P-glycoprotein interactions of novel psychoactive substances – Stimulation of ATP consumption and transport across Caco-2 monolayers Markus R. Meyer a, *, Lea Wagmann a , Nicole Schneider-Daum b , Brigitta Loretz b , Cristiane de Souza Carvalho b , Claus-Michael Lehr b , Hans H. Maurer a a Department of Experimental and Clinical Toxicology, Institute of Experimental and Clinical Pharmacology and Toxicology, Saarland University, 66421 Homburg, Germany b Dept of Drug Delivery, Helmholtz-Institute for Pharmaceutical Research Saarland (HIPS), Helmholtz-Center for Infection Research, Saarland University, 66123 Saarbru ¨cken, Germany 1. Introduction Transport proteins play a major role in absorption, distribution, and excretion of xenobiotics [1]. Besides metabolism, these factors are commonly accepted to have important influences on pharma- cokinetics, bioavailability, and consequently therapeutic efficacy of drugs [2,3]. A well-known group of transport proteins is the ABC (ATP binding cassette) transporter family including P-glycoprotein (P-gp). P-gp acts as a membrane-bound efflux pump in excretory tissues (e.g. intestine, liver, kidney), blood–tissue barriers (e.g. blood–brain barrier), and cancer cells. It actively transports substrates from intra- to extracellular under consumption of ATP [4–7]. Hence, P-gp limits drug entry, promotes drug elimination, and decreases bioavailability of its substrates. Previous findings [8,9] clearly indicated that changes in P-gp activity can be followed by serious drug–drug interactions. The two major mechanisms are induction and inhibition. Induction of P-gp can provoke elimination of P-gp substrates and decrease their bioavailability. In contrast, inhibition can increase bioavailability and amplify therapeutic efficacy, but also toxicity [3,9]. An example of inhibition is the interaction of loperamide and P-gp inhibitors at the blood–brain barrier. Loperamide is an over-the- counter drug used against diarrhea, which binds to opioid receptors of the large intestine and decreases the tone of the smooth muscles of the intestinal wall. P-gp prevents loperamide to enter the central nervous system (CNS) and restricts the effect to the periphery [10]. In combination with P-gp inhibitors (e.g. quinidine [9]) central opiate-characteristic effects such as respira- tory depression might result. However, interactions based on P-gp can also occur at other organs and tissues [9]. In contrast to therapeutic drugs, drugs of abuse (DOA) and particularly the so-called novel psychoactive substances (NPS) are marketed and consumed without preclinical or clinical studies and there are only few data available concerning their interactions with Biochemical Pharmacology 94 (2015) 220–226 A R T I C L E I N F O Article history: Received 18 December 2014 Accepted 21 January 2015 Available online 28 January 2015 Keywords: p-Glycoprotein Substrate Inhibitor Drugs of abuse Novel psychoactive substances A B S T R A C T In contrast to drugs for therapeutic use, there are only few data available concerning interactions between P-glycoprotein (P-gp) and drugs of abuse (DOA). In this work, interactions between structurally diverse DOA and P-gp were investigated using different strategies. First, the effect on the P-gp ATPase activity was studied by monitoring of ATP consumption after addition to recombinant, human P-gp. Second, DOA showing an increased ATP consumption were further characterized regarding their transport across filter grown Caco-2- monolayers. Analyses were performed by luminescence and liquid chromatography–mass spectrometry, respectively. Among the nine DOA initially screened, benzedrone, diclofensine, glaucine, JWH-200, MDBC, WIN-55,212-2 showed an increase of ATP consumption in the ATPase stimulation assay. In Caco-2 transport studies, Glaucine, JWH-200, mitragynine, WIN-55,212-2 could moreover be identified as non-transported substrates, but inhibitors of P-gp activity. Thus, drug– drug or drug–food interactions should be very likely for these compounds. ß 2015 Elsevier Inc. All rights reserved. * Corresponding author. Tel.: +49 6841 16 26430; fax: +49 6841 16 26051. E-mail address: markus.meyer@uks.eu (M.R. Meyer). Contents lists available at ScienceDirect Biochemical Pharmacology jo u rn al h om epag e: ww w.els evier.c o m/lo cat e/bio c hem p har m http://dx.doi.org/10.1016/j.bcp.2015.01.008 0006-2952/ß 2015 Elsevier Inc. All rights reserved.