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Metabolism, Diabetes, and Cancer / Immune Cells in Cancer / GDF15 and Related Biomarkers · Journal article
Frontiers in Oncology · August 14, 2026
Encouraging direction, but not yet definitive.
This preclinical study demonstrates that metformin combined with radiation therapy prolongs survival and reduces tumor burden in syngeneic glioblastoma mouse models by reprogramming tumor-associated macrophages and enhancing CD8+ T-cell infiltration. The effect is context-dependent, functioning as a neutralizer of highly polarized macrophage states rather than a simple M2 inhibitor. Translation to human glioblastoma requires clinical trial validation.
Preclinical study: in vitro mechanistic experiments and syngeneic tumor mouse models. Bone marrow-derived macrophages from mice; syngeneic glioblastoma-bearing mice; no human patients. Intervention: Metformin combined with radiation therapy. Compared with: Radiation therapy alone (implied but not explicitly detailed in abstract).
Metformin inhibited both IL-4/IL-13–induced immunosuppressive effects and LPS-induced immunostimulatory effects on BMDMs, demonstrating bidirectional context-dependent modulation In tumor co-culture, metformin promoted M1-associated activation and counteracted M2 polarization induced by tumor microenvironment Concurrent metformin + RT significantly prolonged survival and reduced tumor burden in syngeneic GBM mouse models
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These preclinical findings suggest metformin may enhance radiotherapy efficacy in glioblastoma through immune modulation, but clinical trials are needed to establish whether this translates to improved outcomes in human patients.
Preclinical syngeneic mouse model study with mechanistic in vitro work showing metformin + radiotherapy prolongs survival and reduces tumor burden through immune reprogramming, but lacks human data and hard clinical endpoints.
As stated by the source record.
Quoted from the source exactly as published.
These preclinical findings suggest metformin may enhance radiotherapy efficacy in glioblastoma through immune modulation, but clinical trials are needed to establish whether this translates to improved outcomes in human patients.
Graded across the dimensions that decide whether you should act, each from what the source actually supports. There is no single score, and where a dimension was not assessed it says so.
Background 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. Methods We first explore 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. Results 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 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. Conclusion 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 to potentiate the anti-tumor effects of RT and by enhancing systemic immune memory.
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