Development and Validation of [3H]OF-NB1 for Preclinical Assessment of GluN1/2B Candidate Drugs

• Published in: Pharmaceuticals (Basel, Switzerland) Vol. 15; no. 8; p. 960
• Main Authors: Ahmed, Hazem, Gisler, Livio, Elghazawy, Nehal H., Keller, Claudia, Sippl, Wolfgang, Liang, Steven H., Haider, Ahmed, Ametamey, Simon M.
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 02.08.2022; MDPI
• Subjects: [3H]ifenprodil; Alzheimer's disease; Amino acids; Drug dosages; GluN1/2B receptors; Ligands; Localization; NMDA; PET imaging; Physiology; receptor occupancy; Signal transduction; σ1 and σ2 receptors
• ISSN: 1424-8247; 1424-8247
• DOI: 10.3390/ph15080960

GluN2B-enriched N-methyl-D-aspartate receptors (NMDARs) are implicated in several neurodegenerative and psychiatric diseases, such as Alzheimer’s disease. No clinically valid GluN1/2B therapeutic exists due to a lack of selective GluN2B imaging tools, and the state-of-the-art [3H]ifenprodil shows poor selectivity in drug screening. To this end, we developed a tritium-labeled form of OF-NB1, a recently reported selective GluN1/2B positron emission tomography imaging (PET) agent, with a molar activity of 1.79 GBq/µmol. The performance of [3H]OF-NB1 and [3H]ifenprodil was compared through head-to-head competitive binding experiments, using the GluN1/2B ligand CP-101,606 and the sigma-1 receptor (σ1R) ligand SA-4503. Contrary to [3H]ifenprodil, the usage of [3H]OF-NB1 differentiated between GluN1/2B and σ1R binding components. These results were corroborated by observations from PET imaging experiments in Wistar rats using the σ1R radioligand [18F]fluspidine. To unravel the binding modes of OF-NB1 and ifenprodil in GluN1/2B and σ1Rs, we performed a retrospective in silico study using a molecular operating environment. OF-NB1 maintained similar interactions to GluN1/2B as ifenprodil, but only ifenprodil successfully fitted in the σ1R pocket, thereby explaining the high GluN1/2B selectivity of OF-NB1 compared to ifenprodil. We successfully showed in a proof-of-concept study the superiority of [3H]OF-NB1 over the gold standard [3H]ifenprodil in the screening of potential GluN1/2B drug candidates.