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      EMT, CTCs and CSCs in tumor relapse and drug-resistance

      1 , 2 , 1

      Oncotarget

      Impact Journals LLC

      tumor relapse, CTCs, CSCs, EMT, clinical trials

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          Abstract

          Tumor relapse and metastasis are the primary causes of poor survival rates in patients with advanced cancer despite successful resection or chemotherapeutic treatment. A primary cause of relapse and metastasis is the persistence of cancer stem cells (CSCs), which are highly resistant to chemotherapy. Although highly efficacious drugs suppressing several subpopulations of CSCs in various tissue-specific cancers are available, recurrence is still common in patients. To find more suitable therapy for relapse, the mechanisms underlying metastasis and drug-resistance associated with relapse-initiating CSCs need to be identified. Recent studies in circulating tumor cells (CTCs) of some cancer patients manifest phenotypes of both CSCs and epithelial-mesenchymal transition (EMT). These patients are unresponsive to standard chemotherapies and have low progression free survival, suggesting that EMT-positive CTCs are related to co-occur with or transform into relapse-initiating CSCs. Furthermore, EMT programming in cancer cells enables in the remodeling of extracellular matrix to break the dormancy of relapse-initiating CSCs. In this review, we extensively discuss the association of the EMT program with CTCs and CSCs to characterize a subpopulation of patients prone to relapses. Identifying the mechanisms by which EMT-transformed CTCs and CSCs initiate relapse could facilitate the development of new or enhanced personalized therapeutic regimens.

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          Most cited references 148

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          Hepatocellular carcinoma.

          Hepatocellular carcinoma is the sixth most prevalent cancer and the third most frequent cause of cancer-related death. Patients with cirrhosis are at highest risk of developing this malignant disease, and ultrasonography every 6 months is recommended. Surveillance with ultrasonography allows diagnosis at early stages when the tumour might be curable by resection, liver transplantation, or ablation, and 5-year survival higher than 50% can be achieved. Patients with small solitary tumours and very well preserved liver function are the best candidates for surgical resection. Liver transplantation is most beneficial for individuals who are not good candidates for resection, especially those within Milano criteria (solitary tumour ≤5 cm and up to three nodules ≤3 cm). Donor shortage greatly limits its applicability. Percutaneous ablation is the most frequently used treatment but its effectiveness is limited by tumour size and localisation. In asymptomatic patients with multifocal disease without vascular invasion or extrahepatic spread not amenable to curative treatments, chemoembolisation can provide survival benefit. Findings of randomised trials of sorafenib have shown survival benefits for individuals with advanced hepatocellular carcinoma, suggesting that molecular-targeted therapies could be effective in this chemoresistant cancer. Research is active in the area of pathogenesis and treatment of hepatocellular carcinoma. Copyright © 2012 Elsevier Ltd. All rights reserved.
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            EMT, cancer stem cells and drug resistance: an emerging axis of evil in the war on cancer.

            Tumors are cellularly and molecularly heterogeneous, with subsets of undifferentiated cancer cells exhibiting stem cell-like features (CSCs). Epithelial to mesenchymal transitions (EMT) are transdifferentiation programs that are required for tissue morphogenesis during embryonic development. The EMT process can be regulated by a diverse array of cytokines and growth factors, such as transforming growth factor (TGF)-beta, whose activities are dysregulated during malignant tumor progression. Thus, EMT induction in cancer cells results in the acquisition of invasive and metastatic properties. Recent reports indicate that the emergence of CSCs occurs in part as a result of EMT, for example, through cues from tumor stromal components. Recent evidence now indicates that EMT of tumor cells not only causes increased metastasis, but also contributes to drug resistance. In this review, we will provide potential mechanistic explanations for the association between EMT induction and the emergence of CSCs. We will also highlight recent studies implicating the function of TGF-beta-regulated noncoding RNAs in driving EMT and promoting CSC self-renewal. Finally we will discuss how EMT and CSCs may contribute to drug resistance, as well as therapeutic strategies to overcome this clinically.
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              Identification of selective inhibitors of cancer stem cells by high-throughput screening.

              Screens for agents that specifically kill epithelial cancer stem cells (CSCs) have not been possible due to the rarity of these cells within tumor cell populations and their relative instability in culture. We describe here an approach to screening for agents with epithelial CSC-specific toxicity. We implemented this method in a chemical screen and discovered compounds showing selective toxicity for breast CSCs. One compound, salinomycin, reduces the proportion of CSCs by >100-fold relative to paclitaxel, a commonly used breast cancer chemotherapeutic drug. Treatment of mice with salinomycin inhibits mammary tumor growth in vivo and induces increased epithelial differentiation of tumor cells. In addition, global gene expression analyses show that salinomycin treatment results in the loss of expression of breast CSC genes previously identified by analyses of breast tissues isolated directly from patients. This study demonstrates the ability to identify agents with specific toxicity for epithelial CSCs.
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                Author and article information

                Journal
                Oncotarget
                Oncotarget
                ImpactJ
                Oncotarget
                Impact Journals LLC
                1949-2553
                10 May 2015
                8 May 2015
                : 6
                : 13
                : 10697-10711
                Affiliations
                1 Department of Pediatrics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
                2 Department of Gastroenterology, Hepatology and Nutrition, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
                Author notes
                Correspondence to: Shulin Li, sli4@ 123456mdanderson.org
                Article
                4484413
                25986923
                Copyright: © 2015 Mitra et al.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                Categories
                Review

                Oncology & Radiotherapy

                clinical trials, emt, cscs, ctcs, tumor relapse

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