Radical Dendrimers Based on Biocompatible Oligoethylene Glycol Dendrimers as Contrast Agents for MRI

Finding alternatives to gadolinium (Gd)-based contrast agents (CA) with the same or even better paramagnetic properties is crucial to overcome their established toxicity. Herein we describe the synthesis and characterization of entirely organic metal-free paramagnetic macromolecules based on biocompatible oligoethylene glycol dendrimers fully functionalized with 5 and 20 organic radicals (OEG Gn-PROXYL (n = 0, 1) radical dendrimers) with the aim to be used as magnetic resonance imaging (MRI) contrast agents. Conferring high water solubility on such systems is often a concern, especially in large generation dendrimers. Our approach to overcome such an issue in this study is by synthesizing dendrimers with highly water-soluble branches themselves. In this work, we show that the highly water-soluble OEG Gn-PROXYL (n = 0, 1) radical dendrimers obtained showed properties that convert them in good candidates to be studied as contrast agents for MRI applications like diagnosis and follow-up of infectious diseases, among others. Importantly, with the first generation radical dendrimer, a similar r₁ relaxivity value (3.4 mM^-1s^-1) in comparison to gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) used in clinics (3.2 mM^-1s^-1, r.t. 7T) has been obtained, and it has been shown to not be cytotoxic, avoiding the toxicity risks associated with the unwanted accumulation of Gd in the body.