PHOTOSENSITIZERS IN PHOTODYNAMIC THERAPY

Photodynamic therapy (PDT) of neoplastic lesions is a rapidly developi ng new modality for treatment of solid tumors. Although more controlle d clinical trials have to be performed to establish its appropriate ro le in clinical practice, PDT seems to have a clear potential to become a treatment of choice for several types of cancer. Its current clinic al status and perspectives are briefly reviewed. The characteristics o f Photofrin, the photosensitizer used in clinical PDT are discussed in detail. The mechanism of tumor localization of Photofrin and other ph otosensitizers is examined. The process of tumor destruction by PDT, w hich includes direct killing of tumor cells and an indirect mechanism involving damage to tumor vasculature followed by induction of tumor n ecrosis, is also presented. The outlined development of new, potential ly more effective photosensitizers is guided by the acquired knowledge on the properties that would be optimal for such drugs when used in c linical PDT. In conclusion, perspectives for potentiation of PDT by co mbining it with immunotherapy are elaborated.