Abstract
Photodynamic therapy (PDT) is a treatment for both neoplastic and nonneoplastic diseases utilizing photochemical reactions induced by a photosensitizer, light and oxygen in the target tissue. PDT consists of administration of a photosensitizer that selectively accumulates in the target tissue and laser irradiation at a specific wavelength to produce photochemical reactions. This photoactivation produces singlet oxygen and other reactive oxygen species that cause oxidative damage to cellular components, triggering either cellular repair and recovery or cell death by apoptosis and/or necrosis. The mechanisms of PDT tumor eradication include the direct damage by phototoxic action, collapse of the tumor vasculature, and induced inflammatory cell infiltration and tumor immunity. Our experimental approach to enhance PDT effects revealed the following results : (1) fractionated laser irradiation improves PDT efficacy due to reoxygenation in the target tissue (2) combined administration of PDT and cisplatin enhances both antitumor effect and apoptotic cell death (3) hyperthermic PDT enhances antitumor effect (4) PDT combined with a biological response modifier, OK-432 improves PDT efficacy. Our clinical trial for oral cancer treatment is described. PDT is a minimally invasive modality and, unlike ionizing radiation, can be applied repeatedly at the same site.
