Understanding the colon cancer stem cells and perspectives on treatment

An area of research that has been recently gaining attention is the relationship between cancer stem cell (CSC) biology and chemo-resistance in colon cancer patients. It is well recognized that tumor initiation, growth, invasion and metastasis are promoted by CSCs. An important reason for the widespread interest in the CSC model is that it can comprehensibly explain essential and poorly understood clinical events, such as therapy resistance, minimal residual disease, and tumor recurrence. This review discusses the recent advances in colon cancer stem cell research, the genes responsible for CSC chemoresistance, and new therapies against CSCs.     

Aldehyde dehydrogenase activity selects for the holoclone phenotype in prostate cancer cells

Aldehyde dehydrogenase 1 (ALDH) activity is considered to be a marker of cancer stem cells (CSCs) in many tumour models, since these cells are more proliferative and tumourigenic than ALDH^Lo cells in experimental models. However it is unclear whether all CSC-like cells are within the ALDH^Hi population, or whether all ALDH^Hi cells are highly proliferative and tumourigenic. The ability to establish a stem cell hierarchy in vitro, whereby sub-populations of cells have differing proliferative and differentiation capacities, is an alternate indication of the presence of stem cell-like populations within cell lines. In this study, we have examined the interaction between ALDH status and the ability to establish a stem cell hierarchy in PC3 prostate cancer cells. We demonstrate that PC3 cells contain a stem cell hierarchy, and isolation of ALDH^Hi cells enriches for the most primitive holoclone population, however holoclone formation is not restricted to ALDH^Hi cells. In addition, we show that ALDH activity undergoes phenotypic plasticity, since the ALDH^Lo population can develop ALDH^Hi populations comparable to parental cells within 2 weeks in culture. Furthermore, we show that the majority of ALDH^Hi cells are found within the least primitive paraclone population, which is circumvented by culturing PC3 cells as spheroids in defined medium favouring stem cell characteristics. Although ALDH^Hi status enriches for holoclone formation, this activity may be mediated by a minority of ALDH^Hi cells.     

A rat mammary gland cancer cell with stem cell properties of self-renewal and multi-lineage differentiation

The cancer stem cell hypothesis posits that tumors are derived from a single cancer-initiating cell with stem cell properties. The task of identifying and characterizing cancer-initiating cells with stem cell properties at the single cell level has proven technically difficult because of the scarcity of the cancer stem cells in the tissue of origin and the lack of specific markers for cancer stem cells. Here we show that a single LA7 cell, derived from rat mammary adenocarcinoma has: the ability to serially re-generate mammospheres in long-term non-adherent cultures, the differentiation potential to generate all the cell lineages of the mammary gland and branched duct-like structures that recapitulate morphologically and functionally the ductal–alveolar-like architecture of the mammary tree. The properties of self-renewal, extensive capacity for proliferation, multi-lineage differentiation and the tubular-like structure formation potential suggest that LA7 cells is a cancer stem model system to study the dynamics of tumor formation at the single cell level. Cinzia Cocola, Sveva Sanzone and Simonetta Astigiano have contributed equally to this work.     

Investigating the link between epithelial-mesenchymal transition and the cancer stem cell phenotype: A mathematical approach

Under the cancer stem cell (CSC) hypothesis, sustained metastatic growth requires the dissemination of a CSC from the primary tumour followed by its re-establishment in a secondary site. The epithelial-mesenchymal transition (EMT), a differentiation process crucial to normal development, has been implicated in conferring metastatic ability on carcinomas. Balancing these two concepts has led researchers to investigate a possible link between EMT and the CSC phenotype—indeed, recent evidence indicates that, following induction of EMT in human breast cancer and related cell lines, stem cell activity increased, as judged by the presence of cells displaying the CD44^high/CD24^low phenotype and an increase in the ability of cells to form mammospheres. We mathematically investigate the nature of this increase in stem cell activity. A stochastic model is used when small number of cells are under consideration, namely in simulating the mammosphere assay, while a related continuous model is used to probe the dynamics of larger cell populations. Two scenarios of EMT-mediated CSC enrichment are considered. In the first, differentiated cells re-acquire a CSC phenotype—this model implicates fully mature cells as key subjects of de-differentiation and entails a delay period of several days before de-differentiation occurs. In the second, pre-existing CSCs experience accelerated division and increased proportion of self-renewing divisions; a lack of perfect CSC biomarkers and cell sorting techniques requires that this model be considered, further emphasizing the need for better characterization of the mammary (cancer) stem cell hierarchy. Additionally, we suggest the utility of comparing mammosphere data to computational mammosphere simulations in elucidating the growth characteristics of mammary (cancer) stem cells.     

From milk to malignancy: the role of mammary stem cells in development, pregnancy and breast cancer

Adult stem cells of the mammary gland (MaSCs) are a highly dynamic population of cells that are responsible for the generation of the gland during puberty and its expansion during pregnancy. In recent years significant advances have been made in understanding how these cells are regulated during these developmentally important processes both in humans and in mice. Understanding how MaSCs are regulated is becoming a particularly important area of research, given that they may be particularly susceptible targets for transformation in breast cancer. Here, we summarize the identification of MaSCs, how they are regulated and the evidence for their serving as the origins of breast cancer. In particular, we focus on how changes in MaSC populations may explain both the increased risk of developing aggressive ER/PR(-) breast cancer shortly after pregnancy and the long-term decreased risk of developing ER/PR(+) tumors.     

Embryonic stem cells in non-human primates: An overview of neural differentiation potential

Non-human primate (NHP) embryonic stem (ES) cells show unlimited proliferative capacities and a great potential to generate multiple cell lineages. These properties make them an ideal resource both for investigating early developmental processes and for assessing their therapeutic potential in numerous models of degenerative diseases. They share the same markers and the same properties with human ES cells, and thus provide an invaluable transitional model that can be used to address the safety issues related to the clinical use of human ES cells. Here, we review the available information on the derivation and the specific features of monkey ES cells. We comment on the capacity of primate ES cells to differentiate into neural lineages and the current protocols to generate self-renewing neural stem cells. We also highlight the signalling pathways involved in the maintenance of these neural cell types. Finally, we discuss the potential of monkey ES cells for neuronal differentiation.     

Doxycycline inhibits the cancer stem cell phenotype and epithelial-to-mesenchymal transition in breast cancer

Experimental evidence suggest that breast tumors originate from breast cancer stem cells (BCSCs), and that mitochondrial biogenesis is essential for the anchorage-independent clonal expansion and survival of CSCs, thus rendering mitochondria a significant target for novel treatment approaches. One of the recognized side effects of the FDA-approved drug, doxycycline is the inhibition of mitochondrial biogenesis. Here we investigate the mechanism by which doxycycline exerts its inhibitory effects on the properties of breast cancer cells and BCSCs, such as mammosphere forming efficiency, invasion, migration, apoptosis, the expression of stem cell markers and epithelial-to-mesenchymal transition (EMT) related markers of breast cancer cells. In addition, we explored whether autophagy plays a role in the inhibitory effect of doxycycline on breast cancer cells. We find that doxycyline can inhibit the viability and proliferation of breast cancer cells and BCSCs, decrease mammosphere forming efficiency, migration and invasion, and EMT of breast cancer cells. Expression of stem cell factors Oct4, Sox2, Nanog and CD44 were also significantly downregulated after doxycycline treatment. Moreover, doxycycline could down-regulate the expression of the autophagy marker LC-3BI and LC-3BII, suggesting that inhibiting autophagy may be responsible in part for the observed effects on proliferation, EMT and stem cell markers. The potent inhibition of EMT and cancer stem-like characteristics in breast cancer cells by doxycycline treatment suggests that this drug can be repurposed as an anti-cancer drug in the treatment of breast cancer patients in the clinic.     

Co-expression of the toleragenic glycoprotein, CD200, with markers for cancer stem cells

Tumor immunology fundamentals suggest immunological surveillance has the ability to recognize malignant cells and kill them before a tumor develops. However, cancer cells employ evasion mechanisms whereby the immune system may be actively suppressed or even tolerized to the tumor. Recently cancer stem cells were linked to tumor initiation and formation. However, no reports have addressed whether these cells participate in a tumor’s ability to evade immune surveillance. Recently the glycoprotein CD200, expressed within the innate immune system and other tissues and cells, was shown to be involved in tolerance. Here we describe CD200 co-expression with stem cell markers found on prostate, breast, brain, and colon cancers. This is the first report describing an immunomodulatory molecule on epithelial cancer stem cells. This important finding suggests a mechanism by which a tumor might evades immune system detection.     

Advances in ovarian cancer screening: health and medicine for women: a multidisciplinary, evidence-based review of mid-life health concerns

Early detection is imperative for improving survival from ovarian cancer, the leading cause of death from gynecological cancer in the United States. At the Health and Medicine for Women continuing medical education (CME) conference at Yale in September 2010, Dr. Gil Mor, a researcher in the Department of OB/GYN at Yale, presented recent advances on the pathophysiology of ovarian cancer. These advances, and particularly our growing understanding of cancer stem cells, may help overcome the limitations of current ovarian cancer detection and treatment methods.     

乳腺癌干细胞分选及相关信号通路研究进展

肿瘤干细胞是指存在于肿瘤组织中的具有干细胞特性,即能够多向分化和自我更新的一类细胞群。随着肿瘤干细胞概念的提出,乳腺癌干细胞成为当今科研领域的一个研究热点。因此,了解如何分选乳腺癌干细胞及如何维持其"干性"对治疗及预防乳腺癌具有至关重要的意义。主要从乳腺癌干细胞分选、相关信号通路、上皮-间充质转换(EMT)等方面进行综述。     

Tumor initiating cells in pancreatic cancer: A critical view

Emerging evidence points to the existence of pancreatic cancer stem cells (CSC) as the culprit in the initiation, maintenance, metastasis, and treatment resistance of pancreatic cancer. The existence of such a cell population would have an important impact on the design of novel therapies against this devastating disease. However, no in vivo validation or rebuttal of the pancreatic CSC hypothesis exists. Major backlashes in the discussion on CSC are firstly, the confusion between the terms CSC and cell of origin of pancreatic ductal adenocarcinoma (PDAC), secondly the ambiguity of the cell of origin itself and thirdly, the fact that the CSC hypothesis is based on cell sorting and xenografting experiments; the latter of which often precludes solid conclusions because of the lack of a natural microenvironment and differences in drug delivery. Nonetheless, recent studies in other cancers partially support the CSC hypothesis by demonstrating a link between epithelial-to-mesenchymal transdifferentiation/transition (EMT) and CSC properties. Such a link is again open to dispute as EMT is a reversible process which is highly dependent on major oncogenic pathways in PDAC [e.g. K-Ras, transforming growth factor-β (TGF-β)] rather than on presumed cancer stem cell pathways. Hence, the available evidence does not robustly support the CSC concept in PDAC and a thorough validation of this hypothesis in well-defined genetically engineered mouse models of pancreatic cancer is required.     

Neural crest stem cells: discovery, properties and potential for therapy

Neural crest (NC) cells are a migratory cell population synonymous with vertebrate evolution. They generate a wide variety of cell and tissue types during embryonic and adult development including cartilage and bone, connective tissue, pigment and endocrine cells as well as neurons and glia amongst many others. Such incredible lineage potential combined with a limited capacity for self-renewal, which persists even into adult life, demonstrates that NC cells bear the key hallmarks of stem and progenitor cells. In this review, we describe the identification, characterization and isolation of NC stem and progenitor cells from different tissues in both embryo and adult organisms. We discuss their specific properties and their potential application in cell-based tissue and disease-specific repair.     

Targeting cancer stem cells expressing an embryonic signature with anti-proteases to decrease their tumor potential

Cancer stem cells (CSCs) are a specific subset of cancer cells that sustain tumor growth and dissemination. They might represent a significant treatment target to reduce malignant progression and prevent tumor recurrence. In solid tumors, several hierarchically organized CSC clones coexist, even within a single tumor. Among them, CSCs displaying an embryonic stem cell ‘stemness'' signature, based on the expression of Oct-4, Nanog and Sox2, are present in distinct high-grade tumor types associated with poor prognosis. We previously designed a model to isolate pure populations of these CSCs from distinct solid tumors and used it to screen for molecules showing selective toxicity for this type of CSC. Here we show that human immunodeficiency virus (HIV)-protease inhibitors (HIV-PIs) specifically target CSCs expressing an embryonic signature derived from tumors with distinct origins. They reduced proliferation in a dose-dependent manner with a higher specificity as compared with the total population of cancer cells and/or healthy stem cells, and they were efficient in inducing cell death. Lopinavir was the most effective HIV-PI among those tested. It reduced self-renewal and induced apoptosis of CSCs, subsequently impairing in vivo CSC-induced allograft formation. Two key pharmacophores in the LPV structure were also identified. They are responsible for the specificity of CSC targeting and also for the overall antitumoral activity. These results contribute to the identification of molecules presenting selective toxicity for CSCs expressing an embryonic stemness signature. This paves the way to promising therapeutic opportunities for patients suffering from solid cancer tumors of poor prognosis.     

Aldehyde dehydrogenase 1 is a putative marker for cancer stem cells in head and neck squamous cancer

Aldehyde dehydrogenase 1 (ALDH1) has been considered to be a marker for cancer stem cells. However, the role of ALDH1 in head and neck squamous cell carcinoma (HNSCC) has yet to be determined. In this study, we isolated ALDH1-positive cells from HNSCC patients and showed that these HNSCC-ALDH1⁺ cells displayed radioresistance and represented a reservoir for generating tumors. Based on microarray findings, the results of Western blotting and immunofluorescent assays further confirmed that ALDH1⁺-lineage cells showed evidence of having epithelial-mesenchymal transition (EMT) shifting and endogenously co-expressed Snail. Furthermore, the knockdown of Snail expression significantly decreased the expression of ALDH1, inhibited cancer stem-like properties, and blocked the tumorigenic abilities of CD44⁺CD24⁻ALDH1⁺ cells. Finally, in a xenotransplanted tumorigenicity study, we confirmed that the treatment effect of chemoradiotherapy for ALDH1⁺ could be improved by Snail siRNA. In summary, it is likely that ALDH1 is a specific marker for the cancer stem-like cells of HNSCC.     

Isolation and characterization of Oct-4+/HLA-G+ mesenchymal stem cells from human umbilical cord matrix: differentiation potential and detection of new markers

The presence of multipotent cells in several adult and embryo-related tissues opened new paths for their use in regenerative medicine. Extraembryonic tissues such as umbilical cord are considered a promising source of stem cells, potentially useful in therapy. The characterization of cells from the umbilical cord matrix (Wharton’s Jelly) and amniotic membrane revealed the presence of a population of mesenchymal-like cells, sharing a set of core-markers expressed by “mesenchymal stem cells”. Several reports enlightened the differentiation capabilities of these cells, even if at times the lack of an extensive characterization of surface markers and immune co-stimulators expression revealed hidden pitfalls when in vivo transplantation was performed. The present work describes a novel isolation protocol for obtaining mesenchymal stem cells from the umbilical cord matrix. These cells are clonogenic, retain long telomeres, can undergo several population doublings in vitro, and can be differentiated in mature mesenchymal tissues as bone and adipose. We describe for the first time that these cells, besides expressing all of the core-markers for mesenchymal stem cells, feature also the expression, at both protein and mRNA level, of tolerogenic molecules and markers of all the three main lineages, potentially important for both their differentiative potential as well as immunological features. G. La Rocca and R. Anzalone have contributed equally to this work.