Asymmetrically functionalized β-cyclodextrin-based star copolymers for integrated gene delivery and magnetic resonance imaging contrast enhancement

Abstract

We report on the synthesis of star copolymers possessing dual functions of gene delivery vectors and magnetic resonance (MR) imaging contrast enhancement. Starting from asymmetrically functionalized β-cyclodextrin (β-CD) comprising 7 azide moieties and 14 α-bromopropionate functionalities at the upper and lower rim of a rigid toroidal β-CD core, (DOTA-Gd)₇-CD-(PDMA)₁₄ star copolymers were synthesized via atom transfer radical polymerization (ATRP) of N,N-dimethylaminoethyl methacrylate (DMA) and subsequent click reaction with an alkynyl-functionalized gadolinium (Gd³⁺) complex, DOTA-Gd, where DOTA is 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid. The obtained Janus-type star copolymers, (DOTA-Gd)₇-CD-(PDMA)₁₄, could completely complex with anionic plasmid DNA (pDNA) via electrostatic interactions at N/P ratios equal to or higher than 2 and exhibit optimal in vitro transfection efficiency at an N/P ratio of 8. In addition, in vitro MR imaging experiments demonstrated considerably enhanced T₁ relaxivity (r₁ ∼ 10.9 s⁻¹ mM⁻¹) for the star copolymer compared to that of commercially available small molecular MR imaging contrast agents (2.4–3.2 s⁻¹ mM⁻¹). The star-type topology of asymmetrically functionalized β-CD based copolymers in combination with the integrated design of diagnostic and therapeutic functions augurs well for their potential applications in the field of image-guided gene therapy.