2,6-Disubstituted pyrazines and related analogs as NR2B site antagonists of the NMDA receptor with anti-depressant activity.

Herein we describe the discovery of compounds that are competitive antagonists of the CP101-606 binding site within the NR2B subtype of the NMDA receptor. The compounds identified do not possess phenolic functional groups such as those in ifenprodil and related analogs. Initial identification of hits in this series focused on a basic, secondary amine side chain which led to good potency, but also presented a hERG liability. Further modifications led to examples of non-basic replacements which demonstrated much less liability in this regard. Finally, one compound in the series, 6a, was tested in the mouse forced swim depression assay and found to show activity (s.c. 60 mg/kg).

Effects of a non-peptide CRF antagonist (DMP696) on the behavioral and endocrine sequelae of maternal separation.

We examined whether blockade of corticotropin-releasing factor (CRF) receptors by a non-peptide CRF antagonist (DMP696) would attenuate the stress hyper-responsiveness that occurs in response to maternal separation. In a social interaction test as well as the elevated plus maze, adult male rats, which had been maternally separated as infants, displayed more anxiety-like behavior compared with handled rats. DMP696 increased social interaction in both groups. In the elevated plus maze however, DMP696 significantly increased open arm time in the maternally separated rats but not in the handled group whereas chlordiazepoxide increased open arm time in both groups. DMP696 also appeared to block stress-induced ACTH secretion more readily in the maternally separated group compared with the handled rats. These observations suggest that CRF antagonists are particularly effective in animals that are hyper-responsive to stress and may therefore have utility in the treatment of anxiety and affective disorders where CRF has been implicated.

Identification of short-acting κ-opioid receptor antagonists with anxiolytic-like activity.

The κ-opioid receptor plays a central role in mediating the response to stressful life events. Inhibiting κ-opioid receptor signaling is proposed as a mechanism for treating stress-related conditions such as depression and anxiety. Preclinical testing consistently confirms that disruption of κ-opioid signaling is efficacious in animal models of mood disorders. However, concerns about the feasibility of developing antagonists into drugs stem from an unusual pharmacodynamic property of prototypic κ-opioid receptor-selective antagonists; they inhibit receptor signaling for weeks to months after a single dose. Several fundamental questions include - is it possible to identify short-acting antagonists; is long-lasting inhibition necessary for efficacy; and is it safe to develop long-acting antagonists in the clinic. Here, we test representative compounds (AZ-ECPC, AZ-MTAB, and LY-DMPF) from three new chemical series of κ-opioid receptor ligands for long-lasting inhibition. Each compound dose-dependently reversed κ-opioid agonist-induced diuresis. However, unlike the prototypic antagonist, nBNI, which fully inhibited evoked diuresis for at least four weeks, the new compounds showed no inhibition after one week. The two compounds with greater potency and selectivity were tested in prenatally-stressed rats on the elevated plus maze, an exploration-based model of anxiety. Spontaneous exploration of open arms in the elevated plus maze was suppressed by prenatal stress and restored with both compounds. These findings indicate that persistent inhibition is not an inherent property of κ-opioid-selective antagonists and that post-stress dosing with transient inhibitors can be effective in a mood disorder model. This further supports κ-opioid receptor as a promising target for developing novel psychiatric medications.