By LEE BOWMAN
Scripps Howard News Service
August 28, 2006
The findings from a team of American and Canadian scientists were published online Monday by the Proceedings of the National Academy of Sciences.
Anthrax toxins, released by the anthrax bacterium, are made of proteins and toxic enzymes that bind together to damage a host organism's cells. Most current therapies, including antibiotic treatments, try to attack either the bacterium or the toxins directly.
But the new inhibitor molecule blocks receptors that toxins use to attach to cells. Infectious bacteria like anthrax can become resistant to antibiotics over time, but such resistance can also be engineered intentionally into a germ that someone wants to distribute as a weapon of terror.
This prospect has haunted officials even before the fall 2001 intentional release of anthrax spores in mailings to news organizations and congressional offices. No one has ever been arrested in connection with the anthrax-laced envelopes. Anthrax from the letters ultimately infected at least 22 people, of whom five died, and prompted more than 30,000 others to take preventive antibiotics.
Antibiotics slow the progression of infection by the anthrax bacterium, but they don't counter the advanced destructive effects of toxins once an infection takes hold. Inhaled anthrax still has a fatality rate of 75 percent even after antibiotics are given, according to the federal Centers for Disease Control and Prevention.
Use of the inhibitor could help address this threat by blocking access to sites the toxins use to gain a lethal foothold. "Combining the inhibitor with antibiotic therapy may increase the likelihood of survival for an infected person," said Ravi Kane, an associate professor of chemical and biological engineering at Rensselaer Polytechnic Institute in Troy, N.Y., the co-author of the new study, which also included scientists from the University of Toronto.
The new approach led to a 50,000-fold increase in activity to block multiple binding sites, compared with the results from a more conventional inhibitor.
The same approach could be used to design blocking agents for other deadly disease agents, including SARS, flu and AIDS, the researchers said.
Blocking "host receptors" is a better approach than trying to constantly match evolutionary changes in bacteria and viruses, Kane said.
"Think about how a virus like HIV becomes resistant to an inhibitor that binds to it," he said. "A subtle change in the viral proteins can drastically reduce the affinity of the drug without compromising the ability of the virus to bind to its target cell.
"But a host protein is not mutating like proteins on the pathogen. So it's a stationary target versus a moving one."
The most potent inhibitor was further refined and tested in rats. Five out of six rats injected with only anthrax toxins died, as did all six rats injected with toxins and an inhibitor that binds to only select sites. But the new inhibitor protected all six rats that got it along with the toxins, and they showed no signs of adverse effects.
On the Net:
Distributed to subscribers for publication by
Scripps Howard News Service, http://www.shns.com
Publish A Letter on SitNews Read Letters/Opinions