Dizocilpine-derived K2060 exhibits enhanced blockage at NMDA receptors with impaired Mg2+ block and provides strong protection against audiogenic seizures

Background and Purpose: Voltage-dependent Mg2+ block is a defining feature of the GluN1/GluN2 subtype of N-methyl-D-aspartate receptors (NMDARs). We tested how impaired Mg2+ block at GluN1/GluN2A receptors mutated at the GluN2A-N615 position modifies inhibition by dizocilpine-derived K2060 compared with clinically used memantine and ketamine. Experimental Approach: Electrophysiological recordings were performed on recombinant wild-type (WT) and mutated GluN1/GluN2A receptors expressed in HEK293T cells. Acute hippocampal slice electrophysiology and behavioural studies were conducted in WT and knock-in GluN2A-N615S mice. In vivo tolerability and efficacy were evaluated using open field testing, prepulse inhibition (PPI), and protection against audiogenic seizures (AGS). Key Results: Mg2+ reduced the apparent potency of all three blockers and slowed onset at the GluN1/GluN2A-WT receptor. These Mg2+-dependent effects were absent or markedly reduced at the GluN1/GluN2A-N615S and GluN1/GluN2A-N615K receptors. In addition, K2060 showed slower unbinding and greater trapping than memantine. In hippocampal slices from GluN2A-N615S mice, K2060 exhibited enhanced but slower onset inhibition than memantine and ketamine. In vivo, K2060 caused no overt behavioural disruption at 5 mg/kg (i.p.) and did not further disrupt PPI. All three blockers protected GluN2A-N615S mice against AGS at 5 mg/kg (i.p.); only K2060 remained protective at 1 mg/kg (i.p.). Conclusions and Implications: Impaired Mg2+; block removes a physiological constraint on the action of NMDAR blockers. K2060 exhibited the most favourable pharmacological profile, supporting its further evaluation for studies with NMDAR hyperfunction models. Additional pharmacokinetic, safety, and disease-model studies are warranted.