A High-throughput two-phase partition assay to measure the activity of lipid-metabolizing enzymes

A Cellular Assay for Inhibitors of the Fatty Acid Biosynthetic Pathway Using Scintillating Microplates

A simplified method for monitoring the incorporation of radiolabeled acetate into lipids in a cellular system is described. The assay eliminates the commonly employed labor-intensive organic extraction step by plating the cells in 96-well tissue culture-treated ScintiPlates(®) that enable direct measurement of radiolabeled cell membrane-embedded lipids. Since the scintillant is entrenched in the plates, radioactivity in close proximity to the scintillant is measured without the need for liquid scintillation cocktail. The utility of this method for evaluating inhibitors of the de novo fatty acid synthetic pathway is demonstrated here with fatty acid synthase (FASN). Due to the upregulation of FASN activity in many tumor types, development of inhibitors to block the FASN activity in cells shows promise as an attractive and tractable approach for therapeutic intervention.

A simplified scintillation proximity assay for fatty acid synthase activity: development and comparison with other FAS activity assays

Fatty acid synthase (FAS), an essential enzyme for de novo lipogenesis, has been implicated in a number of disease states, including obesity, dyslipidemia, and cancer. To identify small-molecule inhibitors of FAS, the authors developed a bead-based scintillation proximity assay (SPA) to detect the fatty acid products of FAS enzymatic activity. This homogeneous SPA assay discriminates between a radiolabeled hydrophilic substrate of FAS (acetyl-coenzyme A) and the labeled lipophilic products of FAS (fatty acids), generating signal only when labeled fatty acids are present. The assay requires a single addition of unmodified polystyrene imaging SPA beads and can be miniaturized to 384- or 1536-well density with appropriate assay statistics for high-throughput screening. High-potency FAS inhibitors were used to compare the sensitivity of the SPA bead assay with previously described assays that measure FAS reaction intermediates (CoA-SH and NADP+). The advantages and disadvantages of these different FAS assays in small-molecule inhibitor discovery are discussed.

A fluorescence-based thiol quantification assay for ultra-high-throughput screening for inhibitors of coenzyme A production

Here we report the development and miniaturization of a cell-free enzyme assay for ultra-high-throughput screening (uHTS) for inhibitors of two potential drug targets for obesity and cancer: fatty acid synthase (FAS) and acetyl-coenzyme A (CoA) carboxylase (ACC) 2. This assay detects CoA, a product of the FAS-catalyzed condensation of malonyl-CoA and acetyl-CoA. The free thiol of CoA can react with 7-diethylamino-3-(4'-maleimidylphenyl)-4-methylcoumarin (CPM), a profluorescent coumarin maleimide derivative that becomes fluorescent upon reaction with thiols. FAS produces long-chain fatty acid and CoA from the condensation of malonyl-CoA and acetyl-CoA. In our FAS assay, CoA released in the FAS reaction forms a fluorescence adduct with CPM that emits at 530 nm when excited at 405 nm. Using this detection method for CoA, we measured the activity of sequential enzymes in the fatty acid synthesis pathway to develop an ACC2/FAS-coupled assay where ACC2 produces malonyl-CoA from acetyl-CoA. We miniaturized the FAS and ACC2/FAS assays to 3,456- and 1,536-well plate format, respectively, and completed uHTSs for small molecule inhibitors of this enzyme system. This report shows the results of assay development, miniaturization, and inhibitor screening for these potential drug targets.

Discovery of acetyl-coenzyme A carboxylase 2 inhibitors: comparison of a fluorescence intensity-based phosphate assay and a fluorescence polarization-based ADP Assay for high-throughput screening

Acetyl-coenzyme A carboxylase (ACC) enzymes exist as two isoforms, ACC1 and ACC2, which play critical roles in fatty acid biosynthesis and oxidation. Though each isoform differs in tissue and subcellular localization, both catalyze the biotin- and ATP-dependent carboxylation of acetyl-coenzyme A to generate malonyl-coenzyme A, a key metabolite in the control of fatty acid synthesis and oxidation. The cytosolic ACC1 is expressed primarily in liver and adipose tissue, and uses malonyl-coenzyme A as a key building block in fatty acid biosynthesis. The mitochondrial ACC2 is primarily expressed in heart and skeletal muscle, where it is involved in the regulation of fatty acid oxidation. Inhibitors of ACC enzymes may therefore be useful therapeutics for diabetes, obesity, and metabolic syndrome. Two assay formats for these ATP-utilizing enzymes amenable to high-throughput screening are compared: a fluorescence intensity-based assay to detect inorganic phosphate and a fluorescence polarization-based assay to detect ADP. Acetyl-coenzyme A carboxylase inhibitors were identified by these high-throughput screening methods and were confirmed in a radiometric high performance liquid chromatography assay of malonyl-coenzyme A production.