Quantum Dot labeled liposomes. Stable fluorescent nanoparticles for targeted delivery

V.SIGOT, D.J. ARNDT-JOVIN, T.M. JOVIN

Göttingen

Simposio; Horizons in Molecular Biology; 2006

The epidermal growth factor receptor (EGFR) is overexpressed in a broad spectrum of malignant tumors and represents a target for delivery of therapeutic liposomes. Fluorescent lipid probes are commonly added to liposomes in order to track receptor-mediated internalization. However due to fast exchange of lipophilic probes with cell membranes and significant quenching, long-term imaging of such uptake is limited. We performed a double labeling of liposomes with highly fluorescent and stable Quantum Dots (QDs) conjugated with EGF ligand to target cells. Biotinylated liposomes were conjugated with streptavidin coated QDs (em.605 nm) together with QDs (em.525 nm) pre-conjugated with EGF.Liposomes labeled with both QDs without EGF were not detected intracellularly. QD605 were not internalized in the absence of ligand and were only detected when they were bound to EGF:QD525-targeted liposomes. Confocal fluorescence microscopy on live cells for 1 h showed a substantial internalization of QDs:EGF-targeted liposomes compared to QDs labeled-non targeted liposomes. Colocalization of both QDs was considered indicative of true uptake of the ligand-liposome conjugate. Our protocol based on streptavidin-QDs allowed us to follow liposome uptake without significant quenching. In addition, the liposomes were able to accomodate multiple ligands for specific targeting. Targeted liposomes loaded with DNA will be evaluated for gene delivery.