Synthesis and Preliminary Evaluation of ¹¹C‐Labeled VU0467485/AZ13713945 and Its Analogues for Imaging Muscarinic Acetylcholine Receptor Subtype 4

Abstract

Muscarinic acetylcholine receptors (mAChRs) have five distinct subunits (M1–M5) and are involved in the action of the neurotransmitter acetylcholine in the central and peripheral nervous system. Attributed to the promising clinical efficacy of xanomeline, an M1/M4‐preferring agonist, in patients of schizophrenia and Alzheimer's disease, M1‐ or M4‐selective mAChR modulators have been developed that target the topographically distinct allosteric sites. Herein we report the synthesis and preliminary evaluation of 11C‐labeled positron emission tomography (PET) ligands based on a validated M4R positive allosteric modulator VU0467485 (AZ13713945) to facilitate drug discovery. [11C]VU0467485 and two other ligands were prepared in high radiochemical yields (>30 %, decay‐corrected) with high radiochemical purity (>99 %) and high molar activity (>74 GBq μmol−1). In vitro autoradiography studies indicated that these three ligands possess moderate‐to‐high in vitro specific binding to M4R. Nevertheless, further physiochemical property optimization is necessary to overcome the challenges associated with limited brain permeability.

Imaging Autotaxin In Vivo with 18F-Labeled Positron Emission Tomography Ligands

“…The in vitro autoradiography was performed as previously described with minor modification in this work . Livers from normal and LPS-treated mice were cut into 20 μm sections and stored at −80 °C until they were used for the experiment.…”

“…The PET imaging studies were performed as previously described with minor modification in this work . Dynamic PET scans of 60 min were conducted by a Genisys PET scanner.…”

“…The in vitro autoradiography was performed as previously described with minor modification in this work. 58 Livers from normal and LPS-treated mice were cut into 20 μm sections and stored at −80 °C until they were used for the experiment. The mouse liver sections were preincubated with Tris−HCl buffer (pH = 7.4, 50 mM) solution for 20 min at ambient temperature, followed by incubation with [ 18 F]20 for 30 min at room temperature.…”

“…The PET imaging studies were performed as previously described with minor modification in this work. 58 Dynamic PET scans of 60 min were conducted by a Genisys 4 PET scanner. CD-1 mice were kept under anesthesia with 1.5% (v/v) isoflurane during the scan.…”

Structure–activity relationship of pyrazol-4-yl-pyridine derivatives and identification of a radiofluorinated probe for imaging the muscarinic acetylcholine receptor M4

“…While numerous therapeutic ligands have been reported, the development of M 4 PET radioligands is lagging behind. We recently reported on the synthesis and biological evaluation of [ 11 C]VU0467485, as well as two other carbon-11 labeled derivatives bearing an additional fluorine atom at different positions of the phenyl moiety 41 . Despite obtaining some degree of specific binding by in vitro autoradiography, this class of compounds was deemed unsuitable for in vivo applications due to low brain uptake 41 .…”