ABSTRACT
Tumor microenvironment (TME) is a complex comprehensive system composed of immune cells, inflammatory cells, tumor-associated fibroblasts, microvessels, and various cytokines and chemokines. As the living environment of tumor cells, it's closely related to the occurrence, metastasis, and recurrence of tumors. The characteristics of tumor microenvironment include: weakly acidic environment, low oxygen, high concentration of reactive oxygen species (ROS) and reducing substances, immunosuppression, etc. A weakly acidic environment favors metastasis of tumor cells, hypoxia is conducive to the emergence of drug resistance, high concentration of ROS and reducing substances are beneficial for tumor treatment, and immunosuppressiveness facilitates immune escape. With the rapid development of nanotechnology, more and more nanostructures have been reported to achieve tumor treatment by regulating the tumor microenvironment. This review summarizes recent advances in the nanostructures used to regulate tumor microenvironment through changing elements, including hydrogen-ion concentration (pH), the concentration of oxygen (O2) and reactive oxygen species, and the activity of immune cells. Moreover, research directions in the future are pointed out in this review.