GRIN2B gain of function mutations are sensitive to radiprodil, a negative allosteric modulator of GluN2B-containing NMDA receptors

&NA; De novo gain of function mutations in GRIN2B encoding the GluN2B subunit of the N‐methyl‐D‐aspartate (NMDA) receptor have been linked with epileptic encephalopathies, including infantile spasms. We investigated the effects of radiprodil, a selective GluN2B negative allosteric modulator and other non‐selective NMDA receptor inhibitors on glutamate currents mediated by NMDA receptors containing mutated GluN2B subunits. The experiments were performed in Xenopus oocytes co‐injected with the following human mRNAs: GRIN1/GRIN2B, GRIN1/GRIN2B‐R540H, GRIN1/GRIN2B‐N615I and GRIN1/GRIN2B‐V618G. Glutamate displayed slightly increased potency in the R540H variant, but not in N615I and V618G variants. However, the inhibition by Mg2+ was completely abolished in N615I and V618G variants. In fact, Mg2+ enhanced glutamate responses in those variants. The potency of radiprodil to block glutamate‐evoked currents was not affected in any of the variants, while the effects by non‐selective NMDA inhibitors were greatly reduced in some of the variants. Additionally, in the Mg2+ insensitive variants, radiprodil blocked glutamate‐activated currents with the same potency as in the absence of Mg2+. The gain of function observed in the reported GRIN2B variants could be a key pathophysiological factor leading to neuronal hyper‐excitability in epileptic encephalopathies. The GluN2B‐selective inhibitor radiprodil fully retained its pharmacological profile under these conditions, while other non‐selective NMDA receptor antagonists lost their potency. Consequently, our data suggest that radiprodil may be a valuable therapeutic option for treatment of pediatric epileptic encephalopathies associated with GRIN2B mutations. HighlightsMg2+ led to increased currents in GluN2B mutations located in the transmembrane domain.The GluN2B‐selective inhibitor radiprodil retained its inhibitory profile in all GRIN2B variants.Radiprodil retained its inhibitory profile in high Mg2+, high glycine and in acidic conditions.Loss of inhibitory effect was observed for non‐selective NMDA receptor inhibitors.Radiprodil may constitute a potential future therapy for patients carrying GRIN2B mutations.