Tumor hypoxia, acidosis, and excessive reactive oxygen species (ROS) were the main characteristics of the bladder tumor microenvironment (TME), and abnormal TME led to autophagy activation, which facilitated cancer cell proliferation. The therapeutic efficacy of autophagy inhibitors might also be impeded by abnormal TME. To address these issues, we proposed a new strategy that utilized manganese dioxide (MnO2) nanoparticles to optimize the abnormal TME and revitalize autophagy inhibitors, and both oxygenation and autophagy inhibition may sensitize the tumor cells to radiation therapy. Methods: By taking advantage of the strong affinity between negatively charged MnO2 and positively charged chloroquine (CQ), the nanoparticles were fabricated by integrating MnO2 and CQ in human serum albumin (HSA)-based nanoplatform (HSA-MnO2-CQ NPs). Results: HSA-MnO2-CQ NPs NPs efficiently generated O2 and increased pH in vitro after reaction with H+/H2O2 and then released the encapsulated CQ in a H+/H2O2 concentration-dependent manner. The NPs restored the autophagy-inhibiting activity of chloroquine in acidic conditions by increasing its intracellular uptake, and markedly blocked hypoxia-induced autophagic flux. In vivo studies showed the NPs improved pharmacokinetic behavior of chloroquine and effectively accumulated in tumor tissues. The NPs exhibited significantly decreased tumor hypoxia areas and increased tumor pH, and had remarkable autophagy inhibition efficacy on bladder tumors. Finally, a significant anti-tumor effect achieved by the enhanced autophagy inhibition and radiation sensitization. Conclusions: HSA-MnO2-CQ NPs synergistically regulated the abnormal TME and inhibited autophagic flux, and effectively sensitized radiation therapy to treat bladder cancers.
Keywords: Tumor microenvironment; autophagy inhibitor; manganese dioxide; radiation therapy.
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