Sugar-coated Nanoparticles Find Hidden Tumors

By Eric Bland, Discovery News

March 30, 2009 -- Nanoparticles that could first illuminate and then destroy hidden tumors have been created by scientists at the University of California, San Diego.

If approved for clinical use, the new technique could improve the odds of survival for cancer patients by letting doctors diagnose and treat cancer earlier. It would also, in theory, minimize the toxic side effects associated with traditional chemotherapy.

"The advantage is that if the nanostructure localizes [near the tumor], it gives you an improved ability to see or treat the tumor," said Michael Sailor, a scientist at the University of California, San Diego, who detailed the research in a recent issue of Nature Materials.

The drawback to most techniques for finding and treating cancer is toxicity. The same radioactive cadmium that accumulates inside tumors and shines light that MRI machines can detect also destroys various internal organs. Chemotherapy drugs such as abraxane destroy tumor cells but also kill plenty of healthy cells.

Scientists started with thin silicon wafers, similar to those used in the semiconductor industry, and broke them into nano-sized pieces using ultrasound. To treat cancer, the particles would soak up whatever cancer drug would work best in a given case. The scientists then coat the particles in a thin layer of dextrose, a form of sugar.

The end result, according to Sailor, are cancer-killing pastries. "They're like little jelly doughnuts, rolled in chocolate to seal everything in," said Sailor.

Once the poisonous particles are injected into the bloodstream, they travel around the body.
Tumors need a lot of blood to grow quickly, but they are not good plumbers. The blood vessels surrounding the tumors are thin and full of holes. Those holes are typically just over 100 nanometers in size, just big enough for the 100-nanometer nanoparticles to slip through and get stuck inside the tumor itself.

The particles, made of nontoxic silicon instead of traditional toxic cadmium, glow under ultraviolet light. After about an hour of circulating through the body, enough of them have physically lodged themselves near the tumor to be detected by an MRI machine, helping doctors pinpoint the location.

As blood flows around the embedded nanoparticles it dissolves the sugar coating and releases the anti-cancer drug, destroying the cancer cells and leaving more healthy cells alive, compared with traditional chemotherapy.

Once the nanoparticles have released the drug, the body continues to break down the particles. Within 24 hours, the nanoparticles are out of the bloodstream, and within a few weeks, they have been excreted from the body entirely.

Sailor and his colleagues used the nanoparticles to identify skin cancer cells in mice. They have not used them to treat cancer yet, but are currently working on it.

Philippe Fauchet, a scientist at the University of Rochester in New York, has developed his own silicon nanoparticles to see tumors, although instead of breaking a large piece of silicon into smaller pieces, he essentially takes small pieces of silicon and makes larger nanoparticles.

"The advantage of using silicon is that it is biocompatable," said Fauchet. "The particles dissolve and are excreted by the urinary tract in 30 days. There is no accumulation, like what you get with heavy metals like cadmium."

However the silicon nanoparticles are made, it will be a while before they can be used to treat humans, pending approval from the U.S. Food and Drug Administration.

Sailor said the earliest clinical trials could begin within six months, although his team is estimating a more conservative two year-time frame.

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