However, solanezumab showed signs that attacking beta amyloid beta was effective. While it didn't help most patients in the study, it slowed mental decline by about a third in patients with mild forms of the disease — a first for that approach.
That's added to researchers' growing belief that patients must be treated early on, before Alzheimer's has destroyed much of their brains.
The big prevention study to start early next year, called DIAN TU, is meant to help find a way to do that, by testing drugs on people with a family history and genes that make them likely to develop Alzheimer's in their 50s, rather than after 65.
—One part will test the Roche Group's biologic antibody drug gantenerumab, which removes amyloid beta plaques from the brain. It's already in late-stage testing in patients who don't have symptoms but have abnormally high levels of amyloid beta in spinal fluid.
—Another part will test Lilly's solanezumab, which binds to smaller bits of amyloid beta and clears them from the brain before they clump into plaques.
—The third study drug could be Lilly's BACE inhibitor, now in midstage testing in Alzheimer's patients. The company expects by mid-2013 to complete work needed to determine whether the drug is right for the prevention study.
Meanwhile, two late-stage patient studies started this fall with a drug called LMTX developed by TauRx Pharmaceuticals Ltd. It targets tangles in the brain with an abnormal version of a protein called tau.
Thies, of the Alzheimer's Association, thinks the disease likely is caused by a combination of those tau tangles and amyloid beta plaques.
The key issue for all these drugs will be what side effects they cause, because patients would take them for many years.
Patients and families are anxious for a drug that slows or stops Alzheimer's.
"When you're faced with a diagnosis that tells you your brain is being eaten up," said patient Ron Grant, "and you start seeing who you were no longer being who you are, and the only thing you can expect is being worse, in this day that's totally unacceptable."
The Oklahoma City prison chaplain was diagnosed with Alzheimer's in 2007 at age 55 and had to stop work barely a year later. He's helped found a support group for early onset Alzheimer's patients, participated in a clinical trial and takes the drugs Namenda and Razadyne, which he thinks have limited his symptoms.
But PET scans of his brain show the disease is progressing. The former avid reader can no longer follow a book's plot or remember where he left off.
The federal government doesn't spend enough on Alzheimer's, said Grant, who helps lobby Congress for more funding.
"The biggest thing standing between us and a treatment for this disease is money," he said.
Online: Alzheimer's Association program to manage patients with clinical trials: www.alz.org .
Info on Merck's study: www.ADstudyinfo.com