Epithelial-mesenchymal transition (EMT) is a critical process for embryogenesis but is abnormally activated during cancer metastasis and recurrence. This process enables epithelial cancer cells to acquire mobility and traits associated with stemness. It is unknown whether epithelial stem cells or epithelial cancer stem cells are able to undergo EMT, and what molecular mechanism regulates this process in these specific cell types. We found that Epithelial Ovarian Cancer Stem cells (EOC stem cells) are the source of metastatic progenitor cells through a differentiation process involving EMT and Mesenchymal-Epithelial Transition (MET). We demonstrate both in vivo and in vitro the differentiation of EOC stem cells into mesenchymal spheroid-forming cells (MSFCs) and their capacity to initiate an active carcinomatosis. Furthermore, we demonstrate that human EOC stem cells injected i.p in mice are able to form ovarian tumors, suggesting that the EOC stem cells have the ability to “home” to the ovaries and establish tumors. Most interestingly, we found that TWIST1 is constitutively degraded in EOC stem cells, and that the acquisition of TWIST1 requires additional signals that will trigger the differentiation process. These findings are relevant for understanding the differentiation and metastasis process in EOC stem cells.
Background: The high relapse rate in ovarian cancer patients is highly consistent with a cancer stem cell (CSC) model in which rare, inherently chemoresistant CSC are capable of proliferating and differentiating to cause disease. We recently demonstrated ovarian CSC (OvCSC) can be defined by Aldehyde Dehydrogenase (ALDH) enzymatic activity. ALDH expression is increased in chemotherapy resistant OvCSC and ALDH KO can reverse chemotherapy resistance. While ALDH inhibitors exist, they are not isoform specific. We therefore identified and screened numerous putative ALDH inhibitors, based on molecular homology to the known ALDH inhibitor DEAB, and assessed their impact on OvCSC. Methods and Results: While most ALDH inhibitors, including DEAB, had no impact on CSC, we identified a novel compound, 673A which specifically depletes OvCSC in vitro. Supporting functional depletion of OvCSC, treatment of primary tumor ascites resulted in 4-20 fold decrease tumor sphere formation. ALDH inhibition is highly synergistic with cisplatin both in vitro and in vivo as assessed by cell growth curves and tumor growth. Pre-treatment of tumor cells with 673 significantly reduced tumor in tumor initiation and growth rates. Unlike non-CSC depleting ALDH inhibitors, 673A is a pan-ALDH1A isoform specific inhibitor with IC50<230 nM for ALDH1A1, 1A2, and 1A3. OvCSC Caspase independent cell death was accompanied by negative Annexin V stain and HMB1 translocation to cytoplasm. IF demonstrated nuclear swelling and loss of DNA in a manner consistent with karyolysis and programmed cell necrosis. TEM of treated cells demonstrated clear cellular, nuclear, and organelle swelling and severe vacuolation of cytoplasm consistent with necrosis. Consistent with the induction of programmed cell necrosis, 673A treatment resulted in increased intracellular calcium. Furthermore, the intracellular calcium chelator BAPTA was able to rescue ALDH inhibition-induced necrosis. As RIP1 and RIP3 kinase activity is known to be a major mediator of necroptosis, we next assessed the impact of the RIP1 kinase inhibitor, Nec-1, and down-regulation of RIP1 and RIP3 by siRNA. Inhibition or depletion of RIP Kinase 1 did not prevent 673A mediated necroptosis of OvCSC. 673A initiates necroptotic cell death through translocation of RIPK3 downstream target, MLKL, to membrane and activation of mitochondria fission protein DRP1 and its translocation from cytoplasm to mitochondria. Conclusions: We have identified a novel ALDH inhibitor, 673A, which selective inhibits three ALDH1A isoforms. 673A mediated ALDH1A isoform inhibition triggers programmed cell necrosis of OvCSC. Our data suggest that pan ALDH1A1 targeted therapy this may be a powerful new therapeutic approach to target OvCSC and bypass their resistance to apoptosis inducing drugs. Future studies will elucidate the importance of mitochondria metabolic pathways (Glycolysis, OXPHOS, and TCA cycle) in ALDH inhibition-induced necroptosis. Citation Format: Ilana Chefetz-Menaker, Kun Yang, Ron Buckanovich. A novel ALDH1A selective inhibitor induces necroptosis in ovarian cancer stem-like cells. [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 3735.
Background: In normal tissues following injury, there is an expansion of tissue specific stem cells prior to their differentiation to initiate injury repair. Once the tissue is repaired, the stem cells return to a quiescent state. Tumor tissue, might follow similar characteristics as in normal tissues, but the control of the expansion process may be significantly altered. Recently, ovarian cancer stem cells (ovCSC) were isolated from ovarian cancer tissue and ascites using CD44/CK18 as markers. We hypothesize that these cells play a critical role in tumor repair and renewal. To test this hypothesis, we used an in vitro wound/healing system. Methods: Cells were plated in an Essen ImageLock plate and wounds were made using an Essen WoundMaker. This sytem allows the generation of consistent wound locations and widths and precise imaging of the wound area. The healing process is monitored using an insitu imaging system (IncuCyte, Essen Instruments, NH) that records and quantifies the repair process in real time. Levels of cancer stem cell markers, CD44, Oct-4, and β-catenin were determined by Western blot analysis or Real Time PCR. Levels of cytokines and chemokines were determined using Luminex Technology. Results: Initially we tested whether an in vitro wound/healing system can be used as a renewal model. Interestingly, ovCSCs showed a well coordinated and organized response to the wound. First, the cells created a “straight line” to replace the irregular edge of the wound. Afterwards, the cells proliferated towards the wound, repairing the wound until confluence was reached. Analysis of cancer stem cell markers by Western blot revealed that the cells which repaired the wound maintained CD44, CK18, Oct4, and β-catenin, previously shown as ovCSC markers. Additionally, the process of repair was characterized by significant and differential up-regulation in IL-6, GRO-α, and MCP-1 expression and secretion. Interestingly, the CD44 expression was increased in wounded wells when compared to control. Moreover, using specific primers for CD44 variant isoforms we found that wound healing promotes expression of different CD44 forms. Conclusions: In this study we demonstrate ovCSCs have the capacity to repair an in vitro wound and that this process is accompanied by increased CD44 expression and cytokine secretion. This increased capacity of self renewal can lead to the accumulation of a large pool of progenitor cells, which has the potential to individually spread to other areas of the body as metastatic cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4229.
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