Monday, July 02, 2007

New Nano Weapon against Cancer

Gold nanoparticles with branching polymers could attack tumors in multiple ways.

By Prachi Patel-Predd

Nano weapon: A gold nanoparticle enveloped in treelike polymer branches could act as a multipurpose tool for fighting cancer. Researchers can attach folic acid (pink) and fluorescent dye (green) to the nanoparticle to target and image tumors. Tumor cells could be killed with cancer drugs, which are attached to the particle, and with lasers that heat up the gold. Credit: Xiangyang Shi, University of Michigan

A new class of specially engineered nanoparticles that can target, image, and kill tumor cells could be a potent weapon against cancer. The new nanoengineered system, designed by physician and researcher James Baker and his colleagues at the University of Michigan, contains gold nanoparticles with branching polymers called dendrimers that sprout off the nanoparticle's surface.

The particles could be used to launch a multiprong attack against tumors. The dendrimer arms can carry a number of different molecules, including molecules that target cancer cells, fluorescent imaging agents, and drugs that slow down or kill the cells. Once enough of the nanoparticles have gathered inside cancer cells, researchers could kill the tumors by using lasers or infrared light to heat up the gold nestled inside the dendrimers. The nanoparticles could thus kill tumors "by combining chemical therapy and physical therapy," says University of Michigan researcher Xiangyang Shi, who was involved in the work.

In a paper published in the July issue of Small, the researchers demonstrated targeting and imaging cancer cells in a laboratory dish with the new gold-dendrimer hybrid nanoparticles. They hooked four or five folic-acid and fluorescent-dye molecules to each of the dendrimer branches. Then they processed the particles to remove any extra surface charge, which can make the otherwise safe polymers toxic.

Cancer cells have many more folic-acid receptors on their surface than healthy cells do. The folic acid-laden nanoparticles attached to human cancer cells, and the cells swallowed them, along with the folic acid. The particles, which are only three nanometers wide, easily passed through the cell membrane.

Using a microscope, the researchers could see the particles that had accumulated inside the cells because of the dye molecules. The gold in the particle enhanced the contrast enough for the researchers to see that the particles gathered inside the cells in tiny spherical structures called lysosomes. The goal, Baker says, is to make particles that target cancer genes inside cells. "You would bind this material to, let's say, an oncogene in a cell and knock out the oncogene without harming anything else," he says.

But first, the researchers will have to show that their material works inside animals. Many other research groups have developed multifunctional nanoparticles to seek out cancer cells and deliver imaging molecules and drugs. Hundreds of different materials are now undergoing tests--gold nanoparticles, silica nanoparticles, polymer shells, and gold-coated glass beads, to name a few. To work in humans, any cancer nanotherapy has to pass three major challenges: the nanoparticles should target only cancer cells; any nanoparticles that do not accumulate inside cells should get eliminated from the body; and the particles should not trigger the body's immune response.