An iron-based T 1 contrast agent made of iron-phosphate complexes: In vitro and in vivo studies

A new iron-based T ₁ contrast agent consisting of a complex of iron ions coordinated to phosphate and amine ligands (Fe_(phos) in short) has been characterized by spectroscopic and magnetic measurements. NMR relaxation studies showed r ₁ values to be dependent on the phosphate salt concentration, K₂HPO₄, present in the medium. r ₁ reaches a maximum value of 2.5 mM^?1 s^?1 for measurements carried out at 7 T and 298 K. ³¹P MRS, Mössbauer spectroscopy and magnetic measurements of Fe_(phos) solutions suggest paramagnetic Fe³⁺ ions present in the studied iron–phosphate complex. In vitro and in vivo toxicity experiments with C6 cells and CD1 mice, respectively, demonstrated lack of toxicity for Fe_(phos) at the highest dose tested in the MRI experiments (12 mM iron for C6 cells and 0.32 mmol iron/kg for mice). Finally, T ₁ weighted images of brain tumours in mice have shown positive contrast enhancement of Fe_(phos) for tumour afflicted regions in the brain.