Eisai Co., Ltd.

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Eisai Co., Ltd. is a Japanese pharmaceutical company headquartered in Tokyo, specializing in oncology, neurology, and specialty care. Founded in 1941, Eisai is a key player in [Alzheimer's disease](/diseases/alzheimers-disease) research, having co-developed [lecanemab](/entities/lecanemab) (Leqembi) with Biogen — the first amyloid-targeting antibody to receive full FDA approval. [@eisai]

Company Overview

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Company Overview

Mermaid diagram (expand to render)

| Attribute | Details |
|-----------|---------|
| Ticker | TSE: 4523 |
| Headquarters | Tokyo, Japan |
| Founded | 1941 |
| CEO | Haruo Naito (CEO) |
| Employees | ~10,000 |
| Revenue | ~$6 billion (FY2023) |

Alzheimer's Disease Pipeline

Approved Therapies

Leqembi (lecanemab)

Mechanism: [Amyloid-beta](/proteins/amyloid-beta) monoclonal antibody targeting Aβ protofibrils
Target: Protofibrils of amyloid-beta ( soluble oligomers)
Approval: FDA accelerated approval January 2023, full approval July 2023
Developer: Jointly developed with Biogen
Status: Marketed in US, Japan, China, South Korea, Taiwan, Israel
Clinical Trial: [Clarity AD (NCT04437511)](https://clinicaltrials.gov/show/NCT04437511)
Efficacy: 27% slowing of clinical decline (CDR-SB) in Clarity AD; 31% slower decline in amyloid-related imaging abnormalities (ARIA)
Sales: ~$18M in Q3 2024 (early launch phase) [@lecanemab-q3-2024]

Leqembi Mechanism of Action:

Leqembi binds to protofibrils — the soluble, toxic oligomeric forms of amyloid-beta that are believed to be primary drivers of synaptic dysfunction and cognitive decline in AD. By selectively targeting protofibrils rather than monomeric Aβ or plaque, Leqembi reduces both soluble toxic species and existing amyloid plaques.

Pipeline Programs

| Drug | Mechanism | Phase | Indication |
|------|-----------|-------|------------|
| Lecanemab (Leqembi) | Anti-amyloid β protofibril mAb | Approved | Early AD |
| E2814 | Anti-tau mAb (Mosaic) | Phase 1/2 | AD (DIAN-TU) |
| E2027 | PDE9 inhibitor | Phase 2 | AD |
| E2028 | Tau aggregation inhibitor | Phase 1 | AD |

E2814 (Anti-tau Monoclonal Antibody)

Mechanism: Anti-tau monoclonal antibody designed to bind multiple phospho-tau epitopes
Target: Pathological phosphorylated tau in brain
Phase: Phase 1/2 being evaluated in DIAN-TU trial (Dominantly Inherited Alzheimer Network Trials Unit)
Rationale: Complement amyloid-targeting with tau-focused approach; prevent spread of tau pathology across brain regions
Unique Feature: "Mosaic" design targets multiple tau epitopes for broader coverage
Clinical Trials: [DIAN-TU (NCT01760005)](https://clinicaltrials.gov/show/NCT01760005) [@diantu]
Research: First-in-human study published showing safety and target engagement [@e2814-phase1]

DIAN-TU Study Context:
The DIAN-TU platform tests therapies in individuals with autosomal dominant AD mutations, allowing for earlier intervention before symptom onset. E2814 is being evaluated alongside other anti-amyloid and anti-tau candidates.

E2027 (PDE9 Inhibitor)

Mechanism: Phosphodiesterase 9 (PDE9) inhibitor
Target: cGMP signaling pathway in neurons
Phase: Phase 2
Rationale: Enhance synaptic plasticity and memory function by increasing cGMP levels
Rationale Basis: PDE9 is enriched in brain regions affected by AD and is involved in NMDA receptor-mediated signaling

E2028 (Tau Aggregation Inhibitor)

Mechanism: Small molecule inhibitor of tau aggregation
Target: Pathological tau protein aggregation
Phase: Phase 1
Rationale: Prevent formation of neurofibrillary tangles (NFTs)

Elenbecestat (E2609 - Discontinued)

Mechanism: BACE (Beta-Secretase) inhibitor
Target: [BACE1](/entities/bace1) enzyme
Status: Discontinued Phase 2/3 (2021)
Reason: Safety concerns (liver toxicity, cognitive worsening in some patients)
Lesson: Taught the field about risks of aggressive amyloid reduction

Parkinson's Disease Pipeline

Eisai has limited [Parkinson's disease](/diseases/parkinsons-disease) programs. The company focuses primarily on Alzheimer's disease. No significant PD candidates in current pipeline.

Other Key Programs

Neurology - Epilepsy

| Drug | Mechanism | Indication |
|------|-----------|------------|
| Fycompa (perampanel) | AMPA receptor antagonist | Epilepsy |
| Zebinix/Bexolvera (eslicarbazepine) | Sodium channel blocker | Epilepsy |

Oncology

| Drug | Mechanism | Indication |
|------|-----------|------------|
| Lenvima (lenvatinib) | VEGFR, FGFR, PDGFRA, KIT inhibitor | Multiple cancers |
| Halaven (eribulin) | Microtubule inhibitor | Breast cancer |
| Kisplyx (lenvatinib) | VEGFR inhibitor | Renal cell carcinoma |

Strategic Partnerships

Biogen Partnership

Scope: Joint development and commercialization of lecanemab (Leqembi)
Structure: 50/50 profit-sharing in US; Eisai leads in Japan and Asia; Biogen receives royalties in other regions
History: Established in 2014; first major collaboration for AD therapeutics

Academic Partnerships

University of Cambridge — Tau research collaboration for E2814
DIAN-TU Consortium — Anti-tau antibody development in familial AD
Various biomarker partnerships with academic medical centers for patient selection and monitoring

Financial Highlights

| Year | Revenue | Key Products |
|------|---------|--------------|
| 2023 | $6.0B | Leqembi, Lenvima, Fycompa |
| 2022 | $5.9B | Lenvima, Halaven, Fycompa |
| 2021 | $5.7B | Lenvima, Halaven, Fycompa |

Clinical Trials

[Leqembi trials](https://clinicaltrials.gov/search?cond=Alzheimer%27s%20disease&spons=Eisai) — Multiple ongoing including extension studies
[E2814 trials](https://clinicaltrials.gov/search?cond=Alzheimer%20Disease&intr=E2814) — DIAN-TU study

Key Leadership

Haruo Naito — Chief Executive Officer
Ivan Cheung — President & CEO, Eisai Inc. (US)
Masamichi Ohno — President, Eisai Japan

[Biogen](/companies/biogen) — Leqembi co-development partner
[Eli Lilly](/companies/eli-lilly) — Competitor in AD space (Kisunla/donanemab)
[Roche](/companies/roche) — Gantenerumab program; anti-amyloid competitor
[Denali Therapeutics](/companies/denali) — Neurodegeneration pipeline
[Prothena](/companies/prothena) — Amyloid programs (pramlintide)
[AC Immune](/companies/ac-immune) — Tau vaccines and antibodies
[BioArctic](/companies/bioarctic) — Swedish biotech with AD pipeline

References

[Eisai Corporate Website](https://www.eisai.com)

[Leqembi FDA Approval](https://www.fda.gov/drugs/news-events-human-drug-alerts/fda-approves-leqembi-lecanemab-amyloid-reducing-therapy-alzheimers-disease)

[Clarity AD Trial Results](https://doi.org/10.1056/NEJMoa2212948)

[DIAN-TU Study](https://clinicaltrials.gov/show/NCT01760005)

[Eisai Annual Report 2023](https://www.eisai.com/en/ir/finance/annual.html)

[Leqembi Q3 2024 Sales](https://www.businesswire.com/news/home/20241029100758/en)

[E2814 First-in-Human Study](https://doi.org/10.1111/tri.14028)

Pathway Diagram

The following diagram shows the key molecular relationships involving Eisai Co., Ltd. discovered through SciDEX knowledge graph analysis:

Mermaid diagram (expand to render)

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Eisai Co., Ltd.

Company Overview

Company Overview

Alzheimer's Disease Pipeline

Approved Therapies

Leqembi (lecanemab)

Pipeline Programs

E2814 (Anti-tau Monoclonal Antibody)

E2027 (PDE9 Inhibitor)

E2028 (Tau Aggregation Inhibitor)

Elenbecestat (E2609 - Discontinued)

Parkinson's Disease Pipeline

Other Key Programs

Neurology - Epilepsy

Oncology

Strategic Partnerships

Biogen Partnership

Academic Partnerships

Financial Highlights

Clinical Trials

Key Leadership

Related Companies

References

Pathway Diagram