Photodynamic Therapy as a New Prospective Method for Cancer TreatmentI. History, Basic Principles

Overview

Photodynamic therapy (PDT) is a new method for the treatment of both cancer or non-cancerdiseases. It combines three basic elements (a photosensitizer, light, oxygen), every single one withno toxicity or biological activity. The photosensitizer (PS) is activated by light and it gets excited. Ittransfers absorbed energy from this excited form to oxygen forming reactive oxygen species (ROS),mainly singlet oxygen. Then ROS attack surrounding biomolecules, inhibit their biological functionleading in the end to a cell death. The complete destruction of the tumour is provided not only bya direct effect on the cells, but also a vasculature shutdown (leading to nourishment and oxygendepletion) and an activation of the immunity response play an important role in this process. Thepresent paper proposes to introduce the readers to the history and basic principles of PDT from thepoint of view of either the physical mechanism of PS activation or biological effects on the targettissue (on molecular, subcellular, cellular, and tissue levels).

Key words:
photodynamic therapy – singlet oxygen – photosensitizer