An iron-based T1 contrast agent made of iron-phosphate complexes:: In vitro and in vivo studies

A new iron-based T, 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. P-31 MRS, Mossbauer 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.