TY - JOUR T1 - IN SILICO AND IN VITRO SCREENING FOR INHIBITION OF CYTOCHROME P450 CYP3A4 BY COMEDICATIONS COMMONLY USED BY PATIENTS WITH CANCER JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 534 LP - 538 DO - 10.1124/dmd.105.007625 VL - 34 IS - 4 AU - Jean-Didier Marechal AU - Jinglei Yu AU - Simon Brown AU - Iouri Kapelioukh AU - Elaine M. Rankin AU - C. Roland Wolf AU - Gordon C. K. Roberts AU - Mark. J. I. Paine AU - Michael J. Sutcliffe Y1 - 2006/04/01 UR - http://dmd.aspetjournals.org/content/34/4/534.abstract N2 - Cytochrome P450 3A4 (CYP3A4) is the major enzyme responsible for phase I drug metabolism of many anticancer agents. It is also a major route for metabolism of many drugs used by patients to treat the symptoms caused by cancer and its treatment as well as their other illnesses, for example, cardiovascular disease. To assess the ability to inhibit CYP3A4 of drugs most commonly used by our patients during cancer therapy, we have made in silico predictions based on the crystal structures of CYP3A4. From this set of 33 common comedicated drugs, 10 were predicted to be inhibitors of CYP3A4, with the antidiarrheal drug loperamide predicted to be the most potent. There was significant correlation (r2 = 0.75–0.66) between predicted affinity and our measured IC50 values, and loperamide was confirmed as a potent inhibitor (IC50 of 0.050 ± 0.006 μM). Active site docking studies predicted an orientation of loperamide consistent with formation of the major (N-demethylated) metabolite, where it interacts with the phenylalanine cluster and Arg-212 and Glu-374; experimental evidence for the latter interaction comes from the ∼12-fold increase in KM for loperamide observed for the Glu-374-Gln mutant. The commonly prescribed drugs loperamide, amitriptyline, diltiazem, domperidone, lansoprazole, omeprazole, and simvastatin were identified by our in silico and in vitro screens as relatively potent inhibitors of CYP3A4 that have the potential to interact with cytotoxic agents to cause adverse effects, highlighting the likelihood of drug-drug interactions affecting chemotherapy treatment. The American Society for Pharmacology and Experimental Therapeutics ER -