Indexed on: 01 Jun '12Published on: 01 Jun '12Published in: Chemical Science
We present the synthesis and characterization of octaarginine-conjugated Copper-Gad-2 (Arg8CG2), a new copper-responsive magnetic resonance imaging (MRI) contrast agent that combines a Gd(3+)-DO3A scaffold with a thioether-rich receptor for copper recognition. The inclusion of a polyarginine appendage leads to a marked increase in cellular uptake compared to previously reported MRI-based copper sensors of the CG family. Arg8CG2 exhibits a 220% increase in relaxivity (r 1 = 3.9 to 12.5 mM(-1) s(-1)) upon 1 : 1 binding with Cu(+), with a highly selective response to Cu(+) over other biologically relevant metal ions. Moreover, Arg8CG2 accumulates in cells at nine-fold greater concentrations than the parent CG2 lacking the polyarginine functionality and is retained well in the cell after washing. In cellulo relaxivity measurements and T 1-weighted phantom images using a Menkes disease model cell line demonstrate the utility of Arg8CG2 to report on biological perturbations of exchangeable copper pools.