Improved Photodynamic Therapy of Hepatocellular Carcinoma via Surface-Modified Protein Nanoparticles

Background: Photodynamic therapy (PDT) has evolved as a reliable therapeutic modality for cancer. However, the broad application of the technique is still limited because of poor bioavailability and the non-selective distribution of photosensitizers within host tissues. Herein, zein, a natural corn protein, was functionalized with glycyrrhetinic acid (GA) and polyethylene glycol (Z-PEG-GA) as a targeting platform for liver cancer cells. Parietin, as novel photosensitizer, was successfully encapsulated into zein via nanoprecipitation and used for the therapy of hepatocellular carcinoma. Methods: The in vitro phototoxicity of Z-PEG-GA nanoparticles and their non-functionalized control (Z-PEG) were assessed against hepatocellular carcinoma (HepG2 cells) and the In vivo biodistribution was determined in an adult male CD-1 Swiss albino mice model. Results: The formulated Z-PEG and Z-PEG-GA showed spherical shapes with average sizes of 82.8 and 94.7 nm for unloaded nanoparticles, respectively, and 109.7 and 111.5 nm for loaded nanoparticles carrying more than 70% of parietin, and Quantum yield measurements show that parietin's photodynamic potential is conserved. Moreover, parietin-loaded Z-PEG-GA exhibited three-fold higher toxicity against liver cancer cells than its non-functionalized control and attained more than an eleven-fold enhancement in the generated intracellular reactive oxygen species (ROS) at a 9 J/cm² radiant exposure. The generated intracellular ROS led to mitochondrial disruption and the release of cytochrome c. In vivo biodistribution studies revealed that fluorescence signals of Z-PEG-GA can persist in the excised animal liver for up to 24 h post-administration. Conclusions: Consequently, tailored zein can hold great potential for delivering several hydrophobic photosensitizers in anticancer PDT.