Photophysicals and photochemicals studies of zinc(II) phthalocyanine in long time circulation micelles for Photodynamic Therapy use

Long time circulation systems, such as polymeric micelles, represent a growing area in biomedical research. These microparticles can be used in many biological systems to provide appropriate drug levels with a specific biodistribution. Long time circulation micelles (LTCM) were routinely prepared using PEG-5000-DSPE (polyethyleneglycol-5000-distearoil-phosphatidyl-ethanolamine) and zinc(II) phthalocyanine (ZnPc) as a photosensitizer and fluorescent probe. This compound belongs to a second generation of photoactive agents, mainly used in photodynamic therapy (PDT) of neoplasic tissues. Their high selectivity for tumoral target tissues as well as high phototoxicity based on singlet oxygen generation renders the utilization of these compounds feasible as an alternative therapy for cancer treatment. LTCM were characterized by classical spectroscopic techniques. Absorbance measurements indicated that the drug was s completely loaded into LTCM (s = 2.41 x 10(5) cm(-1)). This was also verified by steady state and time-resolved fluorescence measurements. The lifetime profiles of ZnPc decay curves were fitted according to biexponential function (tau(1), = 3.9 ns and tau(2) = 15.5 ns) indicating different locations for ZnPc into LTCM. The time-resolved spectroscopy measurements for ZnPc triplet excited state lifetimes (tau(T)) were calculated from the kinetic analysis of transient decays at the absorption maximum (480 nm), by using laser flash photolysis technique. All the spectroscopy measurements performed allowed us to conclude that, ZnPc, in LTCM is a promising drug delivery system (DDS) for PDT. (C) 2004 Elsevier B.V. All rights reserved.