Scientific Resources

BACKGROUND: Cancer stem cells (CSCs) are believed to be responsible for breast cancer formation and recurrence; therefore,therapeutic strategies targeting CSCs must be developed. One approach may be targeting signaling pathways,like Notch,that are involved in stem cell self-renewal and survival. MATERIALS AND METHODS: Breast cancer stem-like cells derived from cell lines and patient samples were examined for Notch expression and activation. The effect of Notch inhibition on sphere formation,proliferation,and colony formation was determined. RESULTS: Breast cancer stem-like cells consistently expressed elevated Notch activation compared with bulk tumor cells. Blockade of Notch signaling using pharmacologic and genomic approaches prevented sphere formation,proliferation,and/or colony formation in soft agar. Interestingly,a gamma-secretase inhibitor,MRK003,induced apoptosis in these cells. CONCLUSION: Our findings support a crucial role for Notch signaling in maintenance of breast cancer stem-like cells,and suggest Notch inhibition may have clinical benefits in targeting CSCs. View Publication

The cell fate determination factor Dachshund was cloned as a dominant inhibitor of the hyperactive epidermal growth factor receptor ellipse. The expression of Dachshund is lost in human breast cancer associated with poor prognosis. Breast tumor-initiating cells (TIC) may contribute to tumor progression and therapy resistance. Here,endogenous DACH1 was reduced in breast cancer cell lines with high expression of TIC markers and in patient samples of the basal breast cancer phenotype. Re-expression of DACH1 reduced new tumor formation in serial transplantations in vivo,reduced mammosphere formation,and reduced the proportion of CD44(high)/CD24(low) breast tumor cells. Conversely,lentiviral shRNA to DACH1 increased the breast (B)TIC population. Genome-wide expression studies of mammary tumors demonstrated DACH1 repressed a molecular signature associated with stem cells (SOX2,Nanog,and KLF4) and genome-wide ChIP-seq analysis identified DACH1 binding to the promoter of the Nanog,KLF4,and Lin28 genes. KLF4/c-Myc and Oct4/Sox2 antagonized DACH1 repression of BTIC. Mechanistic studies demonstrated DACH1 directly repressed the Nanog and Sox2 promoters via a conserved domain. Endogenous DACH1 regulates BTIC in vitro and in vivo. View Publication

BACKGROUND: Cancer stem cells are presumed to have virtually unlimited proliferative and self-renewal abilities and to be highly resistant to chemotherapy,a feature that is associated with overexpression of ATP-binding cassette transporters. We investigated whether prolonged continuous selection of cells for drug resistance enriches cultures for cancer stem-like cells. METHODS: Cancer stem cells were defined as CD44+/CD24�?� cells that could self-renew (ie,generate cells with the tumorigenic CD44+/CD24�?� phenotype),differentiate,invade,and form tumors in vivo. We used doxorubicin-selected MCF-7/ADR cells,weakly tumorigenic parental MCF-7 cells,and MCF-7/MDR,an MCF-7 subline with forced expression of ABCB1 protein. Cells were examined for cell surface markers and side-population fractions by microarray and flow cytometry,with in vitro invasion assays,and for ability to form mammospheres. Xenograft tumors were generated in mice to examine tumorigenicity (n = 52). The mRNA expression of multidrug resistance genes was examined in putative cancer stem cells and pathway analysis of statistically significantly differentially expressed genes was performed. All statistical tests were two-sided. RESULTS: Pathway analysis showed that MCF-7/ADR cells express mRNAs from ABCB1 and other genes also found in breast cancer stem cells (eg,CD44,TGFB1,and SNAI1). MCF-7/ADR cells were highly invasive,formed mammospheres,and were tumorigenic in mice. In contrast to parental MCF-7 cells,more than 30% of MCF-7/ADR cells had a CD44+/CD24�?� phenotype,could self-renew,and differentiate (ie,produce CD44+/CD24�?� and CD44+/CD24+ cells) and overexpressed various multidrug resistance-linked genes (including ABCB1,CCNE1,and MMP9). MCF-7/ADR cells were statistically significantly more invasive in Matrigel than parental MCF-7 cells (MCF-7 cells = 0.82 cell per field and MCF-7/ADR = 7.51 cells per field,difference = 6.69 cells per field,95% confidence interval = 4.82 to 8.55 cells per field,P textless .001). No enrichment in the CD44+/CD24�?� or CD133+ population was detected in MCF-7/MDR. CONCLUSION: The cell population with cancer stem cell characteristics increased after prolonged continuous selection for doxorubicin resistance. View Publication

The classification of breast cancer into multiple molecular subtypes has necessitated the need for biomarkers that can assess tumor progression and the effects of chemopreventive agents on specific breast cancer subtypes. The goal of this study was to identify biomarkers whose expression are altered along with estrogen receptor α (ERα) in the polyoma middle-T antigen (PyMT) transgenic model of breast cancer and to investigate the chemopreventive activity of phenethyl isothiocyanate (PEITC). The diet of PyMT female mice was fortified with PEITC (8 mmol/kg) and the mammary streak and/or gross tumors and metastases in lungs were subjected to immunohistochemical analyses for ERα,FOXA1,and GATA-3. FOXA1 is associated with luminal type A cancers,while GATA-3 is a marker of luminal progenitor cell differentiation. In both control and PEITC-treated groups,there was a progressive loss of ERα and FOXA1 but persistence of GATA-3 expression indicating that the tumors retain luminal phenotype. Overall,the PyMT induced tumors exhibited the entire gamut of phenotypes from ERα+/FOXA1+/GATA-3+ tumors in the early stage to ERα±/FOXA1-/GATA-3+ in the late stage. Thus,PyMT model serves as an excellent model for studying progression of luminal subtype tumors. PEITC treated animals had multiple small tumors,indicating delay in tumor progression. Although these tumors were histologically similar to those in controls,there was a lower expression of these biomarkers in normal luminal cells indicating delay in tumor initiation. In in vitro studies,PEITC depleted AldeFluor-positive putative stem/progenitor cells,which may partly be responsible for the delay in tumor initiation. View Publication

There is increasing evidence that breast cancers contain tumor-initiating cells with stem cell properties. The importance of estrogen in the development of the mammary gland and in breast cancer is well known,but the influence of estrogen on the stem cell population has not been assessed. We show that estrogen reduces the proportion of stem cells in the normal human mammary gland and in breast cancer cells. The embryonic stem cell genes NANOG,OCT4,and SOX2 are expressed in normal breast stem cells and at higher levels in breast tumor cells and their expression decreases upon differentiation. Overexpression of each stem cell gene reduces estrogen receptor (ER) expression,and increases the number of stem cells and their capacity for invasion,properties associated with tumorigenesis and poor prognosis. These results indicate that estrogen reduces the size of the human breast stem cell pool and may provide an explanation for the better prognosis of ER-positive tumors. View Publication

Despite many years of intensive effort,there is surprisingly little consensus on the most suitable markers with which to locate and isolate stem cells from adult tissues. By comparison,the study of cancer stem cells is still in its infancy; so,unsurprisingly,there is great uncertainty as to the identity of these cells. Stem cell markers can be broadly categorized into molecular determinants of self-renewal,clonogenicity,multipotentiality,adherence to the niche,and longevity. This review assesses the utility of recognizing cancer stem cells by virtue of high expression of aldehyde dehydrogenases (ALDHs),probably significant determinants of cell survival through their ability to detoxify many potentially cytotoxic molecules,and contributing to drug resistance. Antibodies are available against the ALDH enzyme family,but the vast majority of studies have used cell sorting techniques to enrich for cells expressing these enzymes. Live cells expressing high ALDH activity are usually identified by the ALDEFLUOR kit and sorted by fluorescence activated cell sorting (FACS). For many human tumours,but notably breast cancer,cell selection based upon ALDH activity appears to be a useful marker for enriching for cells with tumour-initiating activity (presumed cancer stem cells) in immunodeficient mice,and indeed the frequency of so-called ALDH(bri) cells in many tumours can be an independent prognostic indicator. View Publication

The Y-box binding protein-1 (YB-1) is an oncogenic transcription/translation factor that is activated by phosphorylation at S102 whereby it induces the expression of growth promoting genes such as EGFR and HER-2. We recently illustrated by an in vitro kinase assay that a novel peptide to YB-1 was highly phosphorylated by the serine/threonine p90 S6 kinases RSK-1 and RSK-2,and to a lesser degree PKCα and AKT. Herein,we sought to develop this decoy cell permeable peptide (CPP) as a cancer therapeutic. This 9-mer was designed as an interference peptide that would prevent endogenous YB-1(S102) phosphorylation based on molecular docking. In cancer cells,the CPP blocked P-YB-1(S102) and down-regulated both HER-2 and EGFR transcript level and protein expression. Further,the CPP prevented YB-1 from binding to the EGFR promoter in a gel shift assay. Notably,the growth of breast (SUM149,MDA-MB-453,AU565) and prostate (PC3,LNCap) cancer cells was inhibited by ∼90% with the CPP. Further,treatment with this peptide enhanced sensitivity and overcame resistance to trastuzumab in cells expressing amplified HER-2. By contrast,the CPP had no inhibitory effect on the growth of normal immortalized breast epithelial (184htert) cells,primary breast epithelial cells,nor did it inhibit differentiation of hematopoietic progenitors. These data collectively suggest that the CPP is a novel approach to suppressing the growth of cancer cells while sparing normal cells and thereby establishes a proof-of-concept that blocking YB-1 activation is a new course of cancer therapeutics. View Publication

Inflammatory breast carcinoma (IBC) is characterized by exaggerated lymphovascular invasion (LVI),recapitulated in our human xenograft,MARY-X. This model exhibited lymphovascular emboli in vivo and corresponding spheroids in vitro. Owing to the morphological and gene profile resemblance of these spheroids to embryonal blastocysts,we wondered whether they might exhibit embryonic stem cell signaling. Specifically we investigated Notch and observed selective Notch 3 activation by expression profiling,reverse transcriptase- and real-time PCR,western blot and immunofluorescence in vitro,and immunohistochemistry in vivo. Notch 3 intracellular domain (N3icd) and six target genes,HES-5,HEY-1,c-Myc,Deltex-1,NRARP and PBX1,markedly increased in MARY-X. In addition,a significant percentage of MARY-X cells expressed aldehyde dehydrogenase (ALDH),a stem cell marker. Only the ALDH(+) cells were capable of secondary spheroidgenesis,tumorigenicity and self-renewal. Inhibiting Notch 3 activation in vitro with γ-secretase inhibitors (GSIs) or small interfering RNA resulted in a downregulation of Notch target genes,including CD133,and an induction of caspase 3-mediated apoptosis. Transfection of N3icd but not Notch 1 intracellular domain into normal human mammary epithelial cells resulted in increased expression of Notch target genes and induction of spheroidgenesis. GSI in vivo resulted in inhibitory but diffusion-limited effects on Notch 3 signaling,resulting in xenograft growth reduction. The lymphovascular emboli of human IBC exhibited dual N3icd and ALDH1 immunoreactivities independently of molecular subtype. This Notch 3 addiction of lymphovascular emboli might be exploited in future therapeutic strategies. View Publication

There is increasing evidence that breast and other cancers originate from and are maintained by a small fraction of stem/progenitor cells with self-renewal properties. Whether such cancer stem/progenitor cells originate from normal stem cells based on initiation of a de novo stem cell program,by reprogramming of a more differentiated cell type by oncogenic insults,or both remains unresolved. A major hurdle in addressing these issues is lack of immortal human stem/progenitor cells that can be deliberately manipulated in vitro. We present evidence that normal and human telomerase reverse transcriptase (hTERT)-immortalized human mammary epithelial cells (hMECs) isolated and maintained in Dana-Farber Cancer Institute 1 (DFCI-1) medium retain a fraction with progenitor cell properties. These cells coexpress basal (K5,K14,and vimentin),luminal (E-cadherin,K8,K18,or K19),and stem/progenitor (CD49f,CD29,CD44,and p63) cell markers. Clonal derivatives of progenitors coexpressing these markers fall into two distinct types--a K5(+)/K19(-) type and a K5(+)/K19(+) type. We show that both types of progenitor cells have self-renewal and differentiation ability. Microarray analyses confirmed the differential expression of components of stem/progenitor-associated pathways,such as Notch,Wnt,Hedgehog,and LIF,in progenitor cells compared with differentiated cells. Given the emerging evidence that stem/progenitor cells serve as precursors for cancers,these cellular reagents represent a timely and invaluable resource to explore unresolved questions related to stem/progenitor origin of breast cancer. View Publication

OBJECTIVE: The aim of this narrative review was to evaluate the role of cancer stem cells (CSCs) and sex steroids in the pathophysiology of human breast cancer. METHODS: A key-word search was performed using the Scopus database. Preference was given to studies using human cells and tissues. RESULTS: Long-term estrogen-progestin hormone therapy is known to increase breast cancer risk,although the mechanisms are poorly understood. In the last few years,it has become clear that many human breast cancers contain CSCs,which may be responsible for much of the tumor's malignant behavior. Very recently,the impact of estrogen,progesterone,and progestins on breast CSCs and their progeny has been studied and clarified. Most breast CSCs are estrogen receptor negative and progesterone receptor negative,although some intermediary progenitor forms have hormone receptors,especially progesterone receptor. Most mature human breast cancer cellsare estrogen receptor positive and can thus be stimulated by estrogen. Breast CSCs usually elaborate CD44+,CD24j/low and/or ALDEFLUOR+ cell markers and are lineage markers negative. One of the main roles of progesterone and progestin seems to be on certain breast cancer stem intermediate forms,inducing them to revert back to a more primitive breast CSC form. CONCLUSIONS: As the pathophysiology of human breast CSC is clarified,it is probable that this will lead to novel,effective breast cancer treatments and,perhaps,new breast cancer preventive agents. This research may also lead to safer hormone therapy regimens. View Publication

There is increasing evidence that many cancers,including breast cancer,contain populations of cells that display stem-cell properties. These breast cancer stem cells,by virtue of their relative resistance to radiation and cytotoxic chemotherapy,may contribute to treatment resistance and relapse. The elucidation of pathways that regulate these cells has led to the identification of potential therapeutic targets. A number of agents capable of targeting breast cancer stem cells in preclinical models are currently entering clinical trials. Assessment of the efficacy of the agents will require development of innovative clinical trial designs with appropriate biologic and clinical end points. The effective targeting of breast cancer stem cells has the potential to significantly improve outcome for women with both early-stage and advanced breast cancer. View Publication

The origins of the epithelial cells participating in the development,tissue homeostasis,and cancer of the human breast are poorly understood. However,emerging evidence suggests a role for adult tissue-specific stem cells in these processes. In a hierarchical manner,these generate the two main mammary cell lineages,producing an increasing number of cells with distinct properties. Understanding the biological characteristics of human breast stem cells and their progeny is crucial in attempts to compare the features of normal stem cells and cancer precursor cells and distinguish these from nonprecursor cells and cells from the bulk of a tumor. A historical overview of research on human breast stem cells in primary tissue and in culture reveals the progress that has been made in this area,whereas a focus on the cell-of-origin and reprogramming that occurs during neoplastic conversion provides insight into the enigmatic way in which human breast cancers are skewed toward the luminal epithelial lineage. View Publication