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

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In this work, we present the synthesis and evaluation of magnetic resonance (MR) properties of novel phosphorus/iron-containing probes for dual 31 P and 1 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 3+ ions or superparamagnetic maghemite ( γ -Fe 2 O 3 ) nanoparticles via deferoxamine group linked to the end or along the polymer chains. All probes provided very short 1 H T 1 and T 2 relaxation times even at low iron concentrations. The presence of iron had a significant impact on the shortening of 31 P relaxation, with the effect being more pronounced for probes based on γ -Fe 2 O 3 and multivalent polymer. While the water-soluble probe having one Fe 3+ ion per polymer chain was satisfactorily visualized by both 31 P-MRS and 31 P-MRI, the probe with multiple Fe 3+ ions could only be detected by 31 P-MRS, and the probes consisting of γ -Fe 2 O 3 nanoparticles could not be imaged by either technique due to their ultra-short 31 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 1 H MR signal of the surrounding water molecules and the 31 P MR signal of the phospho-polymer probe. Thus, this double contrast can be exploited to simultaneously visualize body anatomy and monitor probe biodistribution.