[32] Mechanism of photodynamic therapy-induced cell death

Photodynamic therapy (PDT) is a promising new therapeutic procedure for the management of a variety of solid tumors and also possesses a potential against many nonmalignant diseases. PDT depends on the uptake of a photosensitizing compound by the diseased tissue to be treated, followed by its irradiation with visible light of an appropriate wavelength that correlates with the absorption spectrum of the photosensitizing compound, in the presence of molecular oxygen. A proper understanding of the mechanism of PDT-mediated cancer cell kill that may result in improving the efficacy of this treatment modality is far from complete. It is believed that PDT, by generating reactive oxygen species (ROS), results in oxidative damage to the cellular organelles. This damage triggers a combination of biochemical, genetic, and molecular events, which have a common cell destruction goal. Necrosis and apoptosis have been shown to contribute for cell kill by PDT. This chapter provides general information on PDT and a brief account of the mechanisms responsible for PDT-mediated cell death.