National Center for Advancing Translational Sciences [NCATS]
NIH Chemical Genomics Center [NCGC]
U.S. Environmental Protection Agency [EPA]
National Institutes of Environmental Health Sciences [NIEHS]
National Toxicology Program [NTP]

Assay overview:

The Pregnane X receptor (PXR), a ligand activated nuclear receptor plays a critical role in the regulation of genes involved in drug metabolism and transporters. PXR binds xenobiotics and when compounds interact with PXR produces enhanced expression of CYP3A genes. In humans PXR activation and CYP3A4 induction can be problematic due to their interactions with co-medicated drugs and decrease their efficacy or increase their own metabolism. However, there are known species-specific differences with regard to PXR activation that should be taken into account when animal PXR data are extrapolated to humans. A cell based rat PXR (rPXR) assay (developed by Puracyp, Inc., CA) was used to assess the activation of rPXR.

Assay Protocol Summary:

2,000 rPXR cells were dispensed at 5 uL/well in the white, solid-bottom 1536-well plates using a Multidrop Combi (Thermo Scientific) dispenser. Following transfer of 23 nL compound or DMSO vehicle by a pin tool, the plates were incubated 24 hr at 37 C and 5% CO2. 5 ul One-Glo (Promega) was then added to each plate and following 30 min incubation at room temperature, luciferase activity was quantified on a ViewLux CCD-based plate reader.

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 activators are ranked higher than compounds that showed apparent inhibition.
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.