PT - JOURNAL ARTICLE AU - Christopher L. Shaffer AU - Raymond S Hurst AU - Renato J Scialis AU - Sarah M Osgood AU - Dianne K Bryce AU - William E Hoffmann AU - John T Lazzaro AU - Ashley N Hanks AU - Susan Lotarski AU - Mark L Weber AU - JianHua Liu AU - Frank S Menniti AU - Christopher J Schmidt AU - Mihaly Hajos TI - Positive Allosteric Modulation of AMPA Receptors from Efficacy to Toxicity: The Interspecies Exposure-Response Continuum of the Novel Potentiator PF-4778574 AID - 10.1124/jpet.113.204735 DP - 2013 Jan 01 TA - Journal of Pharmacology and Experimental Therapeutics PG - jpet.113.204735 4099 - http://jpet.aspetjournals.org/content/early/2013/07/30/jpet.113.204735.short 4100 - http://jpet.aspetjournals.org/content/early/2013/07/30/jpet.113.204735.full AB - α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor (AMPAR) positive allosteric modulation (i.e. "potentiation") has been proposed to overcome cognitive impairments in schizophrenia, but AMPAR overstimulation can be excitotoxic. Thus, it is critical to define carefully a potentiator's mechanism-based therapeutic index (TI) and to determine confidently its translatability from rodents to higher-order species. Accordingly, the novel AMPAR potentiator N-{(3R,4S)-3-[4-(5-cyano-2-thienyl)phenyl]tetrahydro-2H-pyran-4-yl}propane-2-sulfonamide (PF-4778574) was characterized in a series of in vitro assays and single-dose animal studies evaluating AMPAR-mediated activities related to cognition and safety to afford an unbound brain compound concentration (Cb,u)-normalized interspecies exposure-response relationship. Since it is unknown which AMPAR subtype(s) may be selectively potentiated for an optimal TI, PF-4778574 binding affinity and functional potency were determined in rodent tissues expected to express a native mixture of AMPAR subunits and their associated proteins to afford composite pharmacologic values. Functional activity was also quantified in recombinant cell lines stably expressing human GluA2 flip or flop homotetramers. Pro-cognitive effects of PF-4778574 were evaluated in both rat electrophysiological and nonhuman primate (nhp) behavioral models of pharmacologically induced N-methyl-D-aspartate receptor hypofunction. Acute safety studies assessed cerebellum-based AMPAR activation (mouse) and motor coordination disruptions (mouse, dog and nhp), as well as convulsion (mouse, rat and dog). The resulting empirically derived exposure-response continuum for PF-4778574 defines a single-dose-based TI of 8-to-16-fold for self-limiting tremor, a readily monitorable clinical adverse event. Importantly, the Cb,u mediating each physiological effect were highly consistent across species with efficacy and convulsion occurring at just fractions of the in vitro-derived pharmacologic values.