Expression and localization of the multidrug resistance proteins MRP2 and MRP3 in human gallbladder epithelia

Genetics of Gallstone Disease and Their Clinical Significance: A Narrative Review

Gallstone (GS) disease is common and arises from a combination of genetic and environmental factors. Although genetic abnormalities specifically leading to cholesterol GSs are rare, there are clinically significant gene variants associated with cholesterol GSs. In contrast, most bilirubin GSs can be attributed to genetic defects. The pathogenesis of cholesterol and bilirubin GSs differs greatly. Cholesterol GSs are notably influenced by genetic variants within the ABC protein superfamily, including ABCG8, ABCG5, ABCB4, and ABCB11, as well as genes from the apolipoprotein family such as ApoB100 and ApoE (especially the E3/E3 and E3/E4 variants), and members of the MUC family. Conversely, bilirubin GSs are associated with genetic variants in highly expressed hepatic genes, notably UGT1A1, ABCC2 (MRP2), ABCC3 (MRP3), CFTR, and MUC, alongside genetic defects linked to hemolytic anemias and conditions impacting erythropoiesis. While genetic cases constitute a small portion of GS disease, recognizing genetic predisposition is essential for proper diagnosis, treatment, and genetic counseling.

Extracellular Vesicles and Cancer Multidrug Resistance: Undesirable Intercellular Messengers?

Cancer multidrug resistance (MDR) is one of the main mechanisms contributing to therapy failure and mortality. Overexpression of drug transporters of the ABC family (ATP-binding cassette) is a major cause of MDR. Extracellular vesicles (EVs) are nanoparticles released by most cells of the organism involved in cell-cell communication. Their cargo mainly comprises, proteins, nucleic acids, and lipids, which are transferred from a donor cell to a target cell and lead to phenotypical changes. In this article, we review the scientific evidence addressing the regulation of ABC transporters by EV-mediated cell-cell communication. MDR transfer from drug-resistant to drug-sensitive cells has been identified in several tumor entities. This was attributed, in some cases, to the direct shuttle of transporter molecules or its coding mRNA between cells. Also, EV-mediated transport of regulatory proteins (e.g., transcription factors) and noncoding RNAs have been indicated to induce MDR. Conversely, the transfer of a drug-sensitive phenotype via EVs has also been reported. Additionally, interactions between non-tumor cells and the tumor cells with an impact on MDR are presented. Finally, we highlight uninvestigated aspects and possible approaches to exploiting this knowledge toward the identification of druggable processes and molecules and, ultimately, the development of novel therapeutic strategies.

Establishment and characterization of an immortalized epithelial cell line from human gallbladder

Background

Although a plethora of studies have employed multiple gallbladder cancer (GBC) cell lines, it is surprisingly noted that there is still lack of a normal gallbladder epithelial cell line as a normal counterpart, thus impeding substantially the progress of mechanistic studies on the transformation of normal epithelial cells to cancer. Here, we created a normal gallbladder epithelial cell line named L-2F7 from human gallbladder tissue.

Methods

Gallbladder tissues from a diagnosed cholecystitis female patient were collected, and epithelial cells were enriched by magnetic cell sorting. Then, the cells were immortalized by co-introduction of human telomerase reverse transcriptase (hTERT) and Simian virus 40 large T antigen (LT-SV40) via a lentivirus infection system. After clonal selection and isolation, L-2F7 cells were tested for epithelial markers CK7, CK19, CK20, and CD326, genomic feature, cell proliferation, and migration using Western blot, immunofluorescence, whole genome sequencing, karyotyping, and RNA sequencing. L-2F7 cells were also transplanted to Nude (nu/nu) mice to determine tumorigenicity.

Results

We successfully identified one single-cell clone named L-2F7 which highly expressed epithelial markers CD326, CK7, CK19, and CK20. This cell line proliferated with a doubling time of 23 h and the epithelial morphology sustained over 30 passages following immortalization. Transient gene transduction of L-2F7 cells led to expression of exogenous GFP and FLAG protein. L-2F7 cells exhibited both distinct non-synonymous mutations from those of gallbladder cancer tissues and differential non-cancerous gene expression patterns similar to normal tissue. Although they displayed unexpected mobility, L-2F7 cells still lacked the ability to develop tumors.

Conclusion

We developed a non-cancerous gallbladder epithelial cell line, offering a valuable system for the study of gallbladder cancer and other gallbladder-related disorders.

Expression of Chemoresistance-Associated ABC Proteins in Hepatobiliary, Pancreatic and Gastrointestinal Cancers

Simple Summary

One-third of the approximately 10 million deaths yearly caused by cancer worldwide are due to hepatobiliary, pancreatic, and gastrointestinal tumors. One primary reason for this high mortality is the lack of response of these cancers to pharmacological treatment. More than 100 genes have been identified as responsible for seven mechanisms of chemoresistance, but only a few of them play a critical role. These include ABC proteins (mainly MDR1, MRP1-6, and BCRP), whose expression pattern greatly determines the individual sensitivity of each tumor to pharmacotherapy.

Abstract

Hepatobiliary, pancreatic, and gastrointestinal cancers account for 36% of the ten million deaths caused by cancer worldwide every year. The two main reasons for this high mortality are their late diagnosis and their high refractoriness to pharmacological treatments, regardless of whether these are based on classical chemotherapeutic agents, targeted drugs, or newer immunomodulators. Mechanisms of chemoresistance (MOC) defining the multidrug resistance (MDR) phenotype of each tumor depend on the synergic function of proteins encoded by more than one hundred genes classified into seven groups (MOC1-7). Among them, the efflux of active agents from cancer cells across the plasma membrane caused by members of the superfamily of ATP-binding cassette (ABC) proteins (MOC-1b) plays a crucial role in determining tumor MDR. Although seven families of human ABC proteins are known, only a few pumps (mainly MDR1, MRP1-6, and BCRP) have been associated with reducing drug content and hence inducing chemoresistance in hepatobiliary, pancreatic, and gastrointestinal cancer cells. The present descriptive review, which compiles the updated information on the expression of these ABC proteins, will be helpful because there is still some confusion on the actual relevance of these pumps in response to pharmacological regimens currently used in treating these cancers. Moreover, we aim to define the MOC pattern on a tumor-by-tumor basis, even in a dynamic way, because it can vary during tumor progression and in response to chemotherapy. This information is indispensable for developing novel strategies for sensitization.

Bile Acids Transporters of Enterohepatic Circulation for Targeted Drug Delivery

Bile acids (BAs) are important steroidal molecules with a rapidly growing span of applications across a variety of fields such as supramolecular chemistry, pharmacy, and biomedicine. This work provides a systematic review on their transport processes within the enterohepatic circulation and related processes. The focus is laid on the description of specific or less-specific BA transport proteins and their localization. Initially, the reader is provided with essential information about BAs′ properties, their systemic flow, metabolism, and functions. Later, the transport processes are described in detail and schematically illustrated, moving step by step from the liver via bile ducts to the gallbladder, small intestine, and colon; this description is accompanied by descriptions of major proteins known to be involved in BA transport. Spillage of BAs into systemic circulation and urine excretion are also discussed. Finally, the review also points out some of the less-studied areas of the enterohepatic circulation, which can be crucial for the development of BA-related drugs, prodrugs, and drug carrier systems.

Construction of functional biliary epithelial branched networks with predefined geometry using digital light stereolithography

Cholangiocytes, biliary epithelial cells, are known to spontaneously self-organize into spherical cysts with a central lumen. In this work, we explore a promising biocompatible stereolithographic approach to encapsulate cholangiocytes into geometrically controlled 3D hydrogel structures to guide them towards the formation of branched tubular networks. We demonstrate that within the appropriate mix of hydrogels, normal rat cholangiocytes can proliferate, migrate, and organize into branched tubular structures with walls consisting of a cell monolayer, transport fluorescent dyes into the luminal space, and show markers of epithelial maturation such as primary cilia and continuous tight junctions. The resulting structures have dimensions typically found in the intralobular and intrahepatic biliary tree and are stable for weeks, without any requirement of bulk supporting material, thereby offering total access to the external side of these biliary epithelial constructs.

Drug resistance: from bacteria to cancer

The phenomenon of drug resistance has been a hindrance to therapeutic medicine since the late 1940s. There is a plethora of factors and mechanisms contributing to progression of drug resistance. From prokaryotes to complex cancers, drug resistance is a prevailing issue in clinical medicine. Although there are numerous factors causing and influencing the phenomenon of drug resistance, cellular transporters contribute to a noticeable majority. Efflux transporters form a huge family of proteins and are found in a vast number of species spanning from prokaryotes to complex organisms such as humans. During the last couple of decades, various approaches in analyses of biochemistry and pharmacology of transporters have led us to understand much more about drug resistance. In this review, we have discussed the structure, function, potential causes, and mechanisms of multidrug resistance in bacteria as well as cancers.

Hepatic transporter-mediated pharmacokinetic drug-drug interactions: Recent studies and regulatory recommendations

Transporter-mediated drug-drug interactions are one of the major mechanisms in pharmacokinetic-based drug interactions and correspondingly affecting drugs' safety and efficacy. Regulatory bodies underlined the importance of the evaluation of transporter-mediated interactions as a part of the drug development process. The liver is responsible for the elimination of a wide range of endogenous and exogenous compounds via metabolism and biliary excretion. Therefore, hepatic uptake transporters, expressed on the sinusoidal membranes of hepatocytes, and efflux transporters mediating the transport from hepatocytes to the bile are determinant factors for pharmacokinetics of drugs, and hence, drug-drug interactions. In parallel with the growing research interest in this area, regulatory guidances have been updated with detailed assay models and criteria. According to well-established preclinical results, observed or expected hepatic transporter-mediated drug-drug interactions can be taken into account for clinical studies. In this paper, various methods including in vitro, in situ, in vivo, in silico approaches, and combinational concepts and several clinical studies on the assessment of transporter-mediated drug-drug interactions were reviewed. Informative and effective evaluation by preclinical tools together with the integration of pharmacokinetic modeling and simulation can reduce unexpected clinical outcomes and enhance the success rate in drug development.

MRP3-Mediated Chemoresistance in Cholangiocarcinoma: Target for Chemosensitization Through Restoring SOX17 Expression

BACKGROUND AND AIMS

A limitation for the treatment of unresectable cholangiocarcinoma (CCA) is its poor response to chemotherapy, which is partly due to reduction of intracellular levels of anticancer drugs through ATP-binding cassette (ABC) pumps. Low expression of SOX17 (SRY-box containing gene 17), a transcription factor that promotes biliary differentiation and phenotype maintenance, has been associated with cholangiocyte malignant transformation. Whether SOX17 is also involved in CCA chemoresistance is investigated in this study.

APPROACH AND RESULTS

SOX17 expression in human CCA cells (EGI-1 and TFK-1) selectively potentiated cytotoxicity of SN-38, 5-fluorouracil and mitoxantrone, but not that of gemcitabine, capecitabine, cisplatin, or oxaliplatin. The analysis of the resistome by TaqMan low-density arrays revealed changes affecting primarily ABC pump expression. Single-gene quantitative real-time PCR, immunoblot, and immunofluorescence analyses confirmed that MRP3 (multidrug resistance associated protein 3), which was highly expressed in CCA human tumors, was down-regulated in SOX17-transduced CCA cells. The substrate specificity of this pump matched that of SOX17-induced in vitro selective chemosensitization. Functional studies showed lower ability of SOX17-expressing CCA cells to extrude specific MRP3 substrates. Reporter assay of MRP3 promoter (ABCC3pr) revealed that ABCC3pr activity was inhibited by SOX17 expression and SOX2/SOX9 silencing. The latter was highly expressed in CCA. Moreover, SOX2/9, but not SOX17, induced altered electrophoretic mobility of ABCC3pr, which was prevented by SOX17. The growth of CCA tumors subcutaneously implanted into immunodeficient mice was inhibited by 5-fluorouracil. This effect was enhanced by co-treatment with adenoviral vectors encoding SOX17.

CONCLUSIONS

SOX9/2/17 are involved in MRP3-mediated CCA chemoresistance. Restored SOX17 expression, in addition to its tumor suppression effect, induces selective chemosensitization due to MRP3 down-regulation and subsequent intracellular drug accumulation.

Role of membrane-embedded drug efflux ABC transporters in the cancer chemotherapy

One of the major problems being faced by researchers and clinicians in leukemic treatment is the development of multidrug resistance (MDR) which restrict the action of several tyrosine kinase inhibitors (TKIs). MDR is a major obstacle to the success of cancer chemotherapy. The mechanism of MDR involves active drug efflux transport of ABC superfamily of proteins such as Pglycoprotein (P-gp/ABCB1), multidrug resistance-associated protein 2 (MRP2/ABCC2), and breast cancer resistance protein (BCRP/ABCG2) that weaken the effectiveness of chemotherapeutics and negative impact on the future of anticancer therapy. In this review, the authors aim to provide an overview of various multidrug resistance (MDR) mechanisms observed in cancer cells as well as the various strategies developed to overcome these MDR. Extensive studies have been carried out since last several years to enhance the efficacy of chemotherapy by defeating these MDR mechanisms with the use of novel anticancer drugs that could escape from the efflux reaction, MDR modulators or chemosensitizers, multifunctional nanotechnology, and RNA interference (RNAi) therapy.

ATP-binding Cassette Exporters: Structure and Mechanism with a Focus on P-glycoprotein and MRP1

BACKGROUND

Proteins that belong to the ATP-binding cassette superfamily include transporters that mediate the efflux of substrates from cells. Among these exporters, P-glycoprotein and MRP1 are involved in cancer multidrug resistance, protection from endo and xenobiotics, determination of drug pharmacokinetics, and the pathophysiology of a variety of disorders.

OBJECTIVE

To review the information available on ATP-binding cassette exporters, with a focus on Pglycoprotein, MRP1 and related proteins. We describe tissue localization and function of these transporters in health and disease, and discuss the mechanisms of substrate transport. We also correlate recent structural information with the function of the exporters, and discuss details of their molecular mechanism with a focus on the nucleotide-binding domains.

METHODS

Evaluation of selected publications on the structure and function of ATP-binding cassette proteins.

CONCLUSIONS

Conformational changes on the nucleotide-binding domains side of the exporters switch the accessibility of the substrate-binding pocket between the inside and outside, which is coupled to substrate efflux. However, there is no agreement on the magnitude and nature of the changes at the nucleotide- binding domains side that drive the alternate-accessibility. Comparison of the structures of Pglycoprotein and MRP1 helps explain differences in substrate selectivity and the bases for polyspecificity. P-glycoprotein substrates are hydrophobic and/or weak bases, and polyspecificity is explained by a flexible hydrophobic multi-binding site that has a few acidic patches. MRP1 substrates are mostly organic acids, and its polyspecificity is due to a single bipartite binding site that is flexible and displays positive charge.

Sox2 modulates motility and enhances progression of colorectal cancer via the Rho-ROCK signaling pathway

Sox2 (Sry-box2) is essential for a variety of stem cells and is also expressed in colorectal cancer (CRC). However, the underlying mechanism by which Sox2 enhances CRC progression remains unclear. In the present study, we show that elevated Sox2 expression is significantly correlated with poor clinical prognosis. CRC is phenotypically heterogeneous, and harbors several subtypes of cancer cells. Elevated Sox2 expression was always detected in rounded-shape cells, which co-located to poorly differentiated regions, the invasive frontier and metastatic lesions. Knockdown of Sox2 in CRC cells not only decreased the number of round-shaped cells, but also suppressed cell migration, invasion as well as attenuated colony forming capacity and tumorigenicity. By contrast, overexpression of Sox2 in CRC cells was associated with up-regulation of multidrug resistance genes and accelerated CRC progression. Moreover, Sox2 conferred activation of Rho-ROCK signaling, whereas inhibition of ROCK signaling decreased cell migration, invasion, colony formation and self-renewal of CRC. Our results reveal that CRC is phenotypically and functionally heterogeneous. Elevated Sox2 expression activates the Rho-ROCK pathway, which in turn changes cell morphology and promotes cell migration and progression.

Functions of the Gallbladder

The gallbladder stores and concentrates bile between meals. Gallbladder motor function is regulated by bile acids via the membrane bile acid receptor, TGR5, and by neurohormonal signals linked to digestion, for example, cholecystokinin and FGF15/19 intestinal hormones, which trigger gallbladder emptying and refilling, respectively. The cycle of gallbladder filling and emptying controls the flow of bile into the intestine and thereby the enterohepatic circulation of bile acids. The gallbladder also largely contributes to the regulation of bile composition by unique absorptive and secretory capacities. The gallbladder epithelium secretes bicarbonate and mucins, which both provide cytoprotection against bile acids. The reversal of fluid transport from absorption to secretion occurs together with bicarbonate secretion after feeding, predominantly in response to an adenosine 3',5'-cyclic monophosphate (cAMP)-dependent pathway triggered by neurohormonal factors, such as vasoactive intestinal peptide. Mucin secretion in the gallbladder is stimulated predominantly by calcium-dependent pathways that are activated by ATP present in bile, and bile acids. The gallbladder epithelium has the capacity to absorb cholesterol and provides a cholecystohepatic shunt pathway for bile acids. Changes in gallbladder motor function not only can contribute to gallstone disease, but also subserve protective functions in multiple pathological settings through the sequestration of bile acids and changes in the bile acid composition. Cholecystectomy increases the enterohepatic recirculation rates of bile acids leading to metabolic effects and an increased risk of nonalcoholic fatty liver disease, cirrhosis, and small-intestine carcinoid, independently of cholelithiasis. Among subjects with gallstones, cholecystectomy remains a priority in those at risk of gallbladder cancer, while others could benefit from gallbladder-preserving strategies. © 2016 American Physiological Society. Compr Physiol 6:1549-1577, 2016.

Mammalian drug efflux transporters of the ATP binding cassette (ABC) family in multidrug resistance: A review of the past decade

Multidrug resistance (MDR) is a serious phenomenon employed by cancer cells which hampers the success of cancer pharmacotherapy. One of the common mechanisms of MDR is the overexpression of ATP-binding cassette (ABC) efflux transporters in cancer cells such as P-glycoprotein (P-gp/ABCB1), multidrug resistance-associated protein 2 (MRP2/ABCC2), and breast cancer resistance protein (BCRP/ABCG2) that limits the prolonged and effective use of chemotherapeutic drugs. Researchers have found that developing inhibitors of ABC efflux transporters as chemosensitizers could overcome MDR. But the clinical trials have shown that most of these chemosensitizers are merely toxic and only show limited or no benefits to cancer patients, thus new inhibitors are being explored. Recent findings also suggest that efflux pumps of the ABC transporter family are subject to epigenetic gene regulation. In this review, we summarize recent findings of the role of ABC efflux transporters in MDR.

Effect of ABCB1 polymorphism on the clinical outcome of osteosarcoma patients after receiving chemotherapy

Objective: To investigate the role of three genetic polymorphisms of ABC proteins in response to chemotherapy and overall survival of osteosarcoma patients.

Methods: A prospective study was conducted. Genotyping analyses of ABCB1 C3435T, ABCG2 C421A, and ABCC3 C-211T were conducted using the TaqMan methodology. Multivariate Cox proportional hazards models were used to calculate hazard ratio (HR) and 95% CI of effect of each genotype of ABCB1 C3435T, ABCG2 c421A, and ABCC3 C-211T on PFS and OS.

Results: During the follow-up period, 135 patients (74.18%) were alive and 47 died (25.82). The median follow-up periods were 36.7 months. Individuals carrying with ABCB1 3435TT genotype and T allele showed less likely to have a poor response to chemotherapy. Cox regression analysis showed that individuals with ABCB1 TT genotype and T allele were associated with high risk of death from osteosarcoma when compared with wide-type genotype. However, we did not find significant association between ABCG2 C421A and ABCC3 C-211T polymorphisms and overall survival of osteosarcoma.

Conclusion: ABCB1 C3435T polymorphism may be used as a genetic predictor of clinical outcome in osteosarcoma patients treated with chemotherapy. However, no association was found between polymorphisms in ABCG2 C421A and ABCC3 C-211T and clinical outcome of osteosarcoma.

Predictive potential of ABCB1, ABCC3, and GSTP1 gene polymorphisms on osteosarcoma survival after chemotherapy

Genetic polymorphisms in drug metabolism and transport genes can influence the pharmacokinetics and pharmacodynamics of chemotherapy drugs. We investigated the role of genes involved in metabolic and transport pathways in response to chemotherapy and clinical outcome of osteosarcoma patients. The association between the eight polymorphisms with response to chemotherapy and clinical outcome of patients was carried out by unconditional logistic regression analysis and Cox proportional hazard models. Of 186 patients, 98 patients showed good response to chemotherapy, 64 died, and 97 showed progression at the end of the study. Patients carrying ABCB1 rs1128503 TT genotype and T allele were more likely to have a good response to chemotherapy. ABCC3 rs4148416 TT genotype and T allele and GSTP1 rs1695 GG genotype and G allele were associated with poor response to chemotherapy. In the Cox proportional hazards model, after adjusting for potential confounding factors, patients carrying ABCB1 rs1128503 TT genotype and T allele were associated with lower risk of progression-free survival (PFS) and overall survival (OS). ABCC3 rs4148416 TT genotype and T allele and GSTP1 rs1695 GG genotype and G allele were correlated with high risk of PFS and OS. The ABCB1 TT and GSTP1 GG genotypes were significantly associated with a shorter OS. In conclusion, variants of ABCB1 rs128503, ABCC3 rs4148416, and GSTP1 rs1695 are associated with response to chemotherapy and PFS and OS of osteosarcoma patients; these gene polymorphisms could help in the design of individualized therapy.

Hepatobiliary transporters in drug-induced cholestasis: a perspective on the current identifying tools

INTRODUCTION

Impaired bile formation leads to the accumulation of cytotoxic bile salts in hepatocytes and, consequently, cholestasis and severe liver disease. Knowledge of the role of hepatobiliary transporters, especially the bile salt export pump (BSEP), in the pathogenesis of cholestasis is continuously increasing.

AREAS COVERED

This review provides an introduction into the role of these transport proteins in bile formation. It addresses the clinical relevance and pathophysiologic consequences of altered functions of these transporters by genetic mutations and drugs. In particular, the current practical aspects of identification and mitigation of drug candidates with liver liabilities employed during drug development, with an emphasis on preclinical screening for BSEP interaction, are discussed.

EXPERT OPINION

Within the potential pathogenetic mechanisms of acquired cholestasis, the inhibition of BSEP by drugs is well established. Interference of a new compound with BSEP transport activity should raise a warning sign to conduct follow-up experiments and to monitor liver function during clinical development. A combination of in vitro screening for transport interaction, in silico predicting models, and consideration of physicochemical and metabolic properties should lead to a more efficient screening of potential liver liability.

The role of canalicular ABC transporters in cholestasis

Cholestasis, a hallmark feature of hepatobiliary disease, is characterized by the retention of biliary constituents. Some of these constituents, such as bile acids, inflict damage to hepatocytes and bile duct cells. This damage may lead to inflammation, fibrosis, cirrhosis, and eventually carcinogenesis, sequelae that aggravate the underlying disease and deteriorate clinical outcome. Canalicular ATP-binding cassette (ABC) transporters, which mediate the excretion of individual bile constituents, play a key role in bile formation and cholestasis. The study of these transporters and their regulatory nuclear receptors has revolutionized our understanding of cholestatic disease. This knowledge has served as a template to develop novel treatment strategies, some of which are currently already undergoing phase III clinical trials. In this review we aim to provide an overview of the structure, function, and regulation of canalicular ABC transporters. In addition, we will focus on the role of these transporters in the pathogenesis and treatment of cholestatic bile duct and liver diseases.

An updated review on drug-induced cholestasis: mechanisms and investigation of physicochemical properties and pharmacokinetic parameters

Drug-induced cholestasis is an important form of acquired liver disease and is associated with significant morbidity and mortality. Bile acids are key signaling molecules, but they can exert toxic responses when they accumulate in hepatocytes. This review focuses on the physiological mechanisms of drug-induced cholestasis associated with altered bile acid homeostasis due to direct (e.g., bile acid transporter inhibition) or indirect (e.g., activation of nuclear receptors, altered function/expression of bile acid transporters) processes. Mechanistic information about the effects of a drug on bile acid homeostasis is important when evaluating the cholestatic potential of a compound, but experimental data often are not available. The relationship between physicochemical properties, pharmacokinetic parameters, and inhibition of the bile salt export pump among 77 cholestatic drugs with different pathophysiological mechanisms of cholestasis (i.e., impaired formation of bile vs. physical obstruction of bile flow) was investigated. The utility of in silico models to obtain mechanistic information about the impact of compounds on bile acid homeostasis to aid in predicting the cholestatic potential of drugs is highlighted.

Recent advances in 2D and 3D in vitro systems using primary hepatocytes, alternative hepatocyte sources and non-parenchymal liver cells and their use in investigating mechanisms of hepatotoxicity, cell signaling and ADME

This review encompasses the most important advances in liver functions and hepatotoxicity and analyzes which mechanisms can be studied in vitro. In a complex architecture of nested, zonated lobules, the liver consists of approximately 80 % hepatocytes and 20 % non-parenchymal cells, the latter being involved in a secondary phase that may dramatically aggravate the initial damage. Hepatotoxicity, as well as hepatic metabolism, is controlled by a set of nuclear receptors (including PXR, CAR, HNF-4α, FXR, LXR, SHP, VDR and PPAR) and signaling pathways. When isolating liver cells, some pathways are activated, e.g., the RAS/MEK/ERK pathway, whereas others are silenced (e.g. HNF-4α), resulting in up- and downregulation of hundreds of genes. An understanding of these changes is crucial for a correct interpretation of in vitro data. The possibilities and limitations of the most useful liver in vitro systems are summarized, including three-dimensional culture techniques, co-cultures with non-parenchymal cells, hepatospheres, precision cut liver slices and the isolated perfused liver. Also discussed is how closely hepatoma, stem cell and iPS cell-derived hepatocyte-like-cells resemble real hepatocytes. Finally, a summary is given of the state of the art of liver in vitro and mathematical modeling systems that are currently used in the pharmaceutical industry with an emphasis on drug metabolism, prediction of clearance, drug interaction, transporter studies and hepatotoxicity. One key message is that despite our enthusiasm for in vitro systems, we must never lose sight of the in vivo situation. Although hepatocytes have been isolated for decades, the hunt for relevant alternative systems has only just begun.

Transporters and drug-drug interactions: important determinants of drug disposition and effects

Uptake and efflux transporters determine plasma and tissue concentrations of a broad variety of drugs. They are localized in organs such as small intestine, liver, and kidney, which are critical for drug absorption and elimination. Moreover, they can be found in important blood-tissue barriers such as the blood-brain barrier. Inhibition or induction of drug transporters by coadministered drugs can alter pharmacokinetics and pharmacodynamics of the victim drugs. This review will summarize in particular clinically observed drug-drug interactions attributable to inhibition or induction of intestinal export transporters [P-glycoprotein (P-gp), breast cancer resistance protein (BCRP)], to inhibition of hepatic uptake transporters [organic anion transporting polypeptides (OATPs)], or to inhibition of transporter-mediated [organic anion transporters (OATs), organic cation transporter 2 (OCT2), multidrug and toxin extrusion proteins (MATEs), P-gp] renal secretion of xenobiotics. Available data on the impact of nutrition on transport processes as well as genotype-dependent, transporter-mediated drug-drug interactions will be discussed. We will also present and discuss data on the variable extent to which information on the impact of transporters on drug disposition is included in summaries of product characteristics of selected countries (SPCs). Further work is required regarding a better understanding of the role of the drug metabolism-drug transport interplay for drug-drug interactions and on the extrapolation of in vitro findings to the in vivo (human) situation.

Cytotoxicity, toxicity, and anticancer activity of Zingiber officinale Roscoe against cholangiocarcinoma

Cholangiocarcinoma (CCA) is an uncommon adenocarcinoma which arises from the epithelial cells of the bile ducts. The aim of the study was to investigate the cytotoxicity, toxicity, and anticancer activity of a crude ethanolic extract of ginger (Zingiber officinale Roscoe) against CCA. Cytotoxic activity against a CCA cell line (CL-6) was assessed by calcein-AM and Hoechst 33342 assays and anti-oxidant activity was evaluated using the DPPH assay. Investigation of apoptotic activity was performed by DNA fragmentation assay and induction of genes that may be involved in the resistance of CCA to anticancer drugs (MDR1, MRP1, MRP2, and MRP3) was examined by real-time PCR. To investigate anti-CCA activity in vivo, a total of 80 OV and nitrosamine (OV/ DMN)-induced CCA hamsters were fed with the ginger extract at doses of 1000, 3000, and 5000 mg/kg body weight daily or every alternate day for 30 days. Control groups consisting of 10 hamsters for each group were fed with 5-fluorouracil (positive control) or distilled water (untreated control). Median IC50 (concentration that inhibits cell growth by 50%) values for cytotoxicity and anti-oxidant activities of the crude ethanolic extract of ginger were 10.95, 53.15, and 27.86 μg/ml, respectively. More than ten DNA fragments were visualized and up to 7-9 fold up-regulation of MDR1 and MRP3 genes was observed following exposure to the ethanolic extract of ginger. Acute and subacute toxicity tests indicated absence of any significant toxicity at the maximum dose of 5,000 mg/kg body weight given by intragastric gavage. The survival time and survival rate of the CCA-bearing hamsters were significantly prolonged compared to the control group (median of 54 vs 17 weeks). Results from these in vitro and in vivo studies thus indicate promising anticancer activity of the crude ethanolic extract of ginger against CCA with the absence of any significant toxicity. Moreover, MDR1 and MRP3 may be involved in conferring resistance of CCA to the ginger extract.

Multidrug resistance associated proteins in multidrug resistance

Multidrug resistance proteins (MRPs) are members of the C family of a group of proteins named ATP-binding cassette (ABC) transporters. These ABC transporters together form the largest branch of proteins within the human body. The MRP family comprises of 13 members, of which MRP1 to MRP9 are the major transporters indicated to cause multidrug resistance in tumor cells by extruding anticancer drugs out of the cell. They are mainly lipophilic anionic transporters and are reported to transport free or conjugates of glutathione (GSH), glucuronate, or sulphate. In addition, MRP1 to MRP3 can transport neutral organic drugs in free form in the presence of free GSH. Collectively, MRPs can transport drugs that differ structurally and mechanistically, including natural anticancer drugs, nucleoside analogs, antimetabolites, and tyrosine kinase inhibitors. Many of these MRPs transport physiologically important anions such as leukotriene C4, bilirubin glucuronide, and cyclic nucleotides. This review focuses mainly on the physiological functions, cellular resistance characteristics, and probable in vivo role of MRP1 to MRP9.

Effect of ABCB1 and ABCC3 polymorphisms on osteosarcoma survival after chemotherapy: a pharmacogenetic study

BACKGROUND

Standard treatment for osteosarcoma patients consists of a combination of cisplatin, adriamycin, and methotrexate before surgical resection of the primary tumour, followed by postoperative chemotherapy including vincristine and cyclophosphamide. Unfortunately, many patients still relapse or suffer adverse events. We examined whether common germline polymorphisms in chemotherapeutic transporter and metabolic pathway genes of the drugs used in standard osteosarcoma treatment may predict treatment response.

METHODOLOGY/PRINCIPAL FINDINGS

In this study we screened 102 osteosarcoma patients for 346 Single Nucleotide Polymorphisms (SNPs) and 2 Copy Number Variants (CNVs) in 24 genes involved in the metabolism or transport of cisplatin, adriamycin, methotrexate, vincristine, and cyclophosphamide. We studied the association of the genotypes with tumour response and overall survival. We found that four SNPs in two ATP-binding cassette genes were significantly associated with overall survival: rs4148416 in ABCC3 (per-allele HR = 8.14, 95%CI = 2.73-20.2, p-value = 5.1×10⁻⁵), and three SNPs in ABCB1, rs4148737 (per-allele HR = 3.66, 95%CI = 1.85-6.11, p-value = 6.9×10⁻⁵), rs1128503 and rs10276036 (r² = 1, per-allele HR = 0.24, 95%CI = 0.11-0.47 p-value = 7.9×10⁻⁵). Associations with these SNPs remained statistically significant after correction for multiple testing (all corrected p-values [permutation test] ≤ 0.03).

CONCLUSIONS

Our findings suggest that these polymorphisms may affect osteosarcoma treatment efficacy. If these associations are independently validated, these variants could be used as genetic predictors of clinical outcome in the treatment of osteosarcoma, helping in the design of individualized therapy.

ATP-binding cassette efflux transporters in human placenta

Pregnant women are often complicated with diseases including viral or bacterial infections, epilepsy, hypertension, or pregnancy-induced conditions such as depression and gestational diabetes that require treatment with medication. In addition, substance abuse during pregnancy remains a major public health problem. Many drugs used by pregnant women are off label without the necessary dose, efficacy, and safety data required for rational dosing regimens of these drugs. Thus, a major concern arising from the widespread use of drugs by pregnant women is the transfer of drugs across the placental barrier, leading to potential toxicity to the developing fetus. Knowledge regarding the ATP-binding cassette (ABC) efflux transporters, which play an important role in drug transfer across the placental barrier, is absolutely critical for optimizing the therapeutic strategy to treat the mother while protecting the fetus during pregnancy. Such transporters include P-glycoprotein (P-gp, gene symbol ABCB1), the breast cancer resistance protein (BCRP, gene symbol ABCG2), and the multidrug resistance proteins (MRPs, gene symbol ABCCs). In this review, we summarize the current knowledge with respect to developmental expression and regulation, membrane localization, functional significance, and genetic polymorphisms of these ABC transporters in the placenta and their relevance to fetal drug exposure and toxicity.

Multidrug resistance proteins (MRPs/ABCCs) in cancer chemotherapy and genetic diseases

The ATP-binding cassette (ABC) transporters are a superfamily of membrane proteins that are best known for their ability to transport a wide variety of exogenous and endogenous substances across membranes against a concentration gradient via ATP hydrolysis. There are seven subfamilies of human ABC transporters, one of the largest being the 'C' subfamily (gene symbol ABCC). Nine ABCC subfamily members, the so-called multidrug resistance proteins (MRPs) 1-9, have been implicated in mediating multidrug resistance in tumor cells to varying degrees as the efflux extrude chemotherapeutic compounds (or their metabolites) from malignant cells. Some of the MRPs are also known to either influence drug disposition in normal tissues or modulate the elimination of drugs (or their metabolites) via hepatobiliary or renal excretory pathways. In addition, the cellular efflux of physiologically important organic anions such as leukotriene C(4) and cAMP is mediated by one or more of the MRPs. Finally, mutations in several MRPs are associated with human genetic disorders. In this minireview, the current biochemical and physiological knowledge of MRP1-MRP9 in cancer chemotherapy and human genetic disease is summarized. The mutations in MRP2/ABCC2 leading to conjugated hyperbilirubinemia (Dubin-Johnson syndrome) and in MRP6/ABCC6 leading to the connective tissue disorder Pseudoxanthoma elasticum are also discussed.

Resveratrol inhibits genistein-induced multi-drug resistance protein 2 (MRP2) expression in HepG2 cells

The interactions between various dietary cancer chemopreventive phytochemicals in drug transporter functions are not well studied. In this study, the effects of genistein and resveratrol on the multidrug resistance protein 2 (MRP2) expression and the underlying molecular mechanisms were investigated using HepG2-C3 cells that are stably transfected with a construct containing human MRP2 promoter region conjugated with luciferase reporter gene. A 3-fold induction of MRP2 luciferase activity was observed after genistein (50μM) treatment to HepG2-C3 cells, but was diminished by the resveratrol (50μM) cotreatment. This observation was further validated by Western blot analysis and RT-PCR analysis as resveratrol also inhibited genistein-induced MRP2 protein synthesis and mRNA expression. Immunofluorescence study revealed that genistein-induced formation of MRP2 vacuoles was dramatically reduced by resveratrol. The binding affinity between retinoid X receptor alpha (RXRα) and MRP2 promoter was examined by DNA-protein pull-down assay. The results showed that resveratrol inhibited the genistein-induced binding of RXRα to the promoter sequence of MRP2 gene, and this mechanism could potentially contribute to the inhibition of genistein-induced MRP2 expression by resveratrol. Taken together, our present study suggests that naturally occurring phytochemicals can potentially interfere with each other's regulatory function on the cancer chemoprevention-related genes through a competitive mechanism.

Multidrug resistance proteins (MRPs, ABCCs): importance for pathophysiology and drug therapy

The nine multidrug resistance proteins (MRPs) represent the major part of the 12 members of the MRP/CFTR subfamily belonging to the 48 human ATP-binding cassette (ABC) transporters. Cloning, functional characterization, and cellular localization of most MRP subfamily members have identified them as ATP-dependent efflux pumps with a broad substrate specificity for the transport of endogenous and xenobiotic anionic substances localized in cellular plasma membranes. Prototypic substrates include glutathione conjugates such as leukotriene C(4) for MRP1, MRP2, and MRP4, bilirubin glucuronosides for MRP2 and MRP3, and cyclic AMP and cyclic GMP for MRP4, MRP5, and MRP8. Reduced glutathione (GSH), present in living cells at millimolar concentrations, modifies the substrate specificities of several MRPs, as exemplified by the cotransport of vincristine with GSH by MRP1, or by the cotransport of GSH with bile acids or of GSH with leukotriene B(4) by MRP4.The role of MRP subfamily members in pathophysiology may be illustrated by the MRP-mediated release of proinflammatory and immunomodulatory mediators such as leukotrienes and prostanoids. Pathophysiological consequences of many genetic variants leading to a lack of functional MRP protein in the plasma membrane are observed in the hereditary MRP2 deficiency associated with conjugated hyperbilirubinemia in Dubin-Johnson syndrome, in pseudoxanthoma elasticum due to mutations in the MRP6 (ABCC6) gene, or in the type of human earwax and osmidrosis determined by single nucleotide polymorphisms in the MRP8 (ABCC8) gene. The hepatobiliary and renal elimination of many drugs and their metabolites is mediated by MRP2 in the hepatocyte canalicular membrane and by MRP4 as well as MRP2 in the luminal membrane of kidney proximal tubules. Therefore, inhibition of these efflux pumps affects pharmacokinetics, unless compensated by other ATP-dependent efflux pumps with overlapping substrate specificities.

MRP3: a molecular target for human glioblastoma multiforme immunotherapy

Background

Glioblastoma multiforme (GBM) is refractory to conventional therapies. To overcome the problem of heterogeneity, more brain tumor markers are required for prognosis and targeted therapy. We have identified and validated a promising molecular therapeutic target that is expressed by GBM: human multidrug-resistance protein 3 (MRP3).

Methods

We investigated MRP3 by genetic and immunohistochemical (IHC) analysis of human gliomas to determine the incidence, distribution, and localization of MRP3 antigens in GBM and their potential correlation with survival. To determine MRP3 mRNA transcript and protein expression levels, we performed quantitative RT-PCR, raising MRP3-specific antibodies, and IHC analysis with biopsies of newly diagnosed GBM patients. We used univariate and multivariate analyses to assess the correlation of RNA expression and IHC of MRP3 with patient survival, with and without adjustment for age, extent of resection, and KPS.

Results

Real-time PCR results from 67 GBM biopsies indicated that 59/67 (88%) samples highly expressed MRP3 mRNA transcripts, in contrast with minimal expression in normal brain samples. Rabbit polyvalent and murine monoclonal antibodies generated against an extracellular span of MRP3 protein demonstrated reactivity with defined MRP3-expressing cell lines and GBM patient biopsies by Western blotting and FACS analyses, the latter establishing cell surface MRP3 protein expression. IHC evaluation of 46 GBM biopsy samples with anti-MRP3 IgG revealed MRP3 in a primarily membranous and cytoplasmic pattern in 42 (91%) of the 46 samples. Relative RNA expression was a strong predictor of survival for newly diagnosed GBM patients. Hazard of death for GBM patients with high levels of MRP3 RNA expression was 2.71 (95% CI: 1.54-4.80) times that of patients with low/moderate levels (p = 0.002).

Conclusions

Human GBMs overexpress MRP3 at both mRNA and protein levels, and elevated MRP3 mRNA levels in GBM biopsy samples correlated with a higher risk of death. These data suggest that the tumor-associated antigen MRP3 has potential use for prognosis and as a target for malignant glioma immunotherapy.

Drug transporter pharmacogenetics in nucleoside-based therapies

This article focuses on the different types of transporter proteins that have been implicated in the influx and efflux of nucleoside-derived drugs currently used in the treatment of cancer, viral infections (i.e., AIDS) and other conditions, including autoimmune and inflammatory diseases. Genetic variations in nucleoside-derived drug transporter proteins encoded by the gene families SLC15, SLC22, SLC28, SLC29, ABCB, ABCC and ABCG will be specifically considered. Variants known to affect biological function are summarized, with a particular emphasis on those for which clinical correlations have already been established. Given that relatively little is known regarding the genetic variability of the players involved in determining nucleoside-derived drug bioavailability, it is anticipated that major challenges will be faced in this area of research.

Xenobiotic, bile acid, and cholesterol transporters: function and regulation

Transporters influence the disposition of chemicals within the body by participating in absorption, distribution, and elimination. Transporters of the solute carrier family (SLC) comprise a variety of proteins, including organic cation transporters (OCT) 1 to 3, organic cation/carnitine transporters (OCTN) 1 to 3, organic anion transporters (OAT) 1 to 7, various organic anion transporting polypeptide isoforms, sodium taurocholate cotransporting polypeptide, apical sodium-dependent bile acid transporter, peptide transporters (PEPT) 1 and 2, concentrative nucleoside transporters (CNT) 1 to 3, equilibrative nucleoside transporter (ENT) 1 to 3, and multidrug and toxin extrusion transporters (MATE) 1 and 2, which mediate the uptake (except MATEs) of organic anions and cations as well as peptides and nucleosides. Efflux transporters of the ATP-binding cassette superfamily, such as ATP-binding cassette transporter A1 (ABCA1), multidrug resistance proteins (MDR) 1 and 2, bile salt export pump, multidrug resistance-associated proteins (MRP) 1 to 9, breast cancer resistance protein, and ATP-binding cassette subfamily G members 5 and 8, are responsible for the unidirectional export of endogenous and exogenous substances. Other efflux transporters [ATPase copper-transporting beta polypeptide (ATP7B) and ATPase class I type 8B member 1 (ATP8B1) as well as organic solute transporters (OST) alpha and beta] also play major roles in the transport of some endogenous chemicals across biological membranes. This review article provides a comprehensive overview of these transporters (both rodent and human) with regard to tissue distribution, subcellular localization, and substrate preferences. Because uptake and efflux transporters are expressed in multiple cell types, the roles of transporters in a variety of tissues, including the liver, kidneys, intestine, brain, heart, placenta, mammary glands, immune cells, and testes are discussed. Attention is also placed upon a variety of regulatory factors that influence transporter expression and function, including transcriptional activation and post-translational modifications as well as subcellular trafficking. Sex differences, ontogeny, and pharmacological and toxicological regulation of transporters are also addressed. Transporters are important transmembrane proteins that mediate the cellular entry and exit of a wide range of substrates throughout the body and thereby play important roles in human physiology, pharmacology, pathology, and toxicology.

Update information on drug metabolism systems--2009, part II: summary of information on the effects of diseases and environmental factors on human cytochrome P450 (CYP) enzymes and transporters

The present paper is an update of the data on the effects of diseases and environmental factors on the expression and/or activity of human cytochrome P450 (CYP) enzymes and transporters. The data are presented in tabular form (Tables 1 and 2) and are a continuation of previously published summaries on the effects of drugs and other chemicals on CYP enzymes (Rendic, S.; Di Carlo, F. Drug Metab. Rev., 1997, 29(1-2), 413-580., Rendic, S. Drug Metab. Rev., 2002, 34(1-2), 83-448.). The collected information presented here is as stated by the cited author(s), and in cases when several references are cited the latest published information is included. Inconsistent results and conclusions obtained by different authors are highlighted, followed by discussion of the major findings. The searchable database is available as an Excel file, for information about file availability contact the corresponding author.

The membrane-bound bile acid receptor TGR5 is localized in the epithelium of human gallbladders

TGR5 (Gpbar-1) is a plasma membrane-bound, G protein-coupled receptor for bile acids. TGR5 messenger RNA (mRNA) has been detected in many tissues, including rat cholangiocytes and mouse gallbladder. A role for TGR5 in gallstone formation has been suggested, because TGR5 knockout mice did not develop gallstones when fed a lithogenic diet. In this study, expression and localization of TGR5 was studied in human gallbladders. TGR5 mRNA and protein were detected in all 19 gallbladders. Although TGR5 mRNA was significantly elevated in the presence of gallstones, no such relation was found for TGR5 protein levels. In order to study the localization of TGR5 in human gallbladders, a novel antibody was generated. The receptor was localized in the apical membrane and the rab11-positive recycling endosome of gallbladder epithelial cells. Furthermore, the TGR5 staining colocalized with the cyclic adenosine monophosphate-regulated chloride channel cystic fibrosis transmembrane conductance regulator (CFTR) and the apical sodium-dependent bile salt uptake transporter, suggesting a functional coupling of TGR5 to bile acid uptake and chloride secretion. Stimulation with bile acids significantly increased cyclic adenosine monophosphate concentration in human gallbladder tissue. Incubation of gallbladder epithelial cells with a TGR5 agonist led to a rise of N-(ethoxycarbonylmethyl)-6-methoxyquinolinium bromide (MQAE)-fluorescence, suggestive of a decrease in intracellular chloride concentration. The TGR5 agonist-dependent increase in MQAE-fluorescence was absent in TGR5 knockout mice or in the presence of a CFTR inhibitor, indicating that TGR5 mediates chloride secretion via activation of CFTR. The presence of the receptor in both the plasma membrane and the recycling endosome indicate that TGR5 can be regulated by translocation.

CONCLUSION

The data suggest a role for TGR5 in bile acid-induced fluid secretion in biliary epithelial cells.

Modulation of Oral Drug Bioavailability: From Preclinical Mechanism to Therapeutic Application

Currently, more than one fourth of all anticancer drugs are developed as oral formulations, and it is expected that this number will increase substantially in the near future. To enable oral drug therapy, adequate oral bioavailability must be achieved. Factors that have proved to be important in limiting the oral bioavailability are the presence of ATP-binding cassette drug transporters (ABC transporters) and the cytochrome P450 enzymes. We discuss the tissues distribution and physiological function of the ABC transporters in the human body, their expression in tumors, currently known polymorphisms and drugs that are able to inhibit their function as transporter. Furthermore, the role of the ABC transporters and drug-metabolizing enzymes as mechanisms to modulate the pharmacokinetics of anticancer agents, will be reviewed. Finally, some clinical examples of oral drug modulation are discussed. Among these examples are the coadministration of paclitaxel with CsA, a CYP3A4 substrate with P-glycoprotein (P-gp) modulating activity, and topotecan combined with the BCRP/P-gp transport inhibitor elacridar. Both are good examples of improvement of oral drug bioavailability by temporary inhibition of drug transporters in the gut epithelium.

Interplay of conjugating enzymes with OATP uptake transporters and ABCC/MRP efflux pumps in the elimination of drugs

BACKGROUND

Biliary excretion is a major elimination route of many drugs and their metabolites. Hepatobiliary elimination is a vectorial process involving uptake transporters in the basolateral hepatocyte membrane, possibly Phase I and Phase II metabolizing enzymes, and ATP-dependent efflux pumps in the apical hepatocyte membrane.

OBJECTIVES

Because many drugs and their metabolites are anions, this review focuses on transporters involved in their hepatocellular uptake (members of the organic anion transporting polypeptide (OATP) family) and biliary elimination (apical conjugate efflux pump ABCC2/MRP2).

METHODS

The molecular and functional characteristics of the human OATP and ABCC/MRP transporters are presented, including a detailed overview of endogenous and drug substrates. Examples illustrate the interplay of transporters with Phase II conjugating enzymes. Model systems to study the vectorial transport of organic anions are also discussed.

RESULTS/CONCLUSIONS

OATP uptake transporters, conjugating enzymes, and ABCC2/MRP2 work in concert to enable the hepatobiliary elimination of anionic drugs and their metabolites. It is increasingly important to understand how genetic variants of these transporters and enzymes influence the interindividual variability of drug elimination.

Expression of estrogen-metabolizing enzymes and estrogen receptors in cholelithiasis gallbladder

BACKGROUND

Estrogen exposure is a risk factor for gallstone disease (cholelithiasis), which often leads to chronic inflammation (cholecystitis). Studies in various estrogen-sensitive tissues showed that key enzymes involved in the inactivation and activation of estrogens as well as expression of estrogen receptors alpha and beta determine the amount of active estrogen. In estrogen-sensitive tissues, e.g. the female breast, estrone sulfate (E1S), present at high concentrations in the circulation, is converted into the biologically active estrone (E1) by steroid sulfatase (STS) and again reverted into E1S by estrogen sulfotransferase (SULT1E1) providing a local estrogen storage.

AIMS

To assess whether this might also apply for gallbladder epithelia, we determined expression of these two enzymes and of ERalpha and ERbeta in 15 cholelithiasis specimens from tissues with/or without inflammation.

METHODS

Quantitative (Real-time) PCR and immunofluorescence were used as methods.

RESULTS

We demonstrate mRNA expression of SULT1E1, STS, and ERalpha in all specimens with mean enrichment of 3.53- vs. 1.72-fold (n.s.), 3.5- vs. 0.91-fold (n.s.), and 3.04- vs. 1.6-fold (n.s.) in the inflammatory and non-inflammatory groups, respectively. Although high expression levels were seen in many specimens (means 4.88-fold vs. 5.77-fold), ERbeta mRNA was below the detection limit in two specimens from cholecystitis patients. To further investigate this varying expression pattern of ERbeta, immunohistological studies were performed, which indeed showed low expression levels of ERbeta in the damaged mucosa, while in specimens with well preserved mucosa, high ERbeta levels were seen in the cytosol and in the nucleus.

CONCLUSION

The data show expression of an estrogen network of activating STS and inactivating SULT1E1. Together with ERalpha and ERbeta, these enzymes could regulate estrogen concentrations in human gallbladder.

Expression of the multidrug resistance proteins MRP2 and MRP3 in human cholangiocellular carcinomas

BACKGROUND

Cholangiocellular carcinomas and gallbladder carcinomas are highly aggressive tumours with a poor prognosis and are generally regarded as chemoresistant tumours. Overexpression of ATP-binding cassette transporters of the multidrug resistance protein (MDR) and multidrug resistance-related protein (MRP) family in cancer cells is a major cause for the multidrug resistance phenotype in vitro and in vivo. To further define the role of MRP family members in biliary tract cancer, we studied the expression and localization of MRP2 and MRP3 in cholangiocellular carcinomas and gallbladder carcinomas.

MATERIALS AND METHODS

The expression and cellular localization of the multidrug resistance proteins MRP2 and MRP3 in human cholangiocellular carcinomas and gallbladder carcinomas were analysed by immunohistochemistry using isoform-specific antibodies. Expression of MRP isoforms was studied in vitro in Mz-ChA-1 cells derived from gallbladder adenocarcinoma by reverse transcription-polymerase chain reaction (RT-PCR), immunoblotting and immunofluorescence microscopy.

RESULTS

Mz-ChA-1 cells constitutively expressed MDR P-glycoproteins, MRP1, MRP2 and MRP3 by RT-PCR, immunoblotting and immunofluorescence microscopy. MRP2 and MRP3 are expressed in the respective apical and basolateral membrane domains. MRP3 was the predominant MRP isoform in gallbladder carcinomas (93%) and cholangiocellular carcinomas (57%), whereas MRP2 expression was detected in only 29% of gallbladder carcinomas and was undetectable in cholangiocellular carcinomas.

CONCLUSIONS

Our findings suggest that the intrinsic multidrug resistance of cholangiocellular and gallbladder carcinomas seems to be independent of MRP2 expression while the expression of MRP3 may contribute to the MDR phenotype.

ABCC2 (MRP2, cMOAT) can be localized in the nuclear membrane of ovarian carcinomas and correlates with resistance to cisplatin and clinical outcome

PURPOSE

Cisplatin resistance is a major obstacle in the treatment of ovarian carcinoma. ABCC2 is commonly localized in apical cell membranes and could confer cisplatin resistance. Here, we show that ABCC2 can be localized in the cytoplasmic membrane as well as in the nuclear membrane of various human tissues including ovarian carcinoma cells.

EXPERIMENTAL DESIGN

For the subcellular detection of ABCC2, immunohistochemistry was done using 41 Federation Internationale des Gynaecologistes et Obstetristes stage III ovarian carcinoma specimens prepared before treatment with cisplatin-based schemes and 35 specimens from the same group after chemotherapy. Furthermore, 11 ovarian carcinoma cell lines as well as tissue microarrays consisting of various human tissues were analyzed.

RESULTS

Nuclear membranous localization of ABCC2 was associated with response to first-line chemotherapy at primary (P = 0.0013) and secondary surgery (P = 0.0060). Cases with relapse showed higher nuclear membrane expression at primary (P = 0.0003) and secondary surgery (P = 0.0024). Kaplan-Meier analyses showed that weak nuclear membrane ABCC2 expression before treatment was associated with significantly longer overall (P = 0.04) and progression-free survival (P = 0.001); following chemotherapy, it correlated with significantly longer progression-free survival (P = 0.038). Tissue microarrays confirmed nuclear membranous localization of ABCC2, in particular, in poorly differentiated cells. In ovarian carcinoma cells, it correlated with resistance against cisplatin, whereas localization in the cytoplasmic membrane did not.

CONCLUSIONS

ABCC2 confers resistance to cisplatin of ovarian carcinoma in cell culture systems and in clinics when expressed in the nuclear membrane. Thus, ABCC2 localization can predict platinum therapy outcome. Furthermore, expression of ABCC2 in nuclear membranes in human tissues is specific for poorly differentiated cells including stem cells.

Literature-based compound profiling: application to toxicogenomics

Introduction: To reduce continuously increasing costs in drug development, adverse effects of drugs need to be detected as early as possible in the process. In recent years, compound-induced gene expression profiling methodologies have been developed to assess compound toxicity, including Gene Ontology term and pathway over-representation analyses. The objective of this study was to introduce an additional approach, in which literature information is used for compound profiling to evaluate compound toxicity and mode of toxicity. Methods: Gene annotations were built by text mining in Medline abstracts for retrieval of co-publications between genes, pathology terms, biological processes and pathways. This literature information was used to generate compound-specific keyword fingerprints, representing over-represented keywords calculated in a set of regulated genes after compound administration. To see whether keyword fingerprints can be used for assessment of compound toxicity, we analyzed microarray data sets of rat liver treated with 11 hepatotoxicants. Results: Analysis of keyword fingerprints of two genotoxic carcinogens, two nongenotoxic carcinogens, two peroxisome proliferators and two randomly generated gene sets, showed that each compound produced a specific keyword fingerprint that correlated with the experimentally observed histopathological events induced by the individual compounds. By contrast, the random sets produced a flat aspecific keyword profile, indicating that the fingerprints induced by the compounds reflect biological events rather than random noise. A more detailed analysis of the keyword profiles of diethylhexylphthalate, dimethylnitrosamine and methapyrilene (MPy) showed that the differences in the keyword fingerprints of these three compounds are based upon known distinct modes of action. Visualization of MPy-linked keywords and MPy-induced genes in a literature network enabled us to construct a mode of toxicity proposal for MPy, which is in agreement with known effects of MPy in literature. Conclusion: Compound keyword fingerprinting based on information retrieved from literature is a powerful approach for compound profiling, allowing evaluation of compound toxicity and analysis of the mode of action.

Cholesterol gallstones and cancer of gallbladder (CAGB): molecular links

There is a known association between cholesterol gallstones and cancer of gall bladder (CAGB). However, the exact relation is not clear. It is proposed they are linked at molecular level by the activity of the orphan nuclear receptors (ONRs) and ABC transporter pumps involved in cholesterol and xenobiotic efflux from the liver into bile. There is evidence that these two pathways are closely interlinked and influence each other. Genetic and environmental factors that upregulate these systems can lead to the simultaneous pumping of cholesterol (which precipitate as gallstones) and a food carcinogen into the bile in gall bladder; the latter causes malignant transformation. Aflatoxin B, a potent hepatocarcinogen, could be the culprit in endemic regions such as South America and North India.

Structure and function of the MRP2 (ABCC2) protein and its role in drug disposition

The multi-drug resistance protein 2 (MRP2; ABCC2) is an ATP-binding cassette transporter playing an important role in detoxification and chemoprotection by transporting a wide range of compounds, especially conjugates of lipophilic substances with glutathione, glucuronate and sulfate, which are collectively known as phase II products of biotransformation. In addition, MRP2 can also transport uncharged compounds in cotransport with glutathione, and thus can modulate the pharmacokinetics of many drugs. The other way around, its expression and activity are also altered by certain drugs and disease states. Unlike other members of the MRP/ABCC family, MRP2 is specifically expressed on the apical membrane domain of polarised cells as hepatocytes, renal proximal tubular cells, enterocytes and syncytiotrophoblasts of the placenta. Several naturally occurring mutations leading to the absence of functional MRP2 protein from the apical membrane have been described causing the human Dubin-Johnson syndrome associated with conjugated hyperbilirubinaemia. Experimental mutation studies have revealed critical amino acids for substrate binding in the MRP2 molecule. This review is, therefore, focused on the structure and function of MRP2, the substrates transported and the clinical relevance of MRP2.

Tannic acid synergizes the cytotoxicity of chemotherapeutic drugs in human cholangiocarcinoma by modulating drug efflux pathways

BACKGROUND/AIMS

Tannic acid is an orally active plant polyphenol with potential for use as an anti-cancer agent for cholangiocarcinoma. To determine the potential use of tannic acid as an adjunct therapy, we sought to evaluate the interaction between tannic acid and chemotherapeutic agents.

METHODS

Cytotoxicity was assessed in malignant human cholangiocytes. Interactions between tannic acid, mitomycin C, 5-fluorouracil and gemcitabine were quantitated by calculating the combination index and dose reduction index. Cellular efflux pathways were assessed by calcein retention assays, and expression of membrane pumps was assessed by Western blots and real-time PCR.

RESULTS

Tannic acid and the three agents decreased growth of malignant cholangiocytes to a similar extent. Tannic acid had a synergistic effect to mitomycin C and 5-fluorouracil, but not gemcitabine. However, the structurally related polyphenol gallic acid did not have a synergistic interaction with any of the agents. Tannic acid decreased calcein efflux and the expression of PGP, MRP1 and MRP2 membrane efflux pumps.

CONCLUSIONS

Tannic acid has a synergistic effect with selected chemotherapeutic drugs by a mechanism involving modulation of drug efflux pathways. Thus, tannic acid will be a useful adjunct to improve the effectiveness of chemotherapeutic agents in the treatment of cholangiocarcinoma.

Functional analysis of the polymorphism -211C>T in the regulatory region of the human ABCC3 gene

The multidrug resistance protein 3 (MRP3/gene symbol: ABCC3) is an ATP-dependent efflux pump mediating the transport of endogenous glucuronides and conjugated drug metabolites across cell membranes. In humans the hepatic expression of ABCC3 mRNA seems to be influenced by the polymorphism C>T at the position -211 in the promoter of the ABCC3 gene. The aim of this study was to investigate the possible mechanisms of how this SNP influences the MRP3 expression. Promoter luciferase reporter gene constructs representing 0.5, 1.1, 4.4, and 8.1 kb upstream of the translational start site were cloned with cytosine or thymine at position -211 and transfected into HepG2, Caco-2, and LS174T cells. Reporter gene activity was dependent on the length of the promoter sequence but interestingly not on the nucleotide at position -211. Cotransfection with FTF cDNA (Fetoprotein Transcription Factor) binding to elements near the -211 polymorphism increased promoter activity in all constructs except the 0.5 kb fragment also independently of the -211 SNP. Taken together, we did not find any influence of the -211C>T ABCC3 promoter polymorphism on either the basal or the FTF induced reporter gene activity. Whether other tissue specific mechanisms reveal an impact of this SNP on the in vivo regulation of MRP3 remains to be determined.

Hepatobiliary transporters and drug-induced cholestasis

Drug-induced liver injury is an important clinical problem with significant morbidity and mortality. Whereas for most hepatocellular forms of drug-induced hepatic injury the underlying pathophysiological mechanism is poorly understood, there is increasing evidence that cholestatic forms of drug-induced liver damage result from a drug- or metabolite-mediated inhibition of hepatobiliary transporter systems. In addition to their key role in determining hepatic drug exposure and clearance, the coordinated action of these transport systems is essential for bile formation and the biliary secretion of cholephilic compounds and xenobiotics. Any drug-mediated functional disturbance of these processes can lead to an intracellular accumulation of potentially harmful bile constituents and result in the development of cholestatic liver cell damage. In addition to direct drug-mediated inhibition of hepatocellular transport, function of these transporters can be altered by pre-existing hepatic disease and genetic factors, which contribute to the development of drug-induced cholestasis in susceptible individuals. This review summarizes current knowledge about the function of hepatobiliary uptake and efflux systems and discusses factors that might predispose to drug-induced cholestasis.

The apical conjugate efflux pump ABCC2 (MRP2)

ABCC2 is a member of the multidrug resistance protein subfamily localized exclusively to the apical membrane domain of polarized cells, such as hepatocytes, renal proximal tubule epithelia, and intestinal epithelia. This localization supports the function of ABCC2 in the terminal excretion and detoxification of endogenous and xenobiotic organic anions, particularly in the unidirectional efflux of substances conjugated with glutathione, glucuronate, or sulfate, as exemplified by leukotriene C(4), bilirubin glucuronosides, and some steroid sulfates. The hepatic ABCC2 pump contributes to the driving forces of bile flow. Acquired or hereditary deficiency of ABCC2, the latter known as Dubin-Johnson syndrome in humans, causes an increased concentration of bilirubin glucuronosides in blood because of their efflux from hepatocytes via the basolateral ABCC3, which compensates for the deficiency in ABCC2-mediated apical efflux. In this article we provide an overview on the molecular characteristics of ABCC2 and its expression in various tissues and species. We discuss the transcriptional and posttranscriptional regulation of ABCC2 and review approaches to the functional analysis providing information on its substrate specificity. A comprehensive list of sequence variants in the human ABCC2 gene summarizes predicted and proven functional consequences, including variants leading to Dubin-Johnson syndrome.

Characterization of mice lacking the multidrug resistance protein MRP2 (ABCC2)

The multidrug resistance protein Mrp2 is an ATP-binding cassette (ABC) transporter mainly expressed in liver, kidney, and intestine. One of the physiological roles of Mrp2 is to transport bilirubin glucuronides from the liver into the bile. Current in vivo models to study Mrp2 are the transporter-deficient and Eisai hyperbilirubinemic rat strains. Previous reports showed hyperbilirubinemia and induction of Mrp3 in the hepatocyte sinusoidal membrane in the mutant rats. In addition, differences in liver cytochrome P450 and UGT1a levels between wild-type and mutant rats were detected. To study whether these compensatory mechanisms were specific to rats, we characterized Mrp2(-/-) mice. Functional absence of Mrp2 in the knockout mice was demonstrated by showing increased levels of bilirubin and bilirubin glucuronides in serum and urine, a reduction in biliary excretion of bilirubin glucuronides and total glutathione, and a reduction in the biliary excretion of the Mrp2 substrate dibromosulfophthalein. To identify possible compensatory mechanisms in Mrp2(-/-) mice, the expression levels of 98 phase I, phase II, and transporter genes were compared in liver, kidney, and intestine of male and female Mrp2(-/-) and control mice. Unlike in Mrp2 mutant rats, no induction of Mrp3 in Mrp2(-/-) mice was detected. However, Mrp4 mRNA and protein in liver and kidney were increased approximately 6- and 2-fold, respectively. Phenotypic analysis of major cytochrome P450-mediated activities in liver microsomes did not show differences between wild-type and Mrp2(-/-) mice. In conclusion, Mrp2(-/-) mice are a new valuable tool to study the role of Mrp2 in drug disposition.