Progressive Supranuclear Palsy (PSP) and Corticobasal Syndrome (CBS) represent the most common 4R-tauopathies—neurodegenerative disorders characterized by the preferential accumulation of four-repeat tau isoforms in the brain. These conditions cause substantial disability, with PSP typically leading to death within 7-10 years of onset, and CBS causing progressive motor and cognitive decline. Currently, no disease-modifying treatments exist for either condition, creating an urgent unmet medical need.
E2814 (etanlanetug) is an anti-tau monoclonal antibody developed by Eisai that specifically targets the microtubule-binding region (MTBR) of tau protein. This represents a fundamentally different approach from previous anti-tau antibodies that targeted the N-terminal or mid-domain regions of tau. By targeting the MTBR—the core aggregation-prone region that forms the fibrillar core of neurofibrillary tangles (NFTs)—E2814 aims to directly prevent tau aggregation and promote clearance of existing pathology.
This Phase 2 trial (NCT05615614) specifically evaluates E2814 in patients with PSP and CBS, representing the first anti-tau immunotherapy specifically designed for 4R-tauopathies. The trial is currently recruiting at multiple sites in the United Kingdom and United States.
¶ Tau Biology and 4R-Tauopathies
¶ Tau Protein Structure and Function
Tau is a microtubule-associated protein encoded by the MAPT (Microtubule-Associated Protein Tau) gene on chromosome 17q21. In the adult human brain, tau exists as six isoforms generated by alternative splicing of exons 2, 3, and 10. The alternative splicing of exon 10, which contains one of the microtubule-binding repeats, produces isoforms with either three (3R) or four (4R) repeats.
Isoform Composition:
- 3R tau: Excludes exon 10, contains 3 microtubule-binding repeats
- 4R tau: Includes exon 10, contains 4 microtubule-binding repeats
Domain Structure:
- N-terminal projection domain: Projects away from microtubules, interacts with neuronal membranes
- Proline-rich region: Contains multiple phosphorylation sites
- Microtubule-binding region: Contains 3-4 repeats (R1-R4), essential for microtubule binding
- C-terminal region: Regulates aggregation propensity
In the normal brain, tau promotes microtubule assembly and stability, essential for axonal transport. However, in disease states, tau becomes hyperphosphorylated, detaches from microtubules, and aggregates into NFTs.
¶ 4R-Tauopathies: PSP and CBS
The 4R-tauopathies share pathological features but have distinct clinical presentations:
PSP, also known as Steele-Richardson-Olszewski syndrome, is characterized by:
- Parkinsonism: Axial rigidity, bradykinesia, postural instability
- Vertical gaze palsy: Supranuclear ophthalmoplegia, particularly downward gaze
- Cognitive decline: Frontal executive dysfunction, behavioral changes
- Pseudobulbar signs: Dysarthria, dysphagia
Richardson syndrome (classic PSP) accounts for approximately 70% of cases. Other variants include:
- PSP with parkinsonism (PSP-P)
- PSP with corticobasal syndrome (PSP-CBS)
- PSP with pure akinesia with gait freezing (PAGF)
- Primary freezing of gait (PFG)
CBS presents with:
- Asymmetric rigidity: Often affecting one upper limb
- Dystonia: Involuntary muscle contractions
- Myoclonus: Sudden, involuntary muscle jerks
- Alien limb phenomenon: Feeling that limb is not under one's control
- Cognitive dysfunction: Executive impairment, apraxia, cortical sensory loss
CBS may result from various underlying pathologies, with CBD (corticobasal degeneration) representing the most common tauopathy cause.
Both PSP and CBS demonstrate:
- 4R tau accumulation: Neuronal and glial inclusions
- Neurofibrillary tangles: Paired helical filaments composed of hyperphosphorylated tau
- Glial pathology: Astroglial and microglial involvement
- Neuronal loss: Particularly in basal ganglia, brainstem, cortical regions
The distribution of pathology differs between conditions:
- PSP: Globus pallidus, subthalamic nucleus, brainstem, cerebellum
- CBS: Motor cortex, basal ganglia, parietal lobe
E2814 specifically binds to the microtubule-binding region (MTBR) of tau, spanning residues 244-368. This is critically different from previous anti-tau antibodies:
| Antibody |
Target Region |
Key Limitation |
| Gosuranemab (BIIB080) |
N-terminal (aa 6-23) |
Limited brain penetration, no tangles |
| Semorinemab |
Mid-domain (aa 150-230) |
Did not bind NFT tau |
| Tilavonemab (ABBV-8E12) |
N-terminus |
Failed in Phase 2 |
| E2814 |
MTBR (aa 244-368) |
Binds aggregation-prone region |
The MTBR is the most functionally and pathologically important region of tau:
- Contains the hexapeptide motifs (306VQIVYK311) essential for aggregation
- Forms the core of paired helical filaments
- Is the region that remains in proteolytic fragments found in NFTs
- Contains multiple post-translational modification sites critical for pathology
E2814 binds to:
- Monomeric tau (preventing aggregation)
- Oligomeric tau (toxic intermediate species)
- Fibrillar tau (NFTs)
- MTBR fragments (pathological breakdown products)
This broad reactivity allows E2814 to:
- Prevent aggregation of normal tau
- Neutralize toxic oligomers
- Clear existing fibrillar deposits
E2814 is believed to work through multiple mechanisms:
Aggregation Prevention:
- Binding to monomeric MTBR blocks β-sheet formation
- Prevents templated aggregation of adjacent tau molecules
Oligomer Neutralization:
- Antibodies bind toxic oligomers, preventing cell-to-cell transmission
- May facilitate clearance through Fc-mediated mechanisms
Fibril Clearance:
- Antibody binding to NFTs may enhance phagocytosis
- Fcγ receptor-mediated microglial uptake
- Potential for lysosomal degradation
Reduced Propagation:
- Tau is known to spread between neurons in a prion-like manner
- Antibodies in the extracellular space may intercept spreading tau
E2814 is being evaluated across multiple indications in parallel clinical trials:
| Trial |
NCT ID |
Phase |
Population |
Status |
Enrollment |
| DIAN-TU |
NCT05269394 |
Phase 2/3 |
Dominantly inherited AD |
Ongoing |
197 |
| 4R-Tauopathy |
NCT05615614 |
Phase 2 |
PSP, CBS |
Recruiting |
— |
| Dose-Finding |
NCT06602258 |
Phase 2 |
MCI due to AD |
Recruiting |
105 |
| Phase 1 MAD |
— |
Phase 1 |
Healthy volunteers |
Completed |
72 |
This parallel development strategy allows efficient evaluation of E2814 across the tauopathy spectrum.
The most advanced E2814 trial is the Dominantly Inherited Alzheimer Network Trials Unit (DIAN-TU) study, evaluating E2814 in dominantly inherited Alzheimer's disease (DIAD):
- Design: Participants receive lecanemab for 24 weeks, then randomized to E2814 or placebo plus lecanemab for four-year trial
- Population: 197 participants with MCI or dementia due to dominantly inherited AD
- Start: January 2022
- Expected completion: 2028
- Locations: 39 sites worldwide
Key Results:
| Endpoint |
Result |
| CSF MTBR-tau-243 |
30-70% reduction |
| CSF pTau217 |
Estimated 50% reduction after 2 years |
| Safety |
Safe and well-tolerated at doses up to 4,500 mg |
| Target Engagement |
Dose-dependent binding to tau MTBR epitopes in CSF |
These results established proof-of-mechanism for E2814, demonstrating:
- Target engagement in CSF
- Dose-dependent effects
- Acceptable safety profile
- Start: September 2024
- Population: MCI due to Alzheimer's disease
- Design: Four doses of E2814 or placebo monthly plus weekly lecanemab for 18 months
- Primary outcome: Change in CSF MTBR-tau-243 at six months
- Enrollment: 105 participants (target: 90)
- Locations: 34 sites in U.S. and Japan
- Expected completion: August 2027
This study will determine the optimal dose for AD trials.
The focus of this task is the trial specifically evaluating E2814 in PSP and CBS:
- Status: Recruiting
- Population: PSP and CBS
- Design: Not fully disclosed, likely randomized, placebo-controlled
- Primary endpoints: Likely include clinical measures (PSPRS, CBS rating scale) and tau PET
Expected primary endpoints for the 4R-tauopathy trial:
-
Tau PET Imaging
- Change in flortaucipir (FTP) PET binding
- Measures tau pathology load in key brain regions
-
Clinical Rating Scales
- PSP Rating Scale (PSPRS) for PSP patients
- Corticobasal Syndrome rating scale for CBS patients
- Quantifies motor and cognitive symptoms
Expected secondary endpoints:
-
Cognitive Assessment
- MMSE (Mini-Mental State Examination)
- ADAS-Cog (Alzheimer's Disease Assessment Scale-Cognition)
- Trail Making Test, Stroop test
-
Functional Assessment
- Bristol Activities of Daily Living (BADL)
- Functional Assessment Questionnaire
-
Imaging
- MRI brain volumetry
- Regional brain atrophy rates
-
Biomarkers
- CSF tau species (total tau, p-tau, MTBR-tau)
- Plasma tau markers
- Neurodegeneration markers (NFL, NfL)
- Age 40-85 years
- Diagnosis of probable PSP (any subtype) or CBS
- MMSE score ≥ 20
- Ability to undergo MRI and PET imaging
- Stable medications for 30 days prior to enrollment
- Significant psychiatric comorbidity
- History of stroke or significant cerebrovascular disease
- Current enrollment in another clinical trial
- Prior exposure to anti-tau immunotherapy
PSP Diagnosis:
- NINDS-SPSP criteria for probable PSP
- Richardson syndrome or variants
- Presence of vertical gaze palsy, parkinsonism, postural instability
CBS Diagnosis:
- Armstrong criteria for probable CBS
- Asymmetric rigidity, apraxia, cortical sensory loss
- Excluded alternate etiologies
The MTBR represents the optimal target for anti-tau immunotherapy:
- Central to Aggregation: The MTBR contains the self-assembly motifs essential for fibril formation
- Pathological Relevance: MTBR fragments are found in CSF and brain tissue of tauopathy patients
- Unique Epitopes: The MTBR offers unique binding sites not present in N-terminal antibodies
- Mechanism Engagement: Direct effects on the aggregation process rather than just extracellular tau
Preclinical data supporting E2814:
- Binding to recombinant human tau MTBR
- Recognition of tau in brain tissue from PSP/CBS patients
- Activity in mouse models of tauopathy
- Favorable developability characteristics for antibody therapeutic
The DIAN-TU results provide important clinical validation:
- MTBR-tau reduction in CSF demonstrates target engagement
- Dose-response relationship supports mechanism
- Safety established at high doses
- Preliminary efficacy signals warrant continued development
¶ Competitive Landscape
| Agent |
Company |
Target |
Indication |
Stage |
| E2814 |
Eisai |
MTBR |
AD, PSP, CBS |
Phase 2 |
| Semorinemab |
Roche/Genentech |
Mid-domain |
AD |
Phase 2 |
| Gosuranemab |
Biogen |
N-terminal |
AD |
Phase 2 |
| Tilavonemab |
AbbVie |
N-terminal |
PSP |
Phase 2 |
| JNJ-63742057 |
Janssen |
Mid-domain |
AD |
Phase 1 |
E2814 differs from competitors through:
- Unique target: MTBR vs. N-terminal or mid-domain
- Broader binding: Monomer, oligomer, fibril
- PSP/CBS focus: First specifically designed for 4R-tauopathies
- Eisai expertise: Same company that developed lecanemab
¶ Location and Sites
The trial is recruiting at multiple sites:
United Kingdom:
- Multiple sites across England and Scotland
- Expertise in movement disorders and tauopathies
United States:
- Multiple academic medical centers
- Movement disorder specialists
Specific site information should be verified through ClinicalTrials.gov.
This trial is highly relevant for patients with PSP and CBS:
- Disease-Modifying Potential: E2814 targets the underlying tau pathology
- Novel Mechanism: First antibody targeting MTBR
- Unmet Need: No approved disease-modifying treatments
- Established Safety: DIAN-TU data support acceptable safety
Patients should discuss with their neurologists whether participation is appropriate based on individual circumstances.
Positive results would support development in:
- Other 4R-tauopathies (e.g., Primary Age-Related Tauopathy)
- Alzheimer's disease (via dose-finding studies)
- Chronic traumatic encephalopathy
- Other tauopathies
E2814 may be combined with:
- Anti-amyloid antibodies (lecanemab, donanemab)
- Small molecule tau aggregation inhibitors
- Neuroprotective agents
The trial may validate:
- CSF MTBR-tau as pharmacodynamic marker
- Tau PET as patient selection or response marker
- Blood-based tau markers
The E2814 Phase 2 trial in 4R-tauopathies represents a critical test of the MTBR-targeting hypothesis. By specifically binding to the aggregation-prone region of tau, E2814 offers a mechanistically differentiated approach compared to previous anti-tau antibodies that targeted N-terminal or mid-domain regions.
The DIAN-TU results demonstrating 30-70% reduction in CSF MTBR-tau provide proof-of-mechanism and support advancement to late-phase trials. The current trial in PSP and CBS addresses the highest unmet need—disease-modifying treatments for 4R-tauopathies.
If successful, this trial would:
- Validate MTBR as therapeutic target
- Provide first disease-modifying treatment for PSP/CBS
- Establish E2814 as backbone therapy for tauopathies
- Support broader development across tauopathy spectrum
The development of E2814 exemplifies precision medicine in neurodegeneration—matching specific therapies to specific pathological substrates based on mechanistic understanding.
Understanding E2814's mechanism in context of tau biology:
Eisai is a Japanese pharmaceutical company with significant expertise in neurology and Alzheimer's disease:
Key Products:
- Lecanemab (Leqembi): Anti-amyloid antibody approved for early AD
- Donepezil: Acetylcholinesterase inhibitor for AD
- Aricept: Established AD therapy globally
Pipeline Focus:
- Tau-targeted therapies (E2814)
- Next-generation anti-amyloid approaches
- Neurodegeneration prevention
Research Capabilities:
- Translational research in tauopathies
- Clinical trial infrastructure globally
- Companion diagnostic development
E2814 development involves collaboration with:
- DIAN-TU network for dominantly inherited AD
- Academic movement disorder centers
- Regulatory agencies for accelerated pathways
¶ Challenges and Considerations
-
Antibody Brain Penetration
- Peripheral antibodies must cross blood-brain barrier
- Mechanism likely involves FcRn-mediated transport
- Dose optimization required for CNS target engagement
-
Tau Kinetics
- Tau turnover in brain is slow
- Extended treatment may be needed for effects
- Biomarker changes may precede clinical changes
-
Pathology Burden
- Advanced patients may have substantial existing pathology
- Earlier intervention may be more effective
- Patient selection based on disease stage
-
Clinical Endpoints
- PSP Rating Scale validated but may not capture all changes
- CBS rating scales less well established
- Regulatory acceptance of biomarker endpoints uncertain
-
Patient Heterogeneity
- PSP has multiple subtypes
- CBS may have various underlying pathologies
- Biomarker-based stratification may improve signal detection
-
Natural History Variability
- PSP progression rates vary
- Placebo response in recent trials
- Need for robust natural history data
-
Other Anti-Tau Approaches
- Small molecule aggregation inhibitors
- Antisense oligonucleotides
- Gene therapy approaches
-
Combination Potential
- Anti-amyloid + anti-tau combinations
- Multiple mechanisms may be synergistic