Preparation of protoporphyrin IX loaded nanostructured lipid carriers for anticancer photodynamic therapy

Photodynamic therapy (PDT) is a promising strategy for cancer treatment. However, the poor hydrophilicity of most photosensitizers makes them difficult to enter the cells and also susceptible to aggregation-induced quenching in aqueous environment. In this study, we encapsulated protoporphyrin IX (PPIX) by nanostructured lipid carrier to obtain a water-soluble PPIX delivery system (NLC-PPIX). The nanoparticles exhibited high colloidal stability and good fluorescence emission. The generation of ¹O₂ from the NLC-PPIX was verified using 9,10-anthracenediyl-bis(methylene)dicarboxylic acid (ABDA) as ¹O₂ indicator. The ¹O₂ quantum yield of the NLC-PPIX in aqueous solution was calculated to be ∼9%. The flow cytometry and fluorescence imaging confirmed the uptake of NLC-PPIX by the A2058 cells and the generation of ¹O₂ inside the cells under light excitation. The in vitro cytotoxicity assay showed that the NLC-PPIX exerted no toxicity on the A2058 cells under dark conditions, while light irradiation triggered high phototoxicity. The cell viability of the A2058 cells was significantly decreased and the inhibition rate reached approximately 96% by treating the cells with 200 μg/mL NLC-PPIX and 420 nm light irradiation. The successful cancer cell uptake and PDT effect revealed the therapeutic promise of our drug delivery system.