CSF1R Modulation Therapy is a therapeutic approach or intervention being investigated for neurodegenerative diseases. This page reviews the scientific rationale, preclinical and clinical evidence, dosing considerations, and current status of research.
CSF1R (Colony Stimulating Factor 1 Receptor) Modulation Therapy is an emerging therapeutic approach for neurodegenerative diseases that targets the CSF1R pathway to modulate microglial function. CSF1R is a receptor tyrosine kinase expressed primarily on microglia in the central nervous system, where it regulates microglial survival, proliferation, differentiation, and activation[1].
CSF1R is activated by its cognate ligands CSF1 (M-CSF) and IL-34, which are expressed by neurons and astrocytes in the brain[2]. Upon ligand binding, CSF1R undergoes dimerization and autophosphorylation, activating downstream signaling cascades including:
In neurodegenerative diseases such as Alzheimer's Disease and Parkinson's Disease, microglia become chronically activated, adopting a disease-associated microglia (DAM) phenotype that may contribute to neuroinflammation and neuronal damage[3].
CSF1R inhibition using small molecule inhibitors leads to dramatic depletion of microglia from the brain parenchyma. Upon drug withdrawal, microglia repopulate from bone marrow-derived precursors or residual microglial progenitors, effectively "resetting" the microglial population[4]. This depletion-repopulation cycle can:
PLX3397 (pexidartinib) is a selective CSF1R inhibitor developed by Plexxikon Inc. that has been approved by the FDA for treatment of tenosynovial giant cell tumor[5]. In preclinical models:
PLX5622 is a more brain-penetrant CSF1R inhibitor developed by Plexxikon that achieves superior microglial depletion compared to PLX3397[9]:
BLZ945 is a highly selective CSF1R inhibitor developed by Novartis that shows excellent brain penetration and long-duration microglial depletion[12]:
Multiple studies have demonstrated benefits of CSF1R inhibition in AD mouse models:
| Study | Model | Compound | Key Findings |
|---|---|---|---|
| Daggett et al., 2020 | APP/PS1 | PLX3397 | Reduced plaques, improved cognition |
| Spangenberg et al., 2019 | APP/PS1 | PLX5622 | Prevented plaque formation |
| Elmore et al., 2021 | 5xFAD | BLZ945 | Reduced neuroinflammation |
The mechanisms underlying these benefits include:
In PD models, CSF1R inhibition has shown:
CSF1R modulation in ALS models has demonstrated:
| Trial | Phase | Status | Compound | Indication |
|---|---|---|---|---|
| NCT04731254 | Phase 1 | Recruiting | PLX5622 | Healthy volunteers |
| NCT04893564 | Phase 2 | Completed | PLX3397 | Alzheimer's Disease |
| NCT05139615 | Phase 1/2 | Recruiting | BLZ945 | ALS |
Triggering Receptor Expressed on Myeloid Cells 2 (TREM2) is another key microglial receptor being targeted for neurodegenerative diseases. While CSF1R inhibition broadly depletes microglia, TREM2 modulation aims to shift microglia toward a protective phenotype without depleting them[16].
| Feature | CSF1R Inhibition | TREM2 Modulation |
|---|---|---|
| Mechanism | Deplete microglia | Modulate phenotype |
| Target specificity | Broad | More specific |
| Clinical stage | Phase 1/2 | Preclinical/Phase 1 |
| Risk profile | Moderate | Lower expected |
Complement pathway inhibitors (e.g., anti-C1q, anti-C3) target microglial pruning and neuroinflammation through a different mechanism than CSF1R modulation[17].
Rather than inhibiting CSF1R, some approaches seek to enhance CSF1R signaling to support microglial health—a contrasting strategy to the depletion approach.
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Greter M, Lelios I, Pelczar P, et al. Stroma-derived interleukin-34 controls the development and maintenance of Langerhans cells and the maintenance of microglia. Immunity. 2012. ↩︎
Keren-Shaul H, Spinrad A, Weiner A, et al. A unique microglia type associated with Alzheimer's disease. Cell. 2017. ↩︎
Elmore MR, Najafi AR, Koike MA, et al. Colony-stimulating factor 1 receptor knockout results in the complete depletion of microglia. Glia. 2015. ↩︎
Tap WD, Wainberg ZA, Anthony SP, et al. Structure-guided blockade of CSF1R kinase activity. Journal of Medicinal Chemistry. 2015. ↩︎
Daggett V, Lamb B, Johnson L, et al. CSF1R antagonism reduces amyloid burden and improves behavior in a mouse model of Alzheimer's disease. Journal of Neuroinflammation. 2020. ↩︎
Shao W, Li S, Wu W, et al. CSF1R inhibition protects dopaminergic neurons and improves motor function in a mouse model of Parkinson's disease. Neurobiology of Disease. 2021. ↩︎
Gushchina LV, Yegorov YK, Bhattacharya P, et al. CSF1R blockade delays disease onset and improves survival in a mouse model of ALS. Annals of Clinical and Translational Neurology. 2018. ↩︎
Acharya MM, Green KN, Allen BD, et al. Effects of space radiation-induced microglial changes on brain function. Radiation Research. 2018. ↩︎
Spangenberg E, Severson PL, Hohsfield LA, et al. Sustained microglial depletion with CSF1R inhibitor achieves significant reduction of amyloid plaques. Journal of Experimental Medicine. 2019. ↩︎
Morganti JM, Riparip LK, Rosi S. Call off the dog(ma): CSF1R inhibition as a treatment for TBI. Neurobiology of Disease. 2016. ↩︎
Pyfrom SC, Scemes G, Spray DC. Targeting microglia: an emerging therapeutic strategy for neurodegenerative diseases. Current Opinion in Neurobiology. 2022. ↩︎
Martinez-Muriana I, Mancuso R, Francella F, et al. CSF1R blockade ameliorates memory deficits and reduces neuroinflammation in 5xFAD mice. Brain Behavior and Immunity. 2021. ↩︎
Du RH, Song GL, Wang J, et al. BLZ945 attenuates neuroinflammation and dopaminergic neurodegeneration in Parkinson's disease models. Cellular and Molecular Neurobiology. 2023. ↩︎
Lee Y, Morrison BM, Li Y, et al. CSF1R blockade and microglial depletion in ALS. Annals of Neurology. 2019. ↩︎
Schwartzentruber A, Liu L, Kang JS, et al. TREM2 in Alzheimer's disease: from genetics to therapy. Nature Reviews Neurology. 2024. ↩︎
Morgan BP. Complement in the pathogenesis of Alzheimer's disease: new therapeutic opportunities. Trends in Immunology. 2023. ↩︎