Impaired clearance of methotrexate in organic anion transporter 3 (Slc22a8) knockout mice: a gender specific impact of reduced folates

Molecular mechanisms underlying methotrexate-induced intestinal injury and protective strategies

Methotrexate (MTX) is a folic acid reductase inhibitor that manages various malignancies as well as immune-mediated inflammatory chronic diseases. Despite being frequently prescribed, MTX's severe multiple toxicities can occasionally limit its therapeutic potential. Intestinal toxicity is a severe adverse effect associated with the administration of MTX, and patients are significantly burdened by MTX-provoked intestinal mucositis. However, the mechanism of such intestinal toxicity is not entirely understood, mechanistic studies demonstrated oxidative stress and inflammatory reactions as key factors that lead to the development of MTX-induced intestinal injury. Besides, MTX causes intestinal cells to express pro-inflammatory cytokines like interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α), which activate nuclear factor-kappa B (NF-κB). This is followed by the activation of the Janus kinase/signal transducer and activator of the transcription3 (JAK/STAT3) signaling pathway. Moreover, because of its dual anti-inflammatory and antioxidative properties, nuclear factor erythroid-2-related factor 2/heme oxygenase-1 (Nrf2/HO-1) has been considered a critical signaling pathway that counteracts oxidative stress in MTX-induced intestinal injury. Several agents have potential protective effects in counteracting MTX-provoked intestinal injury such as omega-3 polyunsaturated fatty acids, taurine, umbelliferone, vinpocetine, perindopril, rutin, hesperidin, lycopene, quercetin, apocynin, lactobacillus, berberine, zinc, and nifuroxazide. This review aims to summarize the potential redox molecular mechanisms of MTX-induced intestinal injury and how they can be alleviated. In conclusion, studying these molecular pathways might open the way for early alleviation of the intestinal damage and the development of various agent plans to attenuate MTX-mediated intestinal injury.

The Extension of the LeiCNS-PK3.0 Model in Combination with the "Handshake" Approach to Understand Brain Tumor Pathophysiology

Micrometastatic brain tumor cells, which cause recurrence of malignant brain tumors, are often protected by the intact blood–brain barrier (BBB). Therefore, it is essential to deliver effective drugs across not only the disrupted blood-tumor barrier (BTB) but also the intact BBB to effectively treat malignant brain tumors. Our aim is to predict pharmacokinetic (PK) profiles in brain tumor regions with the disrupted BTB and the intact BBB to support the successful drug development for malignant brain tumors. LeiCNS-PK3.0, a comprehensive central nervous system (CNS) physiologically based pharmacokinetic (PBPK) model, was extended to incorporate brain tumor compartments. Most pathophysiological parameters of brain tumors were obtained from literature and two missing parameters of the BTB, paracellular pore size and expression level of active transporters, were estimated by fitting existing data, like a “handshake”. Simultaneous predictions were made for PK profiles in extracellular fluids (ECF) of brain tumors and normal-appearing brain and validated on existing data for six small molecule anticancer drugs. The LeiCNS-tumor model predicted ECF PK profiles in brain tumor as well as normal-appearing brain in rat brain tumor models and high-grade glioma patients within twofold error for most data points, in combination with estimated paracellular pore size of the BTB and active efflux clearance at the BTB. Our model demonstrated a potential to predict PK profiles of small molecule drugs in brain tumors, for which quantitative information on pathophysiological alterations is available, and contribute to the efficient and successful drug development for malignant brain tumors.

The key role of organic anion transporter 3 in the drug-drug interaction between tranilast and methotrexate

Tranilast, N-(3',4'-dimethoxycinnamoyl)-anthranilic acid, is an anti-allergic drug and is considered for use in the treatment of rheumatoid arthritis. Methotrexate, an antimetabolite and folate antagonist to treat some cancers, is also a first-line drug for RA. The aim of this study was to understand whether tranilast could inhibit renal uptake transporters (Oat1, Oat3, and Oct2) and whether MTX combined with TL would have drug-drug interactions. The results of kidney slices and HEK293T-OAT3 cell uptake experiments showed that TL (10 μM) could inhibit the uptake of penicillin G and MTX, which are substrates of OAT3. When TL (10 mg/kg) was combined with MTX (5 mg/kg), the area under the curve and peak concentration of MTX increased by 46.46% and 113.51%, respectively, while the pharmacokinetic process of tranilast (10 mg/kg) was not changed by methotrexate (5 mg/kg). TL could increase plasma exposure of MTX by inhibiting Oat3 in vitro and in vivo.

Concomitant Use of High-dose Methotrexate and Glycyrrhizin Affects Pharmacokinetics of Methotrexate, Resulting in Hepatic Toxicity

BACKGROUND/AIM

High-dose methotrexate is a therapy for acute leukemia, malignant lymphoma, and osteosarcoma. Glycyrrhizin has been used to treat hepatic dysfunction caused by high-dose methotrexate. However, few studies have investigated the interaction between glycyrrhizin and high-dose methotrexate.

MATERIALS AND METHODS

Male Wistar rats were treated with high-dose methotrexate (500 or 1,000 mg/kg) alone, or with co-administration of 100 mg/kg glycyrrhizin. Plasma concentrations of methotrexate, alanine aminotransferase, aspartate aminotransferase, and total bilirubin were measured.

RESULTS

At both methotrexate doses, the blood concentration of methotrexate was significantly increased and total clearance was significantly reduced using co-administration of glycyrrhizin compared with methotrexate alone, which led to increased levels of hepatic enzymes. These results suggest that glycyrrhizin significantly increases the plasma level and delays the clearance of methotrexate, resulting in hepatic toxicity.

CONCLUSION

The concomitant use of methotrexate and glycyrrhizin should be considered with caution.

Systematic Review of Pharmacogenetic Factors That Influence High-Dose Methotrexate Pharmacokinetics in Pediatric Malignancies

Methotrexate (MTX) is a mainstay therapeutic agent administered at high doses for the treatment of pediatric and adult malignancies, such as acute lymphoblastic leukemia, osteosarcoma, and lymphoma. Despite the vast evidence for clinical efficacy, high-dose MTX displays significant inter-individual pharmacokinetic variability. Delayed MTX clearance can lead to prolonged, elevated exposure, causing increased risks for nephrotoxicity, mucositis, seizures, and neutropenia. Numerous pharmacogenetic studies have investigated the effects of several genes and polymorphisms on MTX clearance in an attempt to better understand the pharmacokinetic variability and improve patient outcomes. To date, several genes and polymorphisms that affect MTX clearance have been identified. However, evidence for select genes have conflicting results or lack the necessary replication and validation needed to confirm their effects on MTX clearance. Therefore, we performed a systematic review to identify and then summarize the pharmacogenetic factors that influence high-dose MTX pharmacokinetics in pediatric malignancies. Using the PRISMA guidelines, we analyzed 58 articles and 24 different genes that were associated with transporter pharmacology or the folate transport pathway. We conclude that there is only one gene that reliably demonstrates an effect on MTX pharmacokinetics: SLCO1B1.

Choroid Plexus and Drug Removal Mechanisms

Timely and efficient removal of xenobiotics and metabolites from the brain is crucial in maintaining the homeostasis and normal function of the brain. The choroid plexus (CP) forms the blood-cerebrospinal fluid barrier and vitally removes drugs and wastes from the brain through several co-existing clearance mechanisms. The CP epithelial (CPE) cells synthesize and secrete the cerebrospinal fluid (CSF). As the CSF passes through the ventricular and subarachnoid spaces and eventually drains into the general circulation, it collects and removes drugs, toxins, and metabolic wastes from the brain. This bulk flow of the CSF serves as a default and non-selective pathway for the removal of solutes and macromolecules from the brain interstitium. Besides clearance by CSF bulk flow, the CPE cells express several multispecific membrane transporters to actively transport substrates from the CSF side into the blood side. In addition, several phase I and II drug-metabolizing enzymes are expressed in the CPE cells, which enzymatically inactivate a broad spectrum of reactive or toxic substances. This review summarizes our current knowledge of the functional characteristics and key contributors to the various clearance pathways in the CP-CSF system, overviewing recent developments in our understanding of CSF flow dynamics and the functional roles of CP uptake and efflux transporters in influencing CSF drug concentrations.

The effects of drug transporters on the efficacy of methotrexate in the treatment of rheumatoid arthritis

The ATP-binding cassette (ABC) and solute carrier (SLC) transporter families consist of common drug transporters that mediate the efflux and uptake of drugs, respectively, and play an important role in the absorption, distribution, metabolism and excretion of drugs in vivo. Rheumatoid arthritis (RA) is an autoimmune disease characterized by erosive arthritis, and there are many RA patients worldwide. Methotrexate (MTX), the first-choice treatment for RA, can reduce the level of inflammation, prevent joint erosion and functional damage, and greatly reduce pain in RA patients. However, many patients show resistance to MTX, greatly affecting the efficacy of MTX. Many factors, such as irrational drug use and heredity, are associated with drug resistance. Considering the effect of drug transporters on drugs, many studies have compared the expression of drug transporters in drug-resistant and drug-sensitive patients, and abnormal transporter expression and transport activity have been found in patients with MTX resistance. Thus, drug transporters are involved in drug resistance. This article reviews the effects of transporters on the efficacy of MTX in the treatment of RA.

Risk Factors for Delayed Elimination of Methotrexate in Children, Adolescents and Young Adults With Osteosarcoma

BACKGROUND/AIM

High-dose methotrexate (HD-MTX) is pivotal chemotherapy in the treatment of patients with osteosarcoma. Blood concentrations of MTX are associated with several side effects, but there are large individual differences in the elimination of MTX. The aim of this study was to explore risk factors for delayed elimination of MTX in children, adolescents and young adults with osteosarcoma.

PATIENTS AND METHODS

We conducted a retrospective study on Japanese patients with osteosarcoma who were treated with HD-MTX at Kanazawa University Hospital from April 2006 to March 2015. Risk factors for delayed elimination of methotrexate were identified by multiple logistic regression analysis.

RESULTS

A total of 92 cycles of HD-MTX therapy were analyzed. Female and lower creatinine clearance (CCr) were identified as independent risk factors for delayed elimination of MTX.

CONCLUSION

Knowing the factors associated with delayed elimination of MTX could lead to safer and optimized chemotherapy for patients with osteosarcoma.

Evaluation of possible pharmacokinetic interaction between methotrexate and proton pump inhibitors in rats

BACKGROUND

Methotrexate (MTX), an antifolate agent, is primarily eliminated by the kidney. Organic anion transporter 3 (OAT3) contributes to renal MTX clearance. Several studies have shown an association between co-administration of proton pump inhibitors (PPIs) and delayed elimination of MTX, but the findings are conflicting. In this study, we aimed to evaluate whether the differential inhibitory effects of PPIs on the OAT3-mediated transport of MTX are associated with the risks of delayed MTX elimination.

METHODS

We investigated the effects of PPIs on rat (r) OAT3-mediated MTX uptake using HEK293T cells expressing rOAT3. To examine whether PPIs could affect the pharmacokinetics of MTX, changes in plasma concentration-time profiles were assessed when MTX (50 mg/kg, ip) and a range of PPIs (2 mg/kg, iv) were administered to rats.

RESULTS

In vitro studies demonstrated that PPIs inhibited rOAT3-mediated uptake of MTX, with estimated IC₅₀ values of 2.1-5.2 μM, and a rank order of esomeprazole ≈ lansoprazole ≈ omeprazole > rabeprazole. When MTX and esomeprazole were co-administered to rats, the plasma concentration of MTX 6 h after administration and the t_1/2 were significantly higher than those in the vehicle group. The effect of lansoprazole was not significant, but showed a tendency to prolong plasma MTX levels. Famotidine, a histamine H₂-receptor antagonist, showed a weak inhibitory effect on rOAT3-mediated MTX uptake, although it did not affect plasma concentration-time profile of MTX in vivo.

CONCLUSION

Esomeprazole increases the t_1/2 of MTX in rats, which may be partially attributed to the inhibition of rOAT3.

Unique metabolite preferences of the drug transporters OAT1 and OAT3 analyzed by machine learning

The multispecific organic anion transporters, OAT1 (SLC22A6) and OAT3 (SLC22A8), the main kidney elimination pathways for many common drugs, are often considered to have largely-redundant roles. However, whereas examination of metabolomics data from Oat-knockout mice (Oat1 and Oat3KO) revealed considerable overlap, over a hundred metabolites were increased in the plasma of one or the other of these knockout mice. Many of these relatively unique metabolites are components of distinct biochemical and signaling pathways, including those involving amino acids, lipids, bile acids, and uremic toxins. Cheminformatics, together with a "logical" statistical and machine learning-based approach, identified a number of molecular features distinguishing these unique endogenous substrates. Compared with OAT1, OAT3 tends to interact with more complex substrates possessing more rings and chiral centers. An independent "brute force" approach, analyzing all possible combinations of molecular features, supported the logical approach. Together, the results suggest the potential molecular basis by which OAT1 and OAT3 modulate distinct metabolic and signaling pathways in vivo As suggested by the Remote Sensing and Signaling Theory, the analysis provides a potential mechanism by which "multispecific" kidney proximal tubule transporters exert distinct physiological effects. Furthermore, a strong metabolite-based machine-learning classifier was able to successfully predict unique OAT1 versus OAT3 drugs; this suggests the feasibility of drug design based on knockout metabolomics of drug transporters. The approach can be applied to other SLC and ATP-binding cassette drug transporters to define their nonredundant physiological roles and for analyzing the potential impact of drug-metabolite interactions.

Side effects of methotrexate therapy for rheumatoid arthritis: A systematic review

Methotrexate (MTX) is used as an anchor disease-modifying anti-rheumatic drugs (DMARDs) in treating rheumatoid arthritis (RA) because of its potent efficacy and tolerability. MTX benefits a large number of RA patients but partially suffered from side effects. A variety of side effects can be associated with MTX when treating RA patients, from mild to severe or discontinuation of the treatment. In this report, we reviewed the possible side effects that MTX might cause from the most common gastrointestinal toxicity effects to less frequent malignant diseases. In order to achieve regimen with less side effects, the administration of MTX with appropriate dose and a careful pretreatment inspection is necessary. Further investigations are required when combining MTX with other drugs so as to enhance the efficacy and reduce side effects at the same time. The management of MTX treatment is also discussed to provide strategies for occurred side effects. Thus, this review will provide scholars with a comprehensive understanding the side effects of MTX administration by RA patients.

Genetic Heterogeneity of SLC22 Family of Transporters in Drug Disposition

An important aspect of modern medicine is its orientation to achieve more personalized pharmacological treatments. In this context, transporters involved in drug disposition have gained well-justified attention. Owing to its broad spectrum of substrate specificity, including endogenous compounds and xenobiotics, and its strategical expression in organs accounting for drug disposition, such as intestine, liver and kidney, the SLC22 family of transporters plays an important role in physiology, pharmacology and toxicology. Among these carriers are plasma membrane transporters for organic cations (OCTs) and anions (OATs) with a marked overlap in substrate specificity. These two major clades of SLC22 proteins share a similar membrane topology but differ in their degree of genetic variability. Members of the OCT subfamily are highly polymorphic, whereas OATs have a lower number of genetic variants. Regarding drug disposition, changes in the activity of these variants affect intestinal absorption and target tissue uptake, but more frequently they modify plasma levels due to enhanced or reduced clearance by the liver and secretion by the kidney. The consequences of these changes in transport-associated function markedly affect the effectiveness and toxicity of the treatment in patients carrying the mutation. In solid tumors, changes in the expression of these transporters and the existence of genetic variants substantially determine the response to anticancer drugs. Moreover, chemoresistance usually evolves in response to pharmacological and radiological treatment. Future personalized medicine will require monitoring these changes in a dynamic way to adapt the treatment to the weaknesses shown by each tumor at each stage in each patient.

The drug transporter OAT3 (SLC22A8) and endogenous metabolite communication via the gut-liver-kidney axis

The organic anion transporters OAT1 (SLC22A6) and OAT3 (SLC22A8) have similar substrate specificity for drugs, but it is far from clear whether this holds for endogenous substrates. By analysis of more than 600 metabolites in the Oat3KO (Oat3 knockout) by LC/MS, we demonstrate OAT3 involvement in the movement of gut microbiome products, key metabolites, and signaling molecules, including those flowing through the gut-liver-kidney axis. Major pathways affected included those involved in metabolism of bile acids, flavonoids, nutrients, amino acids (including tryptophan-derivatives that are uremic toxins), and lipids. OAT3 is also critical in elimination of liver-derived phase II metabolites, particularly those undergoing glucuronidation. Analysis of physicochemical features revealed nine distinct metabolite groups; at least one member of most clusters has been previously validated in transport assays. In contrast to drugs interacting with the OATs, endogenous metabolites accumulating in the Oat1KO (Oat1 knockout) versus Oat3KO have distinct differences in their physicochemical properties; they are very different in size, number of rings, hydrophobicity, and molecular complexity. Consistent with the Remote Sensing and Signaling Hypothesis, the data support the importance of the OAT transporters in inter-organ and inter-organismal remote communication via transporter-mediated movement of key metabolites and signaling molecules (e.g. gut microbiome-to-intestine-to-blood-to-liver-to-kidney-to-urine). We discuss the possibility of an intimate connection between OATs and metabolite sensing and signaling pathways (e.g. bile acids). Furthermore, the metabolomics and pathway analysis support the view that OAT1 plays a greater role in kidney proximal tubule metabolism and OAT3 appears relatively more important in systemic metabolism, modulating levels of metabolites flowing through intestine, liver, and kidney.

Acute effects of focused ultrasound-induced increases in blood-brain barrier permeability on rat microvascular transcriptome

Therapeutic treatment options for central nervous system diseases are greatly limited by the blood-brain barrier (BBB). Focused ultrasound (FUS), in conjunction with circulating microbubbles, can be used to induce a targeted and transient increase in BBB permeability, providing a unique approach for the delivery of drugs from the systemic circulation into the brain. While preclinical research has demonstrated the utility of FUS, there remains a large gap in our knowledge regarding the impact of sonication on BBB gene expression. This work is focused on investigating the transcriptional changes in dorsal hippocampal rat microvessels in the acute stages following sonication. Microarray analysis of microvessels was performed at 6 and 24 hrs post-FUS. Expression changes in individual genes and bioinformatic analysis suggests that FUS may induce a transient inflammatory response in microvessels. Increased transcription of proinflammatory cytokine genes appears to be short-lived, largely returning to baseline by 24 hrs. This observation may help to explain some previously observed bioeffects of FUS and may also be a driving force for the angiogenic processes and reduced drug efflux suggested by this work. While further studies are necessary, these results open up intriguing possibilities for novel FUS applications and suggest possible routes for pharmacologically modifying the technique.

Organic anion transporters 1 (OAT1) and OAT3 meditated the protective effect of rhein on methotrexate-induced nephrotoxicity

Rhein protects methotrexate induced kidney damage mediated by OAT1 and OAT3.

Pharmacogenomics of genes involved in antifolate drug response and toxicity in osteosarcoma

INTRODUCTION

Antifolates are structural analogs of folates, which have been used as antitumor drugs for more than 60 years. The antifolate drug most commonly used for treating human tumors is methotrexate (MTX), which is utilized widely in first-line treatment protocols of high-grade osteosarcoma (HGOS). In addition to MTX, two other antifolates, trimetrexate and pemetrexed, have been tested in clinical settings for second-line treatment of recurrent HGOS with patients unfortunately showing modest activity. Areas covered: There is clinical evidence which suggsest that, like other chemotherapeutic agents, not all HGOS patients are equally responsive to antifolates and do not have the same susceptibility to experience adverse drug-related toxicities. Here, we summarize the pharmacogenomic information reported so far for genes involved in antifolate metabolism and transport and in MTX-related toxicity in HGOS patients. Expert opinion: Identification and validation of genetic biomarkers that significantly impact clinical antifolate treatment response and related toxicity may provide the basis for a future treatment modulation based on the pharmacogenetic and pharmacogenomic features of HGOS patients.

Prophylactic Trimethoprim-Sulfamethoxazole Does Not Affect Pharmacokinetics or Pharmacodynamics of Methotrexate

Trimethoprim-sulfamethoxazole (TMP/SMX) is used as prophylaxis against Pneumocystis jiroveci during chemotherapy. Many groups recommend withholding TMP/SMX during high-dose methotrexate (HDMTX) for concerns that it will delay methotrexate clearance. We compared methotrexate exposure following HDMTX (NCT00549848) in 424 patients including 783 courses that were given concurrently and 602 courses that were not given concurrently with TMP/SMX. Among 176 patients (555 courses) on the low-risk arm (HDMTX=2.5 g/m/24 h), there was no difference in clearance (110.7 [1.8%] vs. 108.2 [0.9%] mL/min/m, P=0.3) nor in 42 hour methotrexate concentration (0.37 [5.1%] vs. 0.40 (5.0%) μM, P=0.23). Among 248 patients (830 courses) on the standard/high-risk arm (HDMTX ~5 g/m/24 h), there was slightly higher clearance (95.5 [1.4%] vs. 91.2 [0.8%] mL/min/m, P=0.005) in those receiving TMP/SMX, with no difference in the 42 hour methotrexate concentration (0.59 [4.1%] vs. 0.66 [4.2%] μM, P=0.06). There was no difference in neutrophil counts based on TMP/SMX during HDMTX (P=0.83). TMP/SMX also did not have a significant impact on myelosuppression of low-dose methotrexate (40 mg/m) given during continuation therapy among 230 patients enrolled on a prior study (NCT00137111). Thus, we found no evidence for an interaction between methotrexate and TMP/SMX given prophylactically.

The organic anion transporter (OAT) family: a systems biology perspective

The organic anion transporter (OAT) subfamily, which constitutes roughly half of the SLC22 (solute carrier 22) transporter family, has received a great deal of attention because of its role in handling of common drugs (antibiotics, antivirals, diuretics, nonsteroidal anti-inflammatory drugs), toxins (mercury, aristolochic acid), and nutrients (vitamins, flavonoids). Oats are expressed in many tissues, including kidney, liver, choroid plexus, olfactory mucosa, brain, retina, and placenta. Recent metabolomics and microarray data from Oat1 [Slc22a6, originally identified as NKT (novel kidney transporter)] and Oat3 (Slc22a8) knockouts, as well as systems biology studies, indicate that this pathway plays a central role in the metabolism and handling of gut microbiome metabolites as well as putative uremic toxins of kidney disease. Nuclear receptors and other transcription factors, such as Hnf4α and Hnf1α, appear to regulate the expression of certain Oats in conjunction with phase I and phase II drug metabolizing enzymes. Some Oats have a strong selectivity for particular signaling molecules, including cyclic nucleotides, conjugated sex steroids, odorants, uric acid, and prostaglandins and/or their metabolites. According to the "Remote Sensing and Signaling Hypothesis," which is elaborated in detail here, Oats may function in remote interorgan communication by regulating levels of signaling molecules and key metabolites in tissues and body fluids. Oats may also play a major role in interorganismal communication (via movement of small molecules across the intestine, placental barrier, into breast milk, and volatile odorants into the urine). The role of various Oat isoforms in systems physiology appears quite complex, and their ramifications are discussed in the context of remote sensing and signaling.

What do drug transporters really do?

Potential drug-drug interactions mediated by the ATP-binding cassette (ABC) transporter and solute carrier (SLC) transporter families are of clinical and regulatory concern. However, the endogenous functions of these drug transporters are not well understood. Discussed here is evidence for the roles of ABC and SLC transporters in the handling of diverse substrates, including metabolites, antioxidants, signalling molecules, hormones, nutrients and neurotransmitters. It is suggested that these transporters may be part of a larger system of remote communication ('remote sensing and signalling') between cells, organs, body fluid compartments and perhaps even separate organisms. This broader view may help to clarify disease mechanisms, drug-metabolite interactions and drug effects relevant to diabetes, chronic kidney disease, metabolic syndrome, hypertension, gout, liver disease, neuropsychiatric disorders, inflammatory syndromes and organ injury, as well as prenatal and postnatal development.

Proton pump inhibitors inhibit methotrexate transport by renal basolateral organic anion transporter hOAT3

The coadministration of methotrexate (MTX) and proton pump inhibitors (PPIs) can result in a pharmacokinetic interaction that delays MTX elimination and subsequently increases the MTX blood concentrations. Human organic anion transporters (hOATs) are responsible for the renal tubular secretion of MTX and are thought to be involved in this drug interaction. The aim of this study was to evaluate the inhibitory potencies of PPIs on hOAT1 and hOAT3, which are the two isoforms of OATs predominantly expressed in kidney proximal tubules. Using stably transfected cell systems that express the uptake transporters human embryonic kidney (HEK)-hOAT1 and HEK-hOAT3, we analyzed the inhibitory potencies of omeprazole, lansoprazole, and pantoprazole on OAT-mediated [(3)H]estrone sulfate (ES), [(3)H]p-aminohippuric acid (PAH), and [(3)H]MTX uptake in vitro. hOAT3 is a high affinity transporter for MTX (Km = 21.17 ± 5.65 µM). Omeprazole, lansoprazole, and pantoprazole inhibited [(3)H]MTX uptake in HEK-hOAT3 cells with an IC50 of 6.8 ± 1.16, 1.14 ± 0.26, and 4.45 ± 1.62 µM, respectively, and inhibited the [(3)H]ES uptake in HEK-hOAT3 cells with an IC50 of 20.59 ± 4.07, 3.96 ± 0.96, and 7.89 ± 2.31 µM, respectively. Furthermore, omeprazole, lansoprazole, and pantoprazole exhibited inhibited PAH uptake on hOAT1 in a concentration-dependent manner (IC50 = 4.32 ± 1.26, 7.58 ± 1.06, and 63.21 ± 4.74 µM, respectively). These in vitro results suggest that PPIs inhibit [(3)H]MTX transport via hOAT3 inhibition, which most likely explains the drug-drug interactions between MTX and PPIs and should be considered for other OATs substrates.

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.

Molecular basis for pharmacokinetics and pharmacodynamics of methotrexate in rheumatoid arthritis therapy

  Methotrexate (MTX) is a derivative of folic acid (folate) and commonly used as an anchor drug for the treatment of rheumatoid arthritis (RA). The pharmacokinetics (PK) and pharmacodynamics (PD) of MTX entirely depends on the function of specific transporters that belong to the two major superfamilies, solute carrier transporters and ATP-binding cassette transporters. Several transporters have been identified as being able to mediate the transport of MTX, and suggested to be involved in the disposition in the body and in the regulation of intracellular metabolism in target cells, together with several enzymes involved in folate metabolism. Thus, drug-drug interactions through the transporters and their genetic polymorphisms may alter the PK and PD of MTX, resulting in an interpatient variability of efficacy. This review summarizes the PK and PD of MTX, particularly in relation to RA therapy and focuses on the roles of transporters involved in PK and PD with the aim of facilitating an understanding of the molecular basis of the mechanism of MTX action to achieve its effective use in RA therapy.

Multispecific drug transporter Slc22a8 (Oat3) regulates multiple metabolic and signaling pathways

Multispecific drug transporters of the solute carrier and ATP-binding cassette families are highly conserved through evolution, but their true physiologic role remains unclear. Analyses of the organic anion transporter 3 (OAT3; encoded by Slc22a8/Oat3, originally Roct) knockout mouse have confirmed its critical role in the renal handling of common drugs (e.g., antibiotics, antivirals, diuretics) and toxins. Previous targeted metabolomics of the knockout of the closely related Oat1 have demonstrated a central metabolic role, but the same approach with Oat3 failed to reveal a similar set of endogenous substrates. Nevertheless, the Oat3 knockout is the only Oat described so far with a physiologically significant phenotype, suggesting the disturbance of metabolic or signaling pathways. Here we analyzed global gene expression in Oat3 knockout tissue, which implicated OAT3 in phase I and phase II metabolism (drug metabolizing enzymes or DMEs), as well as signaling pathways. Metabolic reconstruction with the recently developed "mouse Recon1" supported the involvement of Oat3 in the aforementioned pathways. Untargeted metabolomics were used to determine whether the predicted metabolic alterations could be confirmed. Many significant changes were observed; several metabolites were tested for direct interaction with mOAT3, whereas others were supported by published data. Oat3 thus appears critical for the handling of phase I (hydroxylation) and phase II (glucuronidation) metabolites. Oat3 also plays a role in bioenergetic pathways (e.g., the tricarboxylic acid cycle), as well as those involving vitamins (e.g., folate), steroids, prostaglandins, gut microbiome products, uremic toxins, cyclic nucleotides, amino acids, glycans, and possibly hyaluronic acid. The data seemingly consistent with the Remote Sensing and Signaling Hypothesis (Ahn and Nigam, 2009; Wu et al., 2011), also suggests that Oat3 is essential for the handling of dietary flavonoids and antioxidants.

Reduced renal clearance of cefotaxime in asians with a low-frequency polymorphism of OAT3 (SLC22A8)

Organic anion transporter 3 (OAT3, SLC22A8), a transporter expressed on the basolateral membrane of the proximal tubule, plays a critical role in the renal excretion of organic anions including many therapeutic drugs. The goal of this study was to evaluate the in vivo effects of the OAT3-Ile305Phe variant (rs11568482), present at 3.5% allele frequency in Asians, on drug disposition with a focus on cefotaxime, a cephalosporin antibiotic. In HEK293-Flp-In cells, the OAT3-Ile305Phe variant had a lower maximum cefotaxime transport activity, Vmax , [159 ± 3 nmol*(mg protein)(-1) /min (mean ± SD)] compared with the reference OAT3 [305 ± 28 nmol*(mg protein)(-1) /min, (mean ± SD), p < 0.01], whereas the Michaelis-Menten constant values (Km ) did not differ. In healthy volunteers, we found volunteers that were heterozygous for the Ile305Phe variant and had a significantly lower cefotaxime renal clearance (CLR ; mean ± SD: 84.8 ± 32.1 mL/min, n = 5) compared with volunteers that were homozygous for the reference allele (158 ± 44.1 mL/min, n = 10; p = 0.006). Furthermore, the net secretory component of cefotaxime renal clearance (CLsec ) was reduced in volunteers heterozygous for the variant allele [33.3 ± 31.8 mL/min (mean ± SD)] compared with volunteers homozygous for the OAT3 reference allele [97.0 ± 42.2 mL/min (mean ± SD), p = 0.01]. In summary, our study suggests that a low-frequency reduced-function polymorphism of OAT3 associates with reduced cefotaxime CLR and CL(sec) .

Organic anion transporter 3 interacts selectively with lipophilic β-lactam antibiotics

Transporters are major determinants of the disposition of xenobiotics and endogenous chemicals in the body. Organic anion transporter 3 (Oat3) functions in the kidney and brain to remove metabolic waste, toxins, and drugs, and thus transports diverse chemicals. Some β-lactam antibiotics interact with Oat3, and penicillin G exhibits a strong dependence on Oat3 for renal elimination. However, over 80 β-lactams exist, and many have not been assessed for an interaction with Oat3. Moreover, β-lactams continue to receive U.S. Food and Drug Administration approval. This study identified new β-lactam-Oat3 interactions, provided a head-to-head comparison with Oat1, and characterized the physicochemical determinants of affinity for Oat3. Cells expressing mouse Oat3 (mOat3) and Oat1 (mOat1), and human OAT3 (hOAT3) were used to test inhibitors, and high-performance liquid chromatography (HPLC) was used to measure transport. Of 26 β-lactams tested, 12 were clear inhibitors of Oat3, and 14 exhibited poor interactions. Inhibitors exhibited a nearly identical rank-order of potency against mOat3 and hOAT3. Oat1 demonstrated a poor interaction with most β-lactams. The majority of Oat3 inhibitors were substrates, and there were clear physicochemical differences between inhibitors and noninhibitors. That is, inhibitors had nearly 40% fewer hydrogen bond donors (P < 0.001), a lower total polar surface area (P < 0.05), and greater lipophilicity (LogP of inhibitors, +1.41; noninhibitors, -1.54; P < 0.001). Pharmacophore mapping revealed a prohibitive hydrogen bond donor group in noninhibitors adjacent to a hydrophobic moiety that was important for binding to Oat3. These findings indicate that Oat3 recognizes lipophilic β-lactams more readily. Moreover, this study has potential implications for designing β-lactams to avoid renal accumulation or brain efflux via Oat3.

Drug transporters on arachnoid barrier cells contribute to the blood-cerebrospinal fluid barrier

The subarachnoid space, where cerebrospinal fluid (CSF) flows over the brain and spinal cord, is lined on one side by arachnoid barrier (AB) cells that form part of the blood-CSF barrier. However, despite the fact that drugs are administered into the CSF and CSF drug concentrations are used as a surrogate for brain drug concentration following systemic drug administration, the tight-junctioned AB cells have never been examined for whether they express drug transporters that would influence CSF and central nervous system drug disposition. Hence, we characterized drug transporter expression and function in AB cells. Immunohistochemical analysis showed P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) in mouse AB cells but not other meningeal tissue. The Gene Expression Nervous System Atlas (GENSAT) database and the Allen Mouse Brain Atlas confirmed these observations. Microarray analysis of mouse and human arachnoidal tissue revealed expression of many drug transporters and some drug-metabolizing enzymes. Immortalized mouse AB cells express functional P-gp on the apical (dura-facing) membrane and BCRP on both apical and basal (CSF-facing) membranes. Thus, like blood-brain barrier cells and choroid plexus cells, AB cells highly express drug transport proteins and likely contribute to the blood-CSF drug permeation barrier.

Competitive inhibition of human organic anion transporters 1 (SLC22A6), 3 (SLC22A8) and 4 (SLC22A11) by major components of the medicinal herb Salvia miltiorrhiza (Danshen)

When herbal products are used in combination therapy with drugs, alterations in pharmacokinetics, pharmacodynamics, and toxicity can result. Many active components of herbal products are organic anions, and human organic anion transporter 1 (hOAT1, SLC22A6), hOAT3 (SLC22A8), and hOAT4 (SLC22A11) have been identified as potential sites of drug-drug interactions. Therefore, we assessed the effects of lithospermic acid (LSA), rosmarinic acid (RMA), salvianolic acid A (SAA), salvianolic acid B (SAB), and tanshinol (TSL), components of the herbal medicine Danshen, on the function of these transporters. Kinetic analysis demonstrated a competitive mechanism of inhibition for all five. K(i) values (µM) were estimated as 20.8 ± 2.1 (LSA), 0.35 ± 0.06 (RMA), 5.6 ± 0.3 (SAA), 22.2 ± 1.9 (SAB), and 40.4 ± 12.9 (TSL) on hOAT1 and as 0.59 ± 0.26 (LSA), 0.55 ± 0.25 (RMA), 0.16 ± 0.03 (SAA), 19.8 ± 8.4 (SAB), and 8.6 ± 3.3 (TSL) on hOAT3. No significant inhibition of hOAT4 activity by TSL was observed. Using published human pharmacokinetic values, unbound C(max)/K(i) ratios were calculated as an indicator of in vivo drug-drug interaction potential. Analysis indicated a strong interaction potential for RMA and TSL on both hOAT1 and hOAT3 and for LSA on hOAT3. Thus, herb-drug interactions may occur in vivo in situations of co-administration of Danshen and clinical therapeutics known to be hOAT1/hOAT3 substrates.

Methotrexate: the pharmacology behind medical treatment for ectopic pregnancy

Previously established as a chemotherapeutic agent for decades, methotrexate has been adapted for use as a medical therapy for unruptured ectopic pregnancies. Its mechanism of action, competitive inhibition of folate-dependent steps in nucleic acid synthesis, effectively kills the rapidly dividing ectopic trophoblast. However, the same action on normal cells is the basis for many of its adverse effects.

Involvement of Multiple Transporters-mediated Transports in Mizoribine and Methotrexate Pharmacokinetics

Mizoribine is administered orally and excreted into urine without being metabolized. Many research groups have reported a linear relationship between the dose and peak serum concentration, between the dose and AUC, and between AUC and cumulative urinary excretion of mizoribine. In contrast, a significant interindividual variability, with a small intraindividual variability, in oral bioavailability of mizoribine is also reported. The interindividual variability is mostly considered to be due to the polymophisms of transporter genes. Methotrexate (MTX) is administered orally and/or by parenteral routes, depending on the dose. Metabolic enzymes and multiple transporters are involved in the pharmacokinetics of MTX. The oral bioavailability of MTX exhibits a marked interindividual variability and saturation with increase in the dose of MTX, with a small intraindividual variability, where the contribution of gene polymophisms of transporters and enzymes is suggested. Therapeutic drug monitoring of both mizoribine and MTX is expected to improve their clinical efficacy in the treatment of rheumatoid arthritis.

Drug transport by Organic Anion Transporters (OATs)

Common to all so far functionally characterized Organic Anion Transporters (OATs) is their broad substrate specificity and their ability to exchange extracellular against intracellular organic anions. Many OATs occur in renal proximal tubules, the site of active drug secretion. Exceptions are murine Oat6 (nasal epithelium), human OAT7 (liver), and rat Oat8 (renal collecting ducts). In human kidneys, OAT1, OAT2, and OAT3 are localized in the basolateral membrane, and OAT4, OAT10, and URAT1 in the apical cell membrane of proximal tubule cells, respectively. In rats and mice, Oat1 and Oat3 are located basolaterally, and Oat2, Oat5, Oat9, Oat10, and Urat1 apically. Several classes of drugs interact with human OAT1-3, including ACE inhibitors, angiotensin II receptor antagonists, diuretics, HMG CoA reductase inhibitors, β-lactam antibiotics, antineoplastic and antiviral drugs, and uricosuric drugs. For most drugs, interaction was demonstrated in vitro by inhibition of OAT-mediated transport of model substrates; for some drugs, transport by OATs was directly proven. Based on IC₅₀ values reported in the literature, OAT1 and OAT3 show comparable affinities for diuretics, cephalosporins, and nonsteroidal anti-inflammatory drugs whereas OAT2 has a lower affinity to most of these compounds. Drug-drug interactions at OAT1 and OAT3 may retard renal drug secretion and cause untoward effects. OAT4, OAT10, and URAT1 in the apical membrane contribute to proximal tubular urate absorption, and OAT10 to nicotinate absorption. OAT4 is in addition able to release drugs, e.g. diuretics, into the tubule lumen.

Active Hydrophilic Components of the Medicinal Herb Salvia miltiorrhiza (Danshen) Potently Inhibit Organic Anion Transporters 1 (Slc22a6) and 3 (Slc22a8)

Many active components of herbal products are small organic anions, and organic anion transporters were previously demonstrated to be a potential site of drug-drug interactions. In this study, we assessed the inhibitory effects of six hydrophilic components of the herbal medicine Danshen, lithospermic acid, protocatechuic acid, rosmarinic acid, salvianolic acid A, salvianolic acid B, and tanshinol, on the function of the murine organic anion transporters, mOat1 and mOat3. All of Danshen components significantly inhibited mOat1- and mOat3-mediated substrate uptake (P < 0.001) with lithospermic acid (LSA), protocatechuic acid, rosmarinic acid (RMA), and salvianolic acid A (SAA) producing virtually complete inhibition under test conditions. Kinetic analysis demonstrated that LSA, RMA, and SAA were competitive inhibitors. As such, K_i values were estimated as 14.9 ± 4.9 μM for LSA, 5.5 ± 2.2 μM for RMA, and 4.9 ± 2.2 μM for SAA on mOat1-mediated transport, and as 31.1 ± 7.0 μM for LSA, 4.3 ± 0.2 μM for RMA, and 21.3 ± 7.7 μM for SAA on mOat3-mediated transport. These data suggest that herb-drug interactions may occur in vivo on the human orthologs of these transporters in situations of polypharmacy involving Danshen and clinical therapeutics known to be organic anion transporter substrates.

Male-dominant activation of rat renal organic anion transporter 1 (Oat1) and 3 (Oat3) expression by transcription factor BCL6

Background

Organic anion transporters 1 (Oat1) and 3 (Oat3) mediate the transport of organic anions, including frequently prescribed drugs, across cell membranes in kidney proximal tubule cells. In rats, these transporters are known to be male-dominant and testosterone-dependently expressed. The molecular mechanisms that are involved in the sex-dependent expression are unknown. Our aim was to identify genes that show a sex-dependent expression and could be involved in male-dominant regulation of Oat1 and Oat3.

Methodology/Principal Findings

Promoter activities of Oat1 and Oat3 were analyzed using luciferase assays. Expression profiling was done using a SurePrint G3 rat GE 8×60K microarray. RNA was isolated from renal cortical slices of four adult rats per sex. To filter the achieved microarray data for genes expressed in proximal tubule cells, transcription database alignment was carried out. We demonstrate that predicted androgen response elements in the promoters of Oat1 and Oat3 are not functional when the promoters were expressed in OK cells. Using microarray analyses we analyzed 17,406 different genes. Out of these genes, 56 exhibit a sex-dependent expression in rat proximal tubule cells. As genes potentially involved in the regulation of Oat1 and Oat3 expression, we identified, amongst others, the male-dominant hydroxysteroid (17-beta) dehydrogenase 1 (Hsd17b1), B-cell CLL/lymphoma 6 (BCL6), and polymerase (RNA) III (DNA directed) polypeptide G (Polr3g). Moreover, our results revealed that the transcription factor BCL6 activates promoter constructs of Oat1 and Oat3.

Conclusion

The results indicate that the male-dominant expression of both transporters, Oat1 and Oat3, is possibly not directly regulated by the classical androgen receptor mediated transcriptional pathway but appears to be regulated by the transcription factor BCL6.

Contribution of tumoral and host solute carriers to clinical drug response

Members of the solute carrier family of transporters are responsible for the cellular uptake of a broad range of endogenous compounds and xenobiotics in multiple tissues. Several of these solute carriers are known to be expressed in cancer cells or cancer cell lines, and decreased cellular uptake of drugs potentially contributes to the development of resistance. As result, the expression levels of these proteins in humans have important consequences for an individual's susceptibility to certain drug-induced side effects, interactions, and treatment efficacy. In this review article, we provide an update of this rapidly emerging field, with specific emphasis on the direct contribution of solute carriers to anticancer drug uptake in tumors, the role of these carriers in regulation of anticancer drug disposition, and recent advances in attempts to evaluate these proteins as therapeutic targets.

Physiological and molecular characterization of aristolochic acid transport by the kidney

Consumption of herbal medicines derived from Aristolochia plants is associated with a progressive tubulointerstitial disease known as aristolochic acid (AA) nephropathy. The nephrotoxin produced naturally by these plants is AA-I, a nitrophenanthrene carboxylic acid that selectively targets the proximal tubule. This nephron segment is prone to toxic injury because of its role in secretory elimination of drugs and other xenobiotics. Here, we characterize the handling of AA-I by membrane transporters involved in renal organic anion transport. Uptake assays in heterologous expression systems identified murine organic anion transporters (mOat1, mOat2, and mOat3) as capable of mediating transport of AA-I. Kinetic analyses showed that all three transporters have an affinity for AA-I in the submicromolar range and thus are likely to operate at toxicologically relevant concentrations in vivo. Structure-activity relationships revealed that the carboxyl group is critical for high-affinity interaction of AA-I with mOat1, mOat2, and mOat3, whereas the nitro group is required only by mOat1. Furthermore, the 8-methoxy group, although essential for toxicity, was not requisite for transport. Mouse renal cortical slices avidly accumulated AA-I, achieving slice-to-medium concentration ratios >10. Uptake by slices was sensitive to known mOat1 and mOat3 substrates and the organic anion transport inhibitor probenecid, which also blocked the production of DNA adducts formed with reactive intracellular metabolites of AA-I. Taken together, these findings indicate that OAT family members mediate high-affinity transport of AA-I and may be involved in the site-selective toxicity and renal elimination of this nephrotoxin.

In vitro and in vivo evidence of the importance of organic anion transporters (OATs) in drug therapy

Organic anion transporters 1-10 (OAT1-10) and the urate transporter 1 (URAT1) belong to the SLC22A gene family and accept a huge variety of chemically unrelated endogenous and exogenous organic anions including many frequently described drugs. OAT1 and OAT3 are located in the basolateral membrane of renal proximal tubule cells and are responsible for drug uptake from the blood into the cells. OAT4 in the apical membrane of human proximal tubule cells is related to drug exit into the lumen and to uptake of estrone sulfate and urate from the lumen into the cell. URAT1 is the major urate-absorbing transporter in the apical membrane and is a target for uricosuric drugs. OAT10, also located in the luminal membrane, transports nicotinate with high affinity and interacts with drugs. Major extrarenal locations of OATs include the blood-brain barrier for OAT3, the placenta for OAT4, the nasal epithelium for OAT6, and the liver for OAT2 and OAT7. For all transporters we provide information on cloning, tissue distribution, factors influencing OAT abundance, interaction with endogenous compounds and different drug classes, drug/drug interactions and, if known, single nucleotide polymorphisms.

Organic anion transporter 6 (Slc22a20) specificity and Sertoli cell-specific expression provide new insight on potential endogenous roles

Organic anion transporter 6 (Oat6; Slc22a20), a member of the OAT family, was demonstrated previously to mediate the transport of organic anions (Am J Physiol Renal Physiol 291:F314-F321, 2006). In the present study, we sought to further delineate the function of murine Oat6 (mOat6) by analyzing the effect of select organic anions on mOat6-mediated transport by using a Chinese hamster ovary (CHO) cell line stably expressing mOat6 (CHO-mOat6). When examined, kinetic analysis demonstrated that the mechanism of inhibition of mOat6 and mOat3 was competitive. Homovanillic acid, 5-hydroxyindole acetic acid, 2,4-dihydroxyphenylacetate, hippurate, and dehydroepiandrosterone sulfate (DHEAS) each significantly reduced mOat6 activity with inhibitory constant (K(i)) values of 3.0 +/- 0.5, 48.9 +/- 10.3, 61.4 +/- 7.1, 59.9 +/- 4.9, and 38.8 +/- 3.1 microM, respectively. Comparison to K(i) values determined for mOat3 (67.8 +/- 7.2, 134.5 +/- 27.0, 346.7 +/- 97.9, 79.3 +/- 4.0, and 3.8 +/- 1.1 microM, respectively) revealed that there are significant differences in compound affinity between each transporter. Fluoroquinolone antimicrobials and reduced folates were without effect on mOat6-mediated uptake. Investigation of testicular cell type-specific expression of mOat6 by laser capture microdissection and quantitative polymerase chain reaction revealed significant mRNA expression in Sertoli cells, but not in Leydig cells or spermatids. Overall, these data should aid further refinements to the interpretation and modeling of the in vivo disposition of OAT substrates. Specifically, expression in Sertoli cells suggests Oat6 may be an important determinant of blood-testis barrier function, with Oat6-mediated transport of estrone sulfate and DHEAS possibly representing a critical step in the maintenance of testicular steroidogenesis.

Organic anion transporters: discovery, pharmacology, regulation and roles in pathophysiology

Our understanding of the mechanisms behind inter- and intra-patient variability in drug response is inadequate. Advances in the cytochrome P450 drug metabolizing enzyme field have been remarkable, but those in the drug transporter field have trailed behind. Currently, however, interest in carrier-mediated disposition of pharmacotherapeutics is on a substantial uprise. This is exemplified by the 2006 FDA guidance statement directed to the pharmaceutical industry. The guidance recommended that industry ascertain whether novel drug entities interact with transporters. This suggestion likely stems from the observation that several novel cloned transporters contribute significantly to the disposition of various approved drugs. Many drugs bear anionic functional groups, and thus interact with organic anion transporters (OATs). Collectively, these transporters are nearly ubiquitously expressed in barrier epithelia. Moreover, several reports indicate that OATs are subject to diverse forms of regulation, much like drug metabolizing enzymes and receptors. Thus, critical to furthering our understanding of patient- and condition-specific responses to pharmacotherapy is the complete characterization of OAT interactions with drugs and regulatory factors. This review provides the reader with a comprehensive account of the function and substrate profile of cloned OATs. In addition, a major focus of this review is on the regulation of OATs including the impact of transcriptional and epigenetic factors, phosphorylation, hormones and gender.