Cisplatin sensitivity of oral squamous carcinoma cells is regulated by Na+,K+-ATPase activity rather than copper-transporting P-type ATPases, ATP7A and ATP7B

Amphipathic barbiturates as marine product mimics with cytolytic and immunogenic effects on head and neck squamous cell carcinoma cell lines

The incidence of head and neck squamous cell carcinoma (HNSCC) is increasing and the conventional treatments for this form of cancer can be tough. Despite the success of existing immunotherapies in some HNSCC patients, many do not respond to this type of treatment. Thus, the development of novel anti-cancer therapies should be prioritized. In the current study, the anticancer activity of a panel of novel compounds, herein termed marine product mimics (MPMs), against HNSCC cell lines is explored. The previously reported compound MPM-1, which is structurally related to the novel MPMs, was shown to have promising effects on the HNSCC cell line HSC-3. The results from the current study indicate that the novel MPMs are more potent than MPM-1 but cause a similar type of cell death. The results indicated that the MPMs must cross through the cell membrane to exert their action and that they are lysosomotropic. Further experiments showed that some of the MPMs could induce phosphorylation of eukaryotic initiation factor 2α (eIF2α) in HSC-3 and UT-SCC-24A cells, which indicates that they can activate the integrated stress response that is strongly associated with immunogenic cell death. Cell surface expression of calreticulin and release of HMGB1 and ATP, which are all hallmarks of immunogenic cell death, was also demonstrated in HSC-3 and UT-SCC-24A cells treated with MPMs. This suggests that the MPMs are interesting candidates for future HNSCC cancer therapies.

Immunohistochemical validation study of 15-gene biomarker panel predictive of benefit from adjuvant chemotherapy in resected non-small-cell lung cancer: analysis of JBR.10

Objective

There are no validated approaches to predict benefit from adjuvant chemotherapy for resected patients with non-small-cell lung cancer (NSCLC). The aim of this study was to translate a 15-gene mRNA expression profile published by Zhu et al, shown to be prognostic and predictive of benefit, into a readily applicable immunohistochemistry (IHC) panel.

Methods

For seven of the genes in the gene expression profile (GEP) for which suitable commercial antibodies were available, we semiquantitatively assessed the IHC expression and prognostic significance for 173 patients treated at the Saint John Regional Hospital (SJRH). Cut-offs for high and low expression were defined for each marker and applied to IHC scores from 291 of the 482 patients in JBR.10, including patients on both the adjuvant chemotherapy and observation arms. The prognostic and predictive value of these markers on overall survival (OS) or recurrence-free survival (RFS) was assessed by Cox regression models.

Results

In the SJRH cohort, in 62 patients with resected stage II–III NSCLC, the prognostic significance of IHC assays for four proteins were concordant with Zhu’s GEP results. Low FOSL2 (OS, HR=0.15; p=0.0001; RFS, HR=0.14; p<0.0001) and high STMN2 (RFS, HR=2.501; p=0.0197) were adverse prognostic factors. Low ATP1B1 and low TRIM14 expression trended toward worse OS and RFS. Validation of these markers with JBR.10 patients failed to show prognostic significance either individually or in combined risk classifications. Additionally, the interaction between these markers and chemotherapy treatment in predicting OS (FOSL2, p=0.52; STMN2 p=0.14; ATP1B1, p=0.33; TRIM14, p=0.81) or RFS (FOSL2, p=0.63; STMN2, p=0.12; ATP1B1, p=0.66; TRIM14, p=0.57) did not reach significance, individually or in combination panels.

Conclusions

Zhu’s GEP could not be translated into an IHC panel predictive of benefit from adjuvant chemotherapy. Future predictive biomarker analysis in the adjuvant NSCLC setting may need to focus on novel therapies.

Low expression of FXYD5 reverses the cisplatin resistance of epithelial ovarian cancer cells

OBJECTIVE

To investigate the effect of the downregulation of FXYD domain-containing ion transport regulator 5 (FXYD5) on the cisplatin resistance (CisR) of epithelial ovarian cancer (EOC) cells.

METHODS

A2780-CisR and SKOV3-CisR cells were obtained through repeated administrations of different cisplatin concentrations, and the half-maximal inhibition concentration (IC50) was calculated by MTT assays. After transfection with FXYD5 siRNA-1 and FXYD5 siRNA-2, the IC50 values of the A2780-CisR and SKOV3-CisR cells were also detected by the MTT method. Cell proliferation, migration, invasion and apoptosis were evaluated through 5-ethynyl-2'-deoxyuridine (EdU) DNA synthesis, wound healing, Transwell invasion and Annexin-V-FITC/PI dual-staining assays, respectively. qRT-PCR and Western blotting were conducted to detect mRNA and protein expression.

RESULTS

Compared with the sensitive parental cells, the A2780-CisR and SKOV3-CisR cells had increased IC50 and FXYD5 expression. FXYD5 siRNA reduced the IC50 value of cisplatin in the A2780-CisR and SKOV3-CisR cells and decreased the expression of ABCG2 (BCRP) and ABCB1 (MDR1). In addition, FXYD5 inhibition reduced the invasion and migration of the A2780-CisR and SKOV3-CisR cells, with upregulation of E-cadherin and downregulation of Snail and Vimentin. Both FXYD5 siRNA-1 and FXYD5 siRNA-2 inhibited the proliferation and promoted the apoptosis of the A2780-CisR and SKOV3-CisR cells with reduced Ki-67 and increased caspase-3.

CONCLUSION

FXYD5 downregulation may reduce the invasion, migration and EMT formation of EOC cells to increase their sensitivity to cisplatin chemotherapy by inhibiting cell proliferation and promoting cell apoptosis.

Acquisition of Cisplatin Resistance Shifts Head and Neck Squamous Cell Carcinoma Metabolism toward Neutralization of Oxidative Stress

Background: Cisplatin (CDDP) is commonly utilized in the treatment of advanced solid tumors including head and neck squamous cell carcinoma (HNSCC). Cisplatin response remains highly variable among individual tumors and development of cisplatin resistance is common. We hypothesized that development of cisplatin resistance is partially driven by metabolic reprogramming. Methods: Using a pre-clinical HNSCC model and an integrated approach to steady state metabolomics, metabolic flux and gene expression data we characterized the interaction between cisplatin resistance and metabolic reprogramming. Results: Cisplatin toxicity in HNSCC was driven by generation of intra-cellular oxidative stress. This was validated by demonstrating that acquisition of cisplatin resistance generates cross-resistance to ferroptosis agonists despite the fact that cisplatin itself does not trigger ferroptosis. Acquisition of cisplatin resistance dysregulated the expression of genes involved in amino acid, fatty acid metabolism and central carbon catabolic pathways, enhanced glucose catabolism and serine synthesis. Acute cisplatin exposure increased intra-tumoral levels of S-methyl-5-thiadenosine (MTA) precursors and metabotoxins indicative of generalized oxidative stress. Conclusions: Acquisition of cisplatin resistance is linked to metabolic recovery from oxidative stress. Although this portends poor effectiveness for directed metabolic targeting, it supports the potential for biomarker development of cisplatin effectiveness using an integrated approach.

Exploring the Therapeutic Potential of Membrane Transport Proteins: Focus on Cancer and Chemoresistance

Improving the therapeutic efficacy of conventional anticancer drugs represents the best hope for cancer treatment. However, the shortage of druggable targets and the increasing development of anticancer drug resistance remain significant problems. Recently, membrane transport proteins have emerged as novel therapeutic targets for cancer treatment. These proteins are essential for a plethora of cell functions ranging from cell homeostasis to clinical drug toxicity. Furthermore, their association with carcinogenesis and chemoresistance has opened new vistas for pharmacology-based cancer research. This review provides a comprehensive update of our current knowledge on the functional expression profile of membrane transport proteins in cancer and chemoresistant tumours that may form the basis for new cancer treatment strategies.

Photobiomodulation Enhances Cisplatin Cytotoxicity in a Culture Model with Oral Cell Lineages

Cisplatin plays a central role in cancer chemotherapy, but resistance to this drug remains a major obstacle in treatment. Drawbacks related to cisplatin failure may be associated with cell energy metabolism. This study investigated whether photobiomodulation (PBM) can potentiate the effects of cisplatin on keratinocytes (HaCat) and cancer cells (SCC25 and HN12). Cells were treated with laser (GaAlAs; 660 nm; 60 mW; 0.33 J; 2.14 W cm^-2 ; 11.7 J cm^-2 and 6 s) and cisplatin (7.8 μg mL^-1 ) to evaluate cell viability, Ki-67, VEGF, TGF-β1, EGF expression and ROS production. Observations were validated in the SCC25 cell lineage, where the type of cell death (necrosis/apoptosis) and the amount of ATP were assessed. Cell lineages showed increased sensitivity to cisplatin associated with PBM (Cis-PBM). Ki-67 was augmented in all cell lineages treated with Cis-PBM when compared to cisplatin alone (Cis). Cis or Cis-PBM significantly decreased VEGF expression in cancer cells, while no changes were seen in the expression of TGF-β1 or EGF compared to control. ROS levels were similar in the Cis and Cis-PBM groups. Cells treated with Cis-PBM died by apoptosis, leading to greater consumption of ATP. These observations suggest that PBM may potentiate the effects of cisplatin, leading to increased drug cytotoxicity and enhanced cell death.

Effect of cisplatin on the transport activity of PII-type ATPases

Cisplatin (cis-diamminedichlorido-Pt(ii)) is extensively used as a chemotherapeutic agent against various types of tumors. However, cisplatin administration causes serious side effects, including nephrotoxicity, ototoxicity and neurotoxicity. It has been shown that cisplatin can interact with P-type ATPases, e.g., Cu⁺-ATPases (ATP7A and ATP7B) and Na⁺,K⁺-ATPase. Cisplatin-induced inhibition of Na⁺,K⁺-ATPase has been related to the nephrotoxic effect of the drug. To investigate the inhibitory effects of cisplatin on the pumping activity of P_II-type ATPases, electrical measurements were performed on sarcoplasmic reticulum Ca²⁺-ATPase (SERCA) and Na⁺,K⁺-ATPase embedded in vesicles/membrane fragments adsorbed on a solid-supported membrane. We found that cisplatin inhibits SERCA and Na⁺,K⁺-ATPase only when administered without a physiological reducing agent (GSH); in contrast, inhibition was also observed in the case of Cu⁺-ATPases in the presence of 1 mM GSH. Our results indicate that cisplatin is a much stronger inhibitor of SERCA (with an IC₅₀ value of 1.3 μM) than of Na⁺,K⁺-ATPase (with an IC₅₀ value of 11.1 μM); moreover, cisplatin inhibition of Na⁺,K⁺-ATPase is reversible, whereas it is irreversible in the case of SERCA. In the absence of a physiological substrate, while Cu⁺-ATPases are able to translocate cisplatin, SERCA and Na⁺,K⁺-ATPase do not perform ATP-dependent cisplatin displacement.

Cisplatin generates oxidative stress which is accompanied by rapid shifts in central carbon metabolism

Cisplatin is commonly utilized in the treatment of solid tumors. Its mechanism of action is complex and multiple mechanisms of resistance have been described. We sought to determine the impact of cisplatin-generated oxidative stress on head and neck squamous cell carcinoma (HNSCC) proliferation, survival and metabolic activity in order to identify a potential metabolic signature associated with cisplatin response. DNA-bound cisplatin represents a small fraction of total intra-cellular cisplatin but generates a robust oxidative stress response. Neutralization of oxidative stress reverses cisplatin toxicity independent of the mechanism of cell death and TP53 mutational status. Cisplatin-induced oxidative stress triggers rapid shifts in carbon flux in 3 commonly utilized catabolic pathways: glycolysis, pentose phosphate pathway and citric acid cycle. Among these metabolic shifts, decreased flux from pyruvate into lactate is the only metabolic effect consistently observed across multiple HNSCC cell lines of varying genomic backgrounds and may reflect differential cisplatin sensitivity. Oxidative stress is a critical component of cisplatin cytotoxicity in HNSCC and is reflected in acute changes in carbon flux from pyruvate into lactate. This suggests that lactate may contribute to a metabolic signature of acute cisplatin toxicity, and could prove useful in optimizing cisplatin-based treatment regimens in HNSCC.

Ouabain suppresses the growth and migration abilities of glioma U‑87MG cells through inhibiting the Akt/mTOR signaling pathway and downregulating the expression of HIF‑1α

Glioma is one of the most malignant forms of brain tumor, and has been of persistent concern due to its high recurrence and mortality rates, and limited therapeutic options. As a cardiac glycoside, ouabain has widespread applications in congestive heart diseases due to its positive cardiac inotropic effect by inhibiting Na⁺/K⁺-ATPase. Previous studies have demonstrated that ouabain has antitumor activity in several types of human tumor, including glioma. However, the exact underlying mechanism remains to be elucidated. The purpose of present study was to elucidate the effect of ouabain on human glioma cell apoptosis and investigate the exact mechanism. U-87MG cells were treated with various concentrations of ouabain for 24 h, following which cell viability and survival rate were assessed using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The dynamic changes and cell motility were observed using digital holographic microscopy. Additionally, western blot analysis and high-content screening assays were used to detect the protein expression levels of phosphorylated (p-)Akt, mammalian target of rapamycin (mTOR), p-mTOR and hypoxia-inducible factor (HIF)-1α, respectively. Compared with the control group, ouabain suppressed U-87MG cell survival, and attenuated cell motility in a dose-dependent manner (P<0.01). The downregulation of p-Akt, mTOR, p-mTOR and HIF-1α were observed following treatment with 2.5 and 25 µmol/l of ouabain. These results suggested that ouabain exerted suppressive effects on tumor cell growth and motility, leading to cell death via regulating the intracellular Akt/mTOR signaling pathway and inhibiting the expression of HIF-1α in glioma cells. The present study examined the mechanism underlying the antitumor property of ouabain, providing a novel potential therapeutic agent for glioma treatment.

Selection and characterization of a human ovarian cancer cell line resistant to auranofin

The anti-arthritic drug auranofin exerts also potent antitumour activity in in vitro and in vivo models, whose mechanisms are not yet well defined. From an auranofin-sensitive human ovarian cancer cell line A2780, a highly resistant (>20-fold) subline (A2780/AF-R) was developed and characterized. Marked reduction of gold accumulation occurred in auranofin-resistant A2780 cells. Also, moderately higher thioredoxin reductase activity in A2780/AF-R cells was observed while no changes in intracellular glutathione content occurred. Resistance to auranofin was associated with a low level of cross-resistance to some investigational gold compounds as well as to oxaliplatin and other anticancer drugs with different mode of action (i.e. melphalan, vinblastine, doxorubicin, etoposide, and paclitaxel). Reduced gold accumulation was associated to substantial gene expression changes in various influx (e.g. SLC22A1, SLC47A1, SLCO1B1) and efflux (e.g. ABCB1, ABCC2, ABCC3) transporters. The expression levels of selected proteins (i.e. SLC22A1, SLC47A1, P-gp) were also changed accordingly. These data provide evidence that multiple drug transporters may act as mediators of transport of auranofin and other gold compounds in cancer cells. Further investigation into the molecular mechanisms mediating transport of auranofin and new gold complexes in view of their potential clinical application in the treatment of cancer is warranted.

Metabolic interrogation as a tool to optimize chemotherapeutic regimens

Platinum-based (Pt) chemotherapy is broadly utilized in the treatment of cancer. Development of more effective, personalized treatment strategies require identification of novel biomarkers of treatment response. Since Pt compounds are inactivated through cellular metabolic activity, we hypothesized that metabolic interrogation can predict the effectiveness of Pt chemotherapy in a pre-clinical model of head and neck squamous cell carcinoma (HNSCC).We tested the effects of cisplatin (CDDP) and carboplatin (CBP) on DNA damage, activation of cellular death cascades and tumor cell metabolism, specifically lactate production. Pt compounds induced an acute dose-dependent, transient drop in lactate generation in vitro, which correlated with effects on DNA damage and cell death. Neutralization of free radical stress abrogated these effects. The magnitude of this effect on lactate production correlated with the differential sensitivity of HNSCC cells to Pt compounds (CDDP vs CBP) and p53-driven Pt chemotherapy resistance. Using dual flank xenograft tumors, we demonstrated that Pt-driven effects on lactate levels correlate with effects on tumor growth delay in a dose-dependent manner and that lactate levels can define the temporal profile of Pt chemotherapy-induced metabolic stress. Lactate interrogation also predicted doxorubicin effects on cell death in both solid tumor (HNSCC) and acute myelogenous leukemia (AML) cell lines.Real-time metabolic interrogation of acute changes in cell and tumor lactate levels reflects chemotherapy effects on DNA damage, cell death and tumor growth delay. We have identified a real-time biomarker of chemotherapy effectiveness which can be used to develop adaptive, iterative and personalized treatment regimens against a variety of solid and hematopoietic malignancies.

The influence of oxo-bridged binuclear gold(III) complexes on Na/K-ATPase activity: a joint experimental and theoretical approach

The in vitro effects of oxo-bridged binuclear gold(III) complexes, i.e., [(bipy2Me)₂Au₂(μ-O)₂][PF₆]₂ (Auoxo6), Au₂[(bipydmb-H)₂(μ-O)][PF₆] (Au₂bipyC) and [Au₂(phen^2Me)₂(μ-O)₂](PF₆)₂ (Au₂phen) on Na/K-ATPase, purified from the porcine cerebral cortex, were investigated. All three studied gold complexes inhibited the enzyme activity in a concentration-dependent manner achieving IC₅₀ values in the low micromolar range. Kinetic analysis suggested an uncompetitive mode of inhibition for Auoxo6 and Au₂bipyC, and a mixed type one for Au₂phen. Docking studies indicated that the inhibitory actions of all tested complexes are related to E2-P enzyme conformation binding to ion channel and intracellular part between N and P sub-domain. In addition, Au₂phen was able to inhibit the enzyme by interacting with its extracellular part as well. Toxic effects of the gold(III) complexes were evaluated in vitro by following lactate dehydrogenase activity in rat brain synaptosomes and incidence of micronuclei and cytokinesis-block proliferation index in cultivated human lymphocytes. All investigated complexes turned out to induce cytogenetic damage consisting of a significant decrease in cell proliferation and an increase in micronuclei in a dose-dependent manner. On the other hand, lactate dehydrogenase activity, an indicator of membrane integrity/viability, was not affected by Auoxo6 and Au₂bipyC, while Au₂phen slightly modified its activity.

Na/K-ATPase as a target for anticancer drugs: studies with perillyl alcohol

Background

Na/K-ATPase (NKA) is inhibited by perillyl alcohol (POH), a monoterpene used in the treatment of tumors, including brain tumors. The NKA α₁ subunit is known to be superexpressed in glioblastoma cells (GBM). This isoform is embedded in caveolar structures and is probably responsible for the signaling properties of NKA during apoptosis. In this work, we showed that POH acts in signaling cascades associated with NKA that control cell proliferation and/or cellular death.

Methods

NKA activity was measured by the amount of non-radioactive Rb⁺ incorporation into cultured GBM cell lines (U87 and U251) and non-tumor cells (mouse astrocytes and VERO cells). Cell viability was measured by lactate dehydrogenase levels in the supernatants of POH-treated cells. Activated c-Jun N-terminal Kinase (JNK) and p38 were assessed by western blotting. Apoptosis was detected by flow cytometry and immunocytochemistry, and the release of interleukins was measured by ELISA.

Results

All four cell types tested showed a similar sensitivity for POH. Perillic acid (PA), the main metabolite of POH, did not show any effect on these cells. Though the cell viability decreased in a dose-dependent manner when cells were treated with POH, the maximum cytotoxic effect of PA obtained was 30% at 4 mM. 1.5 mM POH activated p38 in U87 cells and JNK in both U87 and U251 cells as well as mouse astrocytes. Dasatinib (an inhibitor of the Src kinase family) and methyl β-cyclodextrin (which promotes cholesterol depletion in cell membranes) reduced the POH-induced activation of JNK1/2 in U87 cells, indicating that the NKA-Src complex participates in this mechanism. Inhibition of JNK1/2 by the JNK inhibitor V reduced the apoptosis of GBM cells that resulted from POH administration, indicating the involvement of JNK1/2 in programmed cell death. 1.5 mM POH increased the production of interleukin IL-8 in the U251 cell supernatant, which may indicate a possible strategy by which cells avoid the cytotoxic effects of POH.

Conclusions

A signaling mechanism mediated by NKA may have an important role in the anti-tumor action of POH in GBM cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0374-5) contains supplementary material, which is available to authorized users.

A re-evaluation of the role of hCTR1, the human high-affinity copper transporter, in platinum-drug entry into human cells

Cisplatin (cDDP) is an anticancer drug used in a number of malignancies, including testicular, ovarian, cervical, bladder, lung, head, and neck cancers. Its use is limited by the development of resistance, often rationalized via effects on cellular uptake. It has been claimed that human copper transporter 1 (hCTR1), the human high-affinity copper transporter, is the major entry pathway for cDDP and related drugs via a mechanism that mimics copper. This is an unexpected property of hCTR1, a highly selective copper (I) transporter. We compared the uptake rates of copper with cDDP (and several analogs) into human embryonic kidney 293 cells overexpressing wild-type or mutant hCTR1, mouse embryonic fibroblasts that do or do not express CTR1, and human ovarian tumor cells that are sensitive or resistant to cDDP. We have also compared the effects of extracellular copper, which causes regulatory endocytosis of hCTR1, to those of cDDP. We confirm the correlation between higher hCTR1 levels and higher platinum drug uptake in tumor cells sensitive to the drug. However, we show that hCTR1 is not the major entry route of platinum drugs, and that the copper transporter is not internalized in response to extracellular drug. Our data suggest the major entry pathway for platinum drugs is not saturable at relevant concentrations and not protein-mediated. Clinical trials have been initiated that depend upon regulating membrane levels of hCTR1. If reduced drug uptake is a major factor in resistance, hCTR1 is unlikely to be a productive target in attempts to enhance efficacy, although the proteins involved in copper homeostasis may play a role.

Contribution of intracellular ATP to cisplatin resistance of tumor cells

Decreased cellular accumulation of cisplatin is a frequently observed mechanism of resistance to the drug. Beside passive diffusion, several cellular proteins using ATP hydrolysis as an energy source are assumed to be involved in cisplatin transport in and out of the cell. This investigation aimed at clarifying the contribution of intracellular ATP as an indicator of energy-dependent transport to cisplatin resistance using the A2780 human ovarian adenocarcinoma cell line and its cisplatin-resistant variant A2780cis. Depletion of intracellular ATP with oligomycin significantly decreased cellular platinum accumulation (measured by flameless atomic absorption spectrometry) in sensitive but not in resistant cells, and did not affect cisplatin efflux in both cell lines. Inhibition of Na(+),K(+)-ATPase with ouabain reduced platinum accumulation in A2780 cells but to a lesser extent compared with oligomycin. Western blot analysis revealed lower expression of Na(+),K(+)-ATPase α(1) subunit in resistant cells compared with sensitive counterparts. The basal intracellular ATP level (determined using a bioluminescence-based assay) was significantly higher in A2780cis cells than in A2780 cells. Our results highlight the importance of ATP-dependent transport, among other processes mediated by Na(+),K(+)-ATPase, for cisplatin influx in sensitive cells. Cellular platinum accumulation in resistant cells is reduced and less dependent on energy sources, which may partly result from Na(+),K(+)-ATPase downregulation. Our data suggest the involvement of other ATP-dependent processes beside those regulated by Na(+),K(+)-ATPase. Higher basal ATP level in cisplatin-resistant cells, which appears to be a consequence of enhanced mitochondrial ATP production, may represent a survival mechanism established during development of resistance.

Covalent binding of cisplatin impairs the function of Na(+)/K(+)-ATPase by binding to its cytoplasmic part

This study was aimed at verifying the hypothesis that acute kidney failure accompanying cisplatin administration in the cancer therapy could be due to cisplatin interaction with the cytoplasmic part of Na(+)/K(+)-ATPase. Our results demonstrated that cisplatin-binding caused inhibition of Na(+)/K(+)-ATPase, in contrast to other platinated chemotherapeutics such as carboplatin and oxaliplatin, which are known to be much less nephrotoxic. To acquire more detailed structural information, we performed a series of experiments with the isolated large cytoplasmic segment connecting transmembrane helices 4 and 5 (C45 loop) of Na(+)/K(+)-ATPase. Electrochemistry showed that cisplatin is bound to the cysteine residues of the C45 loop, mass spectrometry revealed a modification of the C45 peptide fragment GSHMASLEAVETLGSTSTICSDK, which contains the conserved phosphorylated residue Asp369. Hence, we hypothesize that binding of cisplatin to Cys367 can cause sterical obstruction during the phosphorylation or dephosphorylation step of the Na(+)/K(+)-ATPase catalytic cycle.

Mechanism of cisplatin resistance in human urothelial carcinoma cells

An isogenic pair of cisplatin-susceptible (NTUB1) and -resistant (NTUB1/P) human urothelial carcinoma cell lines was used to elucidate the mechanism of cisplatin resistance. The significantly lower intracellular platinum (IP) concentration, which resulted from the decreased cisplatin uptake, was found in NTUB1/P cells. The enhancement of IP concentration did not increase the susceptibility of NTUB1/P cells to cisplatin treatment. The reduction of IP concentration as well was unable to enhance the cisplatin-resistance in susceptible NTUB1 cells. This indicated that reduction of IP concentration was not the account for the development of cisplatin resistance here. Instead, the over expression of anti-apoptotic Bcl-2, anti-oxidative heme oxygenase-1 (HO-1) and cell cycle regulator p16INK4 seemed to be more important for the gaining of cisplatin in these human urothelial carcinoma cell.

Genome-wide gene expression analysis of chemoresistant pulmonary carcinoid cells

PURPOSE

Carcinoids are highly chemoresistant tumors associated with a dismal prognosis. This study involved a comparison of the genome-wide gene expression pattern of a chemoresistant and a chemosensitive pulmonary carcinoid cell line to reveal factors that contribute to the resistant phenotype.

MATERIALS AND METHODS

Gene expression of UMC-11 chemoresistant carcinoid cells as assessed by 32 K microarray was compared with H835 chemosensitive carcinoid cells, and the genes that were differentially expressed and expected to be related to chemoresistance were selected.

RESULTS

Drug-resistant UMC-11 cells exhibited increased expression of transcripts known to confer resistance to different cytostatics such as P-glycoprotein, multidrug resistance-associated proteins 2 and 3, effectors of the glutathione detoxification and xenobiotics degradation pathways, and ion transporters including Na⁺/K⁺-adenosine triphosphatase. In addition, enhanced transcription of several S100 proteins, capable of suppressing apoptosis, regulation of topoisomerase I (topo I) expression by antisense transcripts from TOPO1 pseudogenes, and alterations of the cytoskeleton seem to contribute to the multidrug-resistant phenotype. A multitude of epidermal growth factor (EGF)-related and neuropeptide growth factors, overexpression of proteases, and appearance of aerobic glycolytic metabolism complement the malignant phenotype of the UMC-11 cells.

CONCLUSION

The multidrug-resistant phenotype of the UMC-11 pulmonary carcinoid cell line seems to be mediated by classical efflux pumps, drug metabolization or conjugation systems, and, possibly, modulation of apoptotic cell death by S100 proteins and topo I expression by pseudogene transcripts. Autocrine or paracrine stimulation by a host of EGF-related and neuropeptide growth factors, as well as high metastatic potency indicated by increased expression of components of aerobic glycolysis and proteolytic enzymes, may furthermore account for the failure of therapeutic interventions.

The Na+/K+-ATPase is the Achilles heel of multi-drug-resistant cancer cells

We recently reported that over-expressed Na(+)/K(+)-ATPase alpha subunits are new important anti-cancer targets. Cardiotonic steroids are the natural ligands of Na(+)/K(+)-ATPase and thus potentially potent anti-cancer agents with a novel mechanism of action. We report here that the hemi-synthetic cardenolide 19-hydroxy-2''oxovoruscharin is impressively active in cancer cells expressing diverse forms of multi-drug resistance (MDR) either conferred by the over-expression of selected drug-transporter proteins or induced by a range of chemotherapeutic agents. Together with the inability of tumor cells to acquire resistance to 19-hydroxy-2''oxovoruscharin, our data suggest that this novel compound could be especially applicable to notoriously drug-resistant cancers.

Expression of Na,K-ATPase-beta(1) subunit increases uptake and sensitizes carcinoma cells to oxaliplatin

Purpose

The ovarian carcinoma subline A2780/C10B (C10B) is an oxaliplatin resistant clone derived from the human ovarian carcinoma cell line A2780. The C10B cells are characterized by mesenchymal phenotype, decreased platinum uptake and increased glutathione levels (Hector et al. in Cancer Lett 245:195–204, 2007; Varma et al. in Oncol Rep 14:925–932, 2005). Na,K-ATPase-β subunit (Na,K-β₁) functions as a cell–cell adhesion molecule in epithelial cells and is reduced in a variety of carcinoma cells that show mesenchymal phenotype. The purpose of this study is to evaluate the relationship between Na,K-β expression and sensitivity to oxaliplatin.

Methods

Cell lines used include A2780, C10B, C10B transfected with Na,K-β₁ (C10B-Na,K-β) and a canine kidney carcinoma cell line MSV-MDCK also transfected with Na,K-β₁ (MSV-MDCK-β subunit). Cytotoxicity studies were performed by sulforhodamine-blue assay. The Na,K-α₁ and Na,K-β₁ subunit localization and expression were by immunofluorescence microscopy and Western blot analysis. Platinum accumulation measurements were by atomic absorption spectrophotometry.

Results

C10B cells express highly reduced levels of Na,K-β₁ subunit. Exogenous expression of Na,K-β₁ increased platinum accumulation and sensitized C10B cells to oxaliplatin. The pharmacological inhibitor of Na,K-ATPase ouabain did not alter the oxaliplatin accumulation indicating that Na,K-β₁ sensitizes cells in a Na,K-ATPase enzyme activity independent manner. These findings were also confirmed in MSV-MDCK-β subunit cells.

Conclusions

This study for the first time reveals that reduced expression of the Na,K-β₁ protein is associated with oxaliplatin resistance in cancer cells and demonstrates a novel role for this protein in sensitizing the cells to oxaliplatin. This study suggests a potentially important role for Na,K-β₁ in both prognosis and therapy of oxaliplatin resistant malignancies.