Abstract

To support drug development and registration, Caco-2 cell monolayer assays have previously been set up and validated to determine whether candidate drugs are substrates or inhibitors of human P-glycoprotein (P-gp). In this study, the drug-drug interaction (DDI) potential of N-(1-{(3R)-3-(3,5-difluorophenyl)-3-[4-methanesulfonylphenyl]propyl}piperidin-4-yl)-N-ethyl-2-[4-methanesulfonylphenyl]acetamide (AZD5672) was assessed accordingly, and a subsequent clinical digoxin interaction study was performed. AZD5672 (1–500 μM) demonstrated concentration-dependent efflux across cell monolayers, which was abolished in the presence of ketoconazole and quinidine, identifying AZD5672 as a P-gp substrate. In addition, P-gp-mediated digoxin transport was inhibited in a concentration-dependent manner by AZD5672 (IC₅₀ = 32 μM). Assessment of the calculated theoretical gastrointestinal inhibitor concentration ([I₂]) and predicted steady-state maximum total plasma inhibitor concentration ([I₁]) indicated the potential for a DDI at the intestinal but not the systemic level after the predicted therapeutic dose of AZD5672 (100 mg). A clinical study was performed and the plasma pharmacokinetics [observed maximum plasma drug concentration (C_max) and area under the plasma concentration versus time curve from 0 to 72 h postdose (AUC_{0–72 h})] of orally dosed digoxin (0.5 mg) were found to be unaffected by coadministration of AZD5672 (50 mg) at steady state. In contrast, a 150-mg dose of AZD5672 significantly increased digoxin C_max and AUC_{0–72 h} by 1.82- and 1.33-fold, respectively. Concentration-time profile comparisons indicated that digoxin elimination was unchanged by AZD5672, and the interaction was most likely to have resulted from inhibition of intestinal P-gp leading to increased digoxin absorption. The observed dose-dependent clinically significant interaction was accurately predicted using calculated [I₂] and in vitro P-gp inhibition data, confirming AZD5672 to be a P-gp inhibitor in vivo.