Photosensitizing Activity of Pegylated Pheophorbide a

Photodynamic therapy (PDT) is a non-invasive therapeutic modality used in a various number of diseases and cancer. It involves the systemic or topic administration of a photosensitizer, followed by irradiation with light. The activated photosensitizer converts oxygen to singlet oxygen and/or reactive oxygen species (ROS) which lead to cell death and tissue necrosis. One aim of PDT research is the discovery of new photosensitizers possessing minimal dark cytotoxicity, high photodynamic properties, improved pharmacokinetics, preferential retention in diseased instead of healthy tissues, chemical stability and a good cellular uptake .We recently focused our efforts on pheophorbide a (Pba), a chlorophyll derivative. Pba is characterized by a stronger absorption between 650-700 nm, in the tissuepenetrating wavelength range. For in vivo applications the capacity of the photosensitiser to reach in the diseased tissues becomes critical, in particular when a large peritoneal area is interested as occurring in carcinomatosis and sarcomatosis. To improve the pharmacokinetic and the activity of the photosensitizer we conjugated Pba to polyethylene glycol (PEG). In vivo the pharmacokinetic analysis performed on living female C57/BL6 mice bearing a subcutaneous melanoma mass, showed that injected mPEG-Pba distributes all over the body, with an higher uptake in the tumor respect to free Pba. Moreover, preliminary data suggest that PEG-Pba in mice bearing B78-H1 amelanotic melanoma reduces the tumor growth after light activation in comparison with Pba.