7-Methoxyderivative of tacrine is a ‘foot-in-the-door’ open-channel blocker of GluN1/GluN2 and GluN1/GluN3 NMDA receptors with neuroprotective activity in vivo

N-methyl-d-aspartate receptors (NMDARs) are ionotropic glutamate receptors that mediate excitatory neurotransmission in the mammalian central nervous system (CNS), and their dysregulation results in the aetiology of many CNS syndromes. Several NMDAR modulators have been used successfully in clinical trials (including memantine) and NMDARs remain a promising pharmacological target for the treatment of CNS syndromes. 1,2,3,4-Tetrahydro-9-aminoacridine (tacrine; THA) was the first approved drug for Alzheimer's disease (AD) treatment. 7-methoxyderivative of THA (7-MEOTA) is less toxic and showed promising results in patients with tardive dyskinesia. We employed electrophysiological recordings in HEK293 cells and rat neurones to examine the mechanism of action of THA and 7-MEOTA at the NMDAR. We showed that both THA and 7-MEOTA are "foot-in-the-door" open-channel blockers of GluN1/GluN2 receptors and that 7-MEOTA is a more potent but slower blocker than THA. We found that the IC50 values for THA and 7-MEOTA exhibited the GluN1/GluN2A < GluN1/GluN2B < GluN1/GluN2C = GluN1/GluN2D relationship and that 7-MEOTA effectively inhibits human GluN1/GluN2A-M817V receptors that carry a pathogenic mutation. We also showed that 7-MEOTA is a "foot-in-the-door" open-channel blocker of GluN1/GluN3 receptors, although these receptors were not inhibited by memantine. In addition, the inhibitory potency of 7-MEOTA at synaptic and extrasynaptic hippocampal NMDARs was similar, and 7-MEOTA exhibited better neuroprotective activity when compared with THA and memantine in rats with NMDA-induced lesions of the hippocampus. Finally, intraperitoneal administration of 7-MEOTA attenuated MK-801-induced hyperlocomotion and pre-pulse inhibition deficit in rats. We conclude that 7-MEOTA may be considered for the treatment of diseases associated with the dysfunction of NMDARs.