ATP-binding Cassette Transporter Family Research Articles

Multiple resistance to carcinogens and xenobiotics: P-glycoproteins as universal detoxifiers.

The detoxification of toxic substances is of general relevance in all biological systems. The plethora of exogenous xenobiotic compounds and endogenous toxic metabolic products explains the evolutionary pressure of all organisms to develop molecular mechanisms to detoxify and excrete harmful substances from the body. P-glycoprotein and other members of the ATP-binding cassette (ABC) transporter family extrude innumerous chemical compounds out of cells. Their specific expression in diverse biological contexts cause different phenotypes: (1) multidrug resistance (MDR) and thus failure of cancer chemotherapy, (2) avoidance of accumulation of carcinogens and prevention of carcinogenesis in healthy tissues, (3) absorption, distribution, metabolization and excretion (ADME) of pharmacological drugs in human patients, (4) protection from environmental toxins in aquatic organisms (multi-xenobiotic resistance, MXR). Hence ABC-transporters may have opposing effects for organismic health reaching from harmful in MDR of tumors to beneficial for maintenance of health in MXR. While their inhibition by specific inhibitors may improve treatment success in oncology and avoid carcinogenesis, blocking of ABC-transporter-driven efflux by environmental pollutants leads to ecotoxicological consequences in marine biotopes. Poisoned seafood may enter the food-chain and cause intoxications in human beings. As exemplified with ABC-transporters, joining forces in interdisciplinary research may, therefore, be a wise strategy to fight problems in human medicine and environmental sciences.

The Role of Eukaryotic and Prokaryotic ABC Transporter Family in Failure of Chemotherapy.

Over the years chemotherapy failure has been a vital research topic as researchers have been striving to discover reasons behind it. The extensive studies carried out on chemotherapeutic agents confirm that resistance to chemotherapy is a major reason for treatment failure. “Resistance to chemotherapy,” however, is a comprehensive phrase that refers to a variety of different mechanisms in which ATP-binding cassette (ABC) mediated efflux dominates. The ABC is one of the largest gene superfamily of transporters among both eukaryotes and prokaryotes; it represents a variety of genes that code for proteins, which perform countless functions, including drug efflux – a natural process that protects cells from foreign chemicals. Up to date, chemotherapy failure due to ABC drug efflux is an active research topic that continuously provides further evidence on multiple drug resistance (MDR), aiding scientists in tackling and overcoming this issue. This review focuses on drug resistance by ABC efflux transporters in human, viral, parasitic, fungal and bacterial cells and highlights the importance of the MDR permeability glycoprotein being the mutual ABC transporter among all studied organisms. Current developments and future directions to overcome this problem are also discussed.

Spatiotemporal Changes in P-glycoprotein Levels in Brain and Peripheral Tissues Following Ischemic Stroke in Rats.

P-glycoprotein (P-gp) is known to transport a diverse array of xenobiotics, including therapeutic drugs. A member of the ATP-binding cassette (ABC) transporter family, P-gp is a protein encoded by the gene Mdr1 in humans and Abcb1 in rodents (represented by 2 isoforms Abcb1a and Abcb1b). Lining the luminal and abluminal membrane of brain capillary endothelial cells, P-gp is a promiscuous efflux pump extruding a variety of exogenous toxins and drugs. In this study, we measured dynamic changes in Abcb1a and Abcb1b transcripts and P-gp protein in the brain, liver, and kidney after experimental stroke. P-glycoprotein has been shown to increase in brain endothelial cells following hypoxia in vitro or after exposure to proinflammatory cytokines. Using a rat model of ischemic stroke, we hypothesized that P-gp expression will be increased in the brain, liver, and kidney in response to neuroinflammation following ischemic stroke. Adult Sprague Dawley rats underwent middle cerebral artery occlusion (MCAO) for 90 minutes and were killed at 4, 14, 24, and 48 hours postreperfusion onset to determine the time course of P-gp expression. To mimic ischemia occurring at the blood-brain barrier, rat brain endothelial (RBE4) cells were subjected to hypoxia and low glucose (HLG) for 16 hours. Immunoblotting analyses showed P-gp increases in brain and liver following 90-minute MCAO, as well as in cultured RBE4 cells after 16-hour HLG treatment, but fluctuated in the kidney depending on the time point. The relative roles of each isoform in the protein expression were analyzed with quantitative reverse transcriptase polymerase chain reaction. Ischemic stroke leads to significant increases in P-gp levels not only in the brain but also in the liver. The increase in P-gp could dramatically reduce the bioavailability and efficacy of neuroprotective drugs. Therefore, P-gp represents a big hurdle to drug delivery to the ischemic brain.

Cobalt Chloride Induces Expression and Function of Breast Cancer Resistance Protein (BCRP/ABCG2) in Human Renal Proximal Tubular Epithelial Cell Line HK-2.

The human breast cancer resistance protein (BCRP/ABCG2), a member of the ATP-binding cassette transporter family, is a drug transporter restricting absorption and enhancing excretion of many compounds including anticancer drugs. The cis-regulatory elements in the BCRP promoter include a hypoxia response element, i.e., the DNA binding site for hypoxia-inducible factor-1 (HIF-1). In this study, we investigated the effect of cobalt chloride, a chemical inducer of HIF-1α, on the expression and function of BCRP in human renal proximal tubular cell line HK-2. Cobalt chloride treatment significantly increased the mRNA expression of not only glucose transporter 1 (GLUT1), a typical HIF-1 target gene mRNA, but also ABCG2 mRNA in HK-2 cells. The BCRP inhibitor Ko143-sensitive accumulation of BCRP substrates such as Hoechst33342 and mitoxantrone was significantly enhanced by cobalt chloride treatment. In addition, treatment with cobalt chloride significantly increased the Ko143-sensitive accumulation of fluorescein isothiocyanate-labeled methotrexate in HK-2 cells. Furthermore, cobalt chloride treatment attenuated the cytotoxicity induced by mitoxantrone and methotrexate, which might be, at least in part, due to the increase in BCRP-mediated transport activity via HIF-1 activation. These findings indicate that HIF-1 activation protects renal proximal tubular cells against BCRP substrate-induced cytotoxicity by enhancing the expression and function of BCRP in renal proximal tubular cells.

ABCG2 confers promotion in gastric cancer through modulating downstream CRKL in vitro combining with biostatistics mining.

ABCG2, member of ATP-binding cassette (ABC) transporter family, is known as crucial regulator related to multi-drug resistance in human tumors and has recently been putatively studied as human carcinoma cell biomarker. While, effects of ABCG2 on human gastric cancer (GC) has not been illustrated thoroughly. In this study, by applying biostatistics mining methods, we observed that ABCG2 is frequently aberrantly expressed in GC patients through exploring dataset of GSE19826 in NCBI GEO database. Contemporary, extreme up-regulation of ABCG2 was discovered in both GC specimens and cell lines of our center, from which we observed high level of ABCG2 associated with GC clinicopathologic features and poor outcomes. Depletion of ABCG2 in MKN-45 GC cells, the cell proliferation was significantly impacted along with cell cycle arrest, and cell apoptosis was induced. Interestingly, combined with data mining of NCBI database, CRKL, a pivotal GC promoter, presents a significant positive correlation with ABCG2. And the expression of CRKL in GC cells was obviously affected through ABCG2 depletion. Simultaneously, over-expression of CRKL in MKN-45 cells significantly rescued most of the phenotypes induced by ABCG2 depletion. Thus, we suggest that ABCG2 is a potential biomarker and target upstream CRKL, which could be further studied for GC diagnosis and therapeutic treatment

Deferasirox Associated to Liver Failure and Death in a Sickle Cell Anemia Patient Homozygous for the -1774delG Polymorphism in the ABCC2 Gene Encoding Multidrug Resistance Protein 2 (MRP2)

▪Introduction: Regular blood transfusions may result in hemochromatosis, leading to damage of various organs. Deferasirox exhibits good efficacy as iron chelation therapy, however changes in liver parameters may occur, as well as, despite being rare, more serious complications such as liver failure. Multidrug resistance protein 2 (MRP2) is a member of the ATP-binding cassette (ABC) transporter family of membrane proteins encoded by the ABCC2 gene and is expressed in the canalicular part of the hepatocyte. MRP2 acts in the biliary transport of several endogenous compounds and many drugs, including Deferasirox. Thus, genetic polymorphisms related to the ABCC2 gene, which encodes the MRP2 protein, may influence individual susceptibility to hepatotoxicity related to Deferasirox.Methods: Two functional genetic variants, rs369192412 (-1774delG) and rs717620 (-24C> T), of the ABCC2 gene, were studied using the DNA sequencing technique in 31 genomic DNA samples from patients with iron overload who were currently using or had previously used Deferasirox. The sequencing results were compared to clinical data related to the presence or absence of hepatotoxicity during the use of this drug.Results: Of all patients studied, 9 (29%) of them developed hepatotoxicity based on elevation of AST and/or ALT >5 X ULN or elevation of bilirubins >3 X ULN, which occurred in an average of 239 (14-983) days after initiation of treatment. From the 9 (29%) patients with hepatotoxicity, only 2 (22.2%) of them had the polymorphism -24C> T in only one allele, and the remaining 7 (77.8%) patients did not (OR = 0.77, 95% CI = 0.06 to 5.91, p = 1). Despite no association was detected between the -17774delG polymorphism and hepatotoxicity (OR = lower, 95% CI = 0.06 to bottom, p = 0.29), this polymorphism was present in homozygosis in 1 patient with sickle cell anemia, who, coincidently, had fulminant hepatitis leading to death, with no other causes for liver toxicity and despite all introduced therapies.Conclusions: Our study showed no correlation between ABCC2 polymorphisms (-24C> T, -1774delG) and hepatotoxicity to Deferasirox, however, the rs369192412 (-1774delG) polymorphism was present in homozygosis in the only patient who died due to fulminant hepatitis secondary to the drug. This data may indicate a possible influence of the presence of this polymorphism in the severity of liver damage related to Deferasirox. DisclosuresNo relevant conflicts of interest to declare.

Atomic Structure of the Cystic Fibrosis Transmembrane Conductance Regulator

The cystic fibrosis transmembrane conductance regulator (CFTR) is an anion channel evolved from the ATP-binding cassette (ABC) transporter family. In this study, we determined the structure of zebrafish CFTR in the absence of ATP by electron cryo-microscopy to 3.7Å resolution. Human and zebrafish CFTRshare 55% sequence identity, and 42 of the 46 cystic-fibrosis-causing missense mutational sites are identical. In CFTR, we observe a large anion conduction pathway lined by numerous positively charged residues. A single gate near the extracellular surface closes the channel. The regulatory domain, dephosphorylated, is located in the intracellular opening between the two nucleotide-binding domains (NBDs), preventing NBD dimerization and channel opening. The structure also reveals why many cystic-fibrosis-causing mutations would lead to defects either in folding, ion conduction, or gatingand suggests new avenues for therapeutic intervention.

Genome-wide identification of ATP-binding cassette (ABC) transporters and conservation of their xenobiotic transporter function in the monogonont rotifer (Brachionus koreanus)

The ATP-binding cassette (ABC) transporter family is one of the largest gene family in animals, and members of this family are known to be involved in various biological processes due to their ability to transport a wide range of substrates across membranes using ATP cleavage-derived energy. We identified 61 ABC transporters in the genome of the monogonont rotifer Brachionus koreanus, and classified these into eight distinct subfamilies (A–H) by phylogenetic analysis. ABC transporters in the rotifer B. koreanus are comprised of 11 ABCA genes, 19 ABCB genes, 14 ABCC genes, 3 ABCD genes, 1 ABCE gene, 3 ABCF genes, 8 ABCG genes, and 2 ABCH genes. Extensive gene duplication and loss events in synteny were observed in several subfamilies. In particular, massive gene duplications of P-glycoproteins (P-gps), multidrug resistance proteins (MRPs), and Bk-Abcg-like proteins were observed. The ability of these B. koreanus proteins to function as multixenobiotic resistance (MXR) ABC transporters was validated using specific fluorescence substrates/inhibitors. The ABC transporter superfamily members identified in this study will be useful in future toxicological studies, and will facilitate comparative studies of the evolution of the ABC transporter superfamily in invertebrates.

Expression and regulation of prostaglandin transporters, ATP-binding cassette, subfamily C, member 1 and 9, and solute carrier organic anion transporter family, member 2A1 and 5A1 in the uterine endometrium during the estrous cycle and pregnancy in pigs.

ObjectiveProstaglandins (PGs) function in various reproductive processes, including luteolysis, maternal pregnancy recognition, conceptus development, and parturition. Our earlier study has shown that PG transporters ATP-binding cassette, subfamily C, member 4 (ABCC4) and solute carrier organic anion transporter family, member 2A1 (SLCO2A1) are expressed in the uterine endometrium in pigs. Since several other PG transporters such as ABCC1, ABCC9, SLCO4C1, and SLCO5A1 are known to be present in the uterine endometrium, this study investigated the expression of these PG transporters in the porcine uterine endometrium and placenta.MethodsUterine endometrial tissues were obtained from gilts on day (D) 12 and D15 of the estrous cycle and days 12, 15, 30, 60, 90, and 114 of pregnancy.ResultsABCC1, ABCC9, SLCO4C1, and SLCO5A1 mRNAs were expressed in the uterine endometrium, and levels of expression changed during the estrous cycle and pregnancy. Expression of ABCC1 and ABCC9 mRNAs was localized mainly to luminal and glandular epithelial cells in the uterine endometrium, and chorionic epithelial cells during pregnancy. Conceptuses during early pregnancy and chorioallantoic tissues from mid to late pregnancy also expressed these PG transporters. Estradiol-17β increased the expression of ABCC1 and SLCO5A1, but not ABCC9 and SLCO4C1 mRNAs and increasing doses of interleukin-1β induced the expression of ABCC9, SLCO4C1, and SLCO5A1 mRNAs in endometrial explant tissues.ConclusionThese data showed that several PG transporters such as ABCC1, ABCC9, SLCO4C1, and SLCO5A1 were expressed at the maternal-conceptus interface, suggesting that these PG transporters may play an important role in the establishment and maintenance of pregnancy by regulating PG transport in the uterine endometrium and placenta in pigs.

Simultaneous Prediction of four ATP-binding Cassette Transporters' Substrates Using Multi-label QSAR.

Efflux by the ATP-binding cassette (ABC) transporters affects the pharmacokinetic profile of drugs and it has been implicated in drug-drug interactions as well as its major role in multi-drug resistance in cancer. It is therefore important for the pharmaceutical industry to be able to understand what phenomena rule ABC substrate recognition. Considering a high degree of substrate overlap between various members of ABC transporter family, it is advantageous to employ a multi-label classification approach where predictions made for one transporter can be used for modeling of the other ABC transporters. Here, we present decision tree-based QSAR classification models able to simultaneously predict substrates and non-substrates for BCRP1, P-gp/MDR1 and MRP1 and MRP2, using a dataset of 1493 compounds. To this end, two multi-label classification QSAR modelling approaches were adopted: Binary Relevance (BR) and Classifier Chain (CC). Even though both multi-label models yielded similar predictive performances in terms of overall accuracies (close to 70 %), the CC model overcame the problem of skewed performance towards identifying substrates compared with non-substrates, which is a common problem in the literature. The models were thoroughly validated by using external testing, applicability domain and activity cliffs characterization. In conclusion, a multi-label classification approach is an appropriate alternative for the prediction of ABC efflux.

ABC Transporters in the Development of Multidrug Resistance in Cancer Therapy.

Cancer is one of the leading causes of mortality in the developed countries. The search for novel drug candidates is a priority goal for cancer therapy. However, the emergence of drug resistance reduces the effectiveness of new medications. The ATP binding cassette (ABC) family of proteins are efflux pumps that transport various structurally unrelated and potentially dangerous substances out of the cells. These transporters have evolved as a complex cellular defense system, for the recognition and removal of toxic agents entering the cells from their environment. Several of the ABC transporters are related to chemoresistance in cancer therapy, as the rapidly dividing malignant cells use them to protect themselves from medical interventions. Here we review the members of the ABC transporter families responsible for the multidrug resistance in anticancer therapy.

Computational characterization of TTHA0379: A potential glycerophosphocholine binding protein of Ugp ATP-binding cassette transporter

For the de novo biosynthesis of phospholipids, byproducts such as sn-glycerol-3-phosphate (G3P) and glycerophosphocholine (GPC) of glycerophospholipid metabolic pathway are imported inside the cell by an ATP-binding cassette (ABC) transporter known as UgpABCE. Of which, UgpA and UgpE constitutes the transmembrane domains (TMDs), UgpC forms the dimer of ATP-hydrolyzing component and UgpB is the periplasmic substrate binding protein. Structurally, UgpABCE transporter displays similarity to the maltose ABC transporter of Escherichia coli; thus, has been grouped into the CUT1 (Carbohydrate Uptake Transporter-1) family of bacterial ABC transporters. Being a member of CUT1 family, several Ugp (Uptake glycerol phosphate) protein sequences in biological database(s) exhibit sequence and structure similarity to sugar ABC transporters and have been annotated as sugar binding proteins; one of such proteins is TTHA0379 from Thermus thermophilus HB8. Here, in this study, we used computational method(s) to distinguish UgpB and sugar binding proteins based on their primary and tertiary structure features. A comprehensive analysis of these proteins indicates that they are evolutionarily related to each other having common conserved features at their primary and tertiary structure levels. However, they display differences at their active sites owing to the dissimilarity in their ligand preferences. In addition, phylogenetic analysis of TTHA0379 along with UgpB and sugar binding proteins reveals that both the groups of proteins forms two distinct clades and TTHA0379 groups with UgpB proteins. Furthermore, analysis of the ligand binding pocket shows that all the essential features of glycerophosphocholine binding protein i.e. UgpB, are conserved in TTHA0379 as well. Combining these features, here, we designate TTHA0379 to be a GPC binding protein.

How Phosphorylation and ATPase Activity Regulate Anion Flux though the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR)

The cystic fibrosis transmembrane conductance regulator (CFTR, ABCC7), mutations of which cause cystic fibrosis, belongs to the ATP-binding cassette (ABC) transporter family and works as a channel for small anions, such as chloride and bicarbonate. Anion channel activity is known to depend on phosphorylation by cAMP-dependent protein kinase A (PKA) and CFTR-ATPase activity. Whereas anion channel activity has been extensively investigated, phosphorylation and CFTR-ATPase activity are still poorly understood. Here, we show that the two processes can be measured in a label-free and non-invasive manner in real time in live cells, stably transfected with CFTR. This study reveals three key findings. (i) The major contribution (≥90%) to the total CFTR-related ATP hydrolysis rate is due to phosphorylation by PKA and the minor contribution (≤10%) to CFTR-ATPase activity. (ii) The mutant CFTR-E1371S that is still conductive, but defective in ATP hydrolysis, is not phosphorylated, suggesting that phosphorylation requires a functional nucleotide binding domain and occurs in the post-hydrolysis transition state. (iii) CFTR-ATPase activity is inversely related to CFTR anion flux. The present data are consistent with a model in which CFTR is in a closed conformation with two ATPs bound. The open conformation is induced by ATP hydrolysis and corresponds to the post-hydrolysis transition state that is stabilized by phosphorylation and binding of chloride channel potentiators.

Crystal Structure of a Group I Energy Coupling Factor Vitamin Transporter S Component in Complex with Its Cognate Substrate

SummaryEnergy coupling factor (ECF) transporters are responsible for the uptake of essential scarce nutrients in prokaryotes. This ATP-binding cassette transporter family comprises two subgroups that share a common architecture forming a tripartite membrane protein complex consisting of a translocation component and ATP hydrolyzing module and a substrate-capture (S) component. Here, we present the crystal structure of YkoE from Bacillus subtilis, the S component of the previously uncharacterized group I ECF transporter YkoEDC. Structural and biochemical analyses revealed the constituent residues of the thiamine-binding pocket as well as an unexpected mode of vitamin recognition. In addition, our experimental and bioinformatics data demonstrate major differences between YkoE and group II ECF transporters and indicate how group I vitamin transporter S components have diverged from other group I and group II ECF transporters.

Identification of differentially expressed genes and signalling pathways in bark of Hevea brasiliensis seedlings associated with secondary laticifer differentiation using gene expression microarray

The natural rubber of Para rubber tree, Hevea brasiliensis, is the main crop involved in industrial rubber production due to its superior quality. The Hevea bark is commercially exploited to obtain latex, which is produced from the articulated secondary laticifer. The laticifer is well defined in the aspect of morphology; however, only some genes associated with its development have been reported. We successfully induced secondary laticifer in the jasmonic acid (JA)-treated and linolenic acid (LA)-treated Hevea bark but secondary laticifer is not observed in the ethephon (ET)-treated and untreated Hevea bark. In this study, we analysed 27,195 gene models using NimbleGen microarrays based on the Hevea draft genome. 491 filtered differentially expressed (FDE) transcripts that are common to both JA- and LA-treated bark samples but not ET-treated bark samples were identified. In the Eukaryotic Orthologous Group (KOG) analysis, 491 FDE transcripts belong to different functional categories that reflect the diverse processes and pathways involved in laticifer differentiation. In the Kyoto Encyclopedia of Genes and Genomes (KEGG) and KOG analysis, the profile of the FDE transcripts suggest that JA- and LA-treated bark samples have a sufficient molecular basis for secondary laticifer differentiation, especially regarding secondary metabolites metabolism. FDE genes in this category are from the cytochrome (CYP) P450 family, ATP-binding cassette (ABC) transporter family, short-chain dehydrogenase/reductase (SDR) family, or cinnamyl alcohol dehydrogenase (CAD) family. The data includes many genes involved in cell division, cell wall synthesis, and cell differentiation. The most abundant transcript in FDE list was SDR65C, reflecting its importance in laticifer differentiation. Using the Basic Local Alignment Search Tool (BLAST) as part of annotation and functional prediction, several characterised as well as uncharacterized transcription factors and genes were found in the dataset. Hence, the further characterization of these genes is necessary to unveil their role in laticifer differentiation. This study provides a platform for the further characterization and identification of the key genes involved in secondary laticifer differentiation.

MOLECULAR CLONING, EXPRESSION PATTERN OF MULTIDRUG RESISTANCE ASSOCIATED PROTEIN 1 (MRP1, ABCC1) GENE, AND THE SYNERGISTIC EFFECTS OF VERAPAMIL ON TOXICITY OF TWO INSECTICIDES IN THE BIRD CHERRY‐OAT APHID

The ATP-binding cassette (ABC) transporters are important transmembrane proteins encoded by a supergene family. The majority of ABC proteins are primary active transporters that bind and hydrolyze ATP to mediate the efflux of a diverse range of substrates across lipid membranes. In this study, we cloned and characterized a putative multidrug resistance associated protein 1 (MRP1) from Rhopalosiphum padi encoded by ABCC1. Structural analysis showed that this protein has structural features typical of the ABC transporter family. Phylogenetic analysis indicated that the amino acid sequence was highly similar that of the corresponding protein from Acyrthosiphon pisum. Real-time quantitative polymerase chain reaction (PCR) analysis showed that ABCC1 was expressed throughout all R. padi developmental stages, with the highest level of expression in the fourth larval instar. We also examined ABCC1 expression in four different tissue types and found that it was most highly expressed in the midgut. Exposing R. padi to imidacloprid and chlorpyrifos increased ABCC1 expression. Furthermore, ABCC1 expression was higher in the imidacloprid-resistant (IR) and chlorpyrifos-resistant (CR) strains than in an insecticide-susceptible strain (SS) of R. padi. Exposing R. padi to verapamil in combination with insecticides significantly increased the toxicity of the insecticides. The respective synergy factor of CR and IR R. padi strain was 1.33 and 1.26, which was lower than that (2.72 and 1.64, respectively) of the SS. Our results clarify the biological function of ABCC1 in R. padi, particularly its role in insecticide resistance, and suggest novel strategies for pest management that use ABC transporter inhibitors to increase the effectiveness of insecticides.

ABC transporters as mediators of drug resistance and contributors to cancer cell biology.

The extrusion of anticancer drugs by members of the ATP-binding cassette (ABC) transporter family is one of the most widely recognized mechanisms of multidrug resistance, and can be considered a hijacking of their normal roles in the transport of xenobiotics, metabolites and signaling molecules across cell membranes. While roles in cancer multidrug resistance have been clearly demonstrated for P-glycoprotein (P-gp), Breast Cancer Resistance Protein (BCRP) and Multidrug Resistance Protein 1 (MRP1), direct evidence for a role in multidrug resistance in vivo is lacking for other family members. A less well understood but emerging theme is the drug efflux-independent contributions of ABC transporters to cancer biology, supported by a growing body of evidence that their loss or inhibition impacts on the malignant potential of cancer cells in vitro and in vivo. As with multidrug resistance, these contributions likely represent a hijacking of normal ABC transporter functions in the efflux of endogenous metabolites and signaling molecules, however they may expand the clinical relevance of ABC transporters beyond P-gp, BCRP and MRP1. This review summarizes established and emerging roles for ABC transporters in cancer, with a focus on neuroblastoma and ovarian cancer, and considers approaches to validate and better understand these roles.

In vitro and in vivo evaluations of the P-glycoprotein-mediated efflux of dibenzoylhydrazines

P-glycoprotein (P-gp) is a member of the ATP-binding cassette transporter family. It actively transports a wide variety of compounds out of cells to protect humans from xenobiotics. Thus, determining whether chemicals are substrates and/or inhibitors of P-gp is important in risk assessments of pharmacokinetic interactions among chemicals because P-gp-mediated transport processes play a significant role in their absorption and disposition. We previously reported that dibenzoylhydrazines (DBHs) such as tebufenozide and methoxyfenozide (agrochemicals) stimulated P-gp ATPase activity. However, it currently remains unclear whether these derivatives are transport substrates of P-gp and inhibit transport of other chemicals by P-gp.In the present study, in order to evaluate the interactions of DBHs with other chemicals in humans, we determined whether DBHs are P-gp transport substrates using both the in vitro bidirectional transport assay and the in vivo study of rats. In the in vivo study, we investigated the influence of P-gp inhibitors on the brain to plasma ratio of methoxyfenozide in rats. We also examined the inhibitory effects of DBHs on quinidine (a P-gp substrate) transport by P-gp in order to ascertain whether these derivatives are inhibitors of P-gp. Based on the results, DBHs were concluded to be weak P-gp transport substrates and moderate P-gp inhibitors. However, the risk of DBHs caused by interaction with other chemicals including drugs was considered to be low by considering the DBHs' potential as the substrates and inhibitors of P-gp as well as their plasma concentrations as long as DBHs are properly used.

Know your ABCs: Characterization and gene expression dynamics of ABC transporters in the polyphagous herbivore Helicoverpa armigera

Polyphagous insect herbivores are adapted to many different secondary metabolites of their host plants. However, little is known about the role of ATP-binding cassette (ABC) transporters, a multigene family involved in detoxification processes. To study the larval response of the generalist Helicoverpa armigera (Lepidoptera) and the putative role of ABC transporters, we performed developmental assays on artificial diet supplemented with secondary metabolites from host plants (atropine-scopolamine, nicotine and tomatine) and non-host plants (taxol) in combination with a replicated RNAseq experiment. A maximum likelihood phylogeny identified the subfamily affiliations of the ABC transporter sequences. Larval performance was equal on the atropine-scopolamine diet and the tomatine diet. For the latter we could identify a treatment-specific upregulation of five ABC transporters in the gut. No significant developmental difference was detected between larvae fed on nicotine or taxol. This was also mirrored in the upregulation of five ABC transporters when fed on either of the two diets. The highest number of differentially expressed genes was recorded in the gut samples in response to feeding on secondary metabolites. Our results are consistent with the expectation of a general detoxification response in a polyphagous herbivore. This is the first study to characterize the multigene family of ABC transporters and identify gene expression changes across different developmental stages and tissues, as well as the impact of secondary metabolites in the agricultural pest H. armigera.

Genetic variants in ABCG1 are associated with survival of nonsmall-cell lung cancer patients.

Cell membrane transporters and metabolic enzymes play a crucial role in the transportation of a wide variety of substrates that maintain homeostasis in biological processes. We explored associations between genetic variants in these genes and survival of nonsmall-cell lung cancer (NSCLC) patients by reanalyzing two datasets from published genome-wide association studies (GWASs). In the discovery by using the GWAS dataset of the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial, we evaluated associations of 1,245 single-nucleotide polymorphisms (SNPs) in genes of four transporter families and two metabolic enzyme families with survival of 1,185 NSCLC patients. We then performed a replication analysis in the Harvard University Lung Cancer study (LCS) with 984 NSCLC patients. Multivariate Cox proportional hazards regression and false discovery rate (FDR) corrections were performed to evaluate the associations. We identified that 21 genotyped SNPs in eight gene regions were significantly associated with survival with FDR ≤ 0.1 in the discovery dataset. Subsequently, we confirmed six SNPs, which were putative functional, in ABCG1 of the ATP-binding cassette transporter family in the replication dataset. In the pooled analysis, two tagging (at r(2) > 0.8 for linkage disequilibrium with other replicated SNPs)/functional SNPs were independently associated with survival: rs225388 G > A [adjusted hazards ratio (HR) = 1.12, 95% confidence interval (CI) = 1.03-1.20, Ptrend = 4.6 × 10(-3)] and rs225390 A > G (adjusted HR = 1.16, 95% CI = 1.07-1.25, Ptrend = 3.8 × 10(-4) ). Our results indicated that genetic variants of ABCG1 may be predictors of survival of NSCLC patients.