Tumor AMPK Activation Facilitates NK Cell Anti-tumor Immunity And Synergizes With PD-L1 Blockade Therapy

Cancer is the leading cause of death worldwide.Although immune checkpoint blockade therapy targeting the programmed cell death protein-1/ programmed death ligand-1(PD-1/PD-L1)axis has shown impressive clinical success,only a subset of patients with cancer can benefit from it.Thus,it is of great significance to conduct the in-depth research on the mechanisms that regulate anti-tumor immunity,and further improve the clinical response to cancer immunotherapy.Natural killer(NK)cells are critical components in immunosurveillance against cancer.NK cell infiltration into tumors is reported to correlate with better survival,and with improved response to checkpoint blockade immunotherapy.Currently,NK cellbased immunotherapies have exhibited promising results in clinical trials for malignant tumors.In addition,more and more studies have shown that tumor microenvironment metabolism might be a key factor governing anti-tumor immune response and the efficacy of immunotherapy.AMP-activated protein kinase(AMPK)is a cellular energy sensor,which can be activated under metabolic stress conditions,such as those caused by tumor microenvironment.Once activated,AMPK triggers metabolic remodeling as a mechanism for cell survival.It is reported that AMPK plays a context-dependent role in cancers,behaving as both a tumor-suppressing and a tumor-promoting role.However,the role of tumor AMPK in tumor immune surveillance,as well as in checkpoint blockade immunotherapy,remains largely unknown.In this study,we investigated the effects of tumor AMPK activation on NK cell-mediated tumor immune surveillance and PD-L1 blockade therapy.Firstly,we constructed anti-PD-L1 responsive and anti-PD-L1 nonresponsive tumor models.We found that PD-L1 checkpoint blockade resulted in increased phosphorylation of AMPK in anti-PD-L1 responsive tumors,but not in anti-PD-L1 nonresponsive tumors by analyzing the protein expression in tumor tissues.Pharmacological inhibition of AMPK activation diminished the therapeutic effect of PD-L1 checkpoint blockade,which indicates that AMPK activation is required for the efficacy of PD-L1 blockade immunotherapy.Meanwhile,we also confirmed the role of NK cells in PD-L1 blockade immunotherapy.In order to investigate the interplay between AMPK and NK cells,the two indispensable elements for PD-L1 blockade immunotherapy,we used AMPK activator?Metformin,a first line drug for type 2 diabetes,to induce AMPK activation.The results showed that Metformin-induced AMPK activation significantly inhibited tumor growth in mice in a NK cell-dependent manner,and sensitized tumor cells to NK cell-mediated cytolysis in vitro.Besides,we further confirmed the promoting effect of AMPK activation on NK cell anti-tumor immunity by constructing liver kinase B1(LKB1)-overexpressed cell lines to induce AMPK activation.Transcriptome analysis revealed that genes of the pattern recognition receptor signaling pathways were significantly enriched in LKB1-overexpressed tumor cells.This was accompanied by a chemokine gene expression signature that correlates with higher survival in melanoma patients.Further mechanistic studies suggested that AMPK activation sensitized tumor cells to NK cell cytolysis possibily through inducing excessive accumulation of misfolded proteins.More importantly,AMPK activation by Metformin or LKB1 overexpression synergized with PD-L1 checkpoint blockade to suppress tumor growth in mice.In summary,this study is the first to reveal that AMPK,the cellular energy sensor,is required for the efficacy of anti-PD-L1 immunotherapy.AMPK serves as a tumor suppressor by promoting NK cell anti-tumor immunity and could synergize with PDL1 blockade immunotherapy,which suggests that reinforcing tumor AMPK activation has the potential to increase the efficacy of tumor immunotherapy.