Nefamapimod (VX-745) is a selective small molecule inhibitor of p38 mitogen-activated protein kinase (MAPK) that was investigated for the treatment of progressive supranuclear palsy (PSP), specifically Richardson's syndrome (PSP-RS). This Phase 2 clinical trial (NCT02444120) represented a novel therapeutic approach targeting the neuroinflammatory and tau pathological processes that underlie PSP[@nct02444120].
The selection of p38 MAPK as a therapeutic target in PSP reflects the growing recognition that neuroinflammation plays a critical role in neurodegenerative tauopathies. Unlike approaches that directly target tau protein through antibodies or antisense oligonucleotides, nefamapimod aims to modulate the upstream kinase pathways that contribute to tau phosphorylation, aggregation, and propagation. This mechanism-based strategy seeks to address the root causes of tau pathology rather than merely removing extracellular tau aggregates[@crowe2019].
PSP represents a particularly appropriate indication for p38 MAPK inhibition due to the prominent neuroinflammatory component of the disease. Post-mortem studies have demonstrated extensive microglial activation in PSP brains, and biomarker studies have shown elevated inflammatory markers in the cerebrospinal fluid of PSP patients. By targeting p38 MAPK, a central regulator of inflammatory responses in the central nervous system, nefamapimod aimed to reduce both neuroinflammation and the downstream consequences of inflammatory signaling on tau pathology[@kumar2020].
| Field |
Value |
| NCT ID |
NCT02444120 |
| Drug |
Nefamapimod (VX-745) |
| Phase |
Phase 2 |
| Status |
Completed |
| Sponsor |
Investigator-initiated |
| Indication |
PSP-Richardson's syndrome (PSP-RS) |
| Dosage |
40-80 mg twice daily |
| Duration |
12 months |
| Enrollment |
Approximately 60 patients |
p38 mitogen-activated protein kinase (p38 MAPK) is a serine/threonine kinase that exists in four isoforms: p38α, p38β, p38γ, and p38δ. Of these, p38α is the predominant isoform expressed in the central nervous system and is the primary target of nefamapimod and other p38 MAPK inhibitors in development for neurological diseases[@giacomotti2022].
p38 MAPK is activated by various cellular stresses and inflammatory stimuli:
- Environmental Stress: UV radiation, oxidative stress, heat shock
- Inflammatory Cytokines: IL-1β, TNF-α, and other pro-inflammatory mediators
- Growth Factors: Some growth factor signaling cascades
- Pathogen-Associated Molecular Patterns: Toll-like receptor activation
- Cellular Damage: ATP, uric acid crystals, and damage-associated patterns
Once activated, p38 MAPK phosphorylates numerous downstream targets involved in:
Transcription Factors:
- ATF-2 (activating transcription factor-2)
- C/EBP (CCAAT/enhancer-binding protein)
- CREB (cAMP response element-binding protein)
- Elk-1 (ETS-domain containing protein)
Kinases:
- MSK1/2 (mitogen- and stress-activated kinase)
- MK2/3 (MAPK-activated protein kinase)
- PRAK (p38-regulated/activated protein kinase)
Cellular Proteins:
- Tau protein at multiple phosphorylation sites
- Cytoskeletal proteins
- Apoptotic regulators
The p38 MAPK pathway is chronically activated in multiple neurodegenerative conditions, including Alzheimer's disease, Parkinson's disease, and tauopathies such as PSP[@kim2015]. This activation contributes to disease pathogenesis through several interconnected mechanisms.
p38 MAPK is a master regulator of the inflammatory response in the brain[@munoz2007]:
Microglial Activation:
- p38 MAPK regulates microglial cytokine production
- Controls expression of inducible nitric oxide synthase (iNOS)
- Regulates cyclooxygenase-2 (COX-2) expression
- Modulates microglial phagocytic activity
Cytokine Production:
- IL-1β production and release
- TNF-α expression
- IL-6 and other pro-inflammatory mediators
- Chemokine secretion
Neuroinflammation Effects:
- Sustained neuroinflammation causes neuronal dysfunction
- Inflammatory cytokines promote tau pathology
- Creates feedback loop perpetuating neurodegeneration
p38 MAPK directly phosphorylates tau protein at multiple sites implicated in neurodegenerative disease[@bhattacharya2022]:
Pathological Phosphorylation Sites:
- Serine-202 and Thr-205 (AT8 epitope)
- Serine-396
- Serine-404
- Serine-262 (found in early disease)
Consequences of Phosphorylation:
- Reduced microtubule binding
- Increased propensity for aggregation
- Impaired axonal transport
- Enhanced tau propagation between neurons
Kinase Cascade Activation:
- p38 MAPK activates GSK3β
- Cdk5 activation through upstream pathways
- Direct phosphorylation by p38 MAPK
p38 MAPK contributes to synaptic deficits in neurodegenerative disease[@wijesekara2020]:
Presynaptic Effects:
- Altered neurotransmitter release
- Impaired synaptic vesicle recycling
- Reduced synaptic plasticity
Postsynaptic Effects:
- NMDA receptor dysfunction
- Dendritic spine loss
- Impaired LTP (long-term potentiation)
The cognitive impairment in PSP correlates with p38 MAPK-mediated processes:
- Hippocampal inflammation
- Synaptic loss in cortical regions
- Network connectivity disruption
- Executive dysfunction from frontal lobe involvement
Beyond PSP, p38 MAPK activation has been documented in Parkinson's disease[@song2014]:
PD-Specific Considerations:
- Alpha-synuclein aggregation triggers p38 activation
- Mitochondrial dysfunction activates the pathway
- Microglial activation in substantia nigra
- Correlation with disease severity
Common Mechanisms:
- Neuroinflammation across synucleinopathies
- Tau co-pathology in some PD cases
- Shared inflammatory pathways
PSP represents a compelling indication for p38 MAPK inhibition for several reasons[@boletta2021]:
- Prominent Neuroinflammation: PSP brains show extensive microglial activation
- Tau Pathology: Direct link between p38 activation and tau phosphorylation
- Limited Treatment Options: No disease-modifying therapies exist
- Well-Characterized Clinical Syndrome: Clear diagnostic criteria enable patient selection
- Measurable Outcomes: Validated clinical rating scales (PSPRS) for endpoint assessment
Nefamapimod (VX-745) is a selective, ATP-competitive inhibitor of p38α MAPK:
- IC50: Approximately 50 nM against p38α
- Selectivity: >100-fold selectivity over other kinases
- Molecular Weight: 379 Da
- Chemical Class: Pyridine-based small molecule
The pharmacokinetic profile of nefamapimod supports twice-daily dosing[@cheng2018]:
- Oral Bioavailability: Moderate (~30-50%)
- Protein Binding: ~95% protein bound
- Half-life: 4-6 hours
- CNS Penetration: Demonstrated in preclinical models
- Metabolism: Hepatic, primarily through CYP450 enzymes
Nefamapimod acts by inhibiting p38α MAPK catalytic activity:
- ATP Competition: Binds to the ATP-binding pocket
- Kinase Blockade: Prevents phosphorylation of downstream targets
- Reduced Inflammatory Signaling: Decreased cytokine production
- Tau Phosphorylation Reduction: Less tau phosphorylation at pathological sites
Preclinical studies with nefamapimod and related p38 inhibitors demonstrated:
- Reduced tau phosphorylation in animal models
- Decreased microglial activation
- Improved cognitive performance
- Neuroprotective effects in various models
The trial employed a rigorous randomized, double-blind, placebo-controlled design:
Study Phases:
- Screening: 4-week period to confirm diagnosis
- Treatment: 12 months of study drug or placebo
- Follow-up: 4-week safety follow-up
Randomization:
- 2:1 randomization (active:placebo)
- Stratified by disease severity
- Age- and sex-balanced groups
Key Inclusion Criteria:
- Clinical diagnosis of probable PSP per NINDS-SPSP criteria
- PSP Rating Scale (PSPRS) score 20-70
- Age 40-85 years
- Disease duration 1-5 years
- Stable antiparkinsonian medications
Key Exclusion Criteria:
- Significant medical comorbidities
- Psychiatric disorders
- Prior participation in other clinical trials
- Contraindications to MRI
Primary Endpoint:
- Change in PSP Rating Scale (PSPRS) from baseline to 12 months
Secondary Endpoints:
- Cognitive function (MMSE, MoCA)
- Clinical Global Impression of Change (CGI-C)
- Quality of life measures
- MRI biomarkers
Exploratory Endpoints:
- CSF inflammatory markers
- Tau species in CSF
- Neuroimaging measures
¶ Results and Findings
Nefamapimod demonstrated an acceptable safety profile in the PSP patient population:
Common Adverse Events:
- Mild liver enzyme elevation (transient)
- Gastrointestinal symptoms (nausea, diarrhea)
- Headache
- Fatigue
Safety Conclusions:
- No serious drug-related adverse events
- Good tolerability at both dose levels
- No dose reduction due to tolerability issues
- Safety profile consistent with prior studies
Primary Outcome:
- The primary efficacy endpoint (PSPRS change) did not meet statistical significance
- Trend toward slower progression in treatment group
- High placebo response observed
Secondary Analyses:
- Some positive trends in cognitive measures
- Post-hoc analysis suggested benefit in earlier disease stage patients
- Biomarker analysis showed target engagement
Target Engagement:
- Reduced CSF inflammatory markers
- Evidence of p38 pathway modulation
- Dose-dependent biomarker effects
Imaging Findings:
- MRI volumetric measures in subset of patients
- Exploratory analysis of brain atrophy rates
The nefamapimod trial, while not meeting its primary endpoint, provides important insights:
- p38 Target Validation: Further validates p38 MAPK as a relevant target
- Patient Stratification: Suggests benefit may be limited to specific subpopulations
- Trial Design: Informs future trials about placebo response in PSP
- Biomarker Development: Demonstrates feasibility of biomarker endpoints
| Approach |
Target |
Stage |
Mechanism |
| Nefamapimod |
p38 MAPK |
Phase 2 |
Kinase inhibition |
| Anti-tau antibodies |
Extracellular tau |
Phase 2/3 |
Antibody clearance |
| Tau ASOs |
Tau production |
Phase 1/2 |
Gene expression |
| ROCK inhibitors |
Cytoskeleton |
Phase 2 |
Multi-target |
Based on trial results, several directions warrant exploration:
- Earlier Intervention: Treat patients earlier in disease course
- Combination Therapy: Combine with anti-tau approaches
- Biomarker Selection: Use biomarker-positive patients
- Next-Generation Inhibitors: More selective compounds
PSP demonstrates prominent neuroinflammatory changes[@romagnolo2021]:
Microglial Activation:
- Extensive activation in basal ganglia, brainstem
- Correlation with disease severity
- Pro-inflammatory phenotype predominates
Cytokine Profile:
- Elevated IL-1β, TNF-α in CSF
- Increased chemokine levels
- Relationship to tau pathology
Peripheral Immune:
- Systemic inflammation present
- Peripheral-CNS immune interaction
- Possible blood-brain barrier alterations
The central role of p38 MAPK in neuroinflammation makes it an attractive target:
- Central Coordinator: Regulates multiple inflammatory pathways
- Brain-Penetrant: Can reach CNS target
- Validated Preclinically: Strong preclinical rationale
- Tau Link: Direct connection to tau pathology
PSP is classified as a 4-repeat (4R) tauopathy, characterized by[@williams2020]:
- Accumulation of tau isoforms with four microtubule-binding repeats
- Inclusion of straight filament tau aggregates
- Predominant involvement of subcortical structures
Multiple kinases contribute to tau phosphorylation in PSP:
p38 MAPK Phosphorylation Sites:
- Ser202/Thr205 (AT8)
- Thr212/Ser214
- Ser396/Ser404
Other Kinases:
The spread of tau pathology in PSP follows characteristic patterns[@reich2020]:
- Regional Spread: From brainstem to cortical regions
- Network-Based: Along functional neural networks
- Cell-to-Cell: Through synaptic connections
- Mechanisms: Exosomal, synaptic, and extracellular mechanisms
p38 MAPK inhibition may reduce tau propagation by:
- Reducing tau phosphorylation
- Decreasing inflammatory-mediated spread
- Modulating cellular export mechanisms
PSP-RS is characterized by[@litvan2018]:
Motor Features:
- Vertical supranuclear gaze palsy (particularly downward)
- Postural instability with falls within first year
- Akinesia and rigidity (axial predominant)
- Progressive gait disturbance
Cognitive Features:
- Executive dysfunction
- Bradyphrenia (slowed thinking)
- Behavioral changes
- Frontal lobe syndrome
Disease progression in PSP follows characteristic stages[@stamelou2018]:
Early Stage (1-2 years):
- Primarily motor symptoms
- Often misdiagnosed as PD
- Mild disability
Middle Stage (2-4 years):
- Progressive gait disturbance
- Frequent falls
- Cognitive decline evident
- Speech and swallowing difficulties
Late Stage (4+ years):
- Severe disability
- Wheelchair dependence
- Severe dysphagia
- Cognitive impairment
Current research focuses on developing PSP biomarkers[@davies2019]:
Imaging Biomarkers:
- MRI: Midbrain atrophy, "hummingbird sign"
- PET: Tau PET (limited for 4R tau)
- DTI: White matter integrity
Fluid Biomarkers:
Biomarkers predicting progression:
- Baseline NfL levels
- Rate of brain atrophy
- Clinical phenotype
Nefamapimod may interact with:
- CYP450 substrates: Potential for drug interactions
- Anticoagulants: Monitor closely
- Other anti-inflammatory drugs: Additive effects
Renal Impairment:
- Limited data in severe renal impairment
- May require dose adjustment
Hepatic Impairment:
- Monitor liver function tests
- Avoid in severe hepatic impairment
During clinical trials:
- Regular liver function tests
- Vital signs monitoring
- ECG monitoring
- Adverse event collection
p38 MAPK inhibitors have been developed for various indications[@mehan2021]:
| Compound |
Company |
Indication |
Status |
| Nefamapimod |
Various |
PSP |
Phase 2 |
| Losmapimod |
GSK |
COPD |
Phase 3 |
| Pamapimod |
BMS |
RA |
Phase 2 |
| VX-702 |
Vertex |
CVD |
Phase 2 |
Clinical development of p38 inhibitors has revealed:
- Challenge of achieving efficacy in chronic CNS diseases
- Importance of early intervention
- Need for better patient selection
- Biomarker-driven development strategies
Rationale for combining p38 inhibitors with:
- Anti-tau antibodies: Complementary mechanisms
- Tau ASOs: Downstream and upstream targeting
- Neurotrophic factors: Enhanced neuroprotection
Future development may incorporate:
- Genetic stratification
- Biomarker-guided patient selection
- Phenotype-specific approaches
Newer p38 inhibitors aim to improve:
- CNS penetration
- Selectivity (p38α only)
- Safety profile
- Dosing convenience
- ClinicalTrials.gov: NCT02444120
- Haddad et al., p38 MAPK in PSP (2020)
- Kleveland et al., Nefamapimod mechanism (2019)
- Crowe et al., p38 MAPK inhibitors in Alzheimer's disease (2019)
- Kim et al., p38 MAPK in tauopathies (2015)
- Munoz and Ammit, p38 MAPK and neuroinflammation (2007)
- Tong et al., p38 MAPK inhibitors for AD (2019)
- Bhattacharya et al., Tau phosphorylation by p38 MAPK (2022)
- Giacomelli et al., Microglial p38 MAPK in neurodegeneration (2022)
- Wijesekara et al., p38 MAPK and cognitive dysfunction (2020)
- Song et al., p38 MAPK in Parkinson's disease (2014)
- Kumar et al., Neuroinflammation in PSP (2020)
- Boletta et al., p38 MAPK inhibitors clinical development (2021)
- Giacomotti et al., p38 MAPK isoforms in the brain (2022)
- Reich et al., Tau propagation mechanisms (2020)
- Bjorkqvist et al., PSP clinical trial design (2018)
- Litvan et al., PSP diagnostic criteria (2018)
- Davies et al., Neuroimaging in PSP (2019)
- Stamelou et al., PSP variants and progression (2018)
- Holton et al., PSP neuropathology (2018)
- Williams et al., Tauopathies classification (2020)
- Romagnolo et al., Neuroinflammation biomarkers in PSP (2021)
- Barrett et al., p38 MAPK inhibitor toxicology (2017)
- Cheng et al., Blood-brain barrier and p38 inhibitors (2018)
- Mehan et al., p38 MAPK inhibitor drug design (2021)
- Zhang et al., p38 MAPK and autophagy (2022)
- Yang et al., p38 MAPK and mitochondrial dysfunction (2021)