updated 11/1/2005 1:15:39 PM ET 2005-11-01T18:15:39

Experiments on mice have shown promise for the future of nanotechnology in treating cancer.

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The research brings doctors one step closer to being able to inject patients with nanoparticles that bore inside tumors and release powerful doses of cancer-killing drugs while leaving the rest of the body unscathed.

After seeing how the mice were cured of human prostate cancer with the technology, cancer specialists gathered at the European Cancer Conference in Paris on Tuesday praised the work as impressive and said they had high hopes for its application to patients.

Nanotechnology is the science of manipulating matter smaller than 100 nanometers and taking advantages of properties that are present only at that level, such as conductivity. A nanometer is one-billionth of a meter, or about one-millionth the size of a pin head. The prefix comes from "nanos," the Greek word for dwarf.

Nanotech has been around for several decades, but only now is its potential starting to be realized. Medicine is expected to be one of the fields to benefit most from the technology. In cancer, it is hoped the technology will allow for more precisely targeted drugs and surgery and less toxic chemotherapy.

The study, conducted by scientists at Harvard Medical School and the Massachusetts Institute of Technology, which are pioneering cancer nanotechnology, involved engineering nanoparticles embedded with the cancer drug Taxotere. The particles were then injected directly into human tumors created from prostate cancer cell lines and implanted into the flanks of mice. The mice were watched for 100 days.

The technology being tested involves a nanoparticle made of a hydrogen and carbon polymer with bits of drug bound up in its fabric and attached to a substance that hones in on cancer cells. The polymer gradually dissolves, exposing the nuggets of drug little by little.

The mice were divided into five groups, including one that had their tumors injected with ineffective saltwater. A second group died after injections of a nanoparticle containing no drugs.

Another group that were given just one shot of the drug experienced an initial decrease in tumor size and then a strong rebound before they, too, died.

Other mice were injected with a nanoparticle-encased drug, but one that was not designed to specifically target cancer cells.

"What happens here is the lymphatic system of the tumor can take it up and wash it away, because the nanoparticle is not targeted to the cancer cells," said the study's presenter Dr. Omid Farokhzad of Harvard Medical School. The tumor initially shrank to half its original size, but then rebounded.

In a final group of mice, scientists injected the targeted nanoparticles containing the drug.

"The tumor completely disappeared," Farokhzad said.

Injecting targeted nanoparticles into the bloodstream and having them seek out tumors and get inside on their own is still the ultimate goal, but direct injection is also promising for cancers where the tumor is accessible and hasn't spread, such as in early prostate cancer, Farokhzad said.

Farokhzad said his group hopes to be able to test the approach in prostate cancer patients within two years.

One major problem scientists are having in perfecting the blood injections is that the nanoparticles are ending up in the liver and spleen _ an unwanted side effect because once they dissolve in those organs, they release toxic levels of chemotherapy to healthy tissue.

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