Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198-5800, USA.
School of Physiology, Pharmacology and Neuroscience, Faculty of Life Sciences, University of Bristol, Bristol, BS8 1TD, UK; University of Exeter, St Luke's Campus, Heavitree Road, Exeter, EX1 2LU, UK.
Neuropharmacology. 2021 Dec 15;201:108818. doi: 10.1016/j.neuropharm.2021.108818. Epub 2021 Oct 2.
N-methyl-d-aspartate (NMDA) receptors (NMDARs) are a subtype of ionotropic glutamate receptor with important roles in CNS function. Since excessive NMDAR activity can lead to neuronal cell death and epilepsy, there is interest in developing NMDAR negative allosteric modulators (NAMs) as neuroprotective agents. In this study, we characterize the inhibitory properties of a novel NMDAR antagonist, UBP792. This compound displays partial subtype-selectivity by having a varied maximal inhibition of GluN2A-, GluN2B-, GluN2C-, and GluN2D-containing receptors (52%, 70%, 87%, 89%, respectively) with ICs 4-10 μM. UBP792 inhibited NMDAR responses by reducing l-glutamate and glycine potencies and efficacies. Consistent with non-competitive inhibition, increasing agonist concentrations 30-fold did not reduce UBP792 potency. UBP792 inhibition was also not competitive with the structurally-related positive allosteric modulator (PAM) UBP684. UBP792 activity was voltage-independent, unaffected by GluN1's exon-5, and reduced at low pH (except for GluN1/GluN2A receptors which were more sensitive at acidic pH). UBP792 binding appeared independent of agonist binding and may be entering the plasma membrane to gain access to its binding site. Inhibition by UBP792 is reduced when the ligand-binding domain (LBD) of the GluN2 subunit, but not that of the GluN1 subunit, is cross-linked in the closed-cleft, activated conformation. Thus, UBP792 may be inhibiting by stabilizing an open GluN2-LBD cleft associated with channel inactivation or by stabilizing downstream closed channel conformations allosterically-coupled to the GluN2-LBD. These findings further expand the repertoire displayed by NMDAR NAMs thus expanding the opportunities for developing NMDAR modulators with the most appropriate selectivity and physiological actions for specific therapeutic indications.
N-甲基-D-天冬氨酸（NMDA）受体（NMDAR）是离子型谷氨酸受体的一种亚型，在中枢神经系统功能中具有重要作用。由于过度的 NMDAR 活性会导致神经元细胞死亡和癫痫发作，因此人们对开发 NMDAR 负变构调节剂（NAM）作为神经保护剂产生了兴趣。在这项研究中，我们描述了一种新型 NMDA 拮抗剂 UBP792 的抑制特性。该化合物通过对包含 GluN2A、GluN2B、GluN2C 和 GluN2D 亚基的受体显示出不同的最大抑制作用（分别为 52%、70%、87%和 89%），具有 4-10μM 的 IC50，表现出亚型选择性。UBP792 通过降低 L-谷氨酸和甘氨酸的效力和功效来抑制 NMDAR 反应。与非竞争性抑制一致，增加激动剂浓度 30 倍并不会降低 UBP792 的效力。UBP792 的抑制作用也与结构相关的正变构调节剂（PAM）UBP684 不竞争。UBP792 的活性与电压无关，不受 GluN1 的外显子 5 影响，并且在低 pH 值下降低（除了 GluN1/GluN2A 受体在酸性 pH 值下更敏感）。UBP792 的结合似乎独立于激动剂结合，可能进入质膜以进入其结合位点。当 GluN2 亚基的配体结合域（LBD）而不是 GluN1 亚基的 LBD 在封闭裂隙、激活构象中交联时，UBP792 的抑制作用会降低。因此，UBP792 可能通过稳定与通道失活相关的开放 GluN2-LBD 裂隙，或者通过稳定与 GluN2-LBD 变构偶联的下游闭合通道构象来抑制。这些发现进一步扩展了 NMDAR NAMs 所显示的作用谱，从而为开发具有特定治疗适应症最合适选择性和生理作用的 NMDAR 调节剂提供了更多机会。
