Macromolecular Ligands for Gadolinium MRI Contrast Agents

Macromolecular ligands for gadolinium contrast agents (CAs) were prepared via a grafting to strategy. Copolymers of oligoethylene glycol methyl ether acrylate (OEGA) and an activated ester monomer, pentafluorophenyl acrylate (PFPA), were synthesized and modified with the 1-(5-amino-3-aza-2-oxypentyl)-4,7,10-tris(tert-butoxycarbonylmeth-yl)-1,4,7,10-tetraazacyclododecane (DO3A-tBu-NH2) chelate for the complexation of Gd3+. The relaxivity properties of the ligated Gd3+ agents were then studied to evaluate the effect of macromolecular architecture on their behavior as magnetic resonance imaging (MRI) CAs. Ligands made from linear and hyperbranched macromolecules showed a substantially increased relaxivity in comparison to existing commercial Gd3+ MRI contrast agents. In contrast, star nanogel polymers exhibited a slightly lower relaxivity per Gd3+ ion (but still substantially higher relaxivity than existing low molecular weight commercial CAs). This work shows that macromolecular ligands have the potential to serve as components of Gd MRI agents as there are enhanced effects on relaxivity, allowing for lower Gd concentrations to achieve contrast, while potentially imparting control over pharmacokinetics.