Synergic photosensitizers: A new trend in photodynamic therapy

Photodynamic therapy (PDT) has become an increasingly important method for the chemotherapeutic treatment of some cancers. It involves the systemic, topical, or intraperitoneal administration of a nontoxic drug called a photosensitizer, which, to some extent, preferentially localizes in the tumor [1,2]. When the tumor is illuminated with the wavelength of light that is absorbed by the dye, in the presence of oxygen, toxic oxygen reactive species are produced and they can cause tissue necrosis or apoptosis by a combination of mechanisms [3]. The Phthalocyanine complexhas recently become very popular in different areas of science and technology. Due to many useful physical and chemical properties, these complexes have found use in opticaland semi conducting devices [4], electrochemistry [5], catalysis [6], analytical chemistry [7] and photodynamic therapy [8]; and have been extensively reviewed in the last decade [9,10]. The main disadvantage of using phthalocyanines is their enhanced tendency to participate in aggregation processes dependent on the central metal ion, which leads to low solubility in biological aqueous medium. Photosensitizers could be natural or synthetic [11]. In general,the three main families of photosensitizers are porphyrin-based compounds, chlorophyll-based compounds or phthalocyanine derivatives [12]. A number of novel compounds consisting of multifunctional ligands, such as phthalocyanine-nucleobase conjugates, phthalocyanine-dendrimers and crown ethers or macro-aza group moieties have been reported recently. The objective of this review is to describe recent progress in photosensitizer concepts along with an indication of some prominent synergic photosensitizers.