RT Journal Article SR Electronic T1 The Consequence of Drug–Drug Interactions Influencing the Interplay between P-Glycoprotein and Cytochrome P450 3a: An Ex Vivo Study with Rat Precision-Cut Intestinal Slices JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 683 OP 691 DO 10.1124/dmd.115.068684 VO 44 IS 5 A1 Ming Li A1 Inge A. M. de Graaf A1 Sanna Siissalo A1 Marina H. de Jager A1 Annie van Dam A1 Geny M. M. Groothuis YR 2016 UL http://dmd.aspetjournals.org/content/44/5/683.abstract AB P-glycoprotein (P-gp) and cytochrome P450 3A (CYP3A) are differentially expressed along the intestine and work coordinately to reduce the intracellular concentration of xenobiotics and the absorption of orally taken drugs. Drug–drug interactions (DDIs) based on P-gp/CYP3A interplay are of clinical importance and require preclinical investigation. We investigated the P-gp/Cyp3a interplay and related DDIs with different P-gp inhibitors in the various regions of the rat intestine ex vivo using precision-cut intestinal slices (PCIS) with quinidine (Qi), a dual substrate of P-gp and Cyp3a, as the probe. The results showed that P-gp efflux was the main factor limiting the intracellular Qi content at concentrations below 5 µM, whereas both efflux and metabolism were saturated at [Qi] > 50 µM. The selective P-gp inhibitors CP100356 [N-(3,4-dimethoxyphenethyl)-4-(6,7-dimethoxy-3,4-dihydroisoquinolin-2[1H]-yl)-6,7-dimethoxyquinazolin-2-amine] and PSC833 [valspodar, 6-[(2S,4R,6E)-4-methyl-2-(methylamino)-3-oxo-6-octenoic acid]-7-l-valine-cyclosporin A] enhanced the Qi accumulation in slices in line with the different P-gp expression in the intestinal regions and, as a result, also enhanced metabolism in the jejunum and ileum. Dual inhibitors of both P-gp and Cyp3a (verapamil and ketoconazole) increased the concentration of Qi in the jejunum and ileum, but less 3-hydroxy-quinidine was produced due to inhibition of Cyp3a. The results indicate that the P-gp/Cyp3a interplay depends on the concentration of the drug and on the intestinal region under study. Furthermore, due to the P-gp/Cyp3a interplay, DDIs can lead to remarkable changes in the intracellular concentration of both the parent drug and the metabolite, which varies among the intestinal regions and depends on the selectivity of the inhibitors, with potentially important implications for disposition and toxicity of drugs and their metabolites.