Cancer stem cells and side population cells in breast cancer and metastasis

Therapy-resistant breast cancer in focus: Clinically relevant mitigation by flavonoids targeting cancer stem cells

Significant limitations of the reactive medical approach in breast cancer management are clearly reflected by alarming statistics recorded worldwide. According to the WHO updates, breast malignancies become the leading cancer type. Further, the portion of premenopausal breast cancer cases is permanently increasing and demonstrates particularly aggressive patterns and poor outcomes exemplified by young patients with triple-negative breast cancer that lacks targeted therapy. Accumulating studies suggest the crucial role of stem cells in tumour biology, high metastatic activity, and therapy resistance of aggressive breast cancer. Therefore, targeting breast cancer stem cells is a promising treatment approach in secondary and tertiary breast cancer care. To this end, naturally occurring substances demonstrate high potential to target cancer stem cells which, however, require in-depth analysis to identify effective anti-cancer agents for cost-effective breast cancer management. The current article highlights the properties of flavonoids particularly relevant for targeting breast cancer stem cells to mitigate therapy resistance. The proposed approach is conformed with the principles of 3P medicine by applying predictive diagnostics, patient stratification and treatments tailored to the individualised patient profile. Expected impacts are very high, namely, to overcome limitations of reactive medical services improving individual outcomes and the healthcare economy in breast cancer management. Relevant clinical applications are exemplified in the paper.

High percentage of Cancer Stem cells in metastatic locations: Upregulation of cicBIRC6 in highly metastatic breast Cancer Subline

BACKGROUND

Metastasis is a devastating complication of breast cancer. Cancer relapse and metastasis are associated with cancer stem cells. CicBIRC6 is a circular RNA that is proposed to be involved in the stemness of stem cells. In breast cancer, metastatic tumor cells have higher stem cell properties. In the present study, we evaluate the expression of cicBIRC6 in these cells.

METHODS

After the development of a syngeneic animal model of TNBC, primary breast cancer cells named 4T1T were isolated from the tumor mass. Highly metastatic tumor cells named 4T1B and 4T1L were isolated and expanded from brain metastasis lesions and lungs of cancerous mice respectively. Sphere formation ability in metastatic and primary tumor cells was evaluated separately. The quantitative real-time polymerase chain reaction was performed to analyze the expression of cicBIRC6 in primary and metastatic tumor cells.

RESULTS

Our data revealed that, sphere formation ability among metastatic tumor cells was significantly higher. Surprisingly expression of cicBIRC6 was significantly upregulated in these metastatic tumor cells. In comparison with 4T1T, cicBIRC6 was upregulated 5.7 and 3.5 times in 4T1B and 4T1L respectively.

CONCLUSION

These findings provided important insights regarding the molecular properties of metastatic tumor cells and can be used for designing a targeted therapeutic strategy in combat with these cells.

Role of Cancer Stem-like Cells in the Process of Invasion and Mesenchymal Transformation by a Reconstituted Triple-negative Breast Cancer Cell Population Resistant to p53-induced Apoptosis

We investigated the role of cancer stem cells (CSCs) in a population of triple-negative breast cancer (TNBC) cells that are resistant to apoptosis. A human breast cancer cell population capable of inducing p53 expression with doxycycline (Dox) was created and used as an untreated control (UT). After the addition of Dox to UT for 5 days, the cell population reconstituted with cells showing resistance to apoptosis was named RE. Fluorescence-activated cell sorting (FACS) and immunostaining revealed that after the addition of Dox, the ratio of cells in the S and G2/M phases decreased in UT as apoptosis proceeded, but did not markedly change in apoptosis-resistant RE. CSC-like cells in RE exhibited a cell morphology with a larger ratio of the major/minor axis than UT. FACS showed that RE had a higher proportion of CSC-like cells and contained more CD44+CD24- mesenchymal CSCs than ALDH1A3+ epithelial-like CSCs. In a Matrigel invasion assay, UT was more likely to form a three-dimensional cell population, whereas RE exhibited a planar population, higher migration ability, and the up-regulated expression of epithelial-mesenchymal transition-related genes. These results provide insights into the mechanisms by which TNBC cells acquire treatment resistance at the time of recurrence.

Proteomic Analysis of HCC-1954 and MCF-7 Cell Lines Highlights Crosstalk between αv and β1 Integrins, E-Cadherin and HER-2

Overexpression of human epidermal growth factor receptor-2 (HER-2) occurs in 20% of all breast cancer subtypes, especially those that present the worst prognostic outcome through a very invasive and aggressive tumour. HCC-1954 (HER-2+) is a highly invasive, metastatic cell line, whereas MCF-7 is mildly aggressive and non-invasive. We investigated membrane proteins from both cell lines that could have a pivotal biological significance in metastasis. Membrane protein enrichment for HCC-1954 and MCF-7 proteomic analysis was performed. The samples were analysed and quantified by mass spectrometry. High abundance membrane proteins were confirmed by Western blot, immunofluorescence, and flow cytometry. Protein interaction prediction and correlations with the Cancer Genome Atlas (TCGA) patient data were conducted by bioinformatic analysis. In addition, β1 integrin expression was analysed by Western blot in cells upon trastuzumab treatment. The comparison between HCC-1954 and MCF-7 membrane-enriched proteins revealed that proteins involved in cytoskeleton organisation, such as HER-2, αv and β1 integrins, E-cadherin, and CD166 were more abundant in HCC-1954. β1 integrin membrane expression was higher in the HCC-1954 cell line resistant after trastuzumab treatment. TCGA data analysis showed a trend toward a positive correlation between HER-2 and β1 integrin in HER-2+ breast cancer patients. Differences in protein profile and abundance reflected distinctive capabilities for aggressiveness and invasiveness between HCC-1954 and MCF-7 cell line phenotypes. The higher membrane β1 integrin expression after trastuzumab treatment in the HCC-1954 cell line emphasised the need for investigating the contribution of β1 integrin modulation and its effect on the mechanism of trastuzumab resistance.

Synthesis of doxorubicin-loaded peptosomes hybridized with gold nanorod for targeted drug delivery and CT imaging of metastatic breast cancer

BACKGROUND

Cancer nanomedicines based on synthetic polypeptides have attracted much attention due to their superior biocompatibility and biodegradability, stimuli responsive capability through secondary conformation change, adjustable functionalities for various cargos such as peptides, proteins, nucleic acids and small therapeutic molecules. Recently, a few nanoformulations based on polypeptides comprising NK105, NC6004, NK911, CT2103, have entered phase I-III clinical trials for advanced solid tumors therapy. In the current study, we prepared polypeptide-based vesicles called peptosome via self-assembly of amphiphilic polypeptide-based PEG-PBLG diblock copolymer.

RESULTS

In this regard, poly(γ-benzyl L-glutamate (PBLG) was synthesized via ring opening polymerization (ROP) of γ-benzyl L-glutamate-N-carboxyanhydride (BLG-NCA) using N-hexylamine as initiator. Then amine-terminated PBLG was covalently conjugated to heterofuctional maleimide PEG-carboxylic acid or methyl-PEG-carboxylic acid. The PEG-PBLG peptosomes were prepared through double emulsion method for the co-delivery of doxorubicin.HCl and gold nanorods as hydrophilic and hydrophobic agents in interior compartment and membrane of peptosomes, respectively (Pep@MUA.GNR-DOX) that DOX encapsulation efficiency and loading capacity were determined 42 ± 3.6 and 1.68 ± 3.6. Then, theranostic peptosomes were decorated with thiol-functionalized EpCAM aptamer throught thiol-maleimide reaction producing Apt-Pep@MUA.GNR-DOX for targeted delivery. The non-targeted and targeted peptosomes showed 165.5 ± 1.1 and 185 ± 4.7 nm diameters, respectively while providing sustained, controlled release of DOX. Furthermore, non-targeted and targeted peptosomes showed considerable serum stability. In vitro study on MCF-7 and 4T1 cells showed significantly higher cytotoxicity for Apt-Pep@MUA.GNR-DOX in comparison with Pep@MUA.GNR-DOX while both system did not show any difference in cytotoxicity against CHO cell line. Furthermore, Apt-Pep@MUA.GNR-DOX illustrated higher cellular uptake toward EpCAM-overexpressing 4T1 cells compared to Pep@MUA.GNR-DOX. In preclinical stage, therapeutic and diagnostic capability of the prepared Pep@MUA.GNR-DOX and Apt-Pep@MUA.GNR-DOX were investigated implementing subcutaneous 4T1 tumor model in BALB/c mice. The obtained data indicated highest therapeutic index for Apt-Pep@MUA.GNR-DOX compared to Pep@MUA.GNR-DOX and free DOX. Moreover, the prepared system showed capability of CT imaging of tumor tissue in 4T1 tumorized mice through tumor accumulation even 24 h post-administration.

CONCLUSION

In this regard, the synthesized theranostic peptosomes offer innovative hybrid multipurpose platform for fighting against breast cancer.

Sinomenine Inhibits Vasculogenic Mimicry and Migration of Breast Cancer Side Population Cells via Regulating miR-340-5p/SIAH2 Axis

Hypoxia and its induced vasculogenic mimicry (VM) formation, which both closely related with stem-like side population (SP) cells, are the main culprits leading to tumor invasion and metastasis. Sinomenine exhibits excellent anticancer activity in breast cancer, but whether and how it affects hypoxia-triggered VM formation in breast cancer SP cells remains unclear. In this study, breast cancer SP cells were sorted from MDA-MB-231 cells and cultured with sinomenine under hypoxic conditions. Sinomenine obviously repressed the migration and VM formation of breast cancer SP cells. Through downregulating SIAH2 and HIF-1α, sinomenine can inhibit epithelial-mesenchymal transition process of breast cancer SP cells. SIAH2 was identified as a target of miR-340-5p and was downregulated by it, and sinomenine can upregulate miR-340-5p. Hypoxia-induced downregulation of miR-340-5p and activation of SIAH2/HIF-1α pathway can be both counteracted by the sinomenine. Moreover, miR-340-5p inhibition and SIAH2 overexpression can partly counteract the anticancer effects of sinomenine. Taken together, sinomenine inhibits hypoxia-caused VM formation and metastasis of breast cancer SP cells by regulating the miR-340-5p/SIAH2 axis.

Identification of a Liver Progenitor Cell-Related Genes Signature Predicting Overall Survival for Hepatocellular Carcinoma

Background: Liver progenitor cells (LPCs) play significant roles in the development and progression of hepatocellular carcinoma (HCC). However, no studies on the value of LPC-related genes for evaluating HCC prognosis exist. We developed a gene signature of LPC-related genes for prognostication in HCC. Methods: To identify LPC-related genes, we analyzed mRNA expression arrays from a dataset (GSE57812 & GSE 37071) containing LPCs, mature hepatocytes, and embryonic stem cell samples. HCC RNA-Seq data from The Cancer Genome Atlas (TCGA) were used to explore the differentially expressed genes (DEGs) related to prognosis through DEG analysis and univariate Cox regression analysis. Lasso and multivariate Cox regression analyses were performed to construct the LPC-related gene prognostic model in the TCGA training dataset. This model was validated in the TCGA testing set and an external dataset (International Cancer Genome Consortium [ICGC] dataset). Finally, we investigated the relationship between this prognostic model with tumor-node-metastasis stage, tumor grade, and vascular invasion of HCC. Results: Overall, 1770 genes were identified as LPC-related genes, of which 92 genes were identified as DEGs in HCC tissues compared with normal tissues. Furthermore, we randomly assigned patients from the TCGA dataset to the training and testing cohorts. Twenty-six DEGs correlated with overall survival (OS) in the univariate Cox regression analysis. Lasso and multivariate Cox regression analyses were performed in the TCGA training set, and a 3-gene signature was constructed to stratify patients into 2 risk groups: high-risk and low-risk. Patients in the high-risk group had significantly lower OS than those in the low-risk group. Receiver operating characteristic curve analysis confirmed the signature's predictive capacity. Moreover, the risk score was confirmed to be an independent predictor for patients with HCC. Conclusion: We demonstrated that the LPC-related gene signature can be used for prognostication in HCC. Thus, targeting LPCs may serve as a therapeutic alternative for HCC.

Roles Played by YY1 in Embryonic, Adult and Cancer Stem Cells

Accumulating evidence strongly indicates that the presence of cancer stem cells (CSCs) leads to the emergence of worse clinical scenarios, such as chemo- and radiotherapy resistance, metastasis, and cancer recurrence. CSCs are a highly tumorigenic population characterized by self-renewal capacity and differentiation potential. Thus, CSCs establish a hierarchical intratumor organization that enables tumor adaptation to evade the immune response and resist anticancer therapy. YY1 functions as a transcription factor, RNA-binding protein, and 3D chromatin regulator. Thus, YY1 has multiple effects and regulates several molecular processes. Emerging evidence indicates that the development of lethal YY1-mediated cancer phenotypes is associated with the presence of or enrichment in cancer stem-like cells. Therefore, it is necessary to investigate whether and to what extent YY1 regulates the CSC phenotype. Since CSCs mirror the phenotypic behavior of stem cells, we initially describe the roles played by YY1 in embryonic and adult stem cells. Next, we scrutinize evidence supporting the contributions of YY1 in CSCs from a number of various cancer types. Finally, we identify new areas for further investigation into the YY1-CSCs axis, including the participation of YY1 in the CSC niche.

Breast Cancer Stem Cells: Biomarkers, Identification and Isolation Methods, Regulating Mechanisms, Cellular Origin, and Beyond

Despite recent advances in diagnosis and treatment, breast cancer (BC) is still a major cause of cancer-related mortality in women. Breast cancer stem cells (BCSCs) are a small but significant subpopulation of heterogeneous breast cancer cells demonstrating strong self-renewal and proliferation properties. Accumulating evidence has proved that BCSCs are the driving force behind BC tumor initiation, progression, metastasis, drug resistance, and recurrence. As a heterogeneous disease, BC contains a full spectrum of different BC subtypes, and different subtypes of BC further exhibit distinct subtypes and proportions of BCSCs, which correspond to different treatment responses and disease-specific outcomes. This review summarized the current knowledge of BCSC biomarkers and their clinical relevance, the methods for the identification and isolation of BCSCs, and the mechanisms regulating BCSCs. We also discussed the cellular origin of BCSCs and the current advances in single-cell lineage tracing and transcriptomics and their potential in identifying the origin and lineage development of BCSCs.

Cancer Stem Cell Markers in Relation to Patient Survival Outcomes: Lessons for Integrative Diagnostics and Next-Generation Anticancer Drug Development

Solid tumors display a complex biology that requires a multipronged treatment strategy. Most anticancer interventions, including chemotherapy, are currently unable to prevent treatment resistance and relapse. In general, therapeutics target cancer cells and overlook the tumor microenvironment (TME) and the presence of cancer stem cells (CSCs) with self-renewal and tumorigenic abilities. CSCs have been postulated to play key roles in tumor initiation, progression, therapy resistance, and metastasis. Hence, CSC markers have been suggested as diagnostics to forecast cancer prognosis as well as molecular targets for new-generation cancer treatments, especially in resistant disease. We report here original findings on expression and prognostic significance of CSC markers in several cancers. We examined and compared the transcriptional expression of CSC markers (ABCB1, ABCG2, ALDH1A1, CD24, CD44, CD90, CD133, CXCR4, EPCAM, ICAM1, and NES) in tumor tissues versus the adjacent normal tissues using publicly available databases, The Cancer Genome Atlas and Gene Expression Profiling Interactive Analysis. We found that CSC transcriptional markers were, to a large extent, expressed in higher abundance in solid tumors such as colon, lung, pancreatic, and esophageal cancers. On the other hand, no CSC marker in our analysis was expressed in the same pattern in all cancers, while individual CSC marker expression, alone, was not significantly associated with overall patient survival. Innovation in next-generation cancer therapeutics and diagnostics ought to combine CSC markers as well as integrative diagnostics that pool knowledge from CSCs and other TME components and cancer cells.

Single-cell RNA-sequencing reveals distinct patterns of cell state heterogeneity in mouse models of breast cancer

Breast cancer stem cells (BCSCs) contribute to intra-tumoral heterogeneity and therapeutic resistance. However, the binary concept of universal BCSCs co-existing with bulk tumor cells is over-simplified. Through single-cell RNA-sequencing, we found that Neu, PyMT and BRCA1-null mammary tumors each corresponded to a spectrum of minimally overlapping cell differentiation states without a universal BCSC population. Instead, our analyses revealed that these tumors contained distinct lineage-specific tumor propagating cells (TPCs) and this is reflective of the self-sustaining capabilities of lineage-specific stem/progenitor cells in the mammary epithelial hierarchy. By understanding the respective tumor hierarchies, we were able to identify CD14 as a TPC marker in the Neu tumor. Additionally, single-cell breast cancer subtype stratification revealed the co-existence of multiple breast cancer subtypes within tumors. Collectively, our findings emphasize the need to account for lineage-specific TPCs and the hierarchical composition within breast tumors, as these heterogenous sub-populations can have differential therapeutic susceptibilities.

Linking Cancer Stem Cell Plasticity to Therapeutic Resistance-Mechanism and Novel Therapeutic Strategies in Esophageal Cancer

Esophageal cancer (EC) is an aggressive form of cancer, including squamous cell carcinoma (ESCC) and adenocarcinoma (EAC) as two predominant histological subtypes. Accumulating evidence supports the existence of cancer stem cells (CSCs) able to initiate and maintain EAC or ESCC. In this review, we aim to collect the current evidence on CSCs in esophageal cancer, including the biomarkers/characterization strategies of CSCs, heterogeneity of CSCs, and the key signaling pathways (Wnt/β-catenin, Notch, Hedgehog, YAP, JAK/STAT3) in modulating CSCs during esophageal cancer progression. Exploring the molecular mechanisms of therapy resistance in EC highlights DNA damage response (DDR), metabolic reprogramming, epithelial mesenchymal transition (EMT), and the role of the crosstalk of CSCs and their niche in the tumor progression. According to these molecular findings, potential therapeutic implications of targeting esophageal CSCs may provide novel strategies for the clinical management of esophageal cancer.

Breast cancer stem cell RNA-pulsed dendritic cells enhance tumor cell killing by effector T cells

Cancer stem cells (CSCs) underpin the resistance of breast cancer (BC) cells to therapy. Dendritic cell (DC)-based treatment is efficacious and safe, but the efficiency of this technique for targeting CSCs in BC treatment requires further investigation. The present study aimed to investigate the ability of DCs pulsed with breast CSC antigens to activate effector lymphocytes for killing BC cells. CD44⁺/CD24⁻ CSCs were isolated from BCA55-121, an in-house patient-derived BC cell line, and acquisition of stemness properties was confirmed by upregulated expression of OCT4A and a superior proliferative capacity in colony formation assays compared with whole population of BCA55-121 (BCA55-121-WP). DCs were differentiated from monocytes from peripheral blood of healthy donors and pulsed with CSC total RNA. Maturation of the CSC RNA-pulsed DCs was confirmed by increased expression of CD11c, CD40, CD83, CD86 and HLA-DR, as well as reduced CD14 expression compared with monocytes. Total lymphocytes co-cultured with CSC RNA-pulsed DCs were analyzed by flow cytometry for markers including CD3, CD4, CD8, CD16 and CD56. The results revealed that the co-cultures contained mostly cytotoxic CD8+ T lymphocytes followed by CD4+ T lymphocytes and smaller populations of natural killer (NK) and NKT cells. ELISA was used to measure IFN-γ production, and it was revealed that activated CD4⁺ and CD8+ lymphocytes produced more IFN-γ compared with naïve T cells, suggesting that CD8+ T cells were effector T cells. CSC RNA was a more efficient antigen source compared with RNA from mixed BC cells for activating tumor antigen-specific killing by T cells. These CSC-specific effector T cells significantly induced BC cell apoptosis at a 20:1 effector T cell:tumor cell ratio. Of note, the breast CSCs cultures demonstrated resistance to effector T cell killing, which was in part due to increased expression of programmed death ligand 1 in the CSC population. The present study highlights the potential use of CSC RNA for priming DCs in modulating an anticancer immune response against BC.

Isorhapontigenin (ISO) inhibits stem cell-like properties and invasion of bladder cancer cell by attenuating CD44 expression

Cancer stem cells (CSC) are highly associated with poor prognosis in cancer patients. Our previous studies report that isorhapontigenin (ISO) down-regulates SOX2-mediated cyclin D1 induction and stem-like cell properties in glioma stem-like cells. The present study revealed that ISO could inhibit stem cell-like phenotypes and invasivity of human bladder cancer (BC) by specific attenuation of expression of CD44 but not SOX-2, at both the protein transcription and degradation levels. On one hand, ISO inhibited cd44 mRNA expression through decreases in Sp1 direct binding to its promoter region-binding site, resulting in attenuation of its transcription. On the other hand, ISO also down-regulated USP28 expression, which in turn reduced CD44 protein stability. Further studies showed that ISO treatment induced miR-4295, which specific bound to 3'-UTR activity of usp28 mRNA and inhibited its translation and expression, while miR-4295 induction was mediated by increased Dicer protein to enhance miR-4295 maturation upon ISO treatment. Our results provide the first evidence that ISO has a profound inhibitory effect on human BC stem cell-like phenotypes and invasivity through the mechanisms distinct from those previously noted in glioma stem-like cells.

Cancer stem cells in esophageal squamous cell cancer

Cancer stem cells (CSCs) are hypothesized to govern the origin, progression, drug resistance, recurrence and metastasis of human cancer. CSCs have been identified in nearly all types of human cancer, including esophageal squamous cell cancer (ESCC). Four major methods are typically used to isolate or enrich CSCs, including: i) fluorescence-activated cell sorting or magnetic-activated cell sorting using cell-specific surface markers; ii) stem cell markers, including aldehyde dehydrogenase 1 family member A1; iii) side population cell phenotype markers; and iv) microsphere culture methods. ESCC stem cells have been identified using a number of these methods. An increasing number of stem cell signatures and pathways have been identified, which have assisted in the clarification of molecular mechanisms that regulate the stemness of ESCC stem cells. Certain viruses, such as human papillomavirus and hepatitis B virus, are also considered to be important in the formation of CSCs, and there is a crosstalk between stemness and viruses-associated genes/pathways, which may suggest a potential therapeutic strategy for the eradication of CSCs. In the present review, findings are summarized along these lines of inquiry.

Enrichment of cancer stem-like cells by the induction of epithelial-mesenchymal transition using lentiviral vector carrying E-cadherin shRNA in HT29 cell line

A better understanding of cancer stem cells (CSCs) may facilitate the prevention and treatment of cancers. Epithelial-mesenchymal transition (EMT) is a process activated during invasion and metastasis of tumors. EMT induction in normal and tumor cells makes them more resistant to chemotherapy. E-cadherin is a membrane protein and plays a role in tumor invasion, metastasis, and prognosis. Downregulation of E-cadherin is a hallmark of EMT. Here, we created a model of cancer stem-like cells enrichment via EMT induction using E-cadherin downregulation in HT29 cell line using a lentiviral vector carrying shRNA. We aimed to evaluate cancer and anti-CSC chemotherapeutics screening. The markers of EMT and CSCs were assessed and compared with control cells using flow cytometry, real-time PCR, immunocytochemistry, western blot, migration assay, invasion assay, and colony formation assay. The transduced cells showed a mesenchymal morphology. High levels of EMT-related proteins were also expressed. These results confirmed that the transduced cells underwent EMT. In addition, we observed an increased population of E-cadherin-downregulated HT29 cell line among the cells expressing colon CSC markers (CD133⁺ and CD44⁺ ) after EMT induction. E-cadherin-downregulated cells were morphologically like mesenchymal cells, and the number of CD133⁺ - and CD44⁺ -cells (CSC-like cells) increased. These cells can be used as stable models to study cancer cells and screening of antitumor therapeutics.

Bone Metastasis of Breast Cancer

Bone is the most common site of metastasis for breast cancer. Bone metastasis significantly affects both quality of life and survival of the breast cancer patient. Clinically, complications secondary to bone metastasis include pain, pathologic fractures, spinal cord compression, and hypercalcemia of malignancy. Because bone metastasis is extremely common in patients with metastatic breast cancer, clinical management of bone metastases is an important and challenging aspect of treatment in the metastatic setting.The skeleton is a metabolically active organ system that undergoes continuous remodeling throughout life. A delicate balance of the bone-forming osteoblasts and bone-resorbing osteoclasts in the dynamic microenvironment of the skeleton maintains normal bone remodeling and integrity. The presence of metastatic lesions in bone disrupts the normal bone microenvironment and upsets the fine balance between the key components. The changes in the bone microenvironment then create a vicious cycle that further promotes bone destruction and tumor progression.Various therapeutic options are available for bone metastases of breast cancer. Treatment can be tailored for each patient and, often requires multiple therapeutic interventions. Commonly used modalities include local therapies such as surgery, radiation therapy and radiofrequency ablation (RFA) together with systemic therapies such as endocrine therapy, chemotherapy, monoclonal antibody-based therapy, bone-enhancing therapy and radioisotope therapy. Despite the use of various therapeutic modalities, bone metastases eventually become resistant to therapy, and disease progresses.In this chapter, we describe the clinical picture and biological mechanism of bone metastases in breast cancer. We also discuss known risk factors as well as detection and assessment of bone metastases. We present therapeutic options for bone metastasis using a multidisciplinary approach. Further, we describe future directions for bone metastasis management, focusing on novel bone-specific targeted therapies.

Genetic Models of Leukemia in Zebrafish

The zebrafish animal model is gaining increasing popularity as a tool for studying human disease. Over the past 15 years, many models of leukemia and other hematological malignancies have been developed in the zebrafish. These confer some significant advantages over similar models in other animals and systems, representing a powerful resource for investigation of the molecular basis of human leukemia. This review discusses the various zebrafish models of lymphoid and myeloid leukemia available, the major discoveries that have been made possible by them, and opportunities for future exploration.

Upregulated SCUBE2 expression in breast cancer stem cells enhances triple negative breast cancer aggression through modulation of notch signaling and epithelial-to-mesenchymal transition

BACKGROUND

Metastatic and/or recurrent breast carcinomas are leading causes of cancer-related death worldwide. Breast cancer stem cells (BCSCs) have been implicated in cancer metastases and progression, thus, the need for the discovery and development of effective BCSCs-specific therapies against metastatic and triple negative breast cancer (TNBC). The expression of SCUBE2, originally identified in vascular endothelia, then in several non-endothelial cell types, is downregulated in invasive breast carcinomas. However, the role of SCUBE2 in BCSCs remains unknown. This present study investigated the probable involvements of SCUBE2 in BCSCs and TNBC metastasis.

METHODS

The mRNA expression of SCUBE2, stemness and EMT markers in MDA-MB-231 and Hs578T tumorspheres or adherent cells were evaluated by qRT-PCR and microarray analyses. Using gene overexpression, in vitro migration and invasion assays, as well as in vivo bioluminescence imaging, we evaluated the role of SCUBE2 in MDA-MB-231 or Hs578T BCSCs. Western blot and cytotoxicity assays helped identify and validate SCUBE2 molecular target(s) and inhibitor(s).

RESULTS

Concurrently increased SCUBE2 expression and cell motility were observed in TNBC tumorspheres compared to the parental adherent cells. SCUBE2 overexpression augmented BCSCs motility in vitro, and enhanced TNBC metastasis in vivo. While SCUBE2 overexpression activated Notch signaling its downregulation suppressed Notch signal effectors NICD, Jagged 1, HEY1, and HES1.

CONCLUSIONS

We demonstrate that SCUBE2 expression is upregulated in BCSCs, promote EMT and enhance TNBC metastasis by activating Notch signaling. This reveals a potential druggable molecular target and an effective therapeutic strategy against metastatic and aggressive TNBC.

New use of an old drug: inhibition of breast cancer stem cells by benztropine mesylate

Cancer stem cells (CSCs) play major roles in cancer initiation, metastasis, recurrence and therapeutic resistance. Targeting CSCs represents a promising strategy for cancer treatment. The purpose of this study was to identify selective inhibitors of breast CSCs (BCSCs). We carried out a cell-based phenotypic screening with cell viability as a primary endpoint, using a collection of 2,546 FDA-approved drugs and drug-like molecules in spheres formed by malignant human breast gland-derived cells (HMLER-shEcad cells, representing BCSCs) and control immortalized non-tumorigenic human mammary cells (HMLE cells, representing normal stem cells). 19 compounds were identified from screening. The chemically related molecules benztropine mesylate and deptropine citrate were selected for further validation and both potently inhibited sphere formation and self-renewal of BCSCs in vitro. Benztropine mesylate treatment decreased cell subpopulations with high ALDH activity and with a CD44⁺/CD24⁻ phenotype. In vivo, benztropine mesylate inhibited tumor-initiating potential in a 4T1 mouse model. Functional studies indicated that benztropine mesylate inhibits functions of CSCs via the acetylcholine receptors, dopamine transporters/receptors, and/or histamine receptors. In summary, our findings identify benztropine mesylate as an inhibitor of BCSCs in vitro and in vivo. This study also provides a screening platform for identification of additional anti-CSC agents.

Epigenetic activation of LY6K predicts the presence of metastasis and poor prognosis in breast carcinoma

The role of lymphocyte antigen 6 complex, locus K (LY6K) in breast cancer has been studied, whereas the epigenetic control of LY6K transcription is not fully understood. Here, we report that breast cancer patients with increased LY6K expression had shorter disease-free and overall survival than the patients with low levels of LY6K by multivariate analysis. LY6K also was upregulated in breast cancer patients with distant metastases than those without distant metastases, downregulating E-cadherin expression. Furthermore, xenograft tumor volumes from LY6K knockdown nude mice were reduced than those of mice treated with control lentivirus. Interestingly, LY6K has a CpG island (CGI) around the transcription start site and non-CGI in its promoter, called a CGI shore. LY6K expression was inversely correlated with methylation in not only CGI but CGI shore, which are associated with histone modifications. Additionally, LY6K methylation was increased by the PAX3 transcription factor due to the SNP242 mutation in LY6K CGI shore. Taken together, breast cancer risk and metastasis were significantly associated with not only LY6K expression, but also methylation of CGI shore which induced by SNP242 mutation. Our results suggest that an understanding epigenetic mechanism of the LY6K gene may be useful to diagnose carcinogenic risk and predict outcomes of patients with metastatic breast cancer.

Dual-Mode Imaging-Guided Synergistic Chemo- and Magnetohyperthermia Therapy in a Versatile Nanoplatform To Eliminate Cancer Stem Cells

Cancer stem cells (CSCs) have been identified as a new target for therapy in diverse cancers. Traditional therapies usually kill the bulk of cancer cells, but are often unable to effectively eliminate CSCs, which may lead to drug resistance and cancer relapse. Herein, we propose a novel strategy: fabricating multifunctional magnetic Fe₃O₄@PPr@HA hybrid nanoparticles and loading it with the Notch signaling pathway inhibitor N-[N-(3,5-difluorophenacetyl-l-alanyl)]-S-phenylglycinet-butylester (DAPT) to eliminate CSCs. Hyaluronic acid ligands greatly enhance the accumulation of the hybrid nanoparticles in the tumor site and in the CSCs. Both hyaluronase in the tumor microenvironment and the magnetic hyperthermia effect of the inner magnetic core can accelerate the release of DAPT. This controlled release of DAPT in the tumor site further enhances the ability of the combination of chemo- and magnetohyperthermia therapy to eliminate cancer stem cells. With the help of polypyrrole-mediated photoacoustic and Fe₃O₄-mediated magnetic resonance imaging, the drug release can be precisely monitored in vivo. This versatile nanoplatform enables effective elimination of the cancer stem cells and monitoring of the drugs.

Cisplatin-enriching cancer stem cells confer multidrug resistance in non-small cell lung cancer via enhancing TRIB1/HDAC activity

Chemotherapeutic agents are generally used as a frontline therapy for non-small cell lung cancer (NSCLC). However, resistance to chemotherapy arises rapidly in NSCLC, and the reasons for chemotherapy resistance have not been fully determined. Here, we found cisplatin, but not paclitaxel and doxorubicin, induced the enrichment of cancer stem cell (CSC) and conferred multidrug resistance in NSCLC cell lines. In vivo study confirmed drug-resistant tumors displayed the enhanced expressions of CSC transcription factors. Mechanistically, cisplatin treatment resulted in C/EBP-β-dependent increasing of TRIB1. The crucial role of TRIB1 in cisplatin-induced enrichment of CSC and drug resistance was verified by knockdown TRIB1. Interestingly, cisplatin treatment also contributed to the increasement of HDAC, the interaction of TRIB1 with HDAC, and inactivation of p53. Similarly, the silencing of HDAC led to reduction of cisplatin-induced CSC, and combined knockdown of HDAC and TRIB1 exhibited enhanced effect. Additionally, the combination of HDAC inhibitor and cisplatin showed a reinforced antitumor action in NSCLC cell lines with TRIB1-dependent manner and remarkably shrink tumors in xenograft models. Moreover, cisplatin-treated NSCLC patients with high levels of TRIB1 exhibited a significantly poorer prognosis. Our findings illustrate a novel perspective in the evolution of chemotherapy resistance and provide a promising approach for the treatment of patients with NSCLC.

Evidence for circulating cancer stem-like cells and epithelial-mesenchymal transition phenotype in the pleurospheres derived from lung adenocarcinoma using liquid biopsy

Lung cancer stem cells are supposed to be the main drivers of tumor initiation, maintenance, drug resistance, and relapse of the disease. Hence, identification of the cellular and molecular aspects of these cells is a prerequisite for targeted therapy of lung cancer. Currently, analysis of circulating tumor cells has the potential to become the main diagnostic technique to monitor disease progression or therapeutic response as it is non-invasive. However, accurate detection of circulating tumor cells has remained a challenge, as epithelial cell markers used so far are not always trustworthy for detecting circulating tumor cells, especially during epithelial-mesenchymal transition. As cancer stem cells are the only culprit to initiate metastatic tumors, our aim was to isolate and characterize circulating tumor stem cells rather than circulating tumor cells from the peripheral blood of NSCLC adenocarcinoma as limited data are available addressing the gene expression profiling of lung cancer stem cells. Here, we reveal that CD44(+)/CD24(-) population in circulation not only exhibit stem cell-related genes but also possess epithelial-mesenchymal transition characteristics. In conclusion, the use of one or more cancer stem cell markers along with epithelial, mesenchymal and epithelial mesenchymal transition markers will prospectively provide the most precise assessment of the threat for recurrence and metastatic disease and has a great potential for forthcoming applications in harvesting circulating tumor stem cells and their downstream applications. Our results will aid in developing diagnostic and prognostic modalities and personalized treatment regimens like dendritic cell-based immunotherapy that can be utilized for targeting and eliminating circulating tumor stem cells, to significantly reduce the possibility of relapse and improve clinical outcomes.

Regulation of voltage-gated potassium channels attenuates resistance of side-population cells to gefitinib in the human lung cancer cell line NCI-H460

BACKGROUND

Side-population (SP) cells that exclude anti-cancer drugs have been found in various tumor cell lines. Moreover, SP cells have a higher proliferative potential and drug resistance than main population cells (Non-SP cells). Also, several ion channels are responsible for the drug resistance and proliferation of SP cells in cancer.

METHODS

To confirm the expression and function of voltage-gated potassium (Kv) channels of SP cells, these cells, as well as highly expressed ATP-binding cassette (ABC) transporters and stemness genes, were isolated from a gefitinib-resistant human lung adenocarcinoma cell line (NCI-H460), using Hoechst 33342 efflux.

RESULTS

In the present study, we found that mRNA expression of Kv channels in SP cells was different compared to Non-SP cells, and the resistance of SP cells to gefitinib was weakened with a combination treatment of gefitinib and Kv channel blockers or a Kv7 opener, compared to single-treatment gefitinib, through inhibition of the Ras-Raf signaling pathway.

CONCLUSIONS

The findings indicate that Kv channels in SP cells could be new targets for reducing the resistance to gefitinib.

Are breast cancer stem cells the key to resolving clinical issues in breast cancer therapy?

Despite the dramatic advances in breast cancer treatment over the past two decades, it is still the most common malignancies in women. One of the reasons patients succumb to breast cancer is treatment resistance leading to metastasis and recurrence. Recently, cancer stem cells (CSCs) have been suggested as a cause of metastasis and recurrence in several cancers because of their unique characteristics, including self-renewal, pluripotency, and high proliferative ability. Increasing evidence has implicated breast cancer stem cells (BCSCs) as essential for tumor development, progression, recurrence, and treatment resistance. BCSCs exhibit resistance to treatment owing to several inter-related factors, including overexpression of ATP-binding cassette (ABC) transporters and increased aldehyde dehydrogenase (ALDH) activity, DNA repair, and reactive oxygen species (ROS) scavenging. In addition, the Notch, Hedgehog, and Wnt signaling pathways have been suggested as the major pathways involved in the self-renewal and differentiation of BCSCs. Despite growing evidence suggesting the importance of BCSCs in progression and metastasis, clear criteria for the identification of BCSCs in clinical practice have yet to be established. Several potential markers have been suggested, including CD44⁺/CD24^-/low, ALDH1, EpCAM/ESA, and nestin; however, there is no standard method to detect BCSCs. Triple-negative breast cancer, which shows initial chemosensitivity, demonstrates worsened prognosis due to therapy resistance, which might be related to the presence of BCSCs. Several clinical trials aimed at the identification of BCSCs or the development of BCSC-targeted therapy are in progress. Determining the clinical relevance of BCSCs may provide clues for overcoming therapy resistance in breast cancer.

Nelfinavir targets multiple drug resistance mechanisms to increase the efficacy of doxorubicin in MCF-7/Dox breast cancer cells

Development of multidrug resistance (MDR) remains a significant problem in cancer chemotherapy and underscores the importance of using chemosensitizers. Well known MDR mechanisms include: (i) upregulation of drug-efflux; (ii) increased signaling via AKT; and (iii) decreased apoptosis. Therefore, chemosensitizers should target multiple resistance mechanisms. We investigated the efficacy of nelfinavir (NFV), a clinically approved anti-HIV drug, in increasing doxorubicin (DOX) toxicity in a MDR breast cancer cell line, MCF-7/Dox. As compared to parental MCF-7 cells, the MCF-7/Dox were 15-20 fold more resistant to DOX-induced cytotoxicity at 48 h post-exposure (DOX IC50 = 1.8 μM vs. 32.4 μM). Coexposures to NFV could significantly (p < 0.05) decrease DOX-IC50 in MCF-7/Dox cells. Multiple exposures to physiologic concentrations of NFV (2.25 μM or 6.75 μM) decreased DOX-IC50 by 21-fold and 50-fold, respectively. Interestingly, although single exposure to NFV transiently induced P-glycoprotein (P-gp) levels, multiple treatments with NFV inhibited both P-gp expression and efflux function, which increased intracellular DOX concentrations. Single exposure to NFV augmented the markers of cell-survival (AKT) and autophagy (LC3-II), whereas multiple exposures enabled suppression of both total AKT (t-AKT) and insulin like growth factor-1 (IGF-1)-induced phosphorylated AKT (p-AKT) levels. Multiple exposures to NFV also resulted in increased unfolded protein response (UPR) transducers, e.g. Grp78, p-PERK, p-eIF2α, and ATF-4; and endoplasmic reticulum (ER) stress induced death sensors, e.g. CHOP & TRIB-3. Multiple exposures to NFV also abrogated the mitogenic effects of IGF-1. In mice carrying MCF-7/Dox tumor xenografts, intraperitoneal (i.p.) injection of NFV (20 mg/kg/day) and DOX (2 mg/kg/twice/wk) decreased tumor growth more significantly (p < 0.01) than either agent alone. Immunohistochemical (IHC) analysis revealed decreased p-AKT and Ki-67 levels. Thus, NFV overcomes MDR in breast cancer cells and should be tested as an adjunct to chemotherapy.

Lung cancer stem cells: The root of resistance

In the absence of specific treatable mutations, platinum-based chemotherapy remains the gold standard of treatment for lung cancer patients. However, 5-year survival rates remain poor due to the development of resistance and eventual relapse. Resistance to conventional cytotoxic therapies presents a significant clinical challenge in the treatment of this disease. The cancer stem cell (CSC) hypothesis suggests that tumors are arranged in a hierarchical structure, with the presence of a small subset of stem-like cells that are responsible for tumor initiation and growth. This CSC population has a number of key properties such as the ability to asymmetrically divide, differentiate and self-renew, in addition to having increased intrinsic resistance to therapy. While cytotoxic chemotherapy kills the bulk of tumor cells, CSCs are spared and have the ability to recapitulate the heterogenic tumor mass. The identification of lung CSCs and their role in tumor biology and treatment resistance may lead to innovative targeted therapies that may ultimately improve clinical outcomes in lung cancer patients. This review will focus on lung CSC markers, their role in resistance and their relevance as targets for future therapies.

Adipose mesenchymal stromal cells response to ionizing radiation

BACKGROUND AIMS

This study evaluates the biological response of adipose tissue-derived mesenchymal stromal cells (aMSCs) to ionizing radiation (IR).

METHODS

Irradiated BALB/c mice aMSCs were characterized for functionality and phenotype. The clonogenic capacity of irradiated aMSCs was assessed and compared with those of metastatic breast cancer cell line (4T1) and normal mouse fibroblasts (NIH3T3-wt). We investigated the IR-induced DNA damage response, apoptosis, changes in cell cycle (CC) dynamics and protein and gene expression.

RESULTS

Irradiated and non-irradiated aMSCs were able to differentiate into adipocytes, chondrocytes and osteocytes with no significant difference. Irradiated aMSCs maintained the expression of mesenchymal stromal cells (MSCs) surface antigens and, as expected, were negative for hematopoietic stem cells (HSCs) surface antigens when tested up to 7 days after IR for all irradiation doses with no significant difference. Clonogenically, irradiated aMSCs had higher relative survival fraction and plating efficiency than 4T1 and NIH3T3-wt. Irradiated aMSCs expressed higher □H2AX and significantly showed faster and more time-efficient IR-induced DNA damage response evident by up-regulated DNA-PKcs and RAD51. Two hours after IR, most of aMSCs DNA damage/repair-related genes showed up-regulation that disappeared within 6 h after IR. Irradiated aMSCs showed a significant rise and an earlier peak of p-ATM-dependent and -independent (p84/5E10-mediated) G2/M CC arrest compared with 4T1 and NIH3T3-wt.

CONCLUSIONS

After IR exposure, aMSCs showed a robust and time-efficient radiation-induced DNA damage repair response, stable phenotypical characteristics and multi-lineage differentiation potential, suggesting they may be reliable candidates for cell therapy in radiation oncology regenerative medicine.

Low adherent cancer cell subpopulations are enriched in tumorigenic and metastatic epithelial-to-mesenchymal transition-induced cancer stem-like cells

Cancer stem cells are responsible for tumor progression, metastasis, therapy resistance and cancer recurrence, doing their identification and isolation of special relevance. Here we show that low adherent breast and colon cancer cells subpopulations have stem-like properties. Our results demonstrate that trypsin-sensitive (TS) breast and colon cancer cells subpopulations show increased ALDH activity, higher ability to exclude Hoechst 33342, enlarged proportion of cells with a cancer stem-like cell phenotype and are enriched in sphere- and colony-forming cells in vitro. Further studies in MDA-MB-231 breast cancer cells reveal that TS subpopulation expresses higher levels of SLUG, SNAIL, VIMENTIN and N-CADHERIN while show a lack of expression of E-CADHERIN and CLAUDIN, being this profile characteristic of the epithelial-to-mesenchymal transition (EMT). The TS subpopulation shows CXCL10, BMI-1 and OCT4 upregulation, differing also in the expression of several miRNAs involved in EMT and/or cell self-renewal such as miR-34a-5p, miR-34c-5p, miR-21-5p, miR-93-5p and miR-100-5p. Furthermore, in vivo studies in immunocompromised mice demonstrate that MDA-MB-231 TS cells form more and bigger xenograft tumors with shorter latency and have higher metastatic potential. In conclusion, this work presents a new, non-aggressive, easy, inexpensive and reproducible methodology to isolate prospectively cancer stem-like cells for subsequent biological and preclinical studies.

Cancer stem-like cell: a novel target for nasopharyngeal carcinoma therapy

Nasopharyngeal carcinoma (NPC) is the most common cancer originating in the nasopharynx, and is extremely common in southern regions of China. Although the standard combination of radiotherapy and chemotherapy has improved the efficiency in patients with NPC, relapse and early metastasis are still the common causes of mortality. Cancer stem-like cells (CSCs) or tumor initial cells are hypothesized to be involved in cancer metastasis and recurrence. Over the past decade, increasing numbers of studies have been carried out to identify CSCs from human NPC cells and tissues. The present paper will summarize the investigations on nasopharyngeal CSCs, including isolation, characteristics, and therapeutic approaches. Although there are still numerous challenges to translate basic research into clinical applications, understanding the molecular details of CSCs is essential for developing effective strategies to prevent the recurrence and metastasis of NPC.

Profilin 2 promotes migration, invasion, and stemness of HT29 human colorectal cancer stem cells

We investigated the role of profilin 2 in the stemness, migration, and invasion of HT29 cancer stem cells (CSCs). Increased and decreased levels of profilin 2 significantly enhanced and suppressed the self-renewal, migration, and invasion ability of HT29 CSCs, respectively. Moreover, profilin 2 directly regulated the expression of stemness markers (CD133, SOX2, and β-catenin) and epithelial mesenchymal transition (EMT) markers (E-cadherin and snail). CD133 and β-catenin were up-regulated by overexpression of profilin 2 and down-regulated by depletion of profilin 2. SOX2 was decreased by profilin 2 depletion. E-cadherin was not influenced by profilin 2- overexpression but increased by profilin 2- knockdown. The expression of snail was suppressed by profilin 2- knockdown. We speculated that stemness and the EMT are closely linked through profilin 2-related pathways. Therefore, this study indicates that profilin 2 affects the metastatic potential and stemness of colorectal CSCs by regulating EMT- and stemness-related proteins.

Cancer stem cells: a new approach to tumor development

Many theories have been proposed to explain the origins of cancer. Currently, evidences show that not every tumor cell is capable of initiating a tumor. Only a small part of the cancer cells, called cancer stem cells (CSCs), can generate a tumor identical to the original one, when removed from human tumors and transplanted into immunosuppressed mice. The name given to these cells comes from the resemblance to normal stem cells, except for the fact that their ability to divide is infinite. These cells are also affected by their microenvironment. Many of the signaling pathways, such as Wnt, Notch and Hedgehog, are altered in this tumoral subpopulation, which also contributes to abnormal proliferation. Researchers have found several markers for CSCs; however, much remains to be studied, or perhaps a universal marker does not even exist, since they vary among tumor types and even from patient to patient. It was also found that cancer stem cells are resistant to radiotherapy and chemotherapy. This may explain the re-emergence of the disease, since they are not completely eliminated and minimal amounts of CSCs can repopulate a tumor. Once the diagnosis in the early stages greatly increases the chances of curing cancer, identifying CSCs in tumors is a goal for the development of more effective treatments. The objective of this article is to discuss the origin of cancer according to the theory of stem cell cancer, as well as its markers and therapies used for treatment.

Characterisation of human limbal side population cells isolated using an optimised protocol from an immortalised epithelial cell line and primary limbal cultures

The challenges in limbal stem cell biology largely remain in the process of identification, isolation and expansion of these adult corneal epithelial stem cells of the eye. Due to the absence of specific limbal stem cell markers, identification and isolation of putative limbal stem cells is a complicated task. The side population assay is an isolation method that utilises the ability of stem cells to efflux the DNA-binding dye Hoechst 33342 (or other vital dyes) combined with dual wavelength flow cytometry and is a valuable strategy to enrich for limbal stem cells. This assay has been used to successfully identify stem/ progenitor cell populations in a variety of tissues and cell lines. Here we optimise this assay to identify SP cell populations in both primary human limbal epithelial cultures and in an established human corneal epithelial cell line. The limbal SP fraction showed higher expression of ATP-binding cassette sub-family G member 2 (ABCG2), ΔNp63--a common limbal stem cell marker and the stem cell marker Sox2 compared to non-SP cells (NSP).

Transmission of "split anergy" from tumor infiltrating to peripheral NK cells in a manner similar to "infectious tolerance"

According to a new paradigm of carcinogenesis, a tumor arises not from transformed cell, but only from tumor initiating cells called cancer stem cells (CSCs), which can originate from tissue stem cells. CSC are resistant to conventional therapy and after treatment form new tumors and give rise to metastases. Only natural killer (NK) cells are capable of lysing CSCs, but within different tumor types these cells experience a condition known as "split anergy", whereby the NK cells lose the ability to kill CSCs and being to produce cytokines. As a result, uncontrolled tumor growth arises and tumor stroma accumulates anergic NK cells. We hypothesize that anergic tumor infiltrating NK (TINK) cells transmit their property to naïve NK cells by infecting" them with a state of "split anergy" in a similar manner as T conventional cells are transformed into T regulatory cells during the process of "infectious tolerance". Anergic TINK cells egress from the tumor stroma via the lymphatic system, where they reach regional lymph nodes and transmit their properties to naïve NK cells, which in turn become anergic toward CSCs and lose immunosurveillance functions. The mechanisms proposed for this hypothesis and the methodological approaches for confirming the idea are presented in this issue.

Epithelial-to-mesenchymal transition: what is the impact on breast cancer stem cells and drug resistance

There is increasing interest in cancer stem cells (CSCs) and their role in cancer progression. Recently, CSCs have been identified in brain, skin, and intestinal tumors and it has been suggested that these CSCs are responsible for tumor growth and metastasis. In breast cancer fatality is often due to the development of metastatic disease (MBC). Almost 30% of early breast cancer patients eventually develop MBC and in 90% of these multi-drug resistance (MDR) occurs. This could be attributed to the presence of breast cancer stem cells (BCSCs). Epithelial-to-mesenchymal transition (EMT) is a process known to contribute to metastasis in cancer and it is mainly characterized by loss of E-cadherin expression. The TGF-β signaling pathway has an established role in promoting EMT by down-regulating E-cadherin via a number of transcription factors, such as Twist, Snail and Slug. EMT has also been reported to produce cells with stem cell-like properties. Definition of the exact molecular mechanisms that are involved in the generation of stem cells through EMT could lead to the identification of new potential therapeutic targets and enable the development of more efficient strategies for particular patient groups. In this review we discuss what is known about the relationship between EMT, BCSCs and MDR.

Limbal side population cells: a future treatment for limbal stem cell deficiency

Corneal blindness carries a morbidity that affects quality of life and is often associated with an increased economic burden. In this review, we focus on the severe and painful condition of limbal stem cell deficiency, an important cause of corneal blindness. Conventional corneal transplantation usually results in graft failure and is contraindicated in this condition. Ex vivo-expanded limbal epithelial transplantation has been used as a cellular-based therapy to regenerate and reconstruct the ocular surface as a mode of treatment. Enrichment methods for stem cells are a strategy to improve the outcome of limbal stem cell transplantation. Here we discuss the side population assay as a functional assay to enrich for stem cells as an important source of limbal stem cells. The challenges in ex vivo-expanded limbal stem cell transplantation are wide and varied and will be addressed in this review with regard to improving the clinical outcomes of cultivated limbal stem cell transplantation.