Monocyte/macrophage-mediated transport and intratumoral bacteria-responsive ZIF nanoplatform for enhanced immunotherapy against microsatellite-stable colorectal cancer

The low infiltration and insufficient tumor recognition of cytotoxic-T-lymphocytes (CTLs) are the two primary reasons for the low objective response rate of programmed death-1 protein (PD-1) inhibitors in treating microsatellite-stable colorectal-cancer (MSS-CRC). Ginsenoside Rg1 (Rg1) and atractylenolide-I (Att) can promote CTLs infiltration and recognition of CTLs by facilitating dendritic cells (DCs) maturation and upregulating tumor MHC-I expression, respectively, and the combination of two drugs is expected to improve the efficacy of PD-1 inhibitors. However, due to their poor water solubility and limited tumor targeting, the intratumoral delivery of both drugs faces challenges. Our previously reported a tumor-apoptotic-body-membrane (Ab) modified zeolitic-imidazolate-framework (ZIF) for co-delivering Rg1 and Att (Ab@Rg1/Att-ZIF). It could be transported by monocytes/macrophages into the deep tumor regions, however, partial formulations would be degraded by intracellular lysosomes. To overcome this, we innovatively incorporated inulin into Ab@Rg1/Att-ZIF, constructing an Ab/In@Rg1/Att-ZIF delivery system. By virtue of the Ab and inulin coating on its surface, the system could be specifically phagocytosed by monocytes/macrophages while maintaining stability in the lysosomal. Furthermore, after being transported to CRC tissues, inulin of the Ab/In@Rg1/Att-ZIF is enzymatically degraded by enzymes secreted by intratumoral bacteria, releasing Rg1 and Att to promote DCs maturation and upregulate tumor MHC-I expression, respectively. Ab/In@Rg1/Att-ZIF significantly inhibits tumor growth by enhancing CTLs infiltration and recognition, synergizing with PD-1 inhibitors to achieve a tumor suppression rate of ≈80 %, which is markedly higher than the combined efficacy of Ab@Rg1/Att-ZIF. This study provides new insights for the immunotherapy of MSS-CRC and the intratumoral co-delivery of drugs. • Ab/In@R1/Att-ZIF could be transported to tumor by monocytes/macrophages and remained stable within cells. • Drugs in Ab/In@Rg1/Att-ZIF can be enzymatically released by intratumoral microbiota. • Ab/In@R1/Att-ZIF synergizes with PD-1 inhibitors against microsatellite-stable colorectal cancer.