Ultrasmall Barium Titanate Nanoparticles for Highly Efficient Hypoxic Tumor Therapy via Ultrasound Triggered Piezocatalysis and Water Splitting.

Hypoxia in a solid tumor microenvironment (TME) can lead to the overexpression of hypoxia-inducible factor-1α (HIF-1α), which correlates to tumor metastasis. Reactive oxygen species (ROS) induced tumor cell apoptosis is becoming a promising method in tumor treatment. Currently, the ROS generating systems, e.g., photodynamic treatment and sonodynamic treatment, highly depend on oxygen (O) in the tumor microenvironment (TME). However, the level of O in TME is too low to produce enough ROS. Herein, we developed an ultrasmall DSPE-PEG coated barium titanate nanoparticle (P-BTO) for tumor treatment based on ultrasound triggered piezocatalysis and water splitting. Interestingly, irradiated by ultrasound, the surface of ultasmall P-BTO nanoparticles produced imbalance charges, which induced a cascade of redox reaction processes to simultaneously generate ROS and O, the latter one was hardly generated in large-sized barium titanate nanoparticles. The as-synthesized P-BTO reached the highest accumulation in the tumor site at 4 h after intravenous injection. The results showed that the produced O significantly alleviated the hypoxia of TME to down-regulate the expression of HIF-1α, and the produced ROS can efficiently kill tumor cells. Moreover, the tumor metastasis was also inhibited, providing a different way to treat triple-negative breast cancer, which was easily metastatic and lacked effective treatments in the clinic.