Evaluation of 170 xenobiotics as transactivators of human pregnane X receptor (hPXR) and correlation to known CYP3A4 drug interactions.

The human transcription factor pregnane X receptor (hPXR) is a key regulator of enzyme expression, especially cytochrome P450 3A4 (CYP3A4). Due to the prominence of CYP3A4 in the elimination of many drugs, the development of high throughput in vitro models to predict the effect of drugs on CYP3A4 expression have increased. To better interpret and predict potential drug-drug interactions due to CYP3A4 enzyme induction, we evaluated 170 xenobiotics in a hPXR transactivation assay and compared these results to known clinical drug-drug interactions. Of the 170 xenobiotics tested, 54% of them demonstrated some level of hPXR transactivation. By taking into consideration cell culture conditions (solubility, cytotoxicity, appropriate drug concentration in media), as well as in vivo pharmacokinetics (therapeutic plasma C(max), distribution, route of administration, dosing regimen, liver exposure, potential to inhibit CYP3A4), the risk potential of CYP3A4 enzyme induction for most compounds reduced dramatically. By employing this overall interpretation strategy, the final percentage of compounds predicted to significantly induce CYP3A4 reduced to 5%, all of which are known to cause drug-drug interactions. Also, this is the first report that identifies several potent compounds that have the ability to transactivate hPXR that previously have not been identified, such as terbinafine, diclofenac, sildenafil, glimepiride, montelukast, and ticlopidine.