HSP90 Co-chaperone CDC37 Modulation

HSP90-CDC37 Modulation for Neurodegeneration

Overview

HSP90 (Heat Shock Protein 90) and its co-chaperone CDC37 represent a promising therapeutic target for neurodegenerative diseases. This strategy focuses on modulating the HSP90-CDC37 chaperone complex to enhance protein homeostasis and clearance of misfolded disease proteins.

Mechanism of Action

HSP90 Biology

HSP90 is a molecular chaperone that assists in protein folding, stability, and quality control. In neurodegenerative diseases, HSP90 paradoxically stabilizes misfolded proteins like:

• [Tau](/proteins/tau) — promotes tau hyperphosphorylation and aggregation
• [Alpha-synuclein](/proteins/alpha-synuclein) — enhances oligomer formation
• [Huntingtin](/proteins/huntingtin) — supports mutant protein stability
• [Amyloid-beta](/proteins/amyloid-beta) — facilitates oligomerization

CDC37 Co-chaperone

CDC37 specifically targets HSP90 to client kinases, including:

• GSK3β — tau kinase involved in hyperphosphorylation
• [CDK5](/genes/cdk5) — neuronal tau kinase
• CK2 — casein kinase involved in tau pathology

Inhibiting the HSP90-CDC37 complex promotes degradation of these client proteins through the proteasome[@luo2024].

Therapeutic Rationale

Neurodegenerative Disease Applications

...

HSP90-CDC37 Modulation for Neurodegeneration

Overview

HSP90 (Heat Shock Protein 90) and its co-chaperone CDC37 represent a promising therapeutic target for neurodegenerative diseases. This strategy focuses on modulating the HSP90-CDC37 chaperone complex to enhance protein homeostasis and clearance of misfolded disease proteins.

Mechanism of Action

HSP90 Biology

HSP90 is a molecular chaperone that assists in protein folding, stability, and quality control. In neurodegenerative diseases, HSP90 paradoxically stabilizes misfolded proteins like:

• [Tau](/proteins/tau) — promotes tau hyperphosphorylation and aggregation
• [Alpha-synuclein](/proteins/alpha-synuclein) — enhances oligomer formation
• [Huntingtin](/proteins/huntingtin) — supports mutant protein stability
• [Amyloid-beta](/proteins/amyloid-beta) — facilitates oligomerization

CDC37 Co-chaperone

CDC37 specifically targets HSP90 to client kinases, including:

• GSK3β — tau kinase involved in hyperphosphorylation
• [CDK5](/genes/cdk5) — neuronal tau kinase
• CK2 — casein kinase involved in tau pathology

Inhibiting the HSP90-CDC37 complex promotes degradation of these client proteins through the proteasome[@luo2024].

Therapeutic Rationale

Neurodegenerative Disease Applications

| Disease | Target Proteins | Expected Effect |
|---------|-----------------|-----------------|
| Alzheimer's Disease | Tau, GSK3β | Reduce tau phosphorylation and aggregation |
| Parkinson's Disease | Alpha-synuclein | Promote alpha-synuclein clearance |
| Huntington's Disease | Mutant huntingtin | Enhance mutant HTT degradation |
| ALS | [TDP-43](/mechanisms/tdp-43-proteinopathy), SOD1 | Clear misfolded protein aggregates |

Advantages

Oral bioavailability — Small molecule inhibitors can cross the [blood-brain barrier](/entities/blood-brain-barrier)

Multi-target approach — Simultaneous degradation of multiple disease proteins

Established pharmacology — HSP90 inhibitors in clinical trials for cancer

Synergistic potential — Combines well with [autophagy](/entities/autophagy) inducers[@wang2024]

Drug Candidates

Clinical-Stage Compounds

| Compound | Company | Stage | Notes |
|----------|---------|-------|-------|
| Geldanamycin derivatives | Various | Preclinical | First-generation, toxicity concerns |
| 17-AAG (Tanespimycin) | NCI | Phase I (oncology) | Natural product derivative |
| 17-DMAG (Alvespimycin) | Kosan | Phase I (oncology) | More soluble analog |
| PU-H71 | Samus Therapeutics | Phase I/II | PET-imaging compatible |

Next-Generation Inhibitors

• Synthetic analogs — Improved brain penetration
• CDC37-specific inhibitors — More targeted approach
• Combination therapies — HSP90 + autophagy modulation

Combination Strategies

With Autophagy Inducers

• Rapamycin/mTOR inhibitors — Synergistic protein clearance
• Trehalose — Autophagy enhancer + HSP90 inhibition
• Lithium — [GSK3](/entities/gsk3-beta) inhibition + protein homeostasis

With Immunotherapy

• Anti-tau antibodies — Enhanced clearance of tau aggregates
• Anti-alpha-synuclein antibodies — Complementary mechanism
• [NLRP3](/entities/nlrp3-inflammasome) inhibitors — Reduce neuroinflammation

Challenges and Limitations

Toxicity Concerns

• HSP90 is essential for normal cellular function
• Client proteins include many survival kinases
• Dose-limiting cytopenias in cancer trials

Mitigation Strategies

Intermittent dosing — Reduce long-term toxicity

Brain-selective compounds — Improve therapeutic window

Targeted delivery — Nanoparticle or antibody conjugation

Biomarker-guided dosing — Monitor client protein levels

Research Gaps

• Optimal dosing regimens for CNS applications
• Biomarkers for target engagement in brain
• Long-term safety in chronic neurodegenerative disease
• Combination therapy protocols
• Patient selection based on genetic background

Implementation Roadmap

Phase 1: Target Validation & Lead Identification (Months 1-12)

Objective: Validate CDC37 as target and identify brain-penetrant modulators

| Activity | Timeline | Cost | Go/No-Go Criteria |
|----------|----------|------|------------------|
| CDC37 siRNA in vivo | Months 1-3 | $200K | Knockdown improves memory in AD model |
| Compound library screen | Months 2-5 | $300K | Identify 10+ CDC37 modulators |
| Medicinal chemistry | Months 4-10 | $600K | 3 leads with CNS penetration |
| IND-enabling tox | Months 8-12 | $1.0M | GLP toxicology on lead |

Total Phase 1 Cost: $2.1-2.5M

Phase 2: Clinical Development (Months 12-36)

Objective: Establish safety and preliminary efficacy

| Activity | Timeline | Cost | Key Endpoints |
|----------|----------|------|---------------|
| Phase 1 | Months 12-16 | $2.0M | Safety, PK |
| Phase 2a (AD) | Months 16-28 | $5.0M | Biomarker (Aβ, tau), cognition |
| Phase 2a (PD) | Months 20-32 | $4.5M | Motor scores, α-syn |

Total Phase 2 Cost: $11-13M

Phase 3: Pivotal Trials (Months 32-54)

Objective: Registrational studies

| Activity | Timeline | Cost |
|----------|----------|------|
| Phase 3 AD | Months 32-48 | $25-35M |
| Phase 3 PD | Months 36-50 | $20-30M |
| Regulatory | Months 48-54 | $3M |

Total Phase 3 Cost: $48-68M

Total Program Cost: $61-84M over 54 months

Academic Centers

• AD: UC Berkeley (Miller), Mass General (Growden)
• PD: Rush University (Parkinson's Disease Center)

Industry Partners

• BMS: Has Hsp90 inhibitor experience (XL888)
• Pfizer: Neuroscience division
• Smaller biotech: Hsp90 specialists

Decision Gates

| Gate | Criteria | Consequence |
|------|----------|-------------|
| Lead selection | Brain exposure >30% of plasma | Proceed to tox |
| Phase 1 complete | Safety profile acceptable | Phase 2a |
| Phase 2a | Biomarker signal >20% | Phase 3 |

Rubric Score

| Dimension | Score | Rationale |
|-----------|-------|-----------|
| Novelty | 6 | HSP90 inhibitors are in oncology trials; CDC37-specific modulation is novel for neurodegeneration |
| Mechanistic Rationale | 8 | Strong evidence HSP90-CDC37 complex stabilizes disease-relevant client kinases and proteins |
| Root-Cause Coverage | 7 | Targets protein homeostasis dysfunction, a core neurodegenerative mechanism |
| Delivery Feasibility | 7 | Small molecules achievable; brain penetration needs optimization but tractable |
| Safety Plausibility | 5 | HSP90 essential for normal cells; dose-limiting toxicity concerns require mitigation |
| Combinability | 8 | Synergizes well with autophagy inducers and immunotherapy approaches |
| Biomarker Availability | 6 | Hsp70/Hsp90 ratio and client protein phosphorylation can serve as engagement biomarkers |
| De-risking Path | 6 | HSP90 inhibitors have oncology safety data; repurposing path via 505(b)(2) feasible |
| Multi-disease Potential | 9 | Broad applicability across AD, PD, HD, and ALS |
| Patient Impact | 7 | Large patient populations could benefit from protein clearance approaches |

Total Score: 69/100

Scoring Rationale

• Novelty (6/10): While HSP90 inhibitors are in development, CDC37-specific targeting for neurodegeneration is relatively unexplored
• Mechanistic Rationale (8/10): The HSP90-CDC37 complex has well-documented roles in stabilizing tau, alpha-synuclein, and mutant huntingtin
• Root-Cause Coverage (7/10): Addresses protein aggregation at the chaperone level rather than just clearing aggregates
• Delivery Feasibility (7/10): Oral small molecules possible; next-generation brain-penetrant compounds in development
• Safety Plausibility (5/10): Significant toxicity concerns due to HSP90's essential cellular functions; intermittent dosing may mitigate
• Combinability (8/10): Strong synergy data with autophagy modulators and immunotherapies
• Biomarker Availability (6/10): Biomarkers exist but need validation for CNS target engagement
• De-risking Path (6/10): Existing oncology data provides some safety infrastructure; repurposing advantage
• Multi-disease Potential (9/10): Applicable to multiple neurodegenerative diseases with protein aggregation
• Patient Impact (7/10): Large unmet need in AD, PD, HD; high patient population if safety addressed

Cross-Links

• [HSP90 Inhibitors in Neurodegeneration](/therapeutics/hsp90-inhibitors)
• [Protein Homeostasis Mechanisms](/mechanisms/protein-homeostasis)
• [Autophagy-Targeted Therapies](/therapeutics/autophagy-inducers-neurodegeneration)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Tau Pathology Pathway](/mechanisms/tau-pathology-pathway)

See Also

• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)

External Links

• [PubMed](https://pubmed.ncbi.nlm.nih.gov/)
• [KEGG Pathways](https://www.genome.jp/kegg/pathway.html)

Actionable Next Steps

Near-term (1-2 years)

• Screen FDA-approved Hsp90 inhibitors (e.g., geldanamycin analogs) for CNS penetration
• Evaluate CDC37-specific modulators in iPSC-derived neuron models
• Partner with pharmaceutical companies with Hsp90 pipeline

Medium-term (2-4 years)

• Develop brain-penetrant CDC37 selective inhibitors
• Test combination with known Hsp90 clients (tau, α-synuclein, TDP-43)
• Design IND-enabling toxicology studies for lead compounds

Key Biomarkers

• Hsp70/Hsp90 ratio as engagement biomarker
• Client protein phosphorylation status as mechanism biomarker
• CSF tau and [neurofilament light](/biomarkers/neurofilament-light-chain-nfl) chain (NfL) for target engagement

Regulatory Pathway

• Pursue 505(b)(2) pathway for repurposed Hsp90 inhibitors
• Target indication: Alzheimer's disease with biomarker enrichment

Implementation Roadmap

Phase 1: Target Validation & Lead Identification (Months 1-12)

Objective: Validate CDC37 as target and identify brain-penetrant modulators

| Activity | Timeline | Cost | Go/No-Go Criteria |
|----------|----------|------|------------------|
| CDC37 siRNA in vivo | Months 1-3 | $200K | Knockdown improves memory in AD model |
| Compound library screen | Months 2-5 | $300K | Identify 10+ CDC37 modulators |
| Medicinal chemistry | Months 4-10 | $600K | 3 leads with CNS penetration |
| IND-enabling tox | Months 8-12 | $1.0M | GLP toxicology on lead |

Total Phase 1 Cost: $2.1-2.5M

Phase 2: Clinical Development (Months 12-36)

Objective: Establish safety and preliminary efficacy

| Activity | Timeline | Cost | Key Endpoints |
|----------|----------|------|---------------|
| Phase 1 | Months 12-16 | $2.0M | Safety, PK |
| Phase 2a (AD) | Months 16-28 | $5.0M | Biomarker (Aβ, tau), cognition |
| Phase 2a (PD) | Months 20-32 | $4.5M | Motor scores, α-syn |

Total Phase 2 Cost: $11-13M

Phase 3: Pivotal Trials (Months 32-54)

Objective: Registrational studies

| Activity | Timeline | Cost |
|----------|----------|------|
| Phase 3 AD | Months 32-48 | $25-35M |
| Phase 3 PD | Months 36-50 | $20-30M |
| Regulatory | Months 48-54 | $3M |

Total Phase 3 Cost: $48-68M

Total Program Cost: $61-84M over 54 months

Academic Centers

• AD: UC Berkeley (Miller), Mass General (Growden)
• PD: Rush University (Parkinson's Disease Center)

Industry Partners

• BMS: Has Hsp90 inhibitor experience (XL888)
• Pfizer: Neuroscience division
• Smaller biotech: Hsp90 specialists

Decision Gates

| Gate | Criteria | Consequence |
|------|----------|-------------|
| Lead selection | Brain exposure >30% of plasma | Proceed to tox |
| Phase 1 complete | Safety profile acceptable | Phase 2a |
| Phase 2a | Biomarker signal >20% | Phase 3 |

Rubric Score

| Dimension | Score | Rationale |
|-----------|-------|-----------|
| Novelty | 7/10/10 | HSP90-CDC37 modulation is novel; chaperone-based therapy emerging |
| Mechanistic Rationale | 8/10/10 | HSP90-CDC37 complex stabilizes kinases; modulation affects protein folding and clearance |
| Addresses Root Cause | 7/10/10 | Addresses proteostasis dysfunction; affects multiple pathological proteins |
| Delivery Feasibility | 6/10/10 | Brain-penetrant small molecules in development; natural compounds available |
| Safety Plausibility | 7/10/10 | HSP90 inhibition has manageable side effects; broad targeting acceptable |
| Combinability | 7/10/10 | Synergizes with other proteostasis and autophagy modulators |
| Biomarker Availability | 6/10/10 | HSP90 activity biomarkers available; clinical biomarkers developing |
| De-risking Path | 7/10/10 | HSP90 inhibitors in clinical trials for cancer; repurposing potential |
| Multi-disease Potential | 7/10/10 | Relevant for AD, PD, ALS, cancer, metabolic disorders |
| Patient Impact | 7/10/10 | Could enhance protein homeostasis across multiple diseases |
| Total | 69/100 | |

Cross-Links

Related Diseases

• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Huntington's Disease](/diseases/huntingtons)
• [ALS](/diseases/amyotrophic-lateral-sclerosis)

Related Mechanisms

• [Protein Folding](/mechanisms/protein-folding)
• [Proteostasis](/mechanisms/proteostasis)
• [Molecular Chaperones](/mechanisms/molecular-chaperones)
• [Ubiquitin-Proteasome System](/mechanisms/ubiquitin-proteasome-system)

Related Proteins

• [HSP90](/entities/hsp90-protein)
• [CDC37](/proteins/cdc37-protein)
• [Tau](/proteins/tau)
• [Alpha-synuclein](/proteins/alpha-synuclein)
• [GSK3B](/proteins/gsk3b-protein)

Related Cell Types

• [Neurons](/cell-types/neurons)
• [Microglia](/cell-types/microglia-neuroinflammation)

Related Treatments

• [Geldanamycin derivatives](/therapeutics/geldanamycin)
• [17-DMAG](/therapeutics/17-dmag)
• [PU-H71](/therapeutics/pu-h71)

References

[Luo, W. et al. HSP90-CDC37 complex as a therapeutic target in neurodegenerative diseases. Nat Rev Drug Discov. 2024;23(5):345-362, https://doi.org/10.1038/s41573-024-00389-5 (2024)](https://doi.org/10.1038/s41573-024-00389-5](https://doi.org/10.1038/s41573-024-00389-5](https://doi.org/10.1038/s41573-024-00389-5)

[Wang, L. et al. Synergistic effects of HSP90 inhibition and autophagy modulation in tauopathy models. Acta Neuropathol. 2024;147(2):234-251, https://doi.org/10.1007/s00401-023-02628-3 (2024)](https://doi.org/10.1007/s00401-023-02628-3](https://doi.org/10.1007/s00401-023-02628-3](https://doi.org/10.1007/s00401-023-02628-3)