Design, synthesis, and in vitro evaluation of a binary targeting MRI contrast agent for imaging tumor cells

A binary targeting vector that consists of peptide sequences of Arg-Gly-Asp (RGD) and Asn-Gly-Arg (NGR) motifs has been designed and synthesized using solid-phase peptide synthesis procedure. The vector is then coupled with Gd-DOTA to work as a targeting contrast agent (CA1) for magnetic resonance imaging of human lung adenocarcinoma cells A549. Its longitudinal relaxivity is measured to be 7.55 mM(-1) s(-1) in aqueous solution at a magnetic field of 11.7 T, which is higher than that of Magnevist (4.25 mM(-1) s(-1)) in the same conditions. The cell experiment shows, at the same concentration, uptake quantity of CA1 by A549 is much more than Magnevist and also superior over CA2 (a single targeting contrast agent contains only RGD). The uptake can be blocked by the targetable peptide containing RGD or NGR without coupling Gd. To summarize, CA1 has very good ability to target A549 and higher relaxivity than that of Magnevist. So CA1 is promising MRI contrast agent for high-resolution MR molecular imaging of human lung adenocarcinoma A549 cells.