A small clinical trial of a once-failed Alzheimer's drug offered tantalizing but inconclusive hints of benefit, propelling shares in its biotech maker higher by more than 50% Tuesday.
Treatment with the drug, called semorinemab and discovered by Switzerland's AC Immune, lessened cognitive decline versus placebo among people with mild or moderate Alzheimer's disease, according to a brief statement on the trial's results released by the company.
But those seemingly positive results, measured on one of several widely used assessments of Alzheimer's symptoms, were counterbalanced by the drug's failure to meet three other study goals. The mixed findings raise significant, and for Alzheimer's researchers, familiar questions about whether the experimental treatment actually helped slow disease progression.
The announcement is the latest development in a field that's been upended by the Food and Drug Administration's controversial approval of Biogen's Alzheimer's drug Aduhelm, a decision that effectively endorsed a much-debated hypothesis about the memory-robbing condition's cause.
Aduhelm's approval has also opened the door for other developers, among them Eli Lilly and Roche, to bring forward their own therapies with less supportive evidence than the companies previously expected. Lilly intends to submit its drug donanemab, which works in a similar fashion as Aduhelm, to the FDA later this year.
Against this backdrop, AC Immune's announcement may gin up more enthusiasm among investors, who've grown accustomed to one setback after another for experimental Alzheimer's medicines, including a failed trial for semorinemab just last year.
In the latest study, run by AC Immune's development partner and Roche subsidiary Genentech, 272 people with mild or moderate Alzheimer's disease were randomized to receive either semorinemab or placebo. After nearly a year, the two groups were compared using four common Alzheimer's disease rating scales.
On one, a cognitive assessment called ADAS-Cog11, study participants treated with AC Immune's drug declined by 44% less than those given placebo, a statistically significant difference. The magnitude of that apparent benefit is larger than what Biogen found on a slightly broader, but similar scale in the one positive Phase 3 study of Aduhelm. But AC Immune's trial is much smaller and shorter than Biogen's.
And on three other measures, including one most favored by researchers and drugmakers, AC Immune's drug did not outperform placebo.
There were no unexpected safety signals, AC Immune said, without sharing any details.
Semorinemab targets a toxic protein in the brain called tau rather than the amyloid plaques Aduhelm and Lilly's donanemab are aimed at. Interest in tau-targeting therapies has steadily grown as anti-amyloid drugs continued fail in clinical testing over the past decade.
In a statement, AC Immune CEO Andrea Pfeifer said the new findings are the first evidence of therapeutic effect for an anti-tau antibody drug.
"Nevertheless, despite these interesting results, we are still cautious about what this may mean for patients as there was not an impact on the rate of functional decline or other efficacy endpoints," she added, speculating a longer study could yield more meaningful data.
The trial's readout comes two months after an anti-tau drug from Biogen failed to slow Alzheimer's patients' decline in a Phase 2 study.
Last year, another, slightly larger trial of semorinemab showed the drug had no effect, although that study was conducted earlier in the course of patients' disease.
Shares in AC Immune rose by as much as 80% Tuesday, before falling back to trade up 34% by late morning. Roche stock rose by 1% on American over-the-counter markets.