Cooperative pro-tumorigenic adaptation to oncogenic RAS through epithelial-to-mesenchymal plasticity

In breast cancers, aberrant activation of the RAS/MAPK pathway is strongly associated with mesenchymal features and stemness traits, suggesting an interplay between this mitogenic signaling pathway and epithelial-to-mesenchymal plasticity (EMP). By using inducible models of human mammary epithelial cells, we demonstrate herein that the oncogenic activation of RAS promotes ZEB1-dependent EMP, which is necessary for malignant transformation. Notably, EMP is triggered by the secretion of pro-inflammatory cytokines from neighboring RAS-activated senescent cells, with a prominent role for IL-6 and IL-1α. Our data contrast with the common view of cellular senescence as a tumor-suppressive mechanism and EMP as a process promoting late stages of tumor progression in response to signals from the tumor microenvironment. We highlighted here a pro-tumorigenic cooperation of RAS-activated mammary epithelial cells, which leverages on oncogene-induced senescence and EMP to trigger cellular reprogramming and malignant transformation.

Spatial Transcriptomics Reveal Pitfalls and Opportunities for the Detection of Rare High-Plasticity Breast Cancer Subtypes

Breast cancer is one of the most prominent types of cancers, in which therapeutic resistance is a major clinical concern. Specific subtypes, such as claudin-low and metaplastic breast carcinoma (MpBC), have been associated with high nongenetic plasticity, which can facilitate resistance. The similarities and differences between these orthogonal subtypes, identified by molecular and histopathological analyses, respectively, remain insufficiently characterized. Furthermore, adequate methods to identify high-plasticity tumors to better anticipate resistance are lacking. Here, we analyzed 11 triple-negative breast tumors, including 3 claudin-low and 4 MpBC, via high-resolution spatial transcriptomics. We combined pathological annotations and deconvolution approaches to precisely identify tumor spots, on which we performed signature enrichment, differential expression, and copy number analyses. We used The Cancer Genome Atlas and Cancer Cell Line Encyclopedia public databases for external validation of expression markers. By focusing our spatial transcriptomic analyses on tumor cells in MpBC samples, we bypassed the negative impact of stromal contamination and identified specific markers that are neither expressed in other breast cancer subtypes nor expressed in stromal cells. Three markers (BMPER, POPDC3, and SH3RF3) were validated in external expression databases encompassing bulk tumor material and stroma-free cell lines. We unveiled that existing bulk expression signatures of high-plasticity breast cancers are relevant in mesenchymal transdifferentiated compartments but can be hindered by abundant stromal cells in tumor samples, negatively impacting their clinical applicability. Spatial transcriptomic analyses constitute powerful tools to identify specific expression markers and could thus enhance diagnosis and clinical care of rare high-plasticity breast cancers.

Dissecting the Origin of Heterogeneity in Uterine and Ovarian Carcinosarcomas

Gynecologic carcinosarcomas (CS) are biphasic neoplasms composed of carcinomatous (C) and sarcomatous (S) malignant components. Because of their rarity and histologic complexity, genetic and functional studies on CS are scarce and the mechanisms of initiation and development remain largely unknown. Whole-genome analysis of the C and S components reveals shared genomic alterations, thus emphasizing the clonal evolution of CS. Reconstructions of the evolutionary history of each tumor further reveal that C and S samples are composed of both ancestral cell populations and component-specific subclones, supporting a common origin followed by distinct evolutionary trajectories. However, while we do not find any recurrent genomic features associated with phenotypic divergence, transcriptomic and methylome analyses identify a common mechanism across the cohort, the epithelial-to-mesenchymal transition (EMT), suggesting a role for nongenetic factors in inflicting changes to cellular fate. Altogether, these data accredit the hypothesis that CS tumors are driven by both clonal evolution and transcriptomic reprogramming, essential for susceptibility to transdifferentiation upon encountering environmental cues, thus linking CS heterogeneity to genetic, transcriptomic, and epigenetic influences.

Significance

We have provided a detailed characterization of the genomic landscape of CS and identified EMT as a common mechanism associated with phenotypic divergence, linking CS heterogeneity to genetic, transcriptomic, and epigenetic influences.

Abstract 3595: Epigenetic driven IL32 expression contributes to a JNK related cell stress response in breast cancer stem cells to promote cellular invasion

Metastatic potential in basal-like breast cancers typically correspond with increased enrichment of EpCAM-/CD49f- cancer stem cells (CSC). With this premise in mind, it is important to better understand the mechanistic driver of these cell populations and their distinctive potential to interact with the tumor microenvironment (TME) for cancer promotion. Previous work from our lab has compared the 450K DNA methylation profile of EpCAM-/CD49f- poor breast cancer cell lines to that of EpCAM-/CD49f- enriched breast cancer cell lines and found the IL32 promoter to be hypomethylated in EpCAM-/CD49f- enriched cell lines, a result which corresponded basal-like patient samples in TCGA. By identifying IL32 being differentially regulated in CSC-enriched cell lines, we further sought to characterize IL32’s role in breast cancer aggressiveness. We first were able to identify several overarching mechanisms altered in siIL32 treated SUM15PT cells by RNAseq differential expression analysis (FDR p-value <0.01). Most notable from our RNAseq results was the significant enrichment of upregulated pathways involved in extracellular matrix (ECM) organization as well as significant enrichment of downregulated pathways involved in cellular and replicative stress responses. Particular examples of transcripts differentially expressed between control and siIL32-treated SUM159PT cells included COL6A1, ITGB3, and CD24 that were upregulated as well as NQO1, HMOX1, and CXCL2/CXCL3 that were downregulated. Furthermore, IL32 suppression decreased SUM159PT invasion in both an ECM-matrix cell invasion assay and a chick CAM xenograft/angiogenesis model. From our RNAseq results, we then performed a multi-pathway protein phosphorylation array to determine whether any key signaling events were affected by siIL32 knockdown in SUM159PT cells. Based on this approach, we were able observe a significant decrease in phosphorylated JNK and phosphorylated NFKB in siL32-treated cells when compared to control, both of which are well-established events that can coordinate both cell stress responses and cellular invasion. Collectively, our results reflect the notion that differential IL32 expression by promoter hypomethylation in breast CSCs plays a role to mitigating intracellular stress and subsequently allowing for breast cancer cell invasion and metastasis.

Citation Format: Megan A. Wilson, Elayne M. Benson, Emma Gray, Paige Cairns, Maria Ouzounova, Hasan Korkaya, Austin Y. Shull. Epigenetic driven IL32 expression contributes to a JNK related cell stress response in breast cancer stem cells to promote cellular invasion. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3595.

Abstract 2223: Understanding the pro- and anti-tumorigenic microenvironments in syngeneic mice

Despite the advances in early diagnostics and therapeutics, women with metastatic breast cancer have limited treatment options. Women with TNBC, who constitute 15-20% of breast cancer patients, are often diagnosed with aggressive/metastatic disease. Advanced studies implicated immunosuppressive tumor microenvironment (TME) in aggressive/metastatic properties of TNBC subtype. Alternatively activated immature myeloid cells including tumor-associated macrophages (TAM), tumor-associated neutrophils (TAN), tumor-associated dendritic cells (TADC) and myeloid derived suppressor cells (MDSC) constitute a major component of TME. However, anti-tumorigenic microenvironment is also reported and that may have clinical relevance in early TNBC patients. Therefore, our hypothesis is that myeloid cells polarize to become immunosuppressive and infiltrate tumors and pre-metastatic niches in patients with advanced disease, while patients with early TNBCs may elicit anti-tumor immune response eliminating disseminated tumor cells (DTC). The utilization of syngeneic immunocompetent mouse models has contributed to our current understanding of immunosuppressive or immunomodulatory TME. Using these models, we have demonstrated that tumor dissemination and growth at metastatic sites is facilitated by MDSC’s. Emerging technologies; single cell RNA sequencing (scRNAseq), mass cytometry (CyTOF) or cellular indexing of transcriptomes and epitopes sequencing (CITE-Seq) has been powerful platforms for detailed characterization of tumors and TME compartments. Our bulk gene expression data of the myeloid cell populations of tumor microenvironment, lung, spleen and BM from 4T1 tumor-bearing mice showed distinct MDSC gene signatures. When applied to publicly available scRNAseq data, lung gMDSCs from 4T1 metastatic tumor model appeared to show different trajectory of polarization than the tumor gMDSCs. Consistent with previous findings by Hedrick Lab, lung gMDSCs from 4T1 mice also express higher levels of NeP markers compared to BM and tumor gMDSCs as well as lung gMDSCs from EMT6 mice. However, analyses of immune cells from EMT6 tumor bearing mice exhibited an anti-tumor immune signature which is consistent with the clearance of the DTCs following complete resection of the primary tumors. Using the murine TNBC models in syngeneic mice, we provide evidence that early TNBC tumors may elicit anti-tumor immune responses and thus the survival outcome in those patients is substantially increased after complete surgical resection of the primary tumors. Whereas immunosuppressive tumor microenvironment contributes to the poor overall survival in patients with advanced TNBCs. Therefore, identifying an anti-tumor immune signature in early TNBC patients may be utilized as a clinical biomarker before surgical intervention as well as improve the survival outcome.

Citation Format: Fulya Alkan, Raziye Piranlioglu, Eunmi Lee, Maria Ouzounova, Catherine C Hedrick, Huidong Shi, Hasan Korkaya. Understanding the pro- and anti-tumorigenic microenvironments in syngeneic mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2223.

Cellular Plasticity: A Route to Senescence Exit and Tumorigenesis

Senescence is a dynamic, multistep program that results in permanent cell cycle arrest and is triggered by developmental or environmental, oncogenic or therapy-induced stress signals. Senescence is considered as a tumor suppressor mechanism that prevents the risk of neoplastic transformation by restricting the proliferation of damaged cells. Cells undergoing senescence sustain important morphological changes, chromatin remodeling and metabolic reprogramming, and secrete pro-inflammatory factors termed senescence-associated secretory phenotype (SASP). SASP activation is required for the clearance of senescent cells by innate immunity. Therefore, escape from senescence and the associated immune editing would be a prerequisite for tumor initiation and progression as well as therapeutic resistance. One of the possible mechanisms for overcoming senescence could be the acquisition of cellular plasticity resulting from the accumulation of genomic alterations and genetic and epigenetic reprogramming. The modified composition of the SASP produced by these reprogrammed cancer cells would create a permissive environment, allowing their immune evasion. Additionally, the SASP produced by cancer cells could enhance the cellular plasticity of neighboring cells, thus hindering their recognition by the immune system. Here, we propose a comprehensive review of the literature, highlighting the role of cellular plasticity in the pro-tumoral activity of senescence in normal cells and in the cancer context.

CDYL2 Epigenetically Regulates MIR124 to Control NF-κB/STAT3-Dependent Breast Cancer Cell Plasticity

Epigenetic deregulation of gene transcription is central to cancer cell plasticity and malignant progression but remains poorly understood. We found that the uncharacterized epigenetic factor chromodomain on Y-like 2 (CDYL2) is commonly over-expressed in breast cancer, and that high CDYL2 levels correlate with poor prognosis. Supporting a functional role for CDYL2 in malignancy, it positively regulated breast cancer cell migration, invasion, stem-like phenotypes, and epithelial-to-mesenchymal transition. CDYL2 regulation of these plasticity-associated processes depended on signaling via p65/NF-κB and STAT3. This, in turn, was downstream of CDYL2 regulation of MIR124 gene transcription. CDYL2 co-immunoprecipitated with G9a/EHMT2 and GLP/EHMT1 and regulated the chromatin enrichment of G9a and EZH2 at MIR124 genes. We propose that CDYL2 contributes to poor prognosis in breast cancer by recruiting G9a and EZH2 to epigenetically repress MIR124 genes, thereby promoting NF-κB and STAT3 signaling, as well as downstream cancer cell plasticity and malignant progression.

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Up-regulation of CDYL2 is common in breast cancer and correlates with poor prognosis

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CDYL2 regulates enrichment of methyltransferases G9a and EZH2 at MIR124 genes

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microRNA-124 regulation by CDYL2 impacts STAT3 and NF-κB signaling

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CDYL2 regulation of EMT, migration, invasion, and stemness is STAT3/NF-κB dependent

Abstract 3683: IL32 expression is epigenetically regulated in EpCAM-/Cd49f- basal-like breast cancers and can be suppressed by the bromodomain inhibitor JQ1

Metastatic basal-like breast cancers are believed to correspond with EpCAM-/Cd49f- cancer stem cell (CSC) enrichment. As well, basal-like breast cancers typically correspond with tumor inflammation and immunoediting phenotypes. However, the exact interplay between CSCs and the inflammatory signature of basal-like breast cancers is not well understood. To provide insight regarding the clinical overlap between breast cancer stem cells and tumor inflammation, we compared the 450K DNA methylation profile of EpCAM-/CD49f- CSCs from the isogenic MCF10A p53-/PTEN- breast cell line against the corresponding EpCAM+/CD49f+ and EpCAM-/CD49f+ subpopulations to determine whether differential DNA methylation occurred within the promoters of immune-related genes in CSCs. In addition, we also overlapped the 450K DNA methylation profile from 16 established breast cancer cell lines of varying EpCAM-/CD49f- concentrations to compare against the isolated CSCs. Based on our results, we identified 1432 differentially methylated promoter regions overall (ANOVA FDR p-value <0.001) and found IL32 to be differentially hypomethylated in the EpCAM-/CD49f- enriched cell lines. This hypomethylation of IL32 corresponded with increased expression of the beta isoform of IL32. Results from the cell lines were mirrored in The Cancer Genome Atlas (TCGA) breast cancer datasets, which revealed decreased promoter DNA methylation and increased gene expression of IL32 in basal-like patients. Further analysis of TCGA data using Gene Set Enrichment Analysis (GSEA) revealed that transcripts that tightly correlate with IL32 expression were preferentially involved in NF-kappaB mediated inflammation, with specific examples including REL, CCL5, PIK3CD, and IDO1. Furthermore, publicly available H3K27Ac and BRD4 ChIPseq data revealed that the IL32 promoter in the basal-like breast cancer cell line SUM159PT contains a high presence of H3K27 acetylation and BRD4 recruitment, with the latter event being disrupted by JQ1 treatment. These results complemented qRT-PCR results showing the IL32-beta isoform being quickly suppressed by 1uM JQ1 in SUM159PT as well as chick chorioallanotoic membrane (CAM) xenograft assays demonstrating suppressed metastasis and neovascularization of SUM159PT treated with JQ1. Collectively, these findings highlight the potential impact of IL32 promoter hypomethylation in basal-like breast cancer stem cells and how the overall epigenetic signature may predispose CSCs towards an immunomodulatory phenotype.

Citation Format: Emma V. Gray, Caroline E. Dyar, Maria Ouzounova, Max S. Wicha, Hasan Korkaya, Austin Y. Shull. IL32 expression is epigenetically regulated in EpCAM-/Cd49f- basal-like breast cancers and can be suppressed by the bromodomain inhibitor JQ1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3683.

Abstract 4313: Identifying and characterizing epigenetic «driver» genes («epidrivers») in regulatory pathways involved in tumorigenesis and tumour cell plasticity

One of the ground-breaking discoveries of the international cancer genome sequencing endeavours is the high frequency of mutational and non-mutational changes in epigenetic regulator genes (ERGs), which constitute a “genetic smoking gun” that epigenetic mechanisms lie in the very heart of cancer biology. However, functional importance of disruption of ERGs in tumorigenesis and cancer phenotype is poorly understood. We hypothesise that these genes are candidates to be drivers («epidrivers») of cancer onset and progression, thus regulating mechanisms underpinning cancer development. Moreover, deregulation of epidrivers may play a role in epithelial-to-mesenchymal transition (EMT) and emergence of cancer resilience. The overarching aim of this study was to identify and functionally characterize “Epidrivers” in tumorigenesis and cancer cell plasticity. To this end, we have set up novel epigenome-wide functional screens in human cultured cells (and organoids) combined with state-of-the-art genome-editing approach (based on CRISPR/Cas9 screen) and multiparametric phenotyping. We designed a custom-made lentiviral CRISPR library that consists of 1,649 gRNAs targeting all known ERGs (426 genes). Lentiviral CRISPR library was used to deliver the ERG gRNAs to target cells expressing the RNA-guided DNA endonuclease Cas9. Independent clones (derived from transduced breast and lung cancer cell lines constitutively expressing Cas9) are screened for acquisition of distinct features of transformed cells. The results of the identification of Epidriver genes based on the analysis of deregulation of core cellular processes, epigenome (ChIP-seq) as well as EMT and multiparametric phenotyping, will be presented.

Citation Format: Andrea Halaburkova, Vincent Cahais, Cyrille Cuenin, Rita Khoueiry, Maria Ouzounova, Akram Ghantous, Zdenko Herceg. Identifying and characterizing epigenetic «driver» genes («epidrivers») in regulatory pathways involved in tumorigenesis and tumour cell plasticity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4313.

Abstract 2245: Improving the effectiveness of immunotherapy in breast cancer by targeting the tumor microenvironment

Large cohorts of recent clinical studies have firmly established that increased levels of tumor-infiltrating lymphocytes (TILs) in TNBC and HER2+ subtypes predicted better clinical outcome compared to the luminal subtype. These observations led to the hypothesis that women with TNBC or HER2+ subtypes may respond to a checkpoint blockade. However, early results from these trials using check point inhibitors alone or in combination with chemotherapy have shown very little promise in breast cancer patients, despite the remarkable long-lasting responses in other hard to treat malignancies such as non-small cell lung and melanoma. Although the outcome falls short of the expectation, it has suggested that the combinations of check point blockade with therapeutics that target immunosuppression may potentiate its efficacy. TNFα exhibits paradoxical roles; it may fuel tumor cell growth, invasion and metastasis in some tumor types, while in others it induces cytotoxic cell death. We recently demonstrated that TNFα distinctly induces A20 in TNBC subtype and protects these cells from TNFα-induced cytotoxic cell death by upregulating HSP70 protein and maintaining EMT/CSC phenotype. In contrast, luminal MCF7 or ZR75-1 cells display approximately 70% apoptosis when treated with TNFα. Overexpression of A20 in luminal cells not only protected them from TNFα-induced cytotoxicity by upregulating HSP70 and EMT/CSC phenotype, but also exhibited aggressive metastatic properties in mouse xenograft models. Furthermore, we show that A20/HSP70 pathway attracts tumor-infiltrating lymphocytes (TILs) while inducing the accumulation of immunosuppressive MDSCs in syngeneic mouse models. Interestingly, pulmonary DTCs as well as the immune infiltrates from 4T1 tumor-bearing mice exhibited significantly higher HSP70 expression. Therefore, we proposed that targeting HSP70 may potentiate the efficacy of immunotherapy in preclinical models of breast cancer. As previously reported, murine 4T1 tumors do respond to check point inhibitors. We reasoned that this may be an appropriate model to test the efficacy of HSP70 inhibitor, JG-231. Expectedly, there was no difference in tumor growth and metastasis between control and anti-PDL1 treated animals, however, combination of anti-PDL1 antibody ed with JG-231 and chemotherapy (cyclophosphamide-CTX) significantly reduced primary tumor growth (>10 fold) and eliminated metastasis. Collectively, our pilot experiments provide a strong rationale for testing our hypothesis and may lead to a rapid translation into the clinical utility.

Citation Format: Hasan Korkaya, Eunmi Lee, Raziye Piranioglu, Maria Ouzounova, Ahmet Korkaya, Jason Gestwicki, Max S. Wicha, Esteban Celis. Improving the effectiveness of immunotherapy in breast cancer by targeting the tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2245.

Primary tumor-induced immunity eradicates disseminated tumor cells in syngeneic mouse model

Although clinically apparent metastasis is associated with late stages of cancer development, micro-metastatic dissemination may be an early event. However, the fate of these early disseminated tumor cells (DTC) remains elusive. We show that despite their capacity to disseminate into secondary organs, 4T1 tumor models develop overt metastasis while EMT6-tumor bearing mice clear DTCs shed from primary tumors as well as those introduced by intravenous (IV) injection. Following the surgical resection of primary EMT6 tumors, mice do not develop detectable metastasis and reject IV-injected tumor cells. In contrast, these cells readily grow and metastasize in immuno-deficient athymic or Rag2^−/− mice, an effect mimicked by CD8⁺ T-cell depletion in immunocompetent mice. Furthermore, recombinant G-CSF or adoptive transfer of granulocytic-MDSCs isolated from 4T1 tumor-bearing mice, induce metastasis by suppressing CD8⁺ T-cells in EMT6-primed mice. Our studies support the concept of immune surveillance providing molecular insights into the immune mechanisms during tumor progression.

Dissemination of tumor cells from the primary site is an early event. Here, the authors show that the early disseminated tumor cells are actively cleared by the host cytotoxic T lymphocytes induced by the primary tumor and that infiltration of granulocytic myeloid-derived suppressor cells counteracts such immune protection and allow metastasis development.

Abstract 5321: Deciphering the DNA methylation signature of EpCAM-/CD49f- breast cancer stem cells

The metastatic potential of breast cancer cells is believed to correspond with the preferential enrichment of a tumor population known as cancer stem cells (CSCs). Thus, evaluating the unique molecular characteristics of breast CSCs is of great interest from a prognostic and therapeutic standpoint. In order to provide a more detailed profile of breast cancer stem cells, we compared the 450K DNA methylation landscape of the EpCAM-/CD49f- cancer stem cell subpopulation from the isogenic MCF10A p53-/PTEN- breast cell line against the corresponding EpCAM+/CD49f+ and EpCAM-/CD49f+ subpopulations to determine how DNA methylation varies within the different genomic regions of CSCs. In addition, we also overlapped the 450K DNA methylation profiles from 16 established breast cancer cell lines of varying subtypes and aggressiveness to determine how these cell lines relate epigenetically with the isolated CSCs. Based on unsupervised PCA and matrix dissimilarity clustering, we were able to identify 3 distinct groups that appeared to independently cluster based on EpCAM-/CD49f- enrichment status. It is also interesting to note that the aggressive cell lines SUM149 and MDA-MB-231 would cluster away from the EpCAM-/CD49f- subset when utilizing strictly promoter probes for clustering, whereas SUM149 and MDA-MB-231 would cluster more closely with the EpCAM-/CD49f- subset when utilizing gene body probes, potentially indicating a more sensitive correlation between gene body methylation and CSC-associated aggressiveness. To further investigate the differing promoter and gene body DNA methylation patterns in CSCs, we performed differential methylation analysis between the 3 previously defined groups. Based on our results, we discovered 1432 differentially methylated promoter probes and 7243 differentially methylated gene body probes (ANOVA FDR p-value <0.001), with the majority of the promoter probes being hypermethylated in the CSC group and, inversely, the majority of the gene body probes being hypomethylated in the CSC group. Examples of genes that demonstrated significant hypomethylation throughout the gene body within CSCs included the guanine nucleotide exchange factor MCF2L, the synaptic-associated protein SHANK2, and the protein kinase C isoform PRKCZ. For the promoter regions, genes that were significantly hypermethylated in CSCs included the metabolic regulator GPD2, the e-cadherin protein CDH1, and the transcriptional regulator IRF6, all of which were transcriptionally suppressed in the CSC populations. Based on these findings, our work helps provide clarity to the stochastic nature of DNA methylation changes throughout the genome in EpCAM-/CD49f- breast CSCs and provide further motivation for determining the prognostic potential of these identified CSC-associated epigenetic events.

Citation Format: Austin Y. Shull, Caroline E. Dyar, Maria Ouzounova, Nicole L. Hudson, Max S. Wicha, Hasan Korkaya. Deciphering the DNA methylation signature of EpCAM-/CD49f- breast cancer stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5321.

Bromodomain factors of BET family are new essential actors of pericentric heterochromatin transcriptional activation in response to heat shock

The heat shock response is characterized by the transcriptional activation of both hsp genes and noncoding and repeated satellite III DNA sequences located at pericentric heterochromatin. Both events are under the control of Heat Shock Factor I (HSF1). Here we show that under heat shock, HSF1 recruits major cellular acetyltransferases, GCN5, TIP60 and p300 to pericentric heterochromatin leading to a targeted hyperacetylation of pericentric chromatin. Redistribution of histone acetylation toward pericentric region in turn directs the recruitment of Bromodomain and Extra-Terminal (BET) proteins BRD2, BRD3, BRD4, which are required for satellite III transcription by RNAP II. Altogether we uncover here a critical role for HSF1 in stressed cells relying on the restricted use of histone acetylation signaling over pericentric heterochromatin (HC).

Abstract 3992: Immune regulation of disseminated tumor cell clearance versus metastatic growth

Metastatic disease is the end stage of extremely inefficient processes that entail overcoming multiple barriers including anti-tumor immunity. Although evidences from preclinical and clinical settings suggest that dissemination of malignant cells is an early process, majority of disseminated cells either eliminated or remain dormant in distant organs, while very few cells eventually develop successful metastasis. Therefore, it is widely accepted that dynamic and reversible tumor cell plasticity is required for metastasis, however, in vivo steps and molecular mechanisms are poorly elucidated.

We provide evidence that monocytic and granulocytic subsets of myeloid derived suppressor cells (m-MDS, g-MDSC) infiltrated in primary 4T1 tumor and distant organs with different time kinetics regulate spatiotemporal tumor plasticity. Using co-culture experiments and syngeneic mouse models of murine 4T1 (metastatic) tumor, we demonstrated that tumor infiltrated m-MDSCs facilitate tumor cell dissemination from the primary site by inducing the EMT/CSC phenotype. In contrast, g-MDSCs infiltrated in the lungs support metastatic growth by reverting the EMT/CSC phenotype and thus promoting tumor cell proliferation. In contrast, less invasive EMT6 tumors fail to induce efficient pulmonary infiltration of g-MDSCs and results in clearance of disseminated tumor cells in the lungs. Gene expression analyses of tumors and MDCS subsets in primary tumor site and distant organs at different time points reveal mechanistic temporal regulation of in vivo tumor plasticity by m-MDSC and g-MDSC subsets in 4T1 tumor-bearing mice. However, the lung microenvironment of EMT6 tumor-bearing mice display a gene expression signature of anti-tumor immunity which predict better survival in breast cancer patients. In our functional studies, we demonstrate that EMT6 tumor-bearing animals efficiently eliminate disseminated tumor cells in the lungs. Furthermore, g-MDSCs isolated from 4T1-tumor bearing animals significantly enhance metastatic growth of already disseminated tumor cells.

Consistent with the “seed and soil” hypothesis, our studies provide a molecular mechanism by which the immune system regulate spatiotemporal tumor plasticity and generation of permissive or anti-tumorigenic microenvironment in distant organs determining the fate of disseminated tumor cells.

Citation Format: Hasan Korkaya, Eunmi Lee, Raziye Piranioglu, Maria Ouzounova, Abdeljabar El-Andaloussi, Iskander Asm, Ahmet K. Korkaya, Gang Zhou, Ali Arbab, Paulo Rodriguez. Immune regulation of disseminated tumor cell clearance versus metastatic growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3992. doi:10.1158/1538-7445.AM2017-3992

Abstract 4240: Determination of normative patterns of gene expression levels and breast cancer risk biomarkers in human breast milk

Parity and breastfeeding influence a woman’s risk of developing breast cancer. Understanding the underlying molecular changes in the breast will facilitate identification of additional factors during pregnancy and postpartum that modify breast cancer risk. Most prior studies in humans on this topic, however, have been cross-sectional studies comparing breast tissue samples from nulliparous versus post-pregnant women, and are limited in their ability to characterize longitudinal changes and within-person variations. Breast milk contains cells of the mature gland, and may have a potential as a noninvasive source for studying molecular characteristics of the pregnancy-associated changes in the breast and their impact on breast cancer risk. The objectives of this study were to (1) determine normative patterns of gene expression levels in longitudinally collected breast milk samples and (2) correlate gene expression data in relation to self-reported measures of psychosocial stress during pregnancy and postpartum period. Our preliminary results showed that the post-pregnancy gene expression levels in breast milk samples can be measured reproducibly over a short period of time. Whole-genome transcriptome analysis revealed that expression levels of the post-pregnancy genes are different in early (less than 3 month postpartum) and late lactation period (more than 6 month postpartum). Moreover cytokine expression profiling correlated expression of inflammatory cytokines with early versus late postpartum period. The unique contribution of this study is to capture longitudinal gene expression data from breast milk samples collected over the course of lactation, hence providing a valuable basis for future studies to identify differential dynamics associated with breast cancer susceptibility.

Note: This abstract was not presented at the meeting.

Citation Format: Maria Ouzounova, Georgina Lewis, Raziye Piranlioglu, Tiana Curry-McCoy, Wonsuk Yoo, Nita Maihle, Sangmi Kim, Hasan Korkaya. Determination of normative patterns of gene expression levels and breast cancer risk biomarkers in human breast milk [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4240. doi:10.1158/1538-7445.AM2017-4240

Promoter Methylation Modulates Indoleamine 2,3-Dioxygenase 1 Induction by Activated T Cells in Human Breast Cancers

Triple-negative breast cancer (TNBC) cells are modulated in reaction to tumor-infiltrating lymphocytes. However, their specific responses to this immune pressure are unknown. In order to address this question, we first used mRNA sequencing to compare the immunophenotype of the TNBC cell line MDA-MB-231 and the luminal breast cancer cell line MCF7 after both were cocultured with activated human T cells. Despite similarities in the cytokine-induced immune signatures of the two cell lines, MDA-MD-231 cells were able to transcribe more IDO1 than MCF7 cells. The two cell lines had similar upstream JAK/STAT1 signaling and IDO1 mRNA stability. However, using a series of breast cancer cell lines, IFNγ stimulated IDO1 protein expression and enzymatic activity only in ER^-, not ER⁺, cell lines. Treatment with 5-aza-deoxycytidine reversed the suppression of IDO1 expression in MCF7 cells, suggesting that DNA methylation was potentially involved in IDO1 induction. By analyzing several breast cancer datasets, we discovered subtype-specific mRNA and promoter methylation differences in IDO1, with TNBC/basal subtypes exhibiting lower methylation/higher expression and ER⁺/luminal subtypes exhibiting higher methylation/lower expression. We confirmed this trend of IDO1 methylation by bisulfite pyrosequencing breast cancer cell lines and an independent cohort of primary breast tumors. Taken together, these findings suggest that IDO1 promoter methylation regulates anti-immune responses in breast cancer subtypes and could be used as a predictive biomarker for IDO1 inhibitor-based immunotherapy. Cancer Immunol Res; 5(4); 330-44. ©2017 AACR.

Abstract 908: Immune regulation of tumor dormancy in syngeneic mouse model

Metastatic disease -end stage of tumor progression- is the major cause of cancer-related death.It is widely accepted that malignant cell plasticity between epithelial-mesenchymal-transition (EMT) and mesenchymal-epithelial-transition (MET) is required for metastasis to occur. The classical model of metastasis suggests tumor cell dissemination occur late in tumor development, however emerging studies strongly indicates that dissemination is an early process and provide a striking evidence that tumor cells start to disseminate during the initial steps of tumor development. Late appearing metastases arise from these early-disseminated tumor cells. The mechanism by which some early-disseminated tumor cells colonize and generate metastatic growth while some remain dormant is not well known. In order to understand the underlying factors, we utilized murine mammary tumors (4T1 as metastatic and EMT6 as less metastatic) in a syngeneic mouse model. We performed time course experiments to determine the early factors that may contribute to the metastatic growth. 4T1 or EMT6 tumor cells were implanted orthotopically into the fat pads and tumor cell dissemination was analyzed over 3 weeks time points. We determined that both 4T1 and EMT tumor cells disseminated as early as one week post-implantation, however only 4T1 tumor cells develop metastasis in distant organs. Furthermore, we also resected primary tumors 1,2 and 3 week post implantation of EMT6-Luci or 4T1-Luci tumors and observed distant metastasis via optical imaging of luciferase expression in live animals. Although the majority of 4T1 tumor bearing mice (>80%) develop pulmonary metastasis when 4T1 tumors resected 2 and 3 weeks post-implantation, only 10% of mice develop metastasis when primary tumor resected one week post implantation. In contrast, EMT6 tumors following resection only relapsed in the primary tumor site but failed to develop metastasis. We investigated the possible mechanism of efficient pulmonary metastatic growth following the resection of tumors 2-3 week post implantation. Interestingly we found a significant infiltration of granulocytic subset of myeloid derived suppressor cells (g-MDSC) in 4T1 tumor bearing mice by week 2 and 3. Furthermore, we found that lung infiltrated g-MDSCs promote tumor cell growth via paracrine factors. In co-culture studies we found that there is a reciprocal secretion of panel of inflammatory cytokines, growth factors and matrix metalloproteases between tumor cell and g-MDSCs suggesting that these cells in the lung microenvironment support the metastatic growth. Our studies provide a new paradigm in the understanding of metastatic growth and the role of microenvironment in distant organs.

Citation Format: Raziye Piranlioglu, Maria Ouzounova, Eunmi Lee, Alicia Hudson, Sumeyye Korkaya, Ali Arbab, Hasan Korkaya. Immune regulation of tumor dormancy in syngeneic mouse model. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 908.

Abstract 1555: MDSC mediated spatiotemporal tumor plasticity in breast cancer metastasis

Metastatic breast cancer is the second leading cause of cancer-related death among women. Although the genetic and epigenetic differences between the metastatic versus non-metastatic breast tumors have been well studied, early events between tumor and immune system in metastatic process remain poorly understood. In order to determine early events, we utilized murine mammary tumors (4T1 as metastatic, EMT6 or 67NR as non-metastatic) in syngeneic mouse model. The 4T1 tumor contained a higher proportion of cancer stem cell (CSC) population compared to the non-metastatic EMT6 or 67NR clones. Although, both murine tumor cell lines (50K each) grow to same size tumors within 8 weeks, 4T1 tumors develop spontaneous metastasis in 100% of animals most of which do not survive more than 8 weeks due to extensive wide spread metastasis to lung, liver and bone. We observed immune infiltrates in the lungs of 4T1 tumor bearing mice as early as 1 week. We next assessed the cytokine profile of metastatic 4T1 tumor compared to non-metastatic counterparts (EMT6 or 67NR) secretes significantly higher levels of inflammatory cytokines, including the IL6, IL8, RANTES, GCSF, GM-CSF, IL12, CXCL16 and CXCL5.

MDSCs are potent suppressor of anti-tumor immunity and a significant impediment to cancer therapy. We therefore hypothesized that the tumor secreted inflammatory cytokines promotes the systemic expansion of MDSCs that down regulate immune surveillance and anti-tumor immunity, thus facilitating tumor progression. We sought to determine whether 4T1 tumors could induce MDSCs in mice. Murine 4T1 or EMT6 tumor cells (at 50K cells each) were implanted into the fat pads of BALB/c mice, then sacrificed (4 mice from each group) at weeks 1, 2, 3 and 4 for subsequent evaluation of the MDSC expansion in bone marrow, spleen, lung and tumors. The MDSC induction and infiltration in bone marrow, spleen, lung and tumors were observed as early as one-week post-implantation of 4T1 tumor compared to the EMT6. Furthermore, the MDSCs isolated from 4T1 tumor bearing animals were more suppressive than that of the EMT6 tumor bearing mice.

We determined that non-metastatic EMT6-Luciferase tumor growth and metastasis is robustly enhanced in pre-primed animals (in which metastatic 4T1 cells were pre-implanted in the fat pads and resected after 10 days when tumors were 2mm in size) or by IP injection of inflammatory cytokine rich 4T1 conditioned medium when compared to injection of EMT6-Luci cells into naïve animals. Our preliminary findings suggested that 4T1 tumors within 10 days of implantation created a systemic tumor-promoting microenvironment and thus promoted the metastatic spread of EMT6-Luci. Together these studies strongly suggest that metastatic 4T1 tumor with high CSC phenotype generate a permissive systemic microenvironment for successful metastasis via secretion of inflammatory cytokines in syngeneic BALB/c mice.

Citation Format: Hasan Korkaya, Eunmi Lee, Maria Ouzounova, Raziye Piranlioglu, Abdeljabar El-Andaloussi, Ena Novakovic, Alicia Hudson, Sumeyye Korkaya, Mhmet F. Demirci, Gang Zhou. MDSC mediated spatiotemporal tumor plasticity in breast cancer metastasis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1555.

Abstract 717: Monocytic and granulocytic MDSCs display distinct molecular properties and coordinate the dynamic switches between EMT-MET in breast cancer model

It is widely accepted that the epithelial-mesenchymal plasticity of malignant cells is required during cancer metastatic cascade. The complex phenotypic changes highly depend on the collaboration of various molecular signaling and extracellular cues originating from wide range of stromal cells in the tumor microenvironment. However, the specific mechanisms of how EMT plasticity spatiotemporally regulates metastasis are poorly defined. Myeloid-derived suppressor cells (MDSCs) have been identified in most cancer patients and animal models due to their immune suppressive functions, but recent studies implicate their direct role in promoting metastasis by activating tumor-angiogenesis. To determine the roles of MDSCs in breast cancer metastasis, we utilized murine breast cancer cells, non-metastatic EMT6 and metastatic 4T1 cells. We showed that the metastatic 4T1 murine breast tumors induced early systemic expansion and mobilization of MDSCs in distant sites as well as in the primary tumor. We investigated the direct functions of MDSCs in tumor progression by isolating monocytic and granulocytic MDSCs from primary tumor, lung and bone marrow of tumor-bearing mice and then they were co-cultured with non-metastatic EMT6 cells. We found that tumor infiltrating m-MDSCs from 4T1 tumor-bearing mice increased the expression of Vimentin, Twist1, TGF-â and IL-6 in EMT6 tumor cells. In contrast, flow cytometry sorted lung infiltrating MDSCs from 4T1 tumor-bearing mice enhanced the EpCAM expression and proliferation in EMT6 cells. Cell invasion assay showed that invasive ability of EMT6 cells were significantly increased when they were co-cultured with m-MDSCs while g-MDSCs slightly decreased the number of invaded cells, compared to control group. We utilized immunofluorescence staining and confirmed the increased expression of Vimentin, CK14 (cytokeratin 14) in EMT6 cells co-cultured with m-MDSCs. In contrast, g-MDSCs induced down-regulation of these markers while they increased cell proliferation as assessed by Ki67 staining. Furthermore, flow cytometry analysis showed the increased CD24+CD29+ population, a marker of murine cancer stem cell (CSC) phenotype, in EMT6 cells when co-cultured with m-MDSCs from 4T1 tumor-bearing mice. Tumor sphere assay confirmed that m-MDSCs enhanced sphere forming ability of tumor cells. Taken together, these data suggest that m-MDSCs derived from metastatic 4T1 tumor-bearing mice are able to confer EMT/CSC phenotype on tumor cells while g-MDSCs are more potent in inducing epithelial phenotype and proliferation in tumor cells.

Citation Format: Eunmi Lee, Maria Ouzounova, Raziye Piranlioglu, Abdeljabar El Andaloussi, Mehmet Demirci, Ena Novakovic, Alicia Hudson, Sumeyye Korkaya, Gang Zhou, Hasan Korkaya. Monocytic and granulocytic MDSCs display distinct molecular properties and coordinate the dynamic switches between EMT-MET in breast cancer model. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 717.

Abstract 1554: Myeloid derived suppressor cells-mediated inflammation in metastasis and cancer cachexia

Despite recent advances and better diagnostics, the major challenge is that metastatic breast cancer is still incurable and remains leading cause of cancer related death. Cachexia is considered to be a chronic inflammatory syndrome which is defined by loss of skeletal muscle mass (with or without loss of adipose mass), negative energy and metabolic balance, and systemic inflammation. Cancer patients who develop cachexia are more susceptible to infections and sepsis. Clinical studies suggest that cachexia in cancer patients cannot be fully reversed by conventional nutritional supports, which distinguishes this condition from anorexia. Due to its complexity and lack of clinical biomarkers, currently there is no standard treatment for these patients. Therefore cachexia remains a largely underestimated and untreated condition. Nearly 60-80% of the advanced/ metastatic cancer patients experience cachexia, a condition that accounts for 20% of cancer-related deaths.

Chronic inflammation has been recognized as a risk factor contributing to the etiology of many human malignancies. Accumulating evidence suggest that tumor infiltrating immune cells (mainly myeloid origin) differentiate into cells that promote tumor growth and metastasis via inducing a systemic inflammation. Our preliminary studies suggest that systemic induction and infiltration (tumor, bone marrow, spleen, liver, and lung) of myeloid derived suppressor cells (MDSC) generate a pro-inflammatory micro-environment and are a major source of inflammatory cytokines, many of which are implicated in cancer cachexia. Using a murine breast cancer in a syngeneic (immunocompetent) mouse model we show that metastatic (4T1) murine tumor produce significantly higher level of inflammatory cytokines and is able to induce systemic expansion and infiltration of MDSC compared to non-metastatic murine tumor (EMT6). Furthermore, injection of condition media from metastatic 4T1 tumor cells is also able to induce MDSC expansion in vivo suggesting that tumor-produced factors play role in this process. Moreover, we demonstrate the involvement of the inflammatory cytokines in muscle wasting as shown by co-culture experiments with C2C12 myoepithelial cells and analysed the expression of cachexia markers such as E3 ubiquitin ligases Trim63 and Fbxo3, Myh1(myosin heavy chain), Stat3 and NFkB pathway activation, and elevation of pro-cachexia cytokines.

Our preliminary studies demonstrated that the monocytic MDSC induce EMT phenotype and contribute to the dissemination of tumor cells while the granulocytic MDSC promote the metastatic outgrowth, and present higher infiltration in the lungs. We therefore propose that tumor-induced inflammatory cytokines play role in induction of MDSC and further elevation of inflammatory markers leading to metastasis and cancer cachexia.

Citation Format: Maria Ouzounova, EunMi Lee, Raziye Piranlioglu, Ena Novakovic, Mehmet Demirci, Sumeyye Korkaya, Alicia Hudson, Hasan Korkaya. Myeloid derived suppressor cells-mediated inflammation in metastasis and cancer cachexia. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1554.

Role of a polyphenol-enriched preparation on chemoprevention of mammary carcinoma through cancer stem cells and inflammatory pathways modulation

BACKGROUND

Naturally occurring polyphenolic compounds from fruits, particularly from blueberries, have been reported to be significantly involved in cancer chemoprevention and chemotherapy. Biotransformation of blueberry juice by Serratia vaccinii increases its polyphenolic content and endows it with anti-inflammatory properties.

METHODS

This study evaluated the effect of a polyphenol-enriched blueberry preparation (PEBP) and its non-fermented counterpart (NBJ), on mammary cancer stem cell (CSC) development in in vitro, in vivo and ex vivo settings. Effects of PEBP on cell proliferation, mobility, invasion, and mammosphere formation were measured in vitro in three cell lines: murine 4T1 and human MCF7 and MDA-MB-231. Ex vivo mammosphere formation, tumor growth and metastasis observations were carried out in a BALB/c mouse model.

RESULTS

Our research revealed that PEBP influence cellular signaling cascades of breast CSCs, regulating the activity of transcription factors and, consequently, inhibiting tumor growth in vivo by decreasing metastasis and controlling PI3K/AKT, MAPK/ERK, and STAT3 pathways, central nodes in CSC inflammatory signaling. PEBP significantly inhibited cell proliferation of 4T1, MCF-7 and MDA-MB-231. In all cell lines, PEBP reduced mammosphere formation, cell mobility and cell migration. In vivo, PEBP significantly reduced tumor development, inhibited the formation of ex vivo mammospheres, and significantly reduced lung metastasis.

CONCLUSIONS

This study showed that polyphenol enrichment of a blueberry preparation by fermentation increases its chemopreventive potential by protecting mice against tumor development, inhibiting the formation of cancer stem cells and reducing lung metastasis. Thus, PEBP may represent a novel complementary alternative medicine therapy and a source for novel therapeutic agents against breast cancer.

A Novel IL6 Antibody Sensitizes Multiple Tumor Types to Chemotherapy Including Trastuzumab-Resistant Tumors

Elevated levels of the proinflammatory cytokine IL6 are associated with poor survival outcomes in many cancers. Antibodies targeting IL6 and its receptor have been developed for chronic inflammatory disease, but they have not yet been shown to clearly benefit cancer patients, possibly due to antibody potency or the settings in which they have been tested. In this study, we describe the development of a novel high-affinity anti-IL6 antibody, MEDI5117, which features an extended half-life and potent inhibitory effects on IL6 biologic activity. MEDI5117 inhibited IL6-mediated activation of STAT3, suppressing the growth of several tumor types driven by IL6 autocrine signaling. In the same models, MEDI5117 displayed superior preclinical activity relative to a previously developed anti-IL6 antibody. Consistent with roles for IL6 in promoting tumor angiogenesis, we found that MEDI5117 inhibited the growth of endothelial cells, which can produce IL6 and support tumorigenesis. Notably, in tumor xenograft assays in mice, we documented the ability of MEDI5117 to enhance the antitumor activities of chemotherapy or gefitinib in combination treatment regimens. MEDI5117 also displayed robust activity on its own against trastuzumab-resistant HER2(+) tumor cells by targeting the CD44(+)CD24(-) cancer stem cell population. Collectively, our findings extend the evidence of important pleiotropic roles of IL6 in tumorigenesis and drug resistance, and offer a preclinical proof of concept for the use of IL6 antibodies in combination regimens to heighten therapeutic responses and overcome drug resistance.

Abstract 4060: Promoter methylation regulates interferon-γ induced indoleamine 2,3-dioxygenase expression in breast cancer

Indoleamine 2, 3-dioxygenase 1, encoded by IDO1, is a key immunosuppressive enzyme that catabolizes essential amino acid tryptophan to kynurenine in the tumor microenvironment. Severe depletion of tryptophan by IDO1 affects proliferation of T cells and tryptophan metabolites cause T-cell anergy and induce apoptosis. In this study, we investigated the epigenetic regulation of IDO1 expression by DNA methylation in breast cancer cells. Bisulfite pyrosequencing analysis of IDO1 promoter methylation performed on a panel of 10 breast cancer cell lines revealed that triple negative breast cancer (TNBC) cell lines (i.e. MDA-MB-231, Hs578t, SUM159) are hypomethylated compared to estrogen receptor positive (ER+) cell lines (i.e. MCF7, BT474, T47D). The same analysis was extended to 30 primary breast tumor and normal control samples and the results demonstrated that TNBC tumors had lower IDO1 promoter methylation compared to ER+ tumors. RT-PCR analysis showed that IDO1 mRNA expression is higher in TNBC cell lines than ER+ cell lines. This inverse correlation between IDO1 promoter methylation and mRNA expression can also be observed in TCGA 450K methylation and RNA-seq data sets in which promoter is hypomethylated and mRNA is up-regulated in basal-like molecular subtypes as compared to other breast cancer subtypes. IDO1 promoter is relatively CpG poor with most CpG sites concentrated near interferon γ (IFNg) responsive GAS and ISRE transcription factor binding sites. To investigate the role of CpG methylation in regulating IDO1 induction by IFNg, we cloned either methylated or unmethylated IDO1 promoter DNA into a luciferase reporter plasmid. Methylated promoter reporter exhibited significantly lower luciferase activity at basal or with IFNg stimulation compared to unmethylated reporter plasmid when transfected into MCF-7 or MDA-MB-231 cell lines. Treatment with a demethylating agent, 5-aza-deoxycytidine, synergistically up-regulated IDO1 mRNA expression with IFNg in MCF7 cells which have hypermethylated IDO1 promoter further supporting the influence of CpG methylation on IDO1 expression. IFNg stimulation or co-culture with activated T-cells significantly induced IDO1 protein expression in MDA-MB-231 cells, but not in MCF7 cells. We found no difference in IDO1 mRNA stability and IFNg induced JAK/STAT signaling pathway between MDA-MB-231 and MCF7 cell lines except promoter methylation. Furthermore, RNA-seq analysis of MDA-MB-231 and MCF7 cell lines co-cultured with activated T-cells revealed an active immune signaling mediated through JAK/STAT pathway shared by both cell lines, but also differential induction of IDO1 transcription between these two cell lines. These findings indicate IDO1 promoter methylation status as an important factor that regulates anti-immune responses by tumor cells towards tumor infiltrating lymphocytes and it could be used as a useful biomarker for IDO inhibitor based immunotherapy.

Citation Format: Satish Kumar Reddy Noonepalle, Eun Joon Lee, Maria Ouzounova, Jaejik Kim, Jeong-Hyeon Choi, Austin Shull, Lirong Pei, Ravindra Kolhe, Pei-Yin Hsu, Nagireddy Putluri, Tim Hui-Ming Huang, Arun Sreekumar, Hasan Korkaya, David Munn, Huidong Shi. Promoter methylation regulates interferon-γ induced indoleamine 2,3-dioxygenase expression in breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4060. doi:10.1158/1538-7445.AM2015-4060

Abstract 1984: SOCS3 regulates IDO proteasomal degradation and inflammatory signaling in triple negative breast cancer

An intrinsic claudin-low subtype within the TNBC was recently identified based on low/absent expression of luminal differentiation markers, enrichment of epithelial-to-mesenchymal transition (EMT) and stem cell markers. Interleukin-6 (IL6), a potent pleiotropic cytokine, is induced in response to acute and chronic inflammation. IL6 is a key regulator of inflammatory responses and orchestrates these physiological functions by controlling the Suppressor of cytokine signaling 3 (SOCS3) mediated Stat3/NF-κB pathway. SOCS3 is a critical negative regulator of IL6-mediated pathways. We have showed that constitutive activation of inflammatory loop in transformed cells but not in their untransformed counterparts depends on proteolytic degradation of SOCS3. Several studies indicate that activation of the tryptophan-degrading enzyme indoleamine-2,3-dioxygenase (IDO) represents a key pathway suppressing anti-tumor immunity. Moreover a recent study in dendritic cells found that SOCS3 binds IDO via phosphotyrosine-containing peptides and target the IDO/SOCS3 complex for ubiquitination and subsequent proteasomal degradation. IDO is shown to be constitutively expressed by many tumors. We analyzed a panel of breast cancer cell lines and found an inverse correlation between SOCS3 and IDO1 protein levels. Interestingly IDO protein and transcript levels were significantly increased in TNBC compared to luminal cell lines, thus confirming that IL6-JAK-STAT inflammatory loop is responsible for IDO regulation. Enforced expression of stable form of SOCS3, lacking the PEST and SOCS box domain in TNBC cell lines resulted in decreased expression of IDO. Therapeutic targeting of the IDO-IL6-SOCS3 inflammatory loop would revert the immune suppression mediated by IDO in this breast cancer subtype. These studies would provide a strong rationale for development of inflammatory pathway targeted agents for the treatment of TNBC, an aggressive disease that currently lacks molecularly targeted therapeutics.

Citation Format: Maria Ouzounova, EunMi Lee, Ena Novakovic, Satish Kumar Noonepalle, Raziye Piranlioglu, Huidong Shi, Max Wicha, Hasan Korkaya. SOCS3 regulates IDO proteasomal degradation and inflammatory signaling in triple negative breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1984. doi:10.1158/1538-7445.AM2015-1984

Abstract 466: Systemic early immune priming via tumor-secreted cytokines facilitates breast cancer metastasis in syngeneic mouse model

Metastatic breast cancer is the second leading cause of cancer-related death among women in the United States. Although the genetic and epigenetic differences between the metastatic versus non-metastatic breast tumors have been well studied, early events between tumor and immune system in metastatic process remain poorly understood. In order to determine early events, we utilized murine mammary tumors (4T1 as metastatic, EMT6 or 67NR as non-metastatic) in syngeneic mouse model. The 4T1 tumor contained a higher proportion of cancer stem cell (CSC) population compared to the non-metastatic EMT6 or 67NR clones. Although, both murine tumor cell lines (50K each) grow to same size tumors within 8 weeks, 4T1 tumors develop spontaneous metastasis in 100% of animals most of which do not survive more than 8 weeks due to extensive wide spread metastasis to lung, liver and bone. We observed immune infiltrates in the lungs of 4T1 tumor bearing mice as early as 1 week. We next assessed the cytokine profile of metastatic 4T1 tumor compared to non-metastatic counterparts (EMT6 or 67NR) secretes significantly higher levels of inflammatory cytokines, including the IL6, IL8, RANTES, GCSF, GM-CSF, IL12, CXCL16 and CXCL5.

MDSCs are potent suppressor of anti-tumor immunity and a significant impediment to cancer therapy. We therefore hypothesized that the tumor secreted inflammatory cytokines promotes the systemic expansion of MDSCs that down regulate immune surveillance and anti-tumor immunity, thus facilitating tumor progression. We sought to determine whether 4T1 tumors could induce MDSCs in mice. Murine 4T1 or EMT6 tumor cells (at 50K cells each) were implanted into the fat pads of BALB/c mice, then sacrificed (4 mice from each group) at weeks 1, 2, 3 and 4 for subsequent evaluation of the MDSC expansion in bone marrow, spleen, lung and tumors. The MDSC induction and infiltration in bone marrow, spleen, lung and tumors were observed as early as one-week post-implantation of 4T1 tumor compared to the EMT6. Furthermore, the MDSCs isolated from 4T1 tumor bearing animals were more suppressive than that of the EMT6 tumor bearing mice.

We determined that non-metastatic EMT6-Luciferase tumor growth and metastasis is robustly enhanced in pre-primed animals (in which metastatic 4T1 cells were pre-implanted in the fat pads and resected after 10 days when tumors were 2mm in size) or by IP injection of inflammatory cytokine rich 4T1 conditioned medium when compared to injection of EMT6-Luci cells into naïve animals. Our preliminary findings suggested that 4T1 tumors within 10 days of implantation created a systemic tumor-promoting microenvironment and thus promoted the metastatic spread of EMT6-Luci. Together these studies strongly suggest that metastatic 4T1 tumor with high CSC phenotype generate a permissive systemic microenvironment for successful metastasis via secretion of inflammatory cytokines in syngeneic BALB/c mice.

Citation Format: Hasan Korkaya, Eunmi Lee, Maria Ouzounova, Abdeljabar El Andaloussi, Ena Novakovic, Raziye Piranlioglu, Mehmet F. Demirci, Shawn G. Clouthier, Max S. Wicha. Systemic early immune priming via tumor-secreted cytokines facilitates breast cancer metastasis in syngeneic mouse model. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 466. doi:10.1158/1538-7445.AM2015-466

Notch reporter activity in breast cancer cell lines identifies a subset of cells with stem cell activity

Developmental pathways such as Notch play a pivotal role in tissue-specific stem cell self-renewal as well as in tumor development. However, the role of Notch signaling in breast cancer stem cells (CSC) remains to be determined. We utilized a lentiviral Notch reporter system to identify a subset of cells with a higher Notch activity (Notch(+)) or reduced activity (Notch(-)) in multiple breast cancer cell lines. Using in vitro and mouse xenotransplantation assays, we investigated the role of the Notch pathway in breast CSC regulation. Breast cancer cells with increased Notch activity displayed increased sphere formation as well as expression of breast CSC markers. Interestingly Notch(+) cells displayed higher Notch4 expression in both basal and luminal breast cancer cell lines. Moreover, Notch(+) cells demonstrated tumor initiation capacity at serial dilutions in mouse xenografts, whereas Notch(-) cells failed to generate tumors. γ-Secretase inhibitor (GSI), a Notch blocker but not a chemotherapeutic agent, effectively targets these Notch(+) cells in vitro and in mouse xenografts. Furthermore, elevated Notch4 and Hey1 expression in primary patient samples correlated with poor patient survival. Our study revealed a molecular mechanism for the role of Notch-mediated regulation of breast CSCs and provided a compelling rationale for CSC-targeted therapeutics.

Abstract 3866: Inactivation of p53/PTEN confers a specific epigenetic profile regulated by IL6-SOCS3 signaling

Recent studies by us and others suggested that activation of inflammatory feedback loop play critical role in metastasis and therapeutic resistance by regulating EMT/CSC phenotype. Of these cytokines, IL6 is a key regulator of inflammatory responses and orchestrates these physiological functions by controlling the Stat3/NF-kB pathway which is negatively regulated by the suppressor of cytokine signaling 3 (SOCS3). Consistent with these reports, we demonstrated in our preliminary data that SOCS3 is abundantly expressed in non-malignant MCF10A cells as well as in luminal and HER2+ tumors where it negatively regulates the IL6/Stat3/NF-kB signaling. In contrast, SOCS3 protein was undetectable in basal cluadin-low breast cancer cell lines and primary tumors which express substantially higher levels of IL6. We developed transformed MCF10A model by simultaneous knockdown of p53 and PTEN. In this model single p53 and PTEN deletions result in hyperplasia or DCIS-like lesions. Interestingly, SOCS3 protein expression was undetectable in MCF10A-p53-PTEN- cells compared to parental MCF10A, single p53 (MCF10A-p53-) or PTEN (MCF10A-PTEN-) deleted cells. We demonstrated that IL6 mediated Stat3/NF-kB signaling is negatively regulated by SOCS3 that strongly inhibited the IL6/Stat3/NF-kB pathway when overexpressed in MCF10A-p53-PTEN- cells. Moreover, enforced SOCS3 expression in these cells reduced the tumor growth and inhibited metastasis. Furthermore, loss of SOCS3 expression is strongly associated with increased risk of recurrent disease in breast cancer patients. We hypothesized that loss of SOCS3 in TNBCs results in activation of IL6 feedback loop which drives aggressive metastatic phenotype. Interestingly Stat3/NF-kB signaling drives expression of SOCS3 in response to inflammation and serves as negative feedback loop, although molecular mechanism of SOCS3 expression in cancer has not been investigated. IL6 signaling has been previously reported to be involved in epigenetic regulation. We therefore correlated the gene expression and methylation profile after enforced SOCS3 expression. Our analysis revealed that expression levels of a significant number of genes involved in transcription, migration and metabolism were reverted to those of the parental non transformed cells and their transcription was regulated by methylation. These results suggest that interplay between genetic and epigenetic changes during malignant transformation of mammary epithelial cells may activate multiple signaling cascades and reconstitution of SOCS3 may have therapeutic utility in TNBC.

Citation Format: Maria Ouzounova, Gwangil Kim, April Davis, Ahmed A. Quraishi, Nader Tawakkol, Shalini Kota, Max S. Wicha, Hasan Korkaya. Inactivation of p53/PTEN confers a specific epigenetic profile regulated by IL6-SOCS3 signaling. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3866. doi:10.1158/1538-7445.AM2014-3866

Abstract 3869: SOCS3-mediated regulation of inflammatory cytokines in triple-negative breast cancer

We demonstrated that knock-down of tumor suppressors p53 and PTEN in mammary epithelial MCF10A cells (called MCF10A-p53-PTEN-) results in generation of aggressive tumors. Furthermore MCF10A-p53-PTEN- cells also display an increased EMT phenotype as well as expansion of cancer stem cell (CSC) population. Utilizing Affymetrix gene expression analyses, we confirmed that malignant MCF10Ap53-PTEN- cells displayed a gene expression pattern which closely resembled that of the basal/claudin molecular subtype with the TN. This subtype is previously characterized by the expression of EMT and stem cell genes.

The Inflammatory cytokines IL6 and TGF-β have been found to regulate stem cells and EMT. Consistent with these data, we found that MCF10A-p53-PTEN- cells secreted significantly higher levels of IL6 (>1000 fold) and TGF-β (>200 fold) compared to parental or single gene deleted cells. Furthermore combined deletion of p53 and PTEN compared to single gene knockdown resulted in transformation of MCF10A cells generating aggressive metastatic tumors in NOD/SCID mice.

IL6 is a key regulator of inflammatory responses and orchestrates these physiological functions by controlling the SOCS3 mediated Stat3/NF-κB pathway. Consistent with these reports, we demonstrated that SOCS3 is abundantly expressed in MCF10A cells where it negatively regulates the IL6 feedback loop. Unexpectedly, we found that SOCS3 protein was undetectable in MCF10A-p53-PTEN- cells. Basal/claudin-low breast cancer cell lines that display an activated IL6 feedback loop also had low SOCS3 protein levels. Furthermore, we found a similar discordance between SOCS3 protein and mRNA levels in primary basal/claudin-low breast cancer samples as demonstrated by immunochemistry utilizing a primary breast cancer tissue array. Together these findings suggest that loss of SOCS3 protein expression allows for maintenance of the IL6 mediated inflammatory feedback loop in aggressive/metastatic TN breast cancers. We found that MCF10A-p53-PTEN- cells displayed increased proteasome activity as evidenced by SOCS3 protein accumulation upon proteasome inhibition. Proteolytic degradation of SOCS3 protein in turn is controlled by constitutive activation of the IL6 mediated Stat3/NF-κB pathway.

We demonstrate that enforced expression of SOCS3 or IL6 pathway inhibition interfering with this loop through IL6R blockade repress the CSC population, reducing the tumor growth and metastasis in mouse xenografts. These studies provide a strong rationale for development of IL6 pathway-targeting agents for the treatment of TNBC, an aggressive disease that currently lacks molecularly targeted therapeutics.

Citation Format: Hasan Korkaya, Maria Ouzounova, Gwangil Kim, Ali Quraishi, April Davis, Nader Tawakkol, Sumeyye Korkaya, Max S. Wicha. SOCS3-mediated regulation of inflammatory cytokines in triple-negative breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3869. doi:10.1158/1538-7445.AM2014-3869

SOCS3-mediated regulation of inflammatory cytokines in PTEN and p53 inactivated triple negative breast cancer model

Somatic mutations or deletions of TP53 and PTEN in ductal carcinoma in situ (DCIS) lesions have been implicated in progression to invasive ductal carcinomas. A recent molecular and mutational analysis of breast cancers revealed that inactivation of tumor suppressors, p53 and PTEN are strongly associated with triple negative breast cancer. In addition, these tumor suppressors play important roles in regulating self-renewal in normal and malignant stem cells. To investigate their role in breast carcinogenesis, we knocked down these genes in human mammary cells and in non-transformed MCF10A cells. p53 and PTEN knockdown synergized to activate pro-inflammatory IL6/Stat3/NF-κB signaling. This resulted in generation of highly metastatic EMT-like cancer stem cells (CSCs) resulting in tumors whose gene expression profile mimicked that found in basal/claudin-low molecular subtype within the triple negative breast tumors. Constitutive activation of this loop in transformed cells was dependent on proteolytic degradation of SOCS3 resulting in low levels of this protein in basal/claudin low cell lines and primary tumors. In non-transformed cells, transient activation of the IL6 inflammatory loop induced SOCS3 expression leading to pathway inactivation. In transformed cells, enforced expression of SOCS3 or interfering with IL6 pathway via IL6R blockade inhibited tumor growth and metastasis in mouse xenograft models. Furthermore, circulating tumor cells were significantly reduced in tumor bearing animals when treated with anti-IL6R antibodies. These studies uncover important connections between inflammation and carcinogenesis and suggest that blocking pro-inflammatory cytokines may be utilized as an attractive strategy to target triple negative breast tumors which currently lacks molecularly targeted therapies.

Abstract 5024: Epigenetic regulation of cancer stem cell states in a p53/PTEN inactivated mammary epithelial cells

Inactivation of the tumor suppressors, TP53 and PTEN in pre-neoplastic lesions has been implicated in tumor progression as well as in regulation of normal and malignant stem cell self-renewal. Down regulation of both p53 and PTEN in non-transformed MCF10A cells synergized to expand the cancer stem cell compartment transforming these cells and generating an EMT phenotype in vitro which generated highly metastatic tumors when injected in NOD/SCID mice.

These tumors could be fractionated based on their expression of CD49f and EPCAM. Gene expression analyses of these sub-fractions demonstrate an EMT gene signature in CD49f+/EPCAM- and CD49f-/EPCAM- cell populations. These findings are also supported by DNA methylation analyses. Although CD49f+EPCAM+ cell population express epithelial (MET) gene signature, these cells also generate tumors in mice and give rise to cells with EMT phenotype. Interestingly CD49f+EPCAM+ subpopulation expresses higher ALDH than other two subpopulations with EMT phenotype. Therefore we propose that breast CSCs may exist in two states; EMT state may be represented by CD49f or CD44 and MET state by ALDH expression. Consistent with our hypothesis, ALDH-positive cells compared to ALDH-negative cells within the CD49f+EPCAM+ phenotype have greater capacity to generate CD49f+/EPCAM- phenotype upon IL6 or TGF-b stimulation. Interestingly blocking IL6 and TGF-b in CD49f+/EPCAM- cell population results in MET-CSC phenotype characterized by ALDH expression. It is well known that EMT is characterized by reversible epigenetic changes and therefore we hypothesized that these epigenetic changes might be involved in acquisition of different CSC states.

Our results suggest that interplay between genetic and epigenetic changes during malignant transformation of mammary epithelial cells may activate multiple signaling cascades resulting in expansion of stem cells which display an EMT phenotype. Furthermore, these studies provide a strong rationale for the development of alternative therapeutics which are able to target these different states of cancer stem cells.

Citation Format: Maria Ouzounova, April Davis, Gwangil Kim, Fayaz Malik, Ahmed A. Quraishi, Shawn G. Clouthier, Max S. Wicha, Hasan Korkaya. Epigenetic regulation of cancer stem cell states in a p53/PTEN inactivated mammary epithelial cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5024. doi:10.1158/1538-7445.AM2013-5024

Abstract 3736: IL6 feedback loop regulates breast cancer stem cells which mediate trastuzumab resistance

The development of HER2 targeting agents such as trastuzumab and lapatinib represents one of the greatest achievements in clinical oncology demonstrating the effectiveness of molecularly targeted therapeutics (2). Despite the clinical benefits of trastuzumab in improving progression free and overall survival, majority of patients demonstrate “intrinsic” resistance or develop “acquired” resistance within one-to-two years.

Although inactivation of the PTEN gene has been implicated in the development of resistance to the HER2 targeting antibody trastuzumab, the mechanisms mediating this resistance remain to be investigated. We generated trastuzumab resistant cells by knocking down PTEN expression in HER2 overexpressing breast cancer cell lines and demonstrated that development of trastuzumab resistance in these cells is mediated by activation of an IL6 inflammatory feedback loop leading to expansion of breast cancer stem cell (CSC) population. We and others previously demonstrated that cytokines including IL6 and IL8 regulates breast cancer stem cell self-renewal. Furthermore, elevated serum levels of these cytokines in breast cancer patients strongly correlated with metastatic disease and therapeutic resistance. We therefore hypothesized that activation of IL6 feedback loop may mediate trastuzumab resistance. Utilizing these models, we demonstrated that long term trastuzumab treatment generates highly enriched CSCs which display an EMT phenotype secreting over 100-fold more IL6 than parental cells. Recombinant IL6 or conditioned medium from high-IL6 secreting cells resulted in trastuzumab resistance in parental PTEN wild type cells expanding CSCs with EMT phenotype characterized by the CD44+/CD24- expression and EMT gene signature.

An IL6 receptor antibody interrupted this inflammatory feedback loop reducing the cancer stem cell population resulting in decreased tumor growth and metastasis in mouse xenographs. These studies have important clinical implications demonstrating that trastuzumab resistance may be mediated by an IL-6 inflammatory loop and suggest that blocking this loop represents a novel strategy to overcome trastuzumab resistance.

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Citation Format: April L. Davis, Hasan Korkaya, Maria Ouzounova, Fayaz Malik, Gwangil Kim, Ahmed A. Quraishi, Suling Liu, Shawn G. Clouthier, Max S. Wicha. IL6 feedback loop regulates breast cancer stem cells which mediate trastuzumab resistance. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3736. doi:10.1158/1538-7445.AM2013-3736

Abstract 913: Natural product sulforaphane selectively inhibits breast cancer stem cells in basal and trastuzumab resistant Her2+ breast cancer

The natural product sulforaphane (SF) has demonstrated efficacy against multiple forms of cancers and cancer stem cells. However, it is unclear what are the molecular targets for sulforaphane to inhibit breast cancer stem cells and how efficacy varies among four subtypes of breast cancers. In vitro assay showed that sulforaphane preferentially inhibited triple negative (TNBC) breast cancers, but did not show any efficacy to inhibit Her2+ breast cancer cells (even at >100 uM). However, when Her2+ breast cancer cells (with PTEN deletion) developed resistance to trastuzumab, sulforaphane showed more than 20-fold higher activity. Low concentration of sulforaphane (1 uM) also preferentially eliminates breast cancer stem cells from triple negative breast cancers. Her2+ breast cancer cells (with PTEN deletion and long term treatment of trastuzumab) induced resistance to trastuzumab and increase breast cancer stem cell populations by activating a positive feedback loop of IL-6 and NF-kB. Luciferase reporter assay and immunostaining showed that sulforaphane (1 uM) disrupted NF-kB translocation from cytosol to nucleus and inhibited its activity. Sulforaphane (1 uM) also inhibited endogenous IL-6 production by 50%. Sulforaphane (50 mg/kg, adjuvant therapy) reduced tumor formation rate by 70% and inhibit tumor volume by more than 90% of trastuzumab resistant Her2+ breast cancers in mouse fat pad. These data suggest that sulforaphane inhibits trastuzumab-resistant Her2+ breast cancers and breast cancer stem cells by disrupting NF-kB and IL6 positive feedback loop.

Citation Format: Joseph Burnett, Hasan Korkaya, Bryan Newman, Sarah Conley, Jamie Connarn, Lichao Sun, Hsiu-Fang Lee, Maria Ouzounova, Max Wicha, Duxin Sun. Natural product sulforaphane selectively inhibits breast cancer stem cells in basal and trastuzumab resistant Her2+ breast cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 913. doi:10.1158/1538-7445.AM2013-913

MicroRNA miR-30 family regulates non-attachment growth of breast cancer cells

BACKGROUND

A subset of breast cancer cells displays increased ability to self-renew and reproduce breast cancer heterogeneity. The characterization of these so-called putative breast tumor-initiating cells (BT-ICs) may open the road for novel therapeutic strategies. As microRNAs (miRNAs) control developmental programs in stem cells, BT-ICs may also rely on specific miRNA profiles for their sustained activity. To explore the notion that miRNAs may have a role in sustaining BT-ICs, we performed a comprehensive profiling of miRNA expression in a model of putative BT-ICs enriched by non-attachment growth conditions.

RESULTS

We found breast cancer cells grown under non-attachment conditions display a unique pattern of miRNA expression, highlighted by a marked low expression of miR-30 family members relative to parental cells. We further show that miR-30a regulates non-attachment growth. A target screening revealed that miR-30 family redundantly modulates the expression of apoptosis and proliferation-related genes. At least one of these targets, the anti-apoptotic protein AVEN, was able to partially revert the effect of miR-30a overexpression. Finally, overexpression of miR-30a in vivo was associated with reduced breast tumor progression.

CONCLUSIONS

miR30-family regulates the growth of breast cancer cells in non-attachment conditions. This is the first analysis of target prediction in a whole family of microRNAs potentially involved in survival of putative BT-ICs.

Epigenetic signatures in stem cells and cancer stem cells

The physiological properties of pluripotency in stem cells and the processes of cell specialization are governed by epigenetic mechanisms, as they are inheritable but not dependent on the cell genotype. There is cumulating evidence demonstrating the presence of cells with stem cell properties within tumors, suggesting that these cells are responsible for tumor growth and heterogeneity. As epigenetic control of self-renewal and pluripotency is a hallmark of stem cells, there is increased interest in studying similar epigenetic mechanisms governing these stemness properties in cancer stem cells. Here we will review the evidence supporting a role for epigenetic mechanisms in the induction of cancer stem cells, with an emphasis on the epigenetic regulatory networks involved in the establishment of normal self-renewal and pluripotency, and their potential deregulation in cancer. We will also discuss the data supporting the plasticity of these mechanisms and its potential therapeutic implications.