This experiment addresses the critical knowledge gap: "Why have anti-tau therapies failed in PSP despite strong biological rationale?" (Rank #10, PSP Knowledge Gaps). Multiple anti-tau antibody trials have failed in PSP, including gosuranemab (TANGOS) and tilavonemab, despite compelling preclinical data. This experiment will systematically investigate the mechanisms of these failures to inform next-generation therapeutic development.
Anti-tau antibody failures in PSP result from one or more of the following mechanisms:
- Wrong target: Antibodies target epitopes not primarily involved in 4R-tau pathogenic spreading
- Wrong compartment: Extracellular antibodies fail to reach intracellular tau where pathology initiates
- Wrong timing: Treatment begins too late in disease progression when neurodegeneration is irreversible
- Wrong mechanism: Antibodies clear tau without addressing upstream drivers of 4R-tau production
- Characterize tau species in PSP patient CSF and brain tissue — determine which tau fragments are pathogenic and whether current antibodies target them
- Map tau distribution in PSP brain — compare extracellular vs. intracellular tau, and neuron vs. oligodendrocyte tau
- Test whether anti-tau antibodies can engage pathological tau in PSP brain — ex vivo binding studies
- Identify biomarkers predicting anti-tau therapy response — develop patient stratification tools
Sample: Post-mortem brain tissue from 20 PSP patients (Richardson's syndrome, PSP-P variants) and 10 age-matched controls
Analyses:
- Sequential extraction (RIPA, formic acid) to separate soluble, membrane-bound, and insoluble tau fractions
- SDS-PAGE and western blot to characterize tau isoforms (4R vs. 3R/4R ratio)
- ELISA for specific tau fragments (N-terminal, mid-domain, C-terminal, phosphorylated at Ser202, Thr181, Ser396/404)
- immunohistochemistry for tau distribution (neuronal, oligodendroglial, extracellular)
- Electron microscopy for tau filament structure
Expected output: Detailed tau species catalog in PSP brain
¶ Phase 2: Antibody Epitope Mapping
Antibodies to test:
- Gosuranemab (N-terminal anti-tau)
- Tilavonemab (mid-domain anti-tau)
- Semorinemab (central domain)
- E2814 (MTBR-domain, in clinical trials)
- Posdinemab (phospho-tau specific)
Method:
- Dot blot with synthetic tau peptides spanning full-length tau
- Surface plasmon resonance (SPR) for binding kinetics
- Cryo-EM to visualize antibody-FAB binding to PSP-derived tau filaments
- Competition assays to determine epitope overlap
Expected output: Epitope map showing which antibodies recognize which PSP tau species
¶ Phase 3: Ex Vivo Antibody Engagement
Method:
- Incubate fresh frozen PSP brain sections with each antibody
- Image using confocal microscopy to quantify antibody penetration and binding
- Compare to antibody binding in AD brain (where antibodies have shown efficacy)
- Test whether adding permeabilization or enzymatic treatment improves binding
Expected output: Determine whether antibody access to pathological tau is a limiting factor
Samples: CSF and plasma from 100 PSP patients, 50 PD patients, 50 controls
Biomarkers to measure:
- Total tau, p-tau181, p-tau217, p-tau205
- NfL, GFAP
- Tau种子 (RT-QuIC or PMCA)
- Tau proteoforms (capillary electrophoresis)
Correlate with:
- Clinical severity (PSPRS, MoCA)
- Disease duration
- MRI atrophy patterns
Expected output: Biomarker panel predicting which patients might respond to which anti-tau mechanism
- iPSC-derived neurons from PSP patients (MAPT mutations P301S, S305I)
- iPSC-derived oligodendrocytes (relevant for coiled body pathology)
- Organoid models with 4R-tau pathology
- PS19 mice (P301S tau) — test antibody efficacy
- AAV-mediated 4R-tau overexpression in mice — test timing effects
- Non-human primates for translational studies
- Catalog of pathogenic tau species in PSP — enabling rational antibody design
- Epitope mapping of failed and current antibodies — guiding selection of optimal targets
- Mechanistic understanding of failure — whether timing, target, or compartment is the key factor
- Biomarker panel for patient stratification — enabling enrichment of trials with likely responders
| Dimension |
Score |
Rationale |
| Mechanistic Impact |
10 |
Will directly explain why billions invested in anti-tau trials failed |
| Cure Proximity |
9 |
Enables rational next-generation trial design |
| Feasibility |
7 |
Requires PSP brain tissue, which is available through brain banks |
| Cost Efficiency |
8 |
Leverages existing failed trial materials and data |
| Timeline |
8 |
Can begin within 6 months; 24-month primary analysis |
| Cross-Disease Value |
9 |
Findings apply to CBD, AD, and other tauopathies |
| Biomarker Enablement |
10 |
Directly enables biomarker-driven trial design |
| Combinability |
8 |
Compounds with other experiments (tau spreading, oligodendrocyte function) |
| De-risking Value |
10 |
Critical for avoiding another failed $500M Phase 3 trial |
| Novelty |
9 |
First systematic analysis of anti-tau failure mechanisms |
Total Score: 78/100
| Component |
Cost |
| Brain tissue acquisition (20 PSP, 10 control) |
$50,000 |
| Biochemical analyses |
$80,000 |
| Antibody testing and epitope mapping |
$60,000 |
| Cryo-EM |
$100,000 |
| Biomarker development (100 pts) |
$70,000 |
| iPSC differentiation |
$40,000 |
| Personnel (2 FTE × 2 years) |
$200,000 |
| Total |
$600,000 |
| Milestone |
Timepoint |
| Brain tissue acquired |
Month 6 |
| Phase 1 complete (tau species catalog) |
Month 12 |
| Phase 2 complete (epitope mapping) |
Month 18 |
| Phase 3 complete (ex vivo engagement) |
Month 24 |
| Phase 4 complete (biomarker panel) |
Month 30 |
| Final analysis and publication |
Month 36 |
| Risk |
Mitigation |
| Limited PSP brain tissue availability |
Partner with multiple brain banks (Mayo, UCSF, Cambridge) |
| Antibody manufacturers unwilling to share |
Use publicly available data; test biosimilars |
| Findings too late for current trials |
Publish interim results; engage pharma partners early |