Evaluation of 170 Xenobiotics as Transactivators of Human Pregnane X Receptor (hPXR) and Correlation to Known CYP3A4 Drug Interactions

Abstract

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.

Activity, Inhibition, and Induction of Cytochrome P450 2J2 in Adult Human Primary Cardiomyocytes

“…Of note, rosiglitazone simultaneously induced transcription of mRNA but also inhibited terfenadine hydroxylation. Rosiglitazone is a known mild PXR inducer (Sinz et al, 2006); however, if rosiglitazone was operating through the PXR receptor, then rifampin should have induced mRNA as well. Rosiglitazone is potentially binding and inducing CYP2J2 through peroxisome proliferator-activated receptor (PPAR), which also induces mRNA of CYP2B and CYP4 enzymes (Rogue et al, 2010).…”

A Comprehensive in Vitro and in Silico Analysis of Antibiotics That Activate Pregnane X Receptor and Induce CYP3A4 in Liver and Intestine

“…Previously generated pharmacophores for PXR agonists (Ekins and Erickson, 2002;Bachmann et al, 2004;Ekins et al, 2007) were used to generate predictions for antibiotics tested in this study. These pharmacophores represent 1) the original PXR pharmacophore using 12 diverse ligands (Ekins and Erickson, 2002), with EC 50 data from competition binding assays or CV1 cells, which has previously been used to predict affinity of imidazoles (Bachmann et al, 2004;Ekins et al, 2007); 2) a pharmacophore using 30 steroids, with EC 50 data from HepG2 cells using a reporter assay that may define a unique site within PXR (Ekins et al, 2007); and 3) a pharmacophore using 31 diverse ligands (Ekins et al, 2007), with EC 50 data from HepG2 cells using a reporter assay (Sinz et al, 2006). The structures of antibiotics were sketched in ChemDraw for Excel (CambridgeSoft, Cambridge MA) and exported as sdf files.…”

“…Original (n ϭ 12) Pharmacophore (Ekins and Erickson, 2002;Bachmann et al, 2004) Diverse (n ϭ 31) Pharmacophore (Ekins et al, 2007) Steroidal (n ϭ 30) Pharmacophore (Ekins et al, 2007) Docking FlexX Score (Khandelwal et al, 2007) Although the macrolide antibiotics erythromycin and troleandomycin were efficacious PXR activators, having both increased mRNA expression of CYP3A4, they both failed to induce CYP3A4 activity, consistent with their ability to also act as CYP3A4 inhibitors (McConn et al, 2004;Atkinson et al, 2005). Interestingly, TAO had previously been shown to have an EC 50 value of 8.9 M, whereas erythromycin was inactive in a PXR transactivation assay (Sinz et al, 2006).…”

“…Activation of PXR is recognized as the molecular mechanism responsible for many drug interactions (Sinz et al, 2006). Accord-ingly, this led to the development of high-throughput cell-based assays to test whether xenobiotics would induce CYP3A4 promoterluciferase reporter plasmids in a PXR-dependent manner (Moore and Kliewer, 2000).…”

The Time to Move Cytochrome P450 Induction into Mainstream Pharmacology Is Long Overdue

“…This score correlated highly (r 2 values Ͼ0.92) with decreases in area under the plasma concentration versus time curve values for coadministered CYP3A4 object drugs (midazolam or ethinylestradiol) from previously published clinical drug-drug interaction studies. Similarly, Sinz et al (2006) have recently correlated the concentration-response values for transactivation of human pregnane X receptor, with clinical concentrations and induction response. In addition, a recent comprehensive review of P450 induction discusses the importance of using EC 50 and E max values to interpret in vitro induction data (Lin, 2006).…”