Abstract
Intercellular adhesion molecule 1 (ICAM-1) is a cell-surface protein overexpressed in many diseases and explored for endocytosis and transcytosis of drug delivery systems. All previous evidence demonstrating ICAM-1-mediated transport of therapeutics into or across cells was obtained using nanocarriers or conjugates coupled to multiple copies of anti-ICAM antibodies or peptides. Yet, transport of therapeutics linked to non-multivalent anti-ICAM ligands has never been shown, since multivalency was believed to be necessary to induce transport. Our goal was to explore whether non-multivalent binding to ICAM-1 could drive endocytosis and/or transcytosis of model cargo in different cell types. We found that anti-ICAM was specifically internalized by all tested ICAM-1-expressing cells, including epithelial, fibroblast and neuroblastoma cells, primary or established cell lines. Uptake was inhibited at 4°C and in the presence of an inhibitor of the ICAM-1-associated pathway, rather than inhibitors of the clathrin or caveolar routes. We observed minimal transport of anti-ICAM to lysosomes, yet prominent and specific transcytosis across epithelial monolayers. Finally, we coupled a model cargo (the enzyme horseradish peroxidase (HRP)) to anti-ICAM and separated a 1:2 antibody:enzyme conjugate for non-multivalent ICAM-1 targeting. Similar to anti-ICAM, anti-ICAM-HRP was specifically internalized and transported across cells, which rendered intra- and trans-cellular enzyme activity. Therefore, non-multivalent ICAM-1 targeting also provides transport of cargoes into and across cells, representing a new alternative for future therapeutic applications via this route.