TMIC-60. THE ROLE OF ICAM1 IN GLIOBLASTOMA TUMORIGENESIS UNDER HYPOXIC CONDITIONS

Abstract Glioblastoma (GBM) is a fatal brain cancer in adults with ineffective existing treatment methods. Cell adhesion molecules (CAMs) are proteins that are expressed on the surface of cells and enable them to interact with one another and the surrounding microenvironment. Intracellular adhesion molecule 1 (ICAM-1) is a cell adhesion molecule expressed by macrophages, tumor cells and endothelial cells in GBM. Preliminary data showed that ICAM-1 is associated with poorer overall and progression free survival in GBM patients and ICAM-1 expression levels increase in recurrent GBM tumors. TAMs enhance tumor growth and proliferation, within GBM. The goal of this study was to determine whether and how ICAM-1 expression on TAMs contributes to GBM tumorigenesis, specifically within the hypoxic tumor microenvironment. We hypothesized that ICAM1 facilitates TAM migration, proliferation and phagocytosis, thus enhancing tumor growth. We found that upon incubation of human and mouse primary macrophages in hypoxia, ICAM-1 expression levels increased and were further exasperated upon culturing with tumor cell-conditioned medium. Incubation of ICAM-1 deficient macrophages in hypoxia resulted in lower migration and proliferation in ICAM-1 deficient cells compared to wild type cells. When cultured with tumor cell condition media, migration and proliferation of ICAM-1 deficient macrophages was lower than wild type macrophages. Further, intracranial injection of tumor cells into ICAM-1 deficient and wild type mice revealed that ICAM1 deficient mice survived longer and had lower overall tumor volume than wild type mice. In conclusion, the expression of ICAM1 in TAMs likely promotes GBM tumorigenesis by enhancing their proliferation and migration into the tumor microenvironment. ICAM-1 plays a role in macrophage migration, proliferation, and its expression on TAMs, resulting in more aggressive and invasive tumors. In addition, certain environmental factors like hypoxia further enhance the expression of ICAM-1 in macrophages which is associated with more aggressive features of GBM.