Send to

Choose Destination
J Pharmacol Exp Ther. 2010 Sep 1;334(3):999-1008. doi: 10.1124/jpet.110.168294. Epub 2010 May 26.

Camptothecin attenuates cytochrome P450 3A4 induction by blocking the activation of human pregnane X receptor.

Author information

Department of Medical Microbiology, Immunology, and Cell Biology, Southern Illinois University School of Medicine and SimmonsCooper Cancer Institute, Springfield, IL 62794-9626, USA.


Differential regulation of drug-metabolizing enzymes (DMEs) is a common cause of adverse drug effects in cancer therapy. Due to the extremely important role of cytochrome P450 3A4 (CYP3A4) in drug metabolism and the dominant regulation of human pregnane X receptor (hPXR) on CYP3A4, finding inhibitors for hPXR could provide a unique tool to control drug efficacies in cancer therapy. Camptothecin (CPT) was demonstrated as a novel and potent inhibitor (IC(50) = 0.58 microM) of an hPXR-mediated transcriptional regulation on CYP3A4 in this study. In contrast, one of its analogs, irinotecan (CPT-11), was found to be an hPXR agonist in the same tests. CPT disrupted the interaction of hPXR with steroid receptor coactivator-1 but had effects on neither the competition of ligand binding nor the formation of the hPXR and retinoid X receptor alpha heterodimer, nor the interaction between the regulatory complex and DNA-responsive elements. CPT treatment resulted in delayed metabolism of nifedipine in human hepatocytes treated with rifampicin, suggesting a potential prevention of drug-drug interactions between CYP3A4 inducers and CYP3A4-metabolized drugs. Because CPT is the leading compound of topoisomerase I inhibitors, which comprise a quickly developing class of anticancer agents, the findings indicate the potential of a new class of compounds to modify hPXR activity as agonists/inhibitors and are important in the development of CPT analogs.

[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for HighWire Icon for PubMed Central
Loading ...
Support Center