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Metformin Modulates the Phenotypes of Tumor-associated Macrophages in Glioblastoma in a Context-Dependent Manner by Promoting the Homeostasis of Macrophages

ABSTRACT: Glioblastoma (GBM) remains the most aggressive primary adult brain cancer attributed to its immunosuppressive nature. Radiation therapy (RT) and concurrent temozolomide chemotherapy are the standard treatments for GBM. Emerging evidence indicates that metformin has potential as an anti-tumor agent that can reshape the immune landscape across various malignancies. We thus postulate that metformin may enhance the anti-tumor effect of RT by modulating the immunosuppressive milieu in GBM. We first explored multiple in vitro conditions, with or without pre-induction, and mimicked a tumor microenvironment to demonstrate a highly context-dependent effect of metformin on the polarization of bone marrow-derived macrophages (BMDMs). We then investigated the antitumor activity and immune-modulatory effects of metformin in combination with RT in GBM-bearing mice. The in vitro experiment showed that metformin inhibited the immunosuppressive effects of IL-4/IL-13 but also the immunostimulatory effects of Lipopolysaccharide (LPS) on BMDMs, demonstrating bidirectional immunomodulatory properties that depend on the baseline inflammatory stimulus. In a tumor cell co-culture environment, metformin exhibited context-dependent immunoregulatory effects, predominantly promoting M1-associated activation. Notably, concurrent metformin treatment counteracted M2 polarization typically induced by the tumor microenvironment. In a high m-MCSF inducted M2-dominated condition, metformin preferentially shifted the highly polarized M2 phenotype toward an M1-like state in a time- and dose-dependent manner but with limited promotion of M1 subtype maturation. RNAseq results on BMDM treated with metformin showed increased homeostasis. Metformin showed dose-dependent immunomodulatory effects when combined with RT in vitro. In syngeneic GBM mouse models, concurrent metformin + RT significantly prolonged survival and reduced tumor burden by reprogramming tumor-associated macrophages (TAMs), elevating intratumoral CD8+ T-cell infiltration and the CD8+/Treg ratio, increasing circulating CD8+ T cells, reversing RT-induced expansion of monocytic myeloid-derived suppressor cells (mMDSCs), and expanding CD4+ and CD8+ effector memory populations in peripheral blood. Metformin demonstrates inhibitory effects on M2 phenotype of macrophages. However, it is not a simple M2 inhibitor; instead, it functions primarily as a neutralizer of highly polarized macrophage states by promoting transcriptomic homeostasis. This context-dependent activity enables metformin to relieve the profoundly immunosuppressive TME of GBM, potentiate the anti-tumor effects of RT, and enhance systemic immune memory.

ORGANISM(S): Mus musculus

PROVIDER: GSE342855 | GEO | 2026/08/11

REPOSITORIES: GEO

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Project description:Background: Glioma-associated macrophages (GAMs) are one of the most important cellular components in the tumor immune microenvironment (TIME). GAMs display a mostly M2-like phenotype with anti-inflammatory features, which is closely related to the malignancy and progression of cancers. Extracellular vesicles derived from GAMs (GAM-EVs), which are important components of the TIME, contain a variety of microRNAs (miRNAs). These miRNAs play a crucial role in communication between tumor cells and GAMs. In this study, we aimed to explore the effect of GAM-EVs on the malignancy and progression of glioblastoma multiforme (GBM) through miRNA-mediated communication and its possible signaling pathway. Methods: The GBM and LGG data from The Cancer Genome Atlas (TCGA) were analyzed, and the immunological features of 12 clinical glioma samples, including GBM and low-grade glioma (LGG) samples, were estimated by immunohistochemistry. To evaluate the changes induced by M2-EVs compared to M1-EVs, the human GBM cell lines U87MG and A172 were cocultured with M2-EVs and M1-EVs, and their epithelial-mesenchymal transition (EMT) behaviors were investigated. The contents of M2-EVs and M1-EVs were determined by miRNA sequencing, and the differences were analyzed. Then, the EMT signatures were evaluated after a miRNA mimic was transfected into GBM cells. Six databases were used to predict the targets of the miRNA. Human GBM cell lines with interference and overexpression of the most valuable candidate miRNA targets were established. The related signaling pathways were further explored. Finally, an orthotopic homograft mouse model was employed to verify the results of the in vitro experiments. Results: The immunosuppressive GAM genes were upregulated in GBM compared with LGG, showing that the TIME of GBM is more immunosuppressive. To explore the effect of the immunosuppressive GAMs and TIME on the progression of GBM, we established immunostimulatory (M1-like) and immunosuppressive (M2-like) GAMs and compared the differences in their EVs. The migration and invasion of U87MG and A172 cells were enhanced under coculture with M2-EVs. MiR-146a-5p was deficient in M2-EVs compared with M1-EVs. Upon treatment with the miR-146a-5p mimic, the migration and invasion abilities of GBM cells were weakened, and the EMT signature was correspondingly decreased. According to the database prediction, tumor necrosis factor receptor-associated factor 6 (TRAF6) and interleukin 1 receptor-associated kinase 1 (IRAK1) are the targets of miR-146a-5p. TRAF6 is an E3 ubiquitin ligase, and IRAK1 is the substrate. Bimolecular fluorescence complementation (BiFC) and coimmunoprecipitation assays confirmed interactions between TRAF6 and IRAK1. Interference with both TRAF6 and IRAK1 expression weakened but overexpression of both TRAF6 and IRAK1 promoted the EMT behaviors of GBM cells. The TRAF6-Glioma-associated macrophages (GAMs) are pivotal chains in the tumor immune microenvironment (TIME). GAMs mostly display M2-like phenotypes with anti-inflammatory features related to the malignancy and progression of cancers. Extracellular vesicles derived from immunosuppressive GAMs (M2-EVs), the essential components of the TIME, greatly impact the malignant behavior of GBM cells. M1- or M2-EVs were isolated in vitro, and human GBM cell invasion and migration were reinforced under M2-EV treatment. Signatures of the epithelial-mesenchymal transition (EMT) were also enhanced by M2-EVs. Compared with M1-EVs, miR-146a-5p, considered the key factor in TIME regulation, was deficient in M2-EVs according to miRNA-sequencing. When the miR-146a-5p mimic was added, EMT signatures and the invasive and migratory abilities of GBM cells were correspondingly weakened. Public databases predicted the miRNA binding targets and interleukin 1 receptor-associated kinase 1 (IRAK1) and tumor necrosis factor receptor-associated factor 6 (TRAF6) were screened as miR-146a-5p binding genes. Bimolecular fluorescent complementation and coimmunoprecipitation confirmed interactions between TRAF6 and IRAK1. The correlation between TRAF6 and IRAK1 was evaluated with immunofluorescence (IF)-stained clinical glioma samples. The TRAF6-IRAK1 complex is the switch and the brake that modulates IKK complex phosphorylation and NF-κB pathway activation, as well as the EMT behaviors of GBM cells. Furthermore, a homograft nude mouse model was explored and mice transplanted with TRAF6/IRAK1-overexpressing glioma cells had shorter survival times while mice transplanted with glioma cells with miR-146a-5p overexpression or TRAF6/IRAK1 knockdown lived longer. This work indicated that in the TIME of GBM, the deficiency of miR-146a-5p in M2-EVs enhances tumor EMT through disinhibition of the TRAF6-IRAK1 complex and IKK-dependent NF-κB signaling pathway providing a novel therapeutic strategy targeting the TIME of GBM.

Project description:Tumor-associated macrophages (TAMs) are key components of the tumor microenvironment (TME) which can either promote tumor progression (M2) or induce antitumor immunity (M1). The hypothesis of our study is that the expression of FOLR2 is associated with an M2-like macrophage profile. The main goal of this study is to compare the transcriptomic profile of FOLR2 positive and FOLR2 negative TAMs obtained from the ascites of C57BL/6 mice bearing ovarian ID8 intraperitoneal tumors. Abstract: The immunosuppressive tumor microenvironment (TME) represents a major barrier for effective immunotherapy. Tumor-associated macrophages (TAMs) are highly heterogeneous and plastic cell components of the TME which can either promote tumor progression (M2-like) or boost antitumor immunity (M1-like). Selective targeting of the pro-tumorigenic subset of TAMs represents an attractive therapeutic strategy. Here, we demonstrate that a subset of TAMs that expressing folate receptor β (FRβ) possess an immunosuppressive, tumor-promoting M2-like profile, while FRβ negative TAMs feature pro-inflammatory M1 macrophage properties. In syngeneic tumor mouse models, the administration of FRβ-targeted chimeric antigen receptor (CAR) T-cells mediated elimination of FRβ+ TAMs in the TME, which resulted in an enrichment of pro-inflammatory monocytes, an influx of endogenous tumor-specific CD8+ T-cells, delayed tumor progression, and prolonged survival. Preconditioning of the TME with FRβ-specific CAR T-cells also improved the effectiveness of tumor-directed anti-mesothelin CAR T-cells, while simultaneous co-administration of both CAR products did not. Thus, CAR T-cell-mediated depletion of immunosuppressive M2-like TAMs incites a pro-inflammatory TME that broadens endogenous antitumor immunity and limits tumor progression, highlighting the pro-tumor role of FRβ+ TAMs in the TME and the therapeutic implications of TAM-depleting agents as preparative adjuncts to conventional immunotherapies that directly target tumor antigens.

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Metformin Modulates the Phenotypes of Tumor-associated Macrophages in Glioblastoma in a Context-Dependent Manner by Promoting the Homeostasis of Macrophages

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