New technique speeds up search for Alzheimer's drug

By William J. Cromie

Gazette Staff

A novel technique that can enormously speed up the search for drugs to treat Alzheimer's disease has been developed by Medical School researchers. The technique is capable of screening hundreds of thousands of candidate compounds in a few days.

The disease now affects as many as 10 percent of those more than 65 years old and about 50 percent of all Americans older than 85 years, the fastest growing segment of the U.S. population. Only two drugs have been approved to treat Alzheimer's. Both ease symptoms of senility for some patients, but neither slows the inexorable progression of the disease and both can have serious side-effects.

"Time is a critical factor in fighting Alzheimer's," says John Maggio, associate professor of biological chemistry and molecular pharmacology and leader of a research collaboration that developed the test.

Autopsied brains from Alzheimer's sufferers are peppered with tiny, roughly spherical plaques, or globs of protein fiber. Made of a sticky, stringy type of protein known as beta-amyloid, the plaques are roughly five times bigger than a brain cell. Like sludge in the engine of your brain, plaques cause memory loss, aggressive behavior, and diminish people's ability to walk, talk, and take care of themselves.

Medical scientists take several different approaches to fighting Alzheimer's. Maggio and his team focus on directly combating the growth of plaques. At present, drugs for this purpose are tested one at a time on slices of brain taken from Alzheimer's victims at autopsy. "That's much too slow, and only limited amounts of real brain are available," Maggio notes. "We need to be able to test thousands -- or even a million -- compounds in a very short time and a very small space. We have found a way to do that."

What's more, with this system you don't need to know exactly what you're looking for. Large "libraries" of natural and human-made compounds, suspected of being able to slow or stop runaway growth of plaques, can be quickly checked without worrying about their specific chemical identity.

Maggio's team uses 3-by-5-inch plates riddled with tiny wells, each holding a dot of synthetic amyloid. As the amyloid grows, different test drugs are added to each well.

"Zillions of compounds can be quickly screened in this way to get a relatively small number of promising candidates that could be tested in mice or on human brain tissue," Maggio explains. "Admittedly, we have a long way to go before any such drugs will be tested on patients, but this could be the fastest way to find such drugs."

Cause or Effect

Autopsies show that those who die from Alzheimer's have as much as 20 percent of their brain clogged with plaques. However, it has not been conclusively proved whether the plaque causes the disease or results from it.

Maggio and his collaborators believe enough evidence exists to show that amyloid buildup is the immediate, if not the most basic, cause of Alzheimer's.

"Strong circumstantial evidence that beta-amyloid plays a causative rather than consequential role in Alzheimer's disease comes from several lines of research," says William Esler, a researcher in Maggio's lab. "There is a strong correlation between amyloid burden at death and the degree of dementia during life. Furthermore, several genetically heritable forms of Alzheimer's disease are tightly linked to mutations in genes that carry instructions for making amyloid proteins."

Esler is lead author of an article in a recent issue of Nature Biotechnology that reported development of the new screening system.

The method came from basic research efforts aimed at understanding how plaques grow inside a human brain. "Several years ago, we learned how to make plaques from pieces of autopsied brain grown in test tubes, so we could better study the process," Maggio relates. "That eventually opened the way to making and growing synthetic plaques."

Maggio's group, quite naturally, calls their product "synthaloid" for synthetic amyloid. This material is fixed at the bottom of either 96 or 384 wells in plastic plates the size of index cards. Screeners add a drop of amyloid, tagged with a radioactive label, to each well. Each site then simulates a plaque growing in a live brain.

A different drug with the potential to stop such growth can be put in each well. Using the radioactive tag, testers determine how each compound affects growth of the synthetic plaques. Laboratory experiments prove that inhibition of synthaloid growth by various compounds closely matches the effects of the same chemicals in slices of an Alzheimer's brain.

Even with such a set-up, lab technicians could not screen a million compounds in a few weeks. Maggio sees that being done with the help of robots to put the compounds in the wells and automatic sensors to detect changes in plaque growth.

"We wouldn't do such screening in a research lab at Harvard," he admits. "It would take the resources of a pharmaceutical or biotechnology company. We've applied for a patent and are talking with several interested organizations."

It will, of course, take years of testing in plastic and glass, in animals and in humans, to bring any drug into day-to-day use. But the expectation is that synthaloid will dramatically reduce the time and cost of doing that.

"We don't need to cure the disease to have a substantial beneficial impact," Maggio points out. "By the time plaques begin to cause trouble in most patients, they have frequently been growing in the brain for as long as 20 to 30 years. People don't get into real trouble until plaques takes up a large fraction of certain parts of their brains. If we can delay this stage for 20 years, that could be a cure for someone who is 70 years old. Even a five-year delay would have a tremendous impact."

Maggio and Esler worked with Evelyn Stimson, a research associate at the Medical School, and with collaborators from the University of Minnesota, Minneapolis; Vanderbilt University in Nashville; William Paterson College in Wayne, N.J.; and the University of California, Los Angeles. Their research was supported by the National Institutes of Health, the American Health Assistance Foundation, and the Veterans' Administration.