Chitosan-Poly(Acrylic Acid) Nanoparticles Loaded with R848 and MnCl2 Inhibit Melanoma via Regulating Macrophage Polarization and Dendritic Cell Maturation

Purpose Since immune cells in the tumor microenvironment (TME) can affect the development and progression of tumors, strategies modulating immune cells are considered to have an important therapeutic effect. As a TLR7/8 agonist, R848 effectively activates the innate immune cells to exert an anti-tumor effect. Mn 2+ has been reported to strongly promote the maturation of antigen-presenting cells (APCs), thereby enhancing the cytotoxicity of CD8 + T cells. Thus, we tried to investigate whether chitosan-poly(acrylic acid) nanoparticles (CS-PAA NPs) loaded with R848 and MnCl 2 (R-M@CS-PAA NPs) could exert an anti-tumor effect by regulating the function of immune cells. Methods R-M@CS-PAA NPs were prepared, and their basic characteristics, anti-tumor effect, and potential mechanisms were explored both in vitro and in vivo. Results R-M@CS-PAA NPs easily released MnCl 2 and R848 at low pH. In B16F10 mouse melanoma model, R-M@CS-PAA NPs exerted the most significant anti-melanoma effect compared with the control group and CS-PAA NPs loaded with R848 or MnCl 2 alone. FITC-labeled R-M@CS-PAA NPs were displayed to be accumulated at the tumor site. R-M@CS-PAA NPs significantly increased the infiltration of M1 macrophages and CD8 + T cells but reduced the number of suppressive immune cells in the TME. Moreover, in vitro experiments showed that R-M@CS-PAA NPs polarized macrophages into the M1 phenotype to inhibit the proliferation of B16F10 cells. R-M@CS-PAA NPs also enhanced the killing function of CD8 + T cells to B16F10 cells. Of note, R-M@CS-PAA NPs not only promoted the maturation of APCs such as dendritic cells and macrophages by STING and NF-кB pathways, but also enhanced the ability of dendritic cells to present ovalbumin to OT-I CD8 + T cells to enhance the cytotoxicity of OT-I CD8 + T cells to ovalbumin-expressing B16F10 cells. Conclusion These data indicate that the administration of R-M@CS-PAA NPs is an effective therapeutic strategy against melanoma.