Sodium accumulation in breast cancer predicts malignancy and treatment response

BACKGROUND: Breast cancer remains a leading cause of death in women and novel imaging biomarkers are urgently required. Here, we demonstrate the diagnostic and treatment-monitoring potential of non-invasive sodium ( 23Na) MRI in preclinical models of breast cancer. METHODS: Female Rag2 -/- Il2rg -/- and Balb/c mice bearing orthotopic breast tumours (MDA-MB-231, EMT6 and 4T1) underwent MRI as part of a randomised, controlled, interventional study. Tumour biology was probed using ex vivo fluorescence microscopy and electrophysiology. RESULTS: 23Na MRI revealed elevated sodium concentration ([Na +]) in tumours vs non-tumour regions. Complementary proton-based diffusion-weighted imaging (DWI) linked elevated tumour [Na +] to increased cellularity. Combining 23Na MRI and DWI measurements enabled superior classification accuracy of tumour vs non-tumour regions compared with either parameter alone. Ex vivo assessment of isolated tumour slices confirmed elevated intracellular [Na +] ([Na +] i); extracellular [Na +] ([Na +] e) remained unchanged. Treatment with specific inward Na + conductance inhibitors (cariporide, eslicarbazepine acetate) did not affect tumour [Na +]. Nonetheless, effective treatment with docetaxel reduced tumour [Na +], whereas DWI measures were unchanged. CONCLUSIONS: Orthotopic breast cancer models exhibit elevated tumour [Na +] that is driven by aberrantly elevated [Na +] i. Moreover, 23Na MRI enhances the diagnostic capability of DWI and represents a novel, non-invasive biomarker of treatment response with superior sensitivity compared to DWI alone.