Irradiated Antibodies Show Promise in Cancer Cases

United Press International

A new technique that mixes genetic engineering and nuclear medicine to imitate the body's immune system may be able to locate and kill cancerous tumors before they spread out of control, a government scientist says.

The technique already has proved successful in locating elusive skin and blood cancers not found by other methods and will soon be tested as a treatment for colon cancer, said Dr. Steven Larson of the National Institutes of Health in Bethesda, Md.

"We're very excited about the prospects for treatment," Larson says. "We're just about to start the first of our trials with this therapy, so we don't know if it's going to work yet, but our preliminary work is very, very encouraging."

Larson, presenting his research at a national meeting of radiologists, said his approach essentially works by mimicking the body's own immune system and capitalizing on its natural response to foreign invaders.

'Great Philosophical Appeal'

"That's the great philosophical appeal here," he said. "It should work in concert with the body's defense mechanism, primarily hitting the tumor and leaving the rest of the body alone."

Most cancerous tumors have unique proteins on their surface, called antigens, which attract the attention of defensive cells called antibodies. Once an antibody specific to a particular type of tumor is found, it can be genetically altered and duplicated in huge quantities, then dosed with radiation so it can be tracked in the body.

"You take the antibody, label it with radioactivity, then inject it into the body," Larson explained. "The antibody goes through the tissues and sort of percolates in the blood system, and wherever it finds (cancerous tissue), it attaches. Eventually, it accumulates.

"You can use these radioactive antibodies for the dual purpose of detecting tumors that weren't apparent from other clinical testing, and also as a carrier for enough radioactivity so that it can actually kill the tumor."

Detected Melanomas

Using nuclear medicine devices called gamma cameras, Larson said he and his colleagues have been able to use radioactive antibodies to detect melanomas and lymphomas--skin and blood cancers--that could not be detected otherwise. The antibody, called B72.3, also attaches to colon and ovarian cancers.

The "targeting" of B72.3 to colon tumors has been so successful that NIH researchers next month will begin injecting cancer patients with antibodies subjected to higher doses of radiation, Larson said. The procedure should provide "pinpoint" radiation therapy to the tumors without disturbing other tissues, he said.

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