Phthalocyanines are promising photosensitizers for photodynamic therapy due to their advantageous light absorption properties and low dark toxicity. Two non-peripheral substituted phthalocyanines, tetra-ethoxy-Zn-phthalocyanine (CH3Pc) and its fluorinated analogue (CF3Pc), were combined with different nanocarriers, and their photophysical properties and biological activities were studied. Carrier-encapsulation and phthalocyanines' aggregation state were probed by NMR-, UV-Vis-, and fluorescence spectroscopy. Five different carrier systems were compared: polyvinylpyrrolidone (PVP), two triblock copolymer micelles (Synperonic P84, "P84", and Pluronic F127, "F127"), self-emulsifying detergent micelles (Kolliphor RH40, "RH40"), and 1, 2-dioleoyl-sn-glycero-3-phosphocholine unilamellar vesicles (ULVs). CH3Pc inserted efficiently into P84, F127 and RH40 micelles in monomeric form, while CF3Pc was encapsulated as dimers and oligomers. ULVs were capable to efficiently monomerize and encapsulate both phthalocyanines. PVP was not suitable to solubilize neither of these phthalocyanines. The localization of CH3Pc and CF3Pc at the carrier interfaces was determined by NMR-experiments with atomic resolution. All phthalocyanine-carrier systems - except PVP - exhibited efficient singlet oxygen production, with ULVs reaching the highest quantum yields. The photodynamic potential of the different CH3Pc- and CF3Pc-formulations was studied using a human breast cancer cell line (MCF-7) by measuring the dark toxicity and phototoxicity after light irradiation at 655 nm. Encapsulation into ULVs and RH40 micelles exhibited the highest photodynamic efficiency for both phthalocyanines at low concentrations (0.05-1 µM). The fluorinated phthalocyanine showed enhanced photodynamic activity compared to its non-fluorinated analogue. While micellar carriers easily monomerized CH3Pc, ULV-encapsulated CF3Pc turned out to be the best candidate as efficient sensitizer for photodynamic therapy.
Bruegger et al. (Thu,) studied this question.