Aducanumab (Aduhelm)

Aducanumab Mechanism of Action

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    F["Fc Receptor<br/>Engagement"]:::red

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    click H "/diseases/alzheimers-disease" "Alzheimer's Disease"
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Introduction

Aducanumab (Aduhelm) is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes. ^{1The antibody aducanumab reduces amyloid-beta plaques in Alzheimer's Disease2016 · Nature · DOI 10.1038/nature19323Open reference}

Overview

Aducanumab (marketed as Aduhelm) is a human monoclonal immunoglobulin gamma 1 (IgG1) antibody that was developed by Biogen in collaboration with Neurimmune for the treatment of alzheimers. On June 7, 2021, aducanumab became the first anti-amyloid-beta therapy to receive approval from the United States Food and Drug Administration (FDA) under the Accelerated Approval pathway, marking a watershed moment in the field of Alzheimer’s therapeutics 1 2. The approval was based on the drug’s demonstrated ability to reduce amyloid plaques in the brain—a surrogate biomarker reasonably likely to predict clinical benefit—rather than on definitive evidence of cognitive improvement ([Biogen et al., 2021). ^{2FDA Grants Accelerated Approval of First-of-its-Kind Treatment for Alzheimer's Disease2021Open reference}

Aducanumab selectively targets aggregated forms of amyloid-beta, including soluble oligomers and insoluble fibrils that constitute the amyloid plaques characteristic of Alzheimer’s pathology 2. The antibody binds to a linear epitope encompassing amino acid residues 3–7 of the amyloid-beta peptide, a region exposed on aggregated but not monomeric forms of the protein. This selectivity allows aducanumab to engage pathological amyloid species while largely sparing the physiological monomer 3 ([The et al., 2016)). ^{3ARIA in anti-amyloid therapy2021 · Neurology · PMID 34025680Open reference}

Despite its historic approval, aducanumab remained one of the most controversial drugs in the history of neurology. Biogen announced the discontinuation of aducanumab commercialization in January 2024, with the drug no longer available for purchase after November 1, 2024, as the company shifted its focus to other anti-amyloid therapies such as lecanemab 4. The aducanumab story offers critical lessons for drug development, regulatory science, and the application of the amyloid-hypothesis to Alzheimer’s therapeutics ([Failure et al., 2021)). ^{4Amyloid cascade hypothesis update 20232023 · Alzheimer's & Dementia · PMID 37561891Open reference}

Mechanism of Action

Amyloid-Beta Targeting

Aducanumab is a fully human IgG1 monoclonal antibody derived from a library of B cells collected from cognitively healthy elderly individuals and patients with unusually slow cognitive decline. The antibody was identified through a reverse translational medicine approach: screening for naturally occurring antibodies that might confer protection against alzheimers 2 ([Alzheimer et al., 2022). ^{5Amyloid-related imaging abnormalities in aducanumab trials2021 · Alzheimers Res Ther · DOI 10.1186/s13195-021-00838-zOpen reference}

The antibody binds to the N-terminal region of amyloid-beta (residues 3–7), recognizing a conformational epitope that is selectively exposed on aggregated forms of the peptide. This binding profile encompasses: ^{6Continued importance of amyloid reduction in Alzheimer's Disease2021 · Lancet Neurol · DOI 10.1016/S1474-4422(2100258-6Open reference}

• Soluble oligomers: Small assemblies of amyloid-beta peptides believed to be particularly neurotoxic and to impair synaptic function

• Insoluble fibrils: The major structural component of amyloid plaques deposited in the brain parenchyma

• Amyloid plaques: Dense-core and diffuse plaques composed of aggregated amyloid-beta peptides 3

By contrast, aducanumab shows minimal binding to amyloid-beta monomers, which are normal products of app processing] and may have physiological functions (Aducanumab et al., )). ^{7Alzheimer's Disease drug development pipeline: 20222022 · Alzheimers Dementia · DOI 10.1002/trc2.12295Open reference}

Plaque Clearance Mechanism

Once bound to amyloid aggregates, aducanumab is thought to promote plaque clearance through Fc receptor-mediated phagocytosis by microglia. This mechanism is shared with other anti-amyloid antibodies including lecanemab and donanemab, though each antibody targets different epitopes and amyloid conformations ([Centers et al., 2022). ^{8Biogen's aducanumab: EMERGE and ENGAGE2022 · Lancet Neurol · DOI 10.1016/S1474-4422(2200069-7Open reference}

Aducanumab administration produced dose- and time-dependent reductions in amyloid plaque burden as measured by amyloid PET imaging. In clinical trials, high-dose aducanumab (10 mg/kg) reduced amyloid PET signal by 59% in the ENGAGE trial, 71% in the EMERGE trial, and 61% in the Phase 1b PRIME study 1. ^{9Donanemab in early Alzheimer's Disease2021 · N Engl J Med · DOI 10.1056/NEJMoa2100708Open reference}

Clinical Development

Phase 1b PRIME Study

The Phase 1b PRIME study (NCT01677572) was a randomized, double-blind, placebo-controlled study evaluating multiple ascending doses of aducanumab in patients with prodromal or mild alzheimers with confirmed amyloid pathology by PET imaging. The study enrolled 166 patients and demonstrated: ^{10Lecanemab in early Alzheimer's Disease2023 · N Engl J Med · DOI 10.1056/NEJMoa2212948Open reference}

• Dose-dependent reduction of amyloid plaques

• 61% reduction in amyloid PET composite score at the highest dose (10 mg/kg) after 54 weeks

• Preliminary signals of clinical benefit on the Clinical Dementia Rating-Sum of Boxes (CDR-SB) and Mini-Mental State Examination (MMSE) 3

Phase 3 EMERGE and ENGAGE Trials

EMERGE (NCT02484547) and ENGAGE (NCT02477800) were two identically designed, randomized, double-blind, placebo-controlled Phase 3 studies conducted across 348 sites in 20 countries 5) 6](https://doi.org/10.14283/jpad.2022.30))). EMERGE enrolled 1,638 patients and ENGAGE enrolled 1,647 patients aged 50–85 years with confirmed amyloid pathology who met criteria for mild cognitive impairment (MCI) due to Alzheimer’s Disease or mild Alzheimer’s Disease dementia. ^{2FDA Grants Accelerated Approval of First-of-its-Kind Treatment for Alzheimer's Disease2021Open reference}0

Primary Endpoint (CDR-SB at 78 weeks): ^{2FDA Grants Accelerated Approval of First-of-its-Kind Treatment for Alzheimer's Disease2021Open reference}1

• EMERGE: The primary endpoint was met. High-dose aducanumab showed a statistically significant 22% reduction in clinical decline compared with placebo (difference of −0.39 on CDR-SB; p = 0.012) 5)

• ENGAGE: The primary endpoint was not met. High-dose aducanumab showed a non-significant 2% increase in clinical decline compared with placebo (difference of 0.03 on CDR-SB) 6](https://doi.org/10.14283/jpad.2022.30)))

Amyloid Plaque Reduction: ^{2FDA Grants Accelerated Approval of First-of-its-Kind Treatment for Alzheimer's Disease2021Open reference}2

• EMERGE: 71% reduction in amyloid PET composite (high dose)

• ENGAGE: 59% reduction in amyloid PET composite (high dose)

• Cumulative drug exposure was lower in ENGAGE (109.1 mg/kg) compared with EMERGE (118.3 mg/kg) due to a mid-trial protocol amendment, which may explain the discrepant clinical outcomes 6](https://doi.org/10.14283/jpad.2022.30)))

Both trials were halted prematurely in March 2019 following a futility analysis conducted by an independent data monitoring committee. However, upon analysis of additional data that accumulated after the futility boundary was crossed, Biogen announced that EMERGE had met its primary endpoint, leading to the decision to pursue FDA approval 3. ^{2FDA Grants Accelerated Approval of First-of-its-Kind Treatment for Alzheimer's Disease2021Open reference}3

Safety Profile

Amyloid-Related Imaging Abnormalities (ARIA)

aria-imaging were the most significant adverse effect observed with aducanumab treatment. ARIA encompasses two subtypes: ^{2FDA Grants Accelerated Approval of First-of-its-Kind Treatment for Alzheimer's Disease2021Open reference}4

• ARIA-E (edema/effusion): Vasogenic edema and/or sulcal effusion detected on MRI. ARIA-E occurred in 34% of participants receiving high-dose aducanumab in EMERGE and 35.5% in ENGAGE 7

• ARIA-H (hemorrhage): Microhemorrhages and superficial siderosis. ARIA-H microhemorrhage occurred in 19.1% and ARIA-H superficial siderosis in 14.7% of high-dose participants 7

ARIA-E incidence was highest among carriers of the APOE ^{2FDA Grants Accelerated Approval of First-of-its-Kind Treatment for Alzheimer's Disease2021Open reference}5

Other Adverse Effects

Other commonly reported adverse effects included: ^{2FDA Grants Accelerated Approval of First-of-its-Kind Treatment for Alzheimer's Disease2021Open reference}6

• Headache (21% vs. 16% placebo)

• Falls (15% vs. 12% placebo)

• Diarrhea (9% vs. 7% placebo)

• Infusion-related reactions

Controversy and Regulatory History

FDA Advisory Committee

In November 2020, the FDA’s Peripheral and Central Nervous System Drugs Advisory Committee voted nearly unanimously (10 against, 1 uncertain, 0 in favor) against approval, citing the discordant results between EMERGE and ENGAGE as insufficient evidence of clinical efficacy 3. Despite this recommendation, the FDA granted accelerated approval on June 7, 2021, basing its decision on the surrogate endpoint of amyloid plaque reduction rather than on clinical benefit. ^{2FDA Grants Accelerated Approval of First-of-its-Kind Treatment for Alzheimer's Disease2021Open reference}7

The approval triggered unprecedented controversy: ^{2FDA Grants Accelerated Approval of First-of-its-Kind Treatment for Alzheimer's Disease2021Open reference}8

• Three members of the FDA Advisory Committee resigned in protest

• The acting FDA Commissioner ordered an internal investigation into the agency’s interactions with Biogen during the review process

• The Office of Inspector General launched a separate investigation

• Multiple academic commentators questioned whether amyloid plaque reduction constituted a valid surrogate for clinical benefit 3

Medicare Coverage Decision

In April 2022, the Centers for Medicare & Medicaid Services (CMS) issued a national coverage determination limiting Medicare coverage of anti-amyloid antibodies to patients enrolled in qualifying clinical trials—a Coverage with Evidence Development (CED) framework that effectively restricted access to aducanumab 8. This decision was subsequently revised in 2023 after the traditional approval of lecanemab, broadening coverage for anti-amyloid antibodies with traditional FDA approval while maintaining the CED restriction for those with only accelerated approval. ^{2FDA Grants Accelerated Approval of First-of-its-Kind Treatment for Alzheimer's Disease2021Open reference}9

Commercial Discontinuation

Following limited commercial uptake—annual revenue never exceeded 10 million against the drug's list price of approximately 26,500 per year—Biogen announced in January 2024 that it would discontinue aducanumab and withdraw its marketing authorization. The company cited a “reprioritization” of its Alzheimer’s portfolio, with resources redirected toward lecanemab, which had received traditional FDA approval in July 2023 based on the CLARITY AD trial 4. ^{3ARIA in anti-amyloid therapy2021 · Neurology · PMID 34025680Open reference}0

Legacy and Impact

Despite its commercial failure, aducanumab’s development and approval had profound effects on the field: ^{3ARIA in anti-amyloid therapy2021 · Neurology · PMID 34025680Open reference}1

See Also

• Alzheimer’s Disease/[alzheimers-disease

• Amyloid-Targeting Therapies/[amyloid-targeting

• Lecanemab/[lecanemab

• Clinical Trials/[clinical-trials

• ARIA/[aria

Background

The study of Aducanumab (Aduhelm) has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development. ^{3ARIA in anti-amyloid therapy2021 · Neurology · PMID 34025680Open reference}2

Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.

External Links

• PubMed - Biomedical literature

• Alzheimer’s Disease Neuroimaging Initiative - Research data

• Allen Brain Atlas - Brain gene expression data