Abstract

Modulation of the metabotropic glutamate type 2 (mGlu2) receptor is considered a promising target for the treatment of central nervous system diseases such as schizophrenia. Here, we describe the pharmacological properties of the novel mGlu2 receptor positive allosteric modulator (PAM) 3-cyano-1-cyclopropylmethyl-4-(4-phenyl-piperidin-1-yl)-pyridine-2(1H)-one (JNJ-40068782) and its radioligand [³H]JNJ-40068782. In guanosine 5′-O-(3-[³⁵S]thio)triphosphate binding, JNJ-40068782 produced a leftward and upward shift in the glutamate concentration-effect curve at human recombinant mGlu2 receptors. The EC₅₀ of JNJ-40068782 for potentiation of an EC₂₀-equivalent concentration of glutamate was 143 nM. Although JNJ-40068782 did not affect binding of the orthosteric antagonist [³H]2S-2-amino-2-(1S,2S-2-carboxycyclopropyl-1-yl)-3-(xanth-9-yl)propanoic acid (LY-341495), it did potentiate the binding of the agonist [³H](2S,2′R,3′R)-2-(2′,3′-dicarboxylcyclopropyl)glycine (DCG-IV), demonstrating that it can allosterically affect binding at the agonist recognition site. The binding of [³H]JNJ-40068782 to human recombinant mGlu2 receptors in Chinese hamster ovary cells and rat brain receptors was saturable with a K_D of ∼10 nM. In rat brain, the anatomic distribution of [³H]JNJ-40068782 was consistent with mGlu2 expression previously described and was most abundant in cortex and hippocampus. The ability of structurally unrelated PAMs to displace [³H]JNJ-40068782 suggests that PAMs may bind to common determinants within the same site. It is noteworthy that agonists also increased the binding affinity of [³H]JNJ-40068782. JNJ-40068782 influenced rat sleep-wake organization by decreasing rapid eye movement sleep with a lowest active dose of 3 mg/kg PO. In mice, JNJ-40068782 reversed phencyclidine-induced hyperlocomotion with an ED₅₀ of 5.7 mg/kg s.c. Collectively, the present data demonstrate that JNJ-40068782 has utility in investigating the potential of mGlu2 modulation for the treatment of diseases characterized by disturbed glutamatergic signaling and highlight the value of [³H]JNJ-40068782 in exploring allosteric binding.