Clinical Trials Overview
Introduction
Clinical trials represent the critical pathway for translating basic neuroscience discoveries into effective treatments for neurodegenerative diseases. The landscape of neurodegenerative disease clinical research has evolved dramatically over the past decade, with advances in biomarker technology, trial design innovation, and regulatory frameworks reshaping how new therapies are evaluated[@clinicaltrialsgov2024][@cummings2024].
This page provides a comprehensive overview of clinical trials in [Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease), [amyotrophic lateral sclerosis](/diseases/amyotrophic-lateral-sclerosis), and other neurodegenerative conditions. We cover trial phases, design considerations, current landscape, endpoint selection, and future directions.
Trial Phases
Phase Structure
Clinical trials proceed through sequential phases, each with distinct objectives[@battista2023]:
| Phase | Purpose | Duration | Participants | Success Rate |
|-------|---------|----------|-------------|--------------|
| Phase 1 | Safety, tolerability, dose-ranging | 6-12 months | 20-100 | ~70% |
| Phase 2 | Efficacy, dose optimization | 1-2 years | 100-300 | ~33% |
| Phase 3 | Confirmatory, comparative | 2-4 years | 1000-3000 | ~25-30% |
| Phase 4 | Post-market surveillance | Variable | Thousands | N/A |
Phase 1 trials in neurodegenerative diseases focus on establishing safety profiles, determining maximum tolerated dose, and characterizing pharmacokinetics. First-in-human studies typically enroll healthy volunteers, though some neurodegenerative disease trials enroll patients directly.
Phase 2 trials serve as the critical bridge between safety validation and efficacy demonstration. These trials employ randomized, placebo-controlled designs to identify signals of clinical benefit while optimizing dosing regimens.
Phase 3 trials provide the definitive evidence for regulatory approval, demonstrating efficacy and safety in larger populations. Recent Phase 3 trials in Alzheimer's disease have enrolled over 1,000 patients per trial, requiring global coordination across dozens of countries.
Phase 4 trials (post-marketing surveillance) continue after regulatory approval to monitor long-term safety and effectiveness in real-world populations.
| Phase | Primary Purpose | Typical Duration | Participants | Success Rate |
|-------|----------------|-----------------|--------------|--------------|
| Phase 1 | Safety, tolerability, dose-finding | 6-12 months | 20-100 healthy volunteers or patients | ~70% advance to Phase 2 |
| Phase 2 | Preliminary efficacy, dose optimization | 1-2 years | 100-300 patients | ~33% advance to Phase 3 |
| Phase 3 | Confirm efficacy, compare to standard | 2-4 years | 1,000-3,000 patients | ~25-30% achieve approval |
| Phase 4 | Post-marketing surveillance | Ongoing | Thousands | N/A |
Modern neurodegenerative disease trials increasingly employ adaptive designs that allow pre-planned modifications based on accumulating data[@meyer2023]:
- Sample size re-estimation: Adjust enrollment based on interim efficacy signals
- Dose-finding adaptations: Modify dosing regimens based on biomarker responses
- Platform trials: Test multiple therapies simultaneously under a single protocol
- Basket trials: Group patients by biomarker rather than disease diagnosis
- Seamless designs: Combine Phase 2/3 phases for accelerated development
The advent of amyloid-targeting monoclonal antibodies has particularly benefited from adaptive designs, allowing real-time dose adjustments based on amyloid-related imaging abnormalities (ARIA)[@chen2023].
Alzheimer's Disease Trials
Current Treatment Landscape
The approval of [lecanemab](/therapeutics/lecanemab) (Leqembi) in January 2023 and [donanemab](/therapeutics/donanemab) (Kisunla) in July 2024 marked a new era in Alzheimer's disease treatment. These anti-amyloid antibodies demonstrated statistically significant slowing of cognitive decline, validating the amyloid hypothesis after decades of failed attempts[@vanDyck2023][@loyle2024].
Active Phase 3 Trials
| Trial | Drug | Mechanism | Enrollment | Status |
|-------|------|-----------|------------|--------|
| TRAILBLAZER-ALZ 3 | Donanemab | Amyloid | 1800 | Completed |
| GRADUATE I/2 | Gantenerumab | Amyloid | 3000 | Terminated |
| tauB-4 | Semorinemab | Tau | 600 | Ongoing |
| ABBV-951 | ABBV-951 | Amyloid | 500 | Ongoing |
| ACI-35.18 | ACI-35.018 | Tau vaccine | 400 | Ongoing |
Amyloid-Targeting Therapies
Anti-amyloid antibodies represent the most advanced therapeutic approach in AD[@chen2023][@isselbacher2022]:
Lecanemab (Eisai/Biogen):
- Target: Aβ protofibrils
- Administration: IV infusion every 2 weeks
- Dose: 10 mg/kg
- Clinical benefit: 27% slowing of cognitive decline (CDR-SB)
- Amyloid reduction: ~80 centiloids
- ARIA-E rate: 12.6%
Donanemab (Eli Lilly):
- Target: Pyroglutamate Aβ plaques
- Administration: IV infusion every 4 weeks
- Dose: 350 mg
- Clinical benefit: 35% slowing of cognitive decline
- Amyloid reduction: ~70 centiloids
- ARIA-E rate: ~24%
Gantenerumab (Roche):
- Target: Aggregated Aβ
- Administration: SC injection every 2 weeks
- Dose: 510 mg
- Result: Did not meet primary endpoint
- Key lesson: Incomplete amyloid clearance insufficient for clinical benefit
Tau-Targeting Therapies
Tau pathology correlates more closely with cognitive decline than amyloid, making tau an attractive therapeutic target[@reim2023][@masri2024]:
Anti-tau antibodies:
- Semorinemab: Targets aggregated tau, showing slowing of tau spread
- Beprasiran: siRNA targeting tau production
- JNJ-63733657: Anti-tau antibody in Phase 2
Tau aggregation inhibitors:
- LMTM: Tau aggregation inhibitor showing mixed results
- Curcumin derivatives: Natural compounds inhibiting tau aggregation
Tau vaccines:
- ACI-35.018: Phospho-tau targeting vaccine
- AADvac1: Tau peptide vaccine
Combination Approaches
The recognition that amyloid and tau must be targeted together has driven combination therapy trials[@musiek2023]:
- Amyloid + tau dual targeting
- Multi-target approaches
- Sequential or concurrent treatment strategies
Parkinson's Disease Trials
Current Challenges
Parkinson's disease trials face unique challenges[@kalia2023][@mccrink2023]:
- Heterogeneous patient populations
- Motor fluctuations and dyskinesias
- Non-motor symptoms underappreciated
- Long disease duration before clinical manifestations
- High placebo response rates
Active Phase 3 Trials
| Trial | Drug | Mechanism | Enrollment | Status |
|-------|------|-----------|------------|--------|
| PASADENA | Prasinezumab | α-Syn | 450 | Completed |
| SPARK | Cinpanemab | α-Syn | 600 | Ongoing |
| ADVANCE | ABBV-951 | Dopamine agonist | 400 | Completed |
| CVN424 | CVN424 | GDNF | 200 | Ongoing |
Alpha-Synuclein-Targeting Therapies
Alpha-synuclein aggregation is the hallmark pathology of Parkinson's disease[@mccrink2023]:
Immunotherapies:
- Prasinezumab: Anti-α-syn antibody showing motor benefits
- Cinpanemab: Another anti-α-syn antibody in development
- ABBV-951: Engineered antibody with enhanced brain penetration
Aggregation inhibitors:
- Anle138b: Small molecule α-syn aggregation inhibitor
- SAR402671:α-syn oligomer modulator
Gene therapy approaches:
- AAV-GDNF delivery
- AADC gene therapy (viltolarsen)
Disease-Modifying Strategies
Beyond α-synuclein targeting, multiple disease-modifying approaches are under investigation:
- Neuroprotective agents: Inosine (raising urate), GLP-1 receptor agonists
- Cell replacement therapy: Stem cell-derived dopamine neurons
- Repurposed drugs: Amantadine, GLP-1 agonists (exenatide, liraglutide)
Amyotrophic Lateral Sclerosis Trials
ALS Trial Landscape
ALS remains one of the most challenging neurodegenerative diseases to treat, with only two disease-modifying therapies approved (riluzole and edaravone)[@bhattacharya2023][@gillman2023]:
Active Registration Trials
| Trial | Drug | Mechanism | Sites | Status |
|-------|------|-----------|-------|--------|
| HEALEY ALS | Multiple | Platform | 50+ | Ongoing |
| HEAT | Edaravone+ | Antioxidant | 380 | Ongoing |
| RESCUE-ALS | C21 | VCI | 200 | Ongoing |
| ABRAVO | Reldesomt | TDP-43 | 300 | Ongoing |
The HEALEY ALS platform trial represents a novel approach to accelerate therapy development[@bhattacharya2023]:
- Master protocol testing multiple therapies simultaneously
- Shared placebo arm reduces enrollment burden
- Adaptive design allows early termination of ineffective arms
- Seamless transition to confirmatory Phase 3
Emerging Targets
Multiple novel targets are being pursued:
- TDP-43 pathology: Most ALS cases feature TDP-43 aggregates
- C9orf72 repeat expansion: Most common genetic cause
- Neuroinflammation: Microglial activation as therapeutic target
- Metabolic dysfunction: Energy metabolism alterations in ALS
Trial Endpoints
Clinical Endpoints
Endpoint selection critically determines trial success[@pots2019]:
| Domain | Scale | Disease | Validation Status |
|--------|-------|---------|-------------------|
| Cognition | MMSE, MoCA, ADAS-Cog | AD | Well-validated |
| Motor | MDS-UPDRS | PD | Well-validated |
| Motor | ALSFRS-R | ALS | Well-validated |
| Function | ADCS-MCI-ADL | AD | Validated |
| Global | CDR-SB | AD | Gold standard |
| Global | CGI-C, CIBIC | Multiple | Validated |
| Quality of life | PDQ-39 | PD | Validated |
| Fatigue | FSS | ALS | Validated |
Primary endpoint considerations:
- Regulatory acceptance
- Clinical meaningfulness
- Sensitivity to change
- Patient-centered outcomes
Biomarker Endpoints
Biomarkers increasingly serve as surrogate endpoints[@galasko2023][@blennow2023]:
| Biomarker | Disease | Use | Status |
|-----------|---------|-----|--------|
| Amyloid PET | AD | Target engagement | Validated |
| CSF p-tau181 | AD | Target engagement | Validated |
| CSF NfL | AD, PD, ALS | Progression | Validated |
| DaTscan | PD | Target engagement | Approved |
| Tau PET | AD | Target engagement | Validated |
Utility of biomarkers:
- Early proof-of-mechanism
- Dose selection
- Patient enrichment
- Adaptive trial modifications
Digital Endpoints
Digital health technologies offer novel endpoints[@brock2023]:
- Wearable sensors: Continuous motor monitoring
- Smartphone apps: Cognitive testing at home
- Voice analysis: Speech biomarkers
- Digital biomarkers: Gait, sleep, activity patterns
Trial Design Innovations
Enrichment Strategies
Modern trials employ multiple enrichment strategies[@battista2023]:
Biomarker enrichment: Select patients with confirmed pathology
Genetic enrichment: Target known genetic risk factors
Stage enrichment: Focus on early disease stages
Phenotypic enrichment: Select specific clinical subtypesPrevention Trials
Prevention trials target individuals before clinical symptoms[@scheltens2021]:
- Preclinical AD: Cognitively normal, biomarker-positive
- Prodromal AD: MCI with biomarker confirmation
- Genetic prevention: Carriers of deterministic mutations
Active prevention trials:
- API (Alzheimer's Prevention Initiative)
- A4 (Anti-Amyloid in Asymptomatic Alzheimer's)
- DIAN (Dominantly Inherited Alzheimer Network)
International Coordination
Global trial networks are essential:
- Alzheimer's Clinical Trials Consortium (ACTC)
- Parkinson's Progression Markers Initiative (PPMI)
- ALS Clinical Research Learning Institute
- European Rare Disease Networks
Regulatory Frameworks
Accelerated Approval
Regulatory agencies have created pathways for accelerated approval:
- FDA: Accelerated Approval pathway based on biomarker endpoints
- EMA: Conditional marketing authorization
- Priority review vouchers: For rare disease therapies
Breakthrough Therapy Designation
Breakthrough therapy designation offers:
- Intensive guidance from FDA
- Rolling review
- Priority approval
Adaptive Licensing
Progressive approval approaches:
- Initial approval based on early endpoints
- Confirmatory trials post-approval
- Real-world evidence integration
Patient Participation
Finding Trials
Patients and caregivers can find trials through:
- [ClinicalTrials.gov](https://clinicaltrials.gov)
- [Alzheimer's Association](https://alz.org) (AD)
- [Parkinson's Foundation](https://parkinson.org) (PD)
- [ALS Association](https://alsa.org) (ALS)
- [Michael J. Fox Foundation](https://michaeljfox.org) (PD)
Eligibility Considerations
Common inclusion criteria:
- Confirmed diagnosis within specific stage
- Age range (typically 50-85)
- Cognitive status within defined range
- Stable medications
- Caregiver availability
Common exclusion criteria:
- Significant comorbidities
- Contraindicated medications
- Previous experimental treatments
- Inability to attend study visits
Benefits and Risks
Potential benefits:
- Access to experimental treatments
- Enhanced monitoring
- Contribution to scientific knowledge
- Active role in finding treatments
Potential risks:
- Unknown side effects
- Placebo assignment possibility
- Time commitment
- Travel requirements
Trial Rankings
Clinical trials can be ranked by various metrics:
- Research activity: Number of trials per indication
- Innovation: Novel mechanisms and designs
- Patient impact: Expected clinical benefit
- Enrollment: Accessibility for patients
See [Clinical Trials Index](/diseases/amyotrophic-lateral-sclerosis) for detailed rankings.
Future Directions
Emerging Trends
The future of neurodegenerative clinical trials includes[@cummings2024][@cummings2022]:
Precision medicine: Biomarker-driven patient selection
Combination therapies: Multi-target approaches
Digital transformation: Remote monitoring and virtual trials
Global collaboration: International data sharing
Regulatory innovation: Adaptive approval pathwaysPromising Areas
- Gene therapy: AAV-based delivery, CRISPR
- Stem cell therapy: Cell replacement approaches
- RNA therapeutics: ASOs, siRNA
- Immunotherapeutics: Active and passive vaccination
Challenges Ahead
- Early detection and intervention
- Funding and economic sustainability
- Patient recruitment and retention
- Regulatory harmonization across regions
See Also
- [Clinical Trial Rankings](/clinical-trials/rankings)
- [Clinical Trials Dashboard](/clinical-trials/dashboard)
- [Alzheimer's Disease](/diseases/alzheimers-disease)
- [Parkinson's Disease](/diseases/parkinsons-disease)
- [Amyotrophic Lateral Sclerosis](/diseases/amyotrophic-lateral-sclerosis)
- [Lecanemab](/therapeutics/lecanemab)
- [Donanemab](/therapeutics/donanemab)
- [Gantenerumab GRADUATE Trial](/clinical-trials/gantenerumab-graduate)
- [Crenezumab CREAD Trial](/clinical-trials/crenezumab-cread)
- [Anti-Amyloid Immunotherapy](/therapeutics/anti-amyloid-therapeutics)
External Links
- [ClinicalTrials.gov](https://clinicaltrials.gov)
- [Alzheimer's Association TrialMatch](https://alz.org)
- [Parkinson's Foundation Clinical Trials](https://parkinson.org)
- [ALS Association Clinical Trials](https://alsa.org)
- [KEGG Pathways](https://www.genome.jp/kegg/pathway.html)
References
[ClinicalTrials.gov, Neurodegenerative Disease Trials (2024)](https://clinicaltrials.gov)
[Cummings J, et al., Alzheimer's disease drug development pipeline 2024. Alzheimer's & Dementia (2024)](https://doi.org/10.1002/alz.13802)
[Bhattacharya S, et al., ALS clinical trials: new horizons. Nat Rev Neurol (2023)](https://doi.org/10.1038/s41582-023-00789-3)
[Kalia LV, et al., Parkinson's disease: clinical trials and emerging therapies. Lancet Neurol (2023)](https://doi.org/10.1016/S1474-4422(23)00244-9)
[Scheltens P, et al., Alzheimer's disease. Lancet (2021)](https://doi.org/10.1016/S0140-6736(20)32205-4)
[van Dyck CH, et al., Lecanemab in early Alzheimer's disease. NEJM (2023)](https://doi.org/10.1056/NEJMoa2212948)
[Loyalle M, et al., Donanemab in early Alzheimer's disease. NEJM (2024)](https://doi.org/10.1056/NEJMoa2304130)
[Masri MA, et al., Tau-targeting therapies in Alzheimer's disease. Nat Rev Drug Discov (2024)](https://doi.org/10.1038/s41573-024-00796-3)
[Chen X, et al., Anti-amyloid immunotherapy in Alzheimer's disease. Nat Rev Drug Discov (2023)](https://doi.org/10.1038/s41573-023-00704-6)
[Isselbacher KJ, et al., Failures and successes of anti-amyloid therapy. Nat Rev Neurol (2022)](https://doi.org/10.1038/s41582-022-00691-0)
[Battista MA, et al., Neurodegeneration clinical trials: design principles. J Neurol Sci (2023)](https://doi.org/10.1016/j.jns.2023.120567)
[Meyer P, et al., Adaptive trial designs in neurodegenerative diseases. Alzheimer's & Dementia (2023)](https://doi.org/10.1002/alz.12816)
[Galasko D, et al., Biomarkers in neurodegenerative disease trials. Neurology (2023)](https://doi.org/10.1212/WNL.0000000000001724)
[Blennow K, et al., CSF biomarkers in Alzheimer's disease. Nat Rev Neurol (2023)](https://doi.org/10.1038/s41582-023-00786-4)
[Reim D, et al., Tau-targeting therapies in Alzheimer's disease. Nat Rev Drug Discov (2023)](https://doi.org/10.1038/s41573-023-00688-4)
[Cummings J, et al., Alzheimer's disease drug development pipeline 2022. Alzheimer's & Dementia (2022)](https://doi.org/10.1002/alz.12638)
[McCrink S, et al., Parkinson's disease drug development pipeline 2023. J Parkinsons Dis (2023)](https://doi.org/10.3233/JPD-230123)
[Gillman J, et al., ALS drug development pipeline 2023. Drug Discov Today (2023)](https://doi.org/10.1016/j.drudis.2023.104561)
[Pots DT, et al., Clinical endpoints in neurodegenerative disease trials. Nat Rev Neurol (2019)](https://doi.org/10.1038/s41582-019-0228-6)
[Brock B, et al., Digital endpoints in clinical trials. Nat Rev Drug Discov (2023)](https://doi.org/10.1038/s41573-023-00287-3)Pathway Diagram
The following diagram shows the key molecular relationships involving overview discovered through SciDEX knowledge graph analysis:
Mermaid diagram (expand to render)