Iron-based compounds coordinated with phospho-polymers as biocompatible probes for dual ³¹P/¹H magnetic resonance...

In this work, we present the synthesis and evaluation of magnetic resonance (MR) properties of novel phosphorus/iron-containing probes for dual ³¹P and ¹H MR imaging and spectroscopy (MRI and MRS). The presented probes are composed of biocompatible semitelechelic and multivalent phospho-polymers based on poly(2-methacryloyloxyethyl phosphorylcholine) (pMPC) coordinated with small paramagnetic Fe³⁺ ions or superparamagnetic maghemite (γ-Fe₂O₃) nanoparticles via deferoxamine group linked to the end or along the polymer chains. All probes provided very short ¹H T₁ and T₂ relaxation times even at low iron concentrations. The presence of iron had a significant impact on the shortening of ³¹P relaxation, with the effect being more pronounced for probes based on γ-Fe₂O₃ and multivalent polymer. While the water-soluble probe having one Fe³⁺ ion per polymer chain was satisfactorily visualized by both ³¹P-MRS and ³¹P-MRI, the probe with multiple Fe³⁺ ions could only be detected by ³¹P-MRS, and the probes consisting of γ-Fe₂O₃ nanoparticles could not be imaged by either technique due to their ultra-short ³¹P relaxations. In this proof-of-principle study performed on phantoms at a clinically relevant magnetic fields, we demonstrated how the different forms and concentrations of iron affect both the ¹H MR signal of the surrounding water molecules and the ³¹P MR signal of the phospho-polymer probe. Thus, this double contrast can be exploited to simultaneously visualize body anatomy and monitor probe biodistribution.