Abstract
Cancer cells frequently exhibit MHC-I deficiency, impairing immune-mediated cytotoxicity even in the presence of PD-1 checkpoint inhibition. To date, no clinically approved therapies exist that can upregulate MHC-I expression to boost immune responses against cancer cells. Emerging evidence has shown that autophagy plays a role in MHC-I molecule degradation, contributing to reduced recognition of cancer cells by CD8+ T cells. We previously report that fangchinoline, a bisbenzylisoquinoline alkaloid derived from Chinese herb, is a novel autophagy inhibitor with an adjuvant of chemotherapy against lung cancer. In this study we investigated the modulatory effects of PD-1 blockade combined with fangchinoline on CD8+ T cells within the tumor microenvironment of lung cancer. We showed an inverse correlation between elevated autophagic activity and decreased MHC-I surface expression-a phenomenon often associated with poor clinical efficacies-in various human lung cancer cell lines (NCI-H1299, NCI-H1975, A549, NCI-H1650 and NCI-H446) compared with normal bronchial epithelial cells lung cancer. Knockdown of ATG4 and ATG5 resulted in increased MHC-I expression and enhanced tumor antigen presentation in NCI-H1975, NCI-H1299 and A549 cells. As autophagy receptors were crucial for transporting proteins to autophagosomes for degradation, we sequentially silenced various autophagy receptors and found that NDP52 knockdown specifically restored MHC-I expression, suggesting that NDP52-mediated autophagy might contribute to MHC-I degradation, and autophagy inhibition might enhance immune-mediated cancer cell death. We showed that pretreatment of LLC-OVA cells with the autophagy inhibitor fangchinoline (1.25, 2.5, 5 μM) followed by coculture with CD8+ T cells, dose-dependently enhanced immune killing. In both in vitro and in vivo experiments, we showed that fangchinoline combined with anti-PD-1 therapy significantly increased CD8+ T cell-mediated cytotoxicity. In conclusion, this study highlights NDP52 as a key autophagy receptor involved in MHC-I degradation and provides a new insight into tumor immune evasion. Combining autophagy inhibition with immunotherapy may be a promising therapeutic strategy for anticancer immunity enhancement.