Native Tissue Functional Pharmacology of the mGlu2 Receptor Selective Agonist, LY2812223

LY2812223 was identified via structure-activity studies arising from the potent mGlu2/3 receptor agonist LY354740 as a selective mGlu2 agonist. This pharmacology was determined using cells stably transfected cells either containing the human mGlu2 or mGlu3 receptor. We extended the pharmacological evaluation of LY2812223 to native brain tissues derived from relevant species used for preclinical drug development as well as human post mortem brain tissue. This analysis was conducted to ensure pharmacological translation from animals to human subjects in subsequent clinical studies. A GTP-γ-[35S] functional binding assay, a method for measuring Gi-coupled signaling which is inherent to the Group 2 mGlu receptors, was used to evaluate LY2812223 pharmacology of native mGlu receptors in mouse, rat, non-human primate, and human cortical brain tissue samples. In native tissue membranes, LY2812223 unexpectedly acted as a partial agonist across all species tested. Activity of LY2812223 was lost in cortical membranes collected from mGlu2 knock-out (KO) mice, but not those from mGlu3-KO, providing additional support for mGlu2 selectivity. Other signal transduction assays were used for comparison to the GTP binding assay (cAMP, calcium mobilization, and dynamic mass redistribution). In ectopic cell line-based assays, LY2812223 displayed near maximal agonist responses at the mGlu2 receptor across all assay formats while at the mGlu3 receptor it showed no functional agonist activity except in the cAMP assay. In native brain slices or membranes that express both mGlu2 and mGlu3 receptors, LY2812223 displayed unexpected partial agonist activity which may suggest a functional interplay between these receptor subtypes in the brain.