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Spatio-temporal redistribution of mTHPC from lipid nanovesicles in chick chorioallantoic membrane model
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Liposomal formulations of mTHPC (Foslip, Fospeg) were initially proposed to improve its chemico-biological properties and distribution in targeted tissues. They permitted the preservation of the monomeric state of the molecule and the enhancement of its pharmacokinetic and clearance. Previous experiments realized by our laboratory with mTHPC (Mitra et al. 2005, Garrier et al. 2010; Lassalle et al 2009) demonstrated the primary importance of spatio-temporal distribution of the molecule for optimization of PDT dosimetric parameters (drug- light interval, drug dose...). Optimization of PDT parameters for photosensitizers embedded into the liposomes also requires the comprehension of the PSs repartition from lipid nanovesicles. However, there are not data concerning the distribution of mTHPC in relation with the degradation of lipid nanovesicules administered in vivo. This analysis is actually conducted by using the chick chorioallantoic membrane (CAM) model with lipid nanovesicles which contain mTHPC and a fluorescent probe of nanovesicle integrity pyrene. Activity of pyrene is based on a mechanism of FRET (Fluorescence Resonance Energy Transfer) where pyrene plays the role of energy donor while mTHPC stands for an acceptor of energy. The measurement of their fluorescence lifetimes by FLIM technique (Fluorescence Lifetime Imaging Microscopy) reflects the state of integrity of the lipid nanovesicule. The energy transfer in intact liposome was confirmed by a strong diminution (>1000 fold) of fluorescence lifetime of pyrene in the presence of mTHPC. The optimization of this technique permits to study fluorescence lifetime in CAM in relation with the time after intravenous injection of mTHPC loaded in liposome.
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