Galactose Multivalency Effect on the Cell Uptake Mechanism of Bioconjugated Nanoparticles

Galactose functionalized nanomaterials are commonly used for specific targeting/delivery of cancer cells, as galactose receptors are overexpressed in certain types of cancer cells. However, the role of galactose multivalency on cellular interaction, cell uptake mechanism, and subcellular targeting are largely unexplored. Here we show that the receptor mediated cellular internalization of galactose terminated nanoparticles depends on galactose multivalency. We have synthesized galactose functionalized multivalent quantum dots (QDs) of 15-20 nm hydrodynamic size with the average numbers of galactose per QD of 25, 50, and 80 [designated as QD(gal)(25), QD(gal)(50), and QD(gal)(80)] and investigated their uptake mechanism in galactose receptor overexpressed HepG2 cells. We found three distinct effects of galactose multivalency on the nanoparticle uptake mechanism. First, cellular interaction and uptake kinetics of nanoparticles increase with increasing galactose multivalency. Second, the cell uptake mechanism shifts from predominately lipid raft/caveolae- to predominately clathrin-mediated endocytosis as the nanoparticle multivalency increases from 25 to 50. Third, lower multivalent nanoparticles reside in the cytoplasm for a longer time (more than 12 h), but their endosomal/lysozomal trapping and exocytosis increase as galactose multivalency increases from 25 to 50. This work demonstrates the functional role of galactose multivalency in cellular processes and may be exploited for subcellular targeting applications.