Quantum Dots: Torch bearers into cells

VALERIA SIGOT ; THOMAS JOVIN

Imaging and Microscopy

Wiley-Blackwell

Año: 2008 p. 40 - 43

An efficient receptor-mediated delivery system has been developed using preformed complexes of Quantum Dots (QDs) and the Epidermal Growth Factor (EGF) as ligand.Liposomes are either loaded or surface modified combining two colors of QDs probes. The dual labeling strategies involve only biotin-streptavidin interaction and do not require further purification from free QDs-EGF. Specific uptake of QDs-EGF-labeled liposomes is detected in live cells as colocalization of both dots.The epidermal growth factor receptor (EGFR) is overexpressed in a broad spectrum of malignant tumors and represents a target for delivery of therapeutic liposomes. Labeled liposomes obtained by including a fluorescent phospholipid in the formulation showed spontaneous transfer of the fluorescent lipid from liposomes to cells and significant quenching thus limiting long-term imaging. Quantum Dots (QDs) are bright and extremely photostable fluorescent labels more suitable for     monitoring uptake mechanisms.Previous work in our group showed that QDs conjugated with one or more EGF molecules internalize by receptor mediated endocytosis. Unspecific QDs uptake is not observed in the absence of ligand.We designed a double labeling strategy for biotinylated liposomes using streptavidin coated QD525 (green fluorescence) conjugated to biotinylated EGF (bEGF), and streptavidin coated QD655 without ligand. This mixture were added to A431 cells overexpressing the EGFR and colocalization of both QDs were analized by confocal fluorescence microscopy. QDs labeled  liposomes were internalized specifically through EGF receptor mediated endocytosis.