Photosensitizer loaded HSA nanoparticles. I: Preparation and photophysical properties.

Photodynamic therapy (PDT) is a promising option in the treatment of cancer. Efficient photosensitizers are available but many of them have insufficient physico-chemical properties for parenteral application. We have established nanoparticles consisting of human serum albumin (HSA) as a drug carrier system for 5,10,15,20-tetrakis(m-hydroxyphenyl)porphyrine (mTHPP) and 5,10,15,20-tertrakis(m-hydroxyphenyl)chlorin (mTHPC), two well-known photosensitizers. Nanoparticle loading was performed in water/ethanol mixtures in the presence of dissolved HSA acting as solubilizer for photosensitizers. The HSA concentration was optimized to exclude precipitation in the nanoparticle suspension and to increase binding to nanoparticles. Additionally, the influence of pH and incubation time on drug adsorption was investigated. A freeze drying method was established for mTHPC loaded nanoparticles and the storage stability of the freeze dried formulation was tested. PDT related photophysical parameters of drug loaded HSA nanoparticles, especially singlet oxygen generation, are presented. Both preparations were able to generate singlet oxygen with low quantum yield. In contrast, efficient singlet oxygen generation was obtained when Jurkat cells were incubated with mTHPP and mTHPC loaded HSA nanoparticles. This indicates that the photosensitizer molecules were successfully released from the nanoparticles that were taken up by the cells. Therefore, the efficiency of HSA nanoparticles as drug carriers for photosensitizers was proven under in vitro conditions.

Nanowells on silica particles in water containing long-distance porphyrin heterodimers.

Smooth and nonswelling spherical silica particles with a diameter of 100 nm and an aminopropyl coating are soluble in water at pH 11, coagulate quickly at pH 3, and redissolve at pH 9. Electron microscopy as well as visible spectra of covalently attached porphyrins indicate the aggregation state of the particles. Long-chain alpha,omega-dicarboxylic acids with a terminal oligoethyleneglycol (=OEG)-amide group were attached in a second self-assembly step to the remaining amine groups around the porphyrins. Form-stable 2-nm wells were thus obtained and were characterized by fluorescence quenching experiments using the bottom porphyrin as a target. The one-dimensional diffusion of fitting quencher molecules along the 2-nm pathway took several minutes. Porphyrins with a diameter above 2 nm could not enter the form-stable gaps at all. Added tyrosine stuck irreversibly to the walls of the nanowells and prevented the entrance of quencher molecules, the OEG-headgroups fixated 2,6-diaminoanthraquinone. A ring of methylammonium groups was then fixed at the walls of the wells at a distance of 5 or 10 A with respect to the bottom porphyrin. 2,6-Disulfonatoanthraquinone was attached only loosely to this ring, but the exactly fitting manganese(III) meso-(tetraphenyl-4-sulfonato)porphyrinate (Mn(III) TPPS) was tightly bound. Transient fluorescence experiments showed a fast decay time of 0.2 ns for the bottom porphyrin, when the Mn(III) TPPS was fixated at a distance of 5 A. Two different dyes have thus been immobilized at a defined subnanometer distance in an aqueous medium.