Implications of Stem Cells and Cancer Stem Cells for Understanding Fomation and Therapy of Cancer

Most cancers are heterogeneous with respect to proliferation and differentiation. There is increasing evidence suggesting that only a minority of cancer cells, tumorigenic or tumor initiating cells, possess the capacity to proliferate extensively and form new hematopoietic cancer or solid tumors. Tumor initiating cells share characteristics required for normal stem cells. The dysregulation of self-renewal and proliferation of stem cells is a likely requirement for cancer development. This review formulates a model for the origin of cancer stem cells and regulating self-renewal which influences the way we study and treat cancer.     

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.     

肿瘤干细胞的研究进展

肿瘤干细胞是存在于肿瘤中的一小部分具有干细胞性质的细胞群,具有高度的致瘤性和耐药性。同正常干细胞一样,肿瘤干细胞具有无限的自我更新和多向分化的潜能,使肿瘤在体内不断扩大或形成新的肿瘤,导致肿瘤复发和转移。肿瘤干细胞的研究有助于认识和理解肿瘤发生发展的机制,指导肿瘤的临床治疗。     

BMI-1基因与肿瘤关系研究进展

BMI-1基因为一种致癌基因,属于PcG家族成员,通过抑制INK4a-ARF位点,从而与多种实体瘤的发生发展密切相关;BMI-1基因在维持正常干细胞自我更新及多向分化方面起重要作用;具有促进白血病干细胞增殖的能力。肿瘤干细胞是形成不同分化程度肿瘤细胞和肿瘤不断扩展的源泉,靶向杀死肿瘤干细胞应成为肿瘤治疗的根本目的。     

Isolation of cancer stem-like cells from a side population of a human glioblastoma cell line,SK-MG-1

Accumulating evidence suggests that in several types of brain tumors, including glioma, only a phenotypic subset of tumor cells called brain cancer stem cells (BCSCs) may be capable of initiating tumor growth. Recently, the isolation of side population (SP) cells using Hoechst dye has become a useful method for obtaining cancer stem cells in various tumors. In this study, we isolated cancer stem-like cells from human glioma cell lines using the SP technique. Flow cytometry analysis revealed that SK-MG-1, a human glioblastoma cell line, contained the largest number of SP cells among the five glioma cell lines that were analyzed. The SP cells had a self-renewal ability and were capable of forming spheres in a neurosphere culture medium containing EGF and FGF2. Spheres derived from the SP cells differentiated into three different lineage cells: neurons, astrocytes and oligodendrocytes. RT-PCR analysis revealed that the SP cells expressed a neural stem cell marker, Nestin. The SP cells generated tumors in the brains of NOD/SCID mice at 8 weeks after implantation, whereas the non-SP cells did not generate any tumors in the brain. These results indicate that SP cells isolated from SK-MG-1 possess the properties of cancer stem cells, including their self-renewal ability, multi-lineage differentiation, and tumorigenicity. Therefore, the SP cells from SK-MG-1 may be useful for analyzing BCSCs because of the ease with which they can be handled and their yield.     

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。     

肿瘤干细胞的研究进展

肿瘤干细胞是存在于肿瘤中的一小部分具有干细胞性质的细胞群,具有高度的致瘤性和耐药性。同正常干细胞一样,肿瘤干细胞具有无限的自我更新和多向分化的潜能,使肿瘤在体内不断扩大或形成新的肿瘤,导致肿瘤复发和转移。肿瘤干细胞的研究有助于认识和理解肿瘤发生发展的机制,指导肿瘤的临床治疗。     

Endometrial cancer stem cells: a new target for cancer therapy

Adult stem cells have recently been identified in several types of mature tissue and it has also been suggested that stem-like cells exist in cancerous tissues. In this regard, stem-like cell subpopulations, referred to as side-population (SP) cells, have been identified in several tissue and tumor types, based on their ability to remove intracellular Hoechst 33342, a fluorescent dye. We have isolated and characterized SP cells from normal human endometrium and an endometrial cancer cell line. Endometrial SP cells can function as progenitor cells. Endometrial cancer SP cells possess the following characteristics: i) reduced expression levels of differentiation markers, ii) long-term repopulating properties, iii) self-renewal capacity, iv) enhanced migration and podia formation, v) enhanced tumorigenicity, and vi) bi-potential development (tumor cells and stroma-like cells), suggesting that they have cancer stem-like cell features. Recently, we demonstrated that sodium butyrate, a histone deacetylase (HDAC) inhibitor, inhibited the self-renewal capacity of endometrial cancer SP cells by inducing a DNA damage response. Here, we review recent articles that show the presence of stem cells in normal endometrium and endometrial cancer and introduce the results of our own recent studies.     

Targeting breast cancer‐initiating/stem cells with melanoma differentiation‐associated gene‐7/interleukin‐24

Melanoma differentiation‐associated gene‐7/interleukin‐24 (mda‐7/IL‐24) displays a broad range of antitumor properties including cancer‐specific induction of apoptosis, inhibition of tumor angiogenesis and modulation of antitumor immune responses. In our study, we elucidated the role of MDA‐7/IL‐24 in inhibiting growth of breast cancer‐initiating/stem cells. Ad.mda‐7 infection decreased proliferation of breast cancer‐initiating/stem cells without affecting normal breast stem cells. Ad.mda‐7 induced apoptosis and endoplasmic reticulum stress in breast cancer‐initiating/stem cells similar to unsorted breast cancer cells and inhibited the self‐renewal property of breast cancer‐initiating/stem cells by suppressing Wnt/β‐catenin signaling. Prevention of inhibition of Wnt signaling by LiCl increased cell survival upon Ad.mda‐7 treatment, suggesting that Wnt signaling inhibition might play a key role in MDA‐7/IL‐24‐mediated death of breast cancer‐initiating/stem cells. In a nude mouse subcutaneous xenograft model, Ad.mda‐7 injection profoundly inhibited growth of tumors generated from breast cancer‐initiating/stem cells and also exerted a potent “bystander” activity inhibiting growth of distant uninjected tumors. Further studies revealed that tumor growth inhibition by Ad.mda‐7 was associated with a decrease in proliferation and angiogenesis, two intrinsic features of MDA‐7/IL‐24, and a reduction in vivo in the percentage of breast cancer‐initiating/stem cells. Our findings demonstrate that MDA‐7/IL‐24 is not only nontoxic to normal cells and normal stem cells but also can kill both unsorted cancer cells and enriched populations of cancer‐initiating/stem cells, providing further documentation that MDA‐7/IL‐24 might be a safe and effective way to eradicate cancers and also potentially establish disease‐free survival.     

Self-renewal and solid tumor stem cells

Solid tumors arise in organs that contain stem cell populations. The tumors in these tissues consist of heterogeneous populations of cancer cells that differ markedly in their ability to proliferate and form new tumors. In both breast cancers and central nervous system tumors, cancer cells differ in their ability to form tumors. While the majority of the cancer cells have a limited ability to divide, a population of cancer stem cells that has the exclusive ability to extensively proliferate and form new tumors can be identified based on marker expression. Growing evidence suggests that pathways that regulate the self-renewal of normal stem cells are deregulated in cancer stem cells resulting in the continuous expansion of self-renewing cancer cells and tumor formation. This suggests that agents that target the defective self-renewal pathways in cancer cells might lead to improved outcomes in the treatment of these diseases.     

Cancer stem cells: an old idea--a paradigm shift

Although the concept that cancers arise from "stem cells" or "germ cells" was first proposed about 150 years ago, it is only recently that advances in stem cell biology have given new impetus to the "cancer stem cell hypothesis." Two important related concepts of this hypothesis are that (a) tumors originate in either tissue stem cells or their immediate progeny through dysregulation of the normally tightly regulated process of self-renewal. As a result of this, (b) tumors contain a cellular subcomponent that retains key stem cell properties. These properties include self-renewal, which drives tumorigenesis, and differentiation albeit aberrant that contributes to cellular heterogeneity. Recent experimental evidence in a variety of tumors has lent strong support to the cancer stem cell hypothesis that represents a paradigm shift in our understanding of carcinogenesis and tumor cell biology. This hypothesis has fundamental implications for cancer risk assessment, early detection, prognostication, and prevention. Furthermore, the current development of cancer therapeutics based on tumor regression may have produced agents that kill differentiated tumor cells while sparing the rare cancer stem cell population. The development of more effective cancer therapies may thus require targeting this important cell population.     

Wnt and BMP signals control intestinal adenoma cell fates

Cellular hierarchies and signals that govern stemness and differentiation of intestinal adenoma cells are not well defined. In this study, we used organotypic culture to investigate the impact of β-catenin and BMP signals in cells that form intestinal adenoma in the mouse. We found that activation of β-catenin signaling by loss of APC or transgenic induction of oncogenic mutant β-catenin (Ctnnb1(mut) ) initiates the conversion of untransformed intestinal cells to tumor cells. These tumor cells display cancer stem cell (CSC) traits such as increased expression of the CSC markers Cd133 and Cd44, a high capacity for self-renewal and unlimited proliferative potential. Subsequent inactivation of transgenic Ctnnb1(mut) results in the reversion of tumor cells to normal intestinal stem cells, which immediately reinstall the cellular hierarchy of the normal intestinal epithelium. Our data demonstrate that oncogenic activation of β-catenin signaling initiates the early steps of intestinal cellular transformation in the absence of irreversible genetic or epigenetic changes. Interestingly, we found that tumor cells in culture and in adenoma produce BMP4, which counteracts CSC-like traits by initiating irreversible cellular differentiation and loss of self-renewal capacity. We conclude that the opposition of stemness-maintaining oncogenic β-catenin signals and autocrine differentiating BMP signals within the adenoma cell provides a rationale for the formation of cellular hierarchies in intestinal adenoma and may serve to limit adenoma growth.     

Identification of a cancer stem cell in human brain tumors

Most current research on human brain tumors is focused on the molecular and cellular analysis of the bulk tumor mass. However, there is overwhelming evidence in some malignancies that the tumor clone is heterogeneous with respect to proliferation and differentiation. In human leukemia, the tumor clone is organized as a hierarchy that originates from rare leukemic stem cells that possess extensive proliferative and self-renewal potential, and are responsible for maintaining the tumor clone. We report here the identification and purification of a cancer stem cell from human brain tumors of different phenotypes that possesses a marked capacity for proliferation, self-renewal, and differentiation. The increased self-renewal capacity of the brain tumor stem cell (BTSC) was highest from the most aggressive clinical samples of medulloblastoma compared with low-grade gliomas. The BTSC was exclusively isolated with the cell fraction expressing the neural stem cell surface marker CD133. These CD133+ cells could differentiate in culture into tumor cells that phenotypically resembled the tumor from the patient. The identification of a BTSC provides a powerful tool to investigate the tumorigenic process in the central nervous system and to develop therapies targeted to the BTSC.     

Cancer stem cells and brain tumors: uprooting the bad seeds

The cancer stem cell (CSC) hypothesis is predicated on the idea that not all cells have equal proliferative potential and that, in brain tumors, the cells with the greatest ability to proliferate and contribute to tumorigenesis have phenotypic and functional properties similar to normal neural stem cells (NSCs). Over the past few years, multiple investigators have shown that CSCs isolated from human brain tumors (glioma and medulloblastoma) undergo self-renewal and multilineage cell differentiation, similar to normal NSCs. In addition, CSCs from these tumors, when implanted into rodent brains, generate tumors histologically identical to the parental tumors, suggesting that progenitor/stem cells can fully recapitulate the neoplastic phenotype in vivo. While these seminal studies clearly highlight the central role of stem cells in brain tumors, they also evoke important questions regarding the importance of these unique cells to tumor initiation, maintenance and treatment.     

基因Sox2与肿瘤的研究进展

肿瘤干细胞在肿瘤的发生、发展中起重要的作用,Sox2作为干细胞关键的转录因子,除了具有维持干细胞自我更新和多向分化的潜能外,其异常表达可能促进多种恶性肿瘤的发生和进展,具体的作用机制涉及肿瘤的增殖、分化、侵袭、转移及耐药等多个环节。同时,Sox2与上皮间质转化过程关系密切,而上皮间质转化是上皮细胞来源的恶性肿瘤细胞获得迁移和侵袭能力的重要生物学过程。通过对Sox2在肿瘤领域的研究有助于寻找新的临床治疗手段。     

Mixed lineage leukemia translocations and a leukemia stem cell program

Cancer stem cells (CSC) may provide the self-renewal capacity required to sustain a tumor. One possibility is that CSC arise from the stem cell counterparts in normal tissues. Alternatively, CSC may arise from more differentiated progenitor cells found in certain tissues. In support of this idea, we showed recently that mixed lineage leukemia fusion oncoproteins can convert committed hematopoietic progenitors into leukemias, which include leukemia stem cells expressing a self-renewal associated program in the context of a differentiated myeloid cell. The findings suggest a basis to understand the pathobiology of CSC and possible strategies to attack them to undermine the self-renewal capacity of a tumor.     

Notch信号通路在乳腺癌干细胞中的研究进展

乳腺癌干细胞是一群具有自我更新及多向分化潜能的细胞,在乳腺癌的发生、发展以及转移、复发中起着极其重要的作用。正常情况下,乳腺干细胞的分化、更新能力受相关信号转导通路的严格调控,当这些信号通路发生异常干细胞将会异常分化,形成乳腺癌干细胞,并无限增殖形成肿瘤。随着人们对乳腺癌干细胞的深入研究,Notch信号通路与其他信号通路的相互作用对乳腺癌干细胞的调控逐渐被人们所重视。本文为进一步了解Notch信号通路在乳腺癌的发生、发展以及靶向治疗中的重要意义,结合乳腺癌干细胞信号通路的最新研究进展进行综述。      

干细胞标记物CK19、Notch3、CD133、P75NTR、STRO-1及ABCG2在肺鳞癌中的表达及意义

背景与目的 已有研究表明在肿瘤中存在着能够自我更新与多向分化的肿瘤干细胞,它们与正常人体内的干细胞有着相似的特征.本研究选取了被认为可作为干细胞标记物的部分抗体,以观察它们在肺鳞癌中的表达及意义.方法 采用S-P免疫组织化学方法,对54例手术切除肺鳞癌标本进行了CK19、Notch3、CD133、P75NTR、STRO-1及ABCG2的检测,另外选取了10例正常肺组织标本进行对照.结果 54例肺鳞癌标本中,除发现STRO-1及P75NTR在所有病例均为阴性表达外,其余标记均存在不同程度的阳性表达,但是阳性细胞的分布无规律性.其中,CK19阳性率为66.67%(36/54),Notch3为87.04%(47/54),CD133为50%(27/54),ABCG2为61.11%(33/54),并且Notch3、CD133和ABCG2在中低分化肺鳞癌中的表达高于高分化鳞癌(P＜0.05),而CK19、CD133和ABCG2在有淋巴结转移的肺鳞癌中的表达高于无淋巴结转移(P＜0.05),在连续切片中4种标记同时阳性的细胞数均少于总细胞数目的2%,3种及4种抗体共同阳性细胞所占百分比与鳞癌的分化程度和是否有淋巴结转移无统计学相关.结论 肺鳞癌中存在着某些干细胞标记物的表达,其表达程度与肺鳞癌的分化程度及淋巴结转移相关,但是阳性细胞在组织学的分布上无规律性,同时表达多种干细胞标记的肿瘤细胞数少于2%,可能为肿瘤干细胞.     

间充质干细胞基因治疗肿瘤新进展

骨髓间充质干细胞(MSC)是骨髓内除造血干细胞和多功能前祖细胞外另一种成体干细胞,具有很强的自我更新能力、多向分化潜能.该细胞具有明显的趋向肿瘤移动并与肿瘤组织楔合的生长特性.虽然骨髓间充质干细胞有向肿瘤干细胞转化的风险,但其作为一种克隆载体可以转导治疗基因在体内获得长期稳定表达,对肿瘤的靶向治疗有着广阔的前景.     

Cancer stem cells and brain tumors: uprooting the bad seeds

The cancer stem cell (CSC) hypothesis is predicated on the idea that not all cells have equal proliferative potential and that, in brain tumors, the cells with the greatest ability to proliferate and contribute to tumorigenesis have phenotypic and functional properties similar to normal neural stem cells (NSCs). Over the past few years, multiple investigators have shown that CSCs isolated from human brain tumors (glioma and medulloblastoma) undergo self-renewal and multilineage cell differentiation, similar to normal NSCs. In addition, CSCs from these tumors, when implanted into rodent brains, generate tumors histologically identical to the parental tumors, suggesting that progenitor/stem cells can fully recapitulate the neoplastic phenotype in vivo. While these seminal studies clearly highlight the central role of stem cells in brain tumors, they also evoke important questions regarding the importance of these unique cells to tumor initiation, maintenance and treatment.