Role of Multidrug Resistance Protein 2 (MRP2, ABCC2) in Alkylating Agent Detoxification: MRP2 Potentiates GlutathioneS-Transferase A1-1-Mediated Resistance to Chlorambucil Cytotoxicity

Implications of chronic moderate protein-deficiency malnutrition on doxorubicin pharmacokinetics and cardiotoxicity in early post-weaning stage

BACKGROUND

Malnutrition is a common problem in developing countries, and the impact of severe malnutrition on optimal treatment outcomes of chemotherapy in pediatric cancer patients is well documented. However, despite being a more prevalent and distinct entity, moderate malnutrition is until now unexplored for its effects on treatment outcomes.

AIMS

In this study we aimed to investigate the molecular basis of altered pharmacokinetics and cardiotoxicity of doxorubicin observed in early-life chronic moderate protein deficiency malnutrition.

MATERIALS AND METHODS

We developed an animal model of early-life moderate protein-deficiency malnutrition and validated it using clinical samples. This model was used to study pharmacokinetic and toxicity changes and was further utilized to study the molecular changes in liver and heart to get mechanistic insights.

KEY FINDINGS

Here we show that moderate protein-deficiency malnutrition in weanling rats causes changes in drug disposition in the liver by modification of hepatic ABCC3 and MRP2 transporters through the TNFα signalling axis. Furthermore, malnourished rats in repeat-dose doxorubicin toxicity study showed higher toxicity and mortality. A higher accumulation of doxorubicin in the heart was observed which was associated with alterations in cardiac metabolic pathways and increased cardiotoxicity.

SIGNIFICANCE

Our findings indicate that moderate malnutrition causes increased susceptibility towards toxic side effects of chemotherapy. These results may necessitate further investigations and new guidelines on the dosing of chemotherapy in moderately malnourished pediatric cancer patients.

Structural Basis for Oxidized Glutathione Recognition by the Yeast Cadmium Factor 1

Transporters from the ABCC family have an essential role in detoxifying electrophilic compounds including metals, drugs, and lipids, often through conjugation with glutathione complexes. The Yeast Cadmium Factor 1 (Ycf1) transports glutathione alone as well as glutathione conjugated to toxic heavy metals including Cd2+, Hg2+, and As3+. To understand the complicated selectivity and promiscuity of heavy metal substrate binding, we determined the cryo-EM structure of Ycf1 bound to the substrate, oxidized glutathione. We systematically tested binding determinants with cellular survival assays against cadmium to determine how the substrate site accommodates different-sized metal complexes. We identify a "flex-pocket" for substrate binding that binds glutathione complexes asymmetrically and flexes to accommodate different size complexes.

Overexpression of Glutathione S-Transferases in Human Diseases: Drug Targets and Therapeutic Implications

Glutathione S-transferases (GSTs) are a major class of phase II metabolic enzymes. Besides their essential role in detoxification, GSTs also exert diverse biological activities in the occurrence and development of various diseases. In the past few decades, much research interest has been paid to exploring the mechanisms of GST overexpression in tumor drug resistance. Correspondingly, many GST inhibitors have been developed and applied, solely or in combination with chemotherapeutic drugs, for the treatment of multi-drug resistant tumors. Moreover, novel roles of GSTs in other diseases, such as pulmonary fibrosis and neurodegenerative diseases, have been recognized in recent years, although the exact regulatory mechanisms remain to be elucidated. This review, firstly summarizes the roles of GSTs and their overexpression in the above-mentioned diseases with emphasis on the modulation of cell signaling pathways and protein functions. Secondly, specific GST inhibitors currently in pre-clinical development and in clinical stages are inventoried. Lastly, applications of GST inhibitors in targeting cell signaling pathways and intracellular biological processes are discussed, and the potential for disease treatment is prospected. Taken together, this review is expected to provide new insights into the interconnection between GST overexpression and human diseases, which may assist future drug discovery targeting GSTs.

Understanding and targeting resistance mechanisms in cancer

Resistance to cancer therapies has been a commonly observed phenomenon in clinical practice, which is one of the major causes of treatment failure and poor patient survival. The reduced responsiveness of cancer cells is a multifaceted phenomenon that can arise from genetic, epigenetic, and microenvironmental factors. Various mechanisms have been discovered and extensively studied, including drug inactivation, reduced intracellular drug accumulation by reduced uptake or increased efflux, drug target alteration, activation of compensatory pathways for cell survival, regulation of DNA repair and cell death, tumor plasticity, and the regulation from tumor microenvironments (TMEs). To overcome cancer resistance, a variety of strategies have been proposed, which are designed to enhance the effectiveness of cancer treatment or reduce drug resistance. These include identifying biomarkers that can predict drug response and resistance, identifying new targets, developing new targeted drugs, combination therapies targeting multiple signaling pathways, and modulating the TME. The present article focuses on the different mechanisms of drug resistance in cancer and the corresponding tackling approaches with recent updates. Perspectives on polytherapy targeting multiple resistance mechanisms, novel nanoparticle delivery systems, and advanced drug design tools for overcoming resistance are also reviewed.

The Nitrogen Mustards

The nitrogen mustards are powerful cytotoxic and lymphoablative agents and have been used for more than 60 years. They are employed in the treatment of cancers, sarcomas, and hematologic malignancies. Cyclophosphamide, the most versatile of the nitrogen mustards, also has a place in stem cell transplantation and the therapy of autoimmune diseases. Adverse effects caused by the nitrogen mustards on the central nervous system, kidney, heart, bladder, and gonads remain important issues. Advances in analytical techniques have facilitated the investigation of the pharmacokinetics of the nitrogen mustards, especially the oxazaphosphorines, which are prodrugs requiring metabolic activation. Enzymes involved in the metabolism of cyclophosphamide and ifosfamide are very polymorphic, but a greater understanding of the pharmacogenomic influences on their activity has not yet translated into a personalized medicine approach. In addition to damaging DNA, the nitrogen mustards can act through other mechanisms, such as antiangiogenesis and immunomodulation. The immunomodulatory properties of cyclophosphamide are an area of current exploration. In particular, cyclophosphamide decreases the number and activity of regulatory T cells, and the interaction between cyclophosphamide and the intestinal microbiome is now recognized as an important factor. New derivatives of the nitrogen mustards continue to be assessed. Oxazaphosphorine analogs have been synthesized in attempts to both improve efficacy and reduce toxicity, with varying degrees of success. Combinations of the nitrogen mustards with monoclonal antibodies and small-molecule targeted agents are being evaluated. SIGNIFICANCE STATEMENT: The nitrogen mustards are important, well-established therapeutic agents that are used to treat a variety of diseases. Their role is continuing to evolve.

Short divalent ethacrynic amides as pro-inhibitors of glutathione S-transferase isozyme Mu and potent sensitisers of cisplatin-resistant ovarian cancers

The linking of ethacrynic acid with ethylenediamine and 1,4-butanediamine gave EDEA and BDEA, respectively, as membrane-permeable divalent pro-inhibitors of glutathione S-transferase (GST). Their divalent glutathione conjugates showed subnanomolar inhibition and divalence-binding to GSTmu (GSTM) (PDB: 5HWL) at ∼0.35 min^-1. In cisplatin-resistant SK-OV-3, COC1, SGC7901 and A549 cells, GSTM activities probed by 15 nM BDEA or EDEA revealed 5-fold and 1.0-fold increases in cisplatin-resistant SK-OV-3 and COC1 cells, respectively, in comparison with the susceptible parental cells. Being tolerable by HEK293 and LO2 cells, BDEA at 0.2 μM sensitised resistant SK-OV-3 and COC1 cells by ∼3- and ∼5-folds, respectively, released cytochrome c and increased apoptosis; EDEA at 1.0 μM sensitised resistant SK-OV-3 and A549 cells by ∼5- and ∼7-fold, respectively. EDEA at 1.7 μg/g sensitised resistant SK-OV-3 cells to cisplatin at 3.3 μg/g in nude mouse xenograft model. BDEA and EDEA are promising leads for probing cellular GSTM and sensitising cisplatin-resistant ovarian cancers.

Spheroid Culture Differentially Affects Cancer Cell Sensitivity to Drugs in Melanoma and RCC Models

2D culture as a model for drug testing often turns to be clinically futile. Therefore, 3D cultures (3Ds) show potential to better model responses to drugs observed in vivo. In preliminary studies, using melanoma (B16F10) and renal (RenCa) cancer, we confirmed that 3Ds better mimics the tumor microenvironment. Here, we evaluated how the proposed 3D mode of culture affects tumor cell susceptibility to anti-cancer drugs, which have distinct mechanisms of action (everolimus, doxorubicin, cisplatin). Melanoma spheroids showed higher resistance to all used drugs, as compared to 2D. In an RCC model, such modulation was only observed for doxorubicin treatment. As drug distribution was not affected by the 3D shape, we assessed the expression of MDR1 and mTor. Upregulation of MDR1 in RCC spheroids was observed, in contrast to melanoma. In both models, mTor expression was not affected by the 3D cultures. By NGS, 10 genes related with metabolism of xenobiotics by cytochrome p450 were deregulated in renal cancer spheroids; 9 of them were later confirmed in the melanoma model. The differences between 3D models and classical 2D cultures point to the potential to uncover new non-canonical mechanisms to explain drug resistance set by the tumor in its microenvironment.

The Interaction of Human Glutathione Transferase GSTA1-1 with Reactive Dyes

Human glutathione transferase A1-1 (hGSTA1-1) contributes to developing resistance to anticancer drugs and, therefore, is promising in terms of drug-design targets for coping with this phenomenon. In the present study, the interaction of anthraquinone and diazo dichlorotriazine dyes (DCTD) with hGSTA1-1 was investigated. The anthraquinone dye Procion blue MX-R (PBMX-R) appeared to interact with higher affinity and was selected for further study. The enzyme was specifically and irreversibly inactivated by PBMX-R, following a biphasic pseudo-first-order saturation kinetics, with approximately 1 mol of inhibitor per mol of the dimeric enzyme being incorporated. Molecular modeling and protein chemistry data suggested that the modified residue is the Cys112, which is located at the entrance of the solvent channel at the subunits interface. The results suggest that negative cooperativity exists upon PBMX-R binding, indicating a structural communication between the two subunits. Kinetic inhibition analysis showed that the dye is a competitive inhibitor towards glutathione (GSH) and mixed-type inhibitor towards 1-chloro-2,4-dinitrobenzene (CDNB). The present study results suggest that PBMX-R is a useful probe suitable for assessing by kinetic means the drugability of the enzyme in future drug-design efforts.

Structure and Function of Hepatobiliary ATP Binding Cassette Transporters

The liver is beyond any doubt the most important metabolic organ of the human body. This function requires an intensive crosstalk within liver cellular structures, but also with other organs. Membrane transport proteins are therefore of upmost importance as they represent the sensors and mediators that shuttle signals from outside to the inside of liver cells and/or vice versa. In this review, we summarize the known literature of liver transport proteins with a clear emphasis on functional and structural information on ATP binding cassette (ABC) transporters, which are expressed in the human liver. These primary active membrane transporters form one of the largest families of membrane proteins. In the liver, they play an essential role in for example bile formation or xenobiotic export. Our review provides a state of the art and comprehensive summary of the current knowledge of hepatobiliary ABC transporters. Clearly, our knowledge has improved with a breath-taking speed over the last few years and will expand further. Thus, this review will provide the status quo and will lay the foundation for new and exciting avenues in liver membrane transporter research.

Multiple ATP-binding cassette transporters genes are involved in thiamethoxam resistance in Aphis gossypii glover

ATP-binding cassette (ABC) transporters represent the largest known group of efflux pumps, utilizing ATP to translocate a broad spectrum of substrates across lipid membranes, which play an important role in phase III of the detoxification process. The presence of ABC transporters and their potential association with insecticide resistance have not been investigated in Aphis gossypii, one of the most economically important agricultural pests worldwide. In this study, the ABC transporter inhibitor-verapamil significantly increased thiamethoxam toxicity against resistant cotton aphids, suggesting that ABCs are involved in thiamethoxam resistance. ABC transporter genes were identified using the A. gossypii genome database and transcriptome data. A total of 69 ABC transporters were identified and grouped into seven subfamilies (A-G), including 4 ABCAs, 5 ABCBs, 25 ABCCs, 2 ABCDs, 1 ABCE, 4 ABCFs and 30 ABCGs. Of these ABC transporters, 53 were predicted to be functional, 19 were full transporters, 30 were half-transporters and 4 had two NBDs. Subfamilies C and G accounted for 77% (32 and 45%, respectively) of the genes. The transcripts of 20 of 26 ABCs based on the transcriptome were upregulated, and ABCA1, ABCA2, ABCB1, ABCB4, ABCB8, ABCD1, ABCD2, ABCE1, ABCF1, ABCF3, ABCG7, ABCG15, ABCG17, ABCG24, ABCG27, ABCG30, MRP1, MRP7, MRP14 and MRP21 transcripts were significantly increased in the thiamethoxan resistant strain compared to the susceptible strain with qRT-PCR. The suppression of overexpressed ABCs (ABCA2, ABCD1, ABCD2, ABCE1 and ABCG15) significantly increased the thiamethoxam sensitivity of resistant aphids. These results suggest that ABC transporters might be involved in thiamethoxam resistance in A. gossypii and will facilitate further work to validate the functional roles of these ABCs in thiamethoxam resistance. These results are useful for understanding the multiple resistance mechanisms of thiamethoxam and the management of insecticide-resistant cotton aphids.

The mercapturic acid pathway

The mercapturic acid pathway is a major route for the biotransformation of xenobiotic and endobiotic electrophilic compounds and their metabolites. Mercapturic acids (N-acetyl-l-cysteine S-conjugates) are formed by the sequential action of the glutathione transferases, γ-glutamyltransferases, dipeptidases, and cysteine S-conjugate N-acetyltransferase to yield glutathione S-conjugates, l-cysteinylglycine S-conjugates, l-cysteine S-conjugates, and mercapturic acids; these metabolites constitute a "mercapturomic" profile. Aminoacylases catalyze the hydrolysis of mercapturic acids to form cysteine S-conjugates. Several renal transport systems facilitate the urinary elimination of mercapturic acids; urinary mercapturic acids may serve as biomarkers for exposure to chemicals. Although mercapturic acid formation and elimination is a detoxication reaction, l-cysteine S-conjugates may undergo bioactivation by cysteine S-conjugate β-lyase. Moreover, some l-cysteine S-conjugates, particularly l-cysteinyl-leukotrienes, exert significant pathophysiological effects. Finally, some enzymes of the mercapturic acid pathway are described as the so-called "moonlighting proteins," catalytic proteins that exert multiple biochemical or biophysical functions apart from catalysis.

Roles of Hepatic Drug Transporters in Drug Disposition and Liver Toxicity

Hepatic drug transporters are mainly distributed in parenchymal liver cells (hepatocytes), contributing to drug's liver disposition and elimination. According to their functions, hepatic transporters can be roughly divided into influx and efflux transporters, translocating specific molecules from blood into hepatic cytosol and mediating the excretion of drugs and metabolites from hepatic cytosol to blood or bile, respectively. The function of hepatic transport systems can be affected by interspecies differences and inter-individual variability (polymorphism). In addition, some drugs and disease can redistribute transporters from the cell surface to the intracellular compartments, leading to the changes in the expression and function of transporters. Hepatic drug transporters have been associated with the hepatic toxicity of drugs. Gene polymorphism of transporters and altered transporter expressions and functions due to diseases are found to be susceptible factors for drug-induced liver injury (DILI). In this chapter, the localization of hepatic drug transporters, their regulatory factors, physiological roles, and their roles in drug's liver disposition and DILI are reviewed.

Metabolic and non-metabolic pathways that control cancer resistance to anthracyclines

Anthracyclines Doxorubicin, Epirubicin, Daunorubicin and Idarubicin are used to treat a variety of tumor types in the clinics, either alone or, most often, in combination therapies. While their cardiotoxicity is well known, the emergence of chemoresistance is also a major issue accounting for treatment discontinuation. Resistance to anthracyclines is associated to the acquisition of multidrug resistance conferred by overexpression of permeability glycoprotein-1 or other efflux pumps, by altered DNA repair, changes in topoisomerase II activity, cancer stemness and metabolic adaptations. This review further details the metabolic aspects of resistance to anthracyclines, emphasizing the contributions of glycolysis, the pentose phosphate pathway and nucleotide biosynthesis, glutathione, lipid metabolism and autophagy to the chemoresistant phenotype.

Prognostic implication of ABC transporters and cancer stem cell markers in patients with stage III colon cancer receiving adjuvant FOLFOX-4 chemotherapy

Cancer stem cell (CSC) and ATP-binding cassette (ABC) transporters are associated with treatment resistance and outcomes of patients with cancer. The present study investigated the prognostic implications of pre-therapeutic expression of ABC transporters and CSC markers in patients with colon cancer (CC) who received adjuvant 5-fluorouracil, leucovorin and oxaliplatin combination therapy (FOLFOX-4). The immunohistochemical expression of 3 ABC transporters, including ABC subfamily C member 2 (ABCC2), ABCC3 and ABC subfamily G member 2 (ABCG2), and 3 CSC markers, including sex determining region Y-box 2 (SOX2), leucine-rich repeat-containing G protein-coupled receptor 5 and aldehyde dehydrogenase 1, were determined in 164 CC tissues from patients with stage III CC, who underwent postoperative FOLFOX-4 chemotherapy. The association between the protein expression and patients' prognoses was statistically analyzed. ABCG2 was associated with favorable overall survival rate (OS; P=0.001), and ABCC2, ABCG2 and SOX2 were associated with increased disease-free survival rate (DFS; P=0.001, 0.002 and 0.013, respectively). In multivariate analyses, ABCG2 was an independent prognostic factor for OS [hazard ratio (HR)=2.877; P=0.046], and ABCC2 and SOX2 were independent prognostic factors for DFS (HR=2.831; P=0.014; HR=2.558, P=0.020, respectively). ABCC2, ABCG2 and SOX2 may be promising prognostic markers for patients with CC receiving FOLFOX-4 therapy.

Glutathione Transferases: Potential Targets to Overcome Chemoresistance in Solid Tumors

Multifunctional enzymes glutathione transferases (GSTs) are involved in the development of chemoresistance, thus representing a promising target for a novel approach in cancer treatment. This superfamily of polymorphic enzymes exhibits extraordinary substrate promiscuity responsible for detoxification of numerous conventional chemotherapeutics, at the same time regulating signaling pathways involved in cell proliferation and apoptosis. In addition to upregulated GST expression, different cancer cell types have a unique GST signature, enabling targeted selectivity for isoenzyme specific inhibitors and pro-drugs. As a result of extensive research, certain GST inhibitors are already tested in clinical trials. Catalytic properties of GST isoenzymes are also exploited in bio-activation of specific pro-drugs, enabling their targeted accumulation in cancer cells with upregulated expression of the appropriate GST isoenzyme. Moreover, the latest approach to increase specificity in treatment of solid tumors is development of GST pro-drugs that are derivatives of conventional anti-cancer drugs. A future perspective is based on the design of new drugs, which would selectively target GST overexpressing cancers more prone to developing chemoresistance, while decreasing side effects in off-target cells.

Sulfur mustard resistant keratinocytes obtained elevated glutathione levels and other changes in the antioxidative defense mechanism

BACKGROUND

Sulfur mustard (SM) is a potent blistering chemical warfare agent, which was first used in 1917. Despite the Chemical Weapons Convention, a use was recently reported in Syria in 2015. This emphasizes the importance to develop countermeasures against chemical warfare agents. Despite intensive research, there is still no antidote or prophylaxis available against SM.

METHODS

The newly developed SM-resistant keratinocyte cell line HaCaT/SM was used to identify new target structures for drug development, particularly the adaptations in protective measures against oxidative stress. For this purpose, glutathione (GSH) and NAD(P)H levels, the effect of glutathione S-transferase (GST) inhibition as well as activation and expression of Nrf2, GST, glutamate cysteine ligase (GCL) and glutathione-disulfide reductase (GSR) as well as multi-drug resistance (MDR) proteins 1, 3 and 5 were investigated.

RESULTS

The HaCaT/SM cells showed not only a better survival after treatment with SM or cytostatic drugs, but also hydrogen peroxide (H2O2). They exhibit more GSH even after SM treatment. Nrf2 levels were significantly lower. Inhibition of GST led to significantly decreased, activation to slightly higher IC50 values after SM treatment and a lower expression of GST was observed. The cells also expressed less GCLC and GSR. Expression of MDR1, MDR3 and MDR5 was higher under control conditions, but less stimulated by SM treatment. An increased NADP+/NADPH ratio as well as higher NAD+ levels were shown.

CONCLUSION

In summary, an improved response of the resistant cell line to oxidative stress was observed. The underlying mechanisms are elevated GSH levels as well as lower expression of Nrf2 and its targets GCLC and GST as well as GSR and MDR1, MDR3 and MDR5. GST is an especially interesting target because its inhibition already induced a significant SM sensitivity. SM resistance also caused redox equivalent level differences. Taken together, these findings provide further insight into the mechanism of SM resistance and may open a window for novel therapeutic targets in SM therapy.

Structures of isothiocyanates attributed to reactive oxygen species generation and microtubule depolymerization in HepG2 cells

The structure of the isothiocyanates (ITCs)-erucin, sulforaphane, erysolin, sulforaphene, and phenethyl isothiocyanate-were assessed as well as their respective in vitro anticancer activity on the hepatocellular carcinoma cell line HepG2. All of these ITCs induced both apoptotic and necrotic cell death. FTIR analysis indicated that the ITCs caused changes in cellular components comparable to vinblastine. Despite no observable effect on DNA, the ITCs all induced generation of intracellular reactive oxygen species (ROS) and suppressed microtubule polymerization. The variation in sulfur oxidation states and the presence of an aromatic ring on the ITC side chain affected microtubule depolymerization and intracellular ROS generation, leading to apoptotic and necrotic cancer cell death. Knowing the influences of structural variations of the ITC side chain would be useful for selecting the more potent ITCs (i.e., erysolin) for the design and development of effective chemopreventive agents.

Usefulness of the MRP2 promoter to overcome the chemoresistance of gastrointestinal and liver tumors by enhancing the expression of the drug transporter OATP1B1

Tumor response to chemotherapy is often limited by drug export through ABC proteins. To overcome this problem, here we have investigated the usefulness of inducing the expression of the multidrug uptake transporter OATP1B1 under the control of the MRP2 promoter (MRP2pr). Human hepatoma cells (Alexander) were transfected with MRP2pr fragments of different length fused to the firefly luciferase ORF in order to select the shortest fragment with the highest response to dexamethasone, which was subsequently used to generate the chimeric construct MRP2pr-OATP1B1-V5. Hepatoma cells transduced with MRP2pr-OATP1B1-V5 resulted in dexamethasone-sensitive inducible OATP1B1 expression and enhanced selective antitumor response to OATP1B1 substrates (paclitaxel, Bamet-R2 and Bamet-UD2). In human colon cancer cells LS174T/R, used as a model of endogenous chemoresistance due to MRP2 overexpression, MRP2pr-OATP1B1 induced OATP1B1 expression together with chemosensitivity to OATP1B1 substrates. In nude mice, xenografted tumors formed by LS174T/R cells transduced with MRP2pr-OATP1B1 plus treatment with dexamethasone were markedly sensitized to Bamet-UD2. In conclusion, the induced expression of anticancer drug uptake transporters, under the control of promoters of ABC proteins involved in chemoresistance, constitutes an interesting approach to overcome the poor response of cancer to chemotherapy due to reduced drug uptake and/or enhanced drug export.

Circadian Clock Is Involved in Regulation of Hepatobiliary Transport Mediated by Multidrug Resistance-Associated Protein 2

There has been a growing interest in circadian regulation of the expression and function of drug transporters. In this study, we investigated circadian rhythm in the expression and function of multidrug resistance-associated protein 2 (Mrp2) in mouse liver and involvement of circadian clock in their regulations by using the circadian clock genes (period 1 and period 2) knockout mice. The mRNA and protein expression of Mrp2, P-glycoprotein, and breast cancer resistance protein was measured in the mouse liver at different times of the day. Circadian variation of hepatobiliary excretion of phenolsulfonphthalein, a model substrate of Mrp2, was also investigated in mice. Circadian oscillation of Mrp2 protein expression was clearly observed in the mouse liver with levels down at the light phase and up at the dark phase. The cumulative biliary excretion and biliary clearance of phenolsulfonphthalein from the liver to the bile was 2.37- and 1.74-fold greater in mice administered during the dark phase than in those administered during the light phase, respectively. The circadian oscillation in mRNA expression of Mrp2 disappeared in period 1 and period 2 double knockout mice. These results suggest that the expression and function of Mrp2 show the circadian rhythm, controlled by circadian clock genes.

Metabolism, toxicity and anticancer activities of arsenic compounds

A variety of studies indicated that inorganic arsenic and its methylated metabolites have paradoxical effects, namely, carcinogenic and anticancer effects. Epidemiological studies have shown that long term exposure to arsenic can increase the risk of cancers of lung, skin or bladder in man, which is probably associated with the arsenic metabolism. In fact, the enzymatic conversion of inorganic arsenic by Arsenic (+3 oxidation state) methyltransferase (AS3MT) to mono- and dimethylated arsenic species has long been considered as a major route for detoxification. However, several studies have also indicated that biomethylation of inorganic arsenic, particularly the production of trivalent methylated metabolites, is a process that activates arsenic as a toxin and a carcinogen. On the other hand, arsenic trioxide (As2O3) has recently been recognized as one of the most effective drugs for the treatment of APL. However, elaboration of the cytotoxic mechanisms of arsenic and its methylated metabolites in eradicating cancer is sorely lacking. To provide a deeper understanding of the toxicity and carcinogenicity along with them use of arsenic in chemotherapy, caution is required considering the poor understanding of its various mechanisms of exerting toxicity. Thereby, in this review, we have focused on arsenic metabolic pathway, the roles of the methylated arsenic metabolites in toxicity and in the therapeutic efficacy for the treatments of solid tumors, APL and/or non-APL malignancies.

The detoxification responses, damage effects and bioaccumulation in the scallop Chlamys farreri exposed to single and mixtures of benzo[a]pyrene and chrysene

This study aimed to investigate the detoxification responses, damage effects and biotransformation in scallop Chlamys farreri exposed to benzo[a]pyrene (BaP) (0.1, 1μg/L), chrysene (CHR) (0.1, 1μg/L) and BaP+CHR (0.1+0.1, 1+1μg/L) for 15days. Results demonstrated that BaP and CHR concentration (BaP<CHR) in tissues increased rapidly in a time and dose effect. The mRNA expression of aryl hydrocarbon receptor (AhR), cytochrome P450 1A1 (CYP1A1), CYP1B1, multidrug resistance protein 1 (MRP1/ABCC1), breast cancer resistance protein (BCRP/ABCG2) and P-glycoprotein (P-gp) were induced especially in the mixtures of BaP and CHR. Heat shock protein 90 (HSP90) and aryl hydrocarbon receptor nuclear translocator (ARNT) mRNA expression was significantly elevated at days 1, 10 and 15. Detoxification enzymes of 7-ethoxyresorufin O-deethylase (EROD), uridine-diphosphate-glucuronyl-transferase (UGT) and sulfotransferase (SULT) were significantly induced and then became stable gradually while glutathione-S-transferase (GST) was inhibited in the mixtures of BaP and CHR at days 10 and 15. Superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT) and glutathione (GSH) were all stimulated especially in the mixtures of BaP and CHR. The levels of DNA strand breaks, lipid peroxidation (LPO) and protein carbonyl (PC) contents showed damage effects exposed BaP and CHR. All the results indicated that BaP and CHR have similar induced effect and a majority of the biomarkers pointed to a more toxic effect when BaP and CHR were mixed. These will provide a solid foundation for the study of PAHs detoxification mechanism in bivalves and valuable information for marine pollution monitoring.

Parkinsonism-associated protein DJ-1 is a bona fide deglycase

We discovered recently that Parkinsonism-associated DJ-1 and its bacterial homologs function as protein deglycases that repair glyoxal- and methylglyoxal-glycated proteins. Protein glycation levels are 2- to 10-fold increased in deglycase-depleted cells, and deglycase mutants display up to 500-fold loss of viability in methylglyoxal or glucose-containing media, suggesting that these deglycases play important roles in protecting cells against electrophile and carbonyl stress. Although the deglycase activity of DJ-1 is well supported by extensive biochemical work, Pfaff et al. (J. Biol. Chem. in presshttp://dx.doi.org/10.1074/jbc.M116.743823) claimed in a recent study that deglycation of the hemithioacetal formed upon cysteine glycation by methylglyoxal results from a Tris buffer artefact. Here, we show that this is not the case, and that DJ-1 and its homologs are the bona fide deglycases awaited since the Maillard discovery.

The DJ-1 superfamily members YhbO and YajL from Escherichia coli repair proteins from glycation by methylglyoxal and glyoxal

YhbO and YajL belong to the PfpI/Hsp31/DJ-1 superfamily. Both proteins are involved in protection against environmental stresses. Here, we show that, like DJ-1 and Hsp31, they repair glyoxal- and methylglyoxal-glycated proteins. YhbO and YajL repair glycated serum albumin, collagen, glyceraldehyde-3-phosphate dehydrogenase, and fructose biphosphate aldolase. Bacterial extracts from deglycase mutants display increased glycation levels, whereas deglycase overexpression decreases protein glycation. Moreover, yhbO and yajL mutants display decreased viability in methylglyoxal- or glucose-containing media. Finally, the apparent glyoxalase activities of YhbO and YajL reflect their deglycase activities.

Nrf2 Regulates the Sensitivity of Mouse Keratinocytes to Nitrogen Mustard via Multidrug Resistance-Associated Protein 1 (Mrp1)

Sulfur mustard and nitrogen mustard (mechlorethamine, HN2) are potent vesicants developed as chemical warfare agents. These electrophilic, bifunctional alkylating agents cause skin injury, including inflammation, edema, and blistering. HN2 covalently modifies macromolecules such as DNA, RNA, and proteins or is scavenged by glutathione, forming adducts that can contribute to toxicity. Multidrug resistance-associated protein 1 (Mrp1/MRP1) is a transmembrane ATPase known to efflux glutathione-conjugated electrophiles. In the present studies, we examined the effects of modulating Mrp1-mediated transport activity on the sensitivity of primary and PAM212 mouse keratinocytes to HN2. Primary keratinocytes, and to a lesser extent, PAM212 cells, express Mrp1 mRNA and protein and possess Mrp1 functional activity, as measured by calcein efflux. Sulforaphane, an activator of Nrf2, increased Mrp1 mRNA, protein, and functional activity in primary keratinocytes and PAM212 cells and decreased their sensitivity to HN2-induced growth inhibition (IC(50) = 1.4 and 4.8 µM in primary keratinocytes and 1 and 13 µM in PAM212 cells, in the absence and presence of sulforaphane, respectively). The Mrp1 inhibitor, MK-571, reversed the effects of sulforaphane on HN2-induced growth inhibition in both primary keratinocytes and PAM212 cells. In primary keratinocytes from Nrf2(-/-) mice, sulforaphane had no impact on Mrp1 expression or activity, or on sensitivity to HN2, demonstrating that its effects depend on Nrf2. These data suggest that Mrp1-mediated efflux is important in regulating HN2-induced keratinocyte growth inhibition. Enhancing HN2 efflux from keratinocytes may represent a novel strategy for mitigating vesicant-induced cytotoxicity.

The DJ-1 superfamily member Hsp31 repairs proteins from glycation by methylglyoxal and glyoxal

Hsp31 belongs to the PfpI/Hsp31/DJ-1 superfamily, and has been reported to display chaperone, peptidase and glutathione-independent glyoxalase activities. Here, we show that Hsp31 repairs glyoxal- and methylglyoxal-glycated amino acids and proteins and releases repaired proteins and lactate or glycolate, respectively. Hsp31 deglycates cysteine, arginine and lysine by acting on early glycation intermediates (hemithioacetals and aminocarbinols) and prevents the formation of Schiff bases and advanced glycation endproducts. Hsp31 repairs glycated serum albumin, glyceraldehyde-3-phosphate dehydrogenase, fructose biphosphate aldolase and aspartate aminotransferase. Moreover, we show that bacterial extracts from the hchA mutant display increased glycation levels and that the apparent glyoxalase activity of Hsp31 reflects its deglycase activity. Our results suggest that other Hsp31 members, previously characterized as glutathione-independent glyoxalases, likely function as protein deglycases.

The role of ABC transporters in ovarian cancer progression and chemoresistance

Over 80% of ovarian cancer patients develop chemoresistance which results in a lethal course of the disease. A well-established cause of chemoresistance involves the family of ATP-binding cassette transporters, or ABC transporters that transport a wide range of substrates including metabolic products, nutrients, lipids, and drugs across extra- and intra-cellular membranes. Expressions of various ABC transporters, shown to reduce the intracellular accumulation of chemotherapy drugs, are increased following chemotherapy and impact on ovarian cancer survival. Although clinical trials to date using ABC transporter inhibitors have been disappointing, ABC transporter inhibition remains an attractive potential adjuvant to chemotherapy. A greater understanding of their physiological functions and role in ovarian cancer chemoresistance will be important for the development of more effective targeted therapies. This article will review the role of the ABC transporter family in ovarian cancer progression and chemoresistance as well as the clinical attempts used to date to reverse chemoresistance.

Exploring the structure-activity relationships of ABCC2 modulators using a screening approach

ABCC2 is a transporter with key influence on liver and kidney pharmacokinetics. In order to explore the structure-activity relationships of compounds that modulate ABCC2, and by doing so gain insights into drug-drug interactions, we screened a library of 432 compounds for modulators of radiolabeled β-estradiol 17-(β-d-glucuronide) (EG) and fluorescent 5(6)-carboxy-2',7'-dichlorofluorescein transport (CDCF) in membrane vesicles. Following the primary screen at 80μM, dose-response curves were used to investigate in detail 86 compounds, identifying 16 low μM inhibitors and providing data about the structure-activity relationships in four series containing 19, 24, 10, and eight analogues. Measurements with the CDCF probe were consistently more robust than for the EG probe. Only one compound was clearly probe-selective with a 50-fold difference in the IC50s obtained by the two assays. We built 24 classification models using the SVM and fused-XY Kohonen methods, revealing molecular descriptors related to number of rings, solubility and lipophilicity as important to distinguish inhibitors from inactive compounds. This study is to the best of our knowledge the first to provide details about structure-activity relationships in ABCC2 modulation.

Metallothionein blocks oxidative DNA damage induced by acute inorganic arsenic exposure

We studied how protein metallothionein (MT) impacts arsenic-induced oxidative DNA damage (ODD) using cells that poorly express MT (MT-I/II double knockout embryonic cells; called MT-null cells) and wild-type (WT) MT competent cells. Arsenic (as NaAsO2) was less cytolethal over 24h in WT cells (LC50=11.0±1.3μM; mean±SEM) than in MT-null cells (LC50=5.6±1.2μM). ODD was measured by the immuno-spin trapping method. Arsenic (1 or 5μM; 24h) induced much less ODD in WT cells (121% and 141% of control, respectively) than in MT-null cells (202% and 260%). In WT cells arsenic caused concentration-dependent increases in MT expression (transcript and protein), and in the metal-responsive transcription factor-1 (MTF-1), which is required to induce the MT gene. In contrast, basal MT levels were not detectable in MT-null cells and unaltered by arsenic exposure. Transfection of MT-I gene into the MT-null cells markedly reduced arsenic-induced ODD levels. The transport genes, Abcc1 and Abcc2 were increased by arsenic in WT cells but either showed no or very limited increases in MT-null cells. Arsenic caused increases in oxidant stress defense genes HO-1 and GSTα2 in both WT and MT-null cells, but to much higher levels in WT cells. WT cells appear more adept at activating metal transport systems and oxidant response genes, although the role of MT in these responses is unclear. Overall, MT protects against arsenic-induced ODD in MT competent cells by potential sequestration of scavenging oxidant radicals and/or arsenic.

Parkinsonism-associated protein DJ-1/Park7 is a major protein deglycase that repairs methylglyoxal- and glyoxal-glycated cysteine, arginine, and lysine residues

Glycation is an inevitable nonenzymatic covalent reaction between proteins and endogenous reducing sugars or dicarbonyls (methylglyoxal, glyoxal) that results in protein inactivation. DJ-1 was reported to be a multifunctional oxidative stress response protein with poorly defined function. Here, we show that human DJ-1 is a protein deglycase that repairs methylglyoxal- and glyoxal-glycated amino acids and proteins by acting on early glycation intermediates and releases repaired proteins and lactate or glycolate, respectively. DJ-1 deglycates cysteines, arginines, and lysines (the three major glycated amino acids) of serum albumin, glyceraldehyde-3-phosphate dehydrogenase, aldolase, and aspartate aminotransferase and thus reactivates these proteins. DJ-1 prevented protein glycation in an Escherichia coli mutant deficient in the DJ-1 homolog YajL and restored cell viability in glucose-containing media. These results suggest that DJ-1-associated Parkinsonism results from excessive protein glycation and establishes DJ-1 as a major anti-glycation and anti-aging protein.

New insights in the biology of ABC transporters ABCC2 and ABCC3: impact on drug disposition

INTRODUCTION

For the elimination of environmental chemicals and metabolic waste products, the body is equipped with a range of broad specificity transporters that are present in excretory organs as well as in several epithelial blood-tissue barriers.

AREAS COVERED

ABCC2 and ABCC3 (also known as MRP2 and MRP3) mediate the transport of various conjugated organic anions, including many drugs, toxicants and endogenous compounds. This review focuses on the physiology of these transporters, their roles in drug disposition and how they affect drug sensitivity and toxicity. It also examines how ABCC2 and ABCC3 are coordinately regulated at the transcriptional level by members of the nuclear receptor (NR) family of ligand-modulated transcription factors and how this can be therapeutically exploited.

EXPERT OPINION

Mutations in both ABCC2 and ABCC3 have been associated with changes in drug disposition, sensitivity and toxicity. A defect in ABCC2 is associated with Dubin-Johnson syndrome, a recessively inherited disorder characterized by conjugated hyperbilirubinemia. Pharmacological manipulation of the activity of these transporters can potentially improve the pharmacokinetics and thus therapeutic activity of substrate drugs but also affect the physiological function of these transporters and consequently ameliorate associated disease states.

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

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

The interaction of the chemotherapeutic drug chlorambucil with human glutathione transferase A1-1: kinetic and structural analysis

Glutathione transferases (GSTs) are enzymes that contribute to cellular detoxification by catalysing the nucleophilic attack of glutathione (GSH) on the electrophilic centre of a number of xenobiotic compounds, including several chemotherapeutic drugs. In the present work we investigated the interaction of the chemotherapeutic drug chlorambucil (CBL) with human GSTA1-1 (hGSTA1-1) using kinetic analysis, protein crystallography and molecular dynamics. In the presence of GSH, CBL behaves as an efficient substrate for hGSTA1-1. The rate-limiting step of the catalytic reaction between CBL and GSH is viscosity-dependent and kinetic data suggest that product release is rate-limiting. The crystal structure of the hGSTA1-1/CBL-GSH complex was solved at 2.1 Å resolution by molecular replacement. CBL is bound at the H-site attached to the thiol group of GSH, is partially ordered and exposed to the solvent, making specific interactions with the enzyme. Molecular dynamics simulations based on the crystal structure indicated high mobility of the CBL moiety and stabilization of the C-terminal helix due to the presence of the adduct. In the absence of GSH, CBL is shown to be an alkylating irreversible inhibitor for hGSTA1-1. Inactivation of the enzyme by CBL followed a biphasic pseudo-first-order saturation kinetics with approximately 1 mol of CBL per mol of dimeric enzyme being incorporated. Structural analysis suggested that the modifying residue is Cys112 which is located at the entrance of the H-site. The results are indicative of a structural communication between the subunits on the basis of mutually exclusive modification of Cys112, indicating that the two enzyme active sites are presumably coordinated.

The role of ABC transporters in progression and clinical outcome of colorectal cancer

Worldwide, colorectal cancer (CRC) is the third most common cancer, with the highest mortality rates occurring in Central Europe. The use of chemotherapy to treat CRC is limited by the inter-individual variability in drug response and the development of cancer cell resistance. ATP-binding cassette (ABC) transporters play a crucial role in the development of resistance by the efflux of anticancer agents outside of cancer cells. The aim of this study was to explore transcript levels of all human ABCs in tumours and non-neoplastic control tissues from CRC patients collected before the first line of treatment by 5-fluorouracil (5-FU)-containing regimen. The prognostic potential of ABCs was evaluated by the correlation of transcript levels with clinical factors. Relations between transcript levels of ABCs in tumours and chemotherapy efficacy were also addressed. The transcript profile of all known human ABCs was assessed using real-time polymerase chain reaction with a relative standard curve. The majority of the studied ABCs were down-regulated or unchanged between tumours and control tissues. ABCA12, ABCA13, ABCB6, ABCC1, ABCC2 and ABCE1 were up-regulated in tumours versus control tissues. Transcript levels of ABCA12, ABCC7 and ABCC8 increased in direction from colon to rectum. Additionally, transcript levels of ABCB9, ABCB11, ABCG5 and ABCG8 followed the reverse significant trend, i.e. a decrease in direction from colon to rectum. The transcript level of ABCC10 in tumours correlated with the grade (P = 0.01). Transcript levels of ABCC6, ABCC11, ABCF1 and ABCF2 were significantly lower in non-responders to palliative chemotherapy in comparison with responders. The disease-free interval of patients treated by adjuvant chemotherapy was significantly shorter in patients with low transcript levels of ABCA7, ABCA13, ABCB4, ABCC11 and ABCD4. In conclusion, ABCC11 may be a promising candidate marker for a validation study on 5-FU therapy outcome.

Arsenic-glutathione conjugate transport by the human multidrug resistance proteins (MRPs/ABCCs)

Millions of people world-wide are chronically exposed to inorganic forms of the environmental toxicant arsenic in drinking water. This has led to a public health crisis because arsenic is a human carcinogen, and causes a myriad of other adverse health effects. In order to prevent and treat arsenic-induced toxicity it is critical to understand the cellular handling of this metalloid. A large body of literature describes the importance of the cellular tripeptide glutathione (γ-Glu-Cys-Gly,GSH/GS) in the excretion of arsenic. The triglutathione conjugate of arsenite [As(III)(GS)(3)] and the diglutathione conjugate of monomethylarsonous acid [MMA(III)(GS)(2)] have been isolated from rat bile and mouse urine, and account for the majority of excreted arsenic, suggesting these are important transportable forms. The ATP-binding cassette (ABC) transporter proteins, multidrug resistance protein 1 (MRP1/ABCC1) and the related protein MRP2 (ABCC2), are thought to play an important role in arsenic detoxification through the cellular efflux of arsenic-GSH conjugates. Current knowledge on the cellular handling of arsenic with a special emphasis on the transport pathways of the arsenic-GSH conjugates As(III)(GS)(3), MMA(III)(GS)(2), and dimethylarsenic glutathione DMA(III)(GS), as well as, the seleno-bis(S-glutathionyl) arsinium ion [(GS)(2)AsSe](-) are reviewed.

Enhanced glutathione depletion, protein adduct formation, and cytotoxicity following exposure to 4-hydroxy-2-nonenal (HNE) in cells expressing human multidrug resistance protein-1 (MRP1) together with human glutathione S-transferase-M1 (GSTM1)

4-Hydroxy-2-nonenal (HNE) is one of the most reactive products of lipid peroxidation and has both cytotoxic and genotoxic effects in cells. Several enzymatic pathways have been reported to detoxify HNE, including conjugation by glutathione-S-transferases (GSTs). Removal of the resulting HNE-glutathione conjugate (HNE-SG) by an efflux transporter may be required for complete detoxification. We investigated the effect of expression of GSTM1 and/or the ABC efflux transporter protein, multidrug-resistance protein-1 (MRP1), on HNE-induced cellular toxicity. Stably transfected MCF7 cell lines were used to examine the effect of GSTM1 and/or MRP1 expression on HNE-induced cytotoxicity, GSH depletion, and HNE-protein adduct formation. Co-expression in the MCF7 cell line of GSTM1 with MRP1 resulted in a 2.3-fold sensitization to HNE cytotoxicity (0.44-fold IC(50) value relative to control) rather than the expected protection. Expression of either GSTM1 or MRP1 alone also resulted in slight sensitization to HNE cytotoxicity (0.79-fold and 0.71-fold decreases in IC(50) values, respectively). Co-expression of GSTM1 and MRP1 strongly enhanced the formation of HNE-protein adducts relative to the non-expressing control cell line, whereas expression of either MRP1 alone or GSTM1 alone yielded similarly low levels of HNE-protein adducts to that of the control cell line. Glutathione (GSH) levels were reduced by 10-20% in either the control cell line or the MCF7/GSTM1 cell line with the same HNE exposure for 60min. However, HNE induced >80% depletion of GSH in cells expressing MRP1 alone. Co-expression of both MRP1 and GSTM1 caused slightly greater GSH depletion, consistent with the greater protein adduct formation and cytotoxicity in this cell line. Since expression of GSTM1 or MRP1 alone did not strongly sensitize cells to HNE, or result in greater HNE-protein adducts than in the control cell line, these results indicate that MRP1 and GSTM1 collaborate to enhance HNE-protein adduct formation and HNE cytotoxicity, facilitated by GSH depletion mediated by both MRP1 and GSTM1.

Glutathione transferase P1 interacts strongly with the inner leaflet of the plasma membrane

GSH transferases (GSTs) are a superfamily of proteins best known for detoxifying harmful electrophilic compounds by catalyzing their conjugation with GSH. GSTP1 is the most prevalent and widely distributed GST in human tissues, helping to detoxify a diverse array of carcinogens and drugs. In contrast with its protective role, overexpression of GSTP1 in a variety of malignancies is associated with a poor prognosis due to failure of chemotherapy. Although GSTP1 is classified as a cytosolic GST, we discovered previously that it is associated with the plasma membrane of the small cell lung cancer cell lines, H69 and H69AR. In the current study, endogenous and overexpressed GSTP1 in human embryonic kidney (HEK) 293 and MCF-7 cell lines, respectively, were found also to associate with the plasma membrane, indicating that this interaction is not unique to H69 and H69AR cells. GSTP1 immunostaining in HEK293 and MCF7-GSTP1 cells only occurred under permeabilized conditions, suggesting that GSTP1 is associated with the intracellular surface of the plasma membrane. Cell surface biotinylation studies confirmed this finding. Immunogold electron microscopy revealed the presence of GSTP1 in close proximity to the plasma membrane. GSTP1 was not dissociated from plasma membrane sheets by high salt [potassium iodide (KI; 1 M) or KI/EDTA (1 M/2 mM)] or alkaline Na(2)CO(3) (100 mM, pH 11.4), conditions known to strip peripherally associated membrane proteins. Thus, we report for the first time that GSTP1 is associated with the inner leaflet of the plasma membrane through a remarkably strong interaction.

Group-specific comparison of four lactobacilli isolated from human sources using differential blast analysis

Lactic acid bacteria (LAB) have been used in fermentation processes for centuries. More recent applications including the use of LAB as probiotics have significantly increased industrial interest. Here we present a comparative genomic analysis of four completely sequenced Lactobacillus strains, isolated from the human gastrointestinal tract, versus 25 lactic acid bacterial genomes present in the public database at the time of analysis. Lactobacillus acidophilus NCFM, Lactobacillus johnsonii NCC533, Lactobacillus gasseri ATCC33323, and Lactobacillus plantarum WCFS1are all considered probiotic and widely used in industrial applications. Using Differential Blast Analysis (DBA), each genome was compared to the respective remaining three other Lactobacillus and 25 other LAB genomes. DBA highlighted strain-specific genes that were not represented in any other LAB used in this analysis and also identified group-specific genes shared within lactobacilli. Initial comparative analyses highlighted a significant number of genes involved in cell adhesion, stress responses, DNA repair and modification, and metabolic capabilities. Furthermore, the range of the recently identified potential autonomous units (PAUs) was broadened significantly, indicating the possibility of distinct families within this genetic element. Based on in silico results obtained for the model organism L. acidophilus NCFM, DBA proved to be a valuable tool to identify new key genetic regions for functional genomics and also suggested re-classification of previously annotated genes.

Inhibition characteristics of hypericin on rat small intestine glutathione-S-transferases

Glutathione-S-transferases constitute a family of enzymes involving in the detoxification of xenobiotics, signalling cascades and serving as ligandins or/and catalyzing the conjugation of various chemicals and drugs. The widely expressed cytosolic GST-pi is a marker protein in various cancers and its increased concentration is linked to drug resistance. GST-pi is autoregulated by S-glutathionylation and it catalyzes the S-glutathionylation of other proteins in response to oxidative or nitrosative stress. S-glutathionylation of GST-pi results in multimer formation and the breakage of ligand binding interactions with c-Jun NH(2)-terminal kinase (JNK). Another widely expressed GST enzyme, GST-alpha is assumed as a marker in hepatocellular damage, is implicated in cancer, asthma, cardiovascular disease and response to chemotherapy. Although, it was shown that hypericin binds and inhibits GST-alpha and GST-pi, the inhibition characteristics have not been investigated in detail. The aim of this study was to investigate the effects of hypericin on major GSTs; GST-alpha and GST-pi purified from rat small intestine. When GSH used as varied substrate the inhibition pattern with hypericin was uncompetitive for GST-alpha (K(i)=0.16 + or - 0.02 microM) and noncompetitive for GST-pi (K(i) = 2.46 + or - 0.43 microM). While using CDNB (1-chloro-2,4-dinitrobenzene) as the varied substrate, the inhibition patterns were noncompetitive for GST-alpha and competitive for GST-pi; K(i) values for GST-alpha and GST-pi were 1.91 + or - 0.21 and 0.55 + or - 0.07 microM, respectively. Since hypericin accumulated in cancer cells and important in photodynamic therapy (PDT), inhibition of GST-alpha and GST-pi by hypericin might increase the effectivity of the treatment. Considering that GST-pi is responsible for the drug resistance its inhibition might increase the benefit obtained from chemotherapy.

Glutathione transferases and development of new principles to overcome drug resistance

Chemoresistance is a multifactorial phenomenon and many studies clearly show that a coordinated expression of efflux transporter proteins and phase II conjugating enzymes in tumor cells is linked to the development of the multidrug resistance phenotype. In particular, the overexpression of glutathione S-transferases and efflux pumps in tumors may reduce the reactivity of various anticancer drugs. In recent years it has become evident that glutathione S-transferases are also involved in the control of apoptosis through the inhibition of the JNK signaling pathway. As such, the glutathione S-transferase superfamily has become the focus of extensive pharmaceutical research in attempt to generate more efficient anticancer agents. Here we present an overview of the GST inhibitors and the GST-activated pro-drugs utilized to date to overcome drug resistance.

Early effects of doxorubicin in perfused heart: transcriptional profiling reveals inhibition of cellular stress response genes

Doxorubicin (DXR) belongs to the most efficient anticancer drugs. However, its clinical application is limited by the risk of severe cardiac-specific toxicity, for which an efficient treatment is missing. Underlying molecular mechanisms are not sufficiently understood so far, but nonbiased, systemic approaches can yield new clues to develop targeted therapies. Here, we applied a genome-wide transcriptome analysis to determine the early cardiac response to DXR in a model characterized earlier, that is, rat heart perfusion with 2 muM DXR, leading to only mild cardiac dysfunction. Single-gene and gene set enrichment analysis of DNA microarrays yielded robust data on cardiac transcriptional reprogramming, including novel DXR-responsive pathways. Main characteristics of transcriptional reprogramming were 1) selective upregulation of individual genes or gene sets together with widespread downregulation of gene expression; 2) repression of numerous transcripts involved in cardiac stress response and stress signaling; 3) modulation of genes with cardiac remodeling capacity; 4) upregulation of "energy-related" pathways; and 5) similarities to the transcriptional response of cancer cells. Some early responses like the induction of glycolytic and Krebs cycle genes may have compensatory function. Only minor changes in the cardiac energy status or the respiratory activity of permeabilized cardiac fibers have been observed. Other responses potentially contribute to acute and also chronic toxicity, in particular, those in stress-responsive and cardiac remodeling transcripts. We propose that a blunted response to stress and reduced "danger signaling" is a prime component of toxic DXR action and can drive cardiac cells into pathology.

Noncatalytic interactions between glutathione S-transferases and nitroalkene fatty acids modulate nitroalkene-mediated activation of peroxisomal proliferator-activated receptor gamma

The naturally occurring nitroalkenes, nitrolinoleic (NO(2)-LA) and nitrooleic (NO(2)-OA) acids, are among the most potent endogenous ligand activators of PPARgamma-dependent transcription. In order to understand mechanisms that regulate cellular response to these nitroalkenes, we previously demonstrated that glutathione conjugation of NO(2)-LA and MRP1-mediated efflux of the conjugates were associated with significant attenuation of PPARgamma activation by this nitroalkene [(2006) Biochemistry 45, 7889-7896]. Here we show that NO(2)-OA activation of PPARgamma is similarly affected by nonenzymatic conjugation and MRP1-mediated efflux. Moreover, the roles of glutathione S-transferases (GSTs) in the glutathione conjugation and bioactivities of NO(2)-LA and NO(2)-OA were investigated. While none of the GST isozymes tested (GSTA1-1, A4-4, M1a-1a, and P1a-1a) enhanced the rate of glutathione conjugation, expression of GSTA1-1, M1a-1a, or P1a-1a in MCF7 cells significantly reduced the magnitude of PPARgamma-dependent reporter gene transcription in response to NO(2)-LA and NO(2)-OA treatment, with GSTP1a-1a expression mediating the most potent inhibition of PPARgamma. Although these GSTs failed to catalyze nitroalkene conjugation with glutathione, the nitroalkenes were found to associate avidly with all four GST isozymes as indicated by their ability to inhibit GST activity with K(i)'s in the nanomolar range. Treatment of purified GSTP1a-1a with excess NO(2)-LA and NO(2)-OA resulted in the formation of covalent adducts between GSTP1a monomers and nitroalkenes, although separate experiments indicated that such covalent bond formation was not necessary for avid GST-nitroalkene interactions. These results suggest that GSTs can inhibit the activation of transcription by nitroalkenes via noncatalytic sequestration of these ligands, and their glutathione conjugates, away from their nuclear target, PPARgamma.

Identification of novel specific and general inhibitors of the three major human ATP-binding cassette transporters P-gp, BCRP and MRP2 among registered drugs

PURPOSE

To study the inhibition patterns of the three major human ABC transporters P-gp (ABCB1), BCRP (ABCG2) and MRP2 (ABCC2), using a dataset of 122 structurally diverse drugs.

METHODS

Inhibition was investigated in cellular and vesicular systems over-expressing single transporters. Computational models discriminating either single or general inhibitors from non-inhibitors were developed using multivariate statistics.

RESULTS

Specific (n = 23) and overlapping (n = 19) inhibitors of the three ABC transporters were identified. GF120918 and Ko143 were verified to specifically inhibit P-gp/BCRP and BCRP in defined concentration intervals, whereas the MRP inhibitor MK571 was revealed to inhibit all three transporters within one log unit of concentration. Virtual docking experiments showed that MK571 binds to the ATP catalytic site, which could contribute to its multi-specific inhibition profile. A computational model predicting general ABC inhibition correctly classified 80% of both ABC transporter inhibitors and non-inhibitors in an external test set.

CONCLUSIONS

The inhibitor specificities of P-gp, BCRP and MRP2 were shown to be highly overlapping. General ABC inhibitors were more lipophilic and aromatic than specific inhibitors and non-inhibitors. The identified specific inhibitors can be used to delineate transport processes in complex experimental systems, whereas the multi-specific inhibitors are useful in primary ABC transporter screening in drug discovery settings.

Differential potencies of naturally occurring regioisomers of nitrolinoleic acid in PPARgamma activation

Previous studies demonstrated that the naturally occurring electrophile and PPARgamma ligand, nitrolinoleic acid (NO(2)-LA), exists as a mixture of four regioisomers [Alexander, R. L., et al. (2006) Biochemistry 45, 7889-7896]. We hypothesized that these alternative isomers have distinct bioactivities; therefore, to determine if the regioisomers are quantitatively or qualitatively different with respect to PPARgamma activation, NO(2)-LA was separated into three fractions which were identified by NMR (13-NO(2)-LA, 12-NO(2)-LA, and a mixture of 9- and 10-NO(2)-LA) and characterized for PPARgamma interactions. A competition radioligand binding assay showed that all three NO(2)-LA fractions had similar binding affinities for PPARgamma (IC(50) = 0.41-0.60 microM) that were comparable to that of the pharmaceutical ligand, rosiglitazone (IC(50) = 0.25 microM). However, when PPARgamma-dependent transcription activation was examined, there were significant differences observed among the NO(2)-LA fractions. Each isomer behaved as a partial agonist in this reporter gene assay; however, the 12-NO(2) derivative was the most potent with respect to maximum activation of PPARgamma and an EC(50) of 0.045 microM (compare with the rosiglitazone EC(50) of 0.067 microM), while the 13-NO(2) and 9- and 10-NO(2) derivatives were considerably less effective with EC(50) values of 0.41-0.62 microM. We conclude that the regioisomers of NO(2)-LA are not functionally equivalent. The 12-NO(2) derivative appears to be the most potent in PPARgamma-dependent transcription activation, whereas the weaker PPARgamma agonists, 13-NO(2) and 9- and 10-NO(2), may be relatively more important in signaling via other, PPARgamma-independent pathways in which this family of nitrolipid electrophiles is implicated.