview of PDT-related mechanisms will be discussed.

© 1998 Optical Society of America