AID	Name	Type	Comment
2309	Probe Summary for Inhibitors and Stabilizers of Firefly Luciferase	summary

NCGC Assay Overview:

Firefly (Photinus pyralis) luciferase is one of the most commonly used transcriptional reporters. It is considered one of the more dynamically responsive reporters - that is, responsive to changes in reporter transcription - as it requires no post-translational modifications and is enzymatically active directly after protein synthesis (Wood, 1998). With no endogenous expression in mammalian cells and without the requirement of external excitation, it offers very little background signal, thus generally providing excellent signal to background for most assays.

Previous profiling work to determine the prevalence of compounds that affect FLuc enzymatic activity (PubChem AID 411) identified that ~3% of the MLSMR library (then at ~72K) inhibited FLuc. The MLSMR library was again profiled at a later date (when the library contained significantly more compounds - ~350K) for FLuc activity in a biochemical assay using purified FLuc in the presence of KM concentrations of substrates (D-LH2 and ATP), in an effort to identify compounds in the library that may act as competitive inhibitors. Of the compounds identified in this profile that inhibited FLuc, 151 compounds were selected for further analysis, in an effort to better understand their mode of inhibiting FLuc. The assay described here was to determine the activity of the compounds in an FLuc assay that contained KM concentrations of substrates and 500uM CoASH.

NCGC Assay Protocol Summary:

Reagents: 50mM Tris acetate, pH 7.5; 10mM Mg acetate; 10uM D-luciferin (Sigma #L9504); 10uM ATP; 0.01% Tween-20; 0.05% BSA; 10nM P. pyralis luciferase (Sigma #L9506); 500 uM CoASH
Control compounds used were two known firefly luciferase inhibitors (3-(5-(3-chlorophenyl)-1,2,4-oxadiazol-3-yl)benzoic acid and 5-(2-fluorophenyl)-3-phenyl-1,2,4-oxadiazole), and DMSO.

Three microliters containing firefly luciferase substrates in buffer (final concentrations: 50mM Tris acetate, pH 7.5, 10mM Mg acetate, 0.01% Tween-20, 0.05% BSA, 10uM D-luciferin, 10uM ATP, and 500 uM CoASH) are dispensed into each well of a Greiner white, solid-bottom 1536-well format plate using a flying reagent dispenser (FRD). These assay plates were then treated with 23nL of compound or DMSO using a Kalypsys pin tool, which allows for delivery of a 12-point intraplate titration of each compound to the assay plate (quantitative HTS), with a final compound concentrations ranging from approximately ~60uM to 0.3nM. One microliter of firefly luciferase in 500mM Tris-acetate buffer was then delivered by FRD to each well for a final enzyme concentration of 10nM. Luciferase activity was then measured using a ViewLux CCD imager (PerkinElmer), with an average exposure time of 2-30 seconds (2X binning, medium/high gain).

Compound Ranking:

1. Compounds are first classified as having full titration curves, partial modulation, partial curve (weaker actives), single point activity (at highest concentration only), or inactive. See data field "Curve Description". For this assay, apparent inhibitors are ranked higher than compounds that showed apparent activation.
2. For all inactive compounds, PUBCHEM_ACTIVITY_SCORE is 0. For all active compounds, a score range was given for each curve class type given above. Active compounds have PUBCHEM_ACTIVITY_SCORE between 40 and 100. Inconclusive compounds have PUBCHEM_ACTIVITY_SCORE between 1 and 39. Fit_LogAC50 was used for determining relative score and was scaled to each curve class' score range.