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by claude@2026-07, 2026-07-16
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This study developed and validated [3H]5-MOP, a selective radioligand for the colony stimulating factor 1 receptor (CSF1R), by performing in vitro saturation binding experiments in human and murine tissues and using autoradiography to assess binding affinity and displacement by known CSF1R inhibitors. [3H]5-MOP showed high-affinity binding (KD = 9.8 nM) to a single saturable site in human meningioma tissue, and binding could be displaced by CSF1R inhibitors such as CPPC, sCSF1inh, and GW-2580, while [3H]CPPC exhibited substantial cross-reactivity to other brain kinases. A key caveat is that the validation is based on in vitro binding and autoradiography without detailed in vivo performance metrics reported in the provided text. This paper does not explicitly discuss endometriosis or adenomyosis; it was included in the corpus via a keyword match in the upstream search index.
Abstract
Colony stimulating factor 1 receptor (CSF1R) is a tyrosine kinase receptor that is expressed exclusively in microglia within the CNS. Its endogenous ligands, colony stimulating factor-1 (CSF1) and interleukin-34 (IL-34), are released from neurons, positioning CSF1R as a key mediator receptor of neuron-glia communication. CSF1R is considered not only a potential drug target, but also a biomarker of neuroinflammation. From that perspective, selective radioligands for neuroimaging are of great interest for imaging neuroinflammation and determining drug occupancy. In this study, we have validated the binding characteristics of a CSF1R inhibitor, 4-((5-MethOxy-6-((5-methoxypyridin-2-yl)methoxy)pyridin-3-yl)methyl)-2-(1-methyl-1H-pyrazol-4-yl)pyrimidine (5-MOP) as a novel CSF1R radioligand, by performing in vitro saturation binding experiments in human and murine tissues. 5-MOP was found to be selective for CSF1R among a broad range of kinases. Autoradiography revealed that [ 3 H]5-MOP binds with high affinity (K D = 9.8 nM) to a single saturable binding site in human meningioma tissues, and this binding was displaced with known CSF1R inhibitors, including CPPC, sCSF1 inh and GW-2580. In contrast, CPPC, which has been extensively used as a CSF1R radioligand showed substantial cross-reactivity to other brain kinases, including Trk A/B/C, and [ 3 H]CPPC could only be displaced with CPPC itself, not by other ligands, including 5-MOP. These results identify [ 3 H]5-MOP as the most selective radioligand currently available, enabling accurate detection of drug occupancy and activated microglia. Significance of the study This study identifies and validates a novel selective radioligand that binds CSF1R with high selectivity and low nanomolar affinity. Because CSF1R is selectively expressed in activated microglia, this radioligand could be useful for detecting neuroinflammatory activity.
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Abstract
Colony stimulating factor 1 receptor (CSF1R) is a tyrosine kinase receptor that is expressed exclusively in microglia within the CNS. Its endogenous ligands, colony stimulating factor-1 (CSF1) and interleukin-34 (IL-34), are released from neurons, positioning CSF1R as a key mediator receptor of neuron-glia communication. CSF1R is considered not only a potential drug target, but also a biomarker of neuroinflammation. From that perspective, selective radioligands for neuroimaging are of great interest for imaging neuroinflammation and determining drug occupancy.
In this study, we have validated the binding characteristics of a CSF1R inhibitor, 4-((5-MethOxy-6-((5-methoxypyridin-2-yl)methoxy)pyridin-3-yl)methyl)-2-(1-methyl-1H-pyrazol-4-yl)pyrimidine (5-MOP) as a novel CSF1R radioligand, by performing in vitro saturation binding experiments in human and murine tissues. 5-MOP was found to be selective for CSF1R among a broad range of kinases. Autoradiography revealed that [3H]5-MOP binds with high affinity (KD = 9.8 nM) to a single saturable binding site in human meningioma tissues, and this binding was displaced with known CSF1R inhibitors, including CPPC, sCSF1inh and GW-2580. In contrast, CPPC, which has been extensively used as a CSF1R radioligand showed substantial cross-reactivity to other brain kinases, including Trk A/B/C, and [3H]CPPC could only be displaced with CPPC itself, not by other ligands, including 5-MOP. These results identify [3H]5-MOP as the most selective radioligand currently available, enabling accurate detection of drug occupancy and activated microglia.
Significance of the study This study identifies and validates a novel selective radioligand that binds CSF1R with high selectivity and low nanomolar affinity. Because CSF1R is selectively expressed in activated microglia, this radioligand could be useful for detecting neuroinflammatory activity.
Competing Interest Statement
BBA, MH, TJ and JFB are employees of H. Lundbeck A/S that commercialises pharmacological products for CNS disorder. JDM has been a consultant for H. Lundbeck A/S
List of abbreviations
- 5-MOP
- 4-((5-methoxy-6-((5-methoxypyridin-2-yl)methoxy)pyridin-3-yl)methyl)-2-(1-methyl-1H-pyrazol-4-yl)pyrimidine
- AD
- Alzheimer’s disease
- Bmax
- Maximum binding capacity
- BSA
- Bovin serum albumin
- CNS
- Central nervous system
- CPPC
- 5-cyano-N-(4-(4-methylpiperazin-1 yl)-2-(piperidin-1-yl)phenyl)furan-2-carboxamide
- CSF1R
- Colony stimulating factor 1 receptor
- GW-2580
- 5-(3 Methoxy-4-((4-methoxybenzyl)oxy)benzyl)pyrimidine-2,4-dia mine
- IC50
- Half-maximal inhibitory concentration
- JNJ-CSF1R-1
- 5-cyano-N-(4-(4-(2-(fluoro)ethyl)piperazin-1-yl)-2-(piperidin-1-yl)phenyl)furan-2-carboxamide
- KA
- Kainic acid
- Kd
- Constant of dissociation
- MgCl2
- Magnesium chloride
- MS
- Multiple sclerosis
- mTLE
- Medial temporal lobe epilepsy
- PBR28
- N-(2-methoxybenzyl)-N-(4-phenoxypyridn-3-yl)acetamide
- PD
- Parkinson’s disease
- PET
- Positron emission tomography
- pMCAo
- Permanent medial cerebral artery occlusion
- PK11195
- 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinoline carboxamide
- sCSF1Rinh
- (S)-4-(3-((2-(6-methoxypyridin-3-yl)-2,3-dihydrobenzo[b]dioxin-6-yl)methyl)-3H-imidazo[4,5-b]pyridin-6-yl)-2-methylbut-3-yn-2-amine
- TE
- Tissue equivalent
- TR-FRET
- Time-resolved fluorescence energy transfer
- TSPO
- Translocator protein, 18kDa
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