Meso-tetraphenylporphyrin in liposomes as a suitable photosenzitizer for photodynamic therapy of tumors

The suitability of a liposomal form of hydrophobic nonsulfonated meso-tetra phenyl porphyrin (TPP) for the photodynamic therapy of tumors was investiga ted. TPP was solubilized in small unilamellar lipid vesicles prepared by ex trusion on a LIPOSOFAST apparatus. These samples were studied by laser-exci ted time resolved luminescence and triplet-triplet absorption spectroscopy. In this lipid environment TPP was still an efficient singlet oxygen produc er, as indicated by the characteristic singlet oxygen phosphorescence at 12 70 nm in D2O, when excited with a 28 ns laser pulse at 412 nm. Moreover, un like with sulfonated TPP (TPPS4), liposomal TPP showed the reduced decay ra tes of TPP triplet-states with the increasing time of pre-illumination by a Xenon Tamp. This was shown in an indirect way, based upon the appearance o f a second component of the luminescence decay at 1270 nm in D2O; and by di rect TPP triplet state monitoring, detecting triplet-triplet absorption at 440 nm in H2O The deactivation of higher triplet states was delayed upon pr e-illumination, This reflects an irreversible interaction of singlet oxygen with membrane lipids, thus demonstrating the potential of the liposomal fo rm of TPP to efficiently disintegrate tumor cell membranes and to be a suit able preparation for the photodynamic therapy.