THE ROLE OF OXYGEN IN CUTANEOUS PHOTODYNAMIC THERAPY

Photodynamic therapy (PDT) is based on the dye-sensitized photooxidati on of biological matter in the target tissue, and utilizes light activ ated drugs for the treatment of a wide variety of malignancies. Skin i s a target organ for PDT, because of the increasing incidence of skin cancers and the easy accessibility to photosensitizing drugs and light . Skin oxygen tension changes dramatically during and after PDT and se ems to be an important treatment parameter. Experimental approaches to modulate oxygen tension (e.g., hyperbaric oxygenation, hyperthermia, or perfluorocarbons) have been studied mainly in animals, and some of these techniques may have the potential to be applied in humans to imp rove the efficacy and safety of PDT. The main purpose of this review i s to provide the reader with current information on cutaneous oxygen p hysiology and oximetry, the role of oxygen and singlet oxygen (O-1(2)) in PDT, and approaches to modulate skin oxygen tension. The literatur e indicates that it may be possible to utilize transcutaneous oxygen m easurements as a valuable measure of the clinical effectiveness of PDT and as an in situ predictor of the energy required to elicit a biolog ical response. Consequently the effectiveness of PDT can be manipulate d by modulating skin oxygen tension. (C) 1998 Elsevier Science Inc.