Whole-brain spatial metabolomics reveals metabolic gradient shifts in a murine glioma model following boron neutron capture therapy.

BACKGROUND: Glioblastoma (GBM) is the most aggressive and lethal primary brain tumor, characterized by poor prognosis and resistance to current therapies. Boron neutron capture therapy (BNCT) is a tumor-selective particle radiation therapy in which high-linear energy transfer (LET) α-particles and recoil 7Li nuclei are generated through the capture reaction between 10B and thermal neutrons. Although BNCT has been shown to prolong survival in GBM, its effects on global metabolomic alterations of the whole brain, particularly in relation to the tumor microenvironment (TME), remain incompletely understood.

METHODS: C57BL/6 mice orthotopically implanted with GL261 glioma cells were administered p-boronophenylalanine (BPA) at a dose of 500 mg/kg, followed by thermal neutron irradiation. Brain tissues were analyzed using conventional histopathological methods, including immunohistochemistry, as well as matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI).

RESULTS: Histopathological analysis demonstrated marked regression of the tumor mass following BNCT. Non-targeted MALDI-MSI enabled the extraction and spatial visualization of tumor-associated metabolites, among which UDP-GlcNAc emerged as one of the most prominent oncometabolites in the present analysis. In addition, ADP signals were predominantly colocalized within the corpus callosum of tumor-bearing brains. A metabolic gradient shift from the tumor-implanted hemisphere to the contralateral side was observed, potentially reflecting tumor cell migration. Uniform Manifold Approximation and Projection (UMAP) analysis facilitated the visualization of extracellular metabolites in the ventricular regions, and elevated GDP signals were associated with hydrocephalus. Notably, the adenylate energy charge of the brain was significantly increased after BNCT, followed by a gradual decline over time, whereas it was reduced within the tumor region after treatment.

CONCLUSIONS: Non-targeted MALDI-MSI of brains from a murine glioma model successfully visualized purinergic and pyrimidinergic metabolites that may reflect tumor dynamics, BNCT efficacy, and metabolic responses of the normal brain to treatment. These findings suggest the potential utility of this approach for identifying diagnostic and prognostic biomarkers in glioblastoma.