BIIB080 (MAPTRx) ASO Therapy for PSP

BIIB080 (MAPTRx) Antisense Oligonucleotide Therapy for Progressive Supranuclear Palsy

Overview

BIIB080 (formerly known as MAPTRx) is an antisense oligonucleotide (ASO) therapeutic developed by Biogen in collaboration with Ionis Pharmaceuticals that targets the MAPT gene to reduce production of tau protein. This novel approach aims to treat Progressive Supranuclear Palsy (PSP) and other tauopathies by directly addressing the underlying cause of tau pathology rather than just managing symptoms.

Mechanism of Action

BIIB080 (MAPTRx) Antisense Oligonucleotide Therapy for Progressive Supranuclear Palsy

Overview

BIIB080 (formerly known as MAPTRx) is an antisense oligonucleotide (ASO) therapeutic developed by Biogen in collaboration with Ionis Pharmaceuticals that targets the MAPT gene to reduce production of tau protein. This novel approach aims to treat Progressive Supranuclear Palsy (PSP) and other tauopathies by directly addressing the underlying cause of tau pathology rather than just managing symptoms.

Mechanism of Action

BIIB080 is a gapmer antisense oligonucleotide designed to bind to MAPT messenger RNA (mRNA) and induce RNase H-mediated degradation. This reduces the translation of tau protein from the MAPT gene, thereby lowering total tau production in the brain.

ASO Design

• Chemistry: 5-10-5 gapmer configuration with constrained ethyl (cEt) modifications
• Target: Pre-mRNA splice sites and coding sequences of MAPT
• Delivery: Intrathecal (lumbar puncture) administration to achieve CNS penetration
• Mechanism: RNase H cleavage of RNA-DNA hybrid, preventing translation

Pharmacokinetics

• Distribution throughout the CNS following intrathecal delivery
• Half-life allowing sustained reduction in tau production
• Dose-dependent effects on CSF tau biomarkers

Clinical Trial Program

Phase 1 Study (NCT02459886)

Key Findings:

• Dose-dependent reduction in CSF total tau and phosphorylated tau
• Generally well-tolerated with manageable adverse events
• Target engagement confirmed via biomarker responses

Phase 1b/2a Study in PSP

• Safety and tolerability of multiple ascending doses
• Dose-response relationships for tau lowering
• Clinical outcome measures including [PSP Rating Scale](/diagnostics/clinical-assessment-scales)
• CSF biomarker changes as pharmacodynamic markers

• Randomized, double-blind, placebo-controlled
• Multiple dose cohorts
• 12-month treatment period with follow-up

2026 Clinical Outcome Results

New exploratory analyses from the Phase 1b long-term extension study in Alzheimer's disease were published in Nature Aging (February 2026)[@nataging2026], providing additional evidence for BIIB080's disease-modifying potential:

Key Findings:

• Cognitive Benefit: Consistent trend of slowed decline on cognitive, functional, and global measures favoring high-dose BIIB080 (60 mg or 115 mg)
• Tau PET Reduction: Reductions from baseline in brain neurofibrillary tangles measured with tau PET supported these clinical trends
• Clinical Assessments: CDR, MMSE, FAQ, and RBANS showed favorable trends in treatment groups

Biomarker Data

CSF Total Tau

• Significant dose-dependent reduction from baseline
• Reductions of 30-60% observed at highest doses
• Sustained effect throughout treatment period

CSF Phosphorylated Tau (p-tau181, p-tau217)

• Modest reductions compared to total tau
• May reflect decreased production of all tau isoforms
• Potential for disease modification endpoint

Tau PET Imaging

• Exploratory assessments to measure tau burden
• Investigational to confirm brain tau lowering

Comparison to Other Tau-Targeted Approaches

| Approach | Mechanism | Stage | Advantages | Limitations |
|----------|-----------|-------|------------|-------------|
| BIIB080 (ASO) | Reduce tau production | Phase 1/2 | Direct targeting of root cause | Invasive delivery |
| Anti-tau antibodies | Passive immunization | Phase 3 | Less invasive | Peripheral clearance |
| Tau aggregation inhibitors | Prevent fibril formation | Phase 1/2 | Oral small molecule | Efficacy unclear |
| Microtubule stabilizers | Preserve neuronal transport | Phase 2 | Targets downstream effects | Limited specificity |

Unique Advantages of ASO Approach

Tau Biology in Neurodegeneration

Tau Protein and Its Role

Tau is a microtubule-associated protein encoded by the MAPT (Microtubule-Associated Protein Tau) gene located on chromosome 17q21.31[@mapttau2024]. In the healthy brain, tau functions to stabilize microtubules, which are essential for axonal transport and neuronal connectivity. Six tau isoforms are expressed in the adult human brain, ranging from 352 to 441 amino acids, generated through alternative splicing of exon 2, exon 3, and exon 10.

The tau protein contains multiple phosphorylation sites (approximately 85 serine/threonine residues and 5 tyrosine residues) that regulate its binding to microtubules. Under physiological conditions, tau phosphorylation is tightly regulated by a balance between kinases (such as GSK-3β, CDK5, and MAPK) and phosphatases (including PP2A). This dynamic regulation allows tau to respond to cellular signals and maintain microtubule stability[@tau2023].

Tau Pathology in Tauopathies

In Alzheimer's disease and related tauopathies, tau becomes hyperphosphorylated and aggregates into neurofibrillary tangles (NFTs), neuropil threads, and dystrophic neurites. This pathological transformation involves:

The progression of tau pathology follows a predictable pattern in AD, beginning in the entorhinal cortex and hippocampus (Braak stages I-III) before spreading to adjacent cortical regions (Braak stages IV-VI). This hierarchical spread correlates with cognitive decline[@tau2023].

Tau Propagation Mechanisms

Tau pathology exhibits prion-like properties, with aggregated tau capable of spreading between neurons and brain regions[@tau2023]. This propagation occurs through:

• Cell-to-cell Transfer: Pathological tau can be released from neurons via exocytosis or extracellular vesicles and taken up by neighboring cells
• Trans-synaptic Spread: Tau may travel along neuronal connections, explaining the pattern of pathological progression
• Template-driven Aggregation: Exogenous pathological tau can template the misfolding of endogenous tau

Antisense Oligonucleotide Technology

ASO Mechanism of Action

Antisense oligonucleotides are single-stranded DNA analogs that can modulate gene expression through multiple mechanisms[@asoneuro2024]. BIIB080 employs RNase H-dependent degradation, which requires:

Gapmer Chemistry

BIIB080 utilizes a "gapmer" design consisting of a central DNA "gap" flanked by modified RNA nucleotides[@rnanai2024]:

• Central Gap (10 nucleotides): DNA residues that support RNase H cleavage
• Flanking Regions (5 nucleotides each): Modified with constrained ethyl (cEt) chemistry for enhanced binding affinity and nuclease resistance
• Phosphorothioate Backbone: Provides stability against nucleases while maintaining RNase activity

CNS Delivery Strategy

The delivery of ASOs to the central nervous system presents unique challenges[@brainsampling2024]. BIIB080 uses intrathecal administration to bypass the blood-brain barrier:

• Direct CNS Access: Intrathecal injection delivers ASO directly into the cerebrospinal fluid
• Distribution: ASO distributes throughout the brain and spinal cord via CSF circulation
• Cellular Uptake: ASO enters neurons and glia through receptor-mediated endocytosis and fluid-phase pinocytosis
• Sustained Exposure: The half-life of ASO in CSF allows for monthly or less frequent dosing

• Convection-enhanced delivery for improved distribution
• Focused ultrasound-mediated blood-brain barrier opening
• AAV-mediated gene therapy for lasting expression

Clinical Development Program

Phase 1 Study Design (NCT02459886)

The first-in-human study of BIIB080 employed a classic dose-escalation design to evaluate safety, tolerability, and pharmacokinetics:

Part A (Healthy Volunteers):

• Single ascending dose cohorts
• Safety and tolerability up to 10 mg
• Pharmacokinetic sampling in plasma and CSF

• Multiple ascending dose cohorts
• Multiple dose administration over 12 weeks
• CSF biomarker assessments for target engagement

• 10 mg, 20 mg, 40 mg, 60 mg, 85 mg, 115 mg (single or multiple doses)

Phase 1b/2a Study in PSP

The ongoing Phase 1b/2a study (NCT04144191) specifically enrolls patients with PSP:

Study Population:

• Diagnosis of PSP (Richardson syndrome or other PSP variants)
• Age 40-80 years
• MMSE ≥20
• Able to undergo lumbar puncture

• Randomized, double-blind, placebo-controlled
• Multiple dose cohorts
• 12-month treatment period with 12-month follow-up

• Primary: Safety and tolerability
• Secondary: CSF tau reduction, PSP Rating Scale change
• Exploratory: Tau PET, volumetric MRI

Long-Term Extension Results

The 2026 Nature Aging publication reported 18-month follow-up data from the Phase 1b long-term extension[@nataging2026]:

Cognitive Outcomes:

• High-dose BIIB080 (60 mg and 115 mg) showed slowed decline on ADCOMS
• CDR-SB demonstrated less progression in treatment groups
• MMSE scores remained more stable with active treatment

• CSF total tau reduction correlated with cognitive preservation
• Tau PET showed trends toward reduced NFT burden
• These biomarker-clinical correlations support disease modification

Progressive Supranuclear Palsy as Target Indication

PSP Disease Background

Progressive Supranuclear Palsy (PSP) is a 4R tauopathy characterized by:

• Accumulation of insoluble tau aggregates in neurons and glia
• Predominant involvement of subcortical structures (basal ganglia, brainstem)
• Progressive supranuclear gaze palsy, parkinsonism, and cognitive decline
• Mean survival of 6-9 years from symptom onset

Tau Pathology in PSP

Unlike AD where 3R and 4R tau isoforms are both present in NFTs, PSP predominantly involves 4R tau isoforms. The tau aggregates in PSP exhibit distinct morphological characteristics:

• Globose NFTs: Small, round tangles in subcortical nuclei
• Tufted Astrocytes: Astrocytic tau pathology unique to PSP
• Coiled Bodies: Oligodendroglial tau inclusions

Unmet Medical Need

PSP represents a significant unmet medical need:

• No FDA-approved disease-modifying therapies exist
• Current treatments only address symptoms
• Rapid progression leads to severe disability
• PSP accounts for approximately 5% of parkinsonian disorders

Competitive Landscape

Tau-Targeting Therapeutic Approaches

The tau targeting field has evolved to include multiple therapeutic modalities:

| Therapeutic Category | Examples | Mechanism | Development Stage |
|---------------------|----------|-----------|------------------|
| ASOs | BIIB080 | Reduce tau production | Phase 1/2 |
| Anti-tau antibodies | Gosuranemab, Tilavonemab | Clear extracellular tau | Phase 2 |
| Tau aggregation inhibitors | LMTM, methylene blue | Prevent fibril formation | Phase 3 |
| Microtubule stabilizers | Davunetide, BMS-986241 | Preserve tau function | Phase 2 |
| Kinase inhibitors | Tau-aggregation inhibitors | Reduce phosphorylation | Preclinical |

ASO vs Antibody Approaches

Comparing ASO and antibody approaches reveals distinct profiles:

ASO Advantages:

• Intracellular target engagement (reduces intracellular tau)
• Sustained duration with less frequent dosing
• Lower immunogenicity risk
• May be cost-effective for chronic administration

• Less invasive administration (subcutaneous or IV)
• Established regulatory pathway
• Broader patient access

Emerging Competition

Multiple companies are developing tau-targeting ASOs:

• Ionis/Biogen have BIIB080 in the lead
• Other ASO programs targeting MAPT are in earlier development
• Small interfering RNA (siRNA) approaches are also being explored

Regulatory Considerations

Accelerated Approval Pathway

The FDA's accelerated approval pathway may be relevant for BIIB080 in PSP:

Biomarker-Based Approval:

• CSF tau reduction as surrogate endpoint
• Requires confirmation of clinical benefit post-approval

• FDA has approved ASO therapies for other neurological diseases (nusinersen, tofersen)
• EMA has also granted positive opinions for CNS ASOs

Registration Trial Requirements

Confirmatory trials for PSP would likely require:

• Randomized, placebo-controlled design
• Clinically meaningful primary endpoint (PSP-RS)
• Adequate sample size and duration
• Patient-relevant functional outcomes

Orphan Drug Designation

PSP may qualify for orphan drug designation:

• Rare disease affecting <200,000 patients in US
• Potential for priority review and extended exclusivity
• Regulatory support for small population trials

Future Development Directions

Combination Approaches

Future studies may explore combination strategies:

• ASO + Anti-tau Antibody: Combined intracellular and extracellular targeting
• ASO + Small Molecule: Add symptomatic benefits to disease modification
• ASO + Immunomodulation: Address neuroinflammation alongside tau reduction

Biomarker Development

Continued biomarker development is critical:

• Tau PET: Validate tau PET as patient selection tool
• Neurofilament Light Chain (NfL): Monitor neurodegeneration progression
• Genetic Markers: Identify patients who may benefit most from treatment

Earlier Intervention

Preventive intervention in at-risk populations:

• Genetic testing for MAPT mutations
• Biomarker screening for pre-symptomatic tau pathology
• Clinical trial designs for prodromal PSP

Regulatory Strategy

Development timeline considerations:

• 2026-2027: Complete Phase 1b/2a in PSP
• 2028: Initiate registration trial
• 2030-2031: Potential FDA approval

Challenges and Considerations

Delivery Route

Biomarker Validation

Optimal Timing

Cross-Linked Pages

• [Tau Pathology Pathway](/mechanisms/tau-pathology)
• [Tauopathies](/diseases/tauopathies)
• [Tau-Targeted Therapeutics](/therapeutics/tau-therapies-pipeline)
• [Antisense Oligonucleotide Therapy](/mechanisms/antisense-oligonucleotide-therapy)
• [ASO Brain Delivery](/mechanisms/aso-brain-delivery)
• [Progressive Supranuclear Palsy](/diseases/progressive-supranuclear-palsy)
• [MAPT Gene](/genes/mapt)
• [Tau Protein](/proteins/tau)
• [Biogen](/companies/biogen)
• [CSF Total Tau Biomarker](/biomarkers/csf-total-tau)
• [Phosphorylated Tau 181](/biomarkers/phosphorylated-tau-181)
• [Phosphorylated Tau 217](/biomarkers/phosphorylated-tau-217)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)

External Links

• [ClinicalTrials.gov: NCT02459886](https://clinicaltrials.gov/study/NCT02459886)
• [PubMed](https://pubmed.ncbi.nlm.nih.gov/)

References

Related Hypotheses

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

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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 BIIB080 (MAPTRx) ASO Therapy for PSP discovered through SciDEX knowledge graph analysis: