Preparation of Mn2+@PolyDOPA-b-polysarcosine micelle as MRI contrast agent with high longitudinal relaxivity

Abstract

Magnetic resonance imaging (MRI) is a promising technique widely used in clinical diagnose. Poly(α-amino acid)s are excellent carriers for MRI due to their excellent biocompatibility. PDOPA-b-PSar copolymers (defined as “DoS”) are synthesized by sequential polymerizations of 3,4-dihydroxy-L-phenylalanine N-thiocarboxyanhydride (DOPA-NTA) and sarcosine N-thiocarboxyanhydride (Sar-NTA) initiated by neopentylamine in tetramethylene sulfone. Mn2+@DoS micelles have been prepared as T1-weighted MRI contrast agents according to efficient coordination between catechol units and Mn2+ cation. High longitudinal relaxivity (27.7 mM−1·s−1) of Mn2+@PDOPA12-b-PSar72 was observed, and the aqueous micelle exhibits effective MRI contrast enhancement in vivo of nude mice. Mn2+@DoS shows potential clinical application in diagnostic radiology as a novel MRI contrast agent. Gd3+@DoS micelles are also investigated presenting a longitudinal relaxivity of 16.4 mM−1·s−1. Unfortunately, the Gd3+ loading percentage is quite low as 19%.