Optimization of a High-Throughput Cell-Based Screening Strategy to Identify Small-Molecule Inhibitors of IL-23 Signaling.

Interleukin-23 (IL-23) is a key cytokine implicated in the pathogenesis of autoimmune disorders, including psoriasis and ulcerative colitis. Although targeted IL-23 antibody therapeutics are used clinically, there are no small-molecule therapeutics that selectively inhibit IL-23 signaling. To address this gap, we developed a high-throughput screening strategy employing an IL-23-responsive cell-based luciferase reporter gene assay as the primary screen, with cellular cytotoxicity and off-target counter screening assays to identify IL-23 pathway-specific inhibitors. The primary screening assay utilized avian DT40 cells, genetically engineered to overexpress IL-23R, IL-12Rß1, STAT5, and firefly luciferase, in a 1536-well format. Treatment of these cells with IL-23 resulted in the phosphorylation and activation of STAT5, which was completely inhibited by the pan-JAK inhibitor tofacitinib. Assay performance was robust, with signal-to-background >7-fold and Z' > 0.5 over 40 screening plates (approximately 24,000 compounds), with a hit rate of 5% (>66.9% activity cutoff). Of these 1288 hits, 66% were identified as cytotoxic by incubating the IL-23 reporter cells with compound overnight and measuring cell viability. Further assessment of specificity via examination of impact on off-target IFN-γ signaling eliminated an additional 230 compounds, leaving 209 that were evaluated for dose-response activity. Of these compounds, 24 exhibited IC50 values of <7 µM and ≥80% inhibition of IL-23 activity, with >3-fold selectivity over IFN-γ inhibition, thus representing promising starting points for prospective IL-23 pathway small-molecule inhibitors.

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.

Fluorogenic substrates for high-throughput measurements of endothelial lipase activity.

Endothelial lipase (EL) has been shown to be a critical determinant for high density lipoprotein cholesterol levels in vivo; therefore, assays that measure EL activity have become important for the discovery of small molecule inhibitors that specifically target EL. Here, we describe fluorescent Bodipy-labeled substrates that can be used in homogeneous, ultra-high-throughput kinetic assays that measure EL phospholipase or triglyceride lipase activities. Triton X-100 detergent micelles and synthetic HDL particles containing Bodipy-labeled phospholipid or Bodipy-labeled triglyceride substrates were shown to be catalytic substrates for EL, LPL, and HL. More importantly, only synthetic HDL particles containing Bodipy-labeled triglyceride were ideal substrates for EL, LPL, and HL in the presence of high concentrations of human or mouse serum. These data suggest that substrate presentation is a critical factor when determining EL activity in the presence of serum.

A short-incubation reporter-gene assay for high-throughput screening of estrogen receptor-alpha antagonists.

Estrogen receptor (ER) alpha and beta are ligand-activated nuclear transcription factors that mediate the effects of the steroid hormone 17beta-estradiol. Tissue-selective ER modulators have been developed for the treatment of a variety of diseases, including osteoporosis and hormone-dependent breast cancer. Second- and third-generation selective ER modulators are in development, with the goal of reducing toxicity and improving tissue-selective efficacy. Novel tissue-selective and ERsubtype specific ligands may have the potential of providing a new paradigm for maintaining the health of women. The traditional cell-based screening assays for nuclear receptors require 16-18 h of incubation, which limits the assay miniaturization for ultra-high-throughput screening. We have developed a new cell-based ERalpha transactivation assay for the screening of ERalpha-specific antagonists with only 4 h of incubation time. The assay was optimized and used for a fully automated ultrahigh-throughput screen in 3,456-well nanoplate format. The screening throughput was 250,000-300,000 compounds per day, and a number of valuable leads were identified.

A beta-lactamase-dependent Gal4-estrogen receptor beta transactivation assay for the ultra-high throughput screening of estrogen receptor beta agonists in a 3456-well format.

Estrogen action is mediated via two estrogen receptor (ER) subtypes, ERalpha and ERbeta. Selective ER modulators with balanced high affinity for ERalpha and ERbeta have been developed as therapeutics for the treatment of a variety of diseases, including hormone-responsive breast cancer and osteoporosis. Recent data based primarily on the evaluation of ER-knockout mice have revealed that ERalpha and ERbeta may regulate separate and distinct biological processes. The identification of ERbeta specific ligands could further enhance our understanding of ERbeta biology. In addition, compounds targeting ERbeta may prove useful as therapeutic agents with activity profiles distinguishable from that of estradiol. To discover novel selective ligands for ERbeta, we developed and characterized a cell-based Gal4-ERbeta beta-lactamase reporter gene assay (GERTA) in CHO cells for the ligand-induced activation of the human ERbeta. The sensitivity and selectivity of this assay were found to be comparable to those of an ER ligand-binding assay. The assay was optimized for screening in an ultra high throughput 3456-well nanoplate format and was successfully used to screen a large compound collection for ERbeta agonists. Compounds identified in a primary screen were tested in an in vitro ligand-binding assay to characterize further the selectivity and potency for ERbeta.