By Bill Berkrot

(Reuters) - An experimental drug from Biogen Idec became the first Alzheimer's treatment to significantly slow cognitive decline and reduce brain amyloid plaque in patients with early and mild forms of the disease, according to a small study likely to reignite hopes of a treatment.

Alzheimer's is expected to strike as many as 75 million people worldwide by 2030 without effective treatments, likely costing billions of dollars year in care. A successful treatment would pay some of the richest rewards in medicine.

Biogen is entering a field littered with expensive failures from such players as Pfizer Inc and Eli Lilly and Co.

The 166-patient trial of the Biogen drug, aducanumab, tested four groups who each received a different dose against a fifth group who received a placebo.

The treatment led to reductions in brain amyloid believed to play a key role in the development of Alzheimer's symptoms, according to interim data presented at the 12th International Conference on Alzheimer's and Parkinson's Diseases and Related Neurological Disorders in Nice, France, on Friday.

The plaque reduction was more pronounced as the dose of the drug increased and over time.

It marks the first time an experimental drug demonstrated both a statistically significant reduction in amyloid plaque and a slowing of clinical impairment in patients with mild disease, said Alfred Sandrock, Biogen's chief medical officer.

"It's a bigger treatment effect than we had hoped for," Sandrock said.

Biogen will begin enrolling patients later this year for a large Phase III trial that could be used to seek approval of its drug.

Biogen said it increased its chances of success by carefully screening patients to exclude those with other forms of dementia misdiagnosed as Alzheimer's, and by testing only those early in the disease.

"We imaged every patient coming into study, so we knew that every patient had Alzheimer's disease and plaque," Biogen Chief Executive George Scangos said in an interview. "It's hard to think of a reason why these data are not representative of the actual activity of the drug."


Safety and tolerability was considered acceptable, the company said. There was a big jump in the incidence of amyloid-related imaging abnormalities-edema (ARIA-E) at the two higher doses among patients with a gene associated with the highest risk for developing Alzheimer's. These highest-risk patients also dropped out of the trial at a higher rate. Most of the ARIA-E was asymptomatic or mild and resolved over time, Sandrock said.

Using imaging to measure amyloid in six regions of the brain, researchers found plaque levels were virtually unchanged at 26 and 54 weeks into the study for the placebo group.

Patients who received either 3 milligrams per kilogram of weight, 6 mg/kg or 10 mg/kg of aducanumab showed a significant and dose-dependent increase in plaque reduction at 26 weeks. There was an even greater reduction in plaque for patients at the 3 mg and 10 mg doses when they were tested at 54 weeks.

Data for those in the 6 mg arm was not available at 54 weeks because that group started later. A fourth group of patients who received a 1 mg dose were not helped by the drug.

The trial also used two measures to test cognition: a questionnaire with a 30-point scale to test mental acuity and an 18-point Clinical Dementia Rating scale that also tests for loss of ability to function.

On the first test, placebo patients worsened by 3.14 points after one year versus significantly smaller declines for patients receiving aducanumab 3 mg and 10 mg, of 0.75 and 0.58 points, respectively.

On the second scale, the placebo group worsened by 2.04 points at one year. While the scores were better for all the drug groups, only the 10 mg dose reached statistical significance, with a decline of 0.59 points. The 6 mg dose could still show a significant slowing on both scales when more data becomes available.