Diagnostic and prognostic biomarkers in cholangiocarcinoma

The high mortality rate of cholangiocarcinoma (CCA) is due, in part, to the lack of non-invasive approaches able to accurately detect this silent tumour at early stages, when therapeutic options can be potentially curative or may at least increase the overall survival of patients. The fact that the majority of CCA tumours are not linked to any known aetiological factor highly compromises the monitoring of patients at risk for tumour development and also their early diagnosis. Combination of clinical/biochemical features, imaging techniques and analysis of non-specific tumour biomarkers in serum are commonly used to help in the diagnosis of CCA, but tumour biopsy is usually required to confirm the diagnosis. Moreover, no prognostic biomarkers are currently used in the clinical setting, deserving more innovative research, and international validation and consensus. Important efforts have been made in the last few years to identify accurate non-invasive biomarkers, by using innovative techniques and high-throughput omics technologies. This review summarizes and discusses the advances in the investigation of novel diagnostic and prognostic biomarkers in CCA and envisions the future directions in this field of research.

Association of adverse perinatal outcomes of intrahepatic cholestasis of pregnancy with biochemical markers: results of aggregate and individual patient data meta-analyses

BACKGROUND

Intrahepatic cholestasis of pregnancy is associated with adverse perinatal outcomes, but the association with the concentration of specific biochemical markers is unclear. We aimed to quantify the adverse perinatal effects of intrahepatic cholestasis of pregnancy in women with increased serum bile acid concentrations and determine whether elevated bile acid concentrations were associated with the risk of stillbirth and preterm birth.

METHODS

We did a systematic review by searching PubMed, Web of Science, and Embase databases for studies published from database inception to June 1, 2018, reporting perinatal outcomes for women with intrahepatic cholestasis of pregnancy when serum bile acid concentrations were available. Inclusion criteria were studies defining intrahepatic cholestasis of pregnancy based upon pruritus and elevated serum bile acid concentrations, with or without raised liver aminotransferase concentrations. Eligible studies were case-control, cohort, and population-based studies, and randomised controlled trials, with at least 30 participants, and that reported bile acid concentrations and perinatal outcomes. Studies at potential higher risk of reporter bias were excluded, including case reports, studies not comprising cohorts, or successive cases seen in a unit; we also excluded studies with high risk of bias from groups selected (eg, a subgroup of babies with poor outcomes were explicitly excluded), conference abstracts, and Letters to the Editor without clear peer review. We also included unpublished data from two UK hospitals. We did a random effects meta-analysis to determine risk of adverse perinatal outcomes. Aggregate data for maternal and perinatal outcomes were extracted from case-control studies, and individual patient data (IPD) were requested from study authors for all types of study (as no control group was required for the IPD analysis) to assess associations between biochemical markers and adverse outcomes using logistic and stepwise logistic regression. This study is registered with PROSPERO, number CRD42017069134.

FINDINGS

We assessed 109 full-text articles, of which 23 studies were eligible for the aggregate data meta-analysis (5557 intrahepatic cholestasis of pregnancy cases and 165 136 controls), and 27 provided IPD (5269 intrahepatic cholestasis of pregnancy cases). Stillbirth occurred in 45 (0·83%) of 4936 intrahepatic cholestasis of pregnancy cases and 519 (0·32%) of 163 947 control pregnancies (odds ratio [OR] 1·46 [95% CI 0·73-2·89]; I2=59·8%). In singleton pregnancies, stillbirth was associated with maximum total bile acid concentration (area under the receiver operating characteristic curve [ROC AUC]) 0·83 [95% CI 0·74-0·92]), but not alanine aminotransferase (ROC AUC 0·46 [0·35-0·57]). For singleton pregnancies, the prevalence of stillbirth was three (0·13%; 95% CI 0·02-0·38) of 2310 intrahepatic cholestasis of pregnancy cases in women with serum total bile acids of less than 40 μmol/L versus four (0·28%; 0·08-0·72) of 1412 cases with total bile acids of 40-99 μmol/L (hazard ratio [HR] 2·35 [95% CI 0·52-10·50]; p=0·26), and versus 18 (3·44%; 2·05-5·37) of 524 cases for bile acids of 100 μmol/L or more (HR 30·50 [8·83-105·30]; p<0·0001).

INTERPRETATION

The risk of stillbirth is increased in women with intrahepatic cholestasis of pregnancy and singleton pregnancies when serum bile acids concentrations are of 100 μmol/L or more. Because most women with intrahepatic cholestasis of pregnancy have bile acids below this concentration, they can probably be reassured that the risk of stillbirth is similar to that of pregnant women in the general population, provided repeat bile acid testing is done until delivery.

FUNDING

Tommy's, ICP Support, UK National Institute of Health Research, Wellcome Trust, and Genesis Research Trust.

Epigenetic events involved in organic cation transporter 1-dependent impaired response of hepatocellular carcinoma to sorafenib

BACKGROUND AND PURPOSE

The expression of the human organic cation transporter-1 (hOCT1, gene SLC22A1) is reduced in hepatocellular carcinoma (HCC). The molecular bases of this reduction and its relationship with the poor response of HCC to sorafenib were investigated.

EXPERIMENTAL APPROACH

HCC transcriptomes from 366 samples available at TCGA were analysed. Alternative splicing was determined by RT-PCR. The role of miRNAs in SLC22A1 downregulation was investigated. Expression of Oct1 was measured in rodent HCC models (spontaneously generated in Fxr^-/- mice and chemically-induced in rats). hOCT1 was overexpressed in human hepatoma cells (HuH7 and HepG2). Sorafenib and regorafenib uptake was determined by HPLC-MS/MS.

KEY RESULTS

hOCT1 overexpression enhanced sorafenib, but not regorafenib, quinine-inhibitable uptake by hepatoma cells. In rodent HCC, Oct1 was downregulated, which was accompanied by impaired sorafenib uptake. In mice with s.c.-implanted HCC, sorafenib inhibited the growth of hOCT1 overexpressing tumours. In human HCC, hOCT1 expression was inversely correlated with SLC22A1 promoter methylation, whereas demethylation with decitabine enhanced hOCT1 expression in hepatoma cells. Increased proportion of aberrant hOCT1 mRNA variants was found in HCC samples. In silico analysis identified six miRNAs as candidates to target hOCT1 mRNA. When overexpressed in HepG2 cells a significant hOCT1 mRNA decay was induced by hsa-miR-330 and hsa-miR-1468. Analysis of 39 paired tumour/adjacent samples from TCGA revealed that hsa-mir-330 was consistently upregulated in HCC.

CONCLUSION AND IMPLICATIONS

Impaired hOCT1 expression/function in HCC, in part due to epigenetic modifications, plays an important role in the poor pharmacological response of this cancer to sorafenib.

Role of the placenta in serum autotaxin elevation during maternal cholestasis

Intrahepatic cholestasis of pregnancy (ICP) is frequently accompanied by pruritus, whose etiology has been associated with an enhanced production of lysophosphatidic acid (LPA) by the combined action of phospholipase A1/A2 (PLA1/PLA2) and autotaxin (ATX). Here, we have investigated whether the placenta is involved in LPA release to maternal circulation during ICP. Serum levels of ATX and LPA (determined by ELISA) were elevated in women with ICP, and a correlation between both parameters was found. No relationship between serum levels of ATX or LPA and bile acids was found. Expression levels of ATX and PLA2 were determined by RT-qPCR and Western blot. Placenta ATX but not PLA2 was significantly upregulated in ICP, and a tendency to increase was found at the protein level. A correlation between serum ATX and placental ATX mRNA levels was found. In human placenta at term, ATX was clearly detected (by immunofluorescence) in Hofbauer cells, but only faintly in trophoblast cells. In pregnant rats, the expression of Atx and Pla2 in placenta was lower than in liver. When obstructive cholestasis was imposed by bile duct ligation from day 14 of gestation until term, placenta Atx and Pla2 expression was markedly enhanced, and overexpression was confirmed at the protein level for Pla2, whereas Atx protein was not detected. In conclusion, the placenta substantially participates in LPA production during gestation. This contribution is markedly higher during maternal cholestasis and hence, may be involved in ICP-associated pruritus. NEW & NOTEWORTHY Fetal placental macrophages and, to a lesser extent, trophoblast cells express high levels of autotaxin at term. An increased expression of mRNA and protein autotaxin, the key secretory enzyme responsible for the production of lysophosphatidic acid in serum, has been observed in placentas of women with cholestasis of pregnancy, which supports that the placenta can contribute to an increased production of this pruritogenic compound in women suffering from this liver disease.

Molecular bases of the poor response of liver cancer to chemotherapy

A characteristic shared by most frequent types of primary liver cancer, i.e., hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA) in adults, and in a lesser extent hepatoblastoma (HB) mainly in children, is their high refractoriness to chemotherapy. This is the result of synergic interactions among complex and diverse mechanisms of chemoresistance (MOC) in which more than 100 genes are involved. Pharmacological treatment, although it can be initially effective, frequently stimulates the expression of MOC genes, which results in the relapse of the tumor, usually with a more aggressive and less chemosensitive phenotype. Identification of the MOC genetic signature accounting for the "resistome" present at each moment of tumor life would prevent the administration of chemotherapeutic regimens without chance of success but still with noxious side effects for the patient. Moreover, a better description of cancer cells strength is required to develop novel strategies based on pharmacological, cellular or gene therapy to overcome liver cancer chemoresistance.

Molecular Bases of Chemoresistance in Cholangiocarcinoma

The multidrug resistance (MDR) phenotype accounts for the poor response of cholangiocarcinoma to available antitumor drugs. This is an important limitation to the use of pharmacological approaches, both as adjuvant therapies and for treating advanced CCA when surgical removal is not possible. MDR is the result of a complex combination of defense mechanisms against toxic compounds already present in cholangiocytes, which play a role in the physiology of these cells by protecting the biliary epithelium from the toxins reaching the biliary tree with the blood that perfuses this tissue, or that are secreted by hepatocytes into bile, to which cholangiocytes are exposed. These mechanisms of chemoresistance (MOC) are also present, usually with enhanced efficacy, in tumors derived from cholangiolar cells. The present review article is an update of the state-of-the-art regarding the MOC involved in the poor response of CCA to antitumor drugs. These MOC have been classified as: changes in the amount of drug in the cells due to decreased uptake (MOC-1a) or enhanced efflux (MOC-1b); altered proportions between prodrug, active drug and inactive metabolites (MOC-2); changes in the molecular targets of antitumor drugs (MOC-3); an enhanced ability of tumor cells to repair drug-induced DNA damage (MOC-4), and an impaired apoptosis/survival balance (MOC-5).

Serum extracellular vesicles contain protein biomarkers for primary sclerosing cholangitis and cholangiocarcinoma

Cholangiocarcinoma (CCA) includes a heterogeneous group of biliary cancers with poor prognosis. Several conditions, such as primary sclerosing cholangitis (PSC), are risk factors. Noninvasive differential diagnosis between intrahepatic CCA and hepatocellular carcinoma (HCC) is sometimes difficult. Accurate noninvasive biomarkers for PSC, CCA, and HCC are not available. In the search for novel biomarkers, serum extracellular vesicles (EV) were isolated from CCA (n = 43), PSC (n = 30), or HCC (n = 29) patients and healthy individuals (control, n = 32); and their protein content was characterized. By using nanoparticle tracking analysis, serum EV concentration was found to be higher in HCC than in all the other groups. Round morphology (by transmission electron microscopy), size (∼180 nm diameter by nanoparticle tracking analysis), and markers (clusters of differentiation 9, 63, and 81 by immunoblot) indicated that most serum EV were exosomes. Proteome profiles (by mass spectrometry) revealed multiple differentially expressed proteins among groups. Several of these proteins showed high diagnostic values with maximum area under the receiver operating characteristic curve of 0.878 for CCA versus control, 0.905 for CCA stage I-II versus control, 0.789 for PSC versus control, 0.806 for noncirhottic PSC versus control, 0.796 for CCA versus PSC, 0.956 for CCA stage I-II versus PSC, 0.904 for HCC versus control, and 0.894 for intrahepatic CCA versus HCC. Proteomic analysis of EV derived from CCA human cells in vitro revealed higher abundance of oncogenic proteins compared to EV released by normal human cholangiocytes. Orthotopic implant of CCA human cells in the liver of immunodeficient mice resulted in the release to serum of EV containing some similar human oncogenic proteins.

CONCLUSION

Proteomic signatures found in serum EV of CCA, PSC, and HCC patients show potential usefulness as diagnostic tools. (Hepatology 2017;66:1125-1143).

The lack of the organic cation transporter OCT1 at the plasma membrane of tumor cells precludes a positive response to sorafenib in patients with hepatocellular carcinoma

Background

Sorafenib is the drug of choice in the treatment of advanced hepatocellular carcinoma (HCC). Beneficial effects are limited by mechanisms of chemoresistance, which include downregulation and/or impaired function of plasma membrane transporters accounting for drug uptake. The organic cation transporter 1 (OCT1) plays a major role in sorafenib uptake and decreased expression in HCC has been associated with poorer response.

Methods

The multicenter retrospective TRANSFER study involved tumor biopsies from 39 patients with advanced HCC and sorafenib therapy for ≥4 wk. Endpoint was the relationship between clinicopathological features and immunohistological result. Immunostaining was performed using specific primary anti-OCT1-head and anti-OCT1-tail antibodies. Tumors were classified according to a simplified staining score as absent, weak, moderate or strong, taking into account the localization of the staining at the plasma membrane as positive or negative.

Results

Results confirmed OCT1 downregulation in half of the cases investigated (10% absent, 38% weak). However, only one third of tumors expressing OCT1 displayed plasma membrane location (15% vs. 36% cytosolic expression). When comparing HCC with and without OCT1 expression, no different sorafenib response was found. When tumors expressing OCT1 at the plasma membrane were considered separately, a marked longer survival was found (Log Rank p<0.001). No association between OCT1 expression at the plasma membrane with tumor stage, previous treatment with TACE or radiological response was seen.

In conclusion, these results indicate that the presence of OCT1 at the plasma membrane, rather than its expression levels, is related to better outcome of HCC patients treated with sorafenib.

The search for novel diagnostic and prognostic biomarkers in cholangiocarcinoma

The poor prognosis of cholangiocarcinoma (CCA) is in part due to late diagnosis, which is currently achieved by a combination of clinical, radiological and histological approaches. Available biomarkers determined in serum and biopsy samples to assist in CCA diagnosis are not sufficiently sensitive and specific. Therefore, the identification of new biomarkers, preferably those obtained by minimally invasive methods, such as liquid biopsy, is important. The development of innovative technologies has permitted to identify a significant number of genetic, epigenetic, proteomic and metabolomic CCA features with potential clinical usefulness in early diagnosis, prognosis or prediction of treatment response. Potential new candidates must be rigorously evaluated prior to entering routine clinical application. Unfortunately, to date, no such biomarker has achieved validation for these purposes. This review is an up-to-date of currently used biomarkers and the candidates with promising characteristics that could be included in the clinical practice in the next future. This article is part of a Special Issue entitled: Cholangiocytes in Health and Disease edited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

Mechanisms of Resistance to Chemotherapy in Gastric Cancer

Although surgical resection is the standard curative therapy for gastric cancer, these tumors are often diagnosed at an advanced stage, when surgery is not recommended. Alternative treatments such as radiotherapy and chemotherapy achieve only very modest results. There is therefore an urgent need to advance in this field of oncologic gastroenterology. The poor response of gastric cancer to chemotherapy is usually due to a combination of mechanisms of chemoresistance (MOC), which may include a reduction in drug uptake (MOC-1a), enhanced drug efflux (MOC-1b), a reduced proportion of active agents in tumor cells due to a reduction in pro-drug activation or an enhancement in drug inactivation (MOC-2), changes in the expression/function of the molecular targets of anticancer drugs (MOC-3), an enhanced ability of cancer cells to repair anticancer drug-induced DNA damage (MOC-4), and decreased expression/function of pro-apoptotic factors or up-regulation of anti-apoptotic genes (MOC-5). Two major goals of modern pharmacology aimed at overcoming this situation are the prediction of a lack of response to chemotherapy and the identification of the underlying mechanisms accounting for primary or acquired refractoriness to anticancer drugs. These are important issues if we are to select the best pharmacological regime for each patient and develop novel strategies to overcome chemoresistance. The present review reports updated information regarding the mechanisms of chemoresistance (from MOC-1 to MOC-5) in gastric cancer, the advances made in the prediction of the failure of chemotherapeutic treatment, and novel strategies based on gene therapy currently being developed to treat these tumors.

Bile Acids in Physiology, Pathology and Pharmacology

Bile acids, synthesized by hepatocytes from cholesterol, are specific and quantitatively important organic components of bile, where they are the main driving force of the osmotic process that generates bile flow toward the canaliculus. The bile acid pool comprises a variety of species of amphipathic acidic steroids. They are not mere detergent molecules that play a key role in fat digestion and the intestinal absorption of hydrophobic compounds present in the intestinal lumen after meals, including liposoluble vitamins. They are now known to be involved in the regulation of multiple functions in liver cells, mainly hepatocytes and cholangiocytes, and also in extrahepatic tissues. The identification of nuclear receptors, such as farnesoid X receptor (FXR or NR1H4), and plasma membrane receptors, such as the G protein-coupled bile acid receptor (TGR5, GPBAR1 or MBAR), which are able to trigger specific and complex responses upon activation (with dissimilar sensitivities) by different bile acid molecular species and synthetic agonists, has opened a new and promising field of research whose implications extend to physiology, pathology and pharmacology. In addition, pharmacological development has taken advantage of advances in the understanding of the chemistry and biology of bile acids and the biological systems that interact with them, which in addition to the receptors include several families of transporters and export pumps, to generate novel bile acid derivatives aimed at treating different liver diseases, such as cholestasis, biliary diseases, metabolic disorders and cancer. This review is an update of the role of bile acids in health and disease.

Expert consensus document: Cholangiocarcinoma: current knowledge and future perspectives consensus statement from the European Network for the Study of Cholangiocarcinoma (ENS-CCA)

Cholangiocarcinoma (CCA) is a heterogeneous group of malignancies with features of biliary tract differentiation. CCA is the second most common primary liver tumour and the incidence is increasing worldwide. CCA has high mortality owing to its aggressiveness, late diagnosis and refractory nature. In May 2015, the "European Network for the Study of Cholangiocarcinoma" (ENS-CCA: www.enscca.org or www.cholangiocarcinoma.eu) was created to promote and boost international research collaboration on the study of CCA at basic, translational and clinical level. In this Consensus Statement, we aim to provide valuable information on classifications, pathological features, risk factors, cells of origin, genetic and epigenetic modifications and current therapies available for this cancer. Moreover, future directions on basic and clinical investigations and plans for the ENS-CCA are highlighted.

Effect of ursodeoxycholic acid treatment on the altered progesterone and bile acid homeostasis in the mother-placenta-foetus trio during cholestasis of pregnancy

AIM

Intrahepatic cholestasis of pregnancy (ICP) is characterized by pruritus and elevated bile acid concentrations in maternal serum. This is accompanied by an enhanced risk of intra-uterine and perinatal complications. High concentrations of sulphated progesterone metabolites (PMS) have been suggested to be involved in the multifactorial aetiopathogenesis of ICP. The aim of this study was to investigate further the mechanism accounting for the beneficial effect of oral administration of ursodeoxycholic acid (UDCA), which is the standard treatment, regarding bile acid and PMS homeostasis in the mother-placenta-foetus trio.

METHOD

Using HPLC-MS/MS bile acids and PMS were determined in maternal and foetal serum and placenta. The expression of ABC proteins in placenta was determined by real time quantitative PCR (RT-QPCR) and immunofluorescence.

RESULTS

In ICP, markedly increased concentrations of bile acids (tauroconjugates > glycoconjugates >> unconjugated), progesterone and PMS in placenta and maternal serum were accompanied by enhanced concentrations in foetal serum of bile acids, but not of PMS. UDCA treatment reduced bile acid accumulation in the mother-placenta-foetus trio, but had no significant effect on progesterone and PMS concentrations. ABCG2 mRNA abundance was increased in placentas from ICP patients vs. controls and remained stable following UDCA treatment, despite an apparent further increase in ABCG2.

CONCLUSION

UDCA administration partially reduces ICP-induced bile acid accumulation in mothers and foetuses despite the lack of effect on concentrations of progesterone and PMS in maternal serum. Up-regulation of placental ABCG2 may play an important role in protecting the foetus from high concentrations of bile acids and PMS during ICP.

Cocarcinogenic effects of intrahepatic bile acid accumulation in cholangiocarcinoma development

Bile acid accumulation in liver with cholangiolar neoplastic lesions may occur before cholestasis is clinically detected. Whether this favors intrahepatic cholangiocarcinoma development has been investigated in this study. The E. coli RecA gene promoter was cloned upstream from Luc2 to detect in vitro direct genotoxic ability by activation of SOS genes. This assay demonstrated that bile acids were not able to induce DNA damage. The genotoxic effect of the DNA-damaging agent cisplatin was neither enhanced nor hindered by the hepatotoxic and hepatoprotective glycochenodeoxycholic and glycoursodeoxycholic acids, respectively. In contrast, thioacetamide metabolites, but not thioacetamide itself, induced DNA damage. Thus, thioacetamide was used to induce liver cancer in rats, which resulted in visible tumors after 30 weeks. The effect of bile acid accumulation on initial carcinogenesis phase (8 weeks) was investigated in bile duct ligated (BDL) animals. Serum bile acid measurement and determination of liver-specific healthy and tumor markers revealed that early thioacetamide treatment induced hypercholanemia together with upregulation of the tumor marker Neu in bile ducts, which were enhanced by BDL. Bile acid accumulation was associated with increased expression of interleukin (IL)-6 and downregulation of farnesoid X receptor (FXR). Bile duct proliferation and apoptosis activation, with inverse pattern (BDL > thioacetamide + BDL >> thioacetamide vs. thioacetamide > thioacetamide + BDL > BDL), were observed. In conclusion, intrahepatic accumulation of bile acids does not induce carcinogenesis directly but facilitates a cocarcinogenic effect due to stimulation of bile duct proliferation, enhanced inflammation, and reduction in FXR-dependent chemoprotection.

IMPLICATIONS

This study reveals that bile acids foster cocarcinogenic events that impact cholangiocarcinoma.

Expression of SLC22A1 variants may affect the response of hepatocellular carcinoma and cholangiocarcinoma to sorafenib

Reduced drug uptake is an important mechanism of chemoresistance. Down-regulation of SLC22A1 encoding the organic cation transporter-1 (OCT1) may affect the response of hepatocellular carcinoma (HCC) and cholangiocarcinoma (CGC) to sorafenib, a cationic drug. Here we investigated whether SLC22A1 variants may contribute to sorafenib chemoresistance. Complete sequencing and selective variant identification were carried out to detect single nucleotide polymorphisms (SNPs) in SLC22A1 complementary DNA (cDNA). In HCC and CGC biopsies, in addition to previously described variants, two novel alternative spliced variants and three SNPs were identified. To study their functional consequences, these variants were mimicked by directed mutagenesis and expressed in HCC (Alexander and SK-Hep-1) and CGC (TFK1) cells. The two novel described variants, R61S fs*10 and C88A fs*16, encoded truncated proteins unable to reach the plasma membrane. Both variants abolished OCT1-mediated uptake of tetraethylammonium, a typical OCT1 substrate, and were not able to induce sorafenib sensitivity. In cells expressing functional OCT1 variants, OCT1 inhibition with quinine prevented sorafenib-induced toxicity. Expression of OCT1 variants in Xenopus laevis oocytes and determination of quinine-sensitive sorafenib uptake by high-performance liquid chromatography-dual mass spectrometry confirmed that OCT1 is able to transport sorafenib and that R61S fs*10 and C88A fs*16 abolish this ability. Screening of these SNPs in 23 HCC and 15 CGC biopsies revealed that R61S fs*10 was present in both HCC (17%) and CGC (13%), whereas C88A fs*16 was only found in HCC (17%). Considering all SLC22A1 variants, at least one inactivating SNP was found in 48% HCC and 40% CGC.

CONCLUSION

Development of HCC and CGC is accompanied by the appearance of aberrant OCT1 variants that, together with decreased OCT1 expression, may dramatically affect the ability of sorafenib to reach active intracellular concentrations in these tumors.

Genetic variants in genes involved in mechanisms of chemoresistance to anticancer drugs

Refractoriness to the pharmacological treatment of cancer is dependent on the expression levels of genes involved in mechanisms of chemoresistance and on the existence of genetic variants that may affect their function. Thus, changes in genes encoding solute carriers may account for considerable inter-individual variability in drug uptake and the lack of sensitivity to the substrates of these transporters. Moreover, changes in proteins involved in drug export can affect their subcellular localization and transport ability and hence may also modify the bioavailability of antitumor agents. Regarding pro-drug activation or drug inactivation, genetic variants are responsible for changes in the activity of drug-metabolizing enzymes, which affect drug clearance and may determine the lack of response to anticancer chemotherapy. The presence of genetic variants may also decrease the sensitivity to pharmacological agents acting through molecular targets or signaling pathways. Recent investigations suggest that changes in genes involved in DNA repair may affect the response to platinum-based drugs. Since most anticancer agents activate cell death pathways, the evasion of apoptosis plays an important role in chemoresistance. Several genetic variants affecting death-receptor pathways, the mitochondrial pathway, downstream caspases and their natural modulators, and the p53 pathway, whose elements are mutated in more than half of tumors, and survival pathways, have been reported. The present review summarizes the available data regarding the role of genetic variants in the different mechanisms of chemoresistance and discusses their potential impact in clinical practice and in the development of tools to predict and overcome chemoresistance.

Genetic variants in genes involved in mechanisms of chemoresistance to anticancer drugs

Refractoriness to the pharmacological treatment of cancer is dependent on the expression levels of genes involved in mechanisms of chemoresistance and on the existence of genetic variants that may affect their function. Thus, changes in genes encoding solute carriers may account for considerable inter-individual variability in drug uptake and the lack of sensitivity to the substrates of these transporters. Moreover, changes in proteins involved in drug export can affect their subcellular localization and transport ability and hence may also modify the bioavailability of antitumor agents. Regarding pro-drug activation or drug inactivation, genetic variants are responsible for changes in the activity of drug-metabolizing enzymes, which affect drug clearance and may determine the lack of response to anticancer chemotherapy. The presence of genetic variants may also decrease the sensitivity to pharmacological agents acting through molecular targets or signaling pathways. Recent investigations suggest that changes in genes involved in DNA repair may affect the response to platinum-based drugs. Since most anticancer agents activate cell death pathways, the evasion of apoptosis plays an important role in chemoresistance. Several genetic variants affecting death-receptor pathways, the mitochondrial pathway, downstream caspases and their natural modulators, and the p53 pathway, whose elements are mutated in more than half of tumors, and survival pathways, have been reported. The present review summarizes the available data regarding the role of genetic variants in the different mechanisms of chemoresistance and discusses their potential impact in clinical practice and in the development of tools to predict and overcome chemoresistance.

No correlation between the expression of FXR and genes involved in multidrug resistance phenotype of primary liver tumors

Farnesoid X receptor (FXR) has been recently reported to enhance chemoresistance through bile acid-independent mechanisms. Thus, FXR transfection plus activation with GW4064 resulted in reduced sensitivity to cisplatin-induced toxicity. This is interesting because primary tumors of the liver, an organ where FXR is expressed, exhibit marked refractoriness to pharmacological treatment. Here we have determined whether FXR is upregulated in hepatocellular carcinoma (HCC), cholangiocarcinoma (CGC) and hepatoblastoma (HPB) and whether this is related with the expression of genes involved in mechanisms of chemoresistance. Using RT-QPCR and Taqman low density arrays we have analyzed biopsies from healthy livers or surgically removed tumors from naive patients and cell lines derived from HCC (SK-HEP-1, Alexander and Huh7), CGC (TFK1) and HPB (HepG2), before and after exposure to cisplatin at IC50 for 72 h. In liver tumors FXR expression was not enhanced but significantly decreased (healthy liver > HCC > HPB ≈ CGC). Except for CGC, this was not accompanied by changes in the proportions of FXR isoforms. Changes in 36 genes involved in drug uptake/efflux and metabolism, expression/function of molecular targets, and survival/apoptosis balance were found. Changes affecting SLC22A1, CYP2A1 and BIRC5 were shared by HCC, CGC and HPB. Similarity in gene expression profiles between cell lines and parent tumors was found. Pharmacological challenge with cisplatin induced changes that increased this resemblance. This was not dependent upon FXR expression. Thus, although FXR may play a role in inducing chemoresistance under certain circumstances, its upregulation does not seem to be involved in the multidrug resistance phenotype characteristic of HCC, CGC and HPB.

Further characterization of the electrogenicity and pH sensitivity of the human organic anion-transporting polypeptides OATP1B1 and OATP1B3

Organic anion-transporting polypeptides (OATPs) are involved in the liver uptake of many endogenous and xenobiotic compounds, such as bile acids and drugs, respectively. Using Xenopus laevis oocytes and Chinese hamster ovary (CHO) cells expressing rat Oatp1a1, human OATP1B1, or OATP1B3, the sensitivity of these transporters to extracellular/intracellular pH (pHo/pHi) and changes in plasma membrane potential (ΔΨ) was investigated. In X. laevis oocytes, nonspecific plasma membrane permeability increased only at pHo below 4.5. Above this value, both using oocytes and CHO cells, extracellular acidification affected differently the specific transport of taurocholic acid (TCA) and estradiol 17β-d-glucuronide (E(2)17βG) by Oatp1a1 (stimulation), OATP1B1 (inhibition), and OATP1B3 (stimulation). Changes in substrate uptake in the presence of valinomycin (K(+)-ionophore), carbonyl cyanide 3-chlorophenylhydrazone and nigericin (protonophores), and amiloride (Na(+)/H(+)-inhibitor) and cation replacement in the medium were studied with fluorescent probes for measuring substrate uptake (cholylglycyl amidofluorescein) and changes in pHi (SNARF-4F) and ΔΨ [DilC(1)(5)]. The results suggest that activity of these three carriers is sodium/potassium-independent and affected differently by changes in pHo and ΔΨ: Oatp1a1 was confirmed to be an electroneutral anion exchanger, whereas the function of both OATP1B1 and OATP1B3 was markedly affected by the magnitude of ΔΨ. Moreover, electrophysiological measurements revealed the existence of a net anion influx associated to OATP1B1/OATP1B3-mediated transport of TCA, E(2)17βG, and estrone-3-sulfate. Furthermore, a leakage of Na(+) through OATP1B1 and OATP1B3, which is not coupled to substrate transport, was found. In conclusion, these results suggest that OATP1B1 and OATP1B3 are electrogenic transporters whose activity may be strongly affected under circumstances of displacement of local pH.

TNP-470 Inhibits Oxidative Stress, Nitric Oxide Production and Nuclear Factor Kappa B Activation in a Rat Model of Hepatocellular Carcinoma

The objective of this study is to determine if treatment with the angiogenesis inhibitor TNP-470 results in impairment of oxidative stress, inhibition of nuclear factor kappa B (NF-kappaB) activation and decrease of nitric oxide production in an experimental model of rat hepatocarcinogenesis. Tumour was induced by diethylnitrosamine and promoted by two-thirds hepatectomy plus acetaminofluorene administration. Experiments were carried out at 28 weeks after initiating the treatment. TNP-470 was administered at 30mg/kg, three times per week from 20 to 28 weeks. Carcinomatous tissue growing outside dysplastic nodules and a marked expression of placental glutathione S-transferase were detected in rats with induced carcinogenesis. Liver concentrations of thiobarbituric acid reactive substances, reduced glutathione (GSH) and glutathione disulfide (GSSG) were significantly higher than those of controls and there was a significant increase in the GSSG/GSH ratio. Tumour growth was accompanied by augmented expression of inducible nitric oxide synthase, activation of (NF-kappaB) and proteolysis of IkappaB. All these effects were absent in animals receiving TNP-470. Our results indicate that TNP-470 inhibits oxidative stress, nitric oxide production and NF-kappaB activation induced by experimental hepatocarcinogenesis. These changes would contribute to the beneficial effects of TNP-470 in cancer treatment.

Protective effect of bile acid derivatives in phalloidin-induced rat liver toxicity

Phalloidin causes severe liver damage characterized by marked cholestasis, which is due in part to irreversible polymerization of actin filaments. Liver uptake of this toxin through the transporter OATP1B1 is inhibited by the bile acid derivative BALU-1, which does not inhibit the sodium-dependent bile acid transporter NTCP. The aim of the present study was to investigate whether BALU-1 prevents liver uptake of phalloidin without impairing endogenous bile acid handling and hence may have protective effects against the hepatotoxicity induced by this toxin. In anaesthetized rats, i.v. administration of BALU-1 increased bile flow more than taurocholic acid (TCA). Phalloidin administration decreased basal (-60%) and TCA-stimulated bile flow (-55%) without impairing bile acid output. Phalloidin-induced cholestasis was accompanied by liver necrosis, nephrotoxicity and haematuria. In BALU-1-treated animals, phalloidin-induced cholestasis was partially prevented. Moreover haematuria was not observed, which was consistent with histological evidences of BALU-1-prevented injury of liver and kidney tissue. HPLC-MS/MS analysis revealed that BALU-1 was secreted in bile mainly in non-conjugated form, although a small proportion (<5%) of tauro-BALU-1 was detected. BALU-1 did not inhibit the biliary secretion of endogenous bile acids. When highly choleretic bile acids, - ursodeoxycholic (UDCA) and dehydrocholic acid (DHCA) - were administered, they were found less efficient than BALU-1 in preventing phalloidin-induced cholestasis. Biliary phalloidin elimination was low but it was increased by BALU-1>TCA>DHCA>UDCA. In conclusion, BALU-1 is able to protect against phalloidin-induced hepatotoxicity, probably due to an inhibition of the liver uptake and an enhanced biliary secretion of this toxin.

Cytosol-nucleus traffic and colocalization with FXR of conjugated bile acids in rat hepatocytes

Bile acids (BAs) are natural ligands of nuclear receptors, in particular farnesoid X receptor (FXR). Whether, in addition to protein-mediated cytosolic-nuclear BA translocation, other mechanisms are involved in the access of BAs to nuclear FXR was investigated. When rat hepatocytes were incubated with radiolabeled taurocholic acid, taurodeoxycholic acid, taurochenodeoxycholic acid, and tauroursodeoxycholic acid, their nuclear accumulation was proportional to their intracellular levels. With the use of flow cytometry analysis, the accumulation by nuclei isolated from rat liver cells was found to differ for several fluorescent compounds of similar molecular weight and different charge, including fluorescein-tagged BAs [cholylglycyl amidofluorescein (CGamF), ursodeoxycholylglycyl amidofluorescein, or chenodeoxycholylglycyl amidofluorescein]. When we varied nuclear volume by incubation with different sucrose concentrations, a similar relationship between nuclear volume and content of FITC and 4-kDa FITC-dextran was found. In contrast, this relationship was markedly lower for CGamF. Confocal microscopy studies revealed that fluorescein-tagged BAs, but also FITC or 10-kDa FITC-dextran were found in the nuclear envelope and concentrated in regions where DNA was less densely packed. In contrast to the cytosolic subcellular localization of peroxisome proliferator-activated receptor-alpha, FXR and nucleolin (a marker of transcriptional active chromatin) were also localized by immunoreactivity in these intranuclear regions. In conclusion, although intranuclear levels of small organic molecules including conjugated BAs depend on their concentrations in the extranuclear space, the existence of certain molecular selectivity (not strictly dependent on molecular weight or charge) suggests that, in addition to simple diffusional exchange, other mechanisms may be also involved in determining their overall nuclear content in regions where these compounds coincide and may interact with nuclear receptors such as FXR.

Molecular bases of the fetal liver-placenta-maternal liver excretory pathway for cholephilic compounds

Potentially toxic endogenous compounds, such as bile acids (BAs) and biliary pigments, as well as many xenobiotics, such as drugs and food components, are biotransformed and eliminated by the hepatobiliary system with the collaboration of the kidney. However, the situation is very different during pregnancy because the fetal liver produces biliary compounds despite the fact that this organ, owing to its immaturity, is not able to eliminate them into bile. Moreover, the excretory ability of the fetal kidneys is also very limited. Thus, during the intra-uterine life, the major route to eliminate fetal BAs and biliary pigments is their transfer to the mother across the placenta. The maternal liver and, to a lesser extent, the maternal kidney, are then in charge of their biotransformation and elimination into faeces and urine respectively. This review describes current knowledge of the machinery responsible for the detoxification and excretion of cholephilic compounds through the pathway formed by the fetal liver-placenta-maternal liver trio.