Nanoparticles targeting tumor-associated macrophages: A novel anti-tumor therapy

The immunosuppressive tumor microenvironment (TME) is crucial in the occurrence of tumorigenesis, metastasis, and drug resistance. Among all stromal cells, tumor-associated macrophages (TAMs) are recognized as vital components causing the TME to be favorable for cancer cells and are also main targets in cancer immunotherapy. To date, nanoparticle (NP)-based drug delivery systems, as new technology platforms, have exhibited considerable advantages, such as targeted drug delivery at tumor sites, enhanced drug transport efficiency, and controllable drug release profiles, which provide new approaches for cancer therapy. Regarding TAM-targeting nanoparticles, various therapeutic strategies have been developed by varying their design, namely, by blocking TAM recruitment, promoting TAM transformation, and directly diminishing existing TAMs. In the current review, we provide a brief overview of the role of TAMs in the tumor microenvironment and their functions and highlight strategies for TAM targeting. Moreover, the applications of nanoparticles in targeting TAMs to improve cancer therapeutic efficiency are summarized.