Multiplexing Fluo-4 NW and a GeneBLAzer® Transcriptional Assay for High-Throughput Screening of G-Protein-Coupled Receptors

A novel cell-based duplex high-throughput screening assay combining fluorescent Ca(2+) measurement with homogeneous time-resolved fluorescence technology

Cell-based assays for G-protein-coupled receptor (GPCR) activation applied in high-throughput screening (HTS) monitor various readouts for second messengers or intracellular effectors. Recently, our understanding of diverging signaling pathways downstream of receptor activation and the capability of small molecules to selectively modulate signaling routes has increased substantially, underlining the importance of selecting appropriate readouts in cellular functional screens. To minimize the rate of false negatives in large-scale screening campaigns, it is crucial to maximize the chance of a ligand being detected, and generally applicable methods for detecting multiple analytes from a single well might serve this purpose. The few assays developed so far based on multiplexed GPCR readouts are limited to only certain applications and usually rely on genetic manipulations hindering screening in native or native-like cellular systems. Here we describe a more generally applicable and HTS-compatible homogeneous assay based on the combination of fluorometric detection of [Ca(2+)] with subsequent homogeneous time-resolved fluorescence (HTRF) cAMP readout in the same well. Besides describing development and validation of the assay, using a cell line recombinantly expressing the human PTH1 receptor screening of a small library is also presented, demonstrating the robustness and HTS compatibility of the novel paradigm.

Leukotriene B4 enhances innate immune defense against the puerperal sepsis agent Streptococcus pyogenes

Puerperal sepsis is a leading cause of maternal mortality worldwide. Streptococcus pyogenes [group A Streptococcus; (GAS)] is a major etiologic agent of severe postpartum sepsis, yet little is known regarding the pathogenesis of these infections. Tissue macrophages provide innate defense against GAS, and their actions are highly regulated. The intracellular second messenger cAMP can negatively regulate macrophage actions against GAS. Because leukotriene (LT) B(4) has been shown to suppress intracellular cAMP in macrophages, we hypothesized that it could enhance innate defenses against GAS. We assessed the capacity of LTB(4) to modulate antistreptococcal actions of human macrophages, including placental and decidual macrophages and used a novel intrauterine infection model of GAS in mice lacking the 5-lipoxygenase enzyme to determine the role of endogenous LTs in host defense against this pathogen. Animals lacking 5-lipoxygenase were significantly more vulnerable to intrauterine GAS infection than were wild-type mice and showed enhanced dissemination of bacteria out of the uterus and a more robust inflammatory response than did wild-type mice. In addition, LTB(4) reduced intracellular cAMP levels via the BLT1 receptor and was a potent stimulant of macrophage phagocytosis and NADPH oxidase-dependent intracellular killing of GAS. Importantly, interference was observed between the macrophage immunomodulatory actions of LTB(4) and the cAMP-inducing lipid PGE(2), suggesting that interplay between pro- and anti-inflammatory compounds may be important in vivo. This work underscores the potential for pharmacological targeting of lipid mediator signaling cascades in the treatment of invasive GAS infections.

Novel FK506 and FK520 analogues via mutasynthesis: mutasynthon scope and product characteristics

Novel FK506 and FK520 analogues were generated via biosynthetic engineering in order to generate analogue compounds with equal potency but improved pharmacological profiles compared to FK506.

Development of a β-Lactamase Reporter Gene Assay for Metabotropic Glutamate Receptor 1 by Using Coexpression of Glutamate Transporter

mGluR1 antagonists have been postulated to be novel CNS drugs, including antipsychotics. Toward this end, the authors developed a β-lactamase reporter assay to identify mGluR1 antagonists. β-Lactamase has several interesting features for high-throughput screening, including very high sensitivity and less well-to-well variation than other reporter enzymes. mGluR1-expressing Chinese hamster ovary (CHO) cells with the β-lactamase gene under control of the nuclear factor of activated T cells (NFAT) promoter (CHO-NFAT-bla-hmGluR1b) exhibited very high basal activity, resulting in an inadequate signal-to-basal (S/B) ratio. Coexpression of glutamate/aspartate transporter (GLAST) with mGluR1 in the cell line (CHO-NFAT-bla-hmGluR1b-GLAST) dramatically decreased basal activity and improved the S/B ratio (from 2- to 20-fold). The contribution of GLAST to lowering basal activity and increasing the S/B ratio was validated by the expression level of GLAST mRNA and by a GLAST inhibitor. Antagonistic activities of known mGluR1 antagonists in the β-lactamase reporter assay were comparable with those in the conventional Ca2+ mobilization assay. The Z′ factor of the β-lactamase reporter assay was 0.89 under optimized conditions. Taken together, the β-lactamase reporter assay with CHO-NFAT-bla-hmGluR1b-GLAST could be a novel high-throughput assay for mGluR1 antagonist screening. This is the first description of a successful β-lactamase reporter assay among all mGluR subtypes.

Application of intact cell-based NFAT-beta-lactamase reporter assay for Pasteurella multocida toxin-mediated activation of calcium signaling pathway

Pasteurella multocida toxin (PMT) stimulates and subsequently uncouples phospholipase C beta1 (PLCbeta1) signal transduction through its selective action on the alpha subunit of the Gq-protein. Here, we describe the application of an NFAT-beta-lactamase reporter assay as a functional readout for PMT-induced activation of the Gq-protein-coupled PLCbeta1-IP(3)-Ca(2+) signaling pathway. Use of the NFAT-beta-lactamase reporter assay with a cell-permeable fluorogenic substrate provides high sensitivity due to the absence of endogenous beta-lactamase activity in mammalian cells. This assay system was optimized for cell density, dose and time exposure of PMT stimulation. It is suited for quantitative characterization of PMT activity in mammalian cells and for use as a high-throughput screening method for PMT deletion and point mutants suitable for vaccine development. This method has application's for diagnostic screening of clinical isolates of toxinogenic P. multocida.

Application of a novel design paradigm to generate general nonpeptide combinatorial templates mimicking beta-turns: synthesis of ligands for melanocortin receptors

We report the further application of a novel approach to template and ligand design by the synthesis of agonists of the melanocortin receptor. This design method uses the conserved structural data from the three-dimensional conformations of beta-turn peptides to design rigid nonpeptide templates that mimic the orientation of the main chain C-alpha atoms in a peptide beta-turn. We report details on a new synthesis of derivatives of template 1 that are useful for the synthesis of exploratory libraries. The utility of this technique is further exemplified by several iterative rounds of high-throughput synthesis and screening, which result in new partially optimized nonpeptide agonists for several melanocortin receptors.

A high-throughput cell-based assay to identify specific inhibitors of transcription factor AP-1

The oncogenic transcription factor AP-1 (activator protein-1) is required for tumor promotion and progression. Identification of novel and specific AP-1 inhibitors would be beneficial for cancer prevention and therapy. The authors have developed a high-throughput assay to screen synthetic and natural product libraries for noncytotoxic inhibitors of mitogen-activated AP-1 activity. The cell-based high-throughput screen is conducted in a 384-well format using a fluorescent resonance energy transfer (FRET) substrate to quantify the activity of a beta-lactamase reporter under the control of an AP-1-dependent promoter. The ratiometric FRET readout makes this assay extremely robust and reproducible, particularly for use with natural product extracts. To eliminate false positives due to cell killing, a cytotoxicity assay was incorporated. The AP-1 beta-lactamase reporter was validated with inhibitors of kinases located upstream of AP-1 and with known natural product inhibitors of AP-1 (nordihydroguaiaretic acid and curcumin). The assay was able to identify other known AP-1 inhibitors and protein kinase C modulators, as well as a number of chemically diverse compounds with unknown mechanisms of action from natural products libraries. Application to natural product extracts identified hits from a range of taxonomic groups. Screening of synthetic compounds and natural products should identify novel AP-1 inhibitors that may be useful in the prevention and treatment of cancers.