Transport of Drugs and Endogenous Compounds Mediated by Human OCT1: Studies in Single- and Double-Transfected Cell Models

Abstract

Organic Cation Transporter 1 (OCT1, gene symbol: SLC22A1) is predominately expressed in human liver, localized in the basolateral membrane of hepatocytes and facilitates the uptake of endogenous compounds (e.g. serotonin, acetylcholine, thiamine), and widely prescribed drugs (e.g. metformin, fenoterol, morphine). Furthermore, exogenous compounds such as MPP+, ASP+ and Tetraethylammonium can be used as prototypic substrates to study the OCT1-mediated transport in vitro. Single-transfected cell lines recombinantly overexpressing OCT1 (e.g., HEK-OCT1) were established to study OCT1-mediated uptake and to evaluate transporter-mediated drug-drug interactions in vitro. Furthermore, double-transfected cell models simultaneously overexpressing basolaterally localized OCT1 together with an apically localized export protein have been established. Most of these cell models are based on polarized grown MDCK cells and can be used to analyze transcellular transport, mimicking the transport processes e.g. during the hepatobiliary elimination of drugs. Multidrug and toxin extrusion protein 1 (MATE1, gene symbol: SLC47A1) and the ATP-driven efflux pump P-glycoprotein (P-gp, gene symbol: ABCB1) are both expressed in the canalicular membrane of human hepatocytes and are described as transporters of organic cations. OCT1 and MATE1 have an overlapping substrate spectrum, indicating an important interplay of both transport proteins during the hepatobiliary elimination of drugs. Due to the important role of OCT1 for the transport of endogenous compounds and drugs, in vitro cell systems are important for the determination of the substrate spectrum of OCT1, the understanding of the molecular mechanisms of polarized transport, and the investigation of potential drug-drug interactions. Therefore, the aim of this review article is to summarize the current knowledge on cell systems recombinantly overexpressing human OCT1.

Amino acids in transmembrane helix 1 confer major functional differences between human and mouse orthologs of the polyspecific membrane transporter OCT1

“…Fenoterol was the substrate with the highest affinity of human OCT1 in this study ( Table 1 ) and is among the OCT1 substrates with the highest affinity known in general ( 14 ). We were able to identify a single amino acid substitution—Cys36 (human) to Tyr36 (mouse)—that was sufficient to completely reverse the uptake kinetics of fenoterol between human and mouse and to make fenoterol a substrate of average affinity in human OCT1.…”

“…One important characteristic of OCT1is its polyspecificity. A variety of structurally diverse compounds are OCT1 substrates ( 13 , 14 ). Known substrates are clinically relevant drugs, such as sumatriptan, fenoterol, metformin, morphine, and trospium, and endogenous compounds such as thiamine ( 2 , 5 , 6 , 9 , 11 , 14 , 15 , 16 ).…”

“…A variety of structurally diverse compounds are OCT1 substrates ( 13 , 14 ). Known substrates are clinically relevant drugs, such as sumatriptan, fenoterol, metformin, morphine, and trospium, and endogenous compounds such as thiamine ( 2 , 5 , 6 , 9 , 11 , 14 , 15 , 16 ). The exact amino acids involved in binding and/or translocation of the various OCT1 substrates and thus conferring OCT1 polyspecificity are unclear.…”

Transporter-mediated Natural Product-Drug Interactions

“…than single gene-transfected models when using in uptake assays. To understand the functional interplay between uptake and efflux transporters, several double- [103][104][105],…”

OCT1 Polyspecificity—Friend or Foe?

“…Following the initially identified substrate TEA + , the organic cations MPP + and ASP + and endogenous compounds such as dopamine and histamine were described as substrates (Gründemann et al, 1994;Busch et al, 1996a;Busch et al, 1996b;Mehrens et al, 2000), showing that not only aliphatic, but also aromatic cations with variable structures could be OCT1 substrates. Currently, more than 150 organic cationic compounds with highly variable chemical structures, including also commonly used drugs like metformin, morphine, sumatriptan, fenoterol, and lamotrigine have been reported to be substrates of the organic cation transporter OCT1 (Wang et al, 2002;Dickens et al, 2012;Tzvetkov et al, 2013;Matthaei et al, 2016;Shen et al, 2016;Tzvetkov et al, 2018;Haberkorn et al, 2021).…”