AUTHOR=Lee Ji Youn , Kim Ho Young , Martorano Paul , Riad Aladdin , Taylor Michelle , Luedtke Robert R. , Mach Robert H. 

TITLE=In vitro characterization of [125I]HY-3-24, a selective ligand for the dopamine D3 receptor

JOURNAL=Frontiers in Neuroscience

VOLUME=18

YEAR=2024

URL=https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2024.1380009

DOI=10.3389/fnins.2024.1380009

ISSN=1662-453X

ABSTRACT=<sec><title>Introduction</title><p>Dopamine D3 receptor (D3R) ligands have been studied for the possible treatment of neurological and neuropsychiatric disorders. However, selective D3R radioligands for <italic>in vitro</italic> binding studies have been challenging to identify due to the high structural similarity between the D2R and D3R. In a prior study, we reported a new conformationally-flexible benzamide scaffold having a high affinity for D3R and excellent selectivity vs. D2R. In the current study, we characterized the <italic>in vitro</italic> binding properties of a new radioiodinated ligand, [<sup>125</sup>I]HY-3-24.</p></sec><sec><title>Methods</title><p><italic>In vitro</italic> binding studies were conducted in cell lines expressing D3 receptors, rat striatal homogenates, and rat and non-human primate (NHP) brain tissues to measure regional brain distribution of this radioligand.</p></sec><sec><title>Results</title><p>HY-3-24 showed high potency at D3R (<italic>K<sub>i</sub></italic> = 0.67 ± 0.11 nM, IC<sub>50</sub> = 1.5 ± 0.58 nM) compared to other D2-like dopamine receptor subtypes (D2R <italic>K<sub>i</sub></italic> = 86.7 ± 11.9 nM and D4R <italic>K<sub>i</sub></italic> &gt; 1,000). The <italic>K<sub>d</sub></italic> (0.34 ± 0.22 nM) and B<sub>max</sub> (38.91 ± 2.39 fmol/mg) values of [<sup>125</sup>I]HY-3-24 were determined. <italic>In vitro</italic> binding studies in rat striatal homogenates using selective D2R and D3R antagonists confirmed the D3R selectivity of [<sup>125</sup>I]HY-3-24. Autoradiography results demonstrated that [<sup>125</sup>I]HY-3-24 specifically binds to D3Rs in the nucleus accumbens, islands of Calleja, and caudate putamen in rat and NHP brain sections.</p></sec><sec><title>Conclusion</title><p>These results suggest that [<sup>125</sup>I]HY-3-24 appears to be a novel radioligand that exhibits high affinity binding at D3R, with low binding to other D2-like dopamine receptors. It is anticipated that [<sup>125</sup>I]HY-3-24 can be used as the specific D3R radioligand.</p></sec>