Gold Nanoparticle Aggregates Functionalized with Cyclic RGD Peptides for Targeting and Imaging of Colorectal Cancer Cells

The active targeting strategy has emerged as a promising approach to achieve selectivity in nanobiotechnology applications. Peptides are particularly suited as targeting moieties because the multivalent presentation of these small molecules on a nanoparticle provides high avidity for the target. However, to achieve an efficient targeting activity, the presentation of the peptide on the nanostructure has to be supported by an appropriate design. To optimize the targeting to colorectal cancer cells, we have performed a ligand design study of plasmonic nanostructures covered with a cyclic RGD peptide, a known targeting moiety for the αvβ3 integrin. We find that to achieve a good targeting activity, the RGD peptide has to be linked to plasmonic nanostructures through a long PEG chain and a short oligolysine spacer. When the cyclic RGD peptide is directly linked to the PEG chains of the nanostructures, their targeting ability is lost. Molecular dynamics calculations make possible to understand the difference of the peptide organization in two targeted nanosystems, unveiling an effect of the spacer on the orientation of the active component, which very likely positively affects the targeting properties of the investigated plasmonic nanostructures.