Peptide Quantum Dot Conjugates Detect Integrin αvβ3

Abstract

Quantum dots (QD) are fluorescent semiconductor nanocrystals composed of a CdSe/ZnS core/shell structure. QD have multiplexing capabilities and unique photophysical properties including broad excitation spectra, narrow Gaussian‐shaped emission spectra, enhanced photostability, and near 100% quantum yield, as compared to their fluorophore complements. Functionalization of the QD surface with peptide ligands is an effective method for labeling endogenous proteins in cells and tissues. Development and characterization of QD probes for targeting the pulmonary endothelium could provide a methodology for enhancing in vivo microscopy. Integrin αvβ3 is expressed by vascular endothelial cells, and is a receptor for extracellular matrix proteins, such as vitronectin and fibronectin, with an exposed arginine‐glycine‐aspartic acid (RGD) tripeptide sequence. Prior studies have demonstrated the use of RGD peptide QD conjugates (RGD‐qds) to target integrin αvβ3 in tumor vasculature. In this study, we monitored the labeling of endothelial cells by RGD‐qds under conditions where integrin αvβ3 expression is increased in vitro, by angiotensin II (AngII) exposure of vascular endothelial cells and in mouse lungs in vivo by lipopolysaccharide (LPS) administration. Fluorescence microscopic evaluation showed RGD‐qds to be bound on the treated cells, but not on untreated controls. Western blot analysis supported an increase in integrin αvβ3 expression in endothelial cells exposed to AngII. These results illustrate the use of QD probes for intravital multiphoton microscopic studies of stimulated and naïve pulmonary endothelium.