Effect of ligand density, receptor density, and nanoparticle size on cell targeting

It is generally accepted that the presentation of multiple ligands on a nanoparticle (NP) surface can improve cell targeting; however, little work has been done to determine whether an optimal ligand density exists. We have recently developed a site-specific bioconjugation strategy that allows for distinct control of ligand density on a NP through the combined utilization of expressed protein ligation (EPL) and copper-free click chemistry. This EPL-Click conjugation strategy was applied to create superparamagnetic iron oxide (SPIO) NPs labeled with HER2/neu targeting affibodies at differing ligand densities. It was discovered that an intermediate ligand density provided statistically significant improvements in cell binding in comparison with higher and lower ligand densities. This intermediate optimal ligand density was conserved across NPs with differing hydrodynamic diameters, different HER2/neu targeting ligands and also to cells with lower receptor densities. Additionally, an intermediate optimal ligand density was also evident when NPs were labeled with folic acid.From the Clinical EditorThe authors of this study investigated optimal ligand density with SPIO-based labeling and concluded that intermediate density appears to have the most optimal labeling properties from the standpoint of its T2* shortening effect.

Graphical AbstractExpressed protein ligation and click chemistry were combined to create iron oxide nanoparticles labeled with HER2/neu targeting affibodies at different ligand densities. Nanoparticles with an intermediate ligand density exhibited the optimal cell-targeting capabilities.Figure optionsDownload high-quality image (123 K)Download as PowerPoint slide