Programmable co-delivery of the immune checkpoint inhibitor NLG919 and chemotherapeutic doxorubicin via a redox-responsive immunostimulatory polymeric prodrug carrier

To achieve synergistic therapeutic efficacy and prevent cancer relapse, chemotherapy and immunotherapy have been combined as a new modality for tumor treatment. In this work, we designed a redox-responsive immunostimulatory polymeric prodrug carrier, PSSNIO, for programmable co-delivery of an immune checkpoint inhibitor NLG919 （NLG） and a chemotherapeutic doxorubicin （DOX）, NLG-containing PSSNIO prodrug polymers were self-assembled into nano-sized micelles that served as a carrier to load DOX （DOX/ PSSNIO micelles）. DOX/PSSNIO micelles displayed spherical morphology with a size of -170 nm. DOX was effectively loaded into PSSNIO micelles with a loading efficiency of 84.0%. In vitro DOX release studies showed that rapid drug release could be achieved in the highly redox environment after intracellular uptake by tumor cells. In 4T1.2 tumor-bearing mice, DOX/PSSNIO micelles exhibited greater accumulation of DOX and NLG in the tumor tissues compared with other organs. The PSSNIO carrier dose-dependently enhanced T-cell immune responses in the lymphocyte-Panc02 co-culture experiments, and significantly inhibited tumor growth in vivo. DOX/PSSNIO micelles showed potent cytotoxicity in vitro against 4T1.2 mouse breast cancer cells and PC-3 human prostate cancer cells comparable to that of DOX. In 4T1.2 tumor-bearing mice, DOX/PSSNIO mixed micelles （5 mg DOX/kg, iv） was more effective than DOXlL （a clinical formulation of liposomal DOX） or free DOX in inhibiting the tumor growth and prolonging the survival of the treated mice. In addition, a more immunoactive tumor microenvironment was observed in the mice treated with PSSNIO or DOX/ PSSNIO micelles compared with the other treatment groups. In conclusion, systemic delivery of DOX via PSSNIO nanocarrier results in synergistic anti-tumor activity.