Metformin Regulates Macrophage Polarization in GBM Microenvironment Combined with RT

Abstract

Glioblastoma (GBM) is the most common aggressive and malignant brain tumor in adults. As the major population of the nonneoplastic cells in GBM, tumor associated macrophages, which often express M2-like characteristics, has emerged as a promising target for GBM treatment. Some of the recent promising studies focused on the anti-tumor effect of metformin showed that metformin affects the features of cancer cells by regulating the differentiation of M1 and M2 macrophages in the tumor microenvironment. Thus we propose that metformin might be an appealing candidate to reverse the imbalance between M1 and M2 macrophage combined with radiation therapy in GBM microenvironment and benefit the treatment of GBM. In this study, we first tested the effects of different concentrations of metformin on the polarization of mouse bone marrow derived macrophage (BMDM). Then BMDM was cultured in a variety of GBM environments including monolayer tumor cells condition medium, tumor spheres condition medium as well as the co-cultured system. We further explored the influence of metformin on macrophage polarization in combinations with different doses of radiation (2 Gy, 8 Gy, and 20 Gy). Flow cytometry was used to identify the polarization state of macrophage. Metformin significantly promotes M1 and inhibits M2 polarization of macrophage in high concentration (above 1 mM) while decrease M1 polarization in low concentration (0.1mM). In multiple GBM microenvironments, high concentration of metformin could skew macrophage towards M1 phenotype. When combined with radiation, high concentration of metformin further increased M1 macrophage and prolonged the pro-inflammation effect of both low dose and high dose of radiation. Metformin promotes M1 polarization in GBM microenvironment combined with radiation therapy.