Targeted sonodynamic therapy using protein-modified TiO2 nanoparticles

Our previous study suggested new sonodynamic therapy for cancer cells based on the delivery of titanium dioxide (TiO₂) nanoparticles (NPs) modified with a protein specifically recognizing target cells and subsequent generation of hydroxyl radicals from TiO₂ NPs activated by external ultrasound irradiation (called TiO₂/US treatment). The present study first examined the uptake behavior of TiO₂ NPs modified with pre-S1/S2 (model protein-recognizing hepatocytes) by HepG2 cells for 24 h. It took 6 h for sufficient uptake of the TiO₂ NPs by the cells. Next, the effect of the TiO₂/US treatment on HepG2 cell growth was examined for 96 h after the 1 MHz ultrasound was irradiated (0.1 W/cm², 30 s) to the cells which incorporated the TiO₂ NPs. Apoptosis was observed at 6 h after the TiO₂/US treatment. Although no apparent cell-injury was observed until 24 h after the treatment, the viable cell concentration had deteriorated to 46% of the control at 96 h. Finally, the TiO₂/US treatment was applied to a mouse xenograft model. The pre-S1/S2-immobilized TiO₂ (0.1 mg) was directly injected into tumors, followed by 1 MHz ultrasound irradiation at 1.0 W/cm² for 60 s. As a result of the treatment repeated five times within 13 days, tumor growth could be hampered up to 28 days compared with the control conditions.