Delivering Quantum Dot Probes into the Cytosol

Nanoparticles packaged inside virus-based liposomes identify EGFR proteins within brain tumor cells

The fluorescent nanoparticles known as quantum dots (Qdots) are promising tools for identifying various types of tumor cells, but mechanisms for getting Qdots inside cells have fallen short. Researchers at City College of New York now have devised a flexible technology that releases Qdots inside human brain tumor cells in vitro without killing the cells or interfering with the function of the targeted proteins. As described in the Journal of Nanobiotechnology, this technology can successfully bind Qdots to the epidermal growth factor receptor (EGFR) protein, which is often overexpressed in brain tumors.

When liposomes deliver quantum dot (Qdot) fluorescent nanoparticles into a cell, Qdots may be trapped in endocytic compartments, as shown on the left. Liposomes modified to add the membrane-piercing capabilities of an inactivated Sendai virus can fuse with the cell membrane, allowing Qdots to better enter the cytosol and label intracellular receptors such as EGFR, as shown on the right. [Photo courtesy of Veronica Dudu, PhD]

Previous efforts to deliver Qdots, tiny particles one-thousandth the size of a cell, into cells often left the nanoparticles trapped inside endosomes or clumped together. Lead investigator Maribel Vazquez, ScD, had had some success using liposomes to deliver quantifiable amounts of Qdots into glioblastoma cells, but tests on different types of brain cancer cells yielded varying results.

Instead of looking for the right liposome “recipe” for each cell type, Vazquez turned to the Sendai virus, a mouse parainfluenza virus commonly employed to deliver molecules into cells. “Viruses are honed over millions of years to get their contents into the cytosol,” she says.

Vazquez and her colleagues packaged Qdots with an EGFR antibody in a liposome that incorporated membrane-piercing proteins generated by an inactivated Sendai virus. The virus-based liposome then could break through the cell membrane and merge with it, “like two bubbles fusing to form one large bubble,” she says.

Fluorescence microscopy showed that these liposomes delivered approximately 70% of their Qdots into the cytosol, increasing the labeling rate of EGFR inside the cells by 50% compared with traditional liposome delivery, in glioblastoma and medulloblastoma cells.

This approach could accommodate other antibodies to detect a variety of molecular markers, potentially allowing for rapid diagnosis of tumor malignancy or potential vulnerability to therapeutic treatments. Vazquez hopes to use the technology to better understand and possibly control the migration of brain cancer cells. “But the first step is getting the dots in there,” she says.