Primary target
VCP/p97 (Valosin-Containing Protein)
Therapeutic rationale
Inhibit VCP ATPase activity to enhance autophagy, modulate ERAD, and clear toxic protein aggregates in neurodegenerative diseases
Representative agents
NMS-873, CB-5083, DBeQ, Roscovitine (Seliciclib)
Development status
Preclinical with clinical-stage compounds in oncology repurposing
Valosin-containing protein (VCP), also known as p97, is a highly conserved AAA+ ATPase that plays critical roles in protein homeostasis, autophagy, and cellular stress responses. VCP mutations cause VCP-associated multisystem proteinopathy (MSP), characterized by inclusion body myopathy, Paget disease of bone, and frontotemporal dementia (IBMPFD). Additionally, VCP dysfunction is strongly implicated in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) pathogenesis. VCP-targeted therapy represents a promising therapeutic approach for these devastating neurodegenerative conditions.
VCP/p97 is a hexameric AAA+ ATPase that unfolds and translocates polyubiquitinated substrates through its central channel. Inhibiting VCP ATPase activity disrupts multiple cellular processes that become dysregulated in disease:
- Proteasomal degradation: VCP extracts ubiquitinated proteins from the endoplasmic reticulum for proteasomal degradation via the ER-associated degradation (ERAD) pathway
- Autophagosome-lysosome fusion: VCP facilitates the recruitment of autophagic machinery to damaged organelles and protein aggregates
- DNA repair: VCP regulates DNA double-strand break repair through histone ubiquitination and repair factor recruitment
- Mitochondrial quality control: VCP-mediated mitophagy removes damaged mitochondria
VCP inhibition enhances autophagic flux by promoting autophagosome-lysosome fusion. In cells with VCP mutations or in neurodegenerative diseases with impaired autophagy, VCP inhibitors restore the ability of cells to clear toxic protein aggregates including:
The ERAD pathway is crucial for degrading misfolded proteins from the endoplasmic reticulum. VCP inhibitors modulate ERAD activity, reducing the accumulation of toxic ER stress species that trigger apoptotic pathways in neurons.
¶ VCP-Associated Inclusion Body Myopathy
In preclinical models of VCP-associated inclusion body myopathy (IBM), VCP inhibitors demonstrate:
- Reduced cytoplasmic TDP-43 inclusions in muscle cells
- Improved mitochondrial function and reduced ROS production
- Decreased muscle fiber degeneration
- Enhanced autophagic clearance of mutant VCP aggregates
In cellular and animal models of ALS and FTD:
- VCP knockdown or inhibition reduces TDP-43 aggregation
- VCP inhibitors improve survival of motor neurons in vitro
- In TDP-43 transgenic mice, VCP inhibition decreases TDP-43 pathology and improves behavioral outcomes
- Combination approaches with autophagy inducers show synergistic benefits
Multiple studies support VCP as a therapeutic target in ALS:
- VCP mutations are found in familial ALS cases
- TDP-43 pathology in ALS involves VCP-mediated degradation pathways
- VCP inhibitors reduce excitotoxicity-induced motor neuron death
- Preclinical studies show improved neuromuscular function in ALS models
Cyclin-dependent kinase 5 (CDK5) phosphorylates VCP and modulates its activity. CDK5 inhibitors with VCP-modulating properties are in development:
- Roscovitine (Seliciclib): Multi-CDK inhibitor that indirectly modulates VCP activity; completed Phase II trials for ALS with modest efficacy signals
- AT7519: CDK5/2/9 inhibitor in preclinical development for neurodegenerative diseases
Direct VCP inhibitors are in various stages of development:
- DBeQ: Early-stage VCP inhibitor demonstrating proof-of-concept in cellular models
- NMS-873: Potent VCP allosteric inhibitor showing efficacy in ALS/FTD models
- CB-5083: Clinical-stage VCP inhibitor (oncology); repurposing potential for neurodegeneration
Current clinical development focuses on:
- Optimizing blood-brain barrier penetration
- Achieving sustained target engagement
- Balancing VCP inhibition with essential cellular functions
- Identifying patient populations with VCP dysfunction
VCP inhibition can cause:
- Gastrointestinal effects (nausea, diarrhea)
- Transient liver enzyme elevations
- Potential impact on protein homeostasis in rapidly dividing cells
The therapeutic window for VCP inhibition involves:
- Achieving sufficient CNS exposure for neuroprotective effects
- Avoiding complete VCP blockade (essential for cellular viability)
- Targeting disease-specific pathways at sub-lethal doses
VCP-targeted therapy represents a promising approach for neurodegenerative diseases characterized by impaired protein homeostasis. Key priorities include:
- Developing brain-penetrant VCP inhibitors with optimal pharmacokinetics
- Identifying biomarkers for patient selection and treatment response
- Exploring combination therapies with autophagy modulators and anti-aggregation compounds
- Advancing clinical trials in genetically-defined patient populations