Polymeric indoximod based prodrug nanoparticles with doxorubicin entrapment for inducing immunogenic cell death and improving the immunotherapy of breast cancer.

Immunotherapy based on host immunity has emerged as a powerful therapeutic strategy for tumor treatment. However, utilizing the immune system against tumors often fails to result in a durable immune response due to insufficient immunogenicity and the immunosuppressive conditions in the tumor microenvironment. Herein, we developed prodrug-based nanoparticles (DOX/IND@NPs) for the codelivery of indoximod (IND), an indoleamine 2,3-dioxygenase (IDO) inhibitor that can block the IDO pathway and generate antitumor immunity, and doxorubicin, a DNA-damaging therapeutic agent that can induce tumor immunogenic cell death (ICD). The nanocarrier was designed for tumor chemoimmunotherapy, synergistically promoting immunogenicity and modulating the immunosuppressive tumor microenvironment (ITME). Our data showed that DOX induced tumor immunogenicity and increased the infiltration of CD8 + T cells into the tumor microenvironment; nevertheless, immunosuppressive immune cell components, such like regulatory T cells (Tregs), myeloid-derived suppressor cells (MDSCs), and tumor associated macrophages (TAMs), hindered the antitumor efficacy. The introduction of IND reduced the levels of these protumor immune cells within the tumor microenvironment and further enhanced CD8 + T cell infiltration and the CD8 +/Treg cell ratio. Moreover, significant reductions in vascular endothelial growth factor (VEGF), MMP9, and CD31 (a vascular marker) expression levels were observed after DOX-IND nanoparticle treatment. This resulted in obvious tumor regression in a murine breast cancer model compared to reference formulations, indicating that the codelivery of DOX and IND is a potent potential strategy for breast cancer chemoimmunotherapy.