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.


BACKGROUND
The 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.
Department of Bioengineering, School of Engineering and Applied Science, University of Pennsylvania, Philadelphia, PA 19104, USA.
Drew R
DR
Elias
Andrei
A
Poloukhtine
Vladimir
V
Popik
Andrew
A
Tsourkas
D000818:Animals; D000906:Antibodies / Q000737:chemistry* / Q000276:immunology*; D002460:Cell Line; D045744:Cell Line, Tumor; D057930:Click Chemistry; D016503:Drug Delivery Systems / Q000379:methods; D006801:Humans; D008024:Ligands; D008279:Magnetic Resonance Imaging; D058185:Magnetite Nanoparticles / Q000737:chemistry*; D010316:Particle Size; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000276:immunology*
D000906:Antibodies; D008024:Ligands; D058185:Magnetite Nanoparticles; D018719:Erb-b2 Receptor Tyrosine Kinases