The novel methoxetamine analogs N-ethylnorketamine hydrochloride (NENK), 2-MeO-N-ethylketamine hydrochloride (2-MeO-NEK), and 4-MeO-N-ethylketamine hydrochloride (4-MeO-NEK) elicit rapid antidepressant effects via activation of AMPA and 5-HT2 receptors

Three novel analogs of methoxetamine (MXE), an NMDA receptor antagonist related to ketamine, showed antidepressant-like effects in mice. The compounds—NENK, 2-MeO-NEK, and 4-MeO-NEK—reduced immobility time in the forced swimming and tail suspension tests, indicating reduced behavioral despair. Their effects were blocked by an AMPA receptor antagonist (NBQX) and a 5-HT2 receptor antagonist (ketanserin), suggesting involvement of both glutamatergic and serotonergic systems. The analogs also altered mRNA levels of AMPA receptor subunits and brain-derived neurotrophic factor in the hippocampus and prefrontal cortex. These findings suggest the compounds may offer rapid antidepressant effects, though further research is needed.

Study at a glance

Abstract

RationaleDepressive syndrome or depression is a debilitating brain disorder affecting numerous people worldwide. Although readily available, current antidepressants have low remission rates and late onset times. Recently, N-methyl-D-aspartate (NMDA) receptor antagonists, like ketamine and methoxetamine (MXE), were found to elicit rapid antidepressant effects. As the search for glutamatergic-based antidepressants is increasing, we synthesized three novel MXE analogs, N-ethylnorketamine hydrochloride (NENK), 2-MeO-N-ethylketamine hydrochloride (2-MeO-NEK), and 4-MeO-N-ethylketamine hydrochloride (4-MeO-NEK).ObjectivesTo determine whether the three novel MXE analogs induce antidepressant effects and explore their mechanistic correlation.MethodsWe examined their affinity for NMDA receptors through a radioligand binding assay. Mice were treated with each drug (2.5, 5, and 10 mg/kg), and their behavior was assessed 30 min later in the forced swimming test (FST), tail suspension test (TST), elevated plus-maze (EPM) test, and open-field test (OFT). Another group of mice were pretreated with 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline-2,3-dione (NBQX), an α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist, or ketanserin (KS), a 5-HT2 receptor antagonist, during the FST. We also measured mRNA levels of the AMPA receptor subunits GluA1 and GluA2, brain-derived neurotrophic factor (BDNF), and mammalian target of rapamycin (mTOR) in the hippocampus and prefrontal cortex.ResultsThe MXE analogs showed affinity to NMDA receptors and decreased immobility time during the FST and TST. NBQX and KS blocked their effects in the FST. The compounds did not induce behavioral alteration during the EPM and OFT. The compounds altered GluA1, GluA2, and BDNF mRNA levels.ConclusionThese results suggest that the novel MXE analogs induce antidepressant effects, which is likely via AMPA and 5-HT2 receptor activation.