Ultralow-Field NMR Relaxometry and Bumetanide: A Theranostic Strategy against GBM Invasion

Glioblastoma multiforme (GBM) is a highly invasive brain tumor for which no effective anti-invasive therapy is currently available. This study proposes a water-exchange-based strategy to monitor GBM invasion, integrating ultralow-field nuclear magnetic resonance (NMR) measurements with the repurposed drug bumetanide. At ultralow fields, the proton relaxation rate constant reflects transmembrane water exchange and can serve as both a biomarker of invasion and a readout of treatment response. Bumetanide modulates the membrane transporters (NKCC1 and AQP4), which regulate ion and water fluxes involved in tumor cell invasion. Transmembrane water exchange parameters were noninvasively quantified in vitro and in vivo by ultralow-field NMR measurements across various magnetic field strengths. Invasive glioma cells (U87 stressed under H2O2 and Glio6) were studied. In a Glio6 mouse model (six untreated ten treated), measurements were performed longitudinally during 14 days of bumetanide treatment (5 mg/kg every 12 h). Tumor growth was assessed by T2-weighted MRI. Statistical analysis included t-tests and analysis of variance (alpha = 0.05). Here, we show that ultralow-field parameters detected an early response to bumetanide. Intracellular water lifetime increased significantly in vitro after 17 h of treatment. In vivo, most treated mice showed reduced tumor growth, associated with changes in water exchange parameters. However, the effect gradually diminished, suggesting a progressive dominance of proliferative mechanisms. Ultralow-field NMR enables noninvasive detection of early changes in tumor water dynamics associated with bumetanide treatment. This approach may support the development of personalized strategies to identify responders and monitor therapies targeting tumor invasion.