Chemoinformatics analysis identifies cytotoxic compounds susceptible to chemoresistance mediated by glutathione and cystine/glutamate transport system xc-

Tumorigenic effects of human mesenchymal stromal cells and fibroblasts on bladder cancer cells

Background

Patients with muscle-invasive bladder cancer face a poor prognosis due to rapid disease progression and chemoresistance. Thus, there is an urgent need for a new therapeutic treatment. The tumor microenvironment (TME) has crucial roles in tumor development, growth, progression, and therapy resistance. TME cells may also survive standard treatment of care and fire up disease recurrence. However, whether specific TME components have tumor-promoting or tumor-inhibitory properties depends on cell type and cancer entity. Thus, a deeper understanding of the interaction mechanisms between the TME and cancer cells is needed to develop new cancer treatment approaches that overcome therapy resistance. Little is known about the function and interaction between mesenchymal stromal cells (MSC) or fibroblasts (FB) as TME components and bladder cancer cells.

Methods

We investigated the functional impact of conditioned media (CM) from primary cultures of different donors of MSC or FB on urothelial carcinoma cell lines (UCC) representing advanced disease stages, namely, BFTC-905, VMCUB-1, and UMUC-3. Underlying mechanisms were identified by RNA sequencing and protein analyses of cancer cells and of conditioned media by oncoarrays.

Results

Both FB- and MSC-CM had tumor-promoting effects on UCC. In some experiments, the impact of MSC-CM was more pronounced. CM augmented the aggressive phenotype of UCC, particularly of those with epithelial phenotype. Proliferation and migratory and invasive capacity were significantly increased; cisplatin sensitivity was reduced. RNA sequencing identified underlying mechanisms and molecules contributing to the observed phenotype changes. NRF2 and NF-κB signaling was affected, contributing to improved cisplatin detoxification. Likewise, interferon type I signaling was downregulated and regulators of epithelial mesenchymal transition (EMT) were increased. Altered protein abundance of CXCR4, hyaluronan receptor CD44, or TGFβ-signaling was induced by CM in cancer cells and may contribute to phenotypical changes. CM contained high levels of CCL2/MCP-1, MMPs, and interleukins which are well known for their impact on other cancer entities.

Conclusions

The CM of two different TME components had overlapping tumor-promoting effects and increased chemoresistance. We identified underlying mechanisms and molecules contributing to the aggressiveness of bladder cancer cells. These need to be further investigated for targeting the TME to improve cancer therapy.

System Xc−/GSH/GPX4 axis: An important antioxidant system for the ferroptosis in drug-resistant solid tumor therapy

The activation of ferroptosis is a new effective way to treat drug-resistant solid tumors. Ferroptosis is an iron-mediated form of cell death caused by the accumulation of lipid peroxides. The intracellular imbalance between oxidant and antioxidant due to the abnormal expression of multiple redox active enzymes will promote the produce of reactive oxygen species (ROS). So far, a few pathways and regulators have been discovered to regulate ferroptosis. In particular, the cystine/glutamate antiporter (System Xc−), glutathione peroxidase 4 (GPX4) and glutathione (GSH) (System Xc−/GSH/GPX4 axis) plays a key role in preventing lipid peroxidation-mediated ferroptosis, because of which could be inhibited by blocking System Xc−/GSH/GPX4 axis. This review aims to present the current understanding of the mechanism of ferroptosis based on the System Xc−/GSH/GPX4 axis in the treatment of drug-resistant solid tumors.

Transcriptome analysis of developing zebrafish (Danio rerio) embryo following exposure to Gaudichaudione H reveals teratogenicity and cardiovascular defects caused by abnormal iron metabolism

Gaudichaudione H (GH), a caged polyprenylated xanthone from Garcinia plants, showed anti-cancer and anti-inflammatory effects in vitro. However, the in vivo toxicity of this compound has never been reported. The present study was aimed to address the toxic effects of Gaudichaudione H using zebrafish embryos and larvae as an in vivo test model. The zebrafish embryos were treated with GH having different concentrations (0, 0.28, 0.38 and 0.57 μg/mL). The results revealed that GH induces significant embryonic mortality, decreased heartbeat, cardiotoxicity, cardiovascular defects, increased apoptosis and decreased hemoglobinization in zebrafish embryos and larvae. According to transcriptome analysis, 1841 genes were significantly differentially expressed (1185 down-regulated and 656 up-regulated) after GH treatment. The main functions of these genes were related to iron metabolism pathways. The toxicity of GH on zebrafish embryonic development and cardiovascular may due to large amounts of downregulated genes involved in metabolic pathways and DEGs related to 'Iron ion binding' and 'Heme binding' functions.

Effects of Donor-Recipient Age Difference in Renal Transplantation, an Investigation on Renal Function and Fluid Proteome

Introduction

Our previous study revealed that a young internal environment ameliorated kidney aging by virtue of an animal model of heterochronic parabiosis and a model of heterochronic renal transplantation. In this research, we used proteome to investigate the effects of donor-recipient age difference in clinical renal transplantation.

Methods

This study included 10 pairs of renal transplantation donors and recipients with an age difference of greater than 20 years to their corresponding recipients/donors. All recipients have received transplantation more than 3 years ago. Renal function and the serum/urine proteomes of the donors and recipients were analyzed.

Results

The renal function was similar between the young recipients and the old donors. In contrast, the renal function of the young donors was significantly superior to that of the old recipients. Furthermore, 497 and 975 proteins were identified in the serum and urine proteomes, respectively. The content of SLC3A2 in the blood was found to be related to aging, while the contents of SERPINA1 and SERPINA3 in the urine were related to immune functions after renal transplantation.

Conclusion

This study demonstrated that, in the human body, a younger internal environment could ameliorate kidney aging and provided not only clinical evidence for increasing the age limit of kidney transplant donors but also new information for kidney aging research.

Tumor-Associated Antigen xCT and Mutant-p53 as Molecular Targets for New Combinatorial Antitumor Strategies

The cystine/glutamate antiporter xCT is a tumor-associated antigen that has been newly identified in many cancer types. By participating in glutathione biosynthesis, xCT protects cancer cells from oxidative stress conditions and ferroptosis, and contributes to metabolic reprogramming, thus promoting tumor progression and chemoresistance. Moreover, xCT is overexpressed in cancer stem cells. These features render xCT a promising target for cancer therapy, as has been widely reported in the literature and in our work on its immunotargeting. Interestingly, studies on the TP53 gene have revealed that both wild-type and mutant p53 induce the post-transcriptional down modulation of xCT, contributing to ferroptosis. Moreover, APR-246, a small molecule drug that can restore wild-type p53 function in cancer cells, has been described as an indirect modulator of xCT expression in tumors with mutant p53 accumulation, and is thus a promising drug to use in combination with xCT inhibition. This review summarizes the current knowledge of xCT and its regulation by p53, with a focus on the crosstalk of these two molecules in ferroptosis, and also considers some possible combinatorial strategies that can make use of APR-246 treatment in combination with anti-xCT immunotargeting.

xCT (SLC7A11) expression confers intrinsic resistance to physical plasma treatment in tumor cells

Cold physical plasma is a partially ionized gas investigated as a new anticancer tool in selectively targeting cancer cells in monotherapy or in combination with therapeutic agents. Here, we investigated the intrinsic resistance mechanisms of tumor cells towards physical plasma treatment. When analyzing the dose-response relationship to cold plasma-derived oxidants in 11 human cancer cell lines, we identified four 'resistant' and seven 'sensitive' cell lines. We observed stable intracellular glutathione levels following plasma treatment only in the 'resistant' cell lines indicative of altered antioxidant mechanisms. Assessment of proteins involved in GSH metabolism revealed cystine-glutamate antiporter xCT (SLC7A11) to be significantly more abundant in the 'resistant' cell lines as compared to 'sensitive' cell lines. This decisive role of xCT was confirmed by pharmacological and genetic inhibition, followed by cold physical plasma treatment. Finally, microscopy analysis of ex vivo plasma-treated human melanoma punch biopsies suggested a correlation between apoptosis and basal xCT protein abundance. Taken together, our results demonstrate that xCT holds the potential as a biomarker predicting the sensitivity of tumor cells towards plasma treatment.

In silico characterization of residues essential for substrate binding of human cystine transporter, xCT

xCT is a sodium-independent amino acid antiporter that imports L-cystine and exports L-glutamate in a 1:1 ratio. It is a component of heterodimeric amino acid transporter system Xc- working at the cross-roads of maintaining neurological processes and regulating antioxidant defense. The transporter has 12 transmembrane domains with intracellular N- and C-termini, and like other transporter proteins can undergo various conformational changes while switching the ligand accessibilities from intracellular to extracellular site. In the present study, we generated two homology models of human xCT in two distinct conformations: inward-facing occluded state and outward-facing open state. Our results indicated the substrate translocation channel composed of transmembrane helices TMs 1, 3, 6, 8, and 10. We docked anionic L-cystine and L-glutamate within the cavities to assess the two distinct binding scenarios for xCT as antiporter. We also assessed the interactions between the ligands and transporter and observed that ligands bind to similar residues within the channel. Using MM-PBSA/MM-GBSA approach, we computed the binding energies of these ligands to different conformational states. Cystine and glutamate bind xCT with favorable binding energies, with more favorable binding observed in inward occluded state than in outward open state. We further computed the residue-wise decomposition of these binding energies and identified the residues as essential for substrate binding/permeation. Filtering the residues that form favorable energetic contributions to the ligand binding in both the states, our studies suggest T56, A60, R135, A138, V141, Y244, A247, F250, S330, L392, and R396 as critical residues for ligand binding as well as ligand transport for any conformational state adopted by xCT during its transport cycle. .Graphical Abstract.

The role of ferroptosis in digestive system cancer

Ferroptosis is a type of regulated cell death dependent on iron and reactive oxygen species. Ferroptosis is distinct from other cell death modalities, including apoptosis, autophagy and necrosis. Dysregulated ferroptosis has been implicated in a number of diseases, including neuropathy, ischemia reperfusion injury, acute kidney failure and cancer. The digestive system consists of several organs. The morbidity and mortality rates of digestive system cancer are high. The current review summarizes the role of ferroptosis in digestive system cancer. A large number of molecules, including tumor protein p53, retinoblastoma protein, nuclear factor E2-related factor 2, KH RNA binding domain containing signal transduction associated 1, cysteine dioxygenase type 1, metallothionein-1G, nuclear receptor coactivator 4, CDGSH iron sulfur domain 1, heat shock protein family A (Hsp70) member 5 and acyl-CoA synthetase long chain family member 4, regulate ferroptosis in digestive system cancer. Drugs such as cisplatin, baicalein, haloperidol, artesunate, piperlongumine, saponin and bromelain may cause cancer cell death by inducing ferroptosis. An improved understanding of ferroptosis in digestive system cancer may give rise to novel diagnostic and making therapeutic strategies.

Genome-Wide SNP Discovery in Indigenous Cattle Breeds of South Africa

Single nucleotide polymorphism arrays have created new possibilities for performing genome-wide studies to detect genomic regions harboring sequence variants that affect complex traits. However, the majority of validated SNPs for which allele frequencies have been estimated are limited primarily to European breeds. The objective of this study was to perform SNP discovery in three South African indigenous breeds (Afrikaner, Drakensberger, and Nguni) using whole genome sequencing. DNA was extracted from blood and hair samples, quantified and prepared at 50 ng/μl concentration for sequencing at the Agricultural Research Council Biotechnology Platform using an Illumina HiSeq 2500. The fastq files were used to call the variants using the Genome Analysis Tool Kit. A total of 1,678,360 were identified as novel using Run 6 of 1000 Bull Genomes Project. Annotation of the identified variants classified them into functional categories. Within the coding regions, about 30% of the SNPs were non-synonymous substitutions that encode for alternate amino acids. The study of distribution of SNP across the genome identified regions showing notable differences in the densities of SNPs among the breeds and highlighted many regions of functional significance. Gene ontology terms identified genes such as MLANA, SYT10, and CDC42EP5 that have been associated with coat color in mouse, and ADAMS3, DNAJC3, and PAG5 genes have been associated with fertility in cattle. Further analysis of the variants detected 688 candidate selective sweeps (ZHp Z-scores ≤ -4) across all three breeds, of which 223 regions were assigned as being putative selective sweeps (ZHp scores ≤-5). We also identified 96 regions with extremely low ZHp Z-scores (≤-6) in Afrikaner and Nguni. Genes such as KIT and MITF that have been associated with skin pigmentation in cattle and CACNA1C, which has been associated with biopolar disorder in human, were identified in these regions. This study provides the first analysis of sequence data to discover SNPs in indigenous South African cattle breeds. The information will play an important role in our efforts to understand the genetic history of our cattle and in designing appropriate breed improvement programmes.

xCT (SLC7A11)-mediated metabolic reprogramming promotes non-small cell lung cancer progression

Many tumors increase uptake and dependence on glucose, cystine or glutamine. These basic observations on cancer cell metabolism have opened multiple new diagnostic and therapeutic avenues in cancer research. Recent studies demonstrated that smoking could induce the expression of xCT (SLC7A11) in oral cancer cells, suggesting that overexpression of xCT may support lung tumor progression. We hypothesized that overexpression of xCT occurs in lung cancer cells to satisfy the metabolic requirements for growth and survival. Our results demonstrated that 1) xCT was highly expressed at the cytoplasmic membrane in non-small cell lung cancer (NSCLC), 2) the expression of xCT was correlated with advanced stage and predicted a worse 5-year survival, 3) targeting xCT transport activity in xCT overexpressing NSCLC cells with sulfasalazine decreased cell proliferation and invasion in vitro and in vivo and 4) increased dependence on glutamine was observed in xCT overexpressed normal airway epithelial cells. These results suggested that xCT regulate metabolic requirements during lung cancer progression and be a potential therapeutic target in NSCLC.

Tumor Targeting Synergistic Drug Delivery by Self-Assembled Hybrid Nanovesicles to Overcome Drug Resistance

PURPOSE

To overcome multi-drug resistance (MDR) in tumor chemotherapy, a polymer/inorganic hybrid drug delivery platform with tumor targeting property and enhanced cell uptake efficiency was developed.

METHOD

To evaluate the applicability of our delivery platform for the delivery of different drug resistance inhibitors, two kinds of dual-drug pairs (doxorubicin/buthionine sulfoximine and doxorubicin/tariquidar, respectively) were loaded in heparin-biotin/heparin/protamine sulfate/calcium carbonate nanovesicles to realize simultaneous delivery of an anticancer drug and a drug resistance inhibitor into drug-resistant tumor cells.

RESULTS

Prepared by self-assembly, the drug loaded hybrid nanovesicles with a mean size less than 210 nm and a negative zeta potential exhibit good stability in serum contained aqueous media. The in vitro cytotoxicity evaluation indicates that hybrid nanovesicles with tumor targeting biotin moieties have an enhanced tumor cell inhibitory effect. In addition, dual-drug loaded hybrid nanovesicles exhibit significantly stronger cell growth inhibition as compared with doxorubicin (DOX) mono-drug loaded nanovesicles due to the reduced intracellular glutathione (GSH) content by buthionine sulfoximine (BSO) or the P-glycoprotein (P-gp) inhibition by tariquidar (TQR).

CONCLUSIONS

The tumor targeting nanovesicles prepared in this study, which can simultaneously deliver multiple drugs and effectively reverse drug resistance, have promising applications in drug delivery for tumor treatments. The polymer/inorganic hybrid drug delivery platform developed in this study has good applicability for the co-delivery of different anti-tumor drug/drug resistance inhibitor pairs to overcome MDR. Graphical Abstract A polymer/inorganic hybrid drug delivery platform with enhanced cell uptake was developed for tumor targeting synergistic drug delivery. The heparin-biotin/heparin/protamine sulfate/calcium carbonate nanovesicles prepared in this study can deliver an anticancer drug and a drug resistance inhibitor into drug-resistant tumor cells simultaneously to overcome drug resistance efficiently.

Using Drosophila melanogaster to identify chemotherapy toxicity genes

The severity of the toxic side effects of chemotherapy shows a great deal of interindividual variability, and much of this variation is likely genetically based. Simple DNA tests predictive of toxic side effects could revolutionize the way chemotherapy is carried out. Due to the challenges in identifying polymorphisms that affect toxicity in humans, we use Drosophila fecundity following oral exposure to carboplatin, gemcitabine and mitomycin C as a model system to identify naturally occurring DNA variants predictive of toxicity. We use the Drosophila Synthetic Population Resource (DSPR), a panel of recombinant inbred lines derived from a multiparent advanced intercross, to map quantitative trait loci affecting chemotoxicity. We identify two QTL each for carboplatin and gemcitabine toxicity and none for mitomycin. One QTL is associated with fly orthologs of a priori human carboplatin candidate genes ABCC2 and MSH2, and a second QTL is associated with fly orthologs of human gemcitabine candidate genes RRM2 and RRM2B. The third, a carboplatin QTL, is associated with a posteriori human orthologs from solute carrier family 7A, INPP4A&B, and NALCN. The fourth, a gemcitabine QTL that also affects methotrexate toxicity, is associated with human ortholog GPx4. Mapped QTL each explain a significant fraction of variation in toxicity, yet individual SNPs and transposable elements in the candidate gene regions fail to singly explain QTL peaks. Furthermore, estimates of founder haplotype effects are consistent with genes harboring several segregating functional alleles. We find little evidence for nonsynonymous SNPs explaining mapped QTL; thus it seems likely that standing variation in toxicity is due to regulatory alleles.

Pharmacological inhibition of cystine-glutamate exchange induces endoplasmic reticulum stress and ferroptosis

Exchange of extracellular cystine for intracellular glutamate by the antiporter system xc (-) is implicated in numerous pathologies. Pharmacological agents that inhibit system xc (-) activity with high potency have long been sought, but have remained elusive. In this study, we report that the small molecule erastin is a potent, selective inhibitor of system xc (-). RNA sequencing revealed that inhibition of cystine-glutamate exchange leads to activation of an ER stress response and upregulation of CHAC1, providing a pharmacodynamic marker for system xc (-) inhibition. We also found that the clinically approved anti-cancer drug sorafenib, but not other kinase inhibitors, inhibits system xc (-) function and can trigger ER stress and ferroptosis. In an analysis of hospital records and adverse event reports, we found that patients treated with sorafenib exhibited unique metabolic and phenotypic alterations compared to patients treated with other kinase-inhibiting drugs. Finally, using a genetic approach, we identified new genes dramatically upregulated in cells resistant to ferroptosis.DOI: http://dx.doi.org/10.7554/eLife.02523.001.

miR-22 inhibits osteosarcoma cell proliferation and migration by targeting HMGB1 and inhibiting HMGB1-mediated autophagy

Acquisition of drug-resistant phenotypes is often associated with chemotherapy in osteosarcoma. Studies show that high-mobility group box 1 (HMGB1) plays an important role in facilitating autophagy and promotes drug resistance in osteosarcoma cells. In this study, we determined the targeting role of miR-22 to HMGB1 and the regulation of miR-22 on the HMGB1-mediated cell autophagy and on the cell proliferation, migration, and invasion of osteosarcoma cells. Results demonstrated that miR-22 well paired with the 3'-UTR of HMGB1 downregulated the HMGB1 expression and blocked the HMGB1-mediated autophagy during chemotherapy in osteosarcoma cells in vitro. Further study showed that the blockage of autophagy by miR-22 inhibited the osteosarcoma cell proliferation, migration, and invasion. In summary, this study implied the negative regulation of miR-22 on the HMGB1-mediated autophagy in osteosarcoma cells.

The cystine/glutamate antiporter system x(c)(-) in health and disease: from molecular mechanisms to novel therapeutic opportunities

The antiporter system x(c)(-) imports the amino acid cystine, the oxidized form of cysteine, into cells with a 1:1 counter-transport of glutamate. It is composed of a light chain, xCT, and a heavy chain, 4F2 heavy chain (4F2hc), and, thus, belongs to the family of heterodimeric amino acid transporters. Cysteine is the rate-limiting substrate for the important antioxidant glutathione (GSH) and, along with cystine, it also forms a key redox couple on its own. Glutamate is a major neurotransmitter in the central nervous system (CNS). By phylogenetic analysis, we show that system x(c)(-) is a rather evolutionarily new amino acid transport system. In addition, we summarize the current knowledge regarding the molecular mechanisms that regulate system x(c)(-), including the transcriptional regulation of the xCT light chain, posttranscriptional mechanisms, and pharmacological inhibitors of system x(c)(-). Moreover, the roles of system x(c)(-) in regulating GSH levels, the redox state of the extracellular cystine/cysteine redox couple, and extracellular glutamate levels are discussed. In vitro, glutamate-mediated system x(c)(-) inhibition leads to neuronal cell death, a paradigm called oxidative glutamate toxicity, which has successfully been used to identify neuroprotective compounds. In vivo, xCT has a rather restricted expression pattern with the highest levels in the CNS and parts of the immune system. System x(c)(-) is also present in the eye. Moreover, an elevated expression of xCT has been reported in cancer. We highlight the diverse roles of system x(c)(-) in the regulation of the immune response, in various aspects of cancer and in the eye and the CNS.

System xc⁻ cystine/glutamate antiporter: an update on molecular pharmacology and roles within the CNS

System x(c)(-) is an amino acid antiporter that typically mediates the exchange of extracellular l-cystine and intracellular L-glutamate across the cellular plasma membrane. Studied in a variety of cell types, the import of L-cystine through this transporter is critical to glutathione production and oxidative protection. The exchange-mediated export of L-glutamate takes on added significance within the CNS, as it represents a non-vesicular route of release through which this excitatory neurotransmitter can participate in either neuronal signalling or excitotoxic pathology. When both the import of L-cystine and the export of L-glutamate are taken into consideration, system x(c)(-) has now been linked to a wide range of CNS functions, including oxidative protection, the operation of the blood-brain barrier, neurotransmitter release, synaptic organization, viral pathology, drug addiction, chemosensitivity and chemoresistance, and brain tumour growth. The ability to selectively manipulate system x(c)(-), delineate its function, probe its structure and evaluate it as a therapeutic target is closely linked to understanding its pharmacology and the subsequent development of selective inhibitors and substrates. Towards that goal, this review will examine the current status of our understanding of system x(c)(-) pharmacology and the structure-activity relationships that have guided the development of an initial pharmacophore model, including the presence of lipophilic domains adjacent to the substrate binding site. A special emphasis is placed on the roles of system x(c)(-) within the CNS, as it is these actions that are among the most exciting as potential long-range therapeutic targets.

Mutation of ATF4 mediates resistance of neuronal cell lines against oxidative stress by inducing xCT expression

Selecting neuronal cell lines for resistance against oxidative stress might recapitulate some adaptive processes in neurodegenerative diseases where oxidative stress is involved like Parkinson's disease. We recently reported that in hippocampal HT22 cells selected for resistance against oxidative glutamate toxicity, the cystine/glutamate antiporter system x(c)(-), which imports cystine for synthesis of the antioxidant glutathione, and its specific subunit, xCT, are upregulated. (Lewerenz et al., J Neurochem 98(3):916-25). Here, we show that in these glutamate-resistant HT22 cells upregulation of xCT mediates glutamate resistance, and xCT expression is induced by upregulation of the transcription factor ATF4. The mechanism of ATF4 upregulation consists of a 13 bp deletion in the upstream open reading frame (uORF2) overlapping the ATF4 open reading frame. The resulting uORF2-ATF4 fusion protein is efficiently translated even at a low phosphorylation levels of the translation initiation factor eIF2α, a condition under which ATF4 translation is normally suppressed. A similar ATF4 mutation associated with prominent upregulation of xCT expression was identified in PC12 cells selected for resistance against amyloid β-peptide. Our data indicate that ATF4 has a central role in regulating xCT expression and resistance against oxidative stress. ATF4 mutations might have broader significance as upregulation of xCT is found in tumor cells and associated with anticancer drug resistance.

Alterations of microRNAs in cisplatin-resistant human non-small cell lung cancer cells (A549/DDP)

ABSTRACT MicroRNAs (miRNAs) are a class of small, noncoding RNAs that posttranscriptionally regulate genes expression and play crucial roles in diverse biological processes, such as development, differentiation, apoptosis, and proliferation. Accumulating evidence suggests that miRNAs may play a role in chemoresistance and may be involved in the modulation of some drug resistance-related pathways in cancer cells. Here, the authors investigated the possible role of miRNAs in the development of drug resistance in lung cancer cell line. The results showed that 14 miRNAs were presented significantly (>2-fold), including up-regulation of 9 miRNAs and down-regulation of 5 miRNAs in A549/DDP cell line, compared with the parental A549 cell line. Up-regulation of miR-138 increased the sensitivity of A549/DDP cells to cisplatin in in vitro drug sensitivity assay, and increased apoptosis assessed by flow cytometry. The authors also found that excision repair cross-complementation group 1 (ERCC1) was negatively regulated by miR-138 and that down-regulation of ERCC1 at the protein level largely correlated with elevated levels of miR-138 in A549/DDP cells. Taken together, these findings suggest that miR-138 could play an important role in the development of cisplatin resistance in non-small cell lung cancer (NSCLC).

Downregulation of cystine transporter xc by irinotecan in human head and neck cancer FaDu xenografts

BACKGROUND

The purpose of this study was: (1) to document the critical requirement of cystine for growth of human tumor cells in vitro, and (2) to determine the effect of the anticancer agent irinotecan on the cystine transporter x(c)(-) in head and neck FaDu xenografts.

METHODS

Cell growth was measured by sulforhodamine B assay. xCT protein, glutathione (GSH) and DNA damage were determined using Western blot, spectrophotometry, and immunohistochemistry, respectively.

RESULTS

Depletion of cystine from the medium inhibited tumor cell growth. Treatment of FaDu tumor with a therapeutic dose of irinotecan resulted in depression of xCT protein levels, leading to tumor growth retardation and downregulation of GSH with increased reactive oxygen species (ROS). The accumulation of ROS correlated with increased DNA damage as evidenced by increased H2AX.

CONCLUSION

Depression of xCT protein by irinotecan resulted in downregulation of GSH and increase in ROS, which could be the other possible mechanisms of DNA damage by irinotecan.

Gene expression profiling of drug-resistant small cell lung cancer cells by combining microRNA and cDNA expression analysis

MicroRNAs (miRNAs) are now known to play important roles in the regulation of gene expression for developmental timing, cell proliferation and apoptosis. Therefore, it is likely that they also modulate sensitivity and resistance to anti-cancer drugs. To better understand the molecular mechanisms of multidrug resistance in SCLC and identify novel molecular markers, we evaluated the expression of 856 miRNAs and approximately 22,000 genes using miRNA microarray and cDNA microarray in cellular models of SCLC which were widely used as sensitive (NCI-H69) and resistant cell lines (NCI-H69AR) to chemotherapy. We also analysed the correlations between miRNA and mRNA expression patterns. Further studies were tested to determine whether the differentially expressed miRNAs were involved in multidrug resistance in SCLC. Our results showed that 61 miRNAs are presented significantly (>3-fold) including up-regulation of 24 miRNAs and down-regulation of 37 miRNAs. Among these miRNAs, 48 of 61 differentially expressed miRNAs were firstly reported to be closely associated with drug resistance and 37.7% (24/61) of miRNA genes were organised as 10 clusters in total 61 significantly expressed miRNAs. We also found that only 27 of 69 miRNAs were significantly correlated with 604 of 21,522 70 mRNA transcripts by MAS database. The sensitivity to anti-cancer drugs Cisplatin, Etoposide and Doxorubicin greatly increased or reduced following transfection of the drug-resistant H69AR cells with the mimics or antagomirs of miR-134, miR-379 and miR-495, respectively. miR-134 increases the cell survival by inducing G1 arrest in H69AR cells. MRP1/ABCC1 is negatively regulated by miR-134 and down-regulation of MRP1/ABCC1 at the protein level largely correlates with elevated levels of miR-134 in H69AR cells. Our results support for the first time a substantial role for miRNAs in multidrug resistance in SCLC. miR-134 could be a causal factor of the down-regulation of MRP1/ABCC1 in H69AR cells. These findings provide valuable information for potential utility of these miRNAs as specific diagnostic biomarkers and novel therapeutic approaches for drug resistance of SCLC.

Pharmacogenomic approach reveals a role for the x(c)- cystine/glutamate antiporter in growth and celastrol resistance of glioma cell lines

The x(c)(-) cystine/glutamate antiporter has been implicated in GSH-based chemoresistance because it mediates cellular uptake of cystine/cysteine for sustenance of intracellular GSH levels. Celastrol, isolated from a Chinese medicinal herb, is a novel heat shock protein 90 (Hsp90) inhibitor with potent anticancer activity against glioma in vitro and in vivo. In search of correlations between growth-inhibitory potency of celastrol in NCI-60 cell lines and microarray expression profiles of most known transporters, we found that expression of SLC7A11, the gene encoding the light chain subunit of x(c)(-), showed a strong negative correlation with celastrol activity. This novel gene-drug correlation was validated. In celastrol-resistant glioma cells that highly expressed SLC7A11, sensitivity to celastrol was consistently increased via treatment with x(c)(-) inhibitors, including glutamate, (S)-4-carboxyphenylglycine, sulfasalazine, and SLC7A11 small interfering RNA. The GSH synthesis inhibitor, buthionine sulfoximine, also increased celastrol sensitivity, whereas the GSH booster, N-acetylcysteine, suppressed its cytotoxicity. Furthermore, the glioma cell lines were dependent on x(c)(-)-mediated cystine uptake for viability, because cystine omission from the culture medium resulted in cell death and treatment with sulfasalazine depleted GSH levels and inhibited their growth. Combined treatment of glioma cells with sulfasalazine and celastrol led to chemosensitization, as suggested by increased celastrol-induced cell cycle arrest, apoptosis, and down-regulation of the Hsp90 client protein, epidermal growth factor receptor. These results indicate that the x(c)(-) transporter provides a useful target for glioma therapy. x(c)(-) inhibitors such as sulfasalazine, a Food and Drug Administration-approved drug, may be effective both as an anticancer drug and as an agent for sensitizing gliomas to celastrol.

Gene expression associations with the growth inhibitory effects of small molecules on live cells: specificity of effects and uniformity of mechanisms

The NCI60 human tumor cell line screen is a public resource for studying selective and non-selective growth inhibition of small molecules against cancer cells. By coupling growth inhibition screening data with biological characterizations of the different cell lines, it becomes possible to infer mechanisms of action underlying some of the observable patterns of selective activity. Using these data, mechanistic relationships have been identified including specific associations between single genes and small families of closely related compounds, and less specific relationships between biological processes involving several cooperating genes and broader families of compounds. Here we aim to characterize the degree to which such specific and general relationships are present in these data. A related question is whether genes tend to act with a uniform mechanism for all associated compounds, or whether multiple mechanisms are commonly involved. We address these two issues in a statistical framework placing special emphasis on the effects of measurement error in the gene expression and chemical screening data. We find that as measurement accuracy increases, the pattern of apparent associations shifts from one dominated by isolated gene/compound pairs, to one in which families consisting of an average of 25 compounds are associated to the same gene. At the same time, the number of genes that appear to play a role in influencing compound activities decreases. For less than half of the genes, the presence of both positive and negative correlations indicates pleiotropic associations with molecules via different mechanisms of action.

Extracellular thiol-assisted selenium uptake dependent on the x(c)- cystine transporter explains the cancer-specific cytotoxicity of selenite

The selenium salt selenite (SeO(3)(2-)) is cytotoxic in low to moderate concentrations, with a remarkable specificity for cancer cells resistant to conventional chemotherapy. Our data show that selenium uptake and accumulation, rather than intracellular events, are crucial to the specific selenite cytotoxicity observed in resistant cancer cells. We show that selenium uptake depends on extracellular reduction, and that the extracellular environment is a key factor specific to selenite cytotoxicity. The extracellular reduction is mediated by cysteine, and the efficacy is determined by the uptake of cystine by the x(c)(-) antiporter and secretion of cysteine by multidrug resistance proteins, both of which are frequently overexpressed by resistant cancer cells. This mechanism provides molecular evidence for the existence of an inverse relationship between resistance to conventional chemotherapy and sensitivity to selenite cytotoxicity, and highlights the great therapeutic potential in treating multidrug-resistant cancer.

Genetic variations and gene expression of transporters in drug disposition and response

BACKGROUND

The importance of transporters in drug disposition and response has led to increasing interest in genetic variations and expression differences of their genes.

OBJECTIVE

This review summarizes: i) genetic variations in transporters and associated drug response; and ii) a pharmacogenomic approach to correlate transporter expression and drug response.

METHODS

Several transporters in ATP-binding cassette family and solute carrier family are discussed.

CONCLUSION

The field of transporter pharmacogenomics is in its early stage. Transporter expression at mRNA levels could be more directly related to their functions and more practical to be assayed in high throughput. Correlating microarray expression of transporters with anticancer drug activity in the NCI-60 panel has provided an approach for identifying drug-transporter relationships and predicting drug response.

The x(c)- cystine/glutamate antiporter: a potential target for therapy of cancer and other diseases

The x(c) (-) cystine/glutamate antiporter is a major plasma membrane transporter for the cellular uptake of cystine in exchange for intracellular glutamate. Its main functions in the body are mediation of cellular cystine uptake for synthesis of glutathione essential for cellular protection from oxidative stress and maintenance of a cystine:cysteine redox balance in the extracellular compartment. In the past decade it has become evident that the x(c) (-) transporter plays an important role in various aspects of cancer, including: (i) growth and progression of cancers that have a critical growth requirement for extracellular cystine/cysteine, (ii) glutathione-based drug resistance, (iii) excitotoxicity due to excessive release of glutamate, and (iv) uptake of herpesvirus 8, a causative agent of Kaposi's sarcoma. The x(c) (-) transporter also plays a role in certain CNS and eye diseases. This review focuses on the expression and function of the x(c) (-) transporter in cells and tissues with particular emphasis on its role in disease pathogenesis. The potential use of x(c) (-) inhibitors (e.g., sulfasalazine) for arresting tumor growth and/or sensitizing cancers is discussed.

Cystine-glutamate transporter SLC7A11 mediates resistance to geldanamycin but not to 17-(allylamino)-17-demethoxygeldanamycin

The cystine-glutamate transporter SLC7A11 has been implicated in chemoresistance, by supplying cystine to the cell for glutathione maintenance. In the NCI-60 cell panel, SLC7A11 expression shows negative correlation with growth inhibitory potency of geldanamycin but not with its analog 17-(allylamino)-17-demethoxygeldanamycin (17-AAG), which differs in the C-17 substituent in that the the methoxy moiety of geldanamycin is replaced by an amino group. Structure and potency analysis classified 18 geldanamycin analogs into two subgroups, "17-O/H" (C-17 methoxy or unsubstituted) and "17-N" (C-17 amino), showing distinct SLC7A11 correlation. We used three 17-O/H analogs and four 17-N analogs to test the role of the 17-substituents in susceptibility to SLC7A11-mediated resistance. In A549 cells, which are resistant to geldanamycin and strongly express SLC7A11, inhibition of SLC7A11 by (S)-4-carboxyphenylglycine or small interfering RNA increased sensitivity to 17-O/H, but had no effect on 17-N analogs. Ectopic expression of SLC7A11 in HepG2 cells, which are sensitive to geldanamycin and express low SLC7A11, confers resistance to geldanamycin, but not to 17-AAG. Antioxidant N-acetylcysteine, a precursor for glutathione synthesis, completely suppressed cytotoxic effects of 17-O/H but had no effect on 17-N analogs, whereas the prooxidant ascorbic acid had the opposite effect. Compared with 17-AAG, geldanamycin led to significantly more intracellular reactive oxygen species (ROS) production, which was quenched by addition of N-acetylcysteine. We conclude that SLC7A11 confers resistance selectively to 17-O/H (e.g., geldanamycin) but not to 17-N (e.g., 17-AAG) analogs partly as a result of differential dependence on ROS for cytotoxicity. Distinct mechanisms could significantly affect antitumor response and organ toxicity of these compounds in vivo.

Chemogenomic Analysis Identifies Geldanamycins as Substrates and Inhibitors of ABCB1

PURPOSE

A prerequisite for geldanamycin (GA, NSC122750) to targeting heat shock protein 90 and inhibiting tumor growth is sufficient intracellular drug accumulation. We hypothesized that membrane transporters on tumor cells determine at least in part the response to GA analogues.

MATERIALS AND METHODS

To facilitate a systematic study of chemosensitivity across a group of GA analogues with similar chemical structures, we correlated mRNA expression profiles of most known transporters with growth inhibitory potencies of compounds in 60 tumor cell lines (NCI-60). We subsequently validated the gene-drug correlations using cytotoxicity and transport assays.

RESULTS

Geldanamycin analogues displayed a range of negative correlations coefficients with ABCB1 (MDR1, or P-glycoprotein) expression. Suppressing ABCB1 in multidrug resistant cells (NCI/ADR-RES and K562/DOX) and ABCB1-transfected cells (BC19) increased sensitivity to GA analogues, as expected for substrates. Moreover, ABCB1-mediated efflux of daunorubicin in K562/DOX cells could be blocked markedly by GA analogues in a dose-dependent fashion. The IC(50) values (half-maximum inhibition of daunorubicin efflux) were 5.5, 7.3 and 12 muM for macbecin II (NSC330500), 17-AAG (NSC330507) and GA, respectively.

CONCLUSIONS

These observations demonstrate that GA analogues are substrates as well as inhibitors of ABCB1, suggesting that drug interactions between GA analogues and other agents that are ABCB1 substrates may occur via ABCB1 in normal or tumor cells.