Discovery of a selective GluN2A-containing N-methyl-d-aspartate glutamate receptor positive modulator as a novel post-stroke neuroprotective therapy
N-methyl-d-aspartate glutamate receptors (NMDARs) are fundamental to many normal brain functions such as cognition and memory; however, NMDAR over-activation can cause neuronal death as a result of excitotoxicity. Although the mechanisms underlying these paradoxical roles of NMDARs remain unclear, accumulating evidence from both in-vitro and in-vivo studies suggested that GluN1/GluN2B-NMDAR subtypes mediated signaling may contribute cell death, while GluN1/GluN2A-NMDARs signaling promote
... ling promote pro-survival outcomes. Employing an extensive drug discovery pipeline process, we identified and characterized a class of novel small molecules that specifically potentiate GluN1/GluN2A NMDARs in an allosteric manner. This new class of molecules is referred to as NMDAR positive allosteric modulators (Npams) with the Npam43 being the lead compound. Mutational analysis demonstrates that Npam43 binds to a novel binding site on the N-terminal domain (NTD) at the interface between the GluN1 and GluN2A subunits. Functional characterizations in in-vitro show that Npam43 activates cell survival signaling, increasing phosphorylated CREB levels, and thereby protects neurons against NMDAR-mediated excitotoxicity and NMDA-independent H₂O₂ oxidative stress. Moreover, Npam43 potentiates GluN1/GluN2A-mediated synaptic currents, and facilitates the induction of long-term potentiation (LTP) in hippocampal slices acutely prepared from mouse brain. Using a rat focal ischemia model of stroke in-vivo, we show that systemic administration of Npam43 not only modulates GluN1/GluN2A containing NMDARs but also substantially reduces neuronal damage and improves behavioral outcomes. Together, our study not only develops a novel class of Npams for GluN1/GluN2A NMDARs, but also demonstrates their therapeutic potential as novel neuroprotectants for stroke. In addition, the present work also provides strong evidence supporting a critical role of GluN1/GluN2A subtype of NMDARs in promoting cell survival.