Cell surface biotinylation to identify the receptors involved in nanoparticle uptake into endothelial cells

Targeted drug delivery requires -among others- specific interaction of nanocarriers with cell surface receptors enabling efficient internalization into the targeted cells. Thus, identification of receptors allowing efficient nanocarrier uptake is essential to improve the design of targeted nanomedicines. Here we used methods based on cell surface biotinylation to identify cell surface receptors mediating nanoparticle uptake by cells. We used human brain and liver endothelial cells as representative examples of cells typically showing very low and very high nanoparticle uptake, respectively. Amino-modified and carboxylated silica were used as model nanoparticles usually associated with high and low uptake into cells, respectively, and carrying different coronas after exposure in full human plasma. Using cell surface biotinylation of live cells and receptor pull-down assays, we compared the receptors internalized in control untreated cells and those internalized upon exposure to nanoparticles. In this way, we identified receptors associated with (high) nanoparticle uptake. The candidate receptors were further validated by decorating the nanoparticles with an artificial corona consisting of the respective receptor ligands. We found that a vitronectin corona can be used to target integrin receptors and strongly enhances nanoparticle uptake in brain and liver endothelial cells. The increased uptake was maintained in the presence of serum, suggesting that the vitronectin-corona could resist interaction and competition with serum. Furthermore, plasminogen-coated nanoparticles promoted uptake in endothelial cells of the liver, but not of the brain. The presented approach using reversible biotinylation of cell surface receptors in live cells allows for receptor-based targeting of nanocarriers that are instrumental in nanoparticle uptake, which can be exploited for targeted drug delivery. STATEMENT OF SIGNIFICANCE: In order to deliver drugs to their site of action, drug-loaded nanocarriers can be targeted to cell receptors enabling efficient uptake into target cells. Thus, methods to identify nanocarrier receptors are invaluable. Here we used reversible biotinylation of live cells and receptor pull-down approaches for receptor identification. By comparative analysis of the individual receptors internalized in untreated cells and cells exposed to nanoparticles, we identified receptors enabling high nanoparticle uptake into liver and brain endothelial cells. Their role was confirmed by decorating nanoparticles with an artificial corona composed of the receptor ligands. In conclusion, live cell reversible biotinylation of cell surface proteins is a powerful tool for the identification of potential receptors for receptor-based targeting of nanocarriers.