The inhibition of human multidrug and toxin extrusion 1 is involved in the drug-drug interaction caused by cimetidine

Uptake Transporters at the Blood-Brain Barrier and Their Role in Brain Drug Disposition

Uptake drug transporters play a significant role in the pharmacokinetic of drugs within the brain, facilitating their entry into the central nervous system (CNS). Understanding brain drug disposition is always challenging, especially with respect to preclinical to clinical translation. These transporters are members of the solute carrier (SLC) superfamily, which includes organic anion transporter polypeptides (OATPs), organic anion transporters (OATs), organic cation transporters (OCTs), and amino acid transporters. In this systematic review, we provide an overview of the current knowledge of uptake drug transporters in the brain and their contribution to drug disposition. Here, we also assemble currently available proteomics-based expression levels of uptake transporters in the human brain and their application in translational drug development. Proteomics data suggest that in association with efflux transporters, uptake drug transporters present at the BBB play a significant role in brain drug disposition. It is noteworthy that a significant level of species differences in uptake drug transporters activity exists, and this may contribute toward a disconnect in inter-species scaling. Taken together, uptake drug transporters at the BBB could play a significant role in pharmacokinetics (PK) and pharmacodynamics (PD). Continuous research is crucial for advancing our understanding of active uptake across the BBB.

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.

Auranofin: Past to Present, and repurposing

Auranofin (AF), a gold compound, has been used to treat rheumatoid arthritis (RA) for more than 40 years; however, its mechanism of action remains unknown. We revealed that AF inhibited the induction of proinflammatory proteins and their mRNAs by the inflammatory stimulants, cyclooxygenase-2 and inducible nitric oxide synthase, and their upstream regulator, NF-κB. AF also activated the proteins peroxyredoxin-1, Kelch-like ECH-associated protein 1, and NF-E2-related factor 2, and inhibited thioredoxin reductase, all of which are involved in oxidative or electrophilic stress under physiological conditions. Although the cell membrane was previously considered to be permeable to AF because of its hydrophobicity, the mechanisms responsible for transporting AF into and out of cells as well as its effects on the uptake and excretion of other drugs have not yet been elucidated. Antibodies for cytokines have recently been employed in the treatment of RA, which has had an impact on the use of AF. Trials to repurpose AF as a risk-controlled agent to treat cancers or infectious diseases, including severe acute respiratory syndrome coronavirus 2/coronavirus disease 2019, are ongoing. Novel gold compounds are also under development as anti-cancer and anti-infection agents.

Classification of drugs for evaluating drug interaction in drug development and clinical management

During new drug development, clinical drug interaction studies are carried out in accordance with the mechanism of potential drug interactions evaluated by in vitro studies. The obtained information should be provided efficiently to medical experts through package inserts and various information materials after the drug's launch. A recently updated Japanese guideline presents general procedures that are considered scientifically valid at the present moment. In this review, we aim to highlight the viewpoints of the Japanese guideline and enumerate drugs that were involved or are anticipated to be involved in evident pharmacokinetic drug interactions and classify them by their clearance pathway and potential intensity based on systematic reviews of the literature. The classification would be informative for designing clinical studies during the development stage, and the appropriate management of drug interactions in clinical practice.

Associations between plasma hydroxylated metabolite of itraconazole and serum creatinine in patients with a hematopoietic or immune-related disorder

PURPOSE

Serum markers of renal function have not been characterized in patients treated with itraconazole (ITZ). This study aimed to evaluate the associations between plasma ITZ and its hydroxylated metabolite (OH-ITZ) concentrations and serum markers of renal function in patients with hematopoietic or immune-related disorder.

METHODS

This study enrolled 40 patients with hematopoietic or immune-related disorder who are receiving oral ITZ solution. Plasma concentrations of ITZ and OH-ITZ at 12 h after dosing were determined at steady state. Their relationships with serum levels of creatinine and cystatin C and their estimated glomerular filtration rate (eGFR) were evaluated.

RESULTS

The free plasma concentration of ITZ had no correlation with serum creatinine and serum creatinine-based estimated glomerular filtration rate (eGFR-cre). The free plasma concentration of OH-ITZ was positively and negatively correlated with serum creatinine and eGFR-cre, respectively. The free plasma concentrations of ITZ and OH-ITZ had no association with serum cystatin C and serum cystatin C-based eGFR. Serum creatinine was higher by 16% after than before starting ITZ treatment, while eGFR-cre was lower by 9.3%. The serum creatinine ratio after/before ITZ treatment was positively correlated with the free plasma concentration of OH-ITZ. The patients co-treated with trimethoprim-sulfamethoxazole had higher serum creatinine. Concomitant glucocorticoid administration did not significantly alter serum cystatin C.

CONCLUSIONS

Patients with hematopoietic or immune-related disorder treated with oral ITZ had a higher level of serum creatinine. Although serum creatinine potentially increases in conjunction with the free plasma concentration of OH-ITZ, concomitant ITZ administration has a slight impact on the eGFR-cre level in clinical settings.

Organic Cation Transporters in Health and Disease

The organic cation transporters (OCTs) OCT1, OCT2, OCT3, novel OCT (OCTN)1, OCTN2, multidrug and toxin exclusion (MATE)1, and MATE kidney-specific 2 are polyspecific transporters exhibiting broadly overlapping substrate selectivities. They transport organic cations, zwitterions, and some uncharged compounds and operate as facilitated diffusion systems and/or antiporters. OCTs are critically involved in intestinal absorption, hepatic uptake, and renal excretion of hydrophilic drugs. They modulate the distribution of endogenous compounds such as thiamine, L-carnitine, and neurotransmitters. Sites of expression and functions of OCTs have important impact on energy metabolism, pharmacokinetics, and toxicity of drugs, and on drug-drug interactions. In this work, an overview about the human OCTs is presented. Functional properties of human OCTs, including identified substrates and inhibitors of the individual transporters, are described. Sites of expression are compiled, and data on regulation of OCTs are presented. In addition, genetic variations of OCTs are listed, and data on their impact on transport, drug treatment, and diseases are reported. Moreover, recent data are summarized that indicate complex drug-drug interaction at OCTs, such as allosteric high-affinity inhibition of transport and substrate dependence of inhibitor efficacies. A hypothesis about the molecular mechanism of polyspecific substrate recognition by OCTs is presented that is based on functional studies and mutagenesis experiments in OCT1 and OCT2. This hypothesis provides a framework to imagine how observed complex drug-drug interactions at OCTs arise. Finally, preclinical in vitro tests that are performed by pharmaceutical companies to identify interaction of novel drugs with OCTs are discussed. Optimized experimental procedures are proposed that allow a gapless detection of inhibitory and transported drugs.

Rapid Regulation of Human Multidrug and Extrusion Transporters hMATE1 and hMATE2K

Vectorial transport of organic cations (OCs) in renal proximal tubules is mediated by sequential action of human OC transporter 2 (hOCT2) and human multidrug and toxic extrusion protein 1 and 2K (hMATE1 and hMATE2K), expressed in the basolateral (hOCT2) and luminal (hMATE1 and hMATE2K) plasma membranes, respectively. It is well known that hOCT2 activity is subjected to rapid regulation by several signaling pathways, suggesting that renal OC secretion may be acutely adapted to physiological requirements. Therefore, in this work, the acute regulation of hMATEs stably expressed in human embryonic kidney cells was characterized using the fluorescent substrate 4-(4-(dimethylamino)styryl)-N-methylpyridinium (ASP⁺) as a marker. A specific regulation of ASP⁺ transport by hMATE1 and hMATE2K measured in uptake and efflux configurations was observed. In the example of hMATE1 efflux reduction by inhibition of casein kinase II, it was also shown that this regulation is able to modify transcellular transport of ASP⁺ in Madin–Darby canine kidney II cells expressing hOCT2 and hMATE1 on the basolateral and apical membrane domains, respectively. The activity of hMATEs can be rapidly regulated by some intracellular pathways, which sometimes are common to those found for hOCTs. Interference with these pathways may be important to regulate renal secretion of OCs.

Effect of P-glycoprotein (P-gp) Inducers on Exposure of P-gp Substrates: Review of Clinical Drug-Drug Interaction Studies

Understanding transporter-mediated drug-drug interactions (DDIs) for investigational agents is important during drug development to assess DDI liability, its clinical relevance, and to determine appropriate DDI management strategies. P-glycoprotein (P-gp) is an efflux transporter that influences the pharmacokinetics (PK) of various compounds. Assessing transporter induction in vitro is challenging and is not always predictive of in vivo effects, and hence there is a need to consider clinical DDI studies; however, there is no clear guidance on when clinical evaluation of transporter induction is required. Furthermore, there is no proposed list of index transporter inducers to be used in clinical studies. This review evaluated DDI studies with known P-gp inducers to better understand the mechanism and site of P-gp induction, as well as the magnitude of induction effect on the exposure of P-gp substrates. Our review indicates that P-gp and cytochrome P450 (CYP450) enzymes are co-regulated via the pregnane xenobiotic receptor (PXR) and the constitutive androstane receptor (CAR). The magnitude of the decrease in substrate drug exposure by P-gp induction is generally less than that of CYP3A. Most P-gp inducers reduced total bioavailability with a minor impact on renal clearance, despite known expression of P-gp at the apical membrane of the kidney proximal tubules. Rifampin is the most potent P-gp inducer, resulting in an average reduction in substrate exposure ranging between 20 and 67%. For other inducers, the reduction in P-gp substrate exposure ranged from 12 to 42%. A lower reduction in exposure of the P-gp substrate was observed with a lower dose of the inducer and/or if the administration of the inducer and substrate was simultaneous, i.e. not staggered. These findings suggest that clinical evaluation of the impact of P-gp inducers on the PK of investigational agents that are substrates for P-gp might be warranted only for compounds with a relatively steep exposure-efficacy relationship.

Drug-Drug Interactions of P-gp Substrates Unrelated to CYP Metabolism

BACKGROUND

Recent US Food and Drug Administration (FDA) draft guidance on pharmacokinetic drugdrug interactions (DDIs) has highlighted the clinical importance of ABC transporters B1 or P-glycoprotein (P-gp), hepatic organic anion-transporting polypeptide transporters and breast cancer resistant protein because of their broad substrate specificity and the potential to be involved in DDIs. This guidance has indicated that digoxin, dabigatran etexilate and fexofenadine are P-gp substrate drugs and has defined P-gp inhibitors as those that increase the AUC of digoxin by ≧1.25-fold in clinical DDI studies. However, when substrate drugs of both CYPs and P-gp are involved in DDIs, it remains that the mechanisms of DDIs will be quite ambiguous in assessing how much the CYPs and/or drug transporters partially contribute to DDIs.

OBJECTIVE

Since there are no detailed manuscripts that summarizes P-gp interactions unrelated to CYP metabolism, this article reviews the effects of potent P-gp inhibitors and P-gp inducers on the pharmacokinetics of P-gp substrate drugs, including digoxin, talinolol, dabigatran etexilate, and fexofenadine in human studies. In addition, the present outcome were to determine the PK changes caused by DDIs among P-gp substrate drugs without CYP metabolism in human DDI studies.

CONCLUSION

Our manuscript concludes that the PK changes of the DDIs among P-gp drugs unrelated to CYP metabolism are less likely to be serious, and it appears to be convincing that the absences of clinical effects caused to the PK changes by the P-gp inducers is predominant compared with the excessive effects caused to those by the P-gp inhibitors.

Renal secretion of hydrochlorothiazide involves organic anion transporter 1/3, organic cation transporter 2, and multidrug and toxin extrusion protein 2-K

Hydrochlorothiazide (HCTZ) is the most widely used thiazide diuretic for the treatment of hypertension either alone or in combination with other antihypertensives. HCTZ is mainly cleared by the kidney via tubular secretion, but the underlying molecular mechanisms are unclear. Using cells stably expressing major renal organic anion and cation transporters [human organic anion transporter 1 (hOAT1), human organic anion transporter 3 (hOAT3), human organic cation transporter 2 (hOCT2), human multidrug and toxin extrusion 1 (hMATE1), and human multidrug and toxin extrusion 2-K (hMATE2-K)], we found that HCTZ interacted with both organic cation and anion transporters. Uptake experiments further showed that HCTZ is transported by hOAT1, hOAT3, hOCT2, and hMATE2-K but not by hMATE1. Detailed kinetic analysis coupled with quantification of membrane transporter proteins by targeted proteomics revealed that HCTZ is an excellent substrate for hOAT1 and hOAT3. The apparent affinities (K_m) for hOAT1 and hOAT3 were 112 ± 8 and 134 ± 13 μM, respectively, and the calculated turnover numbers (k_cat) were 2.48 and 0.79 s^-1, respectively. On the other hand, hOCT2 and hMATE2-K showed much lower affinity for HCTZ. The calculated transport efficiency (k_cat/K_m) at the single transporter level followed the rank order of hOAT1> hOAT3 > hOCT2 and hMATE2-K, suggesting a major role of organic anion transporters in tubular secretion of HCTZ. In vitro inhibition experiments further suggested that HCTZ is not a clinically relevant inhibitor for hOAT1 or hOAT3. However, strong in vivo inhibitors of hOAT1/3 may alter renal secretion of HCTZ. Together, our study elucidated the molecular mechanisms underlying renal handling of HCTZ and revealed potential pathways involved in the disposition and drug-drug interactions for this important antihypertensive drug in the kidney.

Investigating Aspects of Renal Physiology and Pharmacology in Organ and Organoid Culture

Some aspects of renal physiology, in particular transport across tubular epithelia, are highly relevant to pharmacokinetics and to drug toxicity. The use of animals to model human renal physiology is limited, but human-derived renal organoids offer an alternative, relevant system in culture. Here, we explain how the activity of specific transport systems can be assessed in renal organoid and organ culture, using a system illustrated mainly for mouse but that can be extended to human organoids.

Enantioselective Drug Recognition by Drug Transporters

Drug transporters mediate the absorption, tissue distribution, and excretion of drugs. The cDNAs of P-glycoprotein, multidrug resistance proteins (MRPs/ABCC), breast cancer resistance protein (BCRP/ABCG2), peptide transporters (PEPTs/SLC15), proton-coupled folate transporters (PCFT/SLC46A1), organic anion transporting polypeptides (OATPs/SLCO), organic anion transporters (OATs/SLC22), organic cation transporters (OCTs/SLC22), and multidrug and toxin extrusions (MATEs/SLC47) have been isolated, and their functions have been elucidated. Enantioselectivity has been demonstrated in the pharmacokinetics and efficacy of drugs, and is important for elucidating the relationship with recognition of drugs by drug transporters from a chiral aspect. Enantioselectivity in the transport of drugs by drug transporters and the inhibitory effects of drugs on drug transporters has been summarized in this review.

Pharmacokinetic Drug-Drug Interaction and Responsible Mechanism between Memantine and Cimetidine

A sensitive and simple chromatography-tandem mass spectrometry (LC-MS/MS) method was developed to evaluate memantine in rat plasma. Memantine and propranolol (internal standard) in rat plasma was extracted using a methanol precipitation method. The standard curve value was 0.2–1000 ng/mL and selectivity, linearity, inter-day and intra-day accuracy and precision were within acceptance criteria. Using this validated method, drug-drug interactions between memantine and cimetidine was measured following co-administration of memantine and cimetidine intravenously and orally. Plasma exposure of memantine was increased by 1.6- and 3.0-fold by co-medication with cimetidine intravenously and orally, respectively. It suggested that the drug interaction occurred during the gut absorption process, which was consistent with the results showing that the intestinal permeability of memantine in the presence of cimetidine was 3.2-fold greater than that of memantine alone. Inhibition of cimetidine on hepatic elimination of memantine rather than renal excretion was also attributed to the drug-drug interaction between memantine and cimetidine, which explained the decreased clearance of memantine by co-medication with cimetidine. In conclusion, the newly developed simple and sensitive LC-MS/MS analytical method was applied to investigate the pharmacokinetic drug-drug interactions of memantine. Plasma exposure of memantine by co-administration with cimetidine was increased because of its enhanced intestinal permeability and the decreased metabolic activity of memantine.

Indinavir Alters the Pharmacokinetics of Lamivudine Partially via Inhibition of Multidrug and Toxin Extrusion Protein 1 (MATE1)

PURPOSE

Lamivudine, a characterized substrate for human multidrug and toxin extrusion protein 1 (hMATE1) in vitro, was commonly used with indinavir as a therapy against human immunodeficiency virus (HIV). We aimed to investigate whether mouse MATE1 is involved in the disposition of lamivudine in vivo, and whether there is any transporter-mediated interaction between indinavir and lamivudine.

METHODS

The role of MATE1 in the disposition of lamivudine was determined using Mate1 wild type (+/+) and knockout (-/-) mice. The inhibitory potencies of indinavir on lamivudine uptake mediated by OCT2 and MATE1 were determined in human embryonic kidney 293 (HEK 293) cells stably expressing these transporters. The role of MATE1 in the interaction between indinavir and lamivudine in vivo was determined using Mate1 (+/+) and Mate1 (-/-) mice.

RESULTS

The plasma concentrations and tissue accumulation of lamivudine were markedly elevated in Mate1 (-/-) mice as compared to those in Mate1 (+/+) mice. Indinavir significantly increased the pharmacokinetic exposure of lamivudine in mice; however, the effect by indinavir was significantly less pronounced in Mate1 (-/-) mice as compared to Mate1(+/+) mice.

CONCLUSION

MATE1 played an important role in lamivudine pharmacokinetics. Indinavir could cause drug-drug interaction with lamivudine in vivo via inhibition of MATE1 and additional mechanism.

Renal Transporter-Mediated Drug-Drug Interactions: Are They Clinically Relevant?

The kidney, through the distinct processes of passive glomerular filtration and active tubular secretion, plays an important role in the elimination of numerous endobiotics (eg, hormones, metabolites), toxins, nutrients, and drugs. Renal transport pathways mediating active tubular secretion and reabsorption in the proximal tubule are complex, involving apical and basolateral transporters acting in concert. Detailed studies of the molecular mechanisms of net active tubular secretion have established the involvement of multiple transporters with overlapping substrate specificity mediating competing secretion and reabsorption pathways. Although drug interactions arising from inhibition of renal transporters are rare relative to other mechanisms, they can involve commonly administered drugs (eg, cimetidine, metformin), may be underappreciated due to muted effects on plasma pharmacokinetics relative to tissue levels, can affect narrow-therapeutic-index medications (eg, antiarrhythmic, oncology medications), and may disproportionately affect sensitive populations where polypharmacy is common (eg, the elderly, diabetics). In particular, there is the potential for larger-magnitude interactions in subjects with reduced glomerular filtration rates due to the increased relative contribution of tubular secretion. The assessment of additional endpoints in drug-drug interaction studies including pharmacodynamics, positron emission tomography imaging, and metabolomics promises to expand our understanding of the clinical relevance of renal drug interactions.

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.

Evaluation of transporters in drug development: Current status and contemporary issues

Transporters govern the access of molecules to cells or their exit from cells, thereby controlling the overall distribution of drugs to their intracellular site of action. Clinically relevant drug-drug interactions mediated by transporters are of increasing interest in drug development. Drug transporters, acting alone or in concert with drug metabolizing enzymes, can play an important role in modulating drug absorption, distribution, metabolism and excretion, thus affecting the pharmacokinetics and/or pharmacodynamics of a drug. The drug interaction guidance documents from regulatory agencies include various decision criteria that may be used to predict the need for in vivo assessment of transporter-mediated drug-drug interactions. Regulatory science research continues to assess the prediction performances of various criteria as well as to examine the strength and limitations of each prediction criterion to foster discussions related to harmonized decision criteria that may be used to facilitate global drug development. This review discusses the role of transporters in drug development with a focus on methodologies in assessing transporter-mediated drug-drug interactions, challenges in both in vitro and in vivo assessments of transporters, and emerging transporter research areas including biomarkers, assessment of tissue concentrations, and effect of diseases on transporters.

Mebendazole, an antiparasitic drug, inhibits drug transporters expression in preclinical model of gastric peritoneal carcinomatosis

The present study aimed to investigate whether MBZ down-regulates drug transporter expression (ABCB1, ABCC1, SLC47A1). mRNA expression level of ABCB1, ABCC1 and SLC47A1 was evaluated by qPCR and protein expression levels MDR-1 was performed by western blotting in malignant ascites cells (AGP-01) treated with MBZ for 24h. The mRNA expression level of ABCB1 and ABCC1 significantly decreased at a 1.0μM of MBZ compared to negative control, while SLC47A1 extremely decreased at all tested concentrations of MBZ. Protein expression levels MDR-1 significantly decreased at a 1.0μM of MBZ compared to negative control. Therefore, our results showed MBZ may play an important role in inhibiting MDR gene expression in malignant ascites cells.

Possible Role of Organic Cation Transporters in the Distribution of [11C]Sulpiride, a Dopamine D2 Receptor Antagonist

We synthesized [¹¹C]sulpiride as a positron emission tomography probe for investigating the drug distribution in the human body. [¹¹C]Sulpiride was injected to healthy male subjects in either tracer dose of [¹¹C]sulpiride (approximately 222 MBq) or with therapeutic dose of sulpiride (500 mg, peroral) 3 h before the injection in a crossover fashion. Whole-body positron emission tomography imaging demonstrated that [¹¹C]sulpiride accumulated exceedingly in the bladder, followed by liver, gall bladder, and kidney, respectively, at 30 min after the injection, whereas scarcely in the brain. Oral dose of sulpiride decreased the hepatic accumulation of the radioactivity by 60%. From in vitro experiments, we found that sulpiride is a substrate of hOCT1 (K_m 2.6 μM), hOCT2 (K_m 68 μM), hMATE1 (K_m 40 μM), and hMATE2-K (K_m 60 μM). Moreover, the uptake of sulpiride by human hepatocytes was diminished by tetraethylammonium, and saturable with K_m of 18 μM. Oct1/2 double knockout mice and wild-type mice received Mate1 inhibitors (pyrimethamine/cimetidine) manifested reduced renal clearance of sulpiride, accompanied with its accumulation in the plasma. In conclusion, we found that sulpiride is a substrate of OCT1, OCT2, MATE1, and MATE2-K, and this suggests that [¹¹C]sulpiride would be a useful radioligand to investigate the organic cation transporters in humans.

Transporters Involved in Metformin Pharmacokinetics and Treatment Response

Metformin, widely used as first-line treatment for type 2 diabetes, exists primarily as a hydrophilic cation at physiological pHs. As such, membrane transporters play a substantial role in its absorption, tissues distribution, and renal elimination. Multiple organic cation transporters are determinants of the pharmacokinetics of metformin, and many of them are important in its pharmacological action, as mediators of metformin entry into target tissues. Furthermore, a recent genome-wide association study in a large multi-ethnic population implicated polymorphisms in SLC2A2, encoding the glucose transporter, GLUT2, as important determinants of response to metformin. Here, we describe the key transporters associated with metformin pharmacokinetics and response.

Involvement of Organic Cation Transporters in the Kinetics of Trimethylamine N-oxide

Recent studies suggest that trimethylamine N-oxide (TMAO) is associated with the development of chronic kidney disease and heart failure. In this study, we investigated the importance of organic cation transporters (OCTs) in the clearance and tissue distribution of TMAO. The low-affinity and high-capacity transport of TMAO by mouse and human OCT1 and OCT2 was observed. Uptake and efflux of TMAO by the mouse hepatocytes as well as TMAO uptake into mouse kidney slices were significantly decreased by the addition of tetraethylammonium or Oct1/2 double knockout (dKO). Plasma concentrations of endogenous TMAO and TMAO-d9 given by intravenous infusion was 2-fold higher in Oct1/2 dKO than in wild-type mice due to significant decrease in its renal clearance. These results indicate that OCTs have a crucial role in the kinetics of TMAO in mice. In human, however, the OCT2-mediated tubular secretion in the urinary excretion of TMAO was insignificant because the renal clearance of TMAO was similar to that of creatinine in both young and elderly subjects, suggesting the species difference in the urinary excretion mechanisms of TMAO between mouse and human.

Metabolomic and Genome-wide Association Studies Reveal Potential Endogenous Biomarkers for OATP1B1

Transporter-mediated drug-drug interactions (DDIs) are a major cause of drug toxicities. Using published genome-wide association studies (GWAS) of the human metabolome, we identified 20 metabolites associated with genetic variants in organic anion transporter, OATP1B1 (P < 5 × 10-8 ). Of these, 12 metabolites were significantly higher in plasma samples from volunteers dosed with the OATP1B1 inhibitor, cyclosporine (CSA) vs. placebo (q-value < 0.2). Conjugated bile acids and fatty acid dicarboxylates were among the metabolites discovered using both GWAS and CSA administration. In vitro studies confirmed tetradecanedioate (TDA) and hexadecanedioate (HDA) were novel substrates of OATP1B1 as well as OAT1 and OAT3. This study highlights the use of multiple datasets for the discovery of endogenous metabolites that represent potential in vivo biomarkers for transporter-mediated DDIs. Future studies are needed to determine whether these metabolites can serve as qualified biomarkers for organic anion transporters. Quantitative relationships between metabolite levels and modulation of transporters should be established.

Structure and function of multidrug and toxin extrusion proteins (MATEs) and their relevance to drug therapy and personalized medicine

Multidrug and toxin extrusion (MATE; SLC47A) proteins are membrane transporters mediating the excretion of organic cations and zwitterions into bile and urine and thereby contributing to the hepatic and renal elimination of many xenobiotics. Transported substrates include creatinine as endogenous substrate, the vitamin thiamine and a number of drug agents with in part chemically different structures such as the antidiabetic metformin, the antiviral agents acyclovir and ganciclovir as well as the antibiotics cephalexin and cephradine. This review summarizes current knowledge on the structural and molecular features of human MATE transporters including data on expression and localization in different tissues, important aspects on regulation and their functional role in drug transport. The role of genetic variation of MATE proteins for drug pharmacokinetics and drug response will be discussed with consequences for personalized medicine.

Effect of Ondansetron on Metformin Pharmacokinetics and Response in Healthy Subjects

The 5-hydroxytryptamine-3 (5-HT3) receptor antagonists such as ondansetron have been used to prevent and treat nausea and vomiting for over 2 decades. This study was to determine whether ondansetron could serve as a perpetrator drug causing transporter-mediated drug-drug interactions in humans. Twelve unrelated male healthy Chinese volunteers were enrolled into a prospective, randomized, double-blind, crossover study to investigate the effects of ondansetron or placebo on the pharmacokinetics of and the response to metformin, a well-characterized substrate of organic cation transporters and multidrug and toxin extrusions (MATEs). Ondansetron treatment caused a statistically significantly higher Cmax of metformin compared with placebo (18.3 ± 5.05 versus 15.2 ± 3.23; P = 0.006) and apparently decreased the renal clearance of metformin by 37% as compared with placebo (P = 0.001). Interestingly, ondansetron treatment also statistically significantly improved glucose tolerance in subjects, as indicated by the smaller glucose area under the curve in the oral glucose tolerance test (10.4 ± 1.43) as compared with placebo (11.5 ± 2.29 mmol∙mg/l) (P = 0.020). It remains possible that ondansetron itself may affect glucose homeostasis in human subjects, but our clinical study, coupled with our previous findings in cells and in animal models, indicates that ondansetron can cause a drug-drug interaction via its potent inhibition of MATE transporters in humans.

Quantitative Targeted Absolute Proteomics for 28 Transporters in Brush-Border and Basolateral Membrane Fractions of Rat Kidney

The purpose of the present study was to determine the absolute protein expression levels of various transporters in renal brush-border membrane (BBM) and basolateral membrane (BLM) fractions, in order to understand the quantitative differences in average transport activities among different transporters at each cellular membrane. BBM and BLM fractions of rat kidney were prepared and digested with trypsin, and simultaneous absolute quantification of 28 transporters and a BLM marker, Na(+)/K(+)-ATPase, was performed using our established quantitative-targeted absolute proteomics (QTAP) technique. In BBM fraction, the protein expression levels of bcrp, urat1, mate1, octl1, mrp4, mdr1a, and abca3 were 40.3, 22.2, 8.90, 4.85, 4.69, 3.22, and 0.976 fmol/μg protein, respectively. In BLM fraction, the protein expression levels of oat1, oat3, oct1, mrp6, and mrp1 were 10.6, 10.2, 4.59, 0.724, and 0.271 fmol/μg protein, respectively. The expression levels of abca2, abca4, abca5, abca12, abcb4, mrp5, abcc9, abcg1, abcg5, lat1, ntcp, pgt, oatp2b1, oatp1b2, oatp3a1, and oct3 were under the limit of quantification in both fractions. The quantitative transporter protein expression profiles at these membranes, as determined by QTAP analysis, should be helpful to understand the contributions of individual transporters to renal excretion of xenobiotics and endogenous compounds.

Role of transporters in the distribution of platinum-based drugs

Platinum derivatives used as chemotherapeutic drugs such as cisplatin and oxaliplatin have a potent antitumor activity. However, severe side effects such as nephro-, oto-, and neurotoxicity are associated with their use. Effects and side effects of platinum-based drugs are in part caused by their transporter-mediated uptake in target and non target cells. In this mini review, the transport systems involved in cellular handling of platinum derivatives are illustrated, focusing on transporters for cisplatin. The copper transporter 1 seems to be of particular importance for cisplatin uptake in tumor cells, while the organic cation transporter (OCT) 2, due to its specific organ distribution, may play a major role in the development of undesired cisplatin side effects. In polarized cells, e.g., in renal proximal tubule cells, apically expressed transporters, such as multidrug and toxin extrusion protein 1, mediate secretion of cisplatin and in this way contribute to the control of its toxic effects. Specific inhibition of cisplatin uptake transporters such as the OCTs may be an attractive therapeutic option to reduce its toxicity, without impairing its antitumor efficacy.

How drugs get into cells: tested and testable predictions to help discriminate between transporter-mediated uptake and lipoidal bilayer diffusion

One approach to experimental science involves creating hypotheses, then testing them by varying one or more independent variables, and assessing the effects of this variation on the processes of interest. We use this strategy to compare the intellectual status and available evidence for two models or views of mechanisms of transmembrane drug transport into intact biological cells. One (BDII) asserts that lipoidal phospholipid Bilayer Diffusion Is Important, while a second (PBIN) proposes that in normal intact cells Phospholipid Bilayer diffusion Is Negligible (i.e., may be neglected quantitatively), because evolution selected against it, and with transmembrane drug transport being effected by genetically encoded proteinaceous carriers or pores, whose “natural” biological roles, and substrates are based in intermediary metabolism. Despite a recent review elsewhere, we can find no evidence able to support BDII as we can find no experiments in intact cells in which phospholipid bilayer diffusion was either varied independently or measured directly (although there are many papers where it was inferred by seeing a covariation of other dependent variables). By contrast, we find an abundance of evidence showing cases in which changes in the activities of named and genetically identified transporters led to measurable changes in the rate or extent of drug uptake. PBIN also has considerable predictive power, and accounts readily for the large differences in drug uptake between tissues, cells and species, in accounting for the metabolite-likeness of marketed drugs, in pharmacogenomics, and in providing a straightforward explanation for the late-stage appearance of toxicity and of lack of efficacy during drug discovery programmes despite macroscopically adequate pharmacokinetics. Consequently, the view that Phospholipid Bilayer diffusion Is Negligible (PBIN) provides a starting hypothesis for assessing cellular drug uptake that is much better supported by the available evidence, and is both more productive and more predictive.

Effects of one-time apple juice ingestion on the pharmacokinetics of fexofenadine enantiomers

PURPOSE

We examined the effect of a single apple juice intake on the pharmacokinetics of fexofenadine enantiomers in healthy Japanese subjects.

METHODS

In a randomized two phase, open-label crossover study, 14 subjects received 60 mg of racemic fexofenadine simultaneously with water or apple juice. For the uptake studies, oocytes expressing organic anion-transporting polypeptide 2B1 (OATP2B1) were incubated with 100 μM (R)- and (S)-fexofenadine in the presence or absence of 10 % apple juice.

RESULTS

One-time ingestion of apple juice significantly decreased the area under the plasma concentration-time curve (AUC0-24) for (R)- and (S)-fexofenadine by 49 and 59 %, respectively, and prolonged the time to reach the maximum plasma concentration (t max) of both enantiomers (P < 0.001). Although apple juice greatly reduced the amount of (R)- and (S)-fexofenadine excretion into urine (Ae0-24) by 54 and 58 %, respectively, the renal clearances of both enantiomers were unchanged between the control and apple juice phases. For in vitro uptake studies, the uptake of both fexofenadine enantiomers into OATP2B1 complementary RNA (cRNA)-injected oocytes was significantly higher than that into water-injected oocytes, and this effect was greater for (R)-fexofenadine. In addition, apple juice significantly decreased the uptake of both enantiomers into OATP2B1 cRNA-injected oocytes.

CONCLUSIONS

These results suggest that OATP2B1 plays an important role in the stereoselective pharmacokinetics of fexofenadine and that one-time apple juice ingestion probably inhibits intestinal OATP2B1-mediated transport of both enantiomers. In addition, this study demonstrates that the OATP2B1 inhibition effect does not require repeated ingestion or a large volume of apple juice.

Organic and inorganic transporters of the testis: A review

Transporters have a huge impact on the toxicology and pharmacological effects of xenobiotics in addition to being implicated in several diseases. While these important proteins have been well studied in organs such as the kidney or liver, characterization of transporters in the testis is still in the early stages. Knowledge of transporter function may greatly advance the field's understanding of the physiological and toxicological processes that occur in the testis. Several foundational studies involving both organic and inorganic transporters have been critical in furthering our understanding of how the testis interacts with endogenous and xenobiotic compounds. This review provides an overview of how transporters function, their clinical significance, and highlights what is known for many of the important transporters in the testis.

Multidrug transport protein norM from vibrio cholerae simultaneously couples to sodium- and proton-motive force

Membrane transporters belonging to the multidrug and toxic compound extrusion family mediate the efflux of unrelated pharmaceuticals from the interior of the cell in organisms ranging from bacteria to human. These proteins are thought to fall into two classes that couple substrate efflux to the influx of either Na(+) or H(+). We studied the energetics of drug extrusion by NorM from Vibrio cholerae in proteoliposomes in which purified NorM protein was functionally reconstituted in an inside-out orientation. We establish that NorM simultaneously couples to the sodium-motive force and proton-motive force, and biochemically identify protein regions and residues that play important roles in Na(+) or H(+) binding. As the positions of protons are not available in current medium and high-resolution crystal structures of multidrug and toxic compound extrusion transporters, our findings add a previously unrecognized parameter to mechanistic models based of these structures.

Phase 0 and phase III transport in various organs: combined concept of phases in xenobiotic transport and metabolism

The historical phasing concept of drug metabolism and elimination was introduced to comprise the two phases of metabolism: phase I metabolism for oxidations, reductions and hydrolyses, and phase II metabolism for synthesis. With this concept, biological membrane barriers obstructing the accessibility of metabolism sites in the cells for drugs were not considered. The concept of two phases was extended to a concept of four phases when drug transporters were detected that guided drugs and drug metabolites in and out of the cells. In particular, water soluble or charged drugs are virtually not able to overcome the phospholipid membrane barrier. Drug transporters belong to two main clusters of transporter families: the solute carrier (SLC) families and the ATP binding cassette (ABC) carriers. The ABC transporters comprise seven families with about 20 carriers involved in drug transport. All of them operate as pumps at the expense of ATP splitting. Embedded in the former phase concept, the term "phase III" was introduced by Ishikawa in 1992 for drug export by ABC efflux pumps. SLC comprise 52 families, from which many carriers are drug uptake transporters. Later on, this uptake process was referred to as the "phase 0 transport" of drugs. Transporters for xenobiotics in man and animal are most expressed in liver, but they are also present in extra-hepatic tissues such as in the kidney, the adrenal gland and lung. This review deals with the function of drug carriers in various organs and their impact on drug metabolism and elimination.

Renal transport of organic anions and cations

Organic anions and cations (OAs and OCs, respectively) comprise an extraordinarily diverse array of compounds of physiological, pharmacological, and toxicological importance. The kidney, primarily the renal proximal tubule, plays a critical role in regulating the plasma concentrations of these organic electrolytes and in clearing the body of potentially toxic xenobiotics agents, a process that involves active, transepithelial secretion. This transepithelial transport involves separate entry and exit steps at the basolateral and luminal aspects of renal tubular cells. Basolateral and luminal OA and OC transport reflects the concerted activity of a suite of separate proteins arranged in parallel in each pole of proximal tubule cells. The cloning of multiple members of several distinct transport families, the subsequent characterization of their activity, and their subcellular localization within distinct regions of the kidney, now allows the development of models describing the molecular basis of the renal secretion of OAs and OCs. New information on naturally occurring genetic variation of many of these processes provides insight into the basis of observed variability of drug efficacy and unwanted drug-drug interactions in human populations. The present review examines recent work on these issues.

Uptake carriers and oncology drug safety

Members of the solute carrier (SLC) family of transporters are responsible for the cellular influx of a broad range of endogenous compounds and xenobiotics in multiple tissues. Many of these transporters are highly expressed in the gastrointestinal tract, liver, and kidney and are considered to be of particular importance in governing drug absorption, elimination, and cellular sensitivity of specific organs to a wide variety of oncology drugs. Although the majority of studies on the interaction of oncology drugs with SLC have been restricted to the use of exploratory in vitro model systems, emerging evidence suggests that several SLCs, including OCT2 and OATP1B1, contribute to clinically important phenotypes associated with those agents. Recent literature has indicated that modulation of SLC activity may result in drug-drug interactions, and genetic polymorphisms in SLC genes have been described that can affect the handling of substrates. Alteration of SLC function by either of these mechanisms has been demonstrated to contribute to interindividual variability in the pharmacokinetics and toxicity associated with several oncology drugs. In this report, we provide an update on this rapidly emerging field.

Genomic and expression analysis of a solute carrier protein (CcSLC25a5) gene from Cyprinus carpio Linnaeus

Using the Genefishing method, we identified seven potential regulatory genes involved in the process of scale morphogenesis in fishes. We further characterized a novel solute carrier protein gene (CcSLC), from the common carp which is differentially expressed in mirror carp and Jianli. The ORF encodes a peptide of 298 amino acids with a molecular mass of 31.5 kDa and a theoretical isoelectric point of 7.49. ScanProsite analysis indicated that it is a putative solute carrier protein that contains a substrate binding site. CcSLC was detected in carp embryos by in situ hybridization in the 70%-epiboly, 6-somite, and 14-somite embryonic stages. Gene expression stopped at the long pec stage. However, CcSLC25a5 was re-expressed during the initiation of scale formation in the regions that were scale covered. These findings provide novel insights into the features of early carp embryo and scale development.

Multidrug and toxin extrusion family SLC47: physiological, pharmacokinetic and toxicokinetic importance of MATE1 and MATE2-K

The kidney plays an important role in the secretion of organic compounds including drugs, toxins and endogeneous metabolites. The renal elimination process of organic cations is mediated by two distinct transport systems expressed on the apical and basolateral membrane of proximal epithelial cells. In 2005, mammalian multidrug and toxin extrusion 1 (MATE1)/SLC47A1 was identified as an orthologue of bacterial NorM. MATE1 is the H(+)/organic cation antiporter at the apical membrane, which mediates the secretion of organic cations. Kidney-specific MATE2-K was isolated from human kidney and localized at the brush-border membrane of proximal tubules. Like MATE1, MATE2-K mediates the secretion of organic cations into urine. MATE1 and MATE2-K are involved in the excretion of important medications and the disruption of these transporters can cause severe pharmacological problems. Recent findings regarding the MATE/SLC47 family are summarized in this review.

Ondansetron can enhance cisplatin-induced nephrotoxicity via inhibition of multiple toxin and extrusion proteins (MATEs)

The nephrotoxicity limits the clinical application of cisplatin. Human organic cation transporter 2 (OCT2) and multidrug and toxin extrusion proteins (MATEs) work in concert in the elimination of cationic drugs such as cisplatin from the kidney. We hypothesized that co-administration of ondansetron would have an effect on cisplatin nephrotoxicity by altering the function of cisplatin transporters. The inhibitory potencies of ondansetron on metformin accumulation mediated by OCT2 and MATEs were determined in the stable HEK-293 cells expressing these transporters. The effects of ondansetron on drug disposition in vivo were examined by conducting the pharmacokinetics of metformin, a classical substrate for OCTs and MATEs, in wild-type and Mate1-/- mice. The nephrotoxicity was assessed in the wild-type and Mate1-/- mice received cisplatin with and without ondansetron. Both MATEs, including human MATE1, human MATE2-K, and mouse Mate1, and OCT2 (human and mouse) were subject to ondansetron inhibition, with much greater potencies by ondansetron on MATEs. Ondansetron significantly increased tissue accumulation and pharmacokinetic exposure of metformin in wild-type but not in Mate1-/- mice. Moreover, ondansetron treatment significantly enhanced renal accumulation of cisplatin and cisplatin-induced nephrotoxicity which were indicated by increased levels of biochemical and molecular biomarkers and more severe pathohistological changes in mice. Similar increases in nephrotoxicity were caused by genetic deficiency of MATE function in mice. Therefore, the potent inhibition of MATEs by ondansetron enhances the nephrotoxicity associated with cisplatin treatment in mice. Potential nephrotoxic effects of combining the chemotherapeutic cisplatin and the antiemetic 5-hydroxytryptamine-3 (5-HT3) receptor antagonists, such as ondansetron, should be investigated in patients.

Conjunctive therapy of cisplatin with the OCT2 inhibitor cimetidine: influence on antitumor efficacy and systemic clearance

The organic cation transporter 2 (OCT2) regulates uptake of cisplatin in proximal tubules, and inhibition of OCT2 protects against severe cisplatin-induced nephrotoxicity. However, it remains uncertain whether potent OCT2 inhibitors, such as cimetidine, can influence the antitumor properties and/or disposition of cisplatin. Using an array of preclinical assays, we found that cimetidine had no effect on the uptake and cytotoxicity of cisplatin in ovarian cancer cells with high OCT2 mRNA levels (IGROV-1 cells). Moreover, the antitumor efficacy of cisplatin in mice bearing luciferase-tagged IGROV-1 xenografts was unaffected by cimetidine (P = 0.39). Data obtained in 18 patients receiving cisplatin (100 mg/m(2)) in a randomized crossover fashion with or without cimetidine (800 mg × 2) revealed that cimetidine did not alter exposure to unbound cisplatin, a marker of antitumor efficacy (4.37 vs. 4.38 µg·h/ml; P = 0.86). These results support the future clinical exploration of OCT2 inhibitors as specific modifiers of cisplatin-induced nephrotoxicity.

Discovery of potent, selective multidrug and toxin extrusion transporter 1 (MATE1, SLC47A1) inhibitors through prescription drug profiling and computational modeling

The human multidrug and toxin extrusion (MATE) transporter 1 contributes to the tissue distribution and excretion of many drugs. Inhibition of MATE1 may result in potential drug-drug interactions (DDIs) and alterations in drug exposure and accumulation in various tissues. The primary goals of this project were to identify MATE1 inhibitors with clinical importance or in vitro utility and to elucidate the physicochemical properties that differ between MATE1 and OCT2 inhibitors. Using a fluorescence assay of ASP(+) uptake in cells stably expressing MATE1, over 900 prescription drugs were screened and 84 potential MATE1 inhibitors were found. We identified several MATE1 selective inhibitors including four FDA-approved medications that may be clinically relevant MATE1 inhibitors and could cause a clinical DDI. In parallel, a QSAR model identified distinct molecular properties of MATE1 versus OCT2 inhibitors and was used to screen the DrugBank in silico library for new hits in a larger chemical space.