Steroid hormones specifically modify the activity of organic anion transporting polypeptides

Non-targeted metabolomics for the identification of plasma metabolites associated with organic anion transporting polypeptide 1B1 function

Our aim was to evaluate biomarkers for organic anion transporting polypeptide 1B1 (OATP1B1) function using a hypothesis-free metabolomics approach. We analyzed fasting plasma samples from 356 healthy volunteers using non-targeted metabolite profiling by liquid chromatography high-resolution mass spectrometry. Based on SLCO1B1 genotypes, we stratified the volunteers to poor, decreased, normal, increased, and highly increased OATP1B1 function groups. Linear regression analysis, and random forest (RF) and gradient boosted decision tree (GBDT) regressors were used to investigate associations of plasma metabolite features with OATP1B1 function. Of the 9152 molecular features found, 39 associated with OATP1B1 function either in the linear regression analysis (p < 10-5) or the RF or GBDT regressors (Gini impurity decrease > 0.01). Linear regression analysis showed the strongest associations with two features identified as glycodeoxycholate 3-O-glucuronide (GDCA-3G; p = 1.2 × 10-20 for negative and p = 1.7 × 10-19 for positive electrospray ionization) and one identified as glycochenodeoxycholate 3-O-glucuronide (GCDCA-3G; p = 2.7 × 10-16). In both the RF and GBDT models, the GCDCA-3G feature showed the strongest association with OATP1B1 function, with Gini impurity decreases of 0.40 and 0.17. In RF, this was followed by one GDCA-3G feature, an unidentified feature with a molecular weight of 809.3521, and the second GDCA-3G feature. In GBDT, the second and third strongest associations were observed with the GDCA-3G features. Of the other associated features, we identified with confidence two representing lysophosphatidylethanolamine 22:5. In addition, one feature was putatively identified as pregnanolone sulfate and one as pregnenolone sulfate. These results confirm GCDCA-3G and GDCA-3G as robust OATP1B1 biomarkers in human plasma.

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.

A comprehensive update of hormone-related pharmacokinetic variations associated with breast cancer drugs

INTRODUCTION

Drugs available for the treatment of breast cancer are increasing, yielding improved oncological outcomes. The efficacy and safety of anticancer drugs significantly depend on pharmacokinetic profiles, which could be influenced by several factors, such as sex hormones.

AREAS COVERED

This article discusses the potential hormone-related pharmacokinetic influences on novel breast cancer pharmacotherapies.

EXPERT OPINION

Recently approved drugs for the treatment of breast cancer belong to different classes, each with unique pharmacokinetic profile. The impact of hormones, such as estrogen and progesterone, may occur at different steps of drug metabolism. Key effects of sex hormones ha ve been reported on multidrug-resistant transporters and enzymes involved in the liver metabolism of drugs, such as cytochromes. Nevertheless, no data is currently available to establish hormone-related metabolic interactions that may account for variability in drug scheduling and selection. Whereas we recognize influences may occur, we do not assume hormones alone can yield clinically significant metabolic changes. Rather, we believe that hormonal influences should be considered along with other elements that may affect drugs metabolism, such as concomitant medications, age-related pharmacokinetic changes, and genetic polymorphisms, in order to deliver treatment personalization and ensure better tolerability and safety of anticancer treatments.

Role of the Sodium-Dependent Organic Anion Transporter (SOAT/SLC10A6) in Physiology and Pathophysiology

The sodium-dependent organic anion transporter (SOAT, gene symbol SLC10A6) specifically transports 3'- and 17'-monosulfated steroid hormones, such as estrone sulfate and dehydroepiandrosterone sulfate, into specific target cells. These biologically inactive sulfo-conjugated steroids occur in high concentrations in the blood circulation and serve as precursors for the intracrine formation of active estrogens and androgens that contribute to the overall regulation of steroids in many peripheral tissues. Although SOAT expression has been detected in several hormone-responsive peripheral tissues, its quantitative contribution to steroid sulfate uptake in different organs is still not completely clear. Given this fact, the present review provides a comprehensive overview of the current knowledge about the SOAT by summarizing all experimental findings obtained since its first cloning in 2004 and by processing SOAT/SLC10A6-related data from genome-wide protein and mRNA expression databases. In conclusion, despite a significantly increased understanding of the function and physiological significance of the SOAT over the past 20 years, further studies are needed to finally establish it as a potential drug target for endocrine-based therapy of steroid-responsive diseases such as hormone-dependent breast cancer.

Characterization of Bile Acid Sulfate Conjugates as Substrates of Human Organic Anion Transporting Polypeptides

Drug interactions involving the inhibition of hepatic organic anion transporting polypeptides (OATPs) 1B1 and OATP1B3 are considered important. Therefore, we sought to study various sulfated bile acids (BA-S) as potential clinical OATP1B1/3 biomarkers. It was determined that BA-S [e.g., glycochenodeoxycholic acid 3-O-sulfate (GCDCA-S) and glycodeoxycholic acid 3-O-sulfate (GDCA-S)] are substrates of OATP1B1, OATP1B3, and sodium-dependent taurocholic acid cotransporting polypeptide (NTCP) transfected into human embryonic kidney 293 cells, with minimal uptake evident for other solute carriers (SLCs) like OATP2B1, organic anion transporter 2, and organic cation transporter 1. It was also shown that BA-S uptake by plated human hepatocytes (PHH) was inhibited (≥96%) by a pan-SLC inhibitor (rifamycin SV), and there was greater inhibition (≥77% versus ≤12%) with rifampicin (OATP1B1/3-selective inhibitor) than a hepatitis B virus myristoylated-preS1 peptide (NTCP-selective inhibitor). Estrone 3-sulfate was also used as an OATP1B1-selective inhibitor. In this instance, greater inhibition was observed with GDCA-S (76%) than GCDCA-S (52%). The study was expanded to encompass the measurement of GCDCA-S and GDCA-S in plasma of SLCO1B1 genotyped subjects. The geometric mean GDCA-S concentration was 2.6-fold (90% confidence interval 1.6, 4.3; P = 2.1 × 10^-4) and 1.3-fold (1.1, 1.7; P = 0.001) higher in individuals homozygous and heterozygous for the SLCO1B1 c.521T > C loss-of-function allele, respectively. For GCDCA-S, no significant difference was noted [1.2-fold (0.8, 1.7; P = 0.384) and 0.9-fold (0.8, 1.1; P = 0.190), respectively]. This supported the in vitro data indicating that GDCA-S is a more OATP1B1-selective substrate (versus GCDCA-S). It is concluded that GCDCA-S and GDCA-S are viable plasma-based OATP1B1/3 biomarkers, but they are both less OATP1B1-selective when compared to their corresponding 3-O-glucuronides (GCDCA-3G and GDCA-3G). Additional studies are needed to determine their utility versus more established biomarkers, such as coproporphyrin I, for assessing inhibitors with different OATP1B1 (versus OATP1B3) inhibition signatures.

Predicting disruptions to drug pharmacokinetics and the risk of adverse drug reactions in non-alcoholic steatohepatitis patients

The liver plays a central role in the pharmacokinetics of drugs through drug metabolizing enzymes and transporters. Non-alcoholic steatohepatitis (NASH) causes disease-specific alterations to the absorption, distribution, metabolism, and excretion (ADME) processes, including a decrease in protein expression of basolateral uptake transporters, an increase in efflux transporters, and modifications to enzyme activity. This can result in increased drug exposure and adverse drug reactions (ADRs). Our goal was to predict drugs that pose increased risks for ADRs in NASH patients. Bibliographic research identified 71 drugs with reported ADRs in patients with liver disease, mainly non-alcoholic fatty liver disease (NAFLD), 54 of which are known substrates of transporters and/or metabolizing enzymes. Since NASH is the progressive form of NAFLD but is most frequently undiagnosed, we identified other drugs at risk based on NASH-specific alterations to ADME processes. Here, we present another list of 71 drugs at risk of pharmacokinetic disruption in NASH, based on their transport and/or metabolism processes. It encompasses drugs from various pharmacological classes for which ADRs may occur when used in NASH patients, especially when eliminated through multiple pathways altered by the disease. Therefore, these results may inform clinicians regarding the selection of drugs for use in NASH patients.

Functions of dehydroepiandrosterone in relation to breast cancer

Although DHEA sulfate (DS) is the most abundant steroid in the circulation, breast fluid contains an approximately 80-fold greater concentration than serum. Transport of DS into cells requires organic anion transporting polypeptides (OATPs), which are specific for cell type, cell location, and substrate, but may have a broader specificity for housekeeping functions. Specific classes, which may be modified by soluble factors including neutral steroids, have been identified in the breast. After transport, DS may be cleaved to DHEA by ubiquitous sulfatases, which may be modified by the cell milieu, or DHEA may enter by diffusion. Synthesis from cholesterol does not occur because CYP17B12 and cytochrome b5 are lacking in breast tissues. Case-control studies reveal a positive association of serum DS with risk of breast cancer. The association is even greater with DHEA, particularly in postmenopausal women with HR + invasive tumors. Metabolites of DHEA, androstenedione and testosterone, are associated with breast cancer but DHEA is likely to have an independent role as well. Mechanisms by which DHEA may promote breast cancer relate to its effect in increasing circulating IGF-I, by inhibiting the suppressive effect of glucocorticoids, and by promoting retention of pre-adipocytes with aromatase activity. In addition, DHEA may interact with the G-protein coupled receptor GPER for stimulation of miR-21 and subsequent activation of the MAPK pathway. DHEA also has antitumor properties that relate to stimulation of immunity, suppression of inflammation, and elevation of adipose tissue adiponectin synthesis. The net effect may depend on the which factors predominate.

Constituents of Passiflora incarnata, but Not of Valeriana officinalis, Interact with the Organic Anion Transporting Polypeptides (OATP)2B1 and OATP1A2

Herbal medication used in the treatment of sleep disorders and anxiety often contain extracts of Valeriana officinalis or Passiflora incarnata. Valerenic acid in V. officinalis and apigenin, orientin, and vitexin in P. incarnata are thought to contribute to their therapeutic effect. It was the aim of this study to test whether these constituents of herbal extracts are interacting with the uptake of estrone 3-sulfate, pregnenolone sulfate, and dehydroepiandrosterone sulfate mediated by the uptake transporters organic anion transporting polypeptide 2B1 (OATP2B1) or organic anion transporting polypeptide 1A2 (OATP1A2). Madin-Darby canine kidney cells overexpressing OATP2B1 or OATP1A2 were used to determine the influence of the constituents on the cellular accumulation of the sulfated steroids. Subsequently, competitive counterflow experiments were applied to test whether identified inhibitors are also substrates of the transporters. Valerenic acid only interacted with OATP2B1, whereas apigenin, orientin, and vitexin interacted with OATP2B1 and OATP1A2. Competitive counterflow revealed that orientin is a substrate of both transporters, while apigenin was transported by OATP1A2 and vitexin by OATP2B1. In a next step, commercially available P. incarnata preparations were assessed for their influence on the transporters, revealing inhibition of transporter-mediated estrone 3-sulfate uptake. HPLC-UV-MS analysis confirmed the presence of orientin and vitexin in these preparations, thereby suggesting that these constituents are involved in the interaction. Our data indicate that constituents of P. incarnata may alter the function of OATP2B1 and OATP1A2, which could affect the uptake of other compounds relying on uptake mediated by the transporters.

Genome-Wide Meta-analysis Identifies Genetic Variants Associated With Glycemic Response to Sulfonylureas

OBJECTIVE

Sulfonylureas, the first available drugs for the management of type 2 diabetes, remain widely prescribed today. However, there exists significant variability in glycemic response to treatment. We aimed to establish heritability of sulfonylurea response and identify genetic variants and interacting treatments associated with HbA1c reduction.

RESEARCH DESIGN AND METHODS

As an initiative of the Metformin Genetics Plus Consortium (MetGen Plus) and the DIabetes REsearCh on patient straTification (DIRECT) consortium, 5,485 White Europeans with type 2 diabetes treated with sulfonylureas were recruited from six referral centers in Europe and North America. We first estimated heritability using the generalized restricted maximum likelihood approach and then undertook genome-wide association studies of glycemic response to sulfonylureas measured as HbA1c reduction after 12 months of therapy followed by meta-analysis. These results were supported by acute glipizide challenge in humans who were naïve to type 2 diabetes medications, cis expression quantitative trait loci (eQTL), and functional validation in cellular models. Finally, we examined for possible drug-drug-gene interactions.

RESULTS

After establishing that sulfonylurea response is heritable (mean ± SEM 37 ± 11%), we identified two independent loci near the GXYLT1 and SLCO1B1 genes associated with HbA1c reduction at a genome-wide scale (P < 5 × 10-8). The C allele at rs1234032, near GXYLT1, was associated with 0.14% (1.5 mmol/mol), P = 2.39 × 10-8), lower reduction in HbA1c. Similarly, the C allele was associated with higher glucose trough levels (β = 1.61, P = 0.005) in healthy volunteers in the SUGAR-MGH given glipizide (N = 857). In 3,029 human whole blood samples, the C allele is a cis eQTL for increased expression of GXYLT1 (β = 0.21, P = 2.04 × 10-58). The C allele of rs10770791, in an intronic region of SLCO1B1, was associated with 0.11% (1.2 mmol/mol) greater reduction in HbA1c (P = 4.80 × 10-8). In 1,183 human liver samples, the C allele at rs10770791 is a cis eQTL for reduced SLCO1B1 expression (P = 1.61 × 10-7), which, together with functional studies in cells expressing SLCO1B1, supports a key role for hepatic SLCO1B1 (encoding OATP1B1) in regulation of sulfonylurea transport. Further, a significant interaction between statin use and SLCO1B1 genotype was observed (P = 0.001). In statin nonusers, C allele homozygotes at rs10770791 had a large absolute reduction in HbA1c (0.48 ± 0.12% [5.2 ± 1.26 mmol/mol]), equivalent to that associated with initiation of a dipeptidyl peptidase 4 inhibitor.

CONCLUSIONS

We have identified clinically important genetic effects at genome-wide levels of significance, and important drug-drug-gene interactions, which include commonly prescribed statins. With increasing availability of genetic data embedded in clinical records these findings will be important in prescribing glucose-lowering drugs.

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.

Effects of perfluoroalkyl carboxylic acids on the uptake of sulfobromophthalein via organic anion transporting polypeptides in human intestinal Caco-2 cells

We performed a detailed investigation of the uptake of sulfobromophthalein (BSP) from the apical membrane of Caco-2 cells, which is a substrate for organic anion transporting polypeptides (OATPs), and calculated the kinetic parameters of BSP uptake as follows: K_m = 13.9 ± 1.3 μM, V_max = 1.15 ± 0.07 nmol (mg protein)^-1 (5 min)^-1, and k_d = 38.2 ± 0.53 μL (mg protein)^-1 (5 min)^-1. Coincubation with medium-chain (C7-C11) perfluoroalkyl carboxylic acids (PFCAs), such as perfluoroheptanoic acid (PFHpA, C7), perfluorooctanoic acid (PFOA, C8), perfluorononanoic acid (PFNA, C9), perfluorodecanoic acid (PFDA, C10) and perfluoroundecanoic acid (PFUnDA, C11), significantly decreased BSP uptake by 27-55%, while coincubation with short- (C3-C6) and long-chain (C12-C14) PFCAs decreased the uptake only slightly. Dixon plotting suggested that PFOA, PFNA and PFDA competitively inhibited the BSP uptake with inhibition constant (K_i) values of 62.2 ± 1.3 μM, 35.3 ± 0.1 μM and 43.2 ± 0.3 μM, respectively. PFCAs with medium-chains could be substrates for OATPs, probably OATP2B1, which is the most abundantly expressed OATP isoform in Caco-2 cells.

Glibenclamide transfer across the perfused human placenta is determined by albumin binding not transporter activity

The placenta mediates the transfer of maternal nutrients into the fetal circulation while removing fetal waste products, drugs and environmental toxins that may otherwise be detrimental to fetal development. This study investigated the role of drug transporters and protein binding in the transfer of the antidiabetic drug glibenclamide across the human placental syncytiotrophoblast using placental perfusion experiments and computational modeling. In the absence of albumin, placental glibenclamide uptake from the fetal circulation was not affected by competitive inhibition with bromosulphothalein (BSP), indicating that OATP2B1 does not mediate placental glibenclamide uptake from the fetus. In the presence of maternal and fetal albumin, BSP increased placental glibenclamide uptake from the fetal circulation by displacing glibenclamide from BSA, increasing the free fraction of glibenclamide driving diffusive transport. The P-gp and BCRP inhibitor GF120918 did not affect placental glibenclamide uptake from the maternal circulation and as such this study did not find any evidence for the apical efflux transporters in placental glibenclamide transfer. Computational modeling confirmed that albumin binding and not transporter activity, is the dominant factor in the transfer of glibenclamide across the human placenta. The effect of BSP binding to albumin on promoting the diffusive transfer of glibenclamide highlights the importance of drug-protein binding interactions and their interpretation using computational modeling.

Structural dissection of 13-epiestrones based on the interaction with human Organic anion-transporting polypeptide, OATP2B1

Human OATP2B1 encoded by the SLCO2B1 gene is a multispecific transporter mediating the cellular uptake of large, organic molecules, including hormones, prostaglandins and bile acids. OATP2B1 is ubiquitously expressed in the human body, with highest expression levels in pharmacologically relevant barriers, like enterocytes, hepatocytes and endothelial cells of the blood-brain-barrier. In addition to its endogenous substrates, OATP2B1 also recognizes clinically applied drugs, such as statins, antivirals, antihistamines and chemotherapeutic agents and influences their pharmacokinetics. On the other hand, OATP2B1 is also overexpressed in various tumors. Considering that elevated hormone uptake by OATP2B1 results in increased cell proliferation of hormone dependent tumors (e.g. breast or prostate), inhibition of OATP2B1 can be a good strategy to inhibit the growth of these tumors. 13-epiestrones represent a potential novel strategy in the treatment of hormone dependent cancers by the suppression of local estrogen production due to the inhibition of the key enzyme of estrone metabolism, 17ß-hydroxysteroid-dehydrogenase type 1 (HSD17ß1). Recently, we have demonstrated that various phosphonated 13-epiestrones are dual inhibitors also suppressing OATP2B1 function. In order to gain better insights into the molecular determinants of OATP2B1 13-epiestrone interaction we investigated the effect of C-2 and C-4 halogen or phenylalkynyl modified epiestrones on OATP2B1 transport function. Potent inhibitors (with EC₅₀ values in the low micromolar range) as well as non-inhibitors of OATP2B1 function were identified. Based on the structure-activity relationship (SAR) of the various 13-epiestrone derivatives we could define structural elements important for OATP2B1 inhibition. Our results may help to understand the drug/inhibitor interaction profile of OATP2B1, and also may be a useful strategy to block steroid hormone entry into tumors.

Stimulatory effect on the transport mediated by organic anion transporting polypeptide 2B1

Drug-drug interaction (DDI) is one of causes of adverse drug events and can result in life-threatening consequences. Organic anion-transporting polypeptide (OATP) 2B1 is a major uptake transporter in the intestine and contributes to transport various clinically used therapeutic agents. The intestine has a high risk of DDI, because it has a special propensity to be exposed to a high concentration of drugs. Thus, understanding drug interaction mediated by OATP2B1 in the absorption process is important for the prevention of adverse drug events, including decrease in the therapeutic effect of co-administered drugs. Acute drug interaction occurs through the direct inhibitory effect on transporters, including OATP2B1. Moreover, some compounds such as clinically used drugs and food components have an acute stimulatory effect on transport of co-administered drugs by OATP2B1. This review summarizes the acute stimulatory effect on the transport mediated by OATP2B1 and discusses the mechanisms of the acute stimulatory effects of compounds. There are two types of acute stimulatory effects, substrate-independent and -dependent interactions on OATP2B1 function. The facilitating translocation of OATP2B1 to the plasma membrane is one of causes for the substrate-independent acute stimulatory effect. On the contrary, the substrate-dependent effect is based on the direct binding to the substrate-binding site or allosteric progesterone-binding site of OATP2B1.

Neurosteroid Transport in the Brain: Role of ABC and SLC Transporters

Neurosteroids, comprising pregnane, androstane, and sulfated steroids can alter neuronal excitability through interaction with ligand-gated ion channels and other receptors and have therefore a therapeutic potential in several brain disorders. They can be formed in brain cells or are synthesized by an endocrine gland and reach the brain by penetrating the blood–brain barrier (BBB). Especially sulfated steroids such as pregnenolone sulfate (PregS) and dehydroepiandrosterone sulfate (DHEAS) depend on transporter proteins to cross membranes. In this review, we discuss the involvement of ATP-binding cassette (ABC)- and solute carrier (SLC)-type membrane proteins in the transport of these compounds at the BBB and in the choroid plexus (CP), but also in the secretion from neurons and glial cells. Among the ABC transporters, especially BCRP (ABCG2) and several MRP/ABCC subfamily members (MRP1, MRP4, MRP8) are expressed in the brain and known to efflux conjugated steroids. Furthermore, several SLC transporters have been shown to mediate cellular uptake of steroid sulfates. These include members of the OATP/SLCO subfamily, namely OATP1A2 and OATP2B1, as well as OAT3 (SLC22A3), which have been reported to be expressed at the BBB, in the CP and in part in neurons. Furthermore, a role of the organic solute transporter OSTα-OSTβ (SLC51A/B) in brain DHEAS/PregS homeostasis has been proposed. This transporter was reported to be localized especially in steroidogenic cells of the cerebellum and hippocampus. To date, the impact of transporters on neurosteroid homeostasis is still poorly understood. Further insights are desirable also with regard to the therapeutic potential of these compounds.

Interaction of Sulfonylureas with Liver Uptake Transporters OATP1B1 and OATP1B3

Sulfonylureas (SUs) such as glibenclamide, gliclazide, glimepiride, glipizide and gliquidone are one of the first oral medicines available for the treatment of type 2 diabetes and are widely used for the treatment of hyperglycaemia. The hepatic transporters, organic anion transporting polypeptide 1B1 (OATP1B1) and organic anion transporting polypeptide 1B3 (OATP1B3), play an important role in the disposition of a variety of drugs by mediating their uptake from blood into hepatocytes. Drug-drug interactions mediated by OATP1B1/1B3 may result in the hepatic transporting change for drug substrates. The inhibitory effects of glibenclamide and glimepiride on sulfobromophthalein (BSP) uptake have been previously studied, and glibenclamide has been reported as the substrate of OATP1B3, but it remains unclear whether other SUs such as gliclazide, glipizide and gliquidone are substrates of OATP1B1 and OATP1B3. Here, we investigated the relationship between the five most commonly applied SUs (glibenclamide, gliclazide, glimepiride, glipizide, gliquidone) and OATP1B1 and OATP1B3. We performed uptake and inhibition assays in HEK293T cells stably expressing OATP1B1 or OATP1B3, respectively, and established a liquid chromatography-mass spectrometry (LC-MS) method for the simultaneous measurement of five SUs. We demonstrated that gliclazide and glimepiride are substrates of OATP1B1 and glibenclamide and glipizide are substrates of OATP1B3. We also confirmed the interaction between these SUs and rosuvastatin. No transporting was observed for gliquidone, suggesting that it is not a substrate of either transporter.

Renal Drug Transporters and Drug Interactions

Transporters in proximal renal tubules contribute to the disposition of numerous drugs. Furthermore, the molecular mechanisms of tubular secretion have been progressively elucidated during the past decades. Organic anions tend to be secreted by the transport proteins OAT1, OAT3 and OATP4C1 on the basolateral side of tubular cells, and multidrug resistance protein (MRP) 2, MRP4, OATP1A2 and breast cancer resistance protein (BCRP) on the apical side. Organic cations are secreted by organic cation transporter (OCT) 2 on the basolateral side, and multidrug and toxic compound extrusion (MATE) proteins MATE1, MATE2/2-K, P-glycoprotein, organic cation and carnitine transporter (OCTN) 1 and OCTN2 on the apical side. Significant drug-drug interactions (DDIs) may affect any of these transporters, altering the clearance and, consequently, the efficacy and/or toxicity of substrate drugs. Interactions at the level of basolateral transporters typically decrease the clearance of the victim drug, causing higher systemic exposure. Interactions at the apical level can also lower drug clearance, but may be associated with higher renal toxicity, due to intracellular accumulation. Whereas the importance of glomerular filtration in drug disposition is largely appreciated among clinicians, DDIs involving renal transporters are less well recognized. This review summarizes current knowledge on the roles, quantitative importance and clinical relevance of these transporters in drug therapy. It proposes an approach based on substrate-inhibitor associations for predicting potential tubular-based DDIs and preventing their adverse consequences. We provide a comprehensive list of known drug interactions with renally-expressed transporters. While many of these interactions have limited clinical consequences, some involving high-risk drugs (e.g. methotrexate) definitely deserve the attention of prescribers.

Comparative Evaluation of Plasma Bile Acids, Dehydroepiandrosterone Sulfate, Hexadecanedioate, and Tetradecanedioate with Coproporphyrins I and III as Markers of OATP Inhibition in Healthy Subjects

Multiple endogenous compounds have been proposed as candidate biomarkers to monitor organic anion transporting polypeptide (OATP) function in preclinical species or humans. Previously, we demonstrated that coproporphyrins (CPs) I and III are appropriate clinical markers to evaluate OATP inhibition and recapitulate clinical drug-drug interactions (DDIs). In the present study, we investigated bile acids (BAs) dehydroepiandrosterone sulfate (DHEAS), hexadecanedioate (HDA), and tetradecanedioate (TDA) in plasma as endogenous probes for OATP inhibition and compared these candidate probes to CPs. All probes were determined in samples from a single study that examined their behavior and their association with rosuvastatin (RSV) pharmacokinetics after administration of an OATP inhibitor rifampin (RIF) in healthy subjects. Among endogenous probes examined, RIF significantly increased maximum plasma concentration (C_max) and area under the concentration-time curve (AUC)_(0-24h) of fatty acids HDA and TDA by 2.2- to 3.2-fold. For the 13 bile acids in plasma examined, no statistically significant changes were detected between treatments. Changes in plasma DHEAS did not correlate with OATP1B inhibition by RIF. On the basis of the magnitude of effects for the endogenous compounds that demonstrated significant changes from baseline over interindividual variations, the overall rank order for the AUC change was found to be CP I > CP III > HDA ≈ TDA ≈ RSV > > BAs. Collectively, these results reconfirmed that CPs are novel biomarkers suitable for clinical use. In addition, HDA and TDA are useful for OATP functional assessment. Since these endogenous markers can be monitored in conjunction with pharmacokinetics analysis, the CPs and fatty acid dicarboxylates, either alone or in combination, offer promise of earlier diagnosis and risk stratification for OATP-mediated DDIs.

Association of Tissue Abiraterone Levels and SLCO Genotype with Intraprostatic Steroids and Pathologic Response in Men with High-Risk Localized Prostate Cancer

Purpose: Germline variation in solute carrier organic anion (SLCO) genes influences cellular steroid uptake and is associated with prostate cancer outcomes. We hypothesized that, due to its steroidal structure, the CYP17A inhibitor abiraterone may undergo transport by SLCO-encoded transporters and that SLCO gene variation may influence intracellular abiraterone levels and outcomes.Experimental Design: Steroid and abiraterone levels were measured in serum and tissue from 58 men with localized prostate cancer in a clinical trial of LHRH agonist plus abiraterone acetate plus prednisone for 24 weeks prior to prostatectomy. Germline DNA was genotyped for 13 SNPs in six SLCO genes.Results: Abiraterone levels spanned a broad range (serum median 28 ng/mL, 108 nmol/L; tissue median 77 ng/mL, 271 nmol/L) and were correlated (r = 0.355, P = 0.001). Levels correlated positively with steroids upstream of CYP17A (pregnenolone, progesterone), and inversely with steroids downstream of CYP17A (DHEA, AED, testosterone). Serum PSA and tumor volumes were higher in men with undetectable versus detectable tissue abiraterone at prostatectomy (median 0.10 vs. 0.03 ng/dL, P = 0.02; 1.28 vs. 0.44 cc, P = 0.09, respectively). SNPs in SLCO2B1 associated with significant differences in tissue abiraterone (rs1789693, P = 0.0008; rs12422149, P = 0.03) and higher rates of minimal residual disease (tumor volume < 0.5 cc; rs1789693, 67% vs. 27%, P = 0.009; rs1077858, 46% vs. 0%, P = 0.03). LNCaP cells expressing SLCO2B1 showed two- to fourfold higher abiraterone levels compared with vector controls (P < 0.05).Conclusions: Intraprostatic abiraterone levels and genetic variation in SLCO genes are associated with pathologic responses in high-risk localized prostate cancer. Variation in SLCO genes may serve as predictors of response to abiraterone treatment. Clin Cancer Res; 23(16); 4592-601. ©2017 AACR.

Role of OATP transporters in steroid uptake by prostate cancer cells in vivo

BACKGROUND

Epidemiologic and in vitro studies suggest that SLCO-encoded organic anion transporting polypeptide (OATP) transporters influence the response of prostate cancer (PCa) to androgen deprivation by altering intratumor androgens. We have previously shown that castration-resistant metastases express multiple SLCO transporters at significantly higher levels than primary PCa, suggesting that OATP-mediated steroid transport is biologically relevant in advanced disease. However, whether OATP-mediated steroid transport can actually modify prostate tumor androgen levels in vivo has never been demonstrated.

METHODS

We sought to determine whether OATP-mediated steroid transport can measurably alter PCa androgen levels in vivo. We evaluated the uptake of dehydroepiandrosterone (DHEAS), E1S and testosterone in LNCaP cells engineered to express OATP1B1, 1B3, 2B1 or 4A1. We measured the uptake via administration of tritiated steroids to castrate mice bearing vector control or OATP1B1-, 2B1- or 4A1-expressing xenografts. We treated tumor-bearing mice with DHEAS and testosterone at physiologically relevant levels and measured intratumor accumulation of administered steroids by mass spectrometry.

RESULTS

OATP1B1- and 2B-expressing xenografts each showed a threefold increase in tritiated-DHEAS uptake vs vector controls (P=0.002 and P=0.036, respectively). At circulating DHEAS levels similar to those in abiraterone-treated men (~15 μg dl^-1), OATP1B1- and 2B1-expressing xenografts showed a 3.9-fold (P=0.057) and 1.9-fold (P=0.048) increase in tumor accumulation of DHEAS and a 1.6-fold (P=0.057) and 2.7-fold (P=0.095) increase in DHEA, respectively. At the substantial circulating testosterone levels found in eugonadal men, a consistent effect of OATP1B1, 2B1 or 4A1 on testosterone uptake in vivo was not detected.

CONCLUSIONS

OATP transporters measurably alter DHEAS uptake and intratumor androgen levels in prostate tumors in vivo, even at circulating androgen levels achieved in abiraterone-treated patients. These novel data emphasize the continued need to inhibit ligand-mediated androgen receptor signaling in PCa tumors, and support prospective evaluation of studies designed to test inhibition of OATP-mediated DHEAS uptake and utilization.

Drug-drug interactions between immunosuppressants and antidiabetic drugs in the treatment of post-transplant diabetes mellitus

Post-transplant diabetes mellitus is a frequent complication of solid organ transplantation that generally requires treatment with lifestyle interventions and antidiabetic medication. A number of demonstrated and potential pharmacokinetic drug-drug interactions (DDIs) exist between commonly used immunosuppressants and antidiabetic drugs, which are comprehensively summarized in this review. Cyclosporine (CsA) itself inhibits the cytochrome P450 (CYP) 3A4 enzyme and a variety of drug transporters. As a result, it increases exposure to repaglinide and sitagliptin, will likely increase the exposure to nateglinide, glyburide, saxagliptin, vildagliptin and alogliptin, and could theoretically increase the exposure to gliquidone and several sodium-glucose transporter (SGLT)-2 inhibitors. Currently available data, although limited, suggest that these increases are modest and, particularly with regard to gliptins and SGLT-2 inhibitors, unlikely to result in hypoglycemia. The interaction with repaglinide is more pronounced but does not preclude concomitant use if repaglinide dose is gradually titrated. Mycophenolate mofetil and azathioprine do not engage in DDIs with any antidiabetic drug. Although calcineurin inhibitors (CNIs) and mammalian target of rapamycin inhibitors (mTORi) are intrinsically prone to DDIs, their disposition is not influenced by metformin, pioglitazone, sulfonylureas (except possibly glyburide) or insulin. An effect of gliptins on the disposition of CNIs and mTORi is unlikely, but has not been definitively ruled out. Based on their disposition profiles, glyburide and canagliflozin could affect CNI and mTORi disposition although this requires further study. Finally, delayed gastric emptying as a result of glucagon-like peptide-1 agonists seems to have a limited, but not necessarily negligible effect on CNI disposition.

Molecular localization and characterization of multiple binding sites of organic anion transporting polypeptide 2B1 (OATP2B1) as the mechanism for substrate and modulator dependent drug–drug interaction

Schematic model of the relationship and locations of putative binding sites of substrates and modulators in OATP2B1. Drug–drug interaction and drug–food interaction on OATP2B1 can be predicted by clarification of multiple binding sites.

Expression of steroid sulfated transporters and 3β-HSD activity in endometrium of women having polycystic ovary syndrome

Intracrinology mechanism involves the metabolism of steroids in peripheral tissues, such as DHEA, to molecules with estrogenic or androgenic activity. Proliferation rate of endometria from Polycystic Ovary Syndrome women (PCOS) is increased, favoring hyperplasia development. Besides, in endometria from PCOS-women the synthesis of androst-5-ene-3β,17β-diol (androstenediol), an estrogenic molecule, is enhanced concomitantly to increased cellular proliferation. DHEA, the major intracrinological precursor, circulates mainly in its sulfated form and requires transporters for cell intake, that belong to the families of organic anion transporting polypeptides (OATP) and organic anion transporters (OAT). The aim of this study was to determine protein levels and activity of sulfated steroid transporters OATP2B1, OATP3A1, OATP4A1 and OAT4 in endometria from control and PCOS-women and to evaluate the activity of the enzyme 3β-HSD. Levels of transporters were done by RT-PCR (OAT4 only) and Western-blot (WB). Additionally, in primary culture cells stimulated with steroids, protein levels by WB and uptake of tritiated DHEAS, were evaluated; 3β-HSD activity was assessed using radiolabel substrate. PCOS-endometrium had higher levels of OATP2B1 and OATP4A1 than CE (p<0.05); decreased OATP4A1 levels were found in androstenediol or testosterone-stimulated cells. Accordingly, the entry of DHEAS to cells was lower in cells stimulated with testosterone (p<0.05); 3β-HSD-activity was similar in control and PCOS-endometria. Therefore, this study describes that steroids can modulate the expression and activity of transporters of OATPs-family in human endometria and that some transporter levels are increased in PCOS-endometria, suggesting a potential role in the pathogenesis of endometrial hyperplasia of these patients.

The Regulation of Steroid Action by Sulfation and Desulfation

Steroid sulfation and desulfation are fundamental pathways vital for a functional vertebrate endocrine system. After biosynthesis, hydrophobic steroids are sulfated to expedite circulatory transit. Target cells express transmembrane organic anion-transporting polypeptides that facilitate cellular uptake of sulfated steroids. Once intracellular, sulfatases hydrolyze these steroid sulfate esters to their unconjugated, and usually active, forms. Because most steroids can be sulfated, including cholesterol, pregnenolone, dehydroepiandrosterone, and estrone, understanding the function, tissue distribution, and regulation of sulfation and desulfation processes provides significant insights into normal endocrine function. Not surprisingly, dysregulation of these pathways is associated with numerous pathologies, including steroid-dependent cancers, polycystic ovary syndrome, and X-linked ichthyosis. Here we provide a comprehensive examination of our current knowledge of endocrine-related sulfation and desulfation pathways. We describe the interplay between sulfatases and sulfotransferases, showing how their expression and regulation influences steroid action. Furthermore, we address the role that organic anion-transporting polypeptides play in regulating intracellular steroid concentrations and how their expression patterns influence many pathologies, especially cancer. Finally, the recent advances in pharmacologically targeting steroidogenic pathways will be examined.

Paroxetine decreased plasma exposure of glyburide partly via inhibiting intestinal absorption in rats

Accumulating evidences have shown that diabetes is often accompanied with depression, thus it is possible that oral antidiabetic agent glyburide and antidepressive agent paroxetine are co-administered in diabetic patients. The aim of this study was to assess interactions between glyburide and paroxetine in rats. Effect of paroxetine on pharmacokinetics of orally administered glyburide was investigated. Effect of naringin (NAR), an inhibitor of rat intestinal organic anion transporting polypeptides 1a5 (Oatp1a5), on pharmacokinetics of glyburide was also studied. The results showed that co-administration of paroxetine markedly reduced plasma exposure and prolonged Tmax of glyburide, accompanied by significant increase in fecal excretion of glyburide. Co-administration of naringin also significantly decreased plasma exposure of glyburide. Data from intestinal perfusion experiments showed that both paroxetine and naringin significantly inhibited intestinal absorption of glyburide. Caco-2 cells were used to investigate whether paroxetine and naringin affected intestinal transport of glyburide and fexofenadine (a substrate of Oatp1a5). The results showed that both paroxetine and naringin greatly inhibited absorption of glyburide and fexofenadine. All results gave a conclusion that co-administration of paroxetine decreased plasma exposure of glyburide in rats via inhibiting intestinal absorption of glyburide, which may partly be attributed to the inhibition of intestinal Oatp1a5 activity.

Minireview: SLCO and ABC transporters: a role for steroid transport in prostate cancer progression

Androgens play a critical role in the development and progression of prostate cancer (PCa), and androgen deprivation therapy via surgical or medical castration is front-line therapy for patients with advanced PCa. However, intratumoral testosterone levels are elevated in metastases from patients with castration-resistant disease, and residual intratumoral androgens have been implicated in mediating ligand-dependent mechanisms of androgen receptor activation. The source of residual tissue androgens present despite castration has not been fully elucidated, but proposed mechanisms include uptake and conversion of adrenal androgens, such as dehdroepiandrosterone to testosterone and dihydrotestosterone, or de novo androgen synthesis from cholesterol or progesterone precursors. In this minireview, we discuss the emerging evidence that suggests a role for specific transporters in mediating transport of steroids into or out of prostate cells, thereby influencing intratumoral androgen levels and PCa development and progression. We focus on the solute carrier and ATP binding cassette gene families, which have the most published data for a role in PCa-related steroid transport, and review the potential impact of genetic variation on steroid transport activity and PCa outcomes. Continued assessment of transport activity in PCa models and human tumor tissue is needed to better delineate the different roles these transporters play in physiologic and neoplastic settings, and in order to determine whether targeting the uptake of steroid substrates by specific transporters may be a clinically feasible therapeutic strategy.

Specific expression of OATPs in primary small cell lung cancer (SCLC) cells as novel biomarkers for diagnosis and therapy

The expression of organic anion transporting polypeptides (OATPs) was elucidated in cell lines from small cell lung cancer (SCLC) and lung carcinoids and in paraffin-embedded samples from primary and metastatic SCLCs. We found a strong relationship between OATP expression and the origin of the cells, as cells from primary or metastatic SCLC and carcinoid tumors differ with respect to OATP levels. OATP4A1 is most prominent in non-malignant lung tissue and in all SCLC and carcinoid cell lines and tissues, OATP5A1 is most prominent in metastatic cells, and OATP6A1 is most prominent in SCLC cell lines and tumors. Treatment with topotecan, etoposide and cisplatin caused significant changes in the expression patterns of OATP4A1, OATP5A1, OATP6A1, chromogranin and synaptophysin. This effect was also evident in GLC-14 cells from an untreated SCLC patient before chemotherapy compared to GLC-16/-19 chemoresistant tumor cells from this patient after therapy. mRNA expression of OATP4A1, 5A1 and 6A1 correlates with protein expression as confirmed by quantitative microscopic image analysis and Western blots. OATPs might be novel biomarkers for tumor progression and the development of metastasis in SCLC patients.

Mechanism-based pharmacokinetic modeling to evaluate transporter-enzyme interplay in drug interactions and pharmacogenetics of glyburide

The purpose of this study is to characterize the involvement of hepato-biliary transport and cytochrome-P450 (CYP)-mediated metabolism in the disposition of glyburide and predict its pharmacokinetic variability due to drug interactions and genetic variations. Comprehensive in vitro studies suggested that glyburide is a highly permeable drug with substrate affinity to multiple efflux pumps and to organic anion transporting polypeptide (OATP)1B1 and OATP2B1. Active hepatic uptake was found to be significantly higher than the passive uptake clearance (15.8 versus 5.3 μL/min/10(6)-hepatocytes), using the sandwich-cultured hepatocyte model. In vitro, glyburide is metabolized (intrinsic clearance, 52.9 μL/min/mg-microsomal protein) by CYP3A4, CYP2C9, and CYP2C8 with fraction metabolism of 0.53, 0.36, and 0.11, respectively. Using these in vitro data, physiologically based pharmacokinetic models, assuming rapid-equilibrium between blood and liver compartments or permeability-limited hepatic disposition, were built to describe pharmacokinetics and evaluate drug interactions. Permeability-limited model successfully predicted glyburide interactions with rifampicin and other perpetrator drugs. Conversely, model assuming rapid-equilibrium mispredicted glyburide interactions, overall, suggesting hepatic uptake as the primary rate-determining process in the systemic clearance of glyburide. Further modeling and simulations indicated that the impairment of CYP2C9 function has a minimal effect on the systemic exposure, implying discrepancy in the contribution of CYP2C9 to glyburide clearance.

OATP transporter-mediated drug absorption and interaction

Although oral administration of drugs is the most favorable route, the precise mechanism of intestinal epithelial permeation is not well understood. Recently, compelling evidence has emerged to show that absorptive transporters such as OATPs contribute to intestinal drug absorption. Since changes in intestinal transporter activity may alter systemic exposure, a thorough understanding of the overall intestinal absorption mechanism is essential to predict possible toxicity and to achieve optimal therapeutic efficacy. The intestinal lumen is exposed continuously to ingested food and beverages, and interaction of their components with drugs during intestinal permeation might also be significant. OATP2B1 is expressed in human intestine and transports various drugs. In this review, we describe the importance of OATP2B1 in drug absorption and the possible influence beverage components have on OATP2B1 function and expression.

Effects of selected OATP and/or ABC transporter inhibitors on the brain and whole-body distribution of glyburide

Glyburide (glibenclamide, GLB) is a widely prescribed antidiabetic with potential beneficial effects in central nervous system injury and diseases. In vitro studies show that GLB is a substrate of organic anion transporting polypeptide (OATP) and ATP-binding cassette (ABC) transporter families, which may influence GLB distribution and pharmacokinetics in vivo. In the present study, we used [(11)C]GLB positron emission tomography (PET) imaging to non-invasively observe the distribution of GLB at a non-saturating tracer dose in baboons. The role of OATP and P-glycoprotein (P-gp) in [(11)C]GLB whole-body distribution, plasma kinetics, and metabolism was assessed using the OATP inhibitor rifampicin and the dual OATP/P-gp inhibitor cyclosporine. Finally, we used in situ brain perfusion in mice to pinpoint the effect of ABC transporters on GLB transport at the blood-brain barrier (BBB). PET revealed the critical role of OATP on liver [(11)C]GLB uptake and its subsequent impact on [(11)C]GLB metabolism and plasma clearance. OATP-mediated uptake also occurred in the myocardium and kidney parenchyma but not the brain. The inhibition of P-gp in addition to OATP did not further influence [(11)C]GLB tissue and plasma kinetics. At the BBB, the inhibition of both P-gp and breast cancer resistance protein (BCRP) was necessary to demonstrate the role of ABC transporters in limiting GLB brain uptake. This study demonstrates that GLB distribution, metabolism, and elimination are greatly dependent on OATP activity, the first step in GLB hepatic clearance. Conversely, P-gp, BCRP, and probably multidrug resistance protein 4 work in synergy to limit GLB brain uptake.

Interaction of Natural Dietary and Herbal Anionic Compounds and Flavonoids with Human Organic Anion Transporters 1 (SLC22A6), 3 (SLC22A8), and 4 (SLC22A11)

Active components of complementary/alternative medicines and natural supplements are often anionic compounds and flavonoids. As such, organic anion transporters (OATs) may play a key role in their pharmacokinetic and pharmacological profiles, and represent sites for adverse drug-drug interactions. Therefore, we assessed the inhibitory effects of nine natural products, including flavonoids (catechin and epicatechin), chlorogenic acids (1,3- and 1,5-dicaffeoylquinic acid), phenolic acids (ginkgolic acids (13 : 0), (15 : 1), and (17 : 1)), and the organic acids ursolic acid and 18β-glycyrrhetinic acid, on the transport activity of the human OATs, hOAT1 (SLC22A6), hOAT3 (SLC22A8), and hOAT4 (SLC22A11). Four compounds, 1,3- and 1,5-dicaffeoylquinic acid, ginkgolic acid (17 : 1), and 18β-glycyrrhetinic acid, significantly inhibited hOAT1-mediated transport (50 μM inhibitor versus 1 μM substrate). Five compounds, 1,3- and 1,5-dicaffeoylquinic acid, ginkgolic acids (15 : 1) and (17 : 1), and epicatechin, significantly inhibited hOAT3 transport under similar conditions. Only catechin inhibited hOAT4. Dose-dependency studies were conducted for 1,3-dicaffeoylquinic acid and 18β-glycyrrhetinic acid on hOAT1, and IC₅₀ values were estimated as 1.2 ± 0.4 μM and 2.7 ± 0.2 μM, respectively. These data suggest that 1,3-dicaffeoylquinic acid and 18β-glycyrrhetinic acid may cause significant hOAT1-mediated DDIs in vivo; potential should be considered for safety issues during use and in future drug development.

Tumor-specific expression of organic anion-transporting polypeptides: transporters as novel targets for cancer therapy

Members of the organic anion transporter family (OATP) mediate the transmembrane uptake of clinical important drugs and hormones thereby affecting drug disposition and tissue penetration. Particularly OATP subfamily 1 is known to mediate the cellular uptake of anticancer drugs (e.g., methotrexate, derivatives of taxol and camptothecin, flavopiridol, and imatinib). Tissue-specific expression was shown for OATP1B1/OATP1B3 in liver, OATP4C1 in kidney, and OATP6A1 in testis, while other OATPs, for example, OATP4A1, are expressed in multiple cells and organs. Many different tumor entities show an altered expression of OATPs. OATP1B1/OATP1B3 are downregulated in liver tumors, but highly expressed in cancers in the gastrointestinal tract, breast, prostate, and lung. Similarly, testis-specific OATP6A1 is expressed in cancers in the lung, brain, and bladder. Due to their presence in various cancer tissues and their limited expression in normal tissues, OATP1B1, OATP1B3, and OATP6A1 could be a target for tumor immunotherapy. Otherwise, high levels of ubiquitous expressed OATP4A1 are found in colorectal cancers and their metastases. Therefore, this OATP might serve as biomarkers for these tumors. Expression of OATP is regulated by nuclear receptors, inflammatory cytokines, tissue factors, and also posttranslational modifications of the proteins. Through these processes, the distribution of the transporter in the tissue will be altered, and a shift from the plasma membrane to cytoplasmic compartments is possible. It will modify OATP uptake properties and, subsequently, change intracellular concentrations of drugs, hormones, and various other OATP substrates. Therefore, screening tumors for OATP expression before therapy should lead to an OATP-targeted therapy with higher efficacy and decreased side effects.

Cynomolgus monkey as a potential model to assess drug interactions involving hepatic organic anion transporting polypeptides: in vitro, in vivo, and in vitro-to-in vivo extrapolation

Organic anion-transporting polypeptides (OATP) 1B1, 1B3, and 2B1 can serve as the loci of drug-drug interactions (DDIs). In the present work, the cynomolgus monkey was evaluated as a potential model for studying OATP-mediated DDIs. Three cynomolgus monkey OATPs (cOATPs), with a high degree of amino acid sequence identity (91.9, 93.5, and 96.6% for OATP1B1, 1B3, and 2B1, respectively) to their human counterparts, were cloned, expressed, and characterized. The cOATPs were stably transfected in human embryonic kidney cells and were functionally similar to the corresponding human OATPs (hOATPs), as evident from the similar uptake rate of typical substrates (estradiol-17β-d-glucuronide, cholecystokinin octapeptide, and estrone-3-sulfate). Moreover, six known hOATP inhibitors exhibited similar IC(50) values against cOATPs. To further evaluate the appropriateness of the cynomolgus monkey as a model, a known hOATP substrate [rosuvastatin (RSV)]-inhibitor [rifampicin (RIF)] pair was examined in vitro; the monkey-derived parameters (RSV K(m) and RIF IC(50)) were similar (within 3.5-fold) to those obtained with hOATPs and human primary hepatocytes. In vivo, the area under the plasma concentration-time curve of RSV (3 mg/kg, oral) given 1 hour after a single RIF dose (15 mg/kg, oral) was increased 2.9-fold in cynomolgus monkeys, consistent with the value (3.0-fold) reported in humans. A number of in vitro-in vivo extrapolation approaches, considering the fraction of the pathways affected and free versus total inhibitor concentrations, were also explored. It is concluded that the cynomolgus monkey has the potential to serve as a useful model for the assessment of OATP-mediated DDIs in a nonclinical setting.