Scheme 1.

Schematic mechanism of CaO₂@HMSNs-PAA serving as tumor environment-responsive nanoparticles for the antitumor therapy of prostate cancer. The natural pH value of the blood and normal tissues can prevent the release of H₂O₂ from CaO₂@HMSNs-PAA. However, the acidic tumor environment (TME) contributes to the responsive release of CaO₂, followed by the tendency to generate more H₂O₂. In addition, after intracellular uptake of CaO₂@HMSNs-PAA by endocytosis, the more acidic environment in the lysosomes can result in the enhanced release of H₂O₂. Compared with normal cells, the extra exogenous ROS that has accumulated in tumor cells cannot be effectively decomposed because of the elevated basal level of ROS and the overburdened antioxidant system, consequently inducing the mitochondria-mediated apoptosis via remarkable oxidative stress.