Campus & Community

New ways found to fight anthrax:

6 min read

Bacteria make their own syringe

Under a diagram of the anthrax molecule, John Collier ponders ways to tame the bacteria’s poison unit, a model of which sits on his desk. (Staff photo by Kris Snibbe)

Two “Eureka!” moments in a Harvard University laboratory have led to new ways to neutralize deadly anthrax bacteria released in bioterrorist attacks.

In one, John Collier looked into a powerful electron microscope and, for the first time, saw a natural syringe made by an anthrax molecule. Seven individual proteins assemble themselves into a minute syringe that pierces human cells and injects a deadly poison. At first, the victim feels only flulike symptoms, but later, an irreversible sequence can start a person on the way to death.

Collier, Presley Professor of Microbiology and Molecular Genetics at the Harvard Medical School, began tinkering with anthrax molecules in 1989. After isolating the syringe subunits, each composed of as many as 568 pieces, he and his colleagues were trying to find ways to prevent the syringe from working. Unexpectedly, they discovered that, if only one of the seven subunits is flawed, the syringe cannot inject its poison into a human cell.

“There’s a lot of chance in the business of discovery,” Collier admits about this second “Eureka!” “When I realized what had happened, I knew we had found a road that could lead to a new type of drug or vaccine. All we needed to do was to mix a mutated copy of a syringe protein with those made by the anthrax itself, and the syringe could not perform its function in poisoning cells.”

Collier’s team made a batch of mutated protein and injected it into lab rats along with anthrax toxin. None of these animals developed any symptoms of the lethal disease, but animals injected with the toxin alone became critically ill in about 90 minutes.

Working on boom docks

At the time, Collier was collaborating with John Young, another Harvard Medical School scientist. Their combined research teams discovered how the anthrax molecule attaches to a human cell in the first place. Before it can assemble its deadly syringe, the molecule must bind to a receptor that sticks up on the cell surface. It’s not too different from a fighter jet docking with the boom of a refueling airplane in the skies over Iraq.

Suppose the receptor boom on a cell wasn’t there. The lethal molecule could not connect to the cell and drop its “bombs” into it.

Young, Collier, and their colleagues began to tinker with the genes necessary to make the proteins that are involved. In 2001, they came up with a mutated piece that docks with the toxin before it can dock with a cell. Without a place to sit and put together its syringe, the molecule no longer is a threat.

The researchers then devised a decoy receptor, a fake boom, expecting that anthrax molecules would dock with decoys rather than cells. The researchers tried it on rats and it worked.

Since then, Young has moved to the University of Wisconsin School of Medicine. It was never clear whether a cell has more than one receptor, so he kept looking for others. In April, he announced the discovery of a second receptor. “It’s about 25 times better than the first one,” Young says.

“It’s a nice piece of work,” comments Collier. “We tested the new decoy receptor on rats, and it proved highly effective in neutralizing the anthrax toxin.” The new decoys mopped up the poison more effectively than those made for the original receptor.

Made into drugs, receptor decoys would be injected after the flulike symptoms of anthrax are first detected, but before the infection fully develops, anywhere from a day to weeks. If, say, bacteria were dropped from an aircraft flying over a major city, quick injections of a decoy drug could save many lives.

Collier envisions a much more fearful and easier-to-pull-off-scenario wherein terrorists mail hundreds of anthrax-laced letters to many addresses. In such a case, spread of the disease would be much harder to contain. Post office workers infected with anthrax in 2001 were diagnosed as having “flulike illnesses.” If they had received injections of a decoy drug immediately, some of those who later died might have been saved.

Vaccine effects

Collier’s syringe strategy appears to have one advantage over decoy drugs. Besides disabling the syringe, it induces formation of antibodies, proteins that provide some immunity against future attacks by anthrax bacteria. In other words, it has a vaccine effect.

“We don’t know which technology (syringe smashing or decoys) will work better in the long run,” Collier admits. “Tests on rats show some promise, but we need to do tests on more humanlike animals.” Tests for safety can be done with humans by giving them the drugs, but it’s impossible to test for efficacy by purposely infecting people with anthrax bacteria.

There is an existing vaccine. However, it is more difficult to make than decoy and syringe drugs, and it is often not free of impurities, which raises the risk of unwanted side effects. Therefore, you might think that drug and biotechnology companies would be standing in line to try the new technologies. Not so. These companies see no clear road to a profit that would make their investment in testing and development worthwhile. The only customers would be governments, which would stockpile anthrax drugs against a bioterrorist attack. But an attack might never come.

To move things along, however, Collier, Young, and others have formed a new company called PharmAthene. The Department of Defense is funding its effort to build a superior anthrax drug or vaccine.

“We are preparing compounds now, and we expect to start testing them later this year,” Collier notes.

Meanwhile, the National Institutes of Health has put development of a new vaccine on a fast track. This vaccine, to be given before an attack, contains a nonlethal subunit of the poison that induces the body to produce a protective response. Collier’s mutated form of the same subunit offers an alternative vaccine, one that may be more appropriate to give to people after they have been exposed to anthrax.

If it works, that would be another “Eureka!” moment.