Transporters OATP1B1 Research Articles

The scaffold protein PDZK1 modulates expression and function of the organic anion transporting polypeptide 2B1

The protein family of Organic Anion Transporting Polypeptides (OATPs) summarizes various transporters known to facilitate cellular uptake of xenobiotics. One member of this family is OATP2B1. This transporter is ubiquitously expressed and possesses a PDZ-binding motif at the C-terminus. PDZK1 (PDZ domain-containing 1) is a scaffold protein that influences function of different membrane proteins by sorting/stabilization of their membrane localization. It was aim of the herein reported study to investigate whether there is an interaction between OATP2B1 and PDZK1, and to further characterize its impact on transport function. At first expression of both OATP2B1 and PDZK1 was evaluated in liver, kidney and intestine. Based on the existence of a C-terminal PDZ-class I binding motif in OATP2B1 and the co-expression in all tested tissues an interaction was likely. Testing the influence of PDZK1 on OATP2B1 transport function revealed enhanced transport capacity for estrone 3-sulfate, thereby suggesting a change in OATP2B1 amount in the membrane. This assumption was validated by Western blot analysis. Finally, deletion of the C-terminal PDZ-binding motif in OATP2B1 lowered the impact of PDZK1 on transport function. Taken together, we report an interaction of PDZK1 with OATP2B1, which influences localization and function of the transporter. Changes in PDZK1 expression may therefore be one factor contributing to interindividual differences in OATP2B1 mediated pharmacokinetic processes.

Development and validation of an analytical method for regorafenib and its metabolites in mouse plasma

An analytical method was developed for measuring the effect of OATP1B2 deficiency on plasma levels of the kinase inhibitor regorafenib and its metabolites regorafenib-N-oxide, N-desmethyl-regorafenib-N-oxide, and regorafenib-N-β-glucuronide (RG) in mice. Compounds were separated by liquid chromatography and monitored by a triple quadrupole mass spectrometer in the selected reaction monitoring mode after positive electrospray ionization. All calibration curves were linear in the selected concentration range (R2 ≥ 0.99). The lower limit of quantification was 5 ng/mL for the four analytes. Within-day precisions, between-day precisions, and accuracies were 2.59–6.82%, 3.97–11.3%, and 94.5–111%, respectively. The identification and structure elucidation of RG, isolated from human urine, was performed by NMR. Compared with wild-type mice given regorafenib (10 mg/kg), deficiency of the drug transporter OATP1B2 in vivo had minimal effects on plasma levels of parent drug and the metabolite regorafenib-N-oxide, and N-desmethyl-regorafenib-N-oxide. However, the area under the curve and peak levels of RG were increased by 5.6-fold and 5.1-fold, respectively, in OATP1B2-knockout mice. In conclusion, our analytical method allowed accurate and precise quantitation of regorafenib and its main metabolites in mouse plasma, and is suitable for evaluation of transporter-dependent pharmacokinetic properties of these agents in vivo.

Baicalin is a substrate of OATP2B1 and OATP1B3.

The use and significance of baicalin, the main bioactive component found in Radix Scutellaria, have been on the rise due to its interesting pharmacological properties. Baicalin, a low passive permeability compound, is directly absorbed from the upper intestine and its hepatic elimination is dominant. However, interaction but no transport studies have implicated organic anion‐transporting polypeptides in its cellular uptake. By using mammalian cells stably expressing the uptake transporters of interest, we are showing that baicalin is a potent substrate of Organic anion‐transporting polypeptide 2B1 (OATP2B1) and less potent substrate of OATP1B3. OATP2B1 and OATP1B3 transport baicalin and may play a role in the hepatic uptake of baicalin formed in the intestine.

Drug interactions of meglitinide antidiabetics involving CYP enzymes and OATP1B1 transporter.

Meglitinides such as repaglinide and nateglinide are useful to treat type 2 diabetes patients who follow a flexible lifestyle. They are short-acting insulin secretagogues and are associated with less risk of hypoglycemia, weight gain and chronic hyperinsulinemia compared with sulfonylureas. Meglitinides are the substrates of cytochrome P450 (CYP) enzymes and organic anion transporting polypeptide 1B1 (OATP1B1 transporter) and the coadministration of the drugs affecting them will result in pharmacokinetic drug interactions. This article focuses on the drug interactions of meglitinides involving CYP enzymes and OATP1B1 transporter. To prevent the risk of hypoglycemic episodes, prescribers and pharmacists must be aware of the adverse drug interactions of meglitinides.

Regulation of Organic Anion Transporting Polypeptides (OATP) 1B1- and OATP1B3-Mediated Transport: An Updated Review in the Context of OATP-Mediated Drug-Drug Interactions.

Organic anion transporting polypeptides (OATP) 1B1 and OATP1B3 are important hepatic transporters that mediate the uptake of many clinically important drugs, including statins from the blood into the liver. Reduced transport function of OATP1B1 and OATP1B3 can lead to clinically relevant drug-drug interactions (DDIs). Considering the importance of OATP1B1 and OATP1B3 in hepatic drug disposition, substantial efforts have been given on evaluating OATP1B1/1B3-mediated DDIs in order to avoid unwanted adverse effects of drugs that are OATP substrates due to their altered pharmacokinetics. Growing evidences suggest that the transport function of OATP1B1 and OATP1B3 can be regulated at various levels such as genetic variation, transcriptional and post-translational regulation. The present review summarizes the up to date information on the regulation of OATP1B1 and OATP1B3 transport function at different levels with a focus on potential impact on OATP-mediated DDIs.

The drug interaction potential of daprodustat when coadministered with pioglitazone, rosuvastatin, or trimethoprim in healthy subjects.

This study was conducted to evaluate the likelihood of daprodustat to act as a perpetrator in drug–drug interactions (DDI) with the CYP2C8 enzyme and OATP1B1 transporter using the probe substrates pioglitazone and rosuvastatin as potential victims, respectively. Additionally, this study assessed the effect of a weak CYP2C8 inhibitor, trimethoprim, as a perpetrator of a DDI with daprodustat.This was a two‐part study: Part A assessed the effect of coadministration of daprodustat on the pharmacokinetics of pioglitazone and rosuvastatin in 20 subjects; Part B assessed the coadministration of trimethoprim on the pharmacokinetics of daprodustat in 20 subjects.Coadministration of 100 mg of daprodustat with pioglitazone or rosuvastatin had no effect on the plasma exposures of either probe substrate. When trimethoprim was coadministered with 25‐mg daprodustat plasma daprodustat AUC and C max increased by 48% and 28%, respectively. Additionally, AUC and C max for the metabolite GSK2531401 were decreased by 32% and 40%, respectively. C max for the other metabolites was slightly decreased (~8–15%) but no changes in AUC were observed.As 100‐mg daprodustat exceeds the planned top therapeutic dose, interaction potential of daprodustat as a perpetrator with substrates of the CYP2C8 enzyme and OATP1B1 transporters is very low. Conversely, daprodustat exposure (AUC and C max) is likely to increase moderately with coadministration of weak CYP2C8 inhibitors.

Interaction of deoxyschizandrin and schizandrin B with liver uptake transporters OATP1B1 and OATP1B3

1. Deoxyschizandrin and schizandrin B have diverse pharmacological effects, including hepatoprotective activity. We aim to study their hepatic uptake and their effects on the hepatic uptake of other clinical drugs mediated by OATP1B1 and OATP1B3.2. Deoxyschizandrin exhibited a high affinity for OATP1B1 with Km of 17.61 ± 0.43 μM but a low affinity for OATP1B3. Similarly, schizandrin B also showed a strong affinity for OATP1B1 with Km of 18.45 ± 1.23 μM but a weak affinity for OATP1B3.3. Atorvastatin and rifampicin could inhibit the uptake of deoxyschizandrin and schizandrin B mediated by OATP1B1.4. Intriguingly, both deoxyschizandrin and schizandrin B significantly promoted the uptake of atorvastatin (with EC50 of 50.58 ± 8.08 and 24.70 ± 5.82 µM, respectively) and rosuvastatin (with EC50 of 13.46 ± 2.70 and 8.99 ± 4.73 µM, respectively) mediated by OATP1B1. Deoxyschizandrin could markedly promote the uptake of fluvastatin but inhibit the uptake of sodium taurocholate (TCNa) mediated by OATP1B1.5. The promotion on hepatic uptake of statins mediated by OATP1B1 might lead to enhanced efficacy of cholesterol lowering and reduced risk of myopathy for hyperlipidemia patients when given statins together with deoxyschizandrin or schizandrin B.

Inhibition of Organic Anion Transporting Polypeptide 1B1 and 1B3 by Betulinic Acid: Effects of Preincubation and Albumin in the Media

Betulinic acid (BA), a plant-derived pentacyclic triterpenoid, may interact with the members of the organic anion transporting polypeptide 1B subfamily. Here, we investigated the interactions of BA and its analogs with OATP1B1/3 and rat Oatp1b2 in vitro and in vivo. BA inhibited the activity of OATP1B1/3 and rat Oatp1b2 in vitro. Systemic exposure of atorvastatin was substantially altered with the intravenous co-administration of BA (20 mg/kg). Preincubation (incubation with inhibitors, followed by washout) with BA led to a sustained inhibition of OATP1B3, which recovered rapidly in the media containing 10% fetal bovine serum. The addition of albumin to the media decreased intracellular concentrations of BA and expedited the recovery of OATP1B3 activity following preincubation. For asunaprevir and cyclosporin A (previously known to inhibit OATP1B3 upon preincubation), the addition of albumin to the media shortened recovery time with asunaprevir, but not with cyclosporin A. Overall, our results showed that BA inhibits OATP1B transporters in vitro and may incur hepatic transporter-mediated drug interactions in vivo. Our results identify BA as another OATP1B3 inhibitor with preincubation effect and suggest that the preincubation effect and its duration is impacted by altered equilibrium of inhibitors between intracellular and extracellular space (e.g., albumin in the media).

Evaluating Hepatobiliary Transport with 18F-Labeled Bile Acids: The Effect of Radiolabel Position and Bile Acid Structure on Radiosynthesis and In Vitro and In Vivo Performance.

Introduction An in vivo determination of bile acid hepatobiliary transport efficiency can be of use in liver disease and preclinical drug development. Given the increased interest in bile acid Positron Emission Tomography- (PET-) imaging, a further understanding of the impact of 18-fluorine substitution on bile acid handling in vitro and in vivo can be of significance. Methods A number of bile acid analogues were conceived for nucleophilic substitution with [18F]fluoride: cholic acid analogues of which the 3-, 7-, or 12-OH function is substituted with a fluorine atom (3α-[18F]FCA; 7β-[18F]FCA; 12β-[18F]FCA); a glycocholic and chenodeoxycholic acid analogue, substituted on the 3-position (3β-[18F]FGCA and 3β-[18F]FCDCA, resp.). Uptake by the bile acid transporters NTCP and OATP1B1 was evaluated with competition assays in transfected CHO and HEK cell lines and efflux by BSEP in membrane vesicles. PET-scans with the tracers were performed in wild-type mice (n = 3 per group): hepatobiliary transport was monitored and compared to a reference tracer, namely, 3β-[18F]FCA. Results Compounds 3α-[18F]FCA, 3β-[18F]FGCA, and 3β-[18F]FCDCA were synthesized in moderate radiochemical yields (4–10% n.d.c.) and high radiochemical purity (>99%); 7β-[18F]FCA and 12β-[18F]FCA could not be synthesized and included further in this study. In vitro evaluation showed that 3α-FCA, 3β-FGCA, and 3β-FCDCA all had a low micromolar Ki-value for NTCP, OATP1B1, and BSEP. In vivo, 3α-[18F]FCA, 3β-[18F]FGCA, and 3β-[18F]FCDCA displayed hepatobiliary transport with varying efficiency. A slight yet significant difference in uptake and efflux rate was noticed between the 3α-[18F]FCA and 3β-[18F]FCA epimers. Conjugation of 3β-[18F]FCA with glycine had no significant effect in vivo. Compound 3β-[18F]FCDCA showed a significantly slower hepatic uptake and efflux towards gallbladder and intestines. Conclusion A set of 18F labeled bile acids was synthesized that are substrates of the bile acid transporters in vitro and in vivo and can serve as PET-biomarkers for hepatobiliary transport of bile acids.

Are OATP1B1, OATP2B1, OATP1B3 and NTCP transporters exclusively expressed in the plasma membrane of transporter-expressing cells?

Are OATP1B1, OATP2B1, OATP1B3 and NTCP transporters exclusively expressed in the plasma membrane of transporter-expressing cells?

Physiologically-based pharmacokinetic predictions of intestinal BCRP-mediated drug interactions of rosuvastatin in Koreans

It was recently reported that the Cmax and AUC of rosuvastatin increases when it is coadministered with telmisartan and cyclosporine. Rosuvastatin is known to be a substrate of OATP1B1, OATP1B3, NTCP, and BCRP transporters. The aim of this study was to explore the mechanism of the interactions between rosuvastatin and two perpetrators, telmisartan and cyclosporine. Published (cyclosporine) or newly developed (telmisartan) PBPK models were used to this end. The rosuvastatin model in Simcyp (version 15)'s drug library was modified to reflect racial differences in rosuvastatin exposure. In the telmisartan–rosuvastatin case, simulated rosuvastatin CmaxI/Cmax and AUCI/AUC (with/without telmisartan) ratios were 1.92 and 1.14, respectively, and the Tmax changed from 3.35 h to 1.40 h with coadministration of telmisartan, which were consistent with the aforementioned report (CmaxI/Cmax: 2.01, AUCI/AUC:1.18, Tmax: 5 h → 0.75 h). In the next case of cyclosporine–rosuvastatin, the simulated rosuvastatin CmaxI/Cmax and AUCI/AUC (with/without cyclosporine) ratios were 3.29 and 1.30, respectively. The decrease in the CLint,BCRP,intestine of rosuvastatin by telmisartan and cyclosporine in the PBPK model was pivotal to reproducing this finding in Simcyp. Our PBPK model demonstrated that the major causes of increase in rosuvastatin exposure are mediated by intestinal BCRP (rosuvastatin–telmisartan interaction) or by both of BCRP and OATP1B1/3 (rosuvastatin–cyclosporine interaction).

Influence of OATPs on Hepatic Disposition of Erlotinib Measured With Positron Emission Tomography

To assess the hepatic disposition of erlotinib, we performed positron emission tomography (PET) scans with [11C]erlotinib in healthy volunteers without and with oral pretreatment with a therapeutic erlotinib dose (300 mg). Erlotinib pretreatment significantly decreased the liver exposure to [11C]erlotinib with a concomitant increase in blood exposure, pointing to the involvement of a carrier‐mediated hepatic uptake mechanism. Using cell lines overexpressing human organic anion‐transporting polypeptides (OATPs) 1B1, 1B3, or 2B1, we show that [11C]erlotinib is selectively transported by OATP2B1. Our data suggest that at PET microdoses hepatic uptake of [11C]erlotinib is mediated by OATP2B1, whereas at therapeutic doses OATP2B1 transport is saturated and hepatic uptake occurs mainly by passive diffusion. We propose that [11C]erlotinib may be used as a hepatic OATP2B1 probe substrate and erlotinib as an OATP2B1 inhibitor in clinical drug–drug interaction studies, allowing the contribution of OATP2B1 to the hepatic uptake of drugs to be revealed.

The metabolism and drug–drug interaction potential of the selective prostacyclin receptor agonist selexipag

1. The metabolism of selexipag has been studied in vivo in man and the main excreted metabolites were identified. Also, metabolites circulating in human plasma have been structurally identified and quantified.2. The main metabolic pathway of selexipag in man is the formation of the active metabolite ACT-333679. Other metabolic pathways include oxidation and dealkylation reactions. All primary metabolites undergo subsequent hydrolysis of the sulphonamide moiety to their corresponding acids. ACT-333679 undergoes conjugation with glucuronic acid and aromatic hydroxylation to P10, the main metabolite detected in human faeces.3. The formation of the active metabolite ACT-333679 is catalysed by carboxylesterases, while the oxidation and dealkylation reactions are metabolized by CYP2C8 and CYP3A4. CYP2C8 is the only P450 isoform catalysing the aromatic hydroxylation to P10. CYP2C8 together with CYP3A4 are also involved in the formation of several minor ACT-333679 metabolites. UGT1A3 and UGT2B7 catalyse the glucuronidation of ACT-333679.4. The potential of selexipag to inhibit or induce cytochrome P450 enzymes or drug transport proteins was studied in vitro. Selexipag is an inhibitor of CYP2C8 and CYP2C9 and induces CYP3A4 and CYP2C9 in vitro. Also, selexipag inhibits the transporters OATP1B1, OATP1B3, OAT1, OAT3, and BCRP. However, due to its low dose and relatively low unbound exposure, selexipag has a low potential for causing drug–drug interactions.

Differential Expression of OATP1B3 Mediates Unconjugated Testosterone Influx.

Castration-resistant prostate cancer (CRPC) has greater intratumoral testosterone concentrations than similar tumors from eugonadal men; simple diffusion does not account for this observation. This study was undertaken to ascertain the androgen uptake kinetics, functional, and clinical relevance of de novo expression of the steroid hormone transporter OATP1B3 (SLCO1B3). Experiments testing the cellular uptake of androgens suggest that testosterone is an excellent substrate of OATP1B3 (Km = 23.2 μmol/L; Vmax = 321.6 pmol/mg/minute), and cells expressing a doxycycline-inducible SLCO1B3 construct had greater uptake of a clinically relevant concentration of 3H-testosterone (50 nmol/L; 1.6-fold, P = 0.0027). When compared with Slco1b2 (-/-) mice, Slco1b2 (-/-)/hSLCO1B3 knockins had greater hepatic uptake (15% greater AUC, P = 0.0040) and lower plasma exposure to 3H-testosterone (17% lower AUC, P = 0.0030). Of 82 transporters genes, SLCO1B3 is the second-most differentially expressed transporter in CRPC cell lines (116-fold vs. androgen-sensitive cells), with a differentially spliced cancer-type ct-SLCO1B3 making up the majority of SLCO1B3 expression. Overexpression of SLCO1B3 in androgen-responsive cells results in 1.5- to 2-fold greater testosterone uptake, whereas siRNA knockdown of SLCO1B3 in CRPC cells did not change intracellular testosterone concentration. Primary human prostate tumors express SLCO1B3 to a greater extent than ct-SLCO1B3 (26% of total SLCO1B3 expression vs. 0.08%), suggesting that androgen uptake in these tumor cells also is greater. Non-liver tumors do not differentially express SLCO1B3.Implications: This study suggests that de novo OATP1B3 expression in prostate cancer drives greater androgen uptake and is consistent with previous observations that greater OATP1B3 activity results in the development of androgen deprivation therapy resistance and shorter overall survival. Mol Cancer Res; 15(8); 1096-105. ©2017 AACR.

Continuous Intestinal Absorption Model Based on the Convection-Diffusion Equation.

Prediction of the rate and extent of drug absorption upon oral dosing needs models that capture the complexities of both the drug molecule and intestinal physiology. We report here the development of a continuous intestinal absorption model based on the convection-diffusion equation. The model includes explicit enterocyte apical membrane and intracellular lipid radial compartments along the length of the intestine. Physiologic functions along length x are built into the model and include velocity, diffusion, surface areas, and pH of the intestine. Also included are expression levels of the intestinal active uptake transporter OATP2B1 and efflux transporter P-gp. Oral dosing of solution as well as solid (with a dissolution function) was modeled for several drugs. The fraction absorbed (FA) and concentration-time (C-t) profiles were predicted and compared with clinical data. Overall, FA was well predicted upon oral (n = 21) or colonic dosing (n = 11), with four outliers. The overall accuracy (prediction of the correct bin) was 81% with outliers and 90% without outliers. Of the nine solution dosing data sets, six drugs were very well predicted with an exposure overlap coefficient (EOC) > 0.9 and predicted Cmax and Tmax values similar to those observed. Of the six solid dose formulations evaluated, the EOC values were > 0.9 for all drugs except budesonide. The observed precipitation of nifedipine at high doses was predicted by the model. Most of the poor predictions were for drugs that are known to be transporter substrates. As proof of concept, incorporating OATP2B1 and P-gp markedly improved the EOC and predicted Cmax and Tmax for fexofenadine. Finally, the continuous intestinal model accurately recapitulated the known relationships between drug absorption and permeability, solubility, and particle size. Together, these results indicate that this preliminary intestinal absorption model offers a simple and straightforward framework to build in complexities such as drug permeability, lipid partitioning, solubility, metabolism, and transport for improved prediction of the rate and extent of drug absorption.

Computational Discovery and Experimental Validation of Inhibitors of the Human Intestinal Transporter OATP2B1.

Human organic anion transporters (OATPs) are vital for the uptake and efflux of drugs and endogenous compounds. Current identification of inhibitors of these transporters is based on experimental screening. Virtual screening remains a challenge due to a lack of experimental three-dimensional protein structures. Here, we describe a workflow to identify inhibitors of the OATP2B1 transporter in the DrugBank library of over 5,000 drugs and druglike molecules. OATP member 2B1 transporter is highly expressed in the intestine, where it participates in oral absorption of drugs. Predictions from a Random forest classifier, prioritized by docking against multiple comparative protein structure models of OATP2B1, indicated that 33 of the 5,000 compounds were putative inhibitors of OATP2B1. Ten predicted inhibitors that are prescription drugs were tested experimentally in cells overexpressing the OATP2B1 transporter. Three of these ten were validated as potent inhibitors of estrone-3-sulfate uptake (defined as more than 50% inhibition at 20 μM) and tested in multiple concentrations to determine exact IC50. The IC50 values of bicalutamide, ticagrelor, and meloxicam suggest that they might inhibit intestinal OATP2B1 at clinically relevant concentrations and therefore modulate the absorption of other concomitantly administered drugs.

β2-adrenergic receptor-mediated in vitro regulation of human hepatic drug transporter expression by epinephrine

The catecholamine epinephrine is known to repress expression of hepatic drug metabolizing enzymes such as cytochromes P-450. The present study was designed to determine whether epinephrine may also target expression of main hepatic drug transporters, that play a major role in liver detoxification and are commonly coordinately regulated with drug detoxifying enzymes. Treatment of primary human hepatocytes with 10μM epinephrine for 24h repressed mRNA expression of various transporters, such as the sinusoidal influx transporters NTCP, OATP1B1, OATP2B1, OAT2, OAT7 and OCT1 and the efflux transporters MRP2, MRP3 and BSEP, whereas it induced that of MDR1, but failed to alter that of BCRP. Most of these changes in transporter mRNA levels were also found in epinephrine-exposed human highly-differentiated hepatoma HepaRG cells, which additionally exhibited reduced protein expression of OATP2B1 and MRP3, increased expression of P-glycoprotein and decreased transport activity of NTCP, OATPs and OCT1. Epinephrine effects towards transporter mRNA expression in human hepatocytes were next shown to be correlated to those of the selective β2-adrenoreceptor (ADR) agonist fenoterol, of the adenylate cyclase activator forskolin and of the cAMP analogue 8-bromo-cAMP. In addition, the non-selective β-ADR antagonist carazolol and the selective β2-ADR antagonist ICI-118,551, unlike the α-ADR antagonist phentolamine, suppressed epinephrine-mediated repressions of transporter mRNA expression. Taken together, these data indicate that epinephrine regulates in vitro expression of main hepatic drug transporters in a β2-ADR/adenylate cyclase/cAMP-dependent manner. Hepatic drug transport appears therefore as a target of the β2-adrenergic system, which may have to deserve attention for drugs interacting with β2-ADRs.

Ochratoxin A transport by the human breast cancer resistance protein (BCRP), multidrug resistance protein 2 (MRP2), and organic anion-transporting polypeptides 1A2, 1B1 and 2B1

Ochratoxin A (OTA) is a fungal secondary metabolite that can contaminate various foods. OTA has several toxic effects like nephrotoxicity, hepatotoxicity, and neurotoxicity in different animal species, but its mechanisms of toxicity are still unclear. How OTA accumulates in kidney, liver, and brain is as yet unknown, but transmembrane transport proteins are likely involved. We studied transport of OTA in vitro, using polarized MDCKII cells transduced with cDNAs of the efflux transporters mouse (m)Bcrp, human (h)BCRP, mMrp2, or hMRP2, and HEK293 cells overexpressing cDNAs of the human uptake transporters OATP1A2, OATP1B1, OATP1B3, or OATP2B1 at pH7.4 and 6.4. MDCKII-mBcrp cells were more resistant to OTA toxicity than MDCKII parental and hBCRP-transduced cells. Transepithelial transport experiments showed some apically directed transport by MDCKII-mBcrp cells at pH7.4, whereas both mBcrp and hBCRP clearly transported OTA at pH6.4. There was modest transport of OTA by mMrp2 and hMRP2 only at pH6.4. OATP1A2 and OATP2B1 mediated uptake of OTA both at pH7.4 and 6.4, but OATP1B1 only at pH7.4. There was no detectable transport of OTA by OATP1B3. Our data indicate that human BCRP and MRP2 can mediate elimination of OTA from cells, thus reducing OTA toxicity. On the other hand, human OATP1A2, OATP1B1, and OATP2B1 can mediate cellular uptake of OTA, which could aggravate OTA toxicity.

Characterization of OATP1B3 and OATP2B1 transporter expression in the islet of the adult human pancreas.

Organic anion-transporting polypeptides (OATPs) are membrane proteins that mediate cellular uptake of structurally diverse endogenous and exogenous compounds, including bile salts, thyroid and sex hormones, pharmacological agents, and toxins. Roles of OATPs in human liver are well established. Our recent report suggested the presence of the hepatic transporter OATP1B3 in human β cells. The aim of this study was to better characterize cellular localization and interindividual variation in OATP1B3 expression in human adult islets as a function of age, sex, and pancreatic disease, and to assess the expression of other OATPs. High transcript levels of OATP1B3, OATP2B1, OATP1A2, but not OATP1B1 were observed in isolated human adult islets. While OATP1B3 protein expression was variable, the carrier co-localized more frequently with glucagon-positive α cells than insulin-positive β cells in islets of normal pancreatic tissues from ten subjects using dual immunostaining. Moreover, OATP1B3 co-staining with endocrine cells was two- to three-fold higher in older (≥60years) than younger (<60years) subjects. In comparison, in a subset of three individuals, OATP2B1 was primarily found in β cells, suggesting a distinct expression pattern for OATP1B3 and OATP2B1 in islets. Abundant OATP1B3 staining was also observed in islet as well as ductal cells of diseased tissues of patients with pancreatitis or pancreatic adenocarcinoma. Considering the abundance of key OATP carriers in β and α cells, potential implications of OATP transport in islet cell function may be suggested. Future studies are needed to gain insights into their specific endocrine roles as well as pharmacological relevance.

Drug-drug interaction potential of the HBV and HDV entry inhibitor myrcludex B assessed in vitro.

Myrcludex B is a first-in-class virus entry inhibitor for patients with chronic hepatitis B or B/D infections. In patients it will be coadministered with drugs needed for the disease or comorbidities. We aimed to define the risk of drug-drug interactions by characterizing the influence of myrcludex B on relevant drug transporting and metabolizing enzymes in vitro. Inhibition of P-glycoprotein (P-gp; ABCB1), breast cancer resistance protein (BCRP/ABCG2), and the organic anion transporting polypeptides 1B1 and 1B3 (OATP1B1/SLCO1B1 and OATP1B3/SLCO1B3) was measured in cells over-expressing the respective transporter using fluorogenic substrates. Inhibition of cytochrome P450 enzymes (CYPs) was assessed with commercially available kits. mRNA induction of drug transporting and metabolizing enzymes was measured in LS180 cells after 4 days of treatment by quantitative real-time PCR. Pregnane X receptor (PXR) activation was assessed using a reporter-gene assay. Whereas activities of P-gp and BCRP were not influenced by myrcludex B, OATP1B1 and OATP1B3 were specifically inhibited with a 50% inhibitory concentration (IC50) of 0.5 and 8.7 µM, respectively. Myrcludex B weakly inhibited all CYPs tested at concentrations ≥10 µM except CYP2D6, which was not inhibited at concentrations up to 2 µM. Myrcludex B had no influence on mRNA expression of CYP1A1, CYP3A4, UGT1A3, ABCB1, ABCC2 and ABCG2, and on PXR activity. Our in vitro study suggests that myrcludex B is not at major risk of acting as a perpetrator drug. A potential inhibition of the uptake transporters OATP1B1 and OATP1B3 and a previous clinical finding of potential CYP3A inhibition, requires further evaluation and should be carefully addressed in future trials.