Initial screens were conducted in quadruplicate at a final concentration of 10 M as detailed previously (Armbruster et al., 2007). In vitro intrinsic hepatic clearance was calculated from the microsomal incubation data using methods similar to those described previously (Lipscomb and Poet, 2008). Specifically, the plasma protein binding data were combined with the results from the microsome stability experiments to predict the theoretical hepatic clearance and hepatic extraction ratio. Brain Penetration Assays. Plasma and brain levels of the compounds were assessed in C57BL6 mice 30 min after dosing 10 mg/kg i.p. Samples were formulated at 2 mg/ml in 10:10:80 DMSO/Tween/water. Blood was collected into EDTA-containing tubes at 30 min, and plasma was generated using standard centrifugation techniques. Brain samples were frozen upon collection, and all samples were stored at ?80C until Firsocostat analyzed. Brain tissue was not perfused before freezing to prevent diffusion of the compound out of the tissue during the process. Plasma samples were analyzed by treating 25 l of plasma with 125 l of acetonitrile containing an internal standard (propranolol) and filtering through a Millipore Multiscreen Solvinter 0.45-m low-binding polytetrafluoroethylene hydrophilic filter. The filtrate was analyzed by LC-MS/MS using an API Sciex 4000 (Applied Biosystems, Foster City, CA). Multiple reaction-monitoring methods were developed Firsocostat in positive-ion mode, and concentrations were determined using a standard curve between 2 and 2000 ng/ml. Samples with concentrations outside of the curve were diluted with blank plasma and reanalyzed. Similar conditions were used to determine brain levels, except the samples were weighed, and acetonitrile was added (10, weight by volume). The samples were sonicated to extract the compound from the brain matrix and then filtered as described above. A density of 1 1 g/ml was used to convert compound per milligram of tissue into molar equivalents. Cell Viability Assays. Cytotoxicity assays were performed as described previously (Madoux et al., 2008). Y2R HEK293-CNG cells were seeded at 500 cells/well in 1536-well plates in 5 l of growth medium. Compounds (in DMSO) prepared as 10-point, 1:3 serial dilutions and added to cells (highest final concentration, 99 M). Plates were then incubated for 72 h at 37C. After incubation, 5 l of CellTiter-Glo (Promega, Madison, WI) was added to each well, and the plates were allowed to incubate for 15 min at room temperature. Luminescence was then measured (ViewLux plate reader; PerkinElmer Life and Analytical Sciences, Turku, Finland). Viability was calculated as a percentage relative to control cells treated with either DMSO alone (0% cytotoxicity) or 100 M doxorubicin (100% cytotoxicity). Data Analysis and Statistics. Data were analyzed using MDL Assay Explorer (version 3.1; Symyx Software, Santa Clara, CA) or Prism (version 5.01; GraphPad Software Inc., San Diego, CA). Curve-fitting and IC50 determinations were performed using the variable slope sigmoidal dose-response analysis tool in Prism. test or using one-way analysis of variance followed by Tukey’s test. Schild nonlinear regression analysis was performed in Prism using the Gaddum/Schild EC50 shift analysis tool. Statistical significance was ascertained by test comparing the calculated Schild slope with a hypothetical Schild analysis with slope of unity. Results High-Throughput Screening Assay for NPY Receptor Antagonists. GPCRs that couple to the Gi signaling pathway, PPIA such as Y1R and Y2R, modulate intracellular cAMP concentrations via adenylate cyclase. Several HTS-compatible assays may be used to measure Gi-coupled receptor activity, including use of GPCR-fluorescent fusion proteins (Milligan et al., 2004), reporter genes (Doucette et al., 2009), or measurement of cellular cAMP concentrations directly (Eglen, 2005). For the research presented here, an HTS-compatible cell-based cAMP assay was used (Visegrdy et al., 2007). In this assay format, measurement of Firsocostat Gi protein-coupled receptor antagonism in mammalian cells is facilitated by the presence.