5,10,15,20-Tetrakis(4-hydroxyphenyl)porphyrin was functionalized by covalent attachment of poly(ethylene glycol) (PEG) chains of various molecular weights, 350, 2000, and 5000 Da. The properties of PEG-functionalized tetraarylporphyrins in aqueous solution and their interactions with liposomes have been studied. Electronic absorption spectroscopy, dynamic light scattering, atomic force microscopy, and fluorescence quenching were used to monitor aggregation of porphyrin chromophores and behavior of the attached PEG chains in the aqueous solution. The tendency for aggregation of porphyrin chromophores in aqueous solution and the efficiency of fluorescence quenching by KI decrease with increasing length of PEG chain linked to the porphyrin ring. The experimental results indicate that polymer clusters are present in aqueous solution of all pegylated porphyrins. The interactions between the pegylated porphyrins and phosphatidylcholine liposomes in the aqueous solution were studied using the fluorescence methods. The apparent binding constants of porphyrin chromophores to liposomes were determined. The degree of binding was found to be dependent on the molecular weight of the attached polymer.
Photodynamic theraphy (PDT) is a clinically approved method for treatment of cancer and some other diseases. It employs the combination of a drug (photosensitizer) and light to induce photoxicity towards the cancerous cells. The efficiency of currently used photosensitizers is limited due to their aggregation in aqueous media and low chemical purity; usually a mixture of various isomers is used. This paper presents the results of our studies on the development of nanostructural materials for PDT. They are constructed from porphyrin (Po) which is covalently attached to the chain of hydrophylic polymer such as poly(methacrylic acid) (PMA) or poly(ethylene glycol) (PEG) and solubilized in lipid bilayer of liposome vesicles. The attachment of Po to the polymer chain improves its solubility in water while the solubilization in liposome carriers helps the dye to penetrate the cell membranes. Physicochemical and photophysical properties of those systems were determined. The in vitro studies on cancer cell lines demonstrated that the photosensitizers are efficiently accumulated in the cells. Their dark toxicity is negligible, while phototoxicity is very high.
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