By Julie Steenhuysen

CHICAGO An experimental Alzheimer's disease drug developed by Acumen Pharmaceuticals targeting a novel form of the toxic protein beta amyloid in the brain passed an early safety test and will advance to a larger trial, the company said on Sunday.

The drug, ACI193, was well tolerated in the first trial testing it in people, the company said. Results of the randomized, placebo-controlled study of 62 patients with early Alzheimer's disease were presented at the Alzheimer's Association's International Conference in Amsterdam.

Acumen's drug targets and binds to amyloid beta oligimers, a toxic, soluble version of the amyloid protein that forms brain plaques associated with the memory-robbing disease, Dr. Eric Siemers, chief medical officer of Acumen, said in an interview.

The target is similar to that of Biogen and Eisai's recently-approved Leqembi, which hits another soluble, toxic form of the protein in the brain. Leqembi won standard U.S. approval earlier this month after showing it could remove amyloid plaques and slow the advance of Alzheimer's in early-stage patients.

In the Acumen trial, 10.4% of treated participants (5 people) developed a brain swelling condition known as ARIA-E associated with amyloid-targeting treatments. Of these, only one had symptoms, which resolved after the drug was stopped.

Another 8.3% developed bleeding in the brain associated with treatment, known as ARIA-H.

"Because this antibody targets oligimers but is not intended to target plaque, we didn't know if we would get any ARIA or not," said Siemers, adding that the ARIA cases may suggest the drug is having an effect.

People who got higher doses of the drug also showed a reduction in amyloid plaque after 6 to 12 weeks, the company said. Acumen said the study suggests the drug can be given as a monthly intravenous infusion.

(Reporting by Julie Steenhuysen; Editing by Bill Berkrot)