Novel Antibody May Reduce Amyloid, Cut AD Symptoms

SEATTLE – An update from a phase 2 study – core and open-label extension – of lecanemab in Alzheimer's disease showed that the antibody reduced amyloid plaques within the first months after treatment initiation, and this effect was associated with improved clinical signs in as early as 6 months. The researchers identified two plasma biomarkers that correlate well with established amyloid PET standard uptake value ratio (SUVr) changes, potentially paving the way for monitoring lecanemab treatment effects. The researchers also found evidence that the plasma biomarker could be used to allow dose frequency reduction after initial reduction in amyloid plaques.

Lecanemab preferably targets aggregated species of amyloid called protofibrils, which is unique among anti-amyloid antibodies, and these are also among the most toxic manifestations of amyloid, according to Chad Swanson, PhD, who presented the study at the 2022 annual meeting of the American Academy of Neurology.

Are Amyloid Plaques a Key Driver of Alzheimer’s Disease?

The study could help answer the question of whether amyloid plaques drive the cognitive decline seen in Alzheimer's disease, in part because the antibody is so effective at what it was designed to do, according to Fernando Testai, MD, PhD, who comoderated the session where the study was presented. "The effect on amyloid content that they measured was persistent over a number of months. Cognition may follow along, so more studies have to be done, but the medication seems to be quite effective doing what it's supposed to do. If it has something to do with disease, these treatments actually should give us the answer, because the effect on amyloid is pretty significant. After so many years of thinking amyloid probably has nothing to do (with Alzheimer's symptoms, these results suggest) it may have something to do with the disease," Testai said in an interview. He is a professor of neurology at the University of Illinois at Chicago.

Swanson is confident that amyloid plaques are a key driver of disease. "I'd say a number of companies now with anti-amyloid agents have shown that targeting amyloid can produce some slowing of clinical decline, as well as a robust reduction in amyloid, supporting this idea that that amyloid is meaningful. And it's very clear that amyloid [deposition] tends to trigger tau pathology," said Swanson in an interview. He is executive director of the neurology business group at Eisai Pharmaceuticals, which is developing the anti-amyloid antibody, called lecanemab.

Searching for the Best Dose and Dose Frequency

Swanson noted that Eisai has already conducted a large phase 2b study which informed the current phase 3 ClarityAD study design. The phase 2b study utilized a Bayesian adaptive design, which allocated more patients in a fully blinded way to doses that had the most potential for slowing clinical decline. "The intent was to maximize the efficiency of the design so that more subjects would go to a dose that looks like it could be the best dose according to the Bayesian algorithm," said Swanson.

The study also included a gap period that followed the randomized phase of the trial, where subjects were not being dosed with the antibody from 9 to 59 months (mean, 2 years), before reinitiation at the start of the open-label extension phase. "[That] allowed us to answer some really important questions about what happens when you remove lecanemab after reducing amyloid, and then what happens when you reintroduce lecanemab in the open-label extension," said Swanson.

The researchers found that amyloid reaccumulated during the treatment gap, and soluble biomarkers were potentially the most sensitive to the change. "Taking all of this information together with clinical data that suggest potential disease-modifying effects, it suggests that we need to continue to treat these individuals, but we may be able to treat with a less-frequent dosing interval once amyloid is removed from the brain. It's a biweekly infusion. Following 18 months of treatment, we may be able to go in once every month or once every 3 months to maintain low levels of amyloid. We're going to be testing that soon in the current phase 2 open-label extension," said Swanson.

The study included 856 patients who were randomized to biweekly placebo or lecanemab 2.5 mg/kg biweekly, 5 mg/kg monthly, 5 mg/kg biweekly, 10 mg/kg monthly, or 10 mg/kg biweekly. The primary endpoint was the Alzheimer's disease composite score at 12 months; secondary endpoints included ADCOMS and various biomarker levels at 18 months.

At 18 months, the 10-mg/kg biweekly group had an adjusted mean change from placebo in brain amyloid of –0.31 SUVr units, with more than 80% of the subjects converting from amyloid positive to amyloid negative by visual read. Most subjects remained amyloid negative at open-label extension baseline following the gap period despite a slow reaccumulation of amyloid plaque in the treated group. Out to 18 months in the core study, the same group had a 30% reduction in cognitive decline, compared with placebo, as measured by ADCOMS (P < .05).

There was a correlation between PET SUVr, clinical outcomes, and the Abeta42/40 ratio and plasma p-tau181. During the gap period, treatment discontinuation was associated with changes in the plasma biomarkers that echoed amyloid re-accumulation and clinical decline. Change from baseline in both plasma biomarkers were associated with a change from baseline in PET SUVr at 18 months.

Amyloid-related imaging abnormalities related to brain edema or sulcal effusion (ARIA-E) occurred in 9.9% of patients during the randomized phase of the trial, and 7.8% during the open-label extension phase. About 2% were symptomatic in both the randomization and open-label extension phases. The majority of ARIA-E cases appeared within 3 months of treatment initiation, and generally resolved in 4-16 weeks. 80% were mild to moderate by radiography.

Swanson is an employee of Eisai Pharmaceuticals, which sponsored the study. Testai has no relevant financial disclosures.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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Cite this: Novel Antibody May Reduce Amyloid, Cut AD Symptoms - Medscape - Apr 12, 2022.