Cancer Stem Cell Activity Research Articles

The WAVE3-YB1 interaction regulates cancer stem cells activity in breast cancer.

Resistance to therapy is the main cause of tumor recurrence and metastasis and cancer stem cells (CSCs) play a crucial role in this process, especially in triple-negative breast cancers (TNBCs). Unfortunately, no FDA-approved treatment is currently available for this subtype of BC, which explains the high rate of mortality in patients with TNBC tumors. WAVE3, a member of the WASP/WAVE actin-cytoskeleton remodeling family of protein, has been established as a major driver of tumor progression and metastasis of several solid tumors, including those originating in the breast. Our recently published studies found WAVE3 to mediate the process of chemoresistance in TNBCs. The molecular mechanisms whereby WAVE3 regulates chemoresistance in TNBC tumors remains largely unknown, as does the role of WAVE3 in CSC maintenance. Here we show that WAVE3 promotes CSC self-renewal and regulates transcription of CSC-specific genes, which, in part, provides a mechanistic explanation for the function of WAVE3 in chemoresistance in TNBCs. Our data show that WAVE3 is enriched in the CSC-subpopulation of TNBC cell lines. Knockout of WAVE3 via CRISPR/Cas9 significantly attenuates the CSC-subpopulation and inhibits transcription of CSC transcription factors. Mechanistically, we established a link between WAVE3 and the Y-box-binding protein-1 (YB1), a transcription factor and CSC-maintenance gene. Indeed, the interaction of WAVE3 with YB1 is required for YB1 translocation to the nucleus of cancer cells, and activation of transcription of CSC-specific genes. Our findings identify a new WAVE3/YB1 signaling axis that regulates the CSC-mediated resistance to therapy and opens a new therapeutic window for TNBCs treatment.

Glucose insult elicits hyperactivation of cancer stem cells through miR-424\u2013cdc42\u2013prdm14 signalling axis

Background:Meta-analysis shows that women with diabetes have a 20% increased risk of breast cancer and also an increased risk for distant metastasis and mortality. The molecular mechanisms for distant metastasis and mortality in breast cancer patients with diabetes are not very well understood.Methods:We compared the effect of physiological (5 mM) and diabetic (10 mM) levels of glucose on malignant breast epithelial cell invasion and stemness capabilities. We performed microRNA array to determine the dysregulated microRNAs in hyperglycaemic conditions and performed functional and molecular analysis of the gene targets.Results:Hyperglycaemia leads to hyperactivation of cancer stem cell pool and enhances invasive ability of breast cancer cells. MiR-424 seems to be a key regulator of cancer cell stemness and invasion. Knockdown of miR-424 in cancer cells under euglycaemic conditions leads to enhanced invasion and stem cell activity, whereas ectopic expression of miR-424 in cancer cells under hyperglycaemic conditions results in suppressed invasion and stem cell activity. Cdc42, a target of miR-424, influences cancer stem cell activity by positively regulating prdm14 through activation of pak1 (p-21-activated kinase 1) and stat5.Conclusions:Our findings establish miR-424→cdc42→prdm14 axis as a key molecular signalling cascade that might influence breast cancer progression in diabetic patients through hyperactivation of cancer stem cells.

Mitoketoscins: Novel mitochondrial inhibitors for targeting ketone metabolism in cancer stem cells (CSCs)

Previous studies have now well-established that epithelial cancer cells can utilize ketone bodies (3-hydroxybutyrate and aceto-acetate) as mitochondrial fuels, to actively promote tumor growth and metastatic dissemination. The two critical metabolic enzymes implicated in this process are OXCT1 and ACAT1, which are both mitochondrial proteins. Importantly, over-expression of OXCT1 or ACAT1 in human breast cancer cells is sufficient to genetically drive tumorigenesis and/or lung metastasis, validating that they indeed behave as metabolic “tumor promoters”. Here, we decided to target these two enzymes, which give cancer cells the ability to recycle ketone bodies into Acetyl-CoA and, therefore, to produce increased ATP. Briefly, we used computational chemistry (in silico drug design) to select a sub-set of potentially promising compounds that spatially fit within the active site of these enzymes, based on their known 3D crystal structures. These libraries of compounds were then phenotypically screened for their effects on total cellular ATP levels. Positive hits were further validated by metabolic flux analysis. Our results indicated that four of these compounds effectively inhibited mitochondrial oxygen consumption. Two of these compounds also induced a reactive glycolytic phenotype in cancer cells. Most importantly, using the mammosphere assay, we showed that these compounds can be used to functionally inhibit cancer stem cell (CSC) activity and propagation. Finally, our molecular modeling studies directly show how these novel compounds are predicted to bind to the active catalytic sites of OXCT1 and ACAT1, within their Coenzyme A binding site. As such, we speculate that these mitochondrial inhibitors are partially mimicking the structure of Coenzyme A. Thus, we conclude that OXCT1 and ACAT1 are important new therapeutic targets for further drug development and optimization. We propose that this new class of drugs should be termed “mitoketoscins”, to reflect that they were designed to target ketone re-utilization and mitochondrial function.

Improved Killing of Ovarian Cancer Stem Cells by Combining a Novel Chimeric Antigen Receptor-Based Immunotherapy and Chemotherapy.

Ovarian cancer represents the most lethal gynecological cancer. Although cytoreductive chemotherapy and surgery lead to complete macroscopic tumor removal, most of the patients in advanced stages suffer from recurrent disease and subsequently die. This may be explained by the activity of cancer stem cells (CSC), which are a subpopulation of cells with an elevated chemoresistance and an increased capacity for self-renewal and metastatic spread. Specifically targeting these cells by adoptive immunotherapy represents a promising strategy to reduce the risk for recurrent disease. This study selected the widely accepted CSC marker CD133 as a target for a chimeric antigen receptor (CAR)-based immunotherapeutic approach to treat ovarian cancer. A lentiviral vector was generated encoding a third-generation anti-CD133-CAR, and clinically used NK92 cells were transduced. These engineered natural killer (NK) cells showed specific killing against CD133-positive ovarian cancer cell lines and primary ovarian cancer cells cultured from sequential ascites harvests. Additionally, specific activation of these engineered NK cells was demonstrated via interferon-gamma secretion assays. To improve clinical efficacy of ovarian cancer treatment, the effect of the chemotherapeutic agent cisplatin was evaluated together with CAR-transduced NK cell treatment. It was demonstrated that NK cells remain cytotoxic and active under cisplatin treatment and, importantly, that sequential treatment with cisplatin followed by CAR-NK cells led to the strongest killing effect. The specific eradication of ovarian CSCs by anti-CD133-CAR expressing NK92 cells represents a promising strategy and, when confirmed in vivo, shall be the basis of future clinical studies with the aim to prevent recurrent disease.

MiR-150 enhances apoptotic and anti-tumor effects of paclitaxel in paclitaxel-resistant ovarian cancer cells by targeting Notch3.

Tumor recurrence by obtaining chemoresistance is a major obstacle to treating ovarian cancer. By TargetScan database and a luciferase reporter assay, we identified miR-150 directly targets Notch3, which is a key oncogene in ovarian cancer. We, therefore, investigated the role of miR-150 in ovarian cancer cells, and the usefulness of miR-150 as a therapeutic target in chemoresistant ovarian cancer, through examining miR-150 expression by qRT-PCR in ovarian cancer cell lines and tissues, and assessing the gain-of-function effect by WST, colony forming, TUNEL, wound healing and angiogenesis assays. Western blotting was performed to evaluate its downstream targets.The miR-150 expression was significantly downregulated in ovarian cancers. Treatment with pre-miR-150 significantly inhibited cancer cell proliferation, and induced apoptosis in PTX (paclitaxel) -resistant SKpac cells, which was not seen by PTX only treatment. On spheroid forming assay, an additional pre-miR-150 treatment with PTX decreased cancer stem cell activation in PTX-resistant SKpac cells. An experimental upregulation of miR-150 also decreased cancer cell migration and angiogenesis in SKpac cells. The Notch3 downstream proteins(NICD3 and HEY2), and cell cycle-related proteins (cyclinD3, pS6, and NF-kB), and apoptosis-related proteins (BCL-2 and BCL-W) were significantly downregulated by pre-miR-150 transfection.Taken together, miR-150 is related with PTX-resistance in ovarian cancer, and treatment with pre-miR-150 resensitizes cancer cells to PTX. Therefore, it may be a promising treatment strategy in chemoresistant and recurrent ovarian cancer.

Targeting the cancer stem cell marker, aldehyde dehydrogenase 1, to circumvent cisplatin resistance in NSCLC.

Non-small cell lung cancer (NSCLC) accounts for a large proportion of cancer deaths and is characterized by low treatment response rates and poor overall prognosis. In the absence of specific treatable mutations, cisplatin-based chemotherapy plays an important role in the treatment of this disease. Unfortunately, the development of resistance has become a major therapeutic challenge in the use of this cytotoxic drug. Elucidating the mechanisms underlying this resistance phenotype, may result in the development of novel agents that enhance sensitivity to cisplatin in lung cancer patients. In this study, targeting the cancer stem cell activity of aldehyde dehydrogenase 1 (ALDH1) was investigated as a strategy to overcome chemoresistance in NSCLC. Tumors from NSCLC patients showed an increase in their profile of pluripotent stemness genes. Cisplatin exposure induced the emergence or expansion of an ALDH1-positive subpopulation in cisplatin sensitive and resistant NSCLC cell lines, respectively, further enhancing cisplatin resistance. Using the Aldefluor assay and FACS analysis, ALDH1 subpopulations were isolated and evaluated in terms of stem cell characteristics. Only ALDH1-positive cells exhibited asymmetric division, cisplatin resistance and increased expression of stem cell factors in vitro. Xenograft studies in NOD/SCID mice demonstrated efficient tumorigenesis from low cell numbers of ALDH1-positive and ALDH1-negative subpopulations. Targeting ALDH1 with Diethylaminobenzaldehyde (DEAB) and Disulfiram, significantly re-sensitized resistant lung cancer cells to the cytotoxic effects of cisplatin. Our data demonstrate the existence of a lung CSC population and suggest a role for targeting ALDH1 as a potential therapeutic strategy in re-sensitizing NSCLC cells to the cytotoxic effects of cisplatin.

Tissue Elasticity Bridges Cancer Stem Cells to the Tumor Microenvironment Through microRNAs: Implications for a "Watch-and-Wait" Approach to Cancer.

Targeting the tumor microenvironment (TME) through which cancer stem cells (CSCs) crosstalk for cancer initiation and progression, may open new treatments different from those centered on the original hallmarks of cancer genetics thereby implying a new approach for suppression of TME driven activation of CSCs. Cancer is dynamic, heterogeneous, evolving with the TME and can be influenced by tissue-specific elasticity. One of the mediators and modulators of the crosstalk between CSCs and mechanical forces is miRNA, which can be developmentally regulated, in a tissue- and cellspecific manner. Here, based on our previous data, we provide a framework through which such gene expression changes in response to external mechanical forces can be understood during cancer progression. Recognizing the ways mechanical forces regulate and affect intracellular signals with applications in cancer stem cell biology. Such TME-targeted pathways shed new light on strategies for attacking cancer stem cells with fewer side effects than traditional gene-based treatments for cancer, requiring a "watchand- wait" approach. We attempt to address both normal brain microenvironment and tumor microenvironment as both works together, intertwining in pathology and physiology - a balance that needs to be maintained for the "watch-and-wait" approach to cancer. This review connected the subjects of tissue elasticity, tumor microenvironment, epigenetic of miRNAs, and stem-cell biology that are very relevant in cancer research and therapy. It attempts to unify apparently separate entities in a complex biological web, network, and system in a realistic and practical manner, i.e., to bridge basic research with clinical application.

MiR-500a-3p promotes cancer stem cells properties via STAT3 pathway in human hepatocellular carcinoma

BackgroundmiR-500a-3p has been demonstrated to be involved in the development, progression and metastasis in several human cancers. Constitutive activation of JAK/STAT3 signaling pathway has been reported to play an important role in the development and progression of hepatocellular carcinoma (HCC).The purpose of this study was to determine the biological roles and clinical significance of miR-500a-3p in HCC and to identify whether miR-500a-3p has an effect on the activity of JAK/STAT3 signaling in HCC.MethodsmiR-500a-3p expression was examined by real-time PCR in 8 paired HCC tissues and individual 120 HCC tissues respectively. Statistical analysis was performed to explore the clinical correlation between miR-500a-3p expression and clinicopathological features and overall and relapse-free survival in HCC patients. In vitro and in vivo assays were performed to investigate the biological roles of miR-500a-3p in HCC. The bioinformatics analysis, real-time PCR, western blot and luciferase reporter assay were performed to discern and examine the relationship between miR-500a-3p and its potential targets. Clinical correlation of miR-500a-3p with its targets was examined in HCC tissues.ResultsmiR-500a-3p is dramatically elevated in HCC tissues and cells and high expression of miR-500a-3p correlates with poor overall and relapse-free survival in HCC patients. Upregulating miR-500a-3p enhances, while silencing miR-500a-3p suppresses, the spheroid formation ability, fraction of side population and expression of cancer stem cell factors in vitro and tumorigenicity in vivo in HCC cells. Our findings further reveal miR-500a-3p promotes the cancer stem cell characteristics via targeting multiple negative regulators of JAK/STAT3 signaling pathway, including SOCS2, SOCS4 and PTPN11, leading to constitutive activation of STAT3 signaling. Moreover, the inhibitory effects of anti-miR-500a-3p on cancer stem cell phenotypes and activity of STAT3 signaling were reversed by silencing SOCS2, SOCS4 and PTPN11 in miR-500a-3p-downexpressing cells, respectively. Clinical correlation of miR-500a-3p with the targets was examined in human HCC tissues.Conclusionour results uncover a novel mechanism by which miR-500a-3p promotes the stemness maintenance of cancer stem cell in HCC, suggesting that silencing miR-500a-3p may serve as a new therapeutic strategy in the treatment of hepatocellular carcinoma.

PKC-δ attenuates the cancer stem cell among squamous cell carcinoma cells through down-regulating p63

Protein kinase C delta (PKC-δ) has been identified as a tumor suppressor. However, the effects of PKC-δ on the cancer stem cells in squamous cell carcinomas (SCC) have not been clarified. The purpose of this study was to detect the regulation of PKC-δ on cancer stem cell among SSC cells and the role of p63 during the regulation.Immunohistochemistry of human cutaneous SCC tissues was performed to detect the expression of PKC-δ. After the human SCC13 cells infected by recombinant adenoviruses, the cell proliferation were determined. The correlation of PKC-δ and p63 was detected by western blot. The colony forming activity and the number of cancer stem cells (CSCs) in SCC identified by double-staining with anti-integrin α6 and anti-CD71 antibodies were detected.The expression of PKC-δ was obviously decreased in SCC tissues compared with that in normal skin tissues. The higher protein level of p63 in SCC was attenuated by the transfection of PKC-δ. The higher proliferation capacity of SCC13 cells, the higher activity and expression of CSCs in SCC13 cells induced by p63 were significantly suppressed by the transfection of PKC-δ.In conclusion, PKC-δ played as a protective role in SCC partly by down-regulating p63, leading to the suppression of SCC cell proliferation, attenuation of the activity and expression of CSCs in SCC cells.

Cross talk between progesterone receptors and retinoic acid receptors in regulation of cytokeratin 5-positive breast cancer cells.

Half of estrogen receptor-positive breast cancers contain a subpopulation of cytokeratin 5 (CK5)-expressing cells that are therapy resistant and exhibit increased cancer stem cell (CSC) properties. We and others have demonstrated that progesterone (P4) increases CK5+ breast cancer cells. We previously discovered that retinoids block P4 induction of CK5+ cells. Here we investigated the mechanisms by which progesterone receptors (PR) and retinoic acid receptors (RAR) regulate CK5 expression and breast CSC activity. After P4 treatment, sorted CK5+ compared to CK5- cells were more tumorigenic in vivo. In vitro, P4-treated breast cancer cells formed larger mammospheres and silencing of CK5 using small hairpin RNA abolished this P4-dependent increase in mammosphere size. Retinoic acid (RA) treatment blocked the P4 increase in CK5+ cells and prevented the P4 increase in mammosphere size. Dual small interfering RNA (siRNA) silencing of RARα and RARγ reversed RA blockade of P4-induced CK5. Using promoter deletion analysis, we identified a region 1.1 kb upstream of the CK5 transcriptional start site that is necessary for P4 activation and contains a putative progesterone response element (PRE). We confirmed by chromatin immunoprecipitation that P4 recruits PR to the CK5 promoter near the -1.1 kb essential PRE, and also to a proximal region near -130 bp that contains PRE half-sites and a RA response element (RARE). RA induced loss of PR binding only at the proximal site. Interestingly, RARα was recruited to the -1.1 kb PRE and the -130 bp PRE/RARE regions with P4, but not RA alone or RA plus P4. Treatment of breast cancer xenografts in vivo with the retinoid fenretinide reduced the accumulation of CK5+ cells during estrogen depletion. This reduction, together with the inhibition of CK5+ cell expansion through RAR/PR cross talk, may explain the efficacy of retinoids in prevention of some breast cancer recurrences.

Expression of phosphatidylinositol 3 kinase/protein kinase B signaling pathway in bladder cancer cells and its relationship with cancer stem cells

Objective To examine the expression of phosphatidylinositol 3 kinase (PI3K)/protein kinase B (Akt) signaling pathway in bladder cancer cells, and demonstrate relationship with cancer stem cells. Methods The expression of PI3K, phosphorylated protein kinase B (p-Akt) in bladder cancer cells was detected by reverse transcription-polymeric chain reaction (RT-PCR) and Western blotting. Double immunofluorescence analysis was applied to detect the expression of CD133, the Co-expression of p-Akt and CD133. CD133 is one of surface marker of bladder cancer stem cells. Results We detected a strong up-regulation of PI3K, p-Akt (PI3K protein: 1.05±0.03, p-Akt protein: 1.21±0.04, PI3K mRNA: 0.68±0.03) in bladder cancer tissue samples compared to normal bladder tissues (PI3K protein: 0.68±0.04, p-Akt protein: 0.71±0.02, PI3K mRNA: 0.42±0.02) by Western blot and RT-PCR approaches. We also detected a strong Co-expression of p-Akt and CD133 in bladder cancer tissue samples. Conclusion The expression of PI3K/Akt signaling pathway is up-regulation in bladder cancer tissues, and the expression of CD133 and p-Akt was co-expressed, suggesting that the activation and differentiation of bladder cancer stem cells could be inhibited by interference with PI3K/Akt signaling pathway to prevent the occurrence and development of bladder cancer. Key words: Bladder cancer; Bladder cancer stem cell; Phosphatidylinositol 3 kinase/protein kinase B signaling pathway

Abstract 4763: Metronomic chemotherapy prevents therapy-induced stromal activation and induction of cancer stem cells

Abstract Whilst traditional chemotherapy kills a fraction of tumor cells, it also activates the stroma and can promote the growth and survival of residual cancer cells to foster tumor recurrence and metastasis. Accordingly, overcoming the host response induced by chemotherapy could substantially improve therapeutic outcome and patient survival. Treatment resistance and metastasis have been attributed to expansion of cancer stem-like cells (CSCs). Molecular analysis of the tumor stroma in neoadjuvant chemotherapy-treated human desmoplastic cancers and orthotopic tumor xenografts revealed that traditional maximal tolerated dose chemotherapy, regardless of the agents used, induces persistent STAT-1 and NF-κB activity in carcinoma-associated fibroblasts that induces the expression and secretion of ELR-motif-positive (ELR+) chemokines, which signal through CXCR-2 on carcinoma cells to trigger their phenotypic conversion into CSCs and promote their invasive behaviors, leading to paradoxical tumor aggression following the therapy. By contrast, the same total accumulated dose administered as a low-dose-metronomic chemotherapy regimen largely prevented the therapy-induced stromal ELR+-chemokine paracrine signaling for CSCs, thereby substantially enhancing treatment response and extending survival of mice carrying desmoplastic cancers (Chan et al, J. Exp. Med. 2016). These studies illustrate the importance of stroma in cancer therapy and how its impact on treatment resistance could be tempered by altering the dosing schedule of systemic chemotherapy. Note: This abstract was not presented at the meeting. Citation Format: Kelvin K. Tsai, Tze-Sian Chan, Chung-Chi Hsu, Vincent C. Pai, Shenq-Shyang Huang, Valerie M. Weaver. Metronomic chemotherapy prevents therapy-induced stromal activation and induction of cancer stem cells [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 4763. doi:10.1158/1538-7445.AM2017-4763

Abstract 4779: Targeting the CCL20-CCR6 axis as a novel opportunity to stimulataneously modulate cancer stem cells and the tumor-immune infiltrate by a dual anti-cancer mechanism

Abstract Drugs that target cancer stem cells (CSCs) are thought to be a critical component of any successful therapy against cancer. CSCs are responsible for chemoresistance, metastasis, and ultimately relapse of the cancer, even after an initial successful therapeutic intervention. While it is well known that CSCs are driven by some of the same major self-renewal pathways that drive embryonic stem cells, knowledge of other cellular pathways that drive CSC activity is still limited. In this work, we uncover a novel role for chemokine (C-C motif) ligand 20 (CCL20) in CSC growth and activity, expanding the role for this chemoattractant protein. We discovered that CSCs of many tumor types overexpress CCL20, which we show drives CSC self-renewal and proliferation by autocrine signaling through its receptor CCR6. Targeting this axis with a neutralizing monoclonal antibody against CCL20 significantly reduces CSC frequency and tumor initiation and growth, supporting the novel therapeutic potential of targeting the CCL20-CCR6 axis as a strategy to eliminate CSCs. Furthermore, we found that CCL20 secreted by tumor cells also strongly influences the frequencies not only of T-cells, particularly immune-suppressive regulatory T-cells (Treg) and Th17 populations, but also dendritic and neutrophil/gMDSC populations, to promote anti-tumor immunity that leads to immune-mediated inhibition of tumor growth. Strikingly, we discovered that tumor-specific CCL20 impacted not just the immune cell balance within the tumor microenvironment, but had far reaching effects into the peripheral immune system as well. Thus, our overall findings propose that CCL20 plays a dual role in the tumor environment: 1) by driving activity and tumorigenic ability of CSCs, and 2) by promoting an immunosuppressive phenotype. In this work we show that therapeutic neutralization of CCL20 can deliver a one-two punch against cancer, by directly inhibiting CSCs, and by relieving immunosuppression, thereby opening this target up as an exciting novel strategy to treat cancer. Citation Format: Lilian E. van Vlerken-Ysla, Jonathan Rios-Doria, James Moynihan, Lu Shan, Robert E. Hollingsworth, Ronald Herbst, Elaine M. Hurt. Targeting the CCL20-CCR6 axis as a novel opportunity to stimulataneously modulate cancer stem cells and the tumor-immune infiltrate by a dual anti-cancer mechanism [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 4779. doi:10.1158/1538-7445.AM2017-4779

Abstract 3901: Therapeutic targeting of C-terminal binding protein: a key dependency for polyposis and cancer stem cell activity in APC mutant neoplasia

Abstract The C terminal binding proteins (CtBP) 1 and 2 are a family of transcriptional co-repressors overexpressed in a variety of cancers, and are frequently associated with poor prognosis and chemoresistance. CtBP has also been characterized in cell culture models as drivers of migration/invasion and epithelial-mesenchymal transition. CtBP mediates its transcriptional corepressor activity via its dehydrogenase domain, and inhibition of this domain interferes with CtBP oncogenic functions. The role of CtBP in APC mutant neoplasia remains obscure even though APC is responsible for degradation of both β-catenin and CtBP in suppressing colorectal tumorigenesis. Our prior work demonstrates that CtBP proteins can be effectively therapeutically targeted with substrate analogues of their intrinsic dehydrogenase domains. We now observe that pharmacologic inhibition of CtBP using either the 1st generation inhibitor 2-keto-4-methylthiobutyrate (MTOB) or the 2nd generation inhibitor hydroxyimino-3-phenylpropanoic acid (HIPP) significantly reduces the burden of intestinal polyps in the Apcmin mouse model of the human cancer predisposition syndrome Familial Adenomatous Polyposis. The number of intestinal polyps in mice with CtBP2 inhibitors were significantly lower (21 polyps/mouse for MTOB, 15 polyps/mouse for HIPP) as compared with vehicle treated mice (45 polyps/mouse) with a P value <0.0001. Pointing to the anti-neoplastic mechanism of MTOB and HIPP, polyps that did grow in MTOB or HIPP treated mice demonstrated robust downregulation of β catenin and Ctbp2 proteins. This observation points to the role of Ctbp2 as a putative driver oncogene that can be therapeutically targeted in vivo. In addition, CtBP2 has been reported to play an important role in human colon cancer stem cells via its interaction with the transcription factor TCF4 on chromatin. We now show that inhibiting CtBP with HIPP or HIPP analogues attenuates CtBP2 protein levels in colon cancer stem cells with resultant decreased expression of CtBP transcriptional target genes, such as the motility/invasion regulator TIAM1, and c-MYC, a known driver of the cancer stem cell phenotype. Moreover, colonospheres treated with CtBP inhibitor showed downregulation of cancer stem cell markers CD133 and c-MYC, as compared with vehicle treatment. Flow cytometry analysis of intestinal epithelium from Apcmin mice treated with CtBP inhibitor vs. vehicle indicated a significant reduction in CD133+/CXCR4+ cells that are associated with a tumor initiating cell phenotype. Our data demonstrate that CtBP inhibition may reduce colon neoplasia via downregulation of c-MYC and the cancer stem cell/tumor initiating cell compartment, and that CtBP is a promising and novel target for therapy in colon cancer. Citation Format: Ayesha T. Chawla, Agnes Cororaton, Rashmi Seth, Barbara Szomju, Evan T. Sumner, Steven R. Grossman. Therapeutic targeting of C-terminal binding protein: a key dependency for polyposis and cancer stem cell activity in APC mutant neoplasia [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 3901. doi:10.1158/1538-7445.AM2017-3901

Abstract 1924: Caveolin-1 inhibits mammary carcinogenesis via suppressing c-myc-induced metabolism reprogramming in breast cancer stem cells

Abstract Purpose: Caveolin-1(CAV1), a membrane constituent protein, exhibits tumor suppressor activities in multiple malignancies, whereas the underlying mechanisms remain unclear. The current study aimed to determine the significance of CAV-1 in regulating cancer metabolism and its relation to breast cancer stem cells (CSCs). Experimental Design: The anti-carcinogenic function of CAV1 was evaluated by in vitro cell model, CAV1 knockout mice and MMTV-PyMT spontaneous breast cancer xenografts. Glycolysis activity and mitochondrial metabolism were assessed by immunoblotting, oxygen consumption and mitotacker staining analysis. Mammosphere formation, tumorigenic ability, reattachment differentiation and signaling pathway analysis were applied to study the regulation effects of CAV1 on breast CSCs. The clinical significance of CAV1 was also analyzed by human tissue microarray. Results: In both mammary transformed cells and spontaneous breast cancer xenografts, CAV1 is found significantly downregulated and positively correlated to increased glycolysis activity and impaired mitochondrial metabolism. Cav1 knockout results in increased ductal hyperplasia, associating with increased stem cell population and glycolysis metabolism. Breast CSCs exhibits glycolytic phenotype and decreased CAV1 expression compared to normal mammary stem cells, and CAV1 overexpression significantly limits CSCs’ self-renewal via inhibiting c-myc induced glycolysis. Clinical investigation suggests that high CAV1 expression is revealed with better overall survival and decreased CSCs population. Conclusions: CAV1 loss facilitates mammary carcinogenesis via enhancing glycolytic activity in breast CSCs, and CAV1 based therapy might become a novel strategy for breast cancer prevention. Note: This abstract was not presented at the meeting. Citation Format: Zhiyu Wang, Neng Wang, Shengqi Wang, Yifeng Zheng. Caveolin-1 inhibits mammary carcinogenesis via suppressing c-myc-induced metabolism reprogramming in breast cancer stem cells [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 1924. doi:10.1158/1538-7445.AM2017-1924

Abstract 691: DFMO synergizes with BET inhibitors targeting ODC and MYCN to impede neuroblastoma cell proliferation and tumor initiation

Abstract Background: Neuroblastoma (NB) is the most common extracranial solid pediatric tumor and is associated with MYCN amplification. MYCN is a regulator of ornithine decarboxylase (ODC), the rate-limiting enzyme of polyamine biosynthesis. Inhibition of this pathway in MYCN-amplified NB tumors has been shown to be a target for treatment. Alpha-difluoromethylornithine (DFMO) inhibits ODC and is currently being used in a Phase II clinical trial for NB. BET inhibitors JQ1 and OTX-015 have been shown to be effective against MYCN-amplified cancers; it is hypothesized that they downregulate MYCN as well as cancer stem cell (CSC) signaling. We propose that inhibiting MYCN with a BET inhibitor, coupled with inhibition of ODC with DFMO, will result in enhanced inhibition of NB growth and tumor-initiating properties. Methods: Single and combination drug treatments were conducted on BE(2)-C, SMS-KCNR, CHLA90, and one patient-derived cell line. CellTiter-Glo Luminescent Cell Viability Assay was used to determine cell viability in 96-well plates. IC50 values were calculated with a four-parameter variable-slope dose response curve using GraphPad Prism v.5 software. Drug combination studies were conducted in MYCN amplified tumors BE(2)-C and SMS-KCNR using ray designs to evaluate for synergism. IncuCyte ZOOM Live-Cell Imaging system was used for kinetic monitoring of cytotoxicity and apoptosis in NB cells. Western blots measured protein levels of apoptosis markers (cleaved caspase 3 and cleaved PARP) and CSC markers (Nanog, Sox2, NF-kB, CXCR4, Lin28B, and MYCN). Neurosphere assays were used to evaluate tumor initiation via sphere formation. Results: Cell viability of MYCN amplified NB showed an IC50 range of 1.48-1.69 μM for JQ1 and 839.3 nM-2.36 μM for OTX-015; MYCN non-amplified NB showed an IC50 range of 4.22-11.58 μM for JQ1 and 2.99-11.03 uM for OTX-015. Combination treatment in MYCN NB had a synergistic effect, based on Loewe-additivity as the null hypothesis, for cell viability suppression by ray design experiments for BE(2)-C and SMS-KCNR. Western blots showed greater expression of apoptosis markers and decreased expression of CSC markers in combination relative to single drug treatments. A greater than 50% decrease in neurosphere formation with combination treatment in BE(2)-C, SMS-KCNR, and the patient cell line provides evidence for reduced CSC activity. IncuCyte imaging showed an increase in cell death with time post-treatment. Conclusion: The combination of DFMO with BET inhibitors has a synergistic effect in treating MYCN amplified NBs as shown by a decrease in cell viability. This combination targets CSC pathways and decreases tumor-initiating ability. Given the lack of effective treatment options for children with relapsed or refractory high-risk NB, this combination may be a promising novel therapy. Citation Format: Sarah DeCou, Ping Zhao, Tracey Avequin, Abhinav Nagulapally, Jeffrey Bond, Giselle Saulnier Sholler. DFMO synergizes with BET inhibitors targeting ODC and MYCN to impede neuroblastoma cell proliferation and tumor initiation [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 691. doi:10.1158/1538-7445.AM2017-691

Abstract 3899: Synthetic small molecule targeting CD24-/CD44+/ALDH+ cell population inhibits cancer stem cell activities in breast cancer

Abstract Purpose of the study: Cancer stem cells (CSCs) have been described as the “seed of tumor”, and have been suggested as the driving force of tumor relapses. In this study we aimed to isolate small molecules via screening of the combinatorial chemical library. The isolated molecules bind CD24-/CD44+/ALDH+ breast cancer cell subpopulation with high selectivity and specificity. Experimental design and plan: Through the unbiased cell based chemical library screening, we identified compound candidates that specifically bind the stem-like cancer cell subpopulations in breast cancer cells and tissues. By performing in vitro, tissue and in vivo-based assessments on ligand-binding specificity and functional activities, we ensured that the isolated ligands target tumorigenic stem-like breast cell or tissue preferentially. Summary of discoveries and findings: The in vitro compound binding validations proved the specificity of the isolated compound candidates toward breast cancer cells and tissues displaying cancer stem cell properties. The compound-targeting cell populations display significantly-higher expressions of the well-known stem cell markers than the unbound cell populations. On the other hand, a series of biological and biochemical functional assays also confirmed the compound candidates exert tumor-suppression activities on breast cancer cell lines, such as slow down proliferation and reduce cell viability. More importantly, our study demonstrated that both isolated compounds have preferential selectivity and higher binding affinity to the TNBC cells and tissues, which have been reported for higher percentage of stem-like cancer cell population detected than in non-TNBC cells or tissues. Through mouse xenograft study followed by histological analysis, we further confirmed the binding specificity of the compound towards cell line models could be retained in vivo in mouse xenograft model. Conclusion: We demonstrated our ligand screening technique is able to identify synthetic compounds targeting cell subgroups or sub-populations of defined interest within one particular type of tumor. High specificity of the isolated molecules could be utilized to develop chemical probes for quantification of percentage of CSC in the tumor, which facilitates clinical evaluation of tumor relapse risk. The screening strategy also provides a new methodology in discovering novel drug targeting CSC subpopulations, not only in breast tumor, but also other types of human cancers. Funding: This project is supported by the Cancer Prevention and Research Institute of Texas (CPRIT) grant, award ID: RP150713. Citation Format: Luxi Chen, Chao Long, Kha A. Tran, Jiyong Lee. Synthetic small molecule targeting CD24-/CD44+/ALDH+ cell population inhibits cancer stem cell activities in breast cancer [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 3899. doi:10.1158/1538-7445.AM2017-3899

Abstract 5909: Microfluidic vertical adhesion-suspension co-culture platform for studying cancer stem cell-fibroblast interactions

Abstract Considerable evidence suggests that cancer-stem-cells (CSCs) play critical roles in tumorigenesis and metastasis .Although surface marker expression or enzymatic activity of CSC has proven useful, variability of expression highlights the need for the development of high throughput functional CSC assays. One such approach utilizes the capability of CSC’s to form single-cell-derived spheres in suspension environments (functional CSCs). Microfluidic tools are suitable for handling and monitoring a large number of single cells in suspension as well as for examining the interaction of these cells with those in the tumor micro-environment including cancer associated fibroblasts (CAF’s).In order to accomplish this, we have developed a high-throughput (10,000-well), simple-to-use, vertical platform for CSC/CAF co-culture. The platform consists of a non-adherent substrate having 10,000 micro wells for single-cell-derived sphere formation and a porous trans well for CAF adherent co-culture. As predicted by Poisson’s distribution, approximately 30% of micro wells capture single cells when T47D breast cancer cells are loaded at a concentration of 200k/ml. After cell seeding, trans wells containing CAFs are placed onto the substrate. 0.4µm pores on the trans well allow for secretion-based cellular interaction while preventing direct CSC/CAF cell contact. This cell separation facilitates sample cell retrieval without cell cross contamination. Utilizing this device, we determined that co-culture of tumor cells with CAF’s doubled the frequency of sphere formation. Spheres derived from individual CSCs were then retrieved and dissociated for single-cell transcriptome analysis utilizing RNA barcoding followed by RNAseq. Molecular analysis revealed significant cellular heterogeneity among sphere derived cells. In addition, principal component analysis of single cell RNAseq, reveled significant differences in gene expression between mono-cultured and CAF co-cultured cells isolated from tumor spheres. These genes represent potential therapeutic targets for interfering with CSC stromal cell interactions in the tumor microenvironment. The vertical adhesion suspension co-culture platform provides a system to identify and evaluate novel CSC targeted therapeutics. Citation Format: Yu-Chih Chen, Zhixiong Zhang, Yu-Heng Cheng, Euisik Yoon, Max S. Wicha. Microfluidic vertical adhesion-suspension co-culture platform for studying cancer stem cell-fibroblast interactions [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 5909. doi:10.1158/1538-7445.AM2017-5909

Abstract AP21: LIPID DESATURATION IS A METABOLIC MARKER AND THERAPEUTIC TARGET OF OVARIAN CANCER STEM CELLS

Abstract OBJECTIVES: Lack of sensitive single-cell analysis tools has limited the characterization of the metabolic activity of cancer stem cells (CSCs). The objectives of this study were to identify and target metabolic pathways specifically deregulated in ovarian CSCs. METHODS: We developed a new technique based on hyperspectral stimulated Raman scattering imaging of single living cells coupled with electrospray ionization mass spectrometry (ESI-MS) analysis of extracted lipids to identify unique metabolic spectra of ovarian CSCs. SiRNA knockdown and pharmacological inhibitors were used to block fatty acid desaturases and to measure effects on the ovarian CSCs charcateristics. RESULTS: We report significantly increased levels of unsaturated lipids in flow-sorted ovarian CSCs (ALDH+CD133+) compared to non-CSCs (ALDH-CD133-). Higher lipid unsaturation levels were also detected in CSC-enriched spheroids compared to monolayer cultures of ovarian cancer cell lines or primary cells derived from human ovarian tumors. ESI-MS identified that the elevated unsaturation in lipid droplets involved an enhanced conversion from saturated fatty acids (18:0) to unsaturated fatty acids (18:1). Expression of fatty acid desaturases was increased in ovarian CSCs compared to non-CSCs. Pharmacological inhibition or siRNA knockdown of lipid desaturases Δ9 (SCD1) or Δ6 effectively eliminated CSCs, suppressed sphere formation in vitro, and blocked tumor initiation capacity in vivo, as measured by a tumor initiation dilution assay. Mechanistically, the lipid desaturase inhibitors suppressed ovarian cancer cell stemness by blocking the NF-κB survival pathway. Chromatin immunoprecipitation and overexpression of RelA demonstrated that NF-κB transcriptionally regulates SCD1 expression. Collectively, our data suggest that a positive feedback loop involving lipid desaturases, NF-κB, and the stem cell marker ALDH1 can be effectively blocked by SCD1 inhibitors, suppressing ovarian CSCs. CONCLUSIONS: These results demonstrate that increased lipid unsaturation is a novel metabolic marker for ovarian CSCs and a target for CSC-specific therapy. Citation Format: Junjie Li, Salvatore Condello, Jessica Thomes-Pepin, Xiaoxiao Ma, Yu Xia, Thomas D. Hurley, Ji-Xin Cheng, Daniela Matei. LIPID DESATURATION IS A METABOLIC MARKER AND THERAPEUTIC TARGET OF OVARIAN CANCER STEM CELLS [abstract]. In: Proceedings of the 11th Biennial Ovarian Cancer Research Symposium; Sep 12-13, 2016; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(11 Suppl):Abstract nr AP21.

Therapeutic PEG-ceramide nanomicelles synergize with salinomycin to target both liver cancer cells and cancer stem cells.

Salinomycin (SAL)-loaded PEG-ceramide nanomicelles (SCM) were prepared to target both liver cancer cells and cancer stem cells. The synergistic ratio of SAL/PEG-ceramide was evaluated to prepare SCM, and the antitumor activity of SCM was examined both in vitro and in vivo. SAL/PEG-ceramide molar ratio of 1:4 was chosen as the synergistic ratio, and SCM showed superior cytotoxic effect and increased apoptosis-inducing activity in both liver cancer cells and cancer stem cells. In vivo, SCM showed the best tumor inhibitory effect with a safety profile. Thus, PEG-ceramide nanomicelles could serve as an effective and safe therapeutic drug carrier to deliver SAL into liver cancer, opening up the avenue of using PEG-ceramide as therapeutic drug carriers.