Elucidating the mechanism of cellular uptake and removal of protein
Both agonist- and antagonist-modified QDs exhibited specific cell binding, but there was a tremendous difference with respect to cellular uptake. The cells formed vesicular structures containing agonist-modified QDs, which indicate that the nanoparticles had been transported into the cells (-stack images.
To further elucidate the location of agonist-modified particles after their interaction with cells, images representing optical sections through the cells were taken from MCF-7 cells after incubation with [Lys, strong fluorescence because of the QDs can be found throughout the cells, except for the cell nuclei.
The receptor functions like a logic “and-gate” that grants cell access only to those particles that carry a receptor ligand “and” where the ligand is an agonist.
We show that quantum dots carrying a surface-immobilized antagonist remain with nanomolar affinity on the cell surface, and particles carrying an agonist are internalized upon receptor binding.
This multiligand binding leads to five orders of magnitude increased-receptor affinities, compared with free ligand, in displacement studies.
We found that agonist- and antagonist-modified nanoparticles bind to several receptor molecules at a time.
The receptor functions like a logic "and-gate" that grants cell access only to those particles that carry a receptor ligand "and" where the ligand is an agonist. Most importantly, however, two classes of GPCR ligands exist: agonists that lead to receptor internalization upon binding and antagonists that do not (14).After activation of the amino-PEG QDs (1) with sulfo-SMCC, the resulting thiol-reactive nanoparticles (2) were connected with either the peptidic agonistic analogs of p NPY or the nonpeptidic antagonist SH-BIBP to yield the ligand-modified QDs (3).R-SH refers to the structures depicted in -receptor, as no binding was observed either to MCF-7 cells in the presence of free antagonist BIBP3226 or when conducting the experiment with MDA cells lacking the receptor.This finding supports the concept that the particles were effectively delivered into the target cells.The cells show spots in the cytoplasm that are typical of endocytotic vesicles formed upon receptor-mediated endocytosis.