High-Relaxivity Magnetic Resonance Imaging (MRI) Contrast Agent Based on Supramolecular Assembly between a Gadolinium Chelate, a Modified Dextran, and Poly-beta-Cyclodextrin

Nanosized contrast agents have great potential in magnetic resonance molecular imaging applications for clinical diagnosis. This study proposes new nanoparticles spontaneously formed under mild conditions and composed of a noncovalent adduct between a gadolinium complex, a polymer of P-cyclodextrin (p beta CD: MW 1.5 x 10(6) g mol(-1)) and a dextran grafted with alkyl chains (MD). The formation of this supramolecular nanoassembly is based upon a "lock-and-key" recognition process in which the hydrophobic alkyl chains of MD and the adamantyl moieties of macrocyclic Gd-III chelates are included in the cavities of p beta CD. The large number of beta CDs contained in the p beta CD resulted in the formation of 200 nm diameter nanoparticles, each entrapping 1.8 x 10(5) molecules of a low-molecular-weight Gd complex. This system, which exhibits a great relaxivity enhancement (48.4 mM(-1) s(-1), at 20 MHz and 37 degrees C) compared to the Gd-III chelate itself (5.2 mM(-1) s(-1)), appears to be a promising strategy for the in vivo targeted delivery of Gd-III complexes. The mechanisms of particle formation, conjugation strategies, and relaxometric characterizations in the field of contrast-enhanced magnetic resonance imaging are discussed.