Study of interaction of hypericin and its pharmaceutical preparation by fluorescence techniques

Accumulation and penetration behavior of hypericin in glioma tumor spheroids studied by fluorescence microscopy and confocal fluorescence lifetime imaging microscopy

Glioblastoma WHO IV belongs to a group of brain tumors that are still incurable. A promising treatment approach applies photodynamic therapy (PDT) with hypericin as a photosensitizer. To generate a comprehensive understanding of the photosensitizer-tumor interactions, the first part of our study is focused on investigating the distribution and penetration behavior of hypericin in glioma cell spheroids by fluorescence microscopy. In the second part, fluorescence lifetime imaging microscopy (FLIM) was used to correlate fluorescence lifetime (FLT) changes of hypericin to environmental effects inside the spheroids. In this context, 3D tumor spheroids are an excellent model system since they consider 3D cell-cell interactions and the extracellular matrix is similar to tumors in vivo. Our analytical approach considers hypericin as probe molecule for FLIM and as photosensitizer for PDT at the same time, making it possible to directly draw conclusions of the state and location of the drug in a biological system. The knowledge of both state and location of hypericin makes a fundamental understanding of the impact of hypericin PDT in brain tumors possible. Following different incubation conditions, the hypericin distribution in peripheral and central cryosections of the spheroids were analyzed. Both fluorescence microscopy and FLIM revealed a hypericin gradient towards the spheroid core for short incubation periods or small concentrations. On the other hand, a homogeneous hypericin distribution is observed for long incubation times and high concentrations. Especially, the observed FLT change is crucial for the PDT efficiency, since the triplet yield, and hence the O₂ activation, is directly proportional to the FLT. Based on the FLT increase inside spheroids, an incubation time > 30 min is required to achieve most suitable conditions for an effective PDT.

Complexes of Chlorin e6 with Pluronics and Polyvinylpyrrolidone: Structure and Photodynamic Activity in Cell Culture

Polymeric carriers are extensively used in photodynamic therapy (PDT) for increase of efficacy of photosensitizers. Here, we report the influence of nine Pluronic copolymers on phototoxicity of chlorin e6 (Ce6), in particular 5- to 7-fold rise in the phototoxicity caused by hydrophilic Pluronics F127, F108, F68 and F87 and practically no influence on Ce6 of more hydrophobic polymers. The revealed value of 0.2 mg mL(-1) of Pluronic F127 concentration sufficient for half-of-maximal increase of Ce6 photodynamic activity proved to be close to 0.16 mg mL(-1) inherent in well-documented carrier poly(N-vinylpyrrolidone) (PVP). The dissociation constants of Ce6 complexes with Pluronic F127 and PVP that were estimated from UV spectra were 0.252 and 0.036 mg mL(-1) , respectively, indicating higher stability of Ce6 complex with PVP. According to the results of (1) H-NMR studies of Ce6 complexes, the porphyrin interacts not only with hydrophobic regions but also with hydrophilic sides of both polymers.