Angew.Chem.Int.Ed.http://dx.doi.org/10.1002/anie201410223(2014)

Cell-derived microvesicles — spherical fragments formed by budding of the plasma membranes of cells — are known to be pivotal in intracellular communication and have also been investigated as siRNA delivery vehicles. However, the long-term labelling and in vitro and in vivo tracing of microvesicles remains a challenge and may offer useful information about their biological behaviour. Now, Dai-Wen Pang, Yi-Fang Zhao and colleagues report the efficient and specific labelling of cell-derived microvesicles with quantum dots, enabling them to be traced while maintaining their structure and function. The biocompatible labelling strategy relies on the formation of biotinylated microvesicles that have been shed from cells with biotinylated membranes. These microvesicles are then functionalized with streptavidin-conjugated quantum dots. The delivery of therapeutic siRNA quantum dot-labelled microvesicles derived from endothelial cells was found to reduce tumour size in an in vivo mouse xenograft model as a consequence of their observed uptake into tumour and angiogenic vascular cells. The labelling technique could also be successfully applied to macrophage-derived and tumour-derived microvesicles.