Stem cell-like cancer cells in cancer cell lines

Both stem cells and cancer cells are thought to be capable of unlimited proliferation. Moreover, a small number of cancer cells express stem cell markers, including CD133 and ATP-binding cassette transporters, by which the cells can pump out specific fluorescence dyes, such as Hoechst33342, as well as anti-cancer drugs, suggesting that either cancer cells resemble stem cells or cancers contain stem cell-like cancer cells, called "cancer stem cells (CSCs)". Using the common characteristics of tissue-specific stem cells, it was demonstrated that many types of tumors and cancer cell lines contain CSCs, which self-renew, express stem cell markers, and are tumorigenic. It was also shown that CSCs are resistant to anti-cancer drugs and irradiation. Thus CSCs might be a crucial target for the therapy. Because tumors contain CSCs and recruited normal stem cells, both of which contribute to tumorigenesis, it is difficult to separate CSCs from tumors. By contrast, cancer cell lines do not have any contaminating normal stem cells that quickly loose mulitpotentiality and differentiate in normal culture condition, suggesting that cancer cell lines could be an attractive alternative source of cells for CSC research. In this review I summarize the recent progress in CSC research using cancer cell lines.     

4EGI-1 targets breast cancer stem cells by selective inhibition of translation that persists in CSC maintenance,proliferation and metastasis

Cancer death is a leading cause of global mortality. An estimated 14.1 million new cancer cases and 8.2 million cancer deaths occurred worldwide in 2012 alone. Cancer stem cells (CSCs) within tumors are essential for tumor metastasis and reoccurrence, the key factors of cancer lethality. Here we report that 4EGI-1, an inhibitor of the interaction between translation initiation factors eIF4E1 and eIF4G1 effectively inhibits breast CSCs through selectively reducing translation persistent in breast CSCs. Translation initiation factor eIF4E1 is significantly enhanced in breast CSCs in comparison to non-CSC breast cancer cells. 4EGI-1 presents increased cytotoxicity to breast CSCs compared to non-CSC breast cancer cells. 4EGI-1 promotes breast CSC differentiation and represses breast CSC induced tube-like structure formation of human umbilical vein endothelial cells (HUVECs). 4EGI-1 isomers suppress breast CSC tumorangiogenesis and tumor growth in vivo. In addition, 4EGI-1 decreases proliferation in and induces apoptosis into breast CSC tumor cells. Furthermore, 4EGI-1 selectively inhibits translation of mRNAs encoding NANOG, OCT4, CXCR4, c-MYC and VEGF in breast CSC tumors. Our study demonstrated that 4EGI-1 targets breast CSCs through selective inhibition of translation critical for breast CSCs, suggesting that selective translation initiation interference might be an avenue targeting CSCs within tumors.     

Sensitizing ovarian cancer cells to chemotherapy by interfering with pathways that are involved in the formation of cancer stem cells

Chemotherapy often fails to eradicate cancer stem cells (CSCs) that drive cancer recurrence. In fact, the treated tumors often contain a higher frequency of chemo-resistant CSCs. It is thought that CSC formation is supported by exposure of cancer cells to sub-cytotoxic chemotherapy doses as a result of poor drug penetration in epithelial tumors. We have shown that low-dos cisplatin triggers the transdifferentiation of ovarian cancer cells into CSCs through processes that are also involved in the generation and maintenance of induced pluripotent stem (iPS) cells. Considering similarities between CSCs and iPS cells, we screened a library of 60 synthetic small-molecule compounds, designed to influence EMT/MET signaling in iPS cells on primary ovarian cancer cells. Using a Nanog reporter system we identified a series of compounds capable of blocking the cisplatin triggered formation of CSCs. We then focused on compound GHDM-1515, a drug that acts on pathways that regulate histone demethylases. We demonstrated that co-treatment of primary ovarian cancer cells with GHDM-1515 significantly increased cisplatin induced apoptosis, specifically apoptosis of CSCs. GHDM-1515 inhibited EMT and the cisplatin-induced formation of CSCs. This suggests that GHDM-1515 can sensitize ovarian cancer cells to low-dose cisplatin and potentially enhance the efficacy of cisplatin chemotherapy.     

肿瘤干细胞的临床意义

肿瘤干细胞(cancer stem cell, CSC)是近年来在许多肿瘤组织中发现的一类特殊干细胞。肿瘤干细胞具有自我更新和分化的能力,可以通过不断分化肿瘤细胞使新的肿瘤产生;肿瘤干细胞具有很强的耐药性和放射抗拒,这可以用来解释肿瘤的复发和转移。肿瘤干细胞可用于对肿瘤的诊断和治疗：通过对肿瘤干细胞标志物的鉴定可实现对一些肿瘤的早期诊断;一些新的治疗手段则通过作用于肿瘤干细胞的信号转导途径、表面标记和其生存的微环境,以及诱导其分化,从而达到靶向治疗肿瘤的目的。深入研究肿瘤干细胞的耐药性以及确定更多的肿瘤干细胞标志物,可为肿瘤治疗提供新途径。     

Cancer Stem Cells and Response to Therapy

The cancer stem cell (CSC) model states that cancers are organized in cellular hierarchies, which explains the functional heterogeneity often seen in tumors. Like normal tissue stem cells, CSCs are capable of self-renewal,either by symmetric or asymmetric cell division, and have the exclusive ability to reproduce malignant tumors indefinitely. Current systemic cancer therapies frequently fail to eliminate advanced tumors, which may be dueto their inability to effectively target CSC populations. It has been shown that embryonic pathways such as Wnt, Hedgehog, and Notch control self-renewal and cell fate decisions of stem cells and progenitor cells. These are evolutionary conserved pathways, involved in CSC maintenance. Targeting these pathways may be effective in eradicating CSCs and preventing chemotherapy or radiotherapy resistance.     

The clinical and therapeutic implications of cancer stem cell biology

Cancer stem cells (CSCs) have provided new insights into the tumorigenesis and metastatic potential of cancer. The discovery of CSCs has provided many new insights into the complexities of cancer therapy: tumor initiation, treatment resistance, metastasis, recurrence, assessment of prognosis and prediction of clinical course. Recent rapid advances in molecular analysis have contributed to the better understanding of the molecular attributes and pathways that give CSCs their unique attributes. Use of these molecular techniques has facilitated elucidation of specific surface markers and pathways that favor propagation of CSCs – allowing for targeted therapy. Furthermore, it has been discovered that a specific microenvironment, or niche, is essential for the genesis of tumors from CSCs. Therapeutic strategies that alter these microenvironments compromise CSC proliferation and constitute another method of targeted cancer therapy. We review the clinical and therapeutic implications of CSCs, with a focus on treatment resistance and metastasis, and the emerging approaches to target CSCs and their microenvironments in order to attain improved outcomes in cancer. It is noteworthy that CSCs are the only cells capable of sustaining tumorigenesis; however, the cell of origin of cancer, in which tumorigenesis is initiated, may be distinct from CSCs that propagate the tumor.     

The clinical and therapeutic implications of cancer stem cell biology

Cancer stem cells (CSCs) have provided new insights into the tumorigenesis and metastatic potential of cancer. The discovery of CSCs has provided many new insights into the complexities of cancer therapy: tumor initiation, treatment resistance, metastasis, recurrence, assessment of prognosis and prediction of clinical course. Recent rapid advances in molecular analysis have contributed to the better understanding of the molecular attributes and pathways that give CSCs their unique attributes. Use of these molecular techniques has facilitated elucidation of specific surface markers and pathways that favor propagation of CSCs - allowing for targeted therapy. Furthermore, it has been discovered that a specific microenvironment, or niche, is essential for the genesis of tumors from CSCs. Therapeutic strategies that alter these microenvironments compromise CSC proliferation and constitute another method of targeted cancer therapy. We review the clinical and therapeutic implications of CSCs, with a focus on treatment resistance and metastasis, and the emerging approaches to target CSCs and their microenvironments in order to attain improved outcomes in cancer. It is noteworthy that CSCs are the only cells capable of sustaining tumorigenesis; however, the cell of origin of cancer, in which tumorigenesis is initiated, may be distinct from CSCs that propagate the tumor.     

Insights into the cell of origin in breast cancer and breast cancer stem cells

The precise cell types that give rise to tumors and mechanisms that underpin tumor heterogeneity are poorly understood. There is increasing evidence to suggest that diverse solid tumors are hierarchically organized and may be sustained by a distinct subpopulation of cancer stem cells (CSCs). The CSC hypothesis provides an attractive cellular mechanism that can account for the therapeutic refractoriness and dormant behavior exhibited by many tumor types. Breast cancer was the first solid malignancy from which CSCs were identified and isolated. Direct evidence for the CSC hypothesis has also recently emerged from mouse models of mammary tumorigenesis, although alternative models to explain heterogeneity also seem to apply. Our group has found that the luminal epithelial progenitor marker CD61/β3 integrin identified a CSC population in mammary tumors from MMTV‐wnt‐1 mice. However, no CSCs could be identified in the more homogeneous MMTV‐neu/erbB2 model, suggesting an alternate (clonal evolution or stochastic) model of tumorigenesis. It seems likely that both paradigms of tumor propagation exist in human cancer. From a clinical perspective, the CSC concept has significant implications. Quiescent CSCs are thought to be more resistant to chemotherapy and targeted therapy. Enrichment of putative CSCs has been noted in studies of chemotherapy‐treated patients, lending support to the CSC hypothesis and their potential role in chemoresistance. Although many unresolved questions on CSCs remain, ongoing efforts to identify and characterize CSCs continue to be an important area of investigation, with the potential to identify novel tumor targeting strategies.     

Effet de la radiothérapie sur les cellules souches cancéreuses de cancer du sein : résistance,reprogrammation et traitements

In the past decade, the identification of cancer stem cells (CSCs) has raised new hope for the development of anticancer therapies. Nevertheless, CSC characterization highlights the relative resistance of CSCs to conventional therapies such as ionizing radiation. Moreover, it has been recently shown that some anti-cancer treatments could induce non- CSCs reprogramming into CSCs through anti-cancer treatment effect, enriching tumors with resistant cells. In this review, we will discuss CSC properties; we will especially describe the radio-resistance of CSC, reprogramming and explore the therapeutic approaches to by-pass these resistances.     

HSP DNAJB8 controls tumor-initiating ability in renal cancer stem-like cells

Cancer stem-like cells (CSC) are a small population of cancer cells with superior tumor initiating, self-renewal, and differentiation properties. In this study, we show that the cancer-testis antigen and HSP40 family member DNAJB8 contributes to the CSC phenotype in renal cell carcinoma (RCC). DNAJB8 overexpression increased the percentage of side population (SP) cells representing CSCs in RCC cells, enhancing their tumor-initiating ability. Conversely, attenuation of DNAJB8 decreased SP cells and reduced tumor-initiating ability. The utility of DNAJB8 as an immunologic target was established in DNA vaccination experiments. Compared with immunization with the tumor-associated antigen survivin, which was expressed in both CSCs and non-CSCs in RCC, immunization with Dnajb8 expression plasmids yielded stronger antitumor effects. Together, our findings suggest that DNAJB8 plays a role in CSC maintenance and that it offers a candidate for CSC-targeting immunotherapy in RCC.     

In vitro models of cancer stem cells and clinical applications

Cancer cells, stem cells and cancer stem cells have for a long time played a significant role in the biomedical sciences. Though cancer therapy is more effective than it was a few years ago, the truth is that still none of the current non-surgical treatments can cure cancer effectively. The reason could be due to the subpopulation called “cancer stem cells” (CSCs), being defined as those cells within a tumour that have properties of stem cells: self-renewal and the ability for differentiation into multiple cell types that occur in tumours.The phenomenon of CSCs is based on their resistance to many of the current cancer therapies, which results in tumour relapse. Although further investigation regarding CSCs is still needed, there is already evidence that these cells may play an important role in the prognosis of cancer, progression and therapeutic strategy. Therefore, long-term patient survival may depend on the elimination of CSCs. Consequently, isolation of pure CSC populations or reprogramming of cancer cells into CSCs, from cancer cell lines or primary tumours, would be a useful tool to gain an in-depth knowledge about heterogeneity and plasticity of CSC phenotypes and therefore carcinogenesis. Herein, we will discuss current CSC models, methods used to characterize CSCs, candidate markers, characteristic signalling pathways and clinical applications of CSCs. Some examples of CSC-specific treatments that are currently in early clinical phases will also be presented in this review.     

Shikonin enhances the antitumor effect of cabazitaxel in prostate cancer stem cells and reverses cabazitaxel resistance by inhibiting ABCG2 and ALDH3A1

Cancer stem cells (CSCs) are a small population among cancer cells, defined as capable of self-renewal, and driving tumor growth, metastasis, and therapeutic relapse. The development of therapeutic strategies to target CSCs is of great importance to prevent tumor metastasis and relapse. Increasing evidence shows that shikonin has inhibiting effects on CSCs. This study was to determine the effect of shikonin on prostate CSCs, and on drug resistant cells. Sphere formation assay was used to enrich prostate CSCs. The effect of shikonin on viability, proliferation, migration, and invasion was studied. Typical CSCs markers were analyzed by flow cytometry and RT-qPCR. The cytotoxic mechanism of shikonin was analyzed by staining for annexin V, reactive oxygen species (ROS) and mitochondrial membrane potential. To study the effect of shikonin on drug-resistant cells a cabazitaxel resistant cell line was established. Shikonin inhibited the viability, proliferation, migration, and invasion of prostate CSCs. Shikonin enhanced the antitumor effect of cabazitaxel, which is a second-line chemotherapeutic drug in advanced prostate cancer. Shikonin induced apoptosis through generating ROS and disrupting the mitochondrial membrane potential. Furthermore, shikonin suppressed the expression of ALDH3A1 and ABCG2 in prostate CSCs, which are two markers related to drug-resistance. When inhibiting the expression of ABCG2 and ALDH3A1, the cabazitaxel resistant cells acquired more sensibility to cabazitaxel. Shikonin enhances the cytotoxic activity of cabazitaxel in prostate CSCs and reverses the cabazitaxel-resistant state.     

Targeting breast cancer stem cells

The cancer stem cell (CSC) hypothesis postulates that tumors are maintained by a self‐renewing CSC population that is also capable of differentiating into non‐self‐renewing cell populations that constitute the bulk of the tumor. Although, the CSC hypothesis does not directly address the cell of origin of cancer, it is postulated that tissue‐resident stem or progenitor cells are the most common targets of transformation. Clinically, CSCs are predicted to mediate tumor recurrence after chemo‐ and radiation‐therapy due to the relative inability of these modalities to effectively target CSCs. If this is the case, then CSC must be efficiently targeted to achieve a true cure. Similarities between normal and malignant stem cells, at the levels of cell‐surface proteins, molecular pathways, cell cycle quiescence, and microRNA signaling present challenges in developing CSC‐specific therapeutics. Approaches to targeting CSCs include the development of agents targeting known stem cell regulatory pathways as well as unbiased high‐throughput siRNA or small molecule screening. Based on studies of pathways present in normal stem cells, recent work has identified potential “Achilles heals” of CSC, whereas unbiased screening provides opportunities to identify new pathways utilized by CSC as well as develop potential therapeutic agents. Here, we review both approaches and their potential to effectively target breast CSC.     

Cancer stem cell niche: the place to be

Tumors are being increasingly perceived as abnormal organs that, in many respects, recapitulate the outgrowth and differentiation patterns of normal tissues. In line with this idea is the observation that only a small fraction of tumor cells is capable of initiating a new tumor. Because of the features that these cells share with somatic stem cells, they have been termed cancer stem cells (CSC). Normal stem cells reside in a "stem cell niche" that maintains them in a stem-like state. Recent data suggest that CSCs also rely on a similar niche, dubbed the "CSC niche," which controls their self-renewal and differentiation. Moreover, CSCs can be generated by the microenvironment through induction of CSC features in more differentiated tumor cells. In addition to a role in CSC maintenance, the microenvironment is hypothesized to be involved in metastasis by induction of the epithelial-mesenchymal transition, leading to dissemination and invasion of tumor cells. The localization of secondary tumors also seems to be orchestrated by the microenvironment, which is suggested to form a premetastatic niche. Thus, the microenvironment seems to be of crucial importance for primary tumor growth as well as metastasis formation. Combined with its role in the protection of CSCs against genotoxic insults, these data strongly put forward the niche as an important target for novel therapies.     

PGE2/EP4 antagonism enhances tumor chemosensitivity by inducing extracellular vesicle‐mediated clearance of cancer stem cells

Cells expressing mesenchymal/basal phenotypes in tumors have been associated with stem cell properties. Cancer stem cells (CSCs) are often resistant to conventional chemotherapy. We explored overcoming mesenchymal CSC resistance to chemotherapeutic agents. Our goal was to reduce CSC numbers in vivo, in conjunction with chemotherapy, to reduce tumor burden. Analysis of clinical samples demonstrated that COX‐2/PGE₂/EP₄ signaling is elevated in basal‐like and chemoresistant breast carcinoma and is correlated with survival and relapse of breast cancer. EP₄ antagonism elicts a striking shift of breast cancer cells from a mesenchymal/CSC state to a more epithelial non‐CSC state. The transition was mediated by EP₄ antagonist‐induced extracellular vesicles [(EVs)/exosomes] which removed CSC markers, mesenchymal markers, integrins, and drug efflux transporters from the CSCs. In addition, EP₄ antagonism‐induced CSC EVs/exosomes can convert tumor epithelial/non‐CSCs to mesenchymal/CSCs able to give rise to tumors and to promote tumor cell dissemination. Because of its ability to induce a CSC‐to‐non‐CSC transition, EP₄ antagonist treatment in vivo reduced the numbers of CSCs within tumors and increased tumor chemosensitivity. EP₄ antagonist treatment enhances tumor response to chemotherapy by reducing the numbers of chemotherapy‐resistant CSCs available to repopulate the tumor. EP₄ antagonism can collaborate with conventional chemotherapy to reduce tumor burden.     

First among equals: the cancer cell hierarchy

Primary cancer cells exhibit heterogeneity in their proliferative ability. The cancer stem cell (CSC) model accounts for this heterogeneity by proposing that each cancer consists of a small population of CSCs that are capable of unlimited growth and self-renewal and a much larger population of cells, descendants of the CSCs, that have lost self-renewal capacity. The CSC model has important implications for cancer therapy. Eradication of CSCs, the cells responsible for maintenance of the neoplasm, would be necessary and sufficient to achieve cure. By extension, both the frequency of stem cells in a tumor and their propensity to undergo self-renewal (P_sr) would have a direct impact on the curability of that tumor. The P_sr is a critical biological characteristic of CSCs—small differences in P_sr have enormous impact on the probability of success in cancer therapy. Differentiation therapy, defined as treatment that reduces the P_sr of CSCs, is one approach to targeting CSCs.     

胃癌干细胞与微环境的研究进展

胃癌目前是仅次于肺癌的第二大致死性肿瘤,目前胃癌的发病机制还不是很清楚。近年来随着对肿瘤干细胞（CSC）和肿瘤生物学的研究,目前已经在多种实体瘤中发现CSC,但是由于胃癌干细胞缺乏特异性的标志物,因此还有很多空白待探究。虽然已发现一些胃癌干细胞表面标志物如CD44、CD133等,但缺乏特异性,仍需进一步探究更具特异性的胃癌干细胞标志物。CSC生存的环境在肿瘤的进程中也起重要的作用。文章对胃癌干细胞和微环境进行研究将有助于胃癌的诊断和治疗。     

The telomerase inhibitor imetelstat depletes cancer stem cells in breast and pancreatic cancer cell lines

Cancer stem cells (CSC) are rare drug-resistant cancer cell subsets proposed to be responsible for the maintenance and recurrence of cancer and metastasis. Telomerase is constitutively active in both bulk tumor cell and CSC populations but has only limited expression in normal tissues. Thus, inhibition of telomerase has been shown to be a viable approach in controlling cancer growth in nonclinical studies and is currently in phase II clinical trials. In this study, we investigated the effects of imetelstat (GRN163L), a potent telomerase inhibitor, on both the bulk cancer cells and putative CSCs. When breast and pancreatic cancer cell lines were treated with imetelstat in vitro, telomerase activity in the bulk tumor cells and CSC subpopulations were inhibited. Additionally, imetelstat treatment reduced the CSC fractions present in the breast and pancreatic cell lines. In vitro treatment with imetelstat, but not control oligonucleotides, also reduced the proliferation and self-renewal potential of MCF7 mammospheres and resulted in cell death after <4 weeks of treatment. In vitro treatment of PANC1 cells showed reduced tumor engraftment in nude mice, concomitant with a reduction in the CSC levels. Differences between telomerase activity expression levels or telomere length of CSCs and bulk tumor cells in these cell lines did not correlate with the increased sensitivity of CSCs to imetelstat, suggesting a mechanism of action independent of telomere shortening for the effects of imetelstat on the CSC subpopulations. Our results suggest that imetelstat-mediated depletion of CSCs may offer an alternative mechanism by which telomerase inhibition may be exploited for cancer therapy.     

Antitumor and anticancer stem cell activities of eribulin mesylate and antiestrogens in breast cancer cells

Background

Eribulin mesylate (eribulin), a non-taxane microtubule dynamic inhibitor, has been widely used in the treatment of patients with advanced or metastatic breast cancer. The combined antitumor and anticancer stem cell (CSC) activities of eribulin with endocrine therapeutic agents have not yet been examined in breast cancer cells. We herein investigated the combined effects of eribulin and antiestrogens.

Methods

A panel of eight breast cancer cell lines, including five estrogen receptor (ER)-positive and three ER-negative cell lines, was used. These cells were treated with eribulin and/or the antiestrogen, 4-hydroxytamoxifen or fulvestrant. Their growth inhibitory activities and effects on cell cycle progression, apoptosis, and the CSC population were investigated. CSCs were detected using the CD44/CD24/EpCAM, Aldefluor, and mammosphere assays.

Results

The 50 % growth inhibitory concentrations of eribulin were 0.38–2.64 nM for the eight cell lines tested. Eribulin exhibited significant antitumor activity under estrogen-supplemented conditions in ER-positive breast cancer cells. The combined antitumor activity of eribulin with an antiestrogen was evaluated using the combination index. The combination index was 0.43–1.46 for ER-positive cell lines. The additive antitumor effect of eribulin with 4-OHT was only significant in MCF-7 cells. Eribulin induced the accumulation of G2/M and apoptosis, while antiestrogens induced the retardation of G1–S cell cycle and apoptosis, respectively. Estrogen markedly increased the proportion of CSCs, whereas antiestrogens inhibited increases in ER-positive cell lines. Moreover, eribulin decreased the proportion of CSCs in either ER-positive or ER-negative cell lines. The combined treatment of eribulin with an antiestrogen did not additively decrease the proportion of CSCs in ER-positive cell lines.

Discussion

The results of the present study demonstrated that eribulin had potent antitumor effects on estrogen-stimulated ER-positive breast cancer cells and the combined treatment of eribulin with an antiestrogen resulted in a weakly additive antitumor effect. We herein suggested for the first time that eribulin exhibited anti-CSC effects on either ER-positive or ER-negative breast cancer cells.

     

The mammary progenitor marker CD61/beta3 integrin identifies cancer stem cells in mouse models of mammary tumorigenesis

The cells of origin and mechanisms that underpin tumor heterogeneity in breast cancer are poorly understood. Here, we have examined three mouse models of mammary tumorigenesis (MMTV-wnt-1, MMTV-neu, and p53(+/-)) for changes in their epithelial cell hierarchy during the preneoplastic and neoplastic stages of tumor progression. In preneoplastic tissue, only MMTV-wnt-1 mice showed a perturbation in their epithelial subpopulations. In addition to an expanded mammary stem cell pool, repopulating cells capable of yielding extensive mammary outgrowths in vivo were revealed in the committed luminal progenitor population. These findings indicate that wnt-1 activation induces the appearance of aberrant progenitor cells, and suggest that both mammary stem and progenitor cells can serve as the cellular targets of wnt-1-induced tumorigenesis. In tumors arising in MMTV-wnt-1 tumors, the luminal epithelial progenitor marker CD61/beta3 integrin identified a cancer stem cell (CSC) population that was highly enriched for tumorigenic capability relative to the CD61(-) subset. CD61 expression also defined a CSC subset in 50% of p53(+/-)-derived tumors. No CSCs, however, could be identified in the more homogeneous MMTV-neu/erbB2 model, suggesting an alternative model of tumorigenesis. Overall, our findings show the utility of the progenitor marker CD61 in the identification of CSCs that sustain specific mammary tumors.