Herb-Drug Interactions Caused by the Nuclear Receptor PXR
Steven Kliewer University of Texas Southwestern Medical Center Dallas, TX St. John’s Wort Causes Drug Interactions
target genes drug PXR RXR metabolism Phase I (oxygenases) Phase II (conjugases) Transporters
PXR screens can be used to prevent herb-drug interactions Nuclear Receptor Signaling
OH H HO I CO2H NH I O 2 I HO OH H Estradiol Thyroid Hormone CO2H
O H trans-Retinoic Acid Dihydrotestosterone
O H
O H OH Progesterone Cytoplasm Nucleus
OH Vitamin D HOO Vitamin D O H OH O HO OH HO OH O Aldosterone O Cortisol Nuclear Receptor Superfamily
N DNADNA LigandLigand C
48 NRs in human genome
Classical Receptors (12) Orphan Receptors (36) Glucocorticoid CAR PXR Mineralocorticoid COUP (α,β,γ) PPAR (α,γ,δ) Progesterone DAX revErb (α,β) Estrogen (α,β) ERR (α,β,γ) RXR (α,β,γ) Androgen FXR ROR (α,β,γ) Thyroid Hormone (α,β) GCNF1 SF1 (α,β) Vitamin D HNF4 (α,γ) SHP all-trans Retinoic Acid (α,β,γ) LXR (α,β) Tlx NGFI-B (α,β,γ) TR2 (α,β) PNR Xenoprotection
Xenobiotics = foreign chemicals Inhaled
Absorbed Ingested
P450 enzymes
oxygenases Liver conjugation enzymes transporters Intestine CYP3A Induction
• Expressed in liver and intestine • Activated by xenobiotics xenobiotics • Bind to XREs
rifampicin most drugs dexamethasone ?? RU486 xenobiotics clotrimazole troglitazone XRE CYP3A tamoxifen CYP3A
• Protects against xenobiotics HO-xenobiotics • Causes drug-drug interactions Pregnane X Receptor (PXR)
human PXR DNADNA LiganLigandd rabbit PXR 94%94% 82%82% mouse PXR 96%96% 77%77% rat PXR 96%96% 76%76%
• Cloned due to homology with other nuclear receptors • Named on basis of activation by natural and synthetic C21 steroids (pregnanes), including pregnenolone 16α- carbonitrile (PCN) PXR Expression in Human
Northern blot n en kidney ovary small intestine colo PBL lung liver muscle pancreas sple thymus testis prostate heart brain placenta
9.5 7.5 4.4
2.4
1.4 CYP3A Inducers Activate Human, Rabbit, and Rat PXR Cell-based reporter assay rifampicin
PCN
dexamethasone
RU486
clotrimazole
troglitazone
tamoxifen
135791113151719 Reporter activity (fold) PXR Regulates CYP3A
• Expressed in liver and intestine • Activated by xenobiotics xenobiotics • Binds to XREs
PXR??RXR xenobiotics (e.g., drugs) XRE CYP3A
CYP3A Other genes?
HO-xenobiotics PXR Regulates Xenobiotic Metabolism
Liver RNA from • Phase I (oxidation) enzymes mice treated with Cyp3a11 (3.5x) –vehicle
Cyp2b10 (12x) solubilization –PCN Aldh1a1 (2.1x) Aldh1a7 (1.6x) • Phase II (conjugation) enzymes Ugt1a1 (2.8x) Gst-a1 (16x) • Transporters Mdr1a (3.2x) Mrp3 (3.0x) Oatp2 (9.2x) excretion ☯ PXR Protects the Body from Toxins , But…
xenobiotics >50% of drugs oral contraceptives cyclosporin rifampicin warfarin dexamethasone indinavir RU486 PXR RXR nevirapine clotrimazole irinotecan troglitazone tamoxifen Phase I Phase II xenobiotic metabolism others? Transporters
Causes Drug-Drug Interactions St. John’s Wort
•Medicinal herb • Widely used for depression – European sales of $6 billion (1998) – US sales of $210 million (2000) • Complex mixture of > two dozen chemicals •Drug interactions – oral contraceptives – cyclosporin –warfarin –indinavir – nevirapine –irinotecan St. John’s Wort Activates PXR Cell-based reporter assay O HO .. O 8
7 O
6 EC50 ~ 30 nM 5
4
Fold activation 3
2
1 rutin pferol luteolin extract 3 extract 1 extract 2 myricetin hypericin sitosterol quercetin quercitrin SR12813 rifampicin hyperforin scopoletin belliferone hyperoside kaem isoquercitrin um
SJW amentoflavone pseudohypericin SJW Interacts with Drugs
SJW oral contraceptives cyclosporin warfarin indinavir nevirapine PXR RXR irinotecan
Phase I Phase II drug metabolism Transporters
SJW is predicted to interact with most drugs SJW Interacts with Drugs cyclosporin…………….immunosuppressant midazolam………anesthetic tacrolimus………………immunosuppressant nevirapine……...antiviral quazepine……………….sedative indinavir………….antiviral warfarin…………………anticoagulant irinotecan………antineoplastic verapamil……………….antihypertensive gleevec…………….antineoplastic nifedipine………………antihypertensive amitriptyline….antidepressant omeprazole……………antiulcerative simvastatin……..anticholesterolemic theophylline………….bronchodilator digoxin…………….cardiotonic ethinylestradiol…..oral contraceptive methadone………analgesic alprazolam……….anxiolytic
Do other herbs activate PXR? Gugulipid Activates PXR
PXR activation • Derived from mukul myrrh tree
• Promoted for reducing 6 cholesterol and treating obesity • Accelerates the metabolism of 4 two antihypertension drugs Activity –diltiazem 2 –propranolol 0 veh rif 0.1 1.0 10 0.1 1.0 10 SJW gugulipid
Gugulipid may counteract other drugs including statins Hops Activates PXR
PXR activation • Promoted for treating 6 –insomnia –anxiety –indigestion 4 • Increases drug metabolizing Activity 2 enzymes in rodents
0 veh rif 0.1 1.0 10 0.1 1.0 10 SJW hops
Hops is predicted to interact with most drugs Herbs Activate PXR
SJW gugulipid hops others?
PXR RXR
Phase I Phase II drug metabolism Transporters
These herbs are predicted to interact with many drugs PXR Assays Predict Herb-Drug Interactions
•Reliable • Efficient
PXR
PXRE Reporter Reporter plasmid
Herb-drug interactions can be predicted and prevented Acknowledgments
GlaxoSmithKline UT Southwestern Linda Moore Li Peng John Moore Jodi Maglich Bryan Goodwin Tim Willson