乳腺癌化疗耐药中肿瘤干细胞的作用及其机制

目的:了解肿瘤干细胞在乳腺癌化疗耐药中的作用及其相关机制的研究进展。方法:应用检索Pubmed及CNKI数据库检索系统,以肿瘤、干细胞、乳腺癌、化疗和耐药等为关键词,检索1999-01-2011-05的相关文献,纳入标准:肿瘤干细胞与乳腺癌化疗耐药。根据纳入标准分析42篇文献。结果:肿瘤干细胞是导致乳腺癌化疗耐药和治疗失败的主要细胞,其耐药的机制包括ATP结合盒转运子的过度表达、细胞解毒酶的过度活化、细胞存活和凋亡相关信号转导通路的异常激活、肿瘤壁龛对肿瘤干细胞的保护作用以及大部分肿瘤干细胞处于静止期。通过对这些耐药机制的干预,可以逆转肿瘤干细胞的耐药性。结论:肿瘤干细胞是导致乳腺癌化疗耐药的关键细胞,对其耐药机制的研究有助于展开针对肿瘤干细胞的靶向治疗,改善患者的预后。     

Characterization of adipose-derived stem cells from subcutaneous and visceral adipose tissues and their function in breast cancer cells

Adipose-derived stem cells are capable of differentiating into multiple cell types and thus considered useful for regenerative medicine. However, this differentiation feature seems to be associated with tumor initiation and metastasis raising safety concerns, which requires further investigation. In this study, we isolated adipose-derived stem cells from subcutaneous as well as from visceral adipose tissues of the same donor and systematically compared their features. Although being characteristic of mesenchymal stem cells, subcutaneous adipose-derived stem cells tend to be spindle form-like and are more able to home to cancer cells, whereas visceral adipose-derived stem cells incline to be “epithelial”-like and more competent to differentiate. Moreover, compared to subcutaneous adipose-derived stem cells, visceral adipose-derived stem cells are more capable of promoting proliferation, inducing the epithelial-to-mesenchymal transition, enhancing migration and invasion of breast cancer cells by cell-cell contact and by secreting interleukins such as IL-6 and IL-8. Importantly, ASCs affect the low malignant breast cancer cells MCF-7 more than the highly metastatic MDA-MB-231 cells. Induction of the epithelial-to-mesenchymal transition is mediated by the activation of multiple pathways especially the PI3K/AKT signaling in breast cancer cells. BCL6, an important player in B-cell lymphoma and breast cancer progression, is crucial for this transition. Finally, this transition fuels malignant properties of breast cancer cells and render them resistant to ATP competitive Polo-like kinase 1 inhibitors BI 2535 and BI 6727.     

Lack of correlation of stem cell markers in breast cancer stem cells

Background:

Various markers are used to identify the unique sub-population of breast cancer cells with stem cell properties. Whether these markers are expressed in all breast cancers, identify the same population of cells, or equate to therapeutic response is controversial.

Methods:

We investigated the expression of multiple cancer stem cell markers in human breast cancer samples and cell lines in vitro and in vivo, comparing across and within samples and relating expression with growth and therapeutic response to doxorubicin, docetaxol and radiotherapy.

Results:

CD24, CD44, ALDH and SOX2 expression, the ability to form mammospheres and side-population cells are variably present in human cancers and cell lines. Each marker identifies a unique rather than common population of cancer cells. In vivo, cells expressing these markers are not specifically localized to the presumptive stem cell niche at the tumour/stroma interface. Repeated therapy does not consistently enrich cells expressing these markers, although ER-negative cells accumulate.

Conclusions:

Commonly employed methods identify different cancer cell sub-populations with no consistent therapeutic implications, rather than a single population of cells. The relationships of breast cancer stem cells to clinical parameters will require identification of specific markers or panels for the individual cancer.     

肿瘤干细胞及其耐药性的研究进展

传统理论认为肿瘤生长是所有肿瘤细胞一起增殖的结果,因而治疗方法主要是针对肿瘤组织内的大多数细胞,其结果是常有复发和转移,使治疗失败。随着肿瘤干细胞(cancer stem cells,CSCs)在不同肿瘤组织中被成功分离及其功能研究的深入,传统的肿瘤治疗方式面临着巨大的挑战。同时为深入探讨肿瘤的发生、发展及评价预后等提供了新的理论依据,也为肿瘤的治疗带来了新的思路。因此,只有杀灭CSCs,才能达到根治肿瘤的目的。本文就CSCs与其耐药性作一综述。     

线粒体自噬在肿瘤干细胞中作用的研究进展

肿瘤干细胞(cancer stem cells,CSCs)是具有自我复制、多细胞分化和治疗抵抗能力的一类肿瘤细胞,被认为是肿瘤治疗失败、复发及转移的关键因素。线粒体稳态在CSCs干性维持和分化的调节中起到关键作用。线粒体自噬作为一种靶向线粒体的选择性自噬,是维持线粒体稳态的重要调节机制之一。然而线粒体自噬在CSCs中的作用尚存争议。一方面,线粒体自噬具有线粒体质量控制的作用,最初被认为是维持细胞内稳态的抑癌因子;另一方面,近年来有报道表明线粒体自噬可以减少肿瘤细胞的氧化应激损伤,进而促进肿瘤进展。对线粒体自噬调控机制的深入研究有望为肿瘤治疗提供新的治疗靶点。本文旨在介绍线粒体自噬在CSCs的干性维持、代谢转化和治疗抵抗中的作用及其机制。     

间质干细胞乳腺癌治疗的新靶点

间质干细胞是多能成体干细胞,可靶向趋化到达肿瘤靶病灶和转移灶。实验证明间质干细胞可促进肿瘤的恶性行为,表现为恶性增殖,转移和复发,并积极参与血管形成,提供免疫保护。现就其在乳腺癌中的研究做一综述。     

MicroRNAs在乳腺癌干细胞中的作用研究进展

乳腺癌干细胞（breast cancer stem cells,BCSCs）是导致乳腺癌发生、转移、耐药、复发等的重要原因。MicroRNAs（miRNAs）是近年来发现的一种非编码小分子RNA,可通过与靶标基因的3 '-非翻译区（3'-UTR）的完全或不完全配对,抑制靶标基因的翻译或降解靶标基因,从而发挥多种生物学功能。miRNAs在BCSCs中的异常表达可调控BCSCs的自我更新、抗凋亡、上皮间质转化（epithelial-mesenchymal transition,EMT）等生物学行为,从而促进乳腺癌的复发、转移。以miRNAs为研究靶点,为乳腺癌的诊断、预后及治疗提供了全新的思路。本文就近年来该方面的研究进展简要综述。     

MicroRNA与乳腺癌干细胞

乳腺癌干细胞是导致乳腺癌复发、转移和耐药的根源之一。microRNA(miRNAs)是一类小分子非编码RNA,可与靶mRNA的3’UTR区域结合而导致该mRNA分子的翻译受到抑制,参与多种生物功能的调节。最近研究发现,miRNAs参与乳腺癌干细胞的分化、自我更新等生物学特性的调控。MiRNAs可以作为乳腺癌干细胞研究的一个新的切入点。本文就近年来该方面的研究进展做简要综述。     

Neoplastic human embryonic stem cells as a model of radiation resistance of human cancer stem cells

Studies have implicated that a small sub-population of cells within a tumour, termed cancer stem cells (CSCs), have an enhanced capacity for tumour formation in multiple cancers and may be responsible for recurrence of the disease after treatment, including radiation. Although comparisons have been made between CSCs and bulk-tumour, the more important comparison with respect to therapy is between tumour-sustaining CSC versus normal stem cells that maintain the healthy tissue. However, the absence of normal known counterparts for many CSCs has made it difficult to compare the radiation responses of CSCs with the normal stem cells required for post-radiotherapy tissue regeneration and the maintenance of tissue homeostasis. Here we demonstrate that transformed human embryonic stem cells (t-hESCs), showing features of neoplastic progression produce tumours resistant to radiation relative to their normal counterpart upon injection into immune compromised mice. We reveal that t-hESCs have a reduced capacity for radiation induced cell death via apoptosis and exhibit altered cell cycle arrest relative to hESCs in vitro. t-hESCs have an increased expression of BclXL in comparison to their normal counterparts and re-sensitization of t-hESCs to radiation upon addition of BH3-only mimetic ABT737, suggesting that overexpression of BclXL underpins t-hESC radiation insensitivity. Using this novel discovery platform to investigate radiation resistance in human CSCs, our study indicates that chemotherapy targeting Bcl2-family members may prove to be an adjuvant to radiotherapy capable of targeting CSCs.     

乳腺癌干细胞抵抗放射治疗及化疗的调控机制

据中国城市癌症报告统计,乳腺癌是中国城市女性发病率最高的癌症。尽管乳腺癌早期原位切除及放射治疗和化疗(简称放化疗)后,患者的5年和10年生存率较好,但依旧有小部分癌细胞逃逸、潜伏和扩散,导致乳腺癌复发和转移。未治愈乳腺癌中,约70%发生肺转移,60%发生骨转移和肝转移,15%发生脑转移。肿瘤干细胞是肿瘤组织中存在的少量具有干细胞特征的细胞亚群,有极强的再生肿瘤能力以及天然放化疗抵抗能力,被视作乳腺癌复发、转移的主要原因。靶向肿瘤干细胞的研究,为人类彻底攻克恶性肿瘤带来了希望。乳腺癌组织中具备乙醛脱氢酶(＋)、CD44^＋ CD24^－Lin^－等特征的细胞亚群已经被证实是乳腺肿瘤干细胞。笔者总结了乳腺肿瘤干细胞的鉴定、起源、特征、调控机制、放化疗不敏感的原因及临床靶向治疗的研究进展,供同行参考。     

Epithelial-mesenchymal transition in breast cancer lines is mediated through PDGF-D released by tissue-resident stem cells

Epithelial-mesenchymal transition (EMT) generates tumor cells with stem cell properties. The aim of our study was to investigate the effects of adipose tissue-derived stem cells (ASCs) on EMT of cancer cells and to further investigate the mechanisms involved. We demonstrate that conditioned medium from ASCs induces breast cancer cells (4T1) to express mesenchymal markers such as fibronectin, alpha smooth muscle actin and vimentin. Flow cytometry analyses show that ASC-conditioned medium promotes the expansion of CD44high/CD24low cancer stem cells. Soft agar assays using T47D, BT474 and MCF-7 breast cancer cells reveals that ASC conditioned medium promotes the anchorage-independent growth of cancer cells. These effects were inhibited by a neutralizing antibody against platelet-derived growth factor-D (PDGF-D). Furthermore, PDGF-D treated breast cancer cells grow faster in a mouse model, and this effect could be neutralized by a PDGF antibody. In conclusion, our data show that tissue-resident stem cells interact with the cancer microenvironment via PDGF-D, induce EMT in the cancer cells in a paracrine fashion, thereby increasing the number of cancer stem cells and increase tumor growth in a PDGF dependent manner. Our findings shed new light on mechanisms where local tissue-resident stem cells are able to promote the growth of breast cancer cells. Possibly this could open up a novel selective therapeutic strategy targeting EMT pathways and the specific communication between tissue-resident normal stem cell and cancer stem cells, assuming that the blockage of PDGF-D pathways is critical for tumor growth but would not affect normal tissue homeostasis.     

Circulating cancer stem cells: the importance to select

It has been demonstrated that even localized tumors without clinically apparent metastasis give rise to circulating tumor cells (CTCs). A growing number of technically diverse platforms are being developed for detecting/isolating CTCs in the circulating blood. Despite the technical challenges of isolating rare CTCs from blood, recent studies have already shown the predictive value of CTCs enumeration. Thus, it is becoming increasingly accepted that CTC numbers are linked to patients’ outcome and may also be used to monitor treatment response and disease relapse, respectively. Further CTCs provide a non-invasive source for tumor material, ‘liquid biopsy’, which is particularly important for patients, where no biopsy material can be obtained or where serial biopsies of the tumor, e.g., following treatment, are practically impossible. On the other hand the molecular and biological characterization of CTCs has still remained at a rather experimental stage. Future studies are necessary to define CTC heterogeneity to establish the crucial role of circulating cancer stem cells for driving metastasis, which represent a distinct subpopulation of CTCs that bear metastasis-initiating capabilities based on their stemness properties and invasiveness and thus are critical for the patients’ clinical outcome. As compared to non-tumorigenic/metastatic bulk CTCs, circulating cancer stem cells may not only be capable of evading from the primary tumor, but also escape from immune surveillance, survive in the circulating blood and subsequently form metastases in distant organs. Thus, circulating cancer stem cells represent a subset of exclusively tumorigenic cancer stem cells characterized by their invasive characteristics and are potential therapeutic targets for preventing disease progression. To date, only a few original reports and reviews have been published focusing on circulating cancer stem cells. This review discusses the potential importance of isolating and characterizing these circulating cancer stem cells, but also highlights current technological limitations.     

乳腺癌研究及治疗新靶点—乳腺癌干细胞的研究进展

随着人们对乳腺癌发生、发展机制的深入研究,乳腺癌干细胞日益受到研究者们的重视,研究表明,乳腺癌干细胞是一群未分化、具有自我更新及多系分化潜能的细胞。这些细胞具有化疗、放疗及缺氧抵抗性,同时具有高致瘤性、高侵袭转移性和在乳腺癌的发生﹑发展乃至转移﹑复发中起着极其重要作用。深入研究乳腺癌干细胞相关信号转导通路和微环境的调控,为临床靶向治疗乳腺癌具有重要的指导意义。因此,本文对乳腺癌干细胞在乳腺癌研究及治疗中的最新进展作一综述。     

P －gp 在人胃癌干细胞中表达的初步研究

目的：通过无血清法富集人胃癌 BGC －823干细胞,并对所获得的 BGC －823干细胞生物学特性进行研究。方法：采用无血清悬浮培养方法富集人胃癌 BGC －823干细胞球。后续实验分为 BGC －823干细胞组和 BGC －823细胞组：采用蛋白印迹（Western Blot）法和 Hoechst33342染色法对所富集细胞的干性进行鉴定;利用平板克隆实验检测细胞单克隆形成能力;采用 CCK －8法检测细胞对紫杉醇的敏感性;RT －PCR 法检测 P －gp mRNA 的表达;细胞免疫荧光双染观察干细胞球 CD44、P －gp 的表达情况。结果：采用无血清悬浮培养法成功获得干细胞球。CCK －8结果显示,BGC －823干细胞对紫杉醇敏感性较 BGC －823细胞降低（P ＜0．05）。干细胞球单克隆形成能力较人胃癌 BGC －823细胞增强（P ＜0．05）。Western Blot 和 Ho-echst33342染色法结果显示无血清富集的细胞为胃癌干细胞。RT －PCR、细胞免疫组化检测显示 BGC －823干细胞 CD44、P －gp 的表达较 BGC －823细胞升高,统计学差异明显（P ＜0．05）。结论：利用无血清富集法收集的人胃癌 BGC －823干细胞球为研究干细胞的理想模型,胃癌干细胞的形成是耐药出现的潜在机制。     

上皮源性卵巢癌干细胞的研究进展

肿瘤干细胞(cancer stem cells,CSCs)是肿瘤组织内具有自我更新能力以及无限增殖和多向分化潜能的一群细胞,对化疗药物耐受.卵巢癌干细胞(epithelial ovarian cancer stem cells,EOCSCs)在卵巢癌的发生发展、侵袭转移和耐药复发过程中都起到了重要作用.传统的肿瘤细胞减灭术联合顺铂、紫杉醇全身化疗对减小肿瘤体积,缓解临床症状具有一定的作用,但治疗后残留的EOCSCs能够短时间内重建肿瘤组织,是卵巢癌复发和难治的根本原因.深入了解EOCSCs的生物学特性,探索EOCSCs的发生发展机制,研究针对EOCSCs的靶向治疗药物,是抗肿瘤治疗的关键.     

Roles of the PI-3K and MEK pathways in Ras-mediated chemoresistance in breast cancer cells

Activated Ras utilises several downstream pathways, including the mitogen-activated protein kinase (MAPK) kinase (MEK)/MAPK pathway and the phosphoinositide 3-kinase (PI-3k)/Akt pathway, to promote cell proliferation and to inhibit apoptosis. To investigate which pathway plays a major role in Ras-induced drug resistance to chemotherapeutic agents in breast cancer cells, we transfected MCF7 breast cancer cells with a constitutively active H-RasG12V and examined the toxicities of three commonly used breast cancer chemotherapeutic agents, paclitaxel, doxorubicin, and 5-fluorouracil in these cells under the conditions that PI-3K or MEK were selectively inhibited by their respective specific inhibitors or dominant negative expression vectors. We found that Ras-mediated drug resistance is well correlated with resistance to apoptosis induced by anticancer agents in MCF7 breast cancer cells. Although inhibition of MEK/MAPK or PI-3K/Akt can each enhance the cytotoxicity of paclitaxel, doxorubicin, or 5-fluorouracil, inhibition of the PI-3K/Akt pathway seems to have a greater effect than inhibition of the MEK/MAPK pathway in reversing Ras-mediated drug resistance. Our results indicate that the PI-3K pathway may play a more important role in receptor tyrosine kinase-mediated resistance to chemotherapy and suggest that PI-3K/Akt might be a critical target molecule for anticancer intervention in breast cancer.     

Pancreatic cancer stem cells: Emerging target for designing novel therapy

In the past few years, there have been significant advances in the research on cancer stem cells (CSCs). The emerging evidences have demonstrated that CSCs and epithelial–mesenchymal transition (EMT)-type cells, which share molecular characteristics with CSCs, play critical roles in drug resistance, invasion, and metastasis. Pancreatic cancer (PC) has a high mortality due to both intrinsic (de novo) and extrinsic (acquired) drug resistance, leading to increased invasive and metastatic potential of PC cells. Therefore, targeting pancreatic CSCs and EMT-type cells could be a novel therapeutic strategy for the treatment of PC. In this article, we will review the current state of our knowledge on the role of pancreatic CSCs and EMT-type cells, and summarize the novel therapeutic strategies that could target pancreatic CSCs and EMT-type cells, leading to the reversal of EMT phenotype, the induction of drug sensitivity, and the inhibition of invasion and metastasis of PC, which is expected to yield better treatment outcome.