Advancements in NMDA Receptor-Targeted Antidepressants: From d-Cycloserine Discovery to Preclinical Efficacy of Lu AF90103

The discovery of d-cycloserine (DCS), a partial agonist of the NMDA Receptor that exhibits antidepressant effects without the psychotomimetic effects of ketamine, has fueled interest in new NMDA-targeting antidepressants. Our objective was to identify potent partial agonists mirroring DCS, particularly tailored for the GluN2B subtype of the NMDA Receptor. Through a structure-based drug design approach, we discovered compound 42d. This compound acts as a partial agonist of the GluN1/GluN2B complex, exhibiting 24% efficacy, and has an EC₅₀ value of 78 nM. Subsequent investigations led us to 42e (Lu AF90103), a methyl ester prodrug of 42d capable of penetrating the blood-brain barrier, as confirmed by rat microdialysis studies. In different rat in vivo models relevant to neuropsychiatric diseases, administering 42e led to 42d demonstrating both acute effects, observed in a seizure model and EEG, and lasting effects in the stress-sensitive hippocampal pathway and an antidepressant-sensitive model.