Assay Method Information

Assay Name:  Fatty Acid Synthase (FASN) Inhibition Scintillation Proximity Assay
Description:  In this assay, inhibition of FASN activity is measured using 3H-acetyl-CoA and malonyl-CoA as substrates. 3H-Acetyl CoA is converted to 3H-palmitate through a series of reactions by the FASN protein, which contains 7 functional domains and carries out 7 enzymatic reactions to ultimately produce 3H-palmitate. The assay principle is based upon the fact that 3H-acetyl-CoA is hydrophilic and the end product, 3H-palmitate is hydrophobic. The hydrophobic 3H-palmitate binds to scintillation proximity assay (SPA) imaging beads (resulting in light emission from the imaging beads) whereas the hydrophilic 3H-acetyl-CoA does not bind to the imaging beads (and therefore does not result in light emission from the imaging beads).10 μL assay buffer (100 mM KH2PO4 pH 7.5, 1 mM DTT) (20 μL in blanks) was added to a 384-well white Opti Plate plate (Perkin Elmer). 0.9 μL test compound (at concentrations of 30 μM, 10 μM, 3 μM, 1 μM, 0.30 μM, 0.10 μM, 0.03 μM and 0.01 μM)/DMSO and 10 μL hFASN enzyme (full length, 300 ng, purified in house) or 10 μL assay buffer was added to the wells. Then 10 μL 450 μM NADPH (Sigma N7505), 18.75 μM [3H]-acetyl-CoA (Perkin Elmer NET-290L), 150 μM malonyl-CoA (Sigma M4263) were added, mixed and incubated at room temperature for 60 minutes. The reaction was stopped by adding 20 μL Streptavidin coupled imaging beads (25 mg/ml). After incubation for 30 minutes at room temperature in the dark, the 384 well plate was centrifuged at 1500 rpm for 3 minutes and was measured after at least 24 hrs by the LEADseeker, measuring emission using a 61020 nm pass filter. (Bays, N. W., et al., A simplified scintillation proximity assay for fatty acid synthase activity: development and comparison with other FAS activity assays, J. Biomol. Screen., 2009, pp 636-642, Vol. 14(6).)Raw data generated by the instrument were normalized to % Controlmin values, which were calculated as: % Controlmin=100*(x−mLC)/(mHC−mLC)where mLC and mHC were the means of the low control wells and high control wells on the plate, after manual exclusion of outliers. A plot of Controlmin versus test compound concentration was fitted to a 4-parameter logistic curve using a non-linear least squares regression method. From the plot, an IC50 (concentration at which 50% inhibition is achieved) was calculated. pIC50 values were calculated as −log(IC50), when IC50 is expressed in molar units.
Affinity data for this assay

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