@article{d3e4a1de8bc845d6a2e6abec38bf5ff4,
title = "Development of [18F]MIPS15692, a radiotracer with in vitro proof-of-concept for the imaging of MER tyrosine kinase (MERTK) in neuroinflammatory disease",
abstract = "MER tyrosine kinase (MERTK) upregulation is associated with M2 polarization of microglia, which plays a vital role in neuroregeneration following damage induced by neuroinflammatory diseases such as multiple sclerosis (MS). Therefore, a radiotracer specific for MERTK could be of great utility in the clinical management of MS, for the detection and differentiation of neuroregenerative and neurodegenerative processes. This study aimed to develop an [18F] ligand with high affinity and selectivity for MERTK as a potential positron emission tomography (PET) radiotracer. MIPS15691 and MIPS15692 were synthesized and kinase assays were utilized to determine potency and selectivity for MERTK. Both compounds were shown to be potent against MERTK, with respective IC50 values of 4.6 nM and 4.0 nM, and were also MERTK-selective. Plasma and brain pharmacokinetics were measured in mice and led to selection of MIPS15692 over MIPS15691. X-ray crystallography was used to visualize how MIPS15692 is recognized by the enzyme. [18F]MIPS15692 was synthesized using an automated iPHASE FlexLab module, with a molar activity (Am) of 49 ± 26 GBq/μmol. The radiochemical purity of [18F]MIPS15692 was >99% and the decay-corrected radiochemical yields (RCYs) were determined as 2.45 ± 0.85%. Brain MERTK protein density was measured by a saturation binding assay in the brain slices of a cuprizone mouse model of MS. High levels of specific binding of [18F]MIPS15692 to MERTK were found, especially in the corpus callosum/hippocampus (CC/HC). The in vivo PET imaging study of [18F]MIPS15692 suggested that its neuroPK is sub-optimal for clinical use. Current efforts are underway to optimize the neuroPK of our next generation PET radiotracers for maximal in vivo utility.",
keywords = "Autoradiography, CNS radiotracer, MER tyrosine Kinase, Multiple sclerosis, Positron emission tomography, X-ray crystallography",
author = "Wong, {Siu Wai} and Lucy Vivash and Ramesh Mudududdla and Nghi Nguyen and Hermans, {Stefan J.} and Shackleford, {David M.} and Judith Field and Lian Xue and Andrea Aprico and Hancock, {Nancy C.} and Mohammad Haskali and Stashko, {Michael A.} and Frye, {Stephen V.} and Xiaodong Wang and Binder, {Michele D.} and Uwe Ackermann and Parker, {Michael W.} and Kilpatrick, {Trevor J.} and Baell, {Jonathan B.}",
note = "Funding Information: The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: L.V. reports NHMRC MRFF funding for unrelated projects, research funding from Biogen, Eisai and LMI for unrelated projects, and personal fees from Biogen. J.F. is a current employee of CSL Innovation Ltd. S.V.F. is a founder, stockholder, and board member of the UNC start-up Meryx Inc. which is commercializing MERTK related UNC intellectual property and conducting a phase 1 clinical trial of MERTK inhibitors. X.W. also holds stock in Meryx Inc.. S.V.F. & X.W. report patent for UNC2876A from the University of North Carolina . Funding Information: The National Health and Medical Research Council of Australia ( NHMRC ) is thanked for research support for J.B.B. (2017–2021 Principal Research Fellowship #1117602 and Project Grant #1142814), for T.J.K (2020–2024 NHMRC Investigator grant ##1175775). and for M.W.P. (2017–2021 Senior Principal Research Fellowship #1117183; 2021–2025 Investigator grant #1194263). The Perpetual Trustees Company Ltd is also thanked for providing research support for this project. The study was also funded by the Melbourne Neuroscience Institute Interdisciplinary Seed Grant. The Australian Institute of Nuclear Science and Engineering (AINSE Ltd.) is thanked for financial support for S.W.W. through the Postgraduate Research Award. Funding Information: Australian Translational Medicinal Chemistry Facility (ATMCF) acknowledges the support of the Australian Government's National Collaborative Research Infrastructure Strategy (NCRIS) program via Therapeutic Innovation Australia (TIA). This research was undertaken in part using the MX2 beamline at the Australian Synchrotron, part of ANSTO, and made use of the Australian Cancer Research Foundation (ACRF) detector. The Florey Institute of Neuroscience and Mental Health and St. Vincent's Institute acknowledge the strong support from the Victorian Government and in particular the funding from the Operational Infrastructure Support Grant. Funding Information: Given the prevalence of efflux mechanisms in limiting compound access to the CNS, the unbound fractions of MIPS15691 and MIPS15692 were measured in both plasma and brain (Table S3) to support preliminary assessment of efflux potential through determination of the unbound brain-to-plasma partitioning ratio, Kp,uu. Kp,uu is calculated as a ratio of unbound drug in brain to unbound drug in plasma (Cu,brain/Cu,plasma). A compound with a Kp,uu value close to 1 is expected to be able to cross the BBB through passive diffusion and is not considered to be a substrate of efflux transporters at the BBB. Compounds with a value of Kp, uu of less than 1 maybe susceptible for efflux transporters, and/or limited brain penetration as a result of low passive permeability across the BBB [15]. For both compounds, Kp,uu values continued to increase over the 1 h post-dose period (Fig. 5 (C)), suggesting that the distributional equilibrium between brain and plasma had not been reached within this timeframe. It has been suggested that interpretation of Kp,uu as an indicator of compound susceptibility to efflux at the blood-brain-barrier assumes that distribution into the CNS is at steady state [15]. On this basis, the increasing Kp,uu values 1 h post-dose suggest that it was not possible to conclude whether flux of MIPS15691 and MIPS15692 across the BBB was efflux-limited. One compound was therefore selected for an extended assessment of the neuroPK.The more preferable parameters (higher fu, brain and Kp, uu) of MIPS15692 compared to MIPS15691 led to its selection for more comprehensive neuroPK characterization for MIPS15692. The Kp, uu of MIPS15692 was close to unity by 2 h (Fig. 6), suggesting that compound accessing the CNS ultimately does so via passive flux across the BBB [15]. Collectively, given its high potency and selectivity for MERTK and promising neuro-PK properties, these data supported the potential utility of MIPS15692 for use as a CNS PET radiotracer for MERTK.The National Health and Medical Research Council of Australia (NHMRC) is thanked for research support for J.B.B. (2017?2021 Principal Research Fellowship #1117602 and Project Grant #1142814), for T.J.K (2020?2024 NHMRC Investigator grant ##1175775). and for M.W.P. (2017?2021 Senior Principal Research Fellowship #1117183; 2021?2025 Investigator grant #1194263). The Perpetual Trustees Company Ltd is also thanked for providing research support for this project. The study was also funded by the Melbourne Neuroscience Institute Interdisciplinary Seed Grant. The Australian Institute of Nuclear Science and Engineering (AINSE Ltd.) is thanked for financial support for S.W.W. through the Postgraduate Research Award.The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: L.V. reports NHMRC MRFF funding for unrelated projects, research funding from Biogen, Eisai and LMI for unrelated projects, and personal fees from Biogen. J.F. is a current employee of CSL Innovation Ltd. S.V.F. is a founder, stockholder, and board member of the UNC start-up Meryx Inc. which is commercializing MERTK related UNC intellectual property and conducting a phase 1 clinical trial of MERTK inhibitors. X.W. also holds stock in Meryx Inc. S.V.F. & X.W. report patent for UNC2876A from the University of North Carolina.Australian Translational Medicinal Chemistry Facility (ATMCF) acknowledges the support of the Australian Government's National Collaborative Research Infrastructure Strategy (NCRIS) program via Therapeutic Innovation Australia (TIA). This research was undertaken in part using the MX2 beamline at the Australian Synchrotron, part of ANSTO, and made use of the Australian Cancer Research Foundation (ACRF) detector. The Florey Institute of Neuroscience and Mental Health and St. Vincent's Institute acknowledge the strong support from the Victorian Government and in particular the funding from the Operational Infrastructure Support Grant. Publisher Copyright: {\textcopyright} 2021 Copyright: Copyright 2021 Elsevier B.V., All rights reserved.",
year = "2021",
month = dec,
day = "15",
doi = "10.1016/j.ejmech.2021.113822",
language = "English",
volume = "226",
journal = "European Journal of Medicinal Chemistry",
issn = "0223-5234",
publisher = "Elsevier",
}