Therapy-resistant Cancer Cells Research Articles

Salinomycin induces apoptosis in cisplatin-resistant colorectal cancer cells by accumulation of reactive oxygen species

Postoperative chemotherapy for Colorectal cancer (CRC) patients is not all effective and the main reason might lie in cancer stem cells (CSCs). Emerging studies showed that CSCs overexpress some drug-resistance related proteins, which efficiently transport the chemotherapeutics out of cancer cells. Salinomycin, which considered as a novel and an effective anticancer drug, is found to have the ability to kill both CSCs and therapy-resistant cancer cells. To explore the potential mechanisms that salinomycin could specifically target on therapy-resistant cancer cells in colorectal cancers, we firstly obtained cisplatin-resistant (Cisp-resistant) SW620 cells by repeated exposure to 5μmol/l of cisplatin from an original colorectal cancer cell line. These Cisp-resistant SW620 cells, which maintained a relative quiescent state (G0/G1 arrest) and displayed stem-like signatures (up-regulations of Sox2, Oct4, Nanog, Klf4, Hes1, CD24, CD26, CD44, CD133, CD166, Lgr5, ALDH1A1 and ALDH1A3 mRNA expressions) (p<0.05), were sensitive to salinomycin (p<0.05). Salinomycin did not show the influence on the cell cycle of Cisp-resistant SW620 cells (p>0.05), but could induce cell death process (p<0.05), with increased levels of LDH release and MDA contents as well as down-regulations of SOD and GSH-PX activities (p<0.05). Our data also showed that the pro-apoptotic genes (Caspase-3, Caspase-8, Caspase-9 and Bax) were up-regulated and the anti-apoptotic gene Bcl-2 were down-regulated in Cisp-resistant SW620 cells (p<0.05). Accumulated reactive oxygen species and dysregulation of some apoptosis-related genes might ultimately lead to apoptosis in Cisp-resistant SW620 cells. These findings will provide new clues for novel and selective chemotherapy on cisplatin-resistant colorectal cancer cells.

Par(−4)oxysm in Breast Cancer

Women suffering from breast cancer often succumb to incurable recurrent disease resulting from therapy-resistant cancer cells. In this issue of Cancer Cell, Alvarez and colleagues identify downregulation of the tumor suppressor Par-4 as the key determinant in apoptosis evasion, which leads to tumor recurrence in breast cancer.

Genome-wide reprogramming of the chromatin landscape underlies endocrine therapy resistance in breast cancer

The estrogen receptor (ER)α drives growth in two-thirds of all breast cancers. Several targeted therapies, collectively termed endocrine therapy, impinge on estrogen-induced ERα activation to block tumor growth. However, half of ERα-positive breast cancers are tolerant or acquire resistance to endocrine therapy. We demonstrate that genome-wide reprogramming of the chromatin landscape, defined by epigenomic maps for regulatory elements or transcriptional activation and chromatin openness, underlies resistance to endocrine therapy. This annotation reveals endocrine therapy-response specific regulatory networks where NOTCH pathway is overactivated in resistant breast cancer cells, whereas classical ERα signaling is epigenetically disengaged. Blocking NOTCH signaling abrogates growth of resistant breast cancer cells. Its activation state in primary breast tumors is a prognostic factor of resistance in endocrine treated patients. Overall, our work demonstrates that chromatin landscape reprogramming underlies changes in regulatory networks driving endocrine therapy resistance in breast cancer.

Novel Interaction between the Co-chaperone Cdc37 and Rho GTPase Exchange Factor Vav3 Promotes Androgen Receptor Activity and Prostate Cancer Growth*

Elevated androgen receptor (AR) activity in castration-resistant prostate cancer may occur through increased levels of AR co-activator proteins. Vav3, a guanine nucleotide exchange factor, is up-regulated following progression to castration resistance in preclinical models and is overexpressed in a significant number of human prostate cancers. Vav3 is a novel co-activator of the AR. We sought to identify Vav3 binding partners in an effort to understand the molecular mechanisms underlying Vav3 enhancement of AR activity and to identify new therapeutic targets. The cell division cycle 37 homolog (Cdc37), a protein kinase-specific co-chaperone for Hsp90, was identified as a Vav3 interacting protein by yeast two-hybrid screening. Vav3-Cdc37 interaction was confirmed by GST pulldown and, for native proteins, by co-immunoprecipitation experiments in prostate cancer cells. Cdc37 potentiated Vav3 co-activation of AR transcriptional activity and Vav3 enhancement of AR N-terminal-C-terminal interaction, which is essential for optimal receptor transcriptional activity. Cdc37 increased prostate cancer cell proliferation selectively in Vav3-expressing cells. Cdc37 did not affect Vav3 nucleotide exchange activity, Vav3 protein levels, or subcellular localization. Disruption of Vav3-Cdc37 interaction inhibited Vav3 enhancement of AR transcriptional activity and AR N-C interaction. Diminished Vav3-Cdc37 interaction also caused decreased prostate cancer cell proliferation selectively in Vav3-expressing cells. Taken together, we identified a novel Vav3 interacting protein that enhances Vav3 co-activation of AR and prostate cancer cell proliferation. Vav3-Cdc37 interaction may provide a new therapeutic target in prostate cancer.

MicroRNAs in breast cancer initiation and progression

The emerging role of microRNAs (miRNAs) in the epigenetic regulation of many cellular processes has become recognized in both basic research and translational medicine as an important way that gene expression can be fine-tuned. Breast cancer is the most frequent cancer in women, with about one million new cases diagnosed each year worldwide. Starting with the early work of miRNA profiling, more effort has now been put on functions of miRNAs in normal mammary stem cells, breast cancer initiating cells and metastatic cells, and therapy-resistant cancer cells. Future translational studies may focus on identifying miRNA signatures as cancer biomarkers and developing miRNA-based targeted therapeutics.

MicroRNA regulatory networks and human disease

MicroRNA regulatory networks and human disease

Eradication of therapy-resistant cancer cells in gastrointestinal organs

Early stages of cancer are curable by surgical removal of the primary lesions, however, more advanced cases are often refractory to therapeutic approaches and are more commonly life-threatening, primarily due to cancer metastasis in gastrointestinal cancers. Such biological events are collectively characterized as tumor heterogeneity, the cause of which is the existence of cancer stem cells. To improve cancer survival, therapy-resistant cancer cells should be eradicated. To this end, recent rapid progress in medical science, such as innovative medical technologies including cancer reprogramming, RNA pharmacology and drug delivery systems, all of which effectively target cancer stem cells, has facilitated this objective.

Targeting the PELP1-KDM1 axis as a potential therapeutic strategy for breast cancer

IntroductionThe estrogen receptor (ER) co-regulator proline glutamic acid and leucine-rich protein 1 (PELP1) is a proto-oncogene that modulates epigenetic changes on ER target gene promoters via interactions with lysine-specific histone demethylase 1 (KDM1). In this study, we assessed the therapeutic potential of targeting the PELP1-KDM1 axis in vivo using liposomal (1,2-dioleoyl-sn-glycero-3-phosphatidylcholine; DOPC) siRNA to downregulate PELP1 expression and KDM1 inhibitors, pargyline and N-((1S)-3-(3-(trans-2-aminocyclopropyl)phenoxy)-1-(benzylcarbamoyl)propyl)benzamide using preclinical models.MethodsPreclinical xenograft models were used to test the efficacy of drugs in vivo. Ki-67 and terminal deoxynucleotidyl transferase dUTP nick end-labeling immunohistochemical analysis of epigenetic markers was performed on tumor tissues. The in vitro effect of PELP1-KDM axis blockers was tested using proliferation, reporter gene, chromatin immunoprecipitation and real-time RT-PCR assays. The efficacy of the KDM1 targeting drugs alone or in combination with letrozole and tamoxifen was tested using therapy-resistant model cells.ResultsTreatment of ER-positive xenograft-based breast tumors with PELP1-siRNA-DOPC or pargyline reduced tumor volume by 58.6% and 62%, respectively. In a postmenopausal model, in which tumor growth is stimulated solely by local estrogen synthesis, daily pargyline treatment reduced tumor volume by 78%. Immunohistochemical analysis of excised tumors revealed a combined decrease in cellular proliferation, induction of apoptosis and upregulation of inhibitory epigenetic modifications. Pharmacological inhibition of KDM1 in vitro increased inhibitory histone mark dimethylation of histone H3 at lysine 9 (H3K9me2) and decreased histone activation mark acetylation of H3K9 (H3K9Ac) on ER target gene promoters. Combining KDM1 targeting drugs with current endocrine therapies substantially impeded growth and restored sensitivity of therapy-resistant breast cancer cells to treatment.ConclusionOur results suggest inhibition of PELP1-KDM1-mediated histone modifications as a potential therapeutic strategy for blocking breast cancer progression and therapy resistance.

Sa1802 SPARC's Interaction With GRP78 Promotes Endoplasmic Reticulum (ER) Stress-Mediated Apoptosis to Improve Chemosensitivity in Therapy-Resistant Colorectal Cancer Cells

Sa1802 SPARC's Interaction With GRP78 Promotes Endoplasmic Reticulum (ER) Stress-Mediated Apoptosis to Improve Chemosensitivity in Therapy-Resistant Colorectal Cancer Cells

Abstract LB-246: Epithelial-mesenchymal transition (EMT) does not necessarily decrease the sensitivity of cancer cells to chemotherapeutic agents

Abstract Epithelial to mesenchymal transition (EMT) has been recently associated with metastatic competence and therapy resistance of cancer cells and the need for development of EMT-targeted therapies has been emphasized. In this report we address the differential responses of breast cancer cell lines with epithelial and mesenchymal phenotypes to anticancer agents using pharmacoinformatics and experimental approaches. First, we identified breast cancer cell lines with epithelial-like and mesenchymal-like phenotypes among the National Cancer Institute (NCI) panel of 60 cell lines and analyzed their differential responses to 10,081 anticancer agents. Second, we evaluated chemotherapeutic response of a mesenchymal-like isogenic breast cancer cell line (MCF-7-Snail) stably transfected to express the EMT-inducing Snail transcription factor and its epithelial-like precursor cell line transfected with the control plasmid (MCF-7-neo). The results of both approaches are inconsistent with the claim that mesenchymal-like cancer cells are generally more resistant to anticancer agents. We found that most of the 10,081 agents examined did not display significantly different potencies between epithelial-like and mesenchymal-like cells. Of the 10,081 anti-cancer agents examined, only 78 displayed consistent differences in effect between epithelial-like and mesenchymal-like cells and all of these agents displayed a more potent effect against mesenchymal-like cell lines. MCF-7-Snail cells were found to be more sensitive to the cytotoxic effects of doxorubicin, 5-FU and methotrexate, while MCF-7-neo cells were more sensitive to gemcitabine and docetaxel and both of these isogenic cell lines were equally responsive to mitomycin C and vincristine. The relatively lower sensitivity of MCF-Snail cells to docetaxel and gemcitabine can be explained by their overexpression of TUBB4 and RRM1, respectively, as demonstrated by gene expression analysis (U133 Plus 2.0 Affymetrix microarrays). In contrast, the higher sensitivity of MCF-7-Snail cells to 5-FU may be due to the down-regulation of the DPYD gene in these cells. Compared to isogenic epithelial cells, MCF-7-Snail cells display down-regulation of the anti-apoptotic genes XIAP, BCL2L1 and NAIP. Collectively, our results indicate that EMT per se does not generally result in a greater resistance of cancer cells to chemotherapeutic agents, but it may, in some instances, result in increased sensitivity of cancer cells to specific chemotherapeutic agents. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-246. doi:1538-7445.AM2012-LB-246

Abstract C65: Drug-tolerant cancer cells show reduced tumor-initiating capacity: Depletion of CD44+ cells and evidence for epigenetic mechanisms

Abstract Cancer stem cells (CSCs) possess high tumor-initiating capacity and have been reported to be resistant to therapeutics. Vice versa, therapy-resistant cancer cells seem to manifest CSC phenotypes and properties. It has been generally assumed that drug-resistant cancer cells may all be CSCs although the generality of this assumption is unknown. Here, we chronically treated Du145 prostate cancer cells with etoposide, paclitaxel and some experimental drugs (i.e., staurosporine and 2 paclitaxel analogs), which led to populations of drug-tolerant cells (DTCs). Surprisingly, these DTCs, when implanted either subcutaneously or orthotopically into NOD/SCID mice, exhibited much reduced tumorigenicity or were even nontumorigenic. Drug-tolerant DLD1 colon cancer cells selected by a similar chronic selection protocol also displayed reduced tumorigenicity whereas drug-tolerant UC14 bladder cancer cells demonstrated either increased or decreased tumor-regenerating capacity. Drug-tolerant Du145 cells demonstrated low proliferative and clonogenic potential and were virtually devoid of CD44+ cells. Prospective knockdown of CD44 in Du145 cells inhibited cell proliferation and tumor regeneration whereas restoration of CD44 expression in drug-tolerant Du145 cells increased cell proliferation and partially increased tumorigenicity. Interestingly, drug-tolerant Du145 cells showed both increases and decreases in many ‘stemness’ genes. Finally, evidence was provided that chronic drug exposure generated DTCs via epigenetic mechanisms involving molecules such as CD44 and KDM5A. Our results thus reveal that 1) not all DTCs are necessarily CSCs; 2) conventional chemotherapeutic drugs such as taxol and etoposide may directly target CD44+ tumor-initiating cells; and 3) DTCs generated via chronic drug selection involve epigenetic mechanisms. Citation Format: Xin Chen, Izabela Fokt, Stanislaw Skora, Waldemar Priebe, Yongyi Bi, Dean G. Tang, Hong Yan, Qiuping Zhang, Jichao Qin, Hangwen Li, Can Liu, Tammy Davis, Luis D. Coletta, Jim Klostergaard. Drug-tolerant cancer cells show reduced tumor-initiating capacity: Depletion of CD44+ cells and evidence for epigenetic mechanisms [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr C65.

237 The multikinase inhibitor sorafenib suppresses AR expression and signaling and induces apoptosis of castration therapy-resistant prostate cancer cells

237 The multikinase inhibitor sorafenib suppresses AR expression and signaling and induces apoptosis of castration therapy-resistant prostate cancer cells

Salinomycin as a Drug for Targeting Human Cancer Stem Cells

Cancer stem cells (CSCs) represent a subpopulation of tumor cells that possess self-renewal and tumor initiation capacity and the ability to give rise to the heterogenous lineages of malignant cells that comprise a tumor. CSCs possess multiple intrinsic mechanisms of resistance to chemotherapeutic drugs, novel tumor-targeted drugs, and radiation therapy, allowing them to survive standard cancer therapies and to initiate tumor recurrence and metastasis. Various molecular complexes and pathways that confer resistance and survival of CSCs, including expression of ATP-binding cassette (ABC) drug transporters, activation of the Wnt/β-catenin, Hedgehog, Notch and PI3K/Akt/mTOR signaling pathways, and acquisition of epithelial-mesenchymal transition (EMT), have been identified recently. Salinomycin, a polyether ionophore antibiotic isolated from Streptomyces albus, has been shown to kill CSCs in different types of human cancers, most likely by interfering with ABC drug transporters, the Wnt/β-catenin signaling pathway, and other CSC pathways. Promising results from preclinical trials in human xenograft mice and a few clinical pilote studies reveal that salinomycin is able to effectively eliminate CSCs and to induce partial clinical regression of heavily pretreated and therapy-resistant cancers. The ability of salinomycin to kill both CSCs and therapy-resistant cancer cells may define the compound as a novel and an effective anticancer drug.

Drug-Tolerant Cancer Cells Show Reduced Tumor-Initiating Capacity: Depletion of CD44+ Cells and Evidence for Epigenetic Mechanisms

Cancer stem cells (CSCs) possess high tumor-initiating capacity and have been reported to be resistant to therapeutics. Vice versa, therapy-resistant cancer cells seem to manifest CSC phenotypes and properties. It has been generally assumed that drug-resistant cancer cells may all be CSCs although the generality of this assumption is unknown. Here, we chronically treated Du145 prostate cancer cells with etoposide, paclitaxel and some experimental drugs (i.e., staurosporine and 2 paclitaxel analogs), which led to populations of drug-tolerant cells (DTCs). Surprisingly, these DTCs, when implanted either subcutaneously or orthotopically into NOD/SCID mice, exhibited much reduced tumorigenicity or were even non-tumorigenic. Drug-tolerant DLD1 colon cancer cells selected by a similar chronic selection protocol also displayed reduced tumorigenicity whereas drug-tolerant UC14 bladder cancer cells demonstrated either increased or decreased tumor-regenerating capacity. Drug-tolerant Du145 cells demonstrated low proliferative and clonogenic potential and were virtually devoid of CD44+ cells. Prospective knockdown of CD44 in Du145 cells inhibited cell proliferation and tumor regeneration, whereas restoration of CD44 expression in drug-tolerant Du145 cells increased cell proliferation and partially increased tumorigenicity. Interestingly, drug-tolerant Du145 cells showed both increases and decreases in many “stemness” genes. Finally, evidence was provided that chronic drug exposure generated DTCs via epigenetic mechanisms involving molecules such as CD44 and KDM5A. Our results thus reveal that 1) not all DTCs are necessarily CSCs; 2) conventional chemotherapeutic drugs such as taxol and etoposide may directly target CD44+ tumor-initiating cells; and 3) DTCs generated via chronic drug selection involve epigenetic mechanisms.

Modulation of androgen receptor signaling in hormonal therapy-resistant prostate cancer cell lines.

BackgroundProstate epithelial cells depend on androgens for survival and function. In (early) prostate cancer (PCa) androgens also regulate tumor growth, which is exploited by hormonal therapies in metastatic disease. The aim of the present study was to characterize the androgen receptor (AR) response in hormonal therapy-resistant PC346 cells and identify potential disease markers.Methodology/Principal FindingsHuman 19K oligoarrays were used to establish the androgen-regulated expression profile of androgen-responsive PC346C cells and its derivative therapy-resistant sublines: PC346DCC (vestigial AR levels), PC346Flu1 (AR overexpression) and PC346Flu2 (T877A AR mutation). In total, 107 transcripts were differentially-expressed in PC346C and derivatives after R1881 or hydroxyflutamide stimulations. The AR-regulated expression profiles reflected the AR modifications of respective therapy-resistant sublines: AR overexpression resulted in stronger and broader transcriptional response to R1881 stimulation, AR down-regulation correlated with deficient response of AR-target genes and the T877A mutation resulted in transcriptional response to both R1881 and hydroxyflutamide. This AR-target signature was linked to multiple publicly available cell line and tumor derived PCa databases, revealing that distinct functional clusters were differentially modulated during PCa progression. Differentiation and secretory functions were up-regulated in primary PCa but repressed in metastasis, whereas proliferation, cytoskeletal remodeling and adhesion were overexpressed in metastasis. Finally, the androgen-regulated genes ENDOD1, MCCC2 and ACSL3 were selected as potential disease markers for RT-PCR quantification in a distinct set of human prostate specimens. ENDOD1 and ACSL3 showed down-regulation in high-grade and metastatic PCa, while MCCC2 was overexpressed in low-grade PCa.Conclusions/SignificanceAR modifications altered the transcriptional response to (anti)androgens in therapy-resistant cells. Furthermore, selective down-regulation of genes involved in differentiation and up-regulation of genes promoting proliferation and invasion suggest a disturbed balance between the growth and differentiation functions of the AR pathway during PCa progression. These findings may have implications in the current treatment and development of novel therapeutical approaches for metastatic PCa.

A Novel Prosurvival Model for Cancer Under Environmental Challenge: The “Heart-Felt” Message for Therapeutic Intervention

In the present review I propose a novel model system to analyze and to aid prediction of suitable targeted treatments aimed at therapy-resistant cancer cells. The concept of cancer cell prosurvival reaction to adverse external tumor microenvironment is explored in the context of the reaction of myocardium to unfavorable physiologic conditions. Many of the protective and indeed nonprotective (tumor suppressor) reactive mechanisms in both cancer and heart tissue challenged with an adverse environment follow similar and predictable patterns. Based on these observations, a model is constructed that may aid prediction of future therapies aimed to target cancer--particularly chemotherapy/radiotherapy resistance and dormant disease. As another feature of the model, ways to better forecast future therapies aimed at augmenting cardioprotective paths is made possible through understanding of pathways used to sustain cancer cells under external challenges.

Roscovitine confers tumor suppressive effect on therapy-resistant breast tumor cells

IntroductionCurrent clinical strategies for treating hormonal breast cancer involve the use of anti-estrogens that block estrogen receptor (ER)α functions and aromatase inhibitors that decrease local and systemic estrogen production. Both of these strategies improve outcomes for ERα-positive breast cancer patients, however, development of therapy resistance remains a major clinical problem. Divergent molecular pathways have been described for this resistant phenotype and interestingly, the majority of downstream events in these resistance pathways converge upon the modulation of cell cycle regulatory proteins including aberrant activation of cyclin dependent kinase 2 (CDK2). In this study, we examined whether the CDK inhibitor roscovitine confers a tumor suppressive effect on therapy-resistant breast epithelial cells.MethodsUsing various in vitro and in vivo assays, we tested the effect of roscovitine on three hormonal therapy-resistant model cells: (a) MCF-7-TamR (acquired tamoxifen resistance model); (b) MCF-7-LTLTca (acquired letrozole resistance model); and (c) MCF-7-HER2 that exhibit tamoxifen resistance (ER-growth factor signaling cross talk model).ResultsHormonal therapy-resistant cells exhibited aberrant activation of the CDK2 pathway. Roscovitine at a dose of 20 μM significantly inhibited the cell proliferation rate and foci formation potential of all three therapy-resistant cells. The drug treatment substantially increased the proportion of cells in G2/M cell cycle phase with decreased CDK2 activity and promoted low cyclin D1 levels. Interestingly, roscovitine also preferentially down regulated the ERα isoform and ER-coregulators including AIB1 and PELP1. Results from xenograft studies further showed that roscovitine can attenuate growth of therapy-resistant tumors in vivo.ConclusionsRoscovitine can reduce cell proliferation and survival of hormone therapy-resistant breast cancer cells. Our results support the emerging concept that inhibition of CDK2 activity has the potential to abrogate growth of hormonal therapy-resistant cells.

Abstract LB-437: ICA-1: A novel PKC-i inhibitor inhibits the proliferation of prostate cancer cells

Abstract Prostate cancers are highly lethal tumors and besides skin cancer, prostate cancer is the most common type of cancer among men in the United States. Approximately one third of men diagnosed with cancer each year will have prostate cancer. Certain prostate cancers are highly lethal tumors due to the emergence of therapy-resistant prostate cancer cells. PKC-iota (PKC-ι) is an oncogene and an atypical protein kinase C isoform that confers resistance to drug-induced apoptosis in cancer cells (J. Biol. Chem. 272; 44: 27521–27524). PKC is of special interest since it is overexpressed in prostate cancers (Proc Natl Acad Sci U S A. 106:16369–16374). The objective of the study was to investigate the effects of inhibiting PKC-ι on the proliferation of prostate cancer cells in-vitro. The methodology involved treating androgen sensitive LnCap cells and androgen independent Du-145 with the novel PKC-ι inhibitor [1H-imidazole-4-carboxamide, 5-amino-1-[2,3-dihydroxy-4-[(phosphonooxy) methyl]cyclopentyl]-[1R-(1α, 2β, 3 β, 4 α)] (ICA-1) that targets a unique sequence (amino acid residues 469–475) in the catalytic domain of PKC-ι. Cell viability and number was quantified 24–72 hours following addition of either vehicle control or ICA-1 by Trypan blue exclusion. Additional ICA-1 was not added to the cells following the initial treatment. Results showed that at 24 hours post treatment, ICA-1 decreased the proliferation of LnCap cells by 46% (10 μM) and 83% (20 μM). ICA-1 reduced the proliferation of Du-145 cells at 24 hours by 43% (10 μM) and 51% (20 μM). The overexpression of PKC-ι in prostate cancer and the anti-proliferative effects of ICA-1 may translate into using PKC-i detection as a biomarker to identify patients that may benefit from anti-PKC-ι therapy with ICA-1 for personalized medicine. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-437. doi:10.1158/1538-7445.AM2011-LB-437

Dysregulated expression of Fau and MELK is associated with poor prognosis in breast cancer

IntroductionProgrammed cell death through apoptosis plays an essential role in the hormone-regulated physiological turnover of mammary tissue. Failure of this active gene-dependent process is central both to the development of breast cancer and to the appearance of the therapy-resistant cancer cells that produce clinical relapse. Functional expression cloning in two independent laboratories has identified Finkel–Biskis–Reilly murine sarcoma virus-associated ubiquitously expressed gene (Fau) as a novel apoptosis regulator and candidate tumour suppressor. Fau modifies apoptosis-controller Bcl-G, which is also a key target for candidate oncoprotein maternal embryonic leucine zipper kinase (MELK).MethodsWe have used RNA interference to downregulate Fau and Bcl-G expression, both simultaneously and independently, in breast cancer cells in vitro to determine the importance of their roles in apoptosis. Expression of Fau, Bcl-G and MELK was measured by quantitative RT-PCR in breast cancer tissue and in matched breast epithelial tissue from the same patients. Expression data of these genes obtained using microarrays from a separate group of patients were related to patient survival in Kaplan–Meier analyses.ResultssiRNA-mediated downregulation of either Fau or Bcl-G expression inhibited apoptosis, and the inhibition produced by combining the two siRNAs was consistent with control of Bcl-G by Fau. Fau expression is significantly reduced in breast cancer tissue and this reduction is associated with poor patient survival, as predicted for a candidate breast cancer tumour suppressor. In addition, MELK expression is increased in breast cancer tissue and this increase is also associated with poor patient survival, as predicted for a candidate oncogene. Bcl-G expression is reduced in breast cancer tissue but decreased Bcl-G expression showed no correlation with survival, indicating that the most important factors controlling Bcl-G activity are post-translational modification (by Fau and MELK) rather than the rate of transcription of Bcl-G itself.ConclusionsThe combination of in vitro functional studies with the analysis of gene expression in clinical breast cancer samples indicates that three functionally interconnected genes, Fau, Bcl-G and MELK, are crucially important in breast cancer and identifies them as attractive targets for improvements in breast cancer risk prediction, prognosis and therapy.

DNA Methylation: Its Role in Cancer Development and Therapy

Ferroptosis is a newly defined form of cell death induced by iron-dependent accumulation of lethal lipid peroxidation. Ferroptosis represent a therapeutic strategy to suppress therapy-resistant cancer cells with more property of epithelial-mesenchymal transition (EMT). However, epigenetic reprogramming of EMT has been rarely studied in the context of ferroptosis susceptibility. Therefore, we examined the therapeutic potentiality of EMT epigenetic reprogramming in promoting ferroptosis in head and neck cancer (HNC) cells. The effects of ferroptosis inducers and EMT inhibition or induction were tested in HNC cell lines and mouse tumor xenograft models. These effects were analyzed concerning cell viability and death, lipid reactive oxygen species and iron production, labile iron pool, glutathione contents, NAD/NADH levels, and mRNA/protein expression. Cell density and the expression levels of E-cadherin, vimentin, and ZEB1 were associated with the different susceptibility to ferroptosis inducers. CDH1 silencing or ZEB1 overexpression increased the susceptibility to ferroptosis, whereas CDH overexpression or ZEB1 silencing decreased the susceptibility, in vitro and in vivo. Histone deacetylase SIRT1 gene silencing or pharmacological inhibition by EX-527 suppressed EMT and consequently decreased ferroptosis, whereas SIRT inducers, resveratrol and SRT1720, increased ferroptosis. MiR-200 family inhibitors induced EMT and increased ferroptosis susceptibility. In HNC cells with low expression of E-cadherin, the treatment of 5-azacitidine diminished the hypermethylation of CDH1, resulting in increased E-cadherin expression and decreased ferroptosis susceptibility. Our data suggest that epigenetic reprogramming of EMT contributes to promoting ferroptosis in HNC cells.