Development of [18F]MIPS15692, a radiotracer with in vitro proof-of-concept for the imaging of MER tyrosine kinase (MERTK) in neuroinflammatory disease

Siu Wai Wong; Lucy Vivash; Ramesh Mudududdla; Nghi Nguyen; Stefan J Hermans; David M Shackleford; Judith Field; Lian Xue; Andrea Aprico; Nancy C Hancock; Mohammad Haskali; Michael A Stashko; Stephen V Frye; Xiaodong Wang; Michele D Binder; Uwe Ackermann; Michael W Parker; Trevor J Kilpatrick; Jonathan B Baell

doi:10.1016/j.ejmech.2021.113822

Development of [¹⁸F]MIPS15692, a radiotracer with in vitro proof-of-concept for the imaging of MER tyrosine kinase (MERTK) in neuroinflammatory disease

Eur J Med Chem. 2021 Dec 15:226:113822. doi: 10.1016/j.ejmech.2021.113822. Epub 2021 Sep 4.

Authors

Siu Wai Wong¹, Lucy Vivash², Ramesh Mudududdla¹, Nghi Nguyen¹, Stefan J Hermans³, David M Shackleford¹, Judith Field⁴, Lian Xue¹, Andrea Aprico⁴, Nancy C Hancock³, Mohammad Haskali⁵, Michael A Stashko⁶, Stephen V Frye⁶, Xiaodong Wang⁶, Michele D Binder⁷, Uwe Ackermann⁸, Michael W Parker⁹, Trevor J Kilpatrick¹⁰, Jonathan B Baell¹¹

Affiliations

¹ Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, 3052, Australia.
² The Central Clinical School and The Alfred Hospital, Monash University, Melbourne, Victoria, Australia.
³ ACRF Rational Drug Discovery Centre, St Vincent's Institute of Medical Research, Fitzroy, Victoria, 3065, Australia.
⁴ Florey Institute of Neuroscience and Mental Health, Parkville, Victoria, 3010, Australia.
⁵ Centre for Molecular Imaging, Peter MacCallum Cancer Centre, Parkville, Victoria, 3052, Australia.
⁶ Center for Integrative Chemical Biology and Drug Discovery, Division of Chemical Biology and Medicinal Chemistry, Eshelman School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, United States.
⁷ Florey Institute of Neuroscience and Mental Health, Parkville, Victoria, 3010, Australia; Department of Anatomy and Physiology, University of Melbourne, Parkville, Victoria, 3010, Australia.
⁸ Department of Nuclear Medicine and Centre for PET, Austin Health, Heidelberg, Victoria, 3084, Australia.
⁹ Department of Biochemistry and Pharmacology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria, 3010, Australia; ACRF Rational Drug Discovery Centre, St Vincent's Institute of Medical Research, Fitzroy, Victoria, 3065, Australia.
¹⁰ Florey Institute of Neuroscience and Mental Health, Parkville, Victoria, 3010, Australia; The Florey Department of Neuroscience and Mental Health, University of Melbourne, Parkville, Victoria, 3010, Australia. Electronic address: tkilpat@florey.edu.au.
¹¹ School of Pharmaceutical Sciences, Nanjing Tech University, No. 30 South Puzhu Road, Nanjing, 211816, People's Republic of China; Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, 3052, Australia. Electronic address: jonathan.baell@monash.edu.

PMID: 34563964
DOI: 10.1016/j.ejmech.2021.113822

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 (A_m) 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.

MeSH terms

Animals
Dose-Response Relationship, Drug
Drug Development*
Fluorine Radioisotopes
Mice
Molecular Structure
Neuroinflammatory Diseases / diagnostic imaging
Neuroinflammatory Diseases / drug therapy*
Positron-Emission Tomography
Radiopharmaceuticals / chemical synthesis
Radiopharmaceuticals / chemistry
Radiopharmaceuticals / pharmacology*
Structure-Activity Relationship
c-Mer Tyrosine Kinase / analysis
c-Mer Tyrosine Kinase / antagonists & inhibitors*
c-Mer Tyrosine Kinase / metabolism

Substances

Fluorine Radioisotopes
Radiopharmaceuticals
MERTK protein, human
c-Mer Tyrosine Kinase
Fluorine-18