Gosuranemab (BIIB092) PSP Trial

Gosuranemab (BIIB092) - Anti-Tau Antibody Trial in Progressive Supranuclear Palsy

Overview

Gosuranemab (formerly BIIB092) is an anti-tau monoclonal antibody developed by Biogen that targets extracellular [tau protein](/proteins/tau). The drug was evaluated in a Phase 2 clinical trial for Progressive Supranuclear Palsy (PSP) but was terminated due to lack of efficacy["@clinicaltrialsgov"]. This trial represents one of the most significant failures in the anti-tau antibody field and provides critical lessons for future therapeutic development in tauopathies.

Gosuranemab (BIIB092) - Anti-Tau Antibody Trial in Progressive Supranuclear Palsy

Overview

Gosuranemab (formerly BIIB092) is an anti-tau monoclonal antibody developed by Biogen that targets extracellular [tau protein](/proteins/tau). The drug was evaluated in a Phase 2 clinical trial for Progressive Supranuclear Palsy (PSP) but was terminated due to lack of efficacy["@clinicaltrialsgov"]. This trial represents one of the most significant failures in the anti-tau antibody field and provides critical lessons for future therapeutic development in tauopathies.

Trial Information

| Parameter | Value |
|-----------|-------|
| NCT Number | NCT03068468 |
| Phase | Phase 2 |
| Status | TERMINATED (2019) |
| Sponsor | Biogen |
| Mechanism | Anti-tau monoclonal antibody (N-terminal tau) |
| Target | Extracellular tau protein |
| Population | PSP patients (Richardson syndrome) |

Background and Rationale

Tau Pathology in PSP

PSP is a 4R-tauopathy characterized by the accumulation of hyperphosphorylated 4-repeat tau isoforms in neurofibrillary tangles, tufted astrocytes, and coiled bodies in subcortical and brainstem structures[@boxer2021]. The [tau protein](/proteins/tau) plays a central role in disease pathogenesis, making it an attractive therapeutic target.

The Extracellular Tau Hypothesis

Gosuranemab was designed based on the hypothesis that extracellular tau—released from dying neurons—mediates prion-like spreading of pathology throughout the brain[@yamada2011]. The antibody was intended to:

This approach differed from intracellular-targeting strategies and represented a novel mechanistic hypothesis for disease modification in tauopathies.

Trial Design

Study Architecture

The Phase 2 trial employed a randomized, double-blind, placebo-controlled design:

• Enrollment: Approximately 450 patients with probable PSP
• Arms: Multiple dose cohorts (placebo, low dose, high dose)
• Duration: 52 weeks
• Primary Endpoint: Change in PSP Rating Scale (PSPRS) score
• Secondary Endpoints: Clinical measures, biomarker endpoints

Target Engagement Biomarkers

The trial included biomarker assessments to evaluate target engagement:

• CSF total tau and phospho-tau measurements
• Plasma tau levels
• PET imaging with tau ligands (flortaucipir)

Trial Results

Primary Outcome

The Phase 2 trial in PSP was terminated early after interim analysis showed that the primary endpoint was unlikely to be met[@clinicaltrialsgov]. The trial failed to demonstrate significant clinical benefit compared to placebo:

• No statistically significant difference in PSPRS decline between treatment and placebo arms
• Substantial placebo response confounded interpretation
• Disease progression continued at similar rates regardless of treatment

Biomarker Findings

The biomarker data revealed important insights:

• Modest reduction in CSF tau was observed at higher doses, but this did not correlate with clinical benefit
• Plasma tau showed dose-dependent reduction, but the clinical significance remained unclear
• No clear relationship between biomarker changes and clinical outcomes

Deep Dive: Why It Failed

1. Timing Hypothesis: Too Little, Too Late

The most widely cited explanation for failure relates to disease stage[@fotuhi2019]:

• Established pathology: By the time patients present with PSP symptoms, substantial tau pathology has already accumulated in the brainstem and subcortical structures
• Neurodegeneration threshold: Significant neuronal loss may have already occurred, making reversal impossible
• Compensatory mechanisms exhausted: The brain's ability to compensate for tau-induced dysfunction may be depleted

2. Target Engagement Limitations

Several factors may have limited adequate target engagement[@sigurdsson2019]:

• Blood-brain barrier penetration: Antibody therapeutics face challenges crossing the BBB; CNS exposure may have been insufficient
• Distribution kinetics: Antibody distribution in brain parenchyma is limited compared to small molecules
• Extracellular space access: While gosuranemab targets extracellular tau, the majority of pathological tau exists intracellularly
• Epitope selection: The N-terminal targeting may not efficiently capture the most pathogenic tau species

3. The Wrong Target: Extracellular vs. Intracellular Tau

The fundamental mechanism hypothesis may have been flawed[@guo2014]:

• Intracellular tau is the driver: Pathological tau primarily exerts its toxic effects inside neurons, where it disrupts microtubule function, causes mitochondrial dysfunction, and triggers synaptic loss
• Extracellular tau may be a consequence: Released tau may represent a cleanup mechanism rather than the primary toxic species
• Antibody cannot reach intracellular space: Therapeutic antibodies cannot access the intracellular compartment where most tau pathology resides

4. 4R-Tauopathy Specificity

PSP presents unique challenges compared to Alzheimer's disease[@dickson2010]:

• 4R isoform predominance: Unlike AD (mixed 3R/4R), PSP involves primarily 4R tau, which may have different propagation mechanisms
• Oligodendroglial pathology: PSP involves significant tau pathology in oligodendrocytes (coiled bodies), which may not be accessible to antibody-based therapies
• Different spreading patterns: The anatomical spread of tau in PSP differs from AD, potentially requiring different intervention strategies

5. Biomarker Gaps

The absence of robust biomarkers for target engagement complicated development[@blennow2018]:

• CSF tau as pharmacodynamic marker: While CSF tau decreased, the relationship to actual brain tau reduction remained uncertain
• No PET signal change: Tau PET ligands may not be sensitive enough to detect treatment-induced changes
• Clinical-biomarker disconnect: Biomarker changes did not translate to clinical benefit, raising questions about appropriate endpoints

6. Trial Design Challenges

PSP-specific trial design issues may have contributed[@boxer2016]:

• Diagnostic heterogeneity: PSP has multiple clinical variants; enrollment may have included patients with other pathologies
• Placebo response: High placebo response rates in neurodegenerative trials complicate signal detection
• Endpoint sensitivity: PSPRS may not be sensitive enough to detect modest disease slowing
• Duration: 52 weeks may be insufficient to observe disease modification

Lessons Learned

For Anti-Tau Antibody Development

• Treat patients before substantial neurodegeneration occurs
• Consider enrichment strategies for prodromal or pre-symptomatic populations
• Genetic risk carriers (MAPT mutations) may provide ideal enrollment populations

• Explore active delivery mechanisms (intrathecal, convection-enhanced delivery)
• Consider bispecific antibodies engineered for enhanced BBB crossing
• Use focused ultrasound to transiently open the BBB

• Focus on intracellular tau reduction rather than extracellular neutralization
• Consider approaches that reduce all tau isoforms (ASOs, small molecules)
• Target oligomeric and seeded species rather than monomeric tau

• Establish clear relationships between biomarker changes and brain tau
• Use PET to directly measure treatment effects on tau burden
• Develop assays for specific pathological tau conformations

• Use more specific diagnostic criteria (e.g., CSF biomarkers, imaging)
• Consider longer treatment durations
• Employ adaptive designs to identify signals more efficiently

For the Broader Field

The gosuranemab failure contributed to a paradigm shift in tau therapeutic development[@wilcock2019]:

• From antibodies to ASOs: The failure accelerated interest in antisense oligonucleotide approaches (e.g., [BIIB080](/entities/biiib080)) that reduce tau production at the source
• From extracellular to intracellular: Focus shifted toward intracellular targets and tau production reduction
• From symptomatic to disease-modifying: Emphasis on earlier intervention and true disease modification
• From single-target to combination: Recognition that multi-target approaches may be necessary

Comparison with Other Failed Anti-Tau Trials

| Trial | Drug | Mechanism | Outcome | Key Learnings |
|-------|------|-----------|---------|---------------|
| PASSPORT | Gosuranemab | Anti-tau antibody | Failed | Extracellular targeting insufficient |
| NCT02460094 | Tilavonemab | Anti-tau antibody | Failed | Timing, target selection issues |
| NCT02880956 | Semorinemab | Anti-tau antibody | Mixed | Different effects in AD subpopulations |
| NCT03068467 | AbbVie programs | Various | Failed | 4R-tauopathies challenging |

Related Therapeutic Approaches

Tau-Lowering ASOs (Current Focus)

The failure of antibody approaches shifted focus to tau-lowering ASOs[@mummery2023]:

• [BIIB080 (MAPTRx)](/entities/biiib080): Reduces tau production at mRNA level, demonstrated 50% CSF tau reduction
• NIO752: Novartis ASO showing proof-of-concept in PSP
• APB-102: Preclinical ASO for 4R-tauopathies

Small Molecule Approaches

Alternative modalities under development:

• Tau aggregation inhibitors: Small molecules preventing tau aggregation
• Tau kinase inhibitors: Targeting tau-phosphorylating enzymes (GSK3β, CDK5)
• Microtubule stabilizers: Supporting neuronal function despite tau pathology

Future Directions

Recommended Trial Designs

Based on lessons from gosuranemab:

Unmet Needs

• Better understanding of tau biology and propagation
• Improved biomarkers for target engagement and response
• Validated animal models reflecting human 4R-tauopathy
• Regulatory pathways for disease-modifying therapies in rare tauopathies

See Also

• [Progressive Supranuclear Palsy](/diseases/progressive-supranuclear-palsy)
• [Tau Protein](/proteins/tau)
• [BIIB080 (MAPTRx) — Tau ASO](/entities/biiib080)
• [Tau Immunotherapy](/therapeutics/tau-immunotherapy)
• [Tauopathies](/mechanisms/tauopathies)
• [4R-Tauopathies](/mechanisms/4r-tauopathies)

References

Related Hypotheses

From the [SciDEX Exchange](/exchange) — scored by multi-agent debate

• [Aquaporin-4 Polarization Rescue](/hypothesis/h-c8ccbee8) — <span style="color:#81c784;font-weight:600">0.67</span> · Target: AQP4
• [Microglial Purinergic Reprogramming](/hypothesis/h-5daecb6e) — <span style="color:#81c784;font-weight:600">0.66</span> · Target: P2RY12
• [Sphingolipid Metabolism Reprogramming](/hypothesis/h-6657f7cd) — <span style="color:#81c784;font-weight:600">0.61</span> · Target: CERS2
• [Complement C1q Subtype Switching](/hypothesis/h-5a55aabc) — <span style="color:#ffd54f;font-weight:600">0.59</span> · Target: C1QA
• [Glial Glycocalyx Remodeling Therapy](/hypothesis/h-c35493aa) — <span style="color:#ffd54f;font-weight:600">0.58</span> · Target: HSPG2
• [Ephrin-B2/EphB4 Axis Manipulation](/hypothesis/h-e6437136) — <span style="color:#ffd54f;font-weight:600">0.56</span> · Target: EPHB4
• [Netrin-1 Gradient Restoration](/hypothesis/h-05b8894a) — <span style="color:#ffd54f;font-weight:600">0.44</span> · Target: NTN1

Related Analyses:

• [4R-tau strain-specific spreading patterns in PSP vs CBD](/analysis/SDA-2026-04-01-gap-005) &#x1f504;

Pathway Diagram

The following diagram shows the key molecular relationships involving Gosuranemab (BIIB092) PSP Trial discovered through SciDEX knowledge graph analysis: