A closely watched treatment for Alzheimer’s disease came up short in a late-stage trial, marking the latest setback in a field wracked by years of failure.

The drug, from biotech company TauRx, did no better than a sugar pill at improving patients’ scores on tests of cognitive and physical function, according to data presented early Wednesday at the Alzheimer’s Association International Conference in Toronto. The study looked at roughly 900 patients with mild to moderate forms of Alzheimer’s.

“I must say I’m disappointed by the results,” said Dr. David Knopman, a Mayo Clinic neurologist not involved with the study.

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TauRx’s drug, LMTX, is meant to block the activity of a bodily protein that many neuroscientists believe contributes to the brain-destroying effects of Alzheimer’s. The treatment is still being tested in a second study, involving about 700 people, with final data expected later this year.

The results are yet another blow to Alzheimer’s research. Academics, startups, and pharmaceutical giants have poured decades of work, and billions of dollars, into finding treatments. One therapy after another has looked promising in the lab — only to crumble when tested in large patient populations.

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Indeed, 99.6 percent of Alzheimer’s treatments tested in the decade between 2002 and 2012 failed in clinical trials, according to an analysis by the Cleveland Clinic.

The disease, irreversibly fatal, affects about 5 million Americans, and that number that will more than triple by 2050, according to AAIC. Analysts peg the market for an effective treatment at more than $10 billion a year.

The Alzheimer’s conference in Toronto did showcase one promising result: Researchers showed that when healthy older adults played a specific computer brain-training game, they cut their risk for dementia.

But treatments that arrest the disease’s progression have been elusive. One issue: Scientists can’t even settle how the disease works.

Here’s what everyone agrees on: The brains of Alzheimer’s patients are ridden with tangles and plaques. The tangles are made up of a protein called tau, and the plaques are made up of another called amyloid beta.

But just which is most to blame for the memory-robbing progression of Alzheimer’s has been the subject of academic debate for decades.

TauRx, as its name suggests, has a partisan bent. And Dr. Claude Wischik, its founder and CEO, is a frequent evangelist for the importance of tau. But the amyloid contingent has for years held sway in academia and industry.

Wischik and others have said they’ve had trouble finding funding for tau research. Indeed, TauRx, which is based in Scotland, has never done business with traditional biotech venture capitalists, instead turning to investors in Malaysia and Singapore to raise the roughly $500 million it needed to get to this point.

Meanwhile, the biggest wheels of industry have largely placed their bets on amyloid. Pharma giant Eli Lilly is in the midst of a final-stage study on an amyloid antibody. It’s failed in two prior trials, but the company is trying once more in patients with milder forms of Alzheimer’s. Data from that study are expected next year.

Biogen is pursuing the same path, staking more than $1 billion on a huge amyloid trial that Wall Street analysts say could make or break the company’s future.

But squabbles over amyloid and tau are quite literally academic to doctors who treat Alzheimer’s patients. They say they simply need good treatments, no matter how they might work.

“I don’t have a dog in that race,” said James Hendrix, director of global science initiatives at the Alzheimer’s Association. “I root for everybody.”

As for TauRx, despite the overall failure of its drug, the company highlighted some results that appeared promising for a small group of patients in the trial.

LMTX, which is also sometimes known as LMTM, had a positive effect on the roughly 15 percent of participants who weren’t taking standard Alzheimer’s drugs during the trial, the company said. But such secondary analyses are hard to interpret, scientists say, and TauRx would need to replicate those results in a much larger group of people before declaring anything resembling a victory.

Correction: An earlier version of this story misstated James Hendrix’s title.