Uptake Mechanisms Dependent on Membrane Trafficking

Applications of transcytosis have been extended to additional receptors, cargos, and delivery sites (36). The TfR has been used to deliver In-labeled DTPA-EGF-PEG-biotin-streptavidin-mABTfR (DTPA = the metal chelator diethylenetriaminepentaacetic acid EGF = endothelial cell-derived growth factor PEG = polyetheylene glycol) across the BBB, where binding to cells expressing EGF receptor (EGFR) was useful 

The vitamin B12 receptor which facilitates uptake of the vitamin-intrinsic factor vitamin-binding protein complex has been used to enhance oral delivery and gastrointestinal uptake of peptides and proteins as their vitamin B12 conjugates (37). Commercial efforts are under way to exploit this receptor as well as the fetal Pc receptor which facilitates intestinal uptake of antibodies from colostrum/milk (38) and the polymeric immunoglobulin receptor which facilitates the serosal to mucosal transport of IgA and IgM (39). 

The ATP-binding cassette (ABC) superfamily and the major facilitator (MF) superfamily account for the majority of membrane transporters. 

2 ABCB1,4 P-Glycoprotein, organic cations, neutrals, lipids 

n ABCCl. n Organic anions, GSX conjugates, GSH CO transport 

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