Quantum dots-tagged liposomes: stable fluorescent nanoparticles with multivalent binding sites for targeted cell delivery.

V. SIGOT Y T.M JOVIN

Valencia, España

Conferencia; Focus on Microscopy; 2007

The epidermal growth factor receptor (EGFR) is overexpressed in a broad spectrum of malignant tumors and represents a target for delivery of therapeutic liposomes. Quantum Dots (QDs) are bright and extremely photostable fluorescent labels 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 was added to A431 cells overexpressing the EGFR and colocalization of both QDs were analyzed by confocal fluorescence microscopy. QDs labeled liposomes were internalized specifically through EGF receptor mediated endocytosis. The colocalization of QD525 and QD655 was quantitated by Manders’s overlap coefficients. The proportion of each QD contributing to the colocalization as described by Manders coefficients varied from 0.4-0.95 for both QDs (n=304 cells). M1=QD655 coloc./Total Intensity QD655, M2=QD525 coloc./Total intensity QD525, R=Pearson Correlation Coefficient. The colocalization of both QDs indicated receptor-mediated liposome internalization. QD655 were not internalized in the absence of ligand and were only detected when they were bound to EGF:QD525 targeted liposomes. Double fluorescence labeling of liposomes allows the monitoring of the true uptake of liposomes and multiple ligand coupling for targeted delivery.