New anthrax treatment works in rats

By distorting a protein in the toxin that makes anthrax deadly, scientists have discovered a potentially better way to treat the disease and perhaps even to prevent it with a vaccine.

The microbe that causes anthrax, Bacillus anthracis, can release its toxin in both animals and people. Although an anthrax infection can be cured with penicillin or tetracycline, it can be lethal if not treated promptly. Antibiotics kill bacteria but don’t disable toxins already unleashed in the body. For years, anthrax has been high on the list of potential biological weapons.

Scientists at Harvard Medical School in Boston set out to ambush the disease by neutralizing the anthrax toxin, which is built from three proteins made by the bacterium. The proteins are harmless individually but deadly together.

To disable the toxin, the researchers have developed a mutant form of one of these proteins, protective antigen (PA). Earlier test-tube experiments established that mutant PA combines with the other two proteins into a complex that fails to effectively invade cells, says biochemist and study coauthor R. John Collier.

He and his colleagues have taken the next step by injecting rats with mutant PA and then exposing them to the bacteria. Those animals survived, but untreated rats exposed to anthrax died within hours, the scientists report in the April 27 Science.

The researchers acknowledge that such a treatment might only work if given within a very short time of exposure. “It will be interesting to see how long after infection with B. anthracis animals can still be protected by mutant PA,” say Sjur Olsnes and Jrgen Wesche of the Norwegian Radium Hospital, Montebello, in Oslo in the same journal. Such animal tests might suggest how quickly people would need treatment after exposure.

There’s already a vaccine against anthrax, but some people claim it has harsh side effects. The existing vaccine is chemically inactivated PA. A vaccine based on the mutant PA might represent an alternative, Collier says.