Nanotech News

May 31, 2005

Carbon Nanotubes Ferry Proteins into Cells

As cancer biologists continue to unravel the complex intracellular signaling networks that turn a healthy cell into a malignant one, they will undoubtedly discover new avenues for developing targeted therapeutics that will stop uncontrolled cell growth. Many of these therapeutic agents may turn out to be proteins, but proteins can be difficult to get across the cell membrane and into the cytoplasm while still retaining their biological function. New research from Stanford University raises the possibility that carbon nanotubes could serve as one tool for getting small proteins into cells.

Reporting their work in the Journal of the American Chemical Society, Hongjie Dai, Ph.D., and graduate student Nadine Wong Shi Kam, have shown that acid-oxidized single-walled carbon nanotubes will bind proteins and transport them through the cell membrane. Acid-treated carbon nanotubes are stable in water and do not aggregate, as do untreated carbon nanotubes. The nanotubes cross the cell membrane via endocytosis, a process that cells use to transport a variety of molecules into the cell. In many instances, a cell will break down proteins transported via endocytosis, but the nanotube-bound proteins avoid this fate if they are delivered along with a small amount of the antimalarial drug chloroquine. For reasons that are still unclear, acid-treated carbon nanotubes were able to bind a large protein, human immunoglobulin, but were not able to transport that protein across the cell membrane.

To test if carbon nanotubes can deliver small proteins that then retain their biological activity once inside the cell, the researchers used the nanotubes to deliver the protein cytochrome c to several cultured cell lines. Cytochrome c is known to trigger apoptosis, and these experiments showed that nanotube-bound cytochrome c did cause significantly higher rates of apoptosis than did either cytochrome c or the nanotubes alone. The researchers noted that these experiments were not capable of determining if cytochrome c remained attached to the nanotubes or if it was released into the cytoplasm. Nevertheless, the protein retained its biological activity.

This work is detailed in a paper titled, "Carbon nanotubes as intracellular protein transporters: generality and biological functionality." This paper was posted online in advance of publication at the journal's website. An abstract is available there.
View abstract.