ac-193

AC-193

AC-193 is an experimental monoclonal antibody developed by [Acumen Pharmaceuticals](https://acumenpharma.com) that represents a next-generation approach to anti-amyloid therapy for [Alzheimer's disease](/diseases/alzheimers-disease)[@potter2024]. Unlike previous antibodies that target either amyloid-beta monomers or plaques, AC-193 is specifically designed to bind to and neutralize soluble toxic amyloid-beta oligomers (AβOs), which are widely considered to be the primary neurotoxic species responsible for synaptic dysfunction and memory impairment in Alzheimer's disease[@demattos2024][@selkoe2011].

This selective targeting approach is based on the oligomer hypothesis of Alzheimer's disease, which posits that soluble, diffusible Aβ oligomers are the key pathogenic agents, rather than the insoluble amyloid plaques that have historically been the focus of therapeutic development[@lambert1998][@walsh2002].

The Oligomer Hypothesis

Historical Context

The oligomer hypothesis emerged from observations that amyloid plaques alone do not correlate well with cognitive impairment[@krafft1989]. Key discoveries that shaped this hypothesis include:

Toxicity of soluble oligomers: Lambert et al. (1998) demonstrated that naturally secreted Aβ oligomers were potent neurotoxins at picomolar concentrations, even without plaque formation[@lambert1998].

Inhibition of LTP: Walsh et al. (2002) showed that soluble AβOs potently inhibited hippocampal long-term potentiation (LTP), a cellular correlate of learning and memory[@walsh2002].

...

AC-193

AC-193 is an experimental monoclonal antibody developed by [Acumen Pharmaceuticals](https://acumenpharma.com) that represents a next-generation approach to anti-amyloid therapy for [Alzheimer's disease](/diseases/alzheimers-disease)[@potter2024]. Unlike previous antibodies that target either amyloid-beta monomers or plaques, AC-193 is specifically designed to bind to and neutralize soluble toxic amyloid-beta oligomers (AβOs), which are widely considered to be the primary neurotoxic species responsible for synaptic dysfunction and memory impairment in Alzheimer's disease[@demattos2024][@selkoe2011].

This selective targeting approach is based on the oligomer hypothesis of Alzheimer's disease, which posits that soluble, diffusible Aβ oligomers are the key pathogenic agents, rather than the insoluble amyloid plaques that have historically been the focus of therapeutic development[@lambert1998][@walsh2002].

The Oligomer Hypothesis

Historical Context

The oligomer hypothesis emerged from observations that amyloid plaques alone do not correlate well with cognitive impairment[@krafft1989]. Key discoveries that shaped this hypothesis include:

Toxicity of soluble oligomers: Lambert et al. (1998) demonstrated that naturally secreted Aβ oligomers were potent neurotoxins at picomolar concentrations, even without plaque formation[@lambert1998].

Inhibition of LTP: Walsh et al. (2002) showed that soluble AβOs potently inhibited hippocampal long-term potentiation (LTP), a cellular correlate of learning and memory[@walsh2002].

Pathological correlation: Studies found that soluble Aβ levels correlate better with cognitive impairment than plaque burden in human brain tissue[@haass2012].

Mechanistic studies: AβOs bind to synapses, causing spine loss and dysfunction through multiple mechanisms[@benilova2010][@hill2008].

Oligomer Structure and Toxicity

Aβ oligomers exist in multiple forms with varying degrees of toxicity[@roychaudhuri2013][@ivanova2021]:

• Dimers: The smallest toxic species, sufficient to impair LTP
• Trimers/Tetramers: Intermediate oligomers with enhanced toxicity
• Protofibrils: Larger soluble aggregates, highly toxic
• Fibrils: Insoluble, less directly toxic but can serve as reservoir

The toxic mechanisms include:

• Direct synaptic binding and internalization
• NMDA receptor dysfunction[@li2012]
• Calcium homeostasis disruption
• Mitochondrial dysfunction
• Oxidative stress
• Inflammation

Mechanism of Action

Selective Oligomer Binding

AC-193 is designed with high specificity for soluble Aβ oligomers, with minimal binding to monomers or plaques[@potter2024]. This selectivity is achieved through:

Conformational targeting: The antibody recognizes a conformational epitope present in oligomeric but not monomeric Aβ

Epitope mapping: Specific N-terminal and central region sequences unique to oligomers

Structural preference: Preference for the β-sheet-rich structure of oligomers

Neuroprotective Mechanisms

Once bound, AC-193 provides neuroprotection through multiple pathways[@demattos2024][@leknine2013]:

Neutralization: Antibodies bind AβOs, preventing their interaction with neuronal receptors

Synaptic protection: Blockade of AβO binding to synapses preserves dendritic spine density

F clearance: Engagement of peripheral immune system for antibody clearance

Inflammation modulation: Reduced microglial activation secondary to decreased oligomer burden

Comparison with Other Anti-Amyloid Antibodies

| Antibody | Company | Target | Specificity | Status |
|----------|---------|--------|-------------|--------|
| Lecanemab | Biogen/Eisai | Aβ monomers + protofibrils | Moderate | Approved |
| Donanemab | Eli Lilly | N-terminal Aβ (plaques) | Moderate | Approved |
| Crenezumab | Roche | Aβ oligomers + plaques | Moderate | Phase 3 |
| AC-193 | Acumen | Soluble Aβ oligomers | High (selective) | Phase 1 |

AC-193's selectivity differentiates it from approved antibodies that target either monomer/protofibrils (lecanemab) or plaques (donanemab)[@swanson2023][@mintun2021].

Preclinical Development

In Vitro Studies

Preclinical characterization demonstrated[@potter2024]:

• High affinity for soluble AβO (sub-nanomolar)
• Minimal binding to Aβ monomers (1000-fold selectivity)
• Negligible binding to amyloid plaques
• Protection against AβO-induced synaptic toxicity in neuronal cultures

In Vivo Studies

Animal models showed[@acumen2024]:

• Reduction in brain AβO levels
• Preservation of synaptic markers
• Improvement in cognitive behavioral paradigms
• No ARIA (amyloid-related imaging abnormalities)
• Favorable brain pharmacokinetics

Mechanism Validation

Key mechanistic studies established:

• AβO-induced synaptic loss is reversible[@mucke2011]
• Early intervention provides maximum benefit[@tomiyama2010]
• Clearance of oligomers is sufficient for functional recovery

Clinical Development

Phase 1 Study (NCT06335586)

AC-193 is currently being evaluated in a first-in-human Phase 1 study[@potter2024]:

Study Design:

• First-in-human, dose-escalation
• Healthy volunteers and patients with early AD
• Single and multiple ascending doses

Primary Endpoints:

• Safety and tolerability
• Pharmacokinetics
• Immunogenicity

Secondary Endpoints:

• Target engagement biomarkers
• CSF AβO levels
• Pharmacodynamic markers

Expected Clinical Program

Based on the selective mechanism, AC-193 is positioned for development in[@demattos2024]:

Early Alzheimer's disease: Patients with mild cognitive impairment (MCI) due to AD or early-stage AD

Prevention trials: Preclinical AD in biomarker-positive individuals

Combination therapy: Potential combination with other disease-modifying agents

Pharmacological Properties

Pharmacokinetics

| Property | Expected Value |
|----------|----------------|
| Administration | Intravenous infusion |
| Dosing | Monthly or quarterly |
| Half-life | 3-4 weeks (typical IgG1) |
| Brain penetration | Moderate (peripheral sink) |
| CSF exposure | To be determined |

Pharmacodynamics

• Target engagement: Reduction in soluble CSF AβO
• Biomarker effects: Preservation of synaptic markers
• Plaque effects: Minimal (selective for oligomers)

Safety Considerations

Expected Advantages

The oligomer-selective mechanism may provide safety advantages:

• Reduced ARIA risk: Less plaque binding may reduce amyloid-related imaging abnormalities compared to plaque-targeting antibodies
• No plaque mobilization: Doesn't cause soluble Aβ release from plaques
• Peripheral clearance: Antibody-AβO complexes cleared peripherally

Clinical Monitoring

Phase 1 will assess:

• Infusion reactions
• Immunogenicity
• MRI changes (ARIA monitoring)
• Cognitive endpoints

Rationale for Oligomer Targeting

Pathological Rationale

Soluble AβOs are the most relevant therapeutic target because[@cullen2022]:

Direct toxicity: Cause synapse loss and neuronal dysfunction

Early appearance: Appear before plaques in disease progression

Reversible: Synaptic damage is reversible if oligomers removed

Correlation: Levels correlate with cognitive impairment

Therapeutic Window

Targeting oligomers provides advantages:

• Earlier intervention possible (before plaques form)
• May preserve function even after plaques develop
• Could be combined with plaque-targeting approaches

Competitive Landscape

Current Anti-Amyloid Therapies

| Drug | Target | Company | Approval |
|------|--------|---------|----------|
| Lecanemab | Aβ protofibrils | Biogen/Eisai | 2023 |
| Donanemab | Aβ plaques | Eli Lilly | 2024 |
| AC-193 | Aβ oligomers | Acumen | Phase 1 |

Differentiation

AC-193 differentiates from approved drugs through:

Higher selectivity: Pure oligomer targeting vs. broader specificity

Different mechanism: Neutralization vs. plaque removal

Safety profile: Potentially reduced ARIA risk

Research Directions

Biomarker Development

• Soluble AβO quantification in CSF/plasma
• Synaptic markers (neurogranin, SNAP-25)
• Tau biomarkers
• Neuroimaging (PET, MRI)

Combination Approaches

• With anti-tau therapies
• With disease-modifying agents
• With symptomatic treatments

Prevention Studies

• Early intervention in prodromal AD
• Genetic risk carriers (APOE4)
• Biomarker-positive preclinical populations

References

[Potter et al., AC-193: a selective amyloid-beta oligomer antibody for Alzheimer's disease (2024)](https://pubmed.ncbi.nlm.nih.gov/38562421/)

[Demattos et al., Anti-Aβ oligomer antibodies as therapeutic agents (2024)](https://pubmed.ncbi.nlm.nih.gov/38653789/)

[Selkoe, Soluble oligomers of the amyloid β-protein (2011)](https://pubmed.ncbi.nlm.nih.gov/21412441/)

[Lambert et al., Diffusible, nonfibrillar ligands derived from Aβ1-42 (1998)](https://pubmed.ncbi.nlm.nih.gov/9501021/)

[Walsh et al., Naturally secreted oligomers of amyloid β-protein (2002)](https://pubmed.ncbi.nlm.nih.gov/11909457/)

[Krafft et al., The role of amyloid β oligomers in Alzheimer's disease (1989)](https://pubmed.ncbi.nlm.nih.gov/2695412/)

[Hill et al., Insights into Aβ oligomer neurotoxicity (2008)](https://pubmed.ncbi.nlm.nih.gov/18514079/)

[Haass & Selkoe, Soluble amyloid β aggregate physiology (2012)](https://pubmed.ncbi.nlm.nih.gov/22395810/)

[Benilova et al., The toxic Aβ oligomer and Alzheimer's disease (2010)](https://pubmed.ncbi.nlm.nih.gov/21149553/)

[Roychaudhuri et al., Aβ oligomers: where they come from (2013)](https://pubmed.ncbi.nlm.nih.gov/23576137/)

[Oda et al., Clusterin (ApoJ) sequesters toxic Aβ oligomers (2003)](https://pubmed.ncbi.nlm.nih.gov/14521936/)

[Li et al., Soluble Aβ oligomers inhibit LTP (2012)](https://pubmed.ncbi.nlm.nih.gov/22157017/)

[Tomiyama et al., A mouse model of Aβ oligomers (2010)](https://pubmed.ncbi.nlm.nih.gov/20739558/)

[Mucke, Alzheimer's disease: can removing Aβ oligomers restore function? (2011)](https://pubmed.ncbi.nlm.nih.gov/21738095/)

[Lekmine et al., Antibody-based therapeutics targeting Aβ oligomers (2013)](https://pubmed.ncbi.nlm.nih.gov/23481534/)

[Ivanova et al., Aβ oligomer structural diversity (2021)](https://pubmed.ncbi.nlm.nih.gov/34146528/)

[Chen et al., Aβ oligomer-specific antibodies in AD therapy (2017)](https://pubmed.ncbi.nlm.nih.gov/28154404/)

[Swanson et al., Lecanemab: an anti-Aβ antibody for early AD (2023)](https://pubmed.ncbi.nlm.nih.gov/37202498/)

[Mintun et al., Donanemab in early Alzheimer's disease (2021)](https://pubmed.ncbi.nlm.nih.gov/33752666/)

[Cullen et al., Soluble aggregates as a therapeutic target in AD (2022)](https://pubmed.ncbi.nlm.nih.gov/34933942/)

See Also

• [Amyloid-Beta](/proteins/amyloid-beta)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Amyloid Hypothesis](/mechanisms/amyloid-cascade)
• [Lecanemab](/entities/lecanemab)
• [Donanemab](/entities/donanemab)
• [Synaptic Dysfunction](/mechanisms/synaptic-dysfunction)

External Links

• [Acumen Pharmaceuticals](https://acumenpharma.com)
• [ClinicalTrials.gov: AC-193](https://clinicaltrials.gov)
• [Alzheimer's Association](https://www.alz.org)
• [Alzheimer's Drug Discovery Foundation](https://www.afar.org)
• [Allen Human Brain Atlas](https://brain-map.org/)