A novel fluorescence‐based functional assay for human OATP1A2 and OATP1C1 identifies interaction between third‐generation P‐gp inhibitors and OATP1A2

Two novel in vitro assays to screen chemicals for their capacity to inhibit thyroid hormone transmembrane transporter proteins OATP1C1 and OAT4

Early brain development depends on adequate transport of thyroid hormones (THs) from the maternal circulation to the fetus. To reach the fetal brain, THs have to cross several physiological barriers, including the placenta, blood-brain-barrier and blood-cerebrospinal fluid-barrier. Transport across these barriers is facilitated by thyroid hormone transmembrane transporters (THTMTs). Some endocrine disrupting chemicals (EDCs) can interfere with the transport of THs by THTMTs. To screen chemicals for their capacity to disrupt THTMT facilitated TH transport, in vitro screening assays are required. In this study, we developed assays for two THTMTs, organic anion transporter polypeptide 1C1 (OATP1C1) and organic anion transporter 4 (OAT4), both known to play a role in the transport of THs across barriers. We used overexpressing cell models for both OATP1C1 and OAT4, which showed an increased uptake of radiolabeled T4 compared to control cell lines. Using these models, we screened various reference and environmental chemicals for their ability to inhibit T4 uptake by OATP1C1 and OAT4. Tetrabromobisphenol A (TBBPA) was identified as an OATP1C1 inhibitor, more potent than any of the reference chemicals tested. Additionally perfluorooctanesulfonic acid (PFOS), perfluoroctanic acid (PFOA), pentachlorophenol and quercetin were identified as OATP1C1 inhibitors in a similar range of potency to the reference chemicals tested. Bromosulfophthalein, TBBPA, PFOA and PFOS were identified as potent OAT4 inhibitors. These results demonstrate that EDCs commonly found in our environment can disrupt TH transport by THTMTs, and contribute to the identification of molecular mechanisms underlying TH system disruption chemicals.

Interaction of mycotoxins zearalenone, α-zearalenol, and β-zearalenol with cytochrome P450 (CYP1A2, 2C9, 2C19, 2D6, and 3A4) enzymes and organic anion transporting polypeptides (OATP1A2, OATP1B1, OATP1B3, and OATP2B1)

Zearalenone (ZEN) is a mycoestrogen produced by Fusarium fungi. ZEN is a frequent contaminant in cereal-based products, representing significant health threat. The major reduced metabolites of ZEN are α-zearalenol (α-ZEL) and β-zearalenol (β-ZEL). Since the toxicokinetic interactions of ZEN/ZELs with cytochrome P450 enzymes (CYPs) and organic anion transporting polypeptides (OATPs) have been barely characterized, we examined these interactions applying in vitro models. ZEN and ZELs were relatively strong inhibitors of CYP3A4 and moderate inhibitors of CYP1A2 and CYP2C9. Both CYP1A2 and CYP3A4 decreased ZEN and β-ZEL concentrations in depletion assays, while only CYP1A2 reduced α-ZEL levels. OATPs tested were strongly or moderately inhibited by ZEN and ZELs; however, these mycotoxins did not show higher cytotoxicity in OATP-overexpressing cells. Our results help the deeper understanding of the toxicokinetic/pharmacokinetic interactions of ZEN, α-ZEL, and β-ZEL.

Molecular Mechanisms of Organic Anion Transporting Polypeptide-Mediated Organic Anion Clearance at the Blood-Cerebrospinal Fluid Barrier

The blood-cerebrospinal fluid barrier (BCSFB), formed by the choroid plexus epithelial (CPE) cells, plays an active role in removing drugs and metabolic wastes from the brain. Recent functional studies in isolated mouse choroid plexus (CP) tissues suggested the presence of organic anion transporting polypeptides (OATPs, encoded by SLCOs) at the apical membrane of BCSFB, which may clear large organic anions from the cerebrospinal fluid (CSF). However, the specific OATP isoform involved is unclear. Using quantitative fluorescence imaging, we showed that the fluorescent anions sulforhodamine 101 (SR101), fluorescein methotrexate (FL-MTX), and 8-fluorescein-cAMP (fluo-cAMP) are actively transported from the CSF to the subepithelial space in CP tissues isolated from wild-type mice. In contrast, transepithelial transport of these compounds across the CPE cells was abolished in Oatp1a/1b-/- mice due to impaired apical uptake. Using transporter-expressing cell lines, SR101, FL-MTX, and fluo-cAMP were additionally shown to be transported by mouse OATP1A5 and its human counterpart OATP1A2. Kinetic analysis showed that estrone-3-sulfate and SR101 are transported by OATP1A2 and OATP1A5 with similar Michaelis-Menten constants (Km). Immunofluorescence staining further revealed the presence of OATP1A2 protein in human CP tissues. Together, our results suggest that large organic anions in the CSF are actively transported into CPE cells by apical OATP1A2 (OATP1A5 in mice), then subsequently effluxed into the blood by basolateral multidrug resistance-associated proteins (MRPs). As OATP1A2 transports a wide array of endogenous compounds and xenobiotics, the presence of this transporter at the BCSFB may imply a novel clearance route for drugs and neurohormones from the CSF. SIGNIFICANCE STATEMENT: Drug transporters at the blood-cerebrospinal fluid (CSF) barrier play an important but understudied role in brain drug disposition. This study revealed a functional contribution of rodent organic anion transporting polypeptide (OATP) 1A5 towards the CSF clearance of organic anions and suggested a similar role for OATP1A2 in humans. Delineating the molecular mechanisms governing CSF organic anion clearance may help to improve the prediction of central nervous system (CNS) pharmacokinetics and identify drug candidates with favorable CNS pharmacokinetic properties.

Dissimilar Effect of P-Glycoprotein and Breast Cancer Resistance Protein Inhibition on the Distribution of Erlotinib to the Retina and Brain in Humans and Mice

P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) are two ATP-binding cassette efflux transporters that are coexpressed at the human blood-brain barrier (BBB) and blood-retina barrier (BRB). While pharmacological inhibition of P-gp and/or BCRP results in increased brain distribution of dual P-gp/BCRP substrate drugs, such as the tyrosine kinase inhibitor erlotinib, the effect of P-gp and/or BCRP inhibition on the retinal distribution of such drugs has hardly been investigated. In this study, we used positron emission tomography (PET) imaging to assess the effect of transporter inhibition on the distribution of [11C]erlotinib to the human retina and brain. Twenty two healthy volunteers underwent two PET scans after intravenous (i.v.) injection of a microdose (<5 μg) of [11C]erlotinib, a baseline scan, and a second scan either with concurrent i.v. infusion of tariquidar to inhibit P-gp (n = 5) or after oral intake of single ascending doses of erlotinib (300 mg, 650 mg, or 1000 mg, n = 17) to saturate erlotinib transport. In addition, transport of [3H]erlotinib to the retina and brain was assessed in mice by in situ carotid perfusion under various drug transporter inhibition settings. In comparison to the baseline PET scan, coadministration of tariquidar or erlotinib led to a significant decrease of [11C]erlotinib total volume of distribution (VT) in the human retina by -25 ± 8% (p ≤ 0.05) and -41 ± 16% (p ≤ 0.001), respectively. In contrast, erlotinib intake led to a significant increase in [11C]erlotinib VT in the human brain (+20 ± 16%, p ≤ 0.001), while administration of tariquidar did not result in any significant changes. In situ carotid perfusion experiments showed that both P-gp and BCRP significantly limit the distribution of erlotinib to the mouse retina and brain but revealed a similar discordant effect at the mouse BRB and BBB following co-perfusion with tariquidar and erlotinib as in humans. Co-perfusion with prototypical inhibitors of solute carrier transporters did not reveal a significant contribution of organic cation transporters (e.g., OCTs and OCTNs) and organic anion-transporting polypeptides (e.g., OATP2B1) to the retinal and cerebral distribution of erlotinib. In conclusion, we observed a dissimilar effect after P-gp and/or BCRP inhibition on the retinal and cerebral distribution of [11C]erlotinib. The exact mechanism for this discrepancy remains unclear but may be related to the function of an unidentified erlotinib uptake carrier sensitive to tariquidar inhibition at the BRB. Our study highlights the great potential of PET to study drug distribution to the human retina and to assess the functional impact of membrane transporters on ocular drug distribution.

The fluorescence-based competitive counterflow assay developed for organic anion transporting polypeptides 1A2, 1B1, 1B3 and 2B1 identifies pentamidine as a selective OATP1A2 substrate

Organic anion transporting polypeptides OATP1A2, OATP1B1, OATP1B3 and OATP2B1 are Na+ - and ATP-independent exchangers of large, organic compounds, encompassing structurally diverse xenobiotics, including various drugs. These OATPs influence intestinal absorption (OATP2B1), hepatic clearance (OATP1B1/3) and blood to brain penetration (OATP1A2, OATP2B1) of their drug substrates. Consequently, OATP-mediated drug or food interactions may lead to altered pharmacokinetics and toxicity. During drug development, investigation of hepatic OATP1B1 and OATP1B3 is recommended by international regulatory agencies. Most frequently, OATP-drug interactions are investigated in an indirect assay, i.e., by examining uptake inhibition of a radioactive or fluorescent probe. However, indirect assays do not distinguish between transported substrates and non-transported OATP inhibitors. To fill this hiatus, a novel assay, termed competitive counterflow (CCF) has been developed and has since been applied for several OATPs to differentiate between substrates and non-transported inhibitors. However, previous OATP CCF assays, with the exception of that for OATP1B1, used radioactive probes. In the current study, we demonstrate that sulforhodamine 101 or pyranine can be used as fluorescent probes in a CCF assay to identify transported substrates of OATP1A2, or OATPs 1B1, 1B3 and 2B1, respectively. With the help of the newly developed fluorescence-based CCF method, we identify the FDA-approved anti-protozoal drug, pentamidine as a unique substrate of OATP1A2. Furthermore, we confirm the selective, OATP1A2-mediated uptake of pentamidine in a cytotoxicity assay. Based on our results, OATP1A2 may be an important determinant of pentamidine transport through the blood-brain barrier.

Interactions of the Anti-SARS-CoV-2 Agents Molnupiravir and Nirmatrelvir/Paxlovid with Human Drug Transporters

Orally administered small molecules may have important therapeutic potential in treating COVID-19 disease. The recently developed antiviral agents, Molnupiravir and Nirmatrelvir, have been reported to be efficient treatments, with only moderate side effects, especially when applied in the early phases of this disease. However, drug-drug and drug-transporter interactions have already been noted by the drug development companies and in the application notes. In the present work, we have studied some of the key human transporters interacting with these agents. The nucleoside analog Molnupiravir (EIDD-2801) and its main metabolite (EIDD-1931) were found to inhibit CNT1,2 in addition to the ENT1,2 nucleoside transporters; however, it did not significantly influence the relevant OATP transporters or the ABCC4 nucleoside efflux transporter. The active component of Paxlovid (PF-07321332, Nirmatrelvir) inhibited the function of several OATPs and of ABCB1 but did not affect ABCG2. However, significant inhibition was observed only at high concentrations of Nirmatrelvir and probably did not occur in vivo. Paxlovid, as used in the clinic, is a combination of Nirmatrelvir (viral protease inhibitor) and Ritonavir (a "booster" inhibitor of Nirmatrelvir metabolism). Ritonavir is known to inhibit several drug transporters; therefore, we have examined these compounds together, in relevant concentrations and ratios. No additional inhibitory effect of Nirmatrelvir was observed compared to the strong transporter inhibition caused by Ritonavir. Our current in vitro results should help to estimate the potential drug-drug interactions of these newly developed agents during COVID-19 treatment.

Fluorescence-based methods for studying activity and drug-drug interactions of hepatic solute carrier and ATP binding cassette proteins involved in ADME-Tox

In humans, approximately 70% of drugs are eliminated through the liver. This process is governed by the concerted action of membrane transporters and metabolic enzymes. Transporters mediating hepatocellular uptake of drugs belong to the SLC (Solute carrier) superfamily of transporters. Drug efflux either toward the portal vein or into the bile is mainly mediated by active transporters of the ABC (ATP Binding Cassette) family. Alteration in the function and/or expression of liver transporters due to mutations, disease conditions, or co-administration of drugs or food components can result in altered pharmacokinetics. On the other hand, drugs or food components interacting with liver transporters may also interfere with liver function (e.g., bile acid homeostasis) and may even cause liver toxicity. Accordingly, certain transporters of the liver should be investigated already at an early stage of drug development. Most frequently radioactive probes are applied in these drug-transporter interaction tests. However, fluorescent probes are cost-effective and sensitive alternatives to radioligands, and are gaining wider application in drug-transporter interaction tests. In our review, we summarize our current understanding about hepatocyte ABC and SLC transporters affected by drug interactions. We provide an update of the available fluorescent and fluorogenic/activable probes applicable in in vitro or in vivo testing of these ABC and SLC transporters, including near-infrared transporter probes especially suitable for in vivo imaging. Furthermore, our review gives a comprehensive overview of the available fluorescence-based methods, not directly relying on the transport of the probe, suitable for the investigation of hepatic ABC or SLC-type drug transporters.

Identification of 5-Carboxyfluorescein as a Probe Substrate of SLC46A3 and Its Application in a Fluorescence-Based In Vitro Assay Evaluating the Interaction with SLC46A3

The therapeutic modalities that involve the endocytosis pathway, including antibody-drug conjugates (ADCs), have recently been developed. Since the drug escape from endosomes/lysosomes is a determinant of their efficacy, it is important to optimize the escape, and the cellular evaluation system is needed. SLC46A3, a lysosomal membrane protein, has been implicated in the pharmacological efficacy of trastuzumab emtansine (T-DM1), a noncleavable ADC used for the treatment of breast cancer, and the cellular uptake efficacy of lipid-based nanoparticles. Recently, we identified the SLC46A3 function as a proton-coupled steroid conjugate and bile acid transporter, which can directly transport active catabolites of T-DM1. Thus, the rapid and convenient assay systems for evaluating the SLC46A3 function may help to facilitate ADC development and to clarify the physiological roles in endocytosis. Here, we show that SLC46A3 dC, which localizes to the plasma membrane owing to lacking a lysosomal-sorting motif, has a great ability to transport 5-carboxyfluorescein (5-CF), a fluorescent probe, in a pH-dependent manner. 5-CF uptake mediated by SLC46A3 was significantly inhibited by compounds reported to be SLC46A3 substrates/inhibitors and competitively inhibited by estrone 3-sulfate, a typical SLC46A3 substrate. The inhibition assays followed by uptake studies revealed that SG3199, a pyrrolobenzodiazepine dimer, which has been used as an ADC payload, is a substrate of SLC46A3. Accordingly, the fluorescence-based assay system for the SLC46A3 function using 5-CF can provide a valuable tool to evaluate the interaction of drugs/drug candidates with SLC46A3.

Interactions of Mycotoxin Alternariol with Cytochrome P450 Enzymes and OATP Transporters

Alternariol (AOH) is an emerging mycotoxin produced by Alternaria strains. The acute toxicity of the mycotoxin is low; however, chronic exposure to AOH may result in the development of endocrine disruptor and/or carcinogenic effects. The toxicokinetic properties of AOH have barely been characterized. Therefore, in this study, we aimed to investigate its interactions with CYP (1A2, 2C9, 2C19, 2D6, and 3A4) enzymes and OATP (1A2, 1B1, 1B3, and 2B1) transporters employing in vitro enzyme assays and OATP overexpressing cells, respectively. Our results demonstrated that AOH is a strong inhibitor of CYP1A2 (IC₅₀ = 0.15 μM) and CYP2C9 (IC₅₀ = 7.4 μM). Based on the AOH depletion assays in the presence of CYP enzymes, CYP1A2 is mainly involved, while CYP2C19 is moderately involved in the CYP-catalyzed biotransformation of the mycotoxin. AOH proved to be a strong inhibitor of each OATP transporter examined (IC₅₀ = 1.9 to 5.4 μM). In addition, both direct and indirect assays suggest the involvement of OATP1B1 in the cellular uptake of the mycotoxin. These findings promote the deeper understanding of certain toxicokinetic interactions of AOH.

P-Glycoprotein (MDR1/ABCB1) Restricts Brain Accumulation of the Novel EGFR Inhibitor EAI045 and Oral Elacridar Coadministration Enhances Its Brain Accumulation and Oral Exposure

EAI045 is a fourth-generation allosteric tyrosine kinase inhibitor (TKI) of the epidermal growth factor receptor (EGFR). It targets T790M and C797S EGFR mutants in the treatment of non-small cell lung cancer (NSCLC). EAI045 and cetuximab combined induce tumor regression in mouse models of EGFR-mutant lung cancer. We investigated the pharmacokinetic roles of the multidrug efflux and uptake transporters ABCB1 (P-gp), ABCG2 (BCRP), and OATP1A/1B, and of the drug-metabolizing enzyme CYP3A in plasma and tissue distribution of EAI045 and its metabolites, using genetically modified mouse models. In vitro, EAI045 was a good transport substrate of human ABCB1. In vivo, oral EAI045 (20 mg/kg) was rapidly absorbed. Relative to wild-type mice, EAI045 brain-to-plasma ratios were increased 3.9-fold in Abcb1a/1b^-/- and 4.8-fold in Abcb1a/1b;Abcg2^-/- mice. However, in single Abcg2^-/- mice they were unchanged. EAI045 oral availability was not markedly altered. Oral coadministration of elacridar, an ABCB1/ABCG2 inhibitor, increased the plasma AUC_0–30min and brain-to-plasma ratios of EAI045 by 4.0-fold and 5.4-fold, respectively, in wild-type mice. EAI045 glucuronide showed an increased plasma AUC_0–30min and a markedly decreased accumulation and tissue-to-plasma ratio in the small intestinal content when Abcb1a/1b and Abcg2 were absent. A large fraction of oral EAI045 was converted to its hydrolyzed metabolite PIA, but Abcb1a/1b, Abcg2, and Oatp1a/1b had little impact on PIA pharmacokinetics. Mouse Cyp3a knockout or transgenic human CYP3A4 overexpression did not significantly affect oral EAI045 pharmacokinetics. Our results show that blood–brain barrier ABCB1 can markedly limit EAI045 brain accumulation. Moreover, elacridar coadministration can effectively reverse this process.

Interactions of resveratrol and its metabolites (resveratrol-3-sulfate, resveratrol-3-glucuronide, and dihydroresveratrol) with serum albumin, cytochrome P450 enzymes, and OATP transporters

Resveratrol (RES) is a widely-known natural polyphenol which is also contained by several dietary supplements. Large doses of RES can result in high micromolar levels of its sulfate and glucuronide conjugates in the circulation, due to the high presystemic metabolism of the parent polyphenol. Pharmacokinetic interactions of RES have been extensively studied, while only limited data are available regarding its metabolites. Therefore, in the current study, we examined the interactions of resveratrol-3-sulfate (R3S), resveratrol-3-glucuronide, and dihydroresveratrol (DHR; a metabolite produced by the colon microbiota) with human serum albumin (HSA), cytochrome P450 (CYP) enzymes, and organic anion transporting polypeptides (OATP) employing in vitro models. Our results demonstrated that R3S and R3G may play a major role in the RES-induced pharmacokinetic interactions: (1) R3S can strongly displace the site I marker warfarin from HSA; (2) R3G showed similarly strong inhibitory action on CYP3A4 to RES; (3) R3S proved to be similarly strong (OATP1B1/3) or even stronger (OATP1A2 and OATP2B1) inhibitor of OATPs tested than RES, while R3G and RES showed comparable inhibitory actions on OATP2B1.

Increased/Targeted Brain (Pro)Drug Delivery via Utilization of Solute Carriers (SLCs)

Membrane transporters have a crucial role in compounds’ brain drug delivery. They allow not only the penetration of a wide variety of different compounds to cross the endothelial cells of the blood–brain barrier (BBB), but also the accumulation of them into the brain parenchymal cells. Solute carriers (SLCs), with nearly 500 family members, are the largest group of membrane transporters. Unfortunately, not all SLCs are fully characterized and used in rational drug design. However, if the structural features for transporter interactions (binding and translocation) are known, a prodrug approach can be utilized to temporarily change the pharmacokinetics and brain delivery properties of almost any compound. In this review, main transporter subtypes that are participating in brain drug disposition or have been used to improve brain drug delivery across the BBB via the prodrug approach, are introduced. Moreover, the ability of selected transporters to be utilized in intrabrain drug delivery is discussed. Thus, this comprehensive review will give insights into the methods, such as computational drug design, that should be utilized more effectively to understand the detailed transport mechanisms. Moreover, factors, such as transporter expression modulation pathways in diseases that should be taken into account in rational (pro)drug development, are considered to achieve successful clinical applications in the future.

8-acetoxy-trisulfopyrene as the first activatable fluorogenic probe for add-and-read assessment of Organic anion-transporting polypeptides, OATP1B1, OATP1B3, and OATP2B1

Organic anion-transporting polypeptides, OATP1B1, OATP1B3, and OATP2B1 are multispecific membrane proteins mediating the hepatocellular uptake of structurally diverse endo- and exogenous compounds, including various kinds of drugs. Co-administration of OATP1B/2B1 substrates may lead to altered pharmacokinetics or even toxicity. Therefore, the study of the interaction with these OATPs is essential in drug development and is recommended by international regulatory agencies, the FDA, EMA, and PMDA. In general, radiolabeled indicators are used to measure drug interactions of OATPs, and, lately, fluorescent probes are also gaining wider application in OATP tests. However, all of the currently available methods (either radioactive or fluorescence-based) comprise multiple steps, including the removal of the indicator in the end of the experiment. Hence, they are not ideally suited for high-throughput screening. In the current study, in order to find an indicator allowing real-time assessment of hepatic OATP function, we searched for an activatable fluorogenic OATP substrate. Here, we show that 8-acetoxypyrene-1,3,6-trisulfonate (Ace), a fluorogenic derivative of the hepatic OATP substrate pyranine (8-hydroxypyrene-1,3,6-trisulfonate) enters the cells via OATP1B1/3 or OATP2B1 function. In living cells, Ace is then converted into highly fluorescent pyranine, allowing "no-wash" measurement of OATP function and drug interactions. Furthermore, we demonstrate that Ace can be used in an indirect assay termed as competitive counterflow suitable to distinguish between transported substrates and inhibitors of OATP1B1. The fluorescence-based methods described here are unique and open the way toward high-throughput screening of interactions between new molecular entities and OATPs.

Interactions of Potential Anti-COVID-19 Compounds with Multispecific ABC and OATP Drug Transporters

During the COVID-19 pandemic, several repurposed drugs have been proposed to alleviate the major health effects of the disease. These drugs are often applied with analgesics or non-steroid anti-inflammatory compounds, and co-morbid patients may also be treated with anticancer, cholesterol-lowering, or antidiabetic agents. Since drug ADME-tox properties may be significantly affected by multispecific transporters, in this study, we examined the interactions of the repurposed drugs with the key human multidrug transporters present in the major tissue barriers and strongly affecting the pharmacokinetics. Our in vitro studies, using a variety of model systems, explored the interactions of the antimalarial agents chloroquine and hydroxychloroquine; the antihelmintic ivermectin; and the proposed antiviral compounds ritonavir, lopinavir, favipiravir, and remdesivir with the ABCB1/Pgp, ABCG2/BCRP, and ABCC1/MRP1 exporters, as well as the organic anion-transporting polypeptide (OATP)2B1 and OATP1A2 uptake transporters. The results presented here show numerous pharmacologically relevant transporter interactions and may provide a warning on the potential toxicities of these repurposed drugs, especially in drug combinations at the clinic.

Synergistic transport of a fluorescent coumarin probe marks coumarins as pharmacological modulators of Organic anion-transporting polypeptide, OATP3A1

Organic anion-transporting polypeptide 3A1 (OATP3A1) is a membrane transporter mediating the cellular uptake of various hormones such as estrone-3-sulfate, prostaglandins E1 and E2 and thyroxine. OATP3A1 is widely expressed in the human body and its presence in tissue-blood barriers, neurons and muscle cells marks it as a potential pharmacological target. Herein we demonstrate that an otherwise membrane impermeant, zwitterionic fluorescent coumarin probe, bearing a sulfonate function is a potent substrate of human OATP3A1, thus readily transported into HEK-293-OATP3A1 cells allowing functional investigation and the screen of drug interactions of the OATP3A1 transporter. At the same time, dyes lacking either the sulfonate motif or the coumarin scaffold showed a dramatic decrease in affinity or even a complete loss of transport. Furthermore, we observed a distinct inhibition/activation pattern in the OATP3A1-mediated uptake of closely related fluorescent coumarin derivatives differing only in the presence of the sulfonate moiety. Additionally, we detected a synergistic effect between one of the probes tested and the endogenous OATP substrate estrone-3-sulfate. These data, together with docking results indicate the presence of at least two cooperative substrate binding sites in OATP3A1. Besides providing the first sensitive probe for testing OATP3A1 substrate/inhibitor interactions, our results also help to understand substrate recognition and transport mechanism of the poorly characterized OATP3A1. Moreover, coumarins are good candidates for OATP3A1-targeted drug delivery and as pharmacological modulators of OATP3A1.

Inhibitory Effects of Quercetin and Its Main Methyl, Sulfate, and Glucuronic Acid Conjugates on Cytochrome P450 Enzymes, and on OATP, BCRP and MRP2 Transporters

Quercetin is a flavonoid, its glycosides and aglycone are found in significant amounts in several plants and dietary supplements. Because of the high presystemic biotransformation of quercetin, mainly its conjugates appear in circulation. As has been reported in previous studies, quercetin can interact with several proteins of pharmacokinetic importance. However, the interactions of its metabolites with biotransformation enzymes and drug transporters have barely been examined. In this study, the inhibitory effects of quercetin and its most relevant methyl, sulfate, and glucuronide metabolites were tested on cytochrome P450 (CYP) (2C19, 3A4, and 2D6) enzymes as well as on organic anion-transporting polypeptides (OATPs) (OATP1A2, OATP1B1, OATP1B3, and OATP2B1) and ATP (adenosine triphosphate) Binding Cassette (ABC) (BCRP and MRP2) transporters. Quercetin and its metabolites (quercetin-3'-sulfate, quercetin-3-glucuronide, isorhamnetin, and isorhamnetin-3-glucuronide) showed weak inhibitory effects on CYP2C19 and 3A4, while they did not affect CYP2D6 activity. Some of the flavonoids caused weak inhibition of OATP1A2 and MRP2. However, most of the compounds tested proved to be strong inhibitors of OATP1B1, OATP1B3, OATP2B1, and BCRP. Our data demonstrate that not only quercetin but some of its conjugates, can also interact with CYP enzymes and drug transporters. Therefore, high intake of quercetin may interfere with the pharmacokinetics of drugs.

Effects of Chrysin and Its Major Conjugated Metabolites Chrysin-7-Sulfate and Chrysin-7-Glucuronide on Cytochrome P450 Enzymes and on OATP, P-gp, BCRP, and MRP2 Transporters

Chrysin is an abundant flavonoid in nature, and it is also contained by several dietary supplements. Chrysin is highly biotransformed in the body, during which conjugated metabolites chrysin-7-sulfate and chrysin-7-glucuronide are formed. These conjugates appear at considerably higher concentrations in the circulation than the parent compound. Based on previous studies, chrysin can interact with biotransformation enzymes and transporters; however, the interactions of its metabolites have been barely examined. In this in vitro study, the effects of chrysin, chrysin-7-sulfate, and chrysin-7-glucuronide on cytochrome P450 enzymes (2C9, 2C19, 3A4, and 2D6) as well as on organic anion-transporting polypeptides (OATPs; 1A2, 1B1, 1B3, and 2B1) and ATP binding cassette [P-glycoprotein, multidrug resistance-associated protein 2, and breast cancer resistance protein (BCRP)] transporters were investigated. Our observations revealed that chrysin conjugates are strong inhibitors of certain biotransformation enzymes (e.g., CYP2C9) and transporters (e.g., OATP1B1, OATP1B3, OATP2B1, and BCRP) examined. Therefore, the simultaneous administration of chrysin-containing dietary supplements with medications needs to be carefully considered due to the possible development of pharmacokinetic interactions. SIGNIFICANCE STATEMENT: Chrysin-7-sulfate and chrysin-7-glucuronide are the major metabolites of flavonoid chrysin. In this study, we examined the effects of chrysin and its conjugates on cytochrome P450 enzymes and on organic anion-transporting polypeptides and ATP binding cassette transporters (P-glycoprotein, breast cancer resistance protein, and multidrug resistance-associated protein 2). Our results demonstrate that chrysin and/or its conjugates can significantly inhibit some of these proteins. Since chrysin is also contained by dietary supplements, high intake of chrysin may interrupt the transport and/or the biotransformation of drugs.

Interplay of drug transporters P-glycoprotein (MDR1), MRP1, OATP1A2 and OATP1B3 in passage of maraviroc across human placenta

Special attention is required when pharmacological treatment is indicated for a pregnant woman. P-glycoprotein (MDR1) is a well-known transporter localized in the maternal blood-facing apical membrane of placental syncytiotrophoblast and is considered to play an important role in protecting the developing fetus. Maraviroc, a MDR1 substrate that is registered for treatment of HIV infection, shows a low toxicity profile, suggesting favorable tolerability also if administered to pregnant women. Nevertheless, there is only poor understanding to date regarding the extent to which it permeates across the placental barrier and what are the transport mechanisms involved. Endeavoring to clarify the passage of maraviroc across placenta, we used in this study the method of closed-circuit perfusion of maraviroc across human placental cotyledon. The data obtained confirmed slight involvement of MDR1, but they also suggest possible interaction with other transport system(s) working in the opposite direction from that of MDR1. Complementary in vitro studies, including cellular experiments on choriocarcinoma BeWo cells as well as transporter-overexpressing MDCKII and A431 cell lines and accumulation in placental fresh villous fragments, revealed maraviroc transport by MRP1, OATP1A2, and OATP1B3 transporters. Based on mRNA expression data in the placental tissue, isolated trophoblasts, and fetal endothelial cells, especially MRP1 and OATP1A2 seem to play a crucial role in cooperatively driving maraviroc into placental tissue. By the example of maraviroc, we show here the important interplay of transporters in placental drug handling and its possibility to overcome the MDR1-mediated efflux.