Dick Purdy was in his mid-70s when he was diagnosed with Alzheimer's disease. Now 82, the former surgeon has steadily declined, but at times he still seems sharp.
"It just never occurred to me someday I would be a patient," Purdy said, sitting in his living room in Connecticut.
For Purdy's wife, Gloria, the goal now is to keep him living at home as normally as possible and to get him enrolled in a clinical drug trial. Even if the treatment doesn't help his memory, she says, taking part in a study gives them both a sense of purpose.
"We've been part of the medical community all our adult lives," the 74-year-old retired nurse said. "We are not going to be part of the cure, clearly—at least we can participate in the work that's being done."
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After more than two decades of research, a treatment that slows or actually reverses the progression of Alzheimer's has proved elusive, in part because researchers still have not pinpointed its cause.
"The scientific community really doesn't understand the disease completely," said Morningstar pharmaceutical analyst Damien Conover. "It's an area where the science still needs to evolve."
Big need, big opportunity, big risk
The need for an effective treatment is massive and growing. Dementia affects more than 5 million people in the U.S. and more than 35 million worldwide, according to Alzheimer's Disease International. With the global population aging, those numbers are expected to triple by 2050.
The handful of Alzheimer's drugs on the market, approved more than a decade ago, treat the symptoms of cognitive decline. They include Aricept from Pfizer, Namenda from Forest Laboratories and Exelon from Novartis. Their combined sales last year just topped $6 billion, according to BCC Research.
Analysts estimate that a treatment for the disease itself could generate sales of $20 billion or more. And getting there is a risky and costly venture.
The Alzheimer's contenders
Many of the next-generation drugs aim to block the production of amyloid deposits, which are present in plaque buildup in the brain of someone diagnosed with Alzheimer's. It's still unclear whether the deposits are a cause or by-product of dementia. What is increasingly clear is that success with these new drugs is hard to come by.
In late-stage trials last year, a highly anticipated drug that was a joint effort of Pfizer, Johnson & Johnson and Elan did not stop development of amyloid deposits. J&J took a $700 million charge for the failure, while Elan wrote off more than $100 million for the value of its stake in the drug, called bapineuzumab.
The failure also caused the three drugmakers to walk away from attempts to find an Alzheimer's treatment. But others remain in hot pursuit.
More than 80 treatments are in development—most of them early to mid-stage, according to the Pharmaceutical Research and Manufacturers of America.
Analysts say Eli Lilly and Merck are the biggest contenders working on next-stage drugs that could make it to market by the end of the decade.
Eli Lilly reported this summer that its stage-three trial of solanezumab, an anti-amyloid, did not slow dementia in Alzheimer's patients with significant memory loss. But the company is continuing to pursue the drug because the data indicate that it slowed cognitive decline in early-stage patients by as much as 34 percent.
(Read more: Lilly plans Alzheimer's disease study after prior failures)
"We have new data that suggests that some of these proteins that are changing the brain may start anywhere between 15 and 20 years before the clinical onset," said Dean Hartley, the director of Science Initiatives at the Alzheimer's Association.
"We've started to realize that some of these treatments that have been used in clinical trials may actually be more effective if we use them earlier in the disease," he said.
Analysts are also watching an experimental drug from Merck, known as a BACE-inhibitor, that targets an enzyme leading to amyloid buildup. The question is whether Merck can build on research where others have failed.
"BACE inhibitor theory has a history of some setbacks, because Bristol-Myers [Squibb] and Eli Lilly also had BACE inhibitors, and they have discontinued development," said Conover at Morningstar.
The fear is that if the next round of late-stage trials doesn't go well, companies may scale back their investments in Alzheimer's until signs point to another breakthrough.
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The government has also committed to expanding research. In 2012, the Obama administration pledged $100 million in additional funding. But with costs for a single drug running in the hundreds of millions, the private sector must drive discovery, said Hartley at the Alzheimer's Association.
"Companies are an important aspect of us finding the solution to this disease," Hartley said.
The new drugs may be too far in the future to make a difference to Dick Purdy's memory. His wife Gloria, sitting by his side on their couch, says that for now, she tries to enjoy the good days they have together.
"It simply is a day at a time, but it's not an unpleasant day at a time," she said. At which point Dick leaned in and whispered in her ear.
"Dick says it's because he's charming," she relayed with a smile.
—By Bertha Coombs. Follow her on Twitter: @berthacoombs.