Mahfooz, Sadaf

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.

Abstract Glioblastoma (GBM) is the most common and lethal primary malignant brain tumor in adults, with median survival remaining approximately 12–15 months despite aggressive multimodal therapy. Therapeutic resistance and tumor recurrence are driven in part by limited drug penetration across the blood–brain barrier (BBB) and the persistence of brain cancer stem cells (BCSCs), highlighting the need for brain-penetrant therapeutic platforms capable of achieving sustained intratumoral delivery. Here, we developed a dendrimer-based nanotherapeutic by conjugating metformin to a fourth-generation hydroxyl-terminated polyamidoamine dendrimer (P4-MET) to enhance intracranial bioavailability and therapeutic efficacy in GBM. P4-MET exhibited favorable pharmacokinetic properties, including prolonged retention within the tumor microenvironment, and demonstrated enhanced cytotoxicity against GBM cell lines relative to free metformin (f-MET). Mechanistical studies with transcriptomic profiling by RNA sequencing revealed distinct treatment-associated molecular signatures, identifying BOLA2B as the most significantly differentially expressed gene between treatment groups. Specifically, BOLA2B expression was markedly elevated in f-MET–treated cells but not so following P4-MET treatment. Given the established association of BOLA2B with mTORC1 signaling and GPX4-mediated ferroptosis resistance, these findings suggest that P4-MET may, at least in part, enhance therapeutic efficacy by modulating ferroptosis-associated pathways. In orthotopic GBM models, combination treatment with P4-MET and radiotherapy (RT) significantly prolonged overall survival and increased tumor cell death compared with either monotherapy alone, consistent with a synergistic radiosensitizing effect. Importantly, P4-MET demonstrated minimal systemic toxicity, supporting its favorable therapeutic index and translational potential. Collectively, these findings establish P4-MET as a brain-penetrant nanomedicine platform that improves metformin delivery, modulates ferroptosis-related signaling networks, and potentiates radiotherapeutic response in GBM. This study highlights the potential of dendrimer-enabled metabolic nanotherapies to overcome therapeutic resistance in malignant brain tumors.