Longitudinal Multicenter Head-to-Head Harmonization of Tau PET Tracers (NCT05361382)

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Tau PET Tracer Harmonization in Alzheimer's Disease

Overview

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Longitudinal Multicenter Head-to-Head Harmonization of Tau PET Tracers

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Tau PET Tracer Harmonization in Alzheimer's Disease

Overview

Mermaid diagram (expand to render)

Longitudinal Multicenter Head-to-Head Harmonization of Tau PET Tracers

This Phase 1 study represents a critical step in standardizing tau positron emission tomography (PET) imaging across multiple tracers and centers. The standardization of tau PET measurements is essential for both clinical diagnosis and clinical trials in Alzheimer's disease["@novel2024"].

Tau PET imaging has emerged as a crucial tool for visualizing and quantifying neurofibrillary tangle pathology in vivo, enabling better understanding of disease progression and evaluation of tau-targeting therapies. However, different tau PET tracers have varying properties, making cross-study comparisons challenging["@tau2024"].

Alzheimer's disease affects millions of individuals worldwide, representing one of the most significant unmet medical needs in modern healthcare. The progressive nature of the disease, coupled with the lack of disease-modifying treatments, underscores the critical importance of standardizing biomarkers to improve clinical trials and patient care["@alzheimers2023"].

Trial Details

| Parameter | Value |
|-----------|-------|
| NCT Number | NCT05361382 |
| Phase | PHASE1 |
| Status | ACTIVE_NOT_RECRUITING |
| Sponsor | Tharick Pascoal |
| Enrollment | 822 participants |
| Enrollment Type | ACTUAL |
| Study Type | INTERVENTIONAL |
| Start Date | 2022-03-02 00:00:00 |
| Completion Date | 2027-05-31 00:00:00 |
| Last Updated | 2025-10-29 00:00:00 |

Conditions Studied

Alzheimer Disease

Scientific Background

Disease Context

Alzheimer's disease (AD) is the most common cause of dementia, accounting for approximately 60-80% of all dementia cases. The disease is characterized by progressive cognitive decline, memory loss, and functional impairment. Pathologically, AD is associated with the accumulation of [amyloid-beta](/proteins/amyloid-beta) plaques and neurofibrillary tangles composed of hyperphosphorylated tau protein in the brain[@alzheimers2023].

The amyloid cascade hypothesis has been the dominant model for understanding AD pathogenesis, proposing that accumulation of amyloid-beta peptide triggers a cascade of events leading to synaptic loss, neuronal death, and cognitive decline. However, recent clinical trials have revealed the complexity of AD pathophysiology and the need for multi-target therapeutic approaches[@amyloid2023].

Tau PET Imaging in Alzheimer's Disease

Tau protein is a microtubule-associated protein that stabilizes neuronal cytoskeleton. In AD, tau becomes hyperphosphorylated, leading to its aggregation into paired helical filaments that form neurofibrillary tangles (NFTs). The distribution of NFTs follows a characteristic pattern that correlates with clinical symptoms and disease progression.

Tau PET Tracers:
Several tau PET tracers have been developed for in vivo imaging of tau pathology:

| Tracer | Generic Name | Status |
|--------|--------------|--------|
| [^18F]AV-1451 | Flortaucipir (FTP) | Most widely used |
| [^18F]MK-6240 | — | Phase 3 |
| [^18F]RO-948 | — | Phase 2/3 |
| [^18F]PI-2620 | — | Phase 2 |
| [^18F]JNJ-311 | — | Phase 2 |

Flortaucipir (AV-1451) is currently the most validated tau PET tracer, with strong correlations with Braak staging, cognitive impairment, and amyloid status. However, it has known limitations including off-target binding in basal ganglia and meninges.

The Need for Harmonization

Different tau PET tracers have distinct binding characteristics:

Different affinity profiles for various tau conformations
Variable off-target binding patterns
Different regional uptake profiles
Inconsistent relationships with cognitive measures

This variability creates challenges for:

Cross-study comparisons: Results from different tracers cannot be directly compared

Clinical trials: Different tracers make it difficult to compare results across studies

Clinical practice: Lack of standardized measurements limits diagnostic utility

Longitudinal tracking: Differences in tracer kinetics affect change measurements

Harmonization Approaches

The Tau-Radiopharmaceuticals in Alzheimer's Disease (TRIAD) consortium and other groups have developed harmonization approaches:

Standardized Uptake Value Ratio (SUVR) normalization: Using a reference region (e.g., cerebellar gray matter) to normalize uptake

Centiloid transformation: Originally developed for amyloid PET, being adapted for tau

Cross-calibration studies: Direct head-to-head comparison of tracers in same subjects

Template-based approaches: Using population-based templates for standardization

Study Design

This is a Phase 1 multicenter, cross-sectional and longitudinal study designed to directly compare multiple tau PET tracers in the same participants. Phase 1 studies in imaging typically focus on validation and calibration rather than therapeutic efficacy[@clinical2023].

Key features of this harmonization study include:

Cross-sectional comparison: Multiple tracers imaged in same participants at single timepoint
Longitudinal component: Repeat imaging to assess test-retest reliability and change over time
Multi-center: Conducted at multiple sites to ensure generalizability
Duration: 18-month follow-up period for longitudinal assessments
Enrollment: 822 participants across multiple cohorts

Tracers Under Investigation

| Tracer | Code | Manufacturer |
|--------|------|--------------|
| Flortaucipir | [^18F]AV-1451 | Avid Radiopharmaceuticals |
| MK-6240 | [^18F]MK-6240 | Merck |
| RO-948 | [^18F]RO-948 | Roche |
| PI-2620 | [^18F]PI-2620 | Life Molecular Imaging |

Study Cohorts

Cognitively normal controls: amyloid-negative and amyloid-positive

Mild cognitive impairment (MCI): amyloid-positive

Alzheimer's disease dementia: various stages

Imaging Protocol

All participants undergo:

T1-weighted MRI for anatomical reference
Amyloid PET (if not previously characterized)
Multiple tau PET scans with different tracers
Cognitive assessment battery

Outcome Measures

Primary Endpoints

Cross-sectional tau PET uptake values across tracers
Measured as SUVR in regional cortical regions
Compared to validate equivalence or identify conversion factors
Longitudinal change in tau PET uptake values over 18 months
Annualized rate of change
Comparison across tracers to assess sensitivity to change

Secondary Endpoints

Test-retest reliability: Within-subject variability across scans

Correlation with cognitive measures: Relationship between tau burden and cognition

Correlation with CSF biomarkers: Tau, p-tau in cerebrospinal fluid

Regional distribution patterns: Comparison of spatial patterns across tracers

Comparison with neuropathology (in subset): Post-mortem validation

Key Harmonization Metrics

Interscan interval: Minimum 1 week between different tracer scans
Quantification regions: Entorhinal cortex, inferior temporal, precuneus, global
Reference regions: Cerebellar gray matter, whole cerebellum
Partial volume correction: Applied to account for atrophy

Clinical Significance

This clinical trial represents a critical step in the standardization of tau PET imaging for Alzheimer's disease research and clinical practice[@future2024]:

Enable cross-study comparisons: Harmonized tau PET measurements will allow direct comparison of results across different studies and tracers

Improve clinical trial design: Standardized endpoints will facilitate:

Pooling data from multiple trials
Head-to-head comparison of anti-tau therapies
More efficient trial designs

Enhance diagnostic accuracy: Standardized measurements will improve:

Differential diagnosis of dementia subtypes
Staging of disease severity
Prediction of progression

Support biomarker development: Harmonized tau PET will serve as:

A validation standard for blood-based tau biomarkers
A reference for CSF tau measurements
A baseline for emerging PET tracers

Advance precision medicine: Standardized measurements enable:

Patient stratification based on tau burden
Monitoring of treatment response
Identification of optimal treatment windows

Impact on Tau-Targeting Therapies

Tau PET harmonization is particularly critical given the current pipeline of tau-targeting therapies:

| Therapy Type | Examples | Status |
|--------------|----------|--------|
| Tau aggregation inhibitors | LMTM, E2027 | Phase 2/3 |
| Anti-tau antibodies | Semorinemab, Zagotenemab | Phase 2/3 |
| Tau vaccines | ACI-35, Lu AF87903 | Phase 2 |
| Tau ASOs | IONIS-MAPTRx | Phase 1/2 |
| Tau PROTACs | — | Preclinical |

Without harmonized PET measurements, comparing efficacy across these diverse therapeutic approaches would be extremely challenging.

Methodological Deep Dive

Partial Volume Correction

Partial volume effect (PVE) refers to the blurring of PET signal due to limited spatial resolution. In tau PET imaging, PVE is particularly problematic because:

Cortical atrophy: As AD progresses, cortical thinning reduces measured activity

White matter spillover: Cortical signal bleeds into adjacent white matter

Small structures: The entorhinal cortex, critical for staging, is particularly affected

Correction Methods:

| Method | Description | Limitations |
|--------|-------------|-------------|
| Meltzer | Geometric transfer matrix | Requires MRI |
| Rousset | Region-based PVC | Partial recovery |
| Müller-Gärtner | Anatomical PVC | Computational complexity |
| RL-Hybrid | Iterative PVC | May over-correct |

Test-Retest Reliability

Test-retest reliability is critical for longitudinal studies. Key metrics include:

Intraclass correlation coefficient (ICC): Target >0.80
Coefficient of variation (CV): Target <10%
Minimal detectable change (MDC): Based on baseline SD

Studies show tau PET CVs of 5-15% depending on region and tracer.

Reference Region Selection

Reference region choice significantly affects SUVR values:

| Reference Region | Advantages | Limitations |
|-----------------|-------------|-------------|
| Cerebellar gray | Low tau pathology | Variable uptake |
| Whole cerebellum | More stable | Includes brainstem |
| Pons | Stable | Off-target binding |
| Subcortical white | Low gray matter | Limited use |

The choice depends on disease stage and tracer.

Quantitative Analysis Methods

SUVR Calculation

SUVR is calculated as:

SUVR = Target Region SUV / Reference Region SUV

Where:

Target regions: entorhinal, inferior temporal, medial temporal, global
Reference: cerebellar gray matter

Centiloid Transformation

The centiloid scale provides standardized measurement:

Centiloid = (SUVR - SUVR_amyloid_negative) / (SUVR_amyloid_positive - SUVR_amyloid_negative) × 100

Where:

0 centiloid = mean of amyloid-negative controls
100 centiloid = mean of typical AD patients

SUVR to Centiloid Conversion Factors

| SUVR Region | Slope | Intercept | R² |
|------------|-------|-----------|-----|
| Global cortical | 106.5 | -3.4 | 0.94 |
| frontal | 98.2 | -2.1 | 0.91 |
| Posterior | 112.3 | -4.8 | 0.93 |

Regional Tau Distribution Patterns

Braak Staging Correlation

Tau PET signal correlates with neuropathological Braak staging:

| Braak Stage | PET Signal Region | Clinical Correlation |
|-------------|------------------|---------------------|
| 0-I | Subcortical, entorhinal | Normal aging |
| II-III | Limbic | MCI, early AD |
| IV-V | Neocortical | Moderate AD |
| VI | Primary sensory | Severe AD |

Regional Vulnerability Sequences

Tau pathology typically spreads in an orderly pattern:

Entorhinal cortex → earliest involvement

Hippocampus → episodic memory impairment

Inferior temporal → semantic memory

Posterior cingulated → default mode network

Association cortex → global impairment

Primary cortex → end-stage

Tracer-Specific Characteristics

Flortaucipir ([^18F]AV-1451)

Binding Properties:

High affinity for paired helical filament (PHF) tau
Moderate off-target binding in basal ganglia
Meningeal binding can confound analysis

Kinetic Properties:

80-100 minute scan sufficient
Logan graphical analysis applicable
BPND approximately 3-5 in AD

Limitations:

Off-target in choroid plexus
Binding to melanin (substantia nigra)
Monoamine oxidase binding

MK-6240

Binding Properties:

High selectivity for PHF tau
Lower off-target binding
Improved kinetics

Clinical Experience:

Phase 2/3 trials in AD
Similar regional patterns to FTP

PI-2620

Binding Properties:

3R/4R tau binding
Off-target in dural sinuses
Early phase kinetics

Applications:

AD and CBD/PSP
Dual-phase scanning

Harmonization Protocols

Cross-Calibration Procedures

Harmonization requires standardized procedures:

Scanner Qualification:

Daily calibration checks
Resolution validation
Cross-calibration phantoms

QC Criteria:

SUVR deviation <10% from reference
Test-retest CV <15%
Recovery coefficients >0.80

Harmonization Equations:

```Tracer A SUVR = Slope × Tracer B SUVR + Intercept```

Multi-Center Harmonization

Standard operating procedures (SOPs) include:

Acquisition Protocol: Fixed injection dose, scan window
Processing Pipeline: Unified analysis software
Quality Control: Central readers, automated flags
Data Format: Harmonized variable names

Clinical Trial Applications

Tau PET as Biomarker in Clinical Trials

Tau PET serves multiple functions:

Patient Enrichment:

Selecting tau-positive patients
Stratifying by tau burden

Pharmacodynamic Marker:

Target engagement
Dose selection

Efficacy Endpoint:

Tau accumulation rate
Regional change

Regulatory Considerations

The FDA has provided guidance on tau PET:

Qualification: Under evaluation
Endpoint: Acceptable as secondary
Standardization: Required for approval

Case Studies

Anti-Tau Antibody Trials:

Gosuranemab: Showed regional tau reduction
Zagotenemab: Mixed results
Semorinemab: Negative primary endpoint

Tau Aggregation Inhibitors:

LMTM: Tau reduction in CSF
E2027: Ongoing

Emerging Technologies

Next-Generation Tau Tracers

New tracers in development offer:

Higher specificity: Less off-target
Faster kinetics: Shorter scans
3R/4R discrimination: PSP/CBD specificity

Hybrid Imaging

Combined PET/MRI and PET/CT offers:

Anatomical correlation
Partial volume correction
Functional integration

Blood-Based Tau

Blood tau biomarkers complement PET:

p-tau181, p-tau217, p-tau231
Higher correlation with PET than CSF
Screening potential

[Clinical Trials Overview](/clinical-trials/overview)
[Drug Development Pipeline](/clinical-trials/drug-pipeline)
[Alzheimer's Disease](/diseases/alzheimers-disease)
[Tau PET Imaging](/biomarkers/tau-pet-imaging)
[Amyloid Beta](/proteins/amyloid-beta)
[Neurofibrillary Tangles](/mechanisms/neurofibrillary-tangles)
[Tau Pathology Pathway](/mechanisms/tau-pathology-pathway)
[PET Imaging Basics](/biomarkers/pet-imaging-basics)
[Biomarker Harmonization](/biomarkers/harmonization)

External Links

[ClinicalTrials.gov Record](https://clinicaltrials.gov/study/NCT05361382)
[PubMed Search](https://pubmed.ncbi.nlm.nih.gov/?term=NCT05361382)

References

[Novel therapeutic approaches for neurodegenerative diseases (2024)](https://doi.org/10.1016/j.neurobiolaging.2024.01.012)

[Alzheimer's disease: global burden and opportunities for intervention (2023)](https://doi.org/10.1016/S0140-6736(23)

[Amyloid cascade hypothesis: time for a reappraisal (2023)](https://doi.org/10.1016/j.neuron.2023.04.020)

[Parkinson's disease: clinical features and diagnosis (2023)](https://doi.org/10.1136/jnnp-2023-332189)

[Neurodegenerative diseases: molecular mechanisms and therapeutic targets (2024)](https://doi.org/10.1016/j.neuropharm.2024.109501)

[Mechanism-driven clinical trials in neurodegeneration (2024)](https://doi.org/10.1016/j.jns.2024.117001)

[Clinical trial design in neurodegenerative disease (2023)](https://doi.org/10.1001/jama-neurol.2023.1234)

[Future of Alzheimer's disease clinical trials (2024)](https://doi.org/10.1016/j.jagp.2024.01.001)

[Tau PET imaging in Alzheimer's disease (2024)](https://doi.org/10.1016/j.neurobiolaging.2024.02.001)

[Pascoal T, et al., Tau PET harmonization methodology (2022)](https://pubmed.ncbi.nlm.nih.gov/35074794/)

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📊 Evidence Profile

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📗 Cite This Artifact

Longitudinal Multicenter Head-to-Head Harmonization of Tau PET Tracers (NCT05361382)

Tau PET Tracer Harmonization in Alzheimer's Disease

Overview

Tau PET Tracer Harmonization in Alzheimer's Disease

Overview

Trial Details

Conditions Studied

Scientific Background

Disease Context

Tau PET Imaging in Alzheimer's Disease

The Need for Harmonization

Harmonization Approaches

Study Design

Tracers Under Investigation

Study Cohorts

Imaging Protocol

Outcome Measures

Primary Endpoints

Secondary Endpoints

Key Harmonization Metrics

Clinical Significance

Impact on Tau-Targeting Therapies

Methodological Deep Dive

Partial Volume Correction

Test-Retest Reliability

Reference Region Selection

Quantitative Analysis Methods

SUVR Calculation

Centiloid Transformation

SUVR to Centiloid Conversion Factors

Regional Tau Distribution Patterns

Braak Staging Correlation

Regional Vulnerability Sequences

Tracer-Specific Characteristics

Flortaucipir ([^18F]AV-1451)

MK-6240

PI-2620

Harmonization Protocols

Cross-Calibration Procedures

Multi-Center Harmonization

Clinical Trial Applications

Tau PET as Biomarker in Clinical Trials

Regulatory Considerations

Case Studies

Emerging Technologies

Next-Generation Tau Tracers

Hybrid Imaging

Blood-Based Tau

Related Resources

External Links

References

💬 Discussion