In Vitro DGAT2 Assay: For determination of IC50 values, the reactions were carried out in 384-well white Polyplates (Perkin Elmer) in a total volume of 20 uL. To 1 uL of compounds dissolved in 100% DMSO and spotted at the bottom of each well, 5 uL of 0.04% bovine serum albumin (BSA) (fatty acid free, Sigma Aldrich) was added and the mixture was incubated at room temperature for 20 minutes. To this mixture, 10 uL of hDGAT2 membrane fraction (0.01 mg/mL) diluted in 100 mM Hepes-NaOH, pH 7.4, 20 mM MgCl2 containing 200 nM methyl arachidonyl fluorophosphonate (Cayman Chemical; dried from ethyl acetate stock solution under argon gas and dissolved in DMSO as 5 mM stock) was added. After this mixture was preincubated at room temperature for 2 hours, DGAT2 reactions were initiated by the addition of 4 uL of substrates containing 30 uM [1-14C]decanoyl-CoA (custom-synthesized by Perkin Elmer, 50 mCi/mmol) and 125 uM 1,2-didecanoyl-sn-glycerol (Avanti Polar Lipids) dissolved in 12.5% acetone. The reaction mixtures were incubated at room temperature for 40 min and the reactions were stopped by addition of 5 uL of 1% H3PO4. After the addition of 45 uL MicroScint-E (Perkin-Elmer), plates were sealed with Top Seal-A covers (Perkin-Elmer) and phase partitioning of substrates and products was achieved using a HT-91100 microplate orbital shaker (Big Bear Automation, Santa Clara, Calif.). Plates were centrifuged at 2,000×g for 1 min in an Allegra 6R Centrifuge (Beckman Coulter) and then were sealed again with fresh covers before reading in a 1450 Microbeta Wallac Trilux Scintillation Counter (Perkin Elmer). DGAT2 activity was measured by quantifying the generated product [14C]tridecanoylglycerol in the upper organic phase.
DGAT2 Cell-Based Assay: For evaluation of the effects of DGAT2 inhibitors in a cell-based setting, cryopreserved human hepatocytes (Lot QOC, Celsis, Chicago, Ill.) were thawed and plated onto type I collagen-coated plates according to the manufacturer's instructions. After 24 hours overnight recovery period, the cells were overlayed with media containing 250 ug/ml Matrigel (BD Biosciences, San Jose, Calif.). The following day, media was aspirated and replaced with serum-free Williams Media E (Life Technologies, Grand Island, N.Y.) containing 400 uM sodium dodecanoate (Sigma-Aldrich, St. Louis, Mo.). Forty minutes later, DGAT2 inhibitors (prepared as 100× stocks in 25% DMSO, 75% Williams' Media E) were added to the desired final concentration. All wells contained a selective DGAT1 inhibitor (Example 3, WO2009016462) at a concentration (3 uM) that completely suppressed endogenous DGAT1 activity. After a 20 minute preincubation, 0.2 uCi [1,3-14C]-glycerol (American Radio Chemicals, St. Louis, Mo.) was added to each well and mixed by gentle pipetting prior to a 3 hour incubation. At this point, media was aspirated and the cells were lysed in isopropyl alcohol:tetrahydrofuran (9:1) prior to centrifugation at 3000 rpm for 5 minutes. Radiolabeled lipids were resolved using a 2-solvent system by thin layer chromatography using standard technique (solvent 1 contained ethyl acetate: isopropyl alcohol: chloroform:methanol:0.25% potassium chloride in water (100:100:100:40.2:36.1, v/v/v/v) and solvent 2 contained hexane: diethyl ether: acetic acid (70:27:3, v/v/v)). After separation, radiolabeled lipids were visualized using a Molecular Dynamics' PhosphorImager system. The half maximal inhibitory concentrations (IC50 values) were determined using Graph Pad Prism (GraphPad Software, Inc., La Jolla, Calif.).