Down-regulation of ATP-binding cassette C2 protein expression in HepG2 cells after rifampicin treatment is mediated by microRNA-379

Extracellular Vesicles as Surrogates for the Regulation of the Drug Transporters ABCC2 (MRP2) and ABCG2 (BCRP)

Drug efflux transporters of the ATP-binding-cassette superfamily play a major role in the availability and concentration of drugs at their site of action. ABCC2 (MRP2) and ABCG2 (BCRP) are among the most important drug transporters that determine the pharmacokinetics of many drugs and whose overexpression is associated with cancer chemoresistance. ABCC2 and ABCG2 expression is frequently altered during treatment, thus influencing efficacy and toxicity. Currently, there are no routine approaches available to closely monitor transporter expression. Here, we developed and validated a UPLC-MS/MS method to quantify ABCC2 and ABCG2 in extracellular vesicles (EVs) from cell culture and plasma. In this way, an association between ABCC2 protein levels and transporter activity in HepG2 cells treated with rifampicin and hypericin and their derived EVs was observed. Although ABCG2 was detected in MCF7 cell-derived EVs, the transporter levels in the vesicles did not reflect the expression in the cells. An analysis of plasma EVs from healthy volunteers confirmed, for the first time at the protein level, the presence of both transporters in more than half of the samples. Our findings support the potential of analyzing ABC transporters, and especially ABCC2, in EVs to estimate the transporter expression in HepG2 cells.

Development and Evaluation of a Novel Hyaluronic Acid and Chitosan-modified Phytosome for Co-delivery of Oxymatrine and Glycyrrhizin for Combination Therapy

BACKGROUND

Multidrug resistance (MDR) of cancer cells is a major obstacle to efficient cancer chemotherapy. Combination therapy is expected to enhance the anticancer effect and reverse MDR. Numerous patents involve different kinds of nanoparticles for the co-delivery of multiple chemotherapeutics, but the FDA has approved none.

OBJECTIVE

In this study, oxymatrine (OMT) and glycyrrhizin (GL) were co-loaded into phytosomes as the core of nanocarriers, and the shell was cross-linked with chitosan (CS) and hyaluronic acid (HA) with the capability for the controlled, sequential release and the targeted drug uptake.

METHODS

Phospholipid complexes of OMT and GL (OGPs) were prepared by a solvent evaporation technique and could self-assemble in an aqueous solution to form phytosomes. CS and HA were sequentially coated on the surface of OGPs via electrostatic interactions to obtain CS coated OGPs (CS-OGPs) and HA modified CS-OGPs (HA-CS-OGPs), respectively. The particle size and zeta potential were measured to optimize the formulations. In vitro cytotoxicity and cellular uptake experiments on HepG2 cells were performed to evaluate the anticancer activity.

RESULTS

OGPs were obtained with nano-size around 100 nm, and CS and HA coating on phytosomes could change the particle size and surface potential. The drug loading of OMT and GL showed that the nanocarriers could maintain a fixed ratio of 1:1. The in vitro release experiments indicated the release of OMT and GL was pH-dependent and sequential: the release of OMT from CS-OGPs and HA-CS-OGPs was significantly increased at pH 5.0 compared to the release at pH 7.4, while GL exhibited sustained released from CS-OGPs and HA-CS-OGPs at pH 5.0. Furthermore, in vitro cytotoxicity and cellular uptake experiments on HepG2 cells demonstrated that the co-delivery system based on phytosomes had significant synergistic anti-tumor activities, and the effects were enhanced by CS and HA modification.

CONCLUSION

The delivery of OMT and GL via HA-CS-OGPs might be a promising treatment to reverse MDR in cancer therapy.

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.

Recent Advances in Novel Recombinant RNAs for Studying Post-transcriptional Gene Regulation in Drug Metabolism and Disposition

Drug-metabolizing enzymes and transporters are major determinants of the absorption, disposition, metabolism, and excretion (ADME) of drugs, and changes in ADME gene expression or function may alter the pharmacokinetics/ pharmacodynamics (PK/PD) and further influence drug safety and therapeutic outcomes. ADME gene functions are controlled by diverse factors, such as genetic polymorphism, transcriptional regulation, and coadministered medications. MicroRNAs (miRNAs) are a superfamily of regulatory small noncoding RNAs that are transcribed from the genome to regulate target gene expression at the post-transcriptional level. The roles of miRNAs in controlling ADME gene expression have been demonstrated, and such miRNAs may consequently influence cellular drug metabolism and disposition capacity. Several types of miRNA mimics and small interfering RNA (siRNA) reagents have been developed and widely used for ADME research. In this review article, we first provide a brief introduction to the mechanistic actions of miRNAs in post-transcriptional gene regulation of drug-metabolizing enzymes, transporters, and transcription factors. After summarizing conventional small RNA production methods, we highlight the latest advances in novel recombinant RNA technologies and applications of the resultant bioengineered RNA (BioRNA) agents to ADME studies. BioRNAs produced in living cells are not only powerful tools for general biological and biomedical research but also potential therapeutic agents amenable to clinical investigations.

A Systematic Review of Clinical Validated and Potential miRNA Markers Related to the Efficacy of Fluoropyrimidine Drugs

Colorectal cancer (CRC) is becoming increasingly prevalent worldwide. Fluoropyrimidine drugs are the primary chemotherapy regimens in routine clinical practice of CRC. However, the survival rate of patients on fluoropyrimidine-based chemotherapy varies significantly among individuals. Biomarkers of fluoropyrimidine drugs'' efficacy are needed to implement personalized medicine. This review summarized fluoropyrimidine drug-related microRNA (miRNA) by affecting metabolic enzymes or showing the relevance of drug efficacy. We first outlined 42 miRNAs that may affect the metabolism of fluoropyrimidine drugs. Subsequently, we filtered another 41 miRNAs related to the efficacy of fluoropyrimidine drugs based on clinical trials. Bioinformatics analysis showed that most well-established miRNA biomarkers were significantly enriched in the cancer pathways instead of the fluoropyrimidine drug metabolism pathways. The result also suggests that the miRNAs screened from metastasis patients have a more critical role in cancer development than those from non-metastasis patients. There are five miRNAs shared between these two lists. The miR-21, miR-215, and miR-218 can suppress fluoropyrimidine drugs'' catabolism. The miR-326 and miR-328 can reduce the efflux of fluoropyrimidine drugs. These five miRNAs could jointly act by increasing intracellular levels of fluoropyrimidine drugs'' cytotoxic metabolites, leading to better chemotherapy responses. In conclusion, we demonstrated that the dynamic changes in the transcriptional regulation via miRNAs might play significant roles in the efficacy and toxicity of the fluoropyrimidine drug. The reported miRNA biomarkers would help evaluate the efficacy of fluoropyrimidine drug-based chemotherapy and improve the prognosis of colorectal cancer patients.

An update on the role of miR-379 in human disorders

miR-379 is a miRNA transcribed from the MIR379 locus on 14q32.31. This miRNA is located in an evolutionarily conserved miRNA cluster in an imprinted region that contains DLK1 and DIO3 genes. The mouse homolog of this miRNA has been shown to be under-expressed in response to glucocorticoid receptor deficiency. Moreover, miR-379 has a tumor-suppressive role in a wide variety of tissues including the brain, breast, lung, and liver. In addition to restraining cell proliferation and migration, miR-379 can suppress the epithelial-mesenchymal transition process. Abnormal expression of this miRNA implies the pathogenesis of Duchene muscular dystrophy, spinal cord injury, diabetic nephropathy, acute myocardial infarction, and premature ovarian failure. This review aims to the summarization of the role of miR-379 in neoplastic and non-neoplastic conditions.

Interaction of Phytocompounds of Echinacea purpurea with ABCB1 and ABCG2 Efflux Transporters

Preparations of Echinacea purpurea (E. purpurea) are widely used for the management of upper respiratory infections, influenza, and common cold, often in combination with other conventional drugs. However, the potential of phytochemical constituents of E. purpurea to cause herb-drug interactions via ABCB1 and ABCG2 efflux transporters remains elusive. The purpose of this study was to investigate the impact of E. purpurea-derived caffeic acid derivatives (cichoric acid and echinacoside) and tetraenes on the mRNA and protein expression levels as well as on transport activity of ABCB1 and ABCG2 in intestinal (Caco-2) and liver (HepG2) cell line models. The safety of these compounds was investigated by estimating EC₂₀ values of cell viability assays in both cell lines. Regulation of ABCB1 and ABCG2 protein in these cell lines were analyzed after 24 h exposure to the compounds at 1, 10, and 50 μg/mL. Bidirectional transport of 0.5 μg/mL Hoechst 33342 and 5 μM rhodamine across Caco-2 monolayer and profiling for intracellular concentrations of the fluorophores in both cell lines were conducted to ascertain inhibition effects of the compounds. Cichoric acid showed no cytotoxic effect, while the EC₂₀ values of tetraenes and echinacoside were 45.0 ± 3.0 and 52.0 ± 4.0 μg/mL in Caco-2 cells and 28.0 ± 4.3 and 62.0 ± 9.9 μg/mL in HepG2 cells, respectively. In general, the compounds showed heterogeneous induction of ABCB1 with the strongest 3.6 ± 1.2-fold increase observed for 10 μg/mL tetraenes in Caco-2 cells (p < 0.001). However, the compounds did not induce ABCG2. None of the phytocompounds inhibited significantly net flux of the fluorophores across Caco-2 monolayers. Overall, tetraenes moderately induced ABCB1 but not ABCG2 in Caco-2 and HepG2 cells while no compound significantly inhibited activity of these transporters at clinically relevant concentration to cause herb-drug interactions.

A genome-wide CRISPR/Cas9 screen in acute myeloid leukemia cells identifies regulators of TAK-243 sensitivity

TAK-243 is a first-in-class inhibitor of ubiquitin-like modifier activating enzyme 1 that catalyzes ubiquitin activation, the first step in the ubiquitylation cascade. Based on its preclinical efficacy and tolerability, TAK-243 has been advanced to phase I clinical trials in advanced malignancies. Nonetheless, the determinants of TAK-243 sensitivity remain largely unknown. Here, we conducted a genome-wide CRISPR/Cas9 knockout screen in acute myeloid leukemia (AML) cells in the presence of TAK-243 to identify genes essential for TAK-243 action. We identified BEN domain-containing protein 3 (BEND3), a transcriptional repressor and a regulator of chromatin organization, as the top gene whose knockout confers resistance to TAK-243 in vitro and in vivo. Knockout of BEND3 dampened TAK-243 effects on ubiquitylation, proteotoxic stress, and DNA damage response. BEND3 knockout upregulated the ATP-binding cassette efflux transporter breast cancer resistance protein (BCRP; ABCG2) and reduced the intracellular levelsof TAK-243. TAK-243 sensitivity correlated with BCRP expression in cancer cell lines of different origins. Moreover, chemical inhibition and genetic knockdown of BCRP sensitized intrinsically resistant high-BCRP cells to TAK-243. Thus, our data demonstrate that BEND3 regulates the expression of BCRP for which TAK-243 is a substrate. Moreover, BCRP expression could serve as a predictor of TAK-243 sensitivity.

ABCB1, ABCG2, ABCC1, ABCC2, and ABCC3 drug transporter polymorphisms and their impact on drug bioavailability: what is our current understanding?

INTRODUCTION

Interindividual differences in drug response are a frequent clinical challenge partly due to variation in pharmacokinetics. ATP-binding cassette (ABC) transporters are crucial determinants of drug disposition. They are subject of gene regulation and drug-interaction; however, it is still under debate to which extend genetic variants in these transporters contribute to interindividual variability of a wide range of drugs.

AREAS COVERED

This review discusses the current literature on the impact of genetic variants in ABCB1, ABCG2 as well as ABCC1, ABCC2, and ABCC3 on pharmacokinetics and drug response. The aim was to evaluate if results from recent studies would increase the evidence for potential clinically relevant pharmacogenetic effects.

EXPERT OPINION

Although enormous efforts have been made to investigate effects of ABC transporter genotypes on drug pharmacokinetics and response, the majority of studies showed only weak if any associations. Despite few unique results, studies mostly failed to confirm earlier findings or still remained inconsistent. The impact of genetic variants on drug bioavailability is only minor and other factors regulating the transporter expression and function seem to be more critical. In our opinion, the findings on the so far investigated genetic variants in ABC efflux transporters are not suitable as predictive biomarkers.

Differential miRNA Expression in Human Macrophage-Like Cells Infected with Histoplasma capsulatum Yeasts Cultured in Planktonic and Biofilm Forms

Histoplasma capsulatum affects healthy and immunocompromised individuals, sometimes causing a severe disease. This fungus has two morphotypes, the mycelial (infective) and the yeast (parasitic) phases. MicroRNAs (miRNAs) are small RNAs involved in the regulation of several cellular processes, and their differential expression has been associated with many disease states. To investigate miRNA expression in host cells during H. capsulatum infection, we studied the changes in the miRNA profiles of differentiated human macrophages infected with yeasts from two fungal strains with different virulence, EH-315 (high virulence) and 60I (low virulence) grown in planktonic cultures, and EH-315 grown in biofilm form. MiRNA profiles were evaluated by means of reverse transcription-quantitative polymerase chain reaction using a commercial human miRNome panel. The target genes of the differentially expressed miRNAs and their corresponding signaling pathways were predicted using bioinformatics analyses. Here, we confirmed biofilm structures were present in the EH-315 culture whose conditions facilitated producing insoluble exopolysaccharide and intracellular polysaccharides. In infected macrophages, bioinformatics analyses revealed especially increased (hsa-miR-99b-3p) or decreased (hsa-miR-342-3p) miRNAs expression levels in response to infection with biofilms or both growth forms of H. capsulatum yeasts, respectively. The results of miRNAs suggested that infection by H. capsulatum can affect important biological pathways of the host cell, targeting two genes: one encoding a protein that is important in the cortical cytoskeleton; the other, a protein involved in the formation of stress granules. Expressed miRNAs in the host’s response could be proposed as new therapeutic and/or diagnostic tools for histoplasmosis.

Expression differences of miR-142-5p between treatment-naïve chronic myeloid leukemia patients responding and non-responding to imatinib therapy suggest a link to oncogenic ABL2, SRI, cKIT and MCL1 signaling pathways critical for development of therapy resistance

Background

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm characterized by constitutive activity of the tyrosine kinase BCR-ABL1. Although the introduction of tyrosine kinase inhibitors (TKIs) has substantially improved patients’ prognosis, drug resistance remains one of the major challenges in CML therapy. MicroRNAs (miRNAs), a class of short non-coding RNAs acting as post-transcriptional regulators, are implicated in CML progression and drug resistance. The aim of the present study was to analyze the miRNA expression profiles of 45 treatment-naïve CML patients in chronic phase (28 peripheral blood and 17 bone marrow samples) with respect to future response to imatinib therapy.

Methods

TaqMan low density arrays were used to analyze the miRNA expression pattern of the patient samples. For selected microRNAs, reporter gene assays were performed to study their ability to regulate CML associated target genes.

Results

Significant lower expression levels of miR-142-5p were identified in both, peripheral blood and bone marrow samples of future non-responders suggesting a potential tumor suppressor role of this miRNA. This was supported by reporter gene assays that identified the survival, proliferation and invasion promoting CML related genes ABL2, cKIT, MCL1 and SRI as targets of miR-142-5p and miR-365a-3p, the latter identified as potential biomarker in peripheral blood samples.

Conclusion

MiR-142-5p and to a certain extend also miR-365a-3p were able to discriminate treatment-naïve CML patients not responding to imatinib in the course of their treatment from patients, who responded to therapy. However, further large-scale studies should clarify if the identified miRNAs have the potential as predictive biomarkers for TKI resistance.

Alternative Polyadenylation of ABC Transporters of the C-Family (ABCC1, ABCC2, ABCC3) and Implications on Posttranscriptional Micro-RNA Regulation

ATP-binding cassette (ABC) transporters represent a large group of efflux pumps that are strongly involved in the pharmacokinetics of various drugs and nutrient distribution. It was recently shown that micro-RNAs (miRNAs) may significantly alter their expression as proven, e.g., for miR-379 and ABCC2 However, alternative mRNA polyadenylation may result in expression of 3'-untranslated regions (3'-UTRs) with varying lengths. Thus, length variants may result in presence or absence of miRNA binding sites for regulatory miRNAs with consequences on posttranscriptional control. In the present study, we report on 3'-UTR variants of ABCC1, ABCC2, and ABCC3 mRNA. Applying in vitro luciferase reporter gene assays, we show that expression of short ABCC2 3'-UTR variants leads to a significant loss of miR-379/ABCC2 interaction and subsequent upregulation of ABCC2 expression. Furthermore, we show that expression of ABCC2 3'-UTR lengths varies significantly between human healthy tissues but is not directly correlated to the respective protein level in vivo. In conclusion, the presence of altered 3'-UTR lengths in ABC transporters could lead to functional consequences regarding posttranscriptional gene expression, potentially regulated by alternative polyadenylation. Hence, 3'-UTR length variability may be considered as a further mechanism contributing to variability of ABCC transporter expression and subsequent drug variation in drug response. SIGNIFICANCE STATEMENT: micro-RNA (miRNA) binding to 3'-untranslated region (3'-UTR) plays an important role in the control of ATP-binding cassette (ABC)-transporter mRNA degradation and translation into proteins. We disclosed various 3'-UTR length variants of ABCC1, C2, and C3 mRNA, with loss of mRNA seed regions partly leading to varying and tissue-dependent interaction with miRNAs, as proven by reporter gene assays. Alternative 3'-UTR lengths may contribute to variable ABCC transporter expression and potentially explains inconsistent findings in miRNA studies.

Up-regulation of miR-let7a-5p Leads to Decreased Expression of ABCC2 in Obstructive Cholestasis

Adenosine triphosphate-binding cassette subfamily C member 2 (ABCC2/Abcc2) is critically important to biliary excretion of many endobiotic and xenobiotic compounds, and is a major driving force for bile acid-independent bile flow. Abcc2 expression is reduced at the messenger RNA (mRNA) and protein levels in various forms of experimental cholestasis. In a microRNA (miRNA) screen of mouse liver after biliary obstruction, we found that miRNA let7a-5p was significantly up-regulated approximately 4-fold. Similarly, ABCC2 mRNA was depleted and miRNA let7a-5p was elevated over 4-fold in livers of children with biliary atresia compared with normal livers. In silico analysis predicted that let7a-5p would target the 3' untranslated region (3' UTR) of ABCC2/Abcc2 RNA. The objective of this study was to determine whether let7a-5p contributes to the depletion of ABCC2/Abcc2 in cholestasis. To demonstrate the functional importance of miRNA let7a-5p in regulating the expression of ABCC2, co-transfection of a let7a-5p mimic and an ABCC2-3' UTR luciferase construct into Huh-7 cells led to a marked inhibition of luciferase activity by about 60%-70% compared with controls, which was reversed by a let7a-5p mimic inhibitor. Expression of this mimic led to a significant decrease in endogenous ABCC2 mRNA and protein levels in a Huh-7 liver cell line, which could be blocked by expression of a let7a-5p mimic inhibitor. Injection of a lentivirus let7a-5p inhibitor into normal mouse liver or into mouse liver after common bile duct ligation led to a significant increase in endogenous Abcc2 mRNA and protein levels and a depletion of let7a-5p mRNA levels compared with untreated, saline-injected livers or livers treated with an inactive lentivirus control. Conclusion: These studies demonstrate that miR-let7a-5p is involved in regulating ABCC2/Abcc2 expression, and is aberrantly up-regulated in obstructive cholestasis.

Role of transportome in the pharmacogenomics of hepatocellular carcinoma and hepatobiliary cancer

An important factor determining the pharmacological response to antitumor drugs is their concentrations in cancer cells, which accounts for the net interaction with their intracellular molecular targets. Accordingly, mechanisms leading to reduced intracellular levels of active agents play a crucial role in cancer chemoresistance. These include impaired drug uptake through solute carrier (SLC) proteins and efficient drug export by ATP-dependent pumps belonging to the ATP-binding cassette (ABC) superfamily of proteins. Since the net movement of drugs in-and-out the cells depends on the overall expression of carrier proteins, defining the so-called transportome, special attention has been devoted to the study of transcriptome regarding these proteins. Nevertheless, genetic variants affecting SLC and ABC genes may markedly affect the bioavailability and, hence, the efficacy of anticancer drugs.

ABC Transporters: Regulation and Association with Multidrug Resistance in Hepatocellular Carcinoma and Colorectal Carcinoma

For most cancers, the treatment of choice is still chemotherapy despite its severe adverse effects, systemic toxicity and limited efficacy due to the development of multidrug resistance (MDR). MDR leads to chemotherapy failure generally associated with a decrease in drug concentration inside cancer cells, frequently due to the overexpression of ABC transporters such as P-glycoprotein (P-gp/MDR1/ABCB1), multidrug resistance-associated proteins (MRPs/ABCCs), and breast cancer resistance protein (BCRP/ABCG2), which limits the efficacy of chemotherapeutic drugs. The aim of this review is to compile information about transcriptional and post-transcriptional regulation of ABC transporters and discuss their role in mediating MDR in cancer cells. This review also focuses on drug resistance by ABC efflux transporters in cancer cells, particularly hepatocellular carcinoma (HCC) and colorectal carcinoma (CRC) cells. Some aspects of the chemotherapy failure and future directions to overcome this problem are also discussed.

Modulation of Hepatic MRP3/ABCC3 by Xenobiotics and Pathophysiological Conditions: Role in Drug Pharmacokinetics

Liver transporters play an important role in the pharmacokinetics and disposition of pharmaceuticals, environmental contaminants, and endogenous compounds. Among them, the family of ATP-Binding Cassette (ABC) transporters is the most important due to its role in the transport of endo- and xenobiotics. The ABCC sub-family is the largest one, consisting of 13 members that include the cystic fibrosis conductance regulator (CFTR/ABCC7); the sulfonylurea receptors (SUR1/ABCC8 and SUR2/ABCC9) and the multidrug resistanceassociated proteins (MRPs). The MRP-related proteins can collectively confer resistance to natural, synthetic drugs and their conjugated metabolites, including platinum-containing compounds, folate anti-metabolites, nucleoside and nucleotide analogs, among others. MRPs can be also catalogued into "long" (MRP1/ABCC1, -2/C2, -3/C3, -6/C6, and -7/C10) and "short" (MRP4/C4, -5/C5, -8/C11, -9/C12, and -10/C13) categories. While MRP2/ABCC2 is expressed in the canalicular pole of hepatocytes, all others are located in the basolateral membrane. In this review, we summarize information from studies examining the changes in expression and regulation of the basolateral hepatic transporter MPR3/ABCC3 by xenobiotics and during various pathophysiological conditions. We also focus, primarily, on the consequences of such changes in the pharmacokinetic, pharmacodynamic and/or toxicity of different drugs of clinical use transported by MRP3.

Dengue virus potentially promotes migratory responses on endothelial cells by enhancing pro-migratory soluble factors and miRNAs

The most life-threatening effect of the Dengue virus (DENV) infection is an acute destabilization of the microvascular endothelial cell (MEC) barrier leading to plasma leakage, hypovolemic shock and haemorrhage. However, the underlying cellular mechanisms responsible for the dysfunction of MECs are not well understood. To identify potential cellular processes altered during DENV infection of MECs, expression profiles of cytokines/growth factors and microRNAs were measured by Luminex assay and next generation sequencing, respectively. Synchronously DENV2-infected MECs increase the secretion of IL-6, IL-8, FGF-2, GM-CSF, G-CSF, TGF-α, GRO, RANTES, MCP-1 and MCP-3. Conditioned media of infected MECs increased the migration of non-infected MECs. Furthermore, six miRNAs deregulated at 24 hpi were predicted to regulate host genes involved in cell migration and vascular developmental processes such as angiogenesis. These in silico analyses provide insights that support that DENV promotes an acute migratory phenotype in MECs that contributes to the vascular destabilization observed in severe dengue cases.

Epigenetics and MicroRNAs in Pharmacogenetics

Germline pharmacogenetics has so far mainly studied common variants in "pharmacogenes," i.e., genes encoding drug metabolizing enzymes and transporters (DMET genes), certain auxiliary and regulatory genes, and drug target genes. Despite remarkable progress in understanding genetically determined differences in pharmacokinetics and pharmacodynamics of drugs, currently known common variants even in important pharmacogenes explain genetic variability only partially. This suggests "missing heritability" that may in part be due to rare variants in the classical pharmacogenes, but current evidence suggests that largely unexplored resources with potential for pharmacogenetics exist, both within already known pharmacogenes and in entirely new areas. In particular, recent studies suggest that epigenetic processes and noncoding RNAs, including mostly microRNAs (miRNAs), represent important and largely unexplored layers of DMET gene regulation that may fill some of the gaps in understanding interindividual variability and lead to new biomarkers. In this chapter we summarize recent advances in the understanding of genetic variability in epigenetic and miRNA-mediated processes with focus on their significance for DMET regulation and pharmacokinetic or pharmacological endpoints.

MicroRNA-212/ABCG2-axis contributes to development of imatinib-resistance in leukemic cells

BCR-ABL-independent resistance against tyrosine kinase inhibitor is an emerging problem in therapy of chronic myeloid leukemia. Such drug resistance can be linked to dysregulation of ATP-binding cassette (ABC)-transporters leading to increased tyrosine kinase inhibitor efflux, potentially caused by changes in microRNA expression or DNA-methylation. In an in vitro-imatinib-resistance model using K-562 cells, microRNA-212 was found to be dysregulated and inversely correlated to ABC-transporter ABCG2 expression, targeting its 3'-UTR. However, the functional impact on drug sensitivity remained unknown. Therefore, we performed transfection experiments using microRNA-mimics and -inhibitors and investigated their effect on imatinib-susceptibility in sensitive and resistant leukemic cell lines. Under imatinib-treatment, miR-212 inhibition led to enhanced cell viability (p = 0.01), reduced apoptosis (p = 0.01) and cytotoxicity (p = 0.03). These effects were limited to treatment-naïve cells and were not observed in cells, which were resistant to various imatinib-concentrations (0.1 μM to 2 μM). Further analysis in treatment-naïve cells revealed that miR-212 inhibition resulted in ABCG2 upregulation and increased ABCG2-dependent efflux. Furthermore, we observed miR-212 promoter hypermethylation in 0.5 and 2 μM IM-resistant sublines, whereas ABCG2 methylation status was not altered. Taken together, the miR-212/ABCG2-axis influences imatinib-susceptibility contributing to development of imatinib-resistance. Our data reveal new insights into mechanisms initiating imatinib-resistance in leukemic cells.

MicroRNA-655-3p regulates Echinacea purpurea mediated activation of ABCG2

1. The aim of this study was to investigate the regulatory effect of Echinacea purpurea (EP) on efflux transporters ABCB1 and ABCG2 and to identify specific microRNAs contributing to their post-transcriptional regulation. 2. ABCB1 and ABCG2 levels were assessed in human hepatoblastoma HepG2 cells treated with 50 µg/mL methanolic extract of commercial EP capsules for different durations. The microRNA expression profile of HepG2 cells after EP treatment was evaluated and in silico target prediction was subsequently conducted to identify specific microRNAs with binding sites in the 3'-UTR of ABCB1 and ABCG2. Luciferase reporter gene assays and site-directed mutagenesis were used to confirm the binding site of identified microRNA within the 3'-UTR of the target gene. 3. EP increased ABCB1 (10-fold ± 3.4, p < 0.001) and ABCG2 (2.7-fold ± 0.5, p < 0.01) mRNA levels after 12 h exposure. Twenty-four microRNAs showed significant expression differences at all durations of exposure to EP. MiR-655-3p showed a 6.79-fold decrease in expression after 12 h exposure compared to 0 h, was predicted in silico to bind ABCG2 3'-UTR and showed a significant negative correlation (p = 0.01) to ABCG2 expression level. The binding of miR-655-3p to ABCG2 3'-UTR was confirmed by reporter gene assays (reduction of reporter gene activity to 60%; p = 0.0001). 4. These results suggest that EP regulates ABCG2 expression via downregulation of miR-655-3p in the liver cells. Thus, miR-655-3p downregulation could be applied to predict EP mediated drug interactions.

microRNAs and Acute Myeloid Leukemia Chemoresistance: A Mechanistic Overview

Up until the early 2000s, a functional role for microRNAs (miRNAs) was yet to be elucidated. With the advent of increasingly high-throughput and precise RNA-sequencing techniques within the last two decades, it has become well established that miRNAs can regulate almost all cellular processes through their ability to post-transcriptionally regulate a majority of protein-coding genes and countless other non-coding genes. In cancer, miRNAs have been demonstrated to play critical roles by modifying or controlling all major hallmarks including cell division, self-renewal, invasion, and DNA damage among others. Before the introduction of anthracyclines and cytarabine in the 1960s, acute myeloid leukemia (AML) was considered a fatal disease. In decades since, prognosis has improved substantially; however, long-term survival with AML remains poor. Resistance to chemotherapy, whether it is present at diagnosis or induced during treatment is a major therapeutic challenge in the treatment of this disease. Certain mechanisms such as DNA damage response and drug targeting, cell cycling, cell death, and drug trafficking pathways have been shown to be further dysregulated in treatment resistant cancers. miRNAs playing key roles in the emergence of these drug resistance phenotypes have recently emerged and replacement or inhibition of these miRNAs may be a viable treatment option. Herein, we describe the roles miRNAs can play in drug resistant AML and we describe miRNA-transcript interactions found within other cancer states which may be present within drug resistant AML. We describe the mechanisms of action of these miRNAs and how they can contribute to a poor overall survival and outcome as well. With the precision of miRNA mimic- or antagomir-based therapies, miRNAs provide an avenue for exquisite targeting in the therapy of drug resistant cancers.

In Vitro Assessment of the Effect of Antiepileptic Drugs on Expression and Function of ABC Transporters and Their Interactions with ABCC2

ABC transporters have a significant role in drug disposition and response and various studies have implicated their involvement in epilepsy pharmacoresistance. Since genetic studies till now are inconclusive, we thought of investigating the role of xenobiotics as transcriptional modulators of ABC transporters. Here, we investigated the effect of six antiepileptic drugs (AEDs) viz. phenytoin, carbamazepine, valproate, lamotrigine, topiramate and levetiracetam, on the expression and function of ABCB1, ABCC1, ABCC2 and ABCG2 in Caco2 and HepG2 cell lines through real time PCR, western blot and functional activity assays. Further, the interaction of AEDs with maximally induced ABCC2 was studied. Carbamazepine caused a significant induction in expression of ABCB1 and ABCC2 in HepG2 and Caco2 cells, both at the transcript and protein level, together with increased functional activity. Valproate caused a significant increase in the expression and functional activity of ABCB1 in HepG2 only. No significant effect of phenytoin, lamotrigine, topiramate and levetiracetam on the transporters under study was observed in either of the cell lines. We demonstrated the interaction of carbamazepine and valproate with ABCC2 with ATPase and 5,6-carboxyfluorescein inhibition assays. Thus, altered functionality of ABCB1 and ABCC2 can affect the disposition and bioavailability of administered drugs, interfering with AED therapy.

Expression, regulation and function of intestinal drug transporters: an update

Although oral drug administration is currently the favorable route of administration, intestinal drug absorption is challenged by several highly variable and poorly predictable processes such as gastrointestinal motility, intestinal drug solubility and intestinal metabolism. One further determinant identified and characterized during the last two decades is the intestinal drug transport that is mediated by several transmembrane proteins such as P-gp, BCRP, PEPT1 and OATP2B1. It is well-established that intestinal transporters can affect oral absorption of many drugs in a significant manner either by facilitating their cellular uptake or by pumping them back to gut lumen, which limits their oral bioavailability. Their functional relevance becomes even more apparent in cases of unwanted drug-drug interactions when concomitantly given drugs that cause transporter induction or inhibition, which in turn leads to increased or decreased drug exposure. The longitudinal expression of several intestinal transporters is not homogeneous along the human intestine, which may have functional implications on the preferable site of intestinal drug absorption. Besides the knowledge about the expression of pharmacologically relevant transporters in human intestinal tissue, their exact localization on the apical or basolateral membrane of enterocytes is also of interest but in several cases debatable. Finally, there is obviously a coordinative interplay of intestinal transporters (apical-basolateral), intestinal enzymes and transporters as well as intestinal and hepatic transporters. This review aims to give an updated overview about the expression, localization, regulation and function of clinically relevant transporter proteins in the human intestine.

Pharmacoepigenetics: an element of personalized therapy?

INTRODUCTION

Epigenetics is a rapidly growing field describing heritable alterations in gene expression that do not involve DNA sequence variations. Advances in epigenetics and epigenomics have influenced pharmacology, leading to the development of a new specialty, pharmacoepigenetics, the study of the epigenetic basis for the individual variation in drug response. Areas covered: We present an overview of the major epigenetic mechanisms and their effects on the expression of drug metabolizing enzymes and drug transporters, as well as the epigenetic status of drug protein targets affecting therapy response. Recent advances in the development of pharmacoepigenetic biomarkers and epidrugs are also discussed. Expert opinion: There is growing evidence that pharmacoepigenetics has the potential to become an important element of personalized medicine. Epigenetic modifications influence drug response, but they can also be modulated by drugs. Moreover, they can be monitored not only in the affected tissue, but also in body fluids. Nevertheless, there are very few examples of epigenetic biomarkers implemented in the clinical setting. Explanation of the interplay between genomic and epigenomic changes will contribute to the personalized medicine approach. Ultimately, both genetic biomarkers and epigenetic mechanisms should be taken into consideration in predicting drug response in the course of successful personalized therapy.

MiRNAs and miRNA Polymorphisms Modify Drug Response

Differences in expression of drug response-related genes contribute to inter-individual variation in drugs’ biological effects. MicroRNAs (miRNAs) are small noncoding RNAs emerging as new players in epigenetic regulation of gene expression at post-transcriptional level. MiRNAs regulate the expression of genes involved in drug metabolism, drug transportation, drug targets and downstream signal molecules directly or indirectly. MiRNA polymorphisms, the genetic variations affecting miRNA expression and/or miRNA-mRNA interaction, provide a new insight into the understanding of inter-individual difference in drug response. Here, we provide an overview of the recent progress in miRNAs mediated regulation of biotransformation enzymes, drug transporters, and nuclear receptors. We also describe the implications of miRNA polymorphisms in cancer chemotherapy response.

MicroRNA-379 suppresses osteosarcoma progression by targeting PDK1

Osteosarcoma is the most common primary bone tumour. Increasing evidence has demonstrated the pathogenic role of microRNA (miRNAs) dysregulation in tumour development. miR-379 was previously reported to function as an oncogenic or tumour-suppressing miRNA in a tissue-dependent manner. However, its function in osteosarcoma remains unknown. In this study, we found that the expression of miR-379 was downregulated in osteosarcoma tissues and cell lines. Further functional characterization revealed that miR-379 suppressed osteosarcoma cell proliferation and invasion in vitro and retarded the growth of osteosarcoma xenografts in vivo. Mechanistically, PDK1 was identified as the direct target of miR-379 in osteosarcoma, in which PDK1 expression was up-regulated and showed inverse correlation with miR-379. Enforced expression of PDK1 promoted osteosarcoma cell proliferation and rescued the anti-proliferative effect of miR-379. These data suggest that miR-379 could function as a tumour-suppressing miRNA via targeting PDK1 in osteosarcoma.

MicroRNAs as key mediators of hepatic detoxification

MicroRNAs (miRNAs) are a class of short noncoding RNAs that modulate gene expression at both transcriptional and post-transcriptional levels. Many studies have extensively revealed the significance of miRNAs in mediating liver development and diseases. However, their role in hepatic detoxification processes has been explored only recently. In this review, we summarized the up-to-date knowledge about miRNA dependent regulation of enzymes involved in all three phases of the drugs and xenobiotics detoxification process. We also discussed the role of miRNA in regulating some upstream nuclear receptors involving gene expression of enzymes for detoxification process in liver. The toxicological significance of miRNAs in liver diseases and future research perspectives are finally presented.

ATP-binding cassette transmembrane transporters and their epigenetic control in cancer: an overview

INTRODUCTION

Members of the ATP-binding cassette (ABC) transmembrane transporters control the passage of several substrates across cell membranes, including drugs. This means that ABC transporters may exert a significant influence on the kinetics and dynamics of pharmacological agents, being responsible for the occurrence of multidrug-resistant (MDR) phenotype. Pharmacogenetic analyses have shed light on gene expression and polymorphisms as possible markers predictive of transporter activity. However, a non-negligible part of the variability in drug pharmacokinetics and pharmacodynamics still remains. Further research has demonstrated that different epigenetic mechanisms exert a coordinated control over ABC genes, and on the corresponding MDR phenotype. Areas covered: DNA methylation and histone modifications (namely acetylation, methylation, phosphorylation, etc.) significantly impact gene expression, as well as noncoding RNA molecules that are involved in the post-transcriptional control of the ABC transporters ABCB1, ABCC1 and ABCG2. We describe the epigenetic mechanisms of gene expression control for ABC transporters and their relevant association with the MDR phenotype in human cancer. Expert opinion: The clinical meaning of those observations is discussed in the review, highlighting the importance of the epigenetic control of the ABC transporters for the clinical therapeutic outcomes that despite their effects and applications, requires further investigation.

Polymorphisms associated with renal adverse effects of antiretroviral therapy in a Southern Brazilian HIV cohort

OBJECTIVE

This study evaluated the impact of seven single nucleotide polymorphisms in five candidate genes (ABCB1, ABCC2, ABCC4, SLC22A6, and SLC22A11) in relation to nephrotoxicity associated with highly active antiretroviral therapy (HAART) in HIV-infected individuals.

METHODS

The following single nucleotide polymorphisms were genotyped by real-time PCR: ABCB1 rs1045642, ABCC2 rs717620 and rs2273697, ABCC4 rs1751034 and rs3742106, SLC22A6 rs11568626, and SLC22A11 rs11231809 in 507 HIV-infected patients from the city of Porto Alegre, Southern Brazil, receiving HAART for, at least, 1 year.

RESULTS

From the 507 HIV-infected patients recruited, 19.1% presented a reduction in estimated glomerular filtration rate (eGFR). A total of 16 (3.2%) patients fulfilled the criteria for chronic kidney disease (defined as eGFR<60 ml/min/1.73 m). Individuals carrying at least one T allele of ABCC2 -24 C>T (rs717620) presented lower eGFR than C/C homozygotes (104 ± 22 vs. 108 ± 22 ml/min/1.73 m, independent-samples t-test, P=0.040). In multivariate analysis, the predictors associated with decreased eGFR were time of treatment, tenofovir use, atazanavir/ritonavir use, and carrying one T allele of ABCC2 -24 C>T.

CONCLUSION

Our data support the importance of genetic factors in the etiology of nephrotoxicity in patients treated with HAART. Studies to verify treatment implications of genotyping before HAART initiation may be advisable to guide the selection of an appropriate antiretroviral therapy regimen.

Rifampin Regulation of Drug Transporters Gene Expression and the Association of MicroRNAs in Human Hepatocytes

Membrane drug transporters contribute to the disposition of many drugs. In human liver, drug transport is controlled by two main superfamilies of transporters, the solute carrier transporters (SLC) and the ATP Binding Cassette transporters (ABC). Altered expression of these transporters due to drug-drug interactions can contribute to differences in drug exposure and possibly effect. In this study, we determined the effect of rifampin on gene expression of hundreds of membrane transporters along with all clinically relevant drug transporters.

METHODS

In this study, primary human hepatocytes (n = 7 donors) were cultured and treated for 24 h with rifampin and vehicle control. RNA was isolated from the hepatocytes, mRNA expression was measured by RNA-seq, and miRNA expression was analyzed by Taqman OpenArray. The effect of rifampin on the expression of selected transporters was also tested in kidney cell lines. The impact of rifampin on the expression of 410 transporter genes from 19 different transporter gene families was compared with vehicle control.

RESULTS

Expression patterns of 12 clinically relevant drug transporter genes were changed by rifampin (FDR < 0.05). For example, the expressions of ABCC2, ABCB1, and ABCC3 were increased 1.9-, 1.7-, and 1.2-fold, respectively. The effects of rifampin on four uptake drug transporters (SLCO1B3, SLC47A1, SLC29A1, SLC22A9) were negatively correlated with the rifampin effects on specific microRNA expression (SLCO1B3/miR-92a, SLC47A1/miR-95, SLC29A1/miR-30d#, and SLC22A9/miR-20; r < -0.79; p < 0.05). Seven hepatic drug transporter genes (SLC22A1, SLC22A5, SLC15A1, SLC29A1, SLCO4C1, ABCC2, and ABCC4), whose expression was altered by rifampin in hepatocytes, were also present in a renal proximal tubular cell line, but in renal cells rifampin did not alter their gene expression. PXR expression was very low in the kidney cells; this may explain why rifampin induces gene expression in a tissue-specific manner.

CONCLUSION

Rifampin alters the expression of many of the clinically relevant hepatic drug transporters, which may provide a rational basis for understanding rifampin-induced drug-drug interactions reported in vivo. The relevance of its effect on many other transporters remains to be studied.

MicroRNA-30c-1-3p is a silencer of the pregnane X receptor by targeting the 3'-untranslated region and alters the expression of its target gene cytochrome P450 3A4

The pregnane X receptor (PXR) is a master regulator of genes involved in drug elimination. Recently, activation of PXR has also been linked to the development of many disease conditions such as metabolic disorders and malignancies. MicroRNAs (miRs) emerge as important molecular species involved in these conditions. This study was undertaken to test a large number of miRs for their ability to regulate PXR expression. As many as 58 miRs were tested and miR-30c-1-3p was identified to suppress PXR expression. The suppression was achieved by targeting the 3'-untranslated region, 438 nucleotides from the stop codon. The suppression was detected in multiple cell lines from different organ origins. In addition, miR-30c-1-3p altered basal and induced expression of cytochrome P450 3A4 (CYP3A4), a prototypical target gene of PXR. The alteration varied depending on the time and amounts of miR-30c-1-3p. CYP3A4 is responsible for the metabolism of more than 50% medicines. The interconnection between miR-30c-1-3p and PXR signifies a role of miRs in drug-drug interactions and chemosensitivity. This article is part of a Special Issue entitled: Xenobiotic nuclear receptors: New Tricks for An Old Dog, edited by Dr. Wen Xie.

MicroRNA-379-5p inhibits tumor invasion and metastasis by targeting FAK/AKT signaling in hepatocellular carcinoma

Some microRNAs (miRNAs) have been implicated in hepatocellular carcinoma (HCC) development and progression. However, the roles and mechanisms of several miRNAs in HCC remain poorly understood. Here, we report that miR-379-5p, which is down-regulated in HCC tissues and cell lines, is associated with advanced TNM stage and metastasis in HCC. The ectopic overexpression of miR-379-5p inhibited HCC cell migration, invasion, epithelial-to-mesenchymal transition (EMT) and metastasis both in vitro and in vivo. Conversely, miR-379 knockdown increased migration, invasion and EMT in HCC cells. Moreover, miR-379-5p exerted this function by directly targeting focal adhesion kinase (FAK) 3'-UTR and repressing FAK expression, thus leading to suppression of AKT signaling. Furthermore, the tumor suppressive effects of miR-379-5p in HCC cells were reversed by activating AKT signaling or restoring FAK expression. In clinical samples of HCC, miR-379-5p negatively correlated with FAK, which was up-regulated in HCC. Taken together, our findings highlight the important role of miR-379-5p in regulating the EMT and metastasis of HCC by targeting FAK/AKT signaling, suggesting that miR-379-5p may represent a novel potential therapeutic target and prognostic marker for HCC.

MicroRNA Pharmacoepigenetics: Posttranscriptional Regulation Mechanisms behind Variable Drug Disposition and Strategy to Develop More Effective Therapy

Knowledge of drug absorption, distribution, metabolism, and excretion (ADME) or pharmacokinetics properties is essential for drug development and safe use of medicine. Varied or altered ADME may lead to a loss of efficacy or adverse drug effects. Understanding the causes of variations in drug disposition and response has proven critical for the practice of personalized or precision medicine. The rise of noncoding microRNA (miRNA) pharmacoepigenetics and pharmacoepigenomics has come with accumulating evidence supporting the role of miRNAs in the modulation of ADME gene expression and then drug disposition and response. In this article, we review the advances in miRNA pharmacoepigenetics including the mechanistic actions of miRNAs in the modulation of Phase I and II drug-metabolizing enzymes, efflux and uptake transporters, and xenobiotic receptors or transcription factors after briefly introducing the characteristics of miRNA-mediated posttranscriptional gene regulation. Consequently, miRNAs may have significant influence on drug disposition and response. Therefore, research on miRNA pharmacoepigenetics shall not only improve mechanistic understanding of variations in pharmacotherapy but also provide novel insights into developing more effective therapeutic strategies.

The effects of microRNA on the absorption, distribution, metabolism and excretion of drugs

The importance of genetic factors (e.g. sequence variation) in the absorption, distribution, metabolism, excretion (ADME) and overall efficacy of therapeutic agents is well established. Our ability to identify, interpret and utilize these factors is the subject of much clinical investigation and therapeutic development. However, drug ADME and efficacy are also heavily influenced by epigenetic factors such as DNA/histone methylation and non-coding RNAs [especially microRNAs (miRNAs)]. Results from studies using tools, such as in silico miRNA target prediction, in vitro functional assays, nucleic acid profiling/sequencing and high-throughput proteomics, are rapidly expanding our knowledge of these factors and their effects on drug metabolism. Although these studies reveal a complex regulation of drug ADME, an increased understanding of the molecular interplay between the genome, epigenome and transcriptome has the potential to provide practically useful strategies to facilitate drug development, optimize therapeutic efficacy, circumvent adverse effects, yield novel diagnostics and ultimately become an integral component of personalized medicine.

Chimeric MicroRNA-1291 Biosynthesized Efficiently in Escherichia coli Is Effective to Reduce Target Gene Expression in Human Carcinoma Cells and Improve Chemosensitivity

In contrast to the growing interests in studying noncoding RNAs (ncRNAs) such as microRNA (miRNA or miR) pharmacoepigenetics, there is a lack of efficient means to cost effectively produce large quantities of natural miRNA agents. Our recent efforts led to a successful production of chimeric pre-miR-27b in bacteria using a transfer RNA (tRNA)-based recombinant RNA technology, but at very low expression levels. Herein, we present a high-yield expression of chimeric pre-miR-1291 in common Escherichia coli strains using the same tRNA scaffold. The tRNA fusion pre-miR-1291 (tRNA/mir-1291) was then purified to high homogeneity using affinity chromatography, whose primary sequence and post-transcriptional modifications were directly characterized by mass spectrometric analyses. Chimeric tRNA/mir-1291 was readily processed to mature miR-1291 in human carcinoma MCF-7 and PANC-1 cells. Consequently, recombinant tRNA/mir-1291 reduced the protein levels of miR-1291 target genes, including ABCC1, FOXA2, and MeCP2, as compared with cells transfected with the same doses of control methionyl-tRNA scaffold with a sephadex aptamer (tRNA/MSA). In addition, tRNA-carried pre-miR-1291 suppressed the growth of MCF-7 and PANC-1 cells in a dose-dependent manner, and significantly enhanced the sensitivity of ABCC1-overexpressing PANC-1 cells to doxorubicin. These results indicate that recombinant miR-1291 agent is effective in the modulation of target gene expression and chemosensitivity, which may provide insights into high-yield bioengineering of new ncRNA agents for pharmacoepigenetics research.

Regulation of multidrug resistance proteins by genistein in a hepatocarcinoma cell line: impact on sorafenib cytotoxicity

Hepatocellular carcinoma (HCC) is the fifth most frequent cancer worldwide. Sorafenib is the only drug available that improves the overall survival of HCC patients. P-glycoprotein (P-gp), Multidrug resistance-associated proteins 2 and 3 (MRP2 and 3) and Breast cancer resistance protein (BCRP) are efflux pumps that play a key role in cancer chemoresistance. Their modulation by dietary compounds may affect the intracellular accumulation and therapeutic efficacy of drugs that are substrates of these transporters. Genistein (GNT) is a phytoestrogen abundant in soybean that exerts its genomic effects through Estrogen-Receptors and Pregnane-X-Receptor (PXR), which are involved in the regulation of the above-mentioned transporters. We evaluated the effect of GNT on the expression and activity of P-gp, MRP2, MRP3 and BCRP in HCC-derived HepG2 cells. GNT (at 1.0 and 10 μM) increased P-gp and MRP2 protein expression and activity, correlating well with an increased resistance to sorafenib cytotoxicity as detected by the methylthiazole tetrazolium (MTT) assay. GNT induced P-gp and MRP2 mRNA expression at 10 but not at 1.0 μM concentration suggesting a different pattern of regulation depending on the concentration. Induction of both transporters by 1.0 μM GNT was prevented by cycloheximide, suggesting translational regulation. Downregulation of expression of the miR-379 by GNT could be associated with translational regulation of MRP2. Silencing of PXR abolished P-gp induction by GNT (at 1.0 and 10 μM) and MRP2 induction by GNT (only at 10 μM), suggesting partial mediation of GNT effects by PXR. Taken together, the data suggest the possibility of nutrient-drug interactions leading to enhanced chemoresistance in HCC when GNT is ingested with soy rich diets or dietary supplements.

MicroRNAs and their relevance to ABC transporters

MicroRNAs (miRNAs) are small noncoding RNAs, which regulate the expression of their target genes post-transcriptionally by RNA interference. They are involved in almost all cellular processes, including proliferation, differentiation, apoptosis, cell survival and the maintenance of tissue specificity. Recent findings also suggest that efflux pumps of the ABC (ATP-binding cassette) transporter family are subject to miRNA-mediated gene regulation. Moreover, it seems that ABC transporters are embedded in a concerted and miRNA-guided network of concurrently regulated proteins that mediate altered drug transport and cell survival in changing environmental conditions. In this review, we summarize recent findings of miRNAs interacting with ABC transporters, which have been connected with drug distribution as well as with drug resistance. Additionally, we specify findings of complex miRNA-protein pathways conferring increased drug export and cell survival.

Rapid production of novel pre-microRNA agent hsa-mir-27b in Escherichia coli using recombinant RNA technology for functional studies in mammalian cells

Noncoding microRNAs (miRNAs or miRs) have been revealed as critical epigenetic factors in the regulation of various cellular processes, including drug metabolism and disposition. However, research on miRNA functions is limited to the use of synthetic RNA and recombinant DNA agents. Herein, we show that novel pre-miRNA-27b (miR-27b) agents can be biosynthesized in Escherichia coli using recombinant RNA technology, and recombinant transfer RNA (tRNA)/mir-27b chimera was readily purified to a high degree of homogeneity (>95%) using anion-exchange fast protein liquid chromatography. The tRNA-fusion miR-27b was revealed to be processed to mature miRNA miR-27b in human carcinoma LS-180 cells in a dose- and time-dependent manner. Moreover, recombinant tRNA/miR-27b agents were biologically active in reducing the mRNA and protein expression levels of cytochrome P450 3A4 (CYP3A4), which consequently led to lower midazolam 1'-hydroxylase activity. These findings demonstrate that pre-miRNA agents can be produced by recombinant RNA technology for functional studies.

The biology of the germ line in echinoderms

The formation of the germ line in an embryo marks a fresh round of reproductive potential. The developmental stage and location within the embryo where the primordial germ cells (PGCs) form, however, differs markedly among species. In many animals, the germ line is formed by an inherited mechanism, in which molecules made and selectively partitioned within the oocyte drive the early development of cells that acquire this material to a germ-line fate. In contrast, the germ line of other animals is fated by an inductive mechanism that involves signaling between cells that directs this specialized fate. In this review, we explore the mechanisms of germ-line determination in echinoderms, an early-branching sister group to the chordates. One member of the phylum, sea urchins, appears to use an inherited mechanism of germ-line formation, whereas their relatives, the sea stars, appear to use an inductive mechanism. We first integrate the experimental results currently available for germ-line determination in the sea urchin, for which considerable new information is available, and then broaden the investigation to the lesser-known mechanisms in sea stars and other echinoderms. Even with this limited insight, it appears that sea stars, and perhaps the majority of the echinoderm taxon, rely on inductive mechanisms for germ-line fate determination. This enables a strongly contrasted picture for germ-line determination in this phylum, but one for which transitions between different modes of germ-line determination might now be experimentally addressed.

Regulation of expression and activity of multidrug resistance proteins MRP2 and MDR1 by estrogenic compounds in Caco-2 cells. Role in prevention of xenobiotic-induced cytotoxicity

ABC transporters including MRP2, MDR1 and BCRP play a major role in tissue defense. Epidemiological and experimental studies suggest a cytoprotective role of estrogens in intestine, though the mechanism remains poorly understood. We evaluated whether pharmacologic concentrations of ethynylestradiol (EE, 0.05pM to 5nM), or concentrations of genistein (GNT) associated with soy ingestion (0.1-10μM), affect the expression and activity of multidrug resistance proteins MRP2, MDR1 and BCRP using Caco-2 cells, an in vitro model of intestinal epithelium. We found that incubation with 5pM EE and 1μM GNT for 48h increased expression and activity of both MRP2 and MDR1. Estrogens did not affect expression of BCRP protein at any concentration studied. Irrespective of the estrogen tested, up-regulation of MDR1 and MRP2 protein was accompanied by increased levels of MDR1 mRNA, whereas MRP2 mRNA remained unchanged. Cytotoxicity assays demonstrated association of MRP2 and MDR1 up-regulation with increased resistance to cell death induced by 1-chloro-2,4-dinitrobenzene, an MRP2 substrate precursor, and by paraquat, an MDR1 substrate. Experiments using an estrogen receptor (ER) antagonist implicate ER participation in MRP2 and MDR1 regulation. GNT but not EE increased the expression of ERβ, the most abundant form in human intestine and in Caco-2 cells, which could lead in turn to increased sensitivity to estrogens. We conclude that specific concentrations of estrogens can confer resistance against cytotoxicity in Caco-2 cells, due in part to positive modulation of ABC transporters involved in extrusion of their toxic substrates. Although extrapolation of these results to the in vivo situation must be cautiously done, the data could explain tentatively the cytoprotective role of estrogens against chemical injury in intestine.