October 22, 2009 / 6:15 AM / 8 years ago

Drugs may make radiation treatments safer, better

CHICAGO (Reuters) - New experimental compounds make cancer cells more vulnerable to radiation while protecting healthy cells, U.S. researchers said on Wednesday in a finding that may lead to safer, more effective treatments for cancer.

Studies in mice and in human cells showed the compounds protected normal cells from radiation injury, they said.

“When we take those agents and give them to animals and human cells, we protect the animals and cells from extreme doses of radiation,” said Dr. Jeff Isenberg of the University of Pittsburgh School of Medicine, whose study appears in the journal Science Translational Medicine.

They found that mice treated with a drug that blocks a molecular doorway or receptor called CD47 made them resistant to radiation injury, protecting skin, muscle and delicate bone marrow cells.

It also made the radiation treatments more effective. Tumors in treated mice grew back more slowly and were 89 percent smaller after exposure to radiation than other mice.

“We were stunned by the initial findings,” Isenberg said in a telephone interview. “We repeated these studies over several years in different kinds of cancers.”

One of the first effects of radiation is the hair falls out, Isenberg said.

“When we protect our animals with the compound, they don’t even lose their hair when exposed to radiation,” he said.

The compounds developed by his team and researchers at the National Cancer Institute, part of the National Institutes of Health, block a specific protein called thrombospondin-1 and keep it from binding to CD47, Isenberg said.

It is not clear why interfering with this process prevents radiation damage, but the researchers think it may be that radiation hampers the immune system’s ability to fight tumors, and blocking CD47 protects immune cells.

If proven safe and effective in people, the agents could address a big drawback with radiation treatments, which are used in more than half of all cancer patients.

“The primary problem with radiation is not only does it kill the cancer. It also kills all the normal tissue anywhere near it,” Isenberg said.

Bone marrow — the body’s chief source of immune system cells — is particularly vulnerable. “It doesn’t take much to wipe out those very important cells,” he said.

So far, interfering with the CD47 pathway has not resulted in any negative effects in genetically altered mice.

“We’ve aged the animals up to three years. In a mouse system that is ancient. They don’t show any adverse effects,” Isenberg said.

“That doesn’t mean it couldn’t be something different in people,” he said, adding that many more tests are needed.

But he expects the treatment would only be used in humans for brief time periods, such as right before a radiation treatment, or right after accidental exposure to radiation.

Editing by Maggie Fox

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