Ligand Density Controls C-Type Lectin-Like Molecule-1 Receptor-Specific Uptake of Polymer Nanoparticles

The newest generation of drug delivery systems (DDSs) exploits ligands to mediate specific targeting of cells and/or tissues. However, studies investigating the link between ligand density and nanoparticle (NP) uptake are limited to a small number of ligand-receptor systems. C-type lectin-like molecule-1 (CLL1) is uniquely expressed on myeloid cells, which enables the development of receptors specifically targeting treat various diseases. This study aims to investigate how NPs with different CLL1 targeting peptide density impact cellular uptake. To this end, poly(styrene-alt-maleic anhydride)-b-poly(styrene) NPs are functionalized with cyclized CLL1 binding peptides (cCBP) ranging from 240 ± 12 to 31 000 ± 940 peptides per NP. Unexpectedly, the percentage of cells with internalized NPs is decreased for all cCBP-NP designs regardless of ligand density compared to unmodified NPs. Internalization through CLL1 receptor-mediated processes is further investigated without confounding the effects of NP size and surface charge. Interestingly, high density cCBP-NPs (>7000 cCBP per NP) uptake is dominated by CLL1 receptor-mediated processes while low density cCBP-NPs (≈200 cCBP per NP) and untargeted NP occurred through non-specific clathrin and caveolin-mediated endocytosis. Altogether, these studies show that ligand density and uptake mechanism should be carefully investigated for specific ligand-receptor systems for the design of targeted DDSs to achieve effective drug delivery.