Characterization of the Uptake and Trafficking of AvB3-targeted and Non-targeted Nanoemulsions in Human Endothelial Cells in vitro

Abstract

RGD-functionalized and non-functionalized oil-in-water nanoemulsions of approximately 100 nm containing DSPC, PEGylated DSPE, cholesterol and Gd-DTPA-DSA at a molar ratio of 1.1/0.15/1/0.75 were prepared. In vitro uptake and trafficking in HUVECs of the nanoemulsions was characterized using confocal laser scanning microscopy and flow cytometry. The RGD peptide recognizes αvβ3 and αvβ5 integrin receptors, which play central roles in angiogenesis. Moreover, the αvβ3 integrin receptor is overexpressed in the endothelium of angiogenic tumor vasculature. It was found that the RGD-emulsion showed a remarkably high uptake in HUVECs expressing αvβ3 integrins compared to its non-conjugated control version. Furthermore, the RGD-emulsion was able to evade the lysosomes at least within the first 3 hours of incubation, while the control-emulsion was not. The uptake of both emulsions was mainly facilitated by caveolae-mediated endocytosis, but also to a lesser extent by clathrin-mediated endocytosis and other un- known mechanisms. It was shown that RGD and control-emulsions were internalized or sorted into distinct vesicles. Both emulsions bypassed the early endosomes, and it was hypothesized that they were mainly trafficked to caveosomes before subsequent traffick- ing of control-emulsion to late endosomes/lysosomes and of RGD-emulsion to cis-Golgi or endoplasmatic reticulum. The results suggest that the RGD-emulsion has promising feasibility as a site-specific targetable delivery system.