Ligand-targeted, receptor-mediated endocytosis is commonly exploited for intracellular
drug delivery. However, cells-surface receptors may follow distinct endocytic fates when bound by monomeric vs multimeric
ligands. Our purpose was to study this paradigm using
ICAM-1, an endothelial receptor involved in
inflammation, to better understand its regulation and potential for
drug delivery. Our procedure involved fluorescence microscopy of human endothelial cells to determine the endocytic behavior of unbound
ICAM-1 vs
ICAM-1 bound by model
ligands: monomeric (anti-ICAM) vs multimeric (anti-ICAM
biotin-
streptavidin conjugates or anti-ICAM coated onto 100 nm nanocarriers). Our findings suggest that both monomeric and multimeric
ligands undergo a similar endocytic pathway sensitive to
amiloride (∼50% inhibition), but not inhibitors of
clathrin-pits or caveoli. After 30 min, ∼60-70% of both
ligands colocalized with Rab11a-compartments. By 3-5 h, ∼65-80% of multimeric anti-ICAM colocalized with perinuclear lysosomes with ∼60-80% degradation, while 70% of monomeric anti-ICAM remained associated with Rab11a at the cell periphery and recycled to and from the cell-surface with minimal (<10%) lysosomal colocalization and minimal (≤15%) degradation. In the absence of
ligands,
ICAM-1 also underwent
amiloride-sensitive endocytosis with peripheral distribution, suggesting that monomeric (not multimeric) anti-ICAM follows the route of this receptor. In conclusion,
ICAM-1 can mediate different intracellular itineraries, revealing new insight into this
biological pathway and alternative avenues for
drug delivery.