Hentzer, M. | bioRxiv Science

bioRxiv2026

5-MOP: a novel and selective colony stimulating factor-1 receptor (CSF1R) radiotracer

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 studyThis 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.

neuroscience↗

bioRxiv2018

LRRK2 exonic variants associated with Parkinson’s disease augment phosphorylation levels for LRRK2-Ser1292 and Rab10-Thr73

Leucine-rich repeat kinase 2 (LRRK2) is associated to Parkinsons disease (PD). The most common form of LRRK2 PD is caused by the G2019S variant. Besides G2019S, eight other LRRK2 variants causing familial PD also have amino acid substitutions located in a LRRK2 enzymatic domainsuggesting that enzymatic activity is at the core of mechanisms underlying disease risk. Common LRRK2 polymorphic risk variations such as G2385R, A419V, R1628 and M1646T all reside in other LRRK2 domains. Prior knowledge is limited on how these variants influence LRRK2 function. To investigate the impact on enzymatic function of both rare and common LRRK2 variation a comprehensive profiling of nineteen LRRK2 exonic variants was pursued. Six LRRK2 phosphorylation sites were identified by mass spectrometry. Besides already known phosphorylation sites such as Ser910, Ser935, Ser955, Ser973 and Ser1292 also Thr826 was confirmed by a targeted MRM assay as a LRRK2 phosphorylation site in mammalian cells. Phosphorylation site occupancy for all six LRRK2 sites was obtained but no obvious correlation to risk of disease was found. Instead, application of phospho-specific antibodies targeting LRRK2 phosphorylation sites confirmed that autophosphorylation at Ser1292 was significantly increased for all disease-causing variants whereas no significant differences could be observed for the common intermediate risk variants. Recently, Rab10 and Rab12 have been shown to be bona fide LRRK2 substrates and we find that both rare and common LRRK2 exonic variants augment the phosphorylation of Rab10. This was not observed with Rab12. Furthermore, the protective variant N551K has reduced Rab10 phosphorylation compared to LRRK2 WT. This was not observed with the protective variant R1398H. Our findings support the hypothesis that increased LRRK2 kinase function is associated with increased PD risk but also highlights the need for more sensitive tools for detection of increases in kinase activity in carriers of LRRK2 PD risk variants.\n\nAbbreviations

biochemistry↗