Nano World: Bio-nanotubes to fight cancer

NEW YORK, Aug. 12 (UPI) -- Nanotubes made with naturally occurring parts of cells at their core someday could serve as nanoscale capsules that deliver genes and drugs into the body, researchers told UPI's Nano World.

Materials scientists and biologists at the University of California, Santa Barbara, have experimented with positively charged lipids as potential gene-delivery mechanisms that can slip past the negatively charged membranes of cells. Specifically, they tested how lipids reacted with cell innards, focusing on microtubules -- hollow, negatively charged nanometer-scale protein cylinders that make up the internal skeleton of cells and serve as highways along which molecules can zip.

"We discovered that, under the right conditions, spontaneous lipid protein nanotubules will form," said lead researcher Uri Raviv.

The scientists worked with synthetic lipids and microtubules purified from cow brain tissue. When the lipids concentration was high enough, they encapsulated the microtubules. Otherwise, the lipids coated the microtubules but left their ends open and exposed.

The research team published its findings in the Aug. 9 issue of the Proceedings of the National Academy of Sciences.

Raviv said the team could inject drugs or genes into open protein-lipid nanotubes and then seal them. After the "bio-nanotubes" are slipped into cells, the proteins within the cell can bind to them and open them.

The team members already are incorporating the anti-cancer drug Taxol into their protein-lipid hybrids, Raviv said, "to stabilize the microtubules and to control the length of the lipid-protein nanotubes. Taxol is a chemotherapy drug that binds to microtubules and therefore might be one of the first drugs that would be delivered in the future, in a specific manner to cancer cells only, thereby reducing the side effects of chemotherapy treatments."

Other researchers are experimenting with nanoscale capsules to deliver genes and drugs into the body, such as silica nanoparticles or bubbles made of lipids. Still, when it comes to these new bio-nanotubes, "the ability to open and close the lipid-protein nanotubes, the relatively large volume of the tubes and the ability to control this volume could be important advantages," Raviv said.

Gerard Wong, a biophysicist at the University of Illinois at Urbana-Champaign, called the research "really elegant work." He said future nanocapsules based on these findings might not actually use natural microtubules but could employ rather more versatile synthetic versions.

"This shows a set of general principles that will help guide people into what they actually wind up making," Wong said.

Raviv cautioned that positively charged lipids "could be toxic in large quantities. Although other lipid-based drug-delivery vehicles typically use a higher percentage of positively charged lipids, this may still limit the amount of drugs and genes that could be delivered."

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Charles Choi covers research and technology for UPI Science News. E-mail: sciencemail@upi.com