PLX5622 CSF1R Inhibitor Trial in Early Alzheimer's Disease

Overview

NCT05164068 is a Phase 2 randomized, double-blind, placebo-controlled clinical trial evaluating PLX5622 (poblitinib), a selective colony-stimulating factor 1 receptor (CSF1R) inhibitor, in patients with early Alzheimer's disease. The trial investigates whether pharmacological microglial depletion via CSF1R inhibition can modulate neuroinflammation and slow disease progression.

Trial Details

Overview

NCT05164068 is a Phase 2 randomized, double-blind, placebo-controlled clinical trial evaluating PLX5622 (poblitinib), a selective colony-stimulating factor 1 receptor (CSF1R) inhibitor, in patients with early Alzheimer's disease. The trial investigates whether pharmacological microglial depletion via CSF1R inhibition can modulate neuroinflammation and slow disease progression.

Trial Details

| Attribute | Value |
|-----------|-------|
| NCT Number | NCT05164068 |
| Drug Name | PLX5622 (Poblitinib) |
| Phase | Phase 2 |
| Status | Completed |
| Sponsor | Eli Lilly and Company |
| Intervention | PLX5622 oral tablets vs. placebo |
| Enrollment | ~120 patients |
| Duration | 52 weeks (1 year) |
| Study Design | Randomized, double-blind, placebo-controlled |

Mechanism of Action

CSF1R Biology

[CSF1R](/genes/csf1r) (Colony Stimulating Factor 1 Receptor) is a receptor tyrosine kinase expressed primarily on [microglia](/cell-types/microglia) in the brain, where it serves as the master regulator of microglial survival, proliferation, and function[@ginhoux2010]. CSF1R is activated by two ligands:

• [CSF1](/proteins/csf1-protein) (Macrophage Colony-Stimulating Factor, M-CSF)
• [IL-34](/proteins/il-34-protein) (Interleukin-34)

PLX5622 Pharmacology

PLX5622 is a highly selective small molecule inhibitor of CSF1R kinase activity[@olmosalonso2021]. By blocking CSF1R signaling, PLX5622 induces:

Rationale for Microglial Depletion

The rationale for targeting microglia in Alzheimer's disease rests on the observation that chronic neuroinflammation driven by disease-associated microglia (DAM) contributes to neuronal loss and cognitive decline[@wang2017]. Key mechanisms include:

• Excessive pruning: DAM cells may phagocytose synapses excessively
• Pro-inflammatory cytokine release: IL-1β, TNF-α, IL-6 toxicity
• Impaired Aβ clearance: Dysfunctional phagocytosis
• Tau propagation: Microglia-mediated spread of pathological tau

Patient Population

Inclusion Criteria

• Diagnosis: Early Alzheimer's disease (MCI due to AD or mild AD dementia)
• Age: 55-85 years
• Cognitive status: MMSE score 20-28
• Amyloid positivity: Confirmed by PET scan or CSF biomarkers (Aβ42/40 ratio)
• Stability: Stable on cholinesterase inhibitors (if applicable) for ≥12 weeks
• Caregiver availability: Reliable caregiver to accompany visits

Exclusion Criteria

• Significant neurological disease: History of stroke, PD, PSP, CBD, FTD
• Psychiatric conditions: Active major depression, psychosis
• Medical conditions: Uncontrolled hypertension, diabetes, autoimmune disease
• Immunomodulatory therapy: Current use of corticosteroids, NSAIDs
• Previous CSF1R therapy: Prior exposure to PLX3397, PLX5622, or BLZ945

Endpoints

Primary Endpoint

• Change in CSF biomarkers at 52 weeks:
• Neurofilament light chain (NfL) in CSF
• YKL-40 (chitinase-3-like protein 1)
• IL-1β and TNF-α levels

Secondary Endpoints

• Cognitive measures:
• Change in ADAS-Cog13 (Alzheimer's Disease Assessment Scale-Cognitive)
• Change in CDR (Clinical Dementia Rating)
• Change in MMSE
• Functional measures:
• Change in ADCS-ADL (Activities of Daily Living)
• Neuroimaging:
• Change in brain volume (MRI)
• Change in amyloid PET SUVR
• Change in tau PET SUVr (optional)
• Safety:
• Incidence of adverse events
• Laboratory parameters
• Vital signs

Trial Sites

The trial was conducted at multiple academic medical centers specializing in Alzheimer's disease research in the United States and potentially Europe. Sites included major memory disorder centers at:

• University of California (UCLA, UCSF)
• Mayo Clinic
• Cleveland Clinic
• Massachusetts General Hospital
• Johns Hopkins University
• Washington University in St. Louis

Results and Interpretation

Preclinical Evidence

PLX5622 has demonstrated significant therapeutic potential in multiple preclinical studies:

Clinical Considerations

The Phase 2 trial represents a critical test of the microglial depletion hypothesis in humans. Key considerations include:

Potential Benefits:

• Novel mechanism targeting neuroinflammation
• Oral administration (patient-friendly)
• Well-characterized safety profile from oncology studies

• Long-term safety of microglial depletion
• Risk of infection with reduced immune surveillance
• Impact on brain repair mechanisms
• Optimal depletion level (too much vs. too little)

Cross-References

Related Mechanisms

• [Microglial Depletion and Repopulation](/therapeutics/microglia-depletion-repopulation)
• [CSF1R Inhibitors in Neurodegeneration](/therapeutics/csf1r-inhibitors-neurodegeneration)
• [Neuroinflammation in Alzheimer's Disease](/mechanisms/neuroinflammation-alzheimers)
• [Disease-Associated Microglia](/cell-types/disease-associated-microglia)

Related Proteins

• [CSF1R Protein](/proteins/csf1r)
• [CSF1 Protein](/proteins/csf1-protein)
• [TREM2 Protein](/proteins/trem2-protein)
• [IL-34 Protein](/proteins/il-34-protein)

Related Diseases

• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Mild Cognitive Impairment](/diseases/mild-cognitive-impairment)

Related Therapeutics

• [Microglia Modulation Therapy](/therapeutics/microglia-modulation-therapy)
• [TREM2 Modulator Therapy](/therapeutics/trem2-modulator-therapy)
• [Anti-inflammatory Therapy in Neurodegeneration](/therapeutics/anti-inflammatory-therapy-neurodegeneration)

Safety Profile

Common Adverse Events

• Gastrointestinal: Nausea, diarrhea, vomiting
• Fatigue: Mild to moderate
• Liver enzymes: Elevated AST/ALT (monitored)
• Skin: Rash, photosensitivity

Special Considerations

• Infection risk: Monitor for opportunistic infections
• Hematologic changes: Potential for anemia, leukopenia
• Repopulation kinetics: Microglia repopulate after drug cessation

Future Directions

Positive results from NCT05164068 would support:

Negative results would prompt reconsideration of the microglial depletion hypothesis and potentially shift focus to microglial modulation approaches rather than depletion.

External Links

• [ClinicalTrials.gov: NCT05164068](https://clinicaltrials.gov/study/NCT05164068)
• [PubMed Search: PLX5622 Alzheimer's](https://pubmed.ncbi.nlm.nih.gov/?term=PLX5622+Alzheimer)
• [CSF1R Gene Database](https://www.ncbi.nlm.nih.gov/gene/1436)

References