Researchers at Boston Children's Hospital have discovered a naturally occurring protein fragment which has been shown to inhibit tumor growth in mice, the third isolated at the hospital's labs.

The Medical School's Andrus Professor of Pediatric Surgery M. Judah Folkman announced last Friday that tests at his lab at the Children's Hospital had confirmed the effectiveness in mice of the protein fragment, called antiangiogenic antithrombin (aaAT), in suppressing the formation of blood vessels that feed tumor growth.

This discovery comes less than two years after Folkman published his lab's detection of the second of two protein fragments thought to suppress tumor growth. The three fragments have only been tested in animals, and it will be impossible to judge the potential of these substances in fighting human cancers until extensive clinical trials are held, at least.

In a 1997 article in the journal Cell, researchers in Folkman's lab, including Folkman and angiostatin discoverer Michael S. O'Reilly, wrote that their findings and experimental data "suggest a theme of fragments of proteins as angiogenesis [blood vessel growth] inhibitors."

As explained in an article in the Sept. 17 issue of the journal Science, the human body contains numerous proteins which limit blood vessel growth under normal conditions such as menstruation and wound healing.

Now researchers speculate that these proteins may also inhibit cancer growth.

The aaAT fragment was first discovered in human lung cancer cells by O'Reilly, a clinical fellow at the Children's Hospital.

The protein's sequence was first analyzed at the Harvard Microchemistry Facility. William S. Lane, director of the facility, said that although his lab's high-tech equipment aided the discovery, it is the Folkman lab that should be congratulated.

"We determined the peptide sequence," Lane said. "But kudos to Folkman and O'Reilly for isolating the protein," he stressed.