AID	Name	Type	Comment
887	qHTS Assay for Inhibitors of 15-hLO (15-human lipoxygenase)	confirmatory	primary qHTS assay for 15hLO-1
2169	Probe Development Summary of Inhibitors of 15-hLO-1 (15-human lipoxygenase 1)	summary

Assay Provider: Holman, T.R., University of California, Santa Cruz
Screening Center PI: Austin, Christopher P.
Screening Center: NIH Chemical Genomics Center

Human lipoxygenase 15hLO-1 is a member of the closely related lipoxygenase family of enzymes which catalyze the site-specific oxidation of arachidonic acid to various hormone precursor molecules and as such is a candidate for drug development in a variety of disease areas, such as cancer and inflammation. Inhibition of 15hLO-1 activity was screened by utilizing arachidonic acid as a substrate. The extent of hydroperoxide product formation was measured by a secondary chromogenic reaction in which xylenol orange (XO, Sigma-Aldrich, cat. number 39,818-7) reacts with the ferric ions produced from the reaction between the hydroperoxide and ferrous ions. The Fe(III)-XO complex is characterized with red-shifted absorbance at 560 nm. A purified preparation of human 15hLO-1 was supplied by Professor Ted Holman, University of California, Santa Cruz.

This assay includes some confirmation and follow-up compounds for related primary screening assay AID 887.

Assay Protocol:

Buffer: 25 mM Hepes pH 7.5, 0.01% Triton X-100.

Reagents/Controls:
Buffer in columns 3 and 4 as negative control (no enzyme). Substrate solution: 50 uM arachidonic acid (Sigma-Aldrich, St. Louis, MO) final concentration dispensed throughout the plate. Enzyme: 40 nM 15hLO-1 final concentration in columns 1, 2, 5-48. Column 1 is neutral (100% activity). Column 2 contained pin-transferred titration of NDGA (nordihidroguaiaretic acid, Sigma-Aldrich, N 5023, top concentration 10 mM in DMSO, then 1:2 dilution in duplicate). (Dilution factor: 23 nL into 4 uL.) Chromogenic detection reagent (divalent iron/xylenol orange, Fe-XO): 200 uM xylenol orange plus 300 uM ferrous ammonium sulfate prepared freshly in 50 mM sulfuric acid.

Assay Steps:
Three uL of enzyme were dispensed to 1536-well Greiner black clear bottom plates. Compounds and controls (23 nL) were transferred via Kalypsys PinTool. The plates were incubated for 15 min at room temperature, and then 1 uL of substrate solution was added to start the reaction. After room temperature incubation for 6 minutes, 4 uL of Fe-XO solution was added to each well followed by a short spin (1000 rpm, 15 sec) and the plates were then incubated for 30 min. The absorbance at 405 and 573 nm were measured using ViewLux (Perkin-Elmer) High-throughput CCD imager and absorbance protocol settings. The 573-to-405 absorbance ratio was used to compute reaction progress.

Keywords: NIH Roadmap, MLSCN, MLPCN, MLI, MLSMR, qHTS, NCGC, human
lipoxygenase, 15hLO1, 15-hLO-1

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.

Grant Number: MH081283-01