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By Maggie Fox, Health and Science Correspondent

WASHINGTON, Nov 15 (Reuters) - Tiny radioactive generators that home in on cancer cells and zap them with deadly particles may provide an entirely new approach to treating several forms of cancer, researchers said on Thursday.

The molecule-sized devices are a kind of biological Trojan horse that can seek out cancer cells anywhere in the body, attach to them, and fry them with a radioactive molecule, the scientists report in Friday's issue of the journal Science.

So far they have kept mice alive for weeks longer than they would have been expected to survive with prostate cancer and lymphoma, Dr. David Scheinberg, a leukemia specialist at Memorial Sloan-Kettering Cancer Center in New York, who helped lead the study, said.

The technology combines two time-tested approaches to cancer -- radioactive treatment and monoclonal antibodies.

Scheinberg's team took a single atom of actinium-225, a radioactive atom that emits alpha particles that can kill cells, and enclosed it in a molecular cage. This was attached to a monoclonal antibody, which is an engineered antibody programmed to target specific cancer cells.

"We have found an effective way of containing and then delivering this highly potent element directly into cancer cells," Scheinberg said in a statement.

They tested their devices, which they have named nanogenerators, on various human cancers grown in laboratory dishes -- leukemia, lymphoma, breast, ovarian, neuroblastoma and prostate cancer.

Just a few of the nanogenerators killed the cancer cells, they reported.

INFECTED MICE SERVIVE LONGER

Then they tried mice. A standard method of cancer research is to inject mice with cells taken from human tumors, wait until the mice develop cancer, and then treat them.

"We waited for the tumor to be established," Scheinberg said in an interview conducted by e-mail.

Mice infected with prostate cancer and lymphoma both survived much longer than expected when the nanogenerators were used, Scheinberg said. Untreated mice lived about 28 days, while treated mice lived 173 days and some as long as 10 months.

And in many of the mice with prostate cancer, levels of prostate-specific antigen (PSA) -- produced in great quantities by prostate cancer cells and used in people as a measure of their cancer -- plummeted to zero.

Scheinberg said treating mice infected with cancer can be much easier than treating people who have developed cancer over time, so it is too soon to say whether his team's method will work in humans. "We will not know until we treat people," he said.

Scheinberg said if the approach works, it should be able to catch cancer that has spread, or metastasized, through the body. He said actinium-225 was useful because it has a long half-life -- it persists for a long time -- and thus might be able to kill larger tumors.

Yet overall, the amount of radioactivity delivered to the body would be small, because single atoms are used, the researchers said.

10:26 11-15-01
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