Iron-based compounds coordinated with phospho-polymers as biocompatible probes for dual P/H magnetic resonance imaging and spectroscopy.

In this work, we present the synthesis and evaluation of magnetic resonance (MR) properties of novel phosphorus/iron-containing probes for dual P and H 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 Fe ions or superparamagnetic maghemite (γ-FeO) nanoparticles via deferoxamine group linked to the end or along the polymer chains. All probes provided very short H T and T relaxation times even at low iron concentrations. The presence of iron had a significant impact on the shortening of P relaxation, with the effect being more pronounced for probes based on γ-FeO and multivalent polymer. While the water-soluble probe having one Fe ion per polymer chain was satisfactorily visualized by both P-MRS and P-MRI, the probe with multiple Fe ions could only be detected by P-MRS, and the probes consisting of γ-FeO nanoparticles could not be imaged by either technique due to their ultra-short P 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 H MR signal of the surrounding water molecules and the P MR signal of the phospho-polymer probe. Thus, this double contrast can be exploited to simultaneously visualize body anatomy and monitor probe biodistribution.