ABSTRACT
Historically speaking, the rst photosensitizer (PS) to be used in a clinical setting was psoralen, still used today in psoriasis treatment (PUVA, psoralene and ultraviolet A radiation) (Figure 6.1). However, most commonly, photosensitizers are porphyrin derivatives due to not only their high absorption in the rednear-infrared region of light (signicantly increasing the depth at which PDT can be used in tissue), but they are also naturally occurring compounds and/or can be chemically synthesized and modied using “simple” chemical synthetic approaches (Juzeniene and Moan, 2007). With regard to porphyrins, hematoporphyrin derivative (HpD) was the rst to be developed for clinical use and is generally considered a rst-generation PS. Attempts to improve on its poor light absorption, long tissue retention times, low tumor-tissue ratios, low water solubility, and prolonged photosensitization of patients led to so-called second-generation PS, typical examples being Visudyne, Temoporn, and δ-aminolevulinic acid (ALA), the biosynthetic precursor of protoporphyrin IX (Juzeniene et al., 2007).
