Thermo-Magnetic Induction of Pro-Inflammatory Microglia: A Lipid-Based Nanovector Strategy for Glioblastoma Immunotherapy

Microglia, the main immune cells in the central nervous system (CNS), maintain physiological homeostasis and react to pathological changes. Besides their neuroprotective function, they play a crucial role in brain tumor microenvironments such as glioblastoma (GBM), by composing up 40% of the tumor mass. Glioma-associated microglia exhibit a dynamic activation state characterized mainly by an immunosuppressive (M2-like) response, with a lesser contribution of pro-inflammatory (M1-like) response. Modulating microglial into M1-like phenotype offers antitumor response and a promising immunotherapy strategy against GBM. Nanoparticles can induce microglial polarization, also modulating pro-inflammatory responses for tumor suppression. Magnetically responsive nanoparticles are promising nanotransducers due to their remote-control capabilities via external magnetic fields, enabling precise therapeutic interventions. This study proposes a novel strategy that exploits lipid-based magnetic nanovectors (LMNVs) composed of a lipid matrix doped with iron oxide nanoparticles to induce M1-like microglial response through magneto-thermal conversion. Results demonstrated that LMNVs exhibit excellent biocompatibility and efficient internalization within human microglia (HMC3 cells). Upon alternating magnetic field (AMF) stimulation, LMNVs triggered a sustained increase in intracellular Ca²⁺ levels, leading to the polarization of microglia toward a pro-inflammatory M1-like phenotype. This activation was confirmed by the upregulation of key inflammatory markers (CD40, CD86) and cytokine release (IL-6, IL-8, and TNF-α), mirroring the effects of IFN-γ stimulation. These findings were further corroborated by comparative transcriptomic analysis. Notably, conditioned medium from LMNVs + AMF-stimulated microglia significantly impaired the viability and proliferation of both immortalized and patient-derived GBM cells, demonstrating a potent antitumor response. The tumor cell death was associated with immunogenic cell death (ICD), as indicated by the translocation of the damage-associated molecular patterns, in particular high mobility group box 1 (HMGB1) and calreticulin (CRT). Overall, these results highlight the potential of LMNVs as a remotely activatable nanoplatform capable of reprogramming microglia and to promote antitumor immunity in GBM.