Photodynamic therapy is a clinical treatment that employs a combination of a photosensitizer, oxygen, and visible light for the therapy of cancer. This technique is characterized by the systemic administration of photosensitizer, which is preferentially retained by tumoral tissue. The subsequent irradiation, with visible light, cause excitation of the photosensitizer resulting in the production of reactive oxygen species such as superoxide radical and singlet oxygen. These reactive species generate a sequence of oxidative events resulting in cancer cell death. The superoxide is generated in the type I mechanism by electron transference from excited photosensitizer to ground-state oxygen. Singlet oxygen is generated in the type II mechanism by energy transference from excited photosensitizer to ground-state oxygen. In this study we investigated the photosensitizing properties of three porphyrins. The results allow for the conclusion that the three porphyrins caused the destruction of cells in the presence of light and oxygen. This event was increased by deuterium oxide and inhibited by singlet oxygen scavengers indicating the predominance of type II mechanism.
Photodynamic Therapy; porphyrins; reactive oxygen species
