P01.32 NDRG1 induced downregulation of CCL2 influences the migration of macrophages and impacts the tumor microenvironement.

AbstractBACKGROUND: Malignant gliomas belong to the most aggressive neoplasms in humans. The interactions and intercellular communication between malignant and non-malignant cells in the tumor microenvironment are tumor-promoting and critically to improve the understanding of the disease. N-myc downstream regulated gene 1 (NDRG1) is a stress inducible gene and key determinant of resistance towards alkylating chemotherapy in glioblastoma. NDRG1 promotes invasive growth and acts antiapoptotic in hepatocellular carcinoma. In human pancreatic cancer cells NDRG1 suppresses chemokine expression, decreases macrophage infiltration and microvascular density. Further understanding the influence of NDRG1 on the tumor microenvironment may lead to new therapeutic approaches in glioma. METHODS: To analyze the NDRG1 effects on the glioma microenvironment, we used human and murine NDRG1 knockdown (KD) cells. In orthotopic xenograft experiments control and KD microenvironments were compared for infiltrating immune cells dependent on NDRG1. Interaction and signaling mechanisms were evaluated in vitro using western blots, cytokine and migration assays and treatment with the NF-kB inhibitor JSH-23 as well as SGK1 inhibitor EMD638683 to assess the influence of NDRG1. Results: Orthotopic NDRG1 KD tumors were significantly larger compared to control tumors. Ex vivo flow cytometry analyses of the tumor microenvironment revealed a significant increase in peripheral macrophages, dendritic cells and monocytic myeloid derived suppressor cells in NDRG1 KD tumors. In vitro cytokine array analyses showed an increase of the chemokine CCL2 in NDRG1 KD cells compared to control cells. This was confirmed by ELISA. Macrophages showed an increased migration rate in the NDRG1 knockdown environment. To analyze molecular mechanisms CCL2 secretion was blocked with a NF-κB inhibitor (JSH-23) and stimulated with a SGK1 inhibitor (EMD638683). We found that NDRG1 induced NF-κB signaling attenuation is mediated through decreases in IKK α expression and IκBα phosphorylation. CONCLUSION: We identified CCL2 as a NDRG1-induced NF-κB target gene that triggers macrophage recruitment. Our findings support an immunomodulatory effect of NDRG1 on the tumor microenvironment and provide novel insights into the biological relevance of the tumor stroma and the function of NDRG1 with important implications for the development of cancer therapeutics.