Photocytotoxicity of mTHPC (temoporfin) loaded polymeric micelles mediated by lipase catalyzed degradation.

PURPOSE: To study the in vitro photocytotoxicity and cellular uptake of biodegradable polymeric micelles loaded with the photosensitizer mTHPC, including the effect of lipase-catalyzed micelle degradation. METHODS: Micelles of mPEG750-b-oligo(epsilon-caprolactone)5 (mPEG750-b-OCL5) with a hydroxyl (OH), benzoyl (Bz) or naphthoyl (Np) end group were formed and loaded with mTHPC by the film hydration method. The cellular uptake of the loaded micelles, and their photocytotoxicity on human neck squamous carcinoma cells in the absence and presence of lipase were compared with free and liposomal mTHPC (Fospeg). RESULTS: Micelles composed of mPEG750-b-OCL5 with benzoyl and naphtoyl end groups had the highest loading capacity up to 30% (w/w), likely due to pi-pi interactions between the aromatic end group and the photosensitizer. MTHPC-loaded benzoylated micelles (0.5 mg/mL polymer) did not display photocytotoxicity or any mTHPC-uptake by the cells, in contrast to free and liposomal mTHPC. After dilution of the micelles below the critical aggregation concentration (CAC), or after micelle degradation by lipase, photocytotoxicity and cellular uptake of mTHPC were restored. CONCLUSION: The high loading capacity of the micelles, the high stability of mTHPC-loaded micelles above the CAC, and the lipase-induced release of the photosensitizer makes these micelles very promising carriers for photodynamic therapy in vivo.

Photosensitiser-loaded biodegradable polymeric micelles: preparation, characterisation and in vitro PDT efficacy.

The application of photosensitisers (PSs) in photodynamic therapy (PDT) is often hampered by their hydrophobicity, as this complicates their formulation and results in an unfavourable biodistribution. Consequently, there is an urgent need for novel delivery vehicles for PSs. In this paper, the loading and stability of thermosensitive mPEG-b-p(HPMAm-Lac2) micelles with a hydrophobic solketal-substituted phthalocyanine (Si(sol)2Pc) photosensitiser were studied. It was shown that the Si(sol)2Pc could be loaded efficiently in the micelles (diameter 75 nm) up to a concentration of approximately 2 mg/mL. UV/Vis and fluorescence spectroscopy showed that at low concentrations (< or =0.05 microM, 0.45 mg/mL polymer), the PS was molecularly dissolved in the micellar core, whereas it was present in an aggregated form at higher concentrations. In B16F10 and 14C cells, the photocytotoxicity of Si(sol)2Pc-loaded micelles (PS<0.05 microM) was similar to free PS, i.e. IC(50) of 3.0+/-0.2 nM (10% serum). The cellular uptake of high-loaded micelles (10 microM Si(sol)2Pc) was low and independent of the serum concentration. The nanoaggregates of Si(sol)2Pc loaded in the micellar core were only released upon hydrolysis-induced micellar dissociation, which was observed after 5.5 h at pH 8.7 at 37 degrees C. The stability of the high-loaded micellar Si(sol)2Pc formulation also in the presence of serum, the controlled release of the PS upon micellar disintegration and the high photodynamic activity of Si(sol)2Pc make these micelles interesting for future in vivo studies.

Peripheral and axial substitution of phthalocyanines with solketal groups: synthesis and in vitro evaluation for photodynamic therapy.

Phthalocyanines (Pcs) are a class of photosensitizers (PSs) with a strong tendency to aggregate in aqueous environment, which has a negative influence on their photosensitizing ability in photodynamic therapy. Pcs with either peripheral or axial solketal substituents, that is, ZnPc(sol)8 and Si(sol)2Pc, respectively, were synthesized and their tendency to aggregate as well as their photodynamic properties in 14C and B16F10 cell lines were evaluated. The results were compared to more hydrophilic silicon Pcs, that is, Si(PEG750)2Pc and Pc4. The order of cellular uptake was Pc4 > ZnPc(sol)8 > Si(PEG750)2Pc > Si(sol2)Pc. In contrast, Si(sol2)Pc showed the highest photocytotoxicity, while ZnPc(sol)8 did not show any photocytotoxicity up to a concentration of 10 microM in both cell types. UV/vis spectroscopy showed that Si(sol)2Pc is less prone to aggregation than ZnPc(sol)8, which can explain the lack of photoactivity of the latter. Si(sol)2Pc was predominantly located in lipid droplets, whereas Si(PEG750)2Pc was homogeneously distributed in the cytosol, which is probably the main cause of their difference in photoactivity. The very high photodynamic efficacy of Si(sol)2Pc makes this PS an interesting candidate for future studies.