The findings were dramatic, but their relevance to people with Alzheimer’s disease is unknown. But because the drug is already approved for human use, finding out may be easier than if the drug were an entirely new chemical compound.
“It has to work in humans like it works in mice or we can pick up and go home,” said Gary E. Landreth, a neuroscientist at Case Western Reserve University School of Medicine, who headed the experiment.
A study of bexarotene’s effects in normal brains will start in a few months. Clinical trials in people with early Alzheimer’s — or at high risk for the disease for genetic reasons — will take years. If the drug’s effect in human brains turns out to be different, it may never move on to be tested in Alzheimer’s patients.
Nevertheless, the researchers think speed is important, as they fear that people might start using the drug before it is fully evaluated. A few days ago, Landreth got a call from a physician in another city. A person who had heard of the drug through the grapevine had asked for a prescription for bexarotene.
“We’ve got to work fast, and we have got to be right. We can’t screw this up,” Landreth said.
About 5.4 million Americans have Alzheimer’s disease, which is the leading cause of dementia. About 5 percent of people in their late 60s suffer from it, and possibly half of people in their late 80s. By 2050, 1 in 85 people worldwide will have the disease, according to one estimate.
Bexarotene is in the retinoid family of compounds, which are all chemically related to Vitamin A. Retinoids affect cell division and growth, immunity and other essential biological functions.
Sold under the trade name Targretin, bexarotene is approved by the Food and Drug Administration as a treatment for cutaneous T-cell lymphoma, a disease diagnosed in about 3,000 Americans a year. It is an “orphan drug,” a designation that gives drug companies an incentive to develop medicines for rare diseases. Orphan drugs stay under patent protection longer than regular drugs. It has been tried against other forms of cancer, without impressive results.
Numerous “candidate” Alzheimer’s drugs, which looked promising in lab studies, have washed out in recent years.
Last month, Pfizer and a smaller partner announced that they were abandoning a drug called Dimebon as a possible Alzheimer’s drug after it failed to show benefit in a clinical trial. In 2010, Lilly halted development of a different compound, semagacestat.
At the Alzheimer’s Association, an advocacy organization, the new study’s results were greeted with that history noted.