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BACKGROUND: Cancer stem cells (CSCs) are purported to be epithelial tumour cells expressing CD44(+)CD24(lo) that exhibit aldehyde dehydrogenase activity (Aldefluor(+)). We hypothesised that if CSCs are responsible for tumour dissemination,disseminated cells in the bone marrow (BM) would be positive for putative breast CSC markers. Therefore,we assessed the presence of Aldefluor(+) epithelial (CD326(+)CD45(dim)) cells for the presence of the CD44(+)CD24(lo) phenotype in BM of patients with primary breast cancer (PBC). METHODS: BM aspirates were collected at the time of surgery from 66 patients with PBC. Thirty patients received neoadjuvant chemotherapy (NACT) prior to aspiration. BM was analysed for Aldefluor(+) epithelial cells with or without CD44(+)CD24(lo) expression by flow cytometry. BM aspirates from three healthy donors (HD) were subjected to identical processing and analyses and served as controls. RESULTS: Patients with triple-receptor-negative (TN) tumours had a significantly higher median percentage of CD44(+)CD24(lo) CSC within Aldefluor(+) epithelial cell population than patients with other immunohistochemical subtypes (P=0.018). Patients with TN tumours or with pN2 or higher pathologic nodal status were more likely to have a proportion of CD44(+)CD24(lo) CSC within Aldefluor(+) epithelial cell population above the highest level of HD. Furthermore,patients who received NACT were more likely to have percentages of Aldefluor(+) epithelial cells than the highest level of HD (P=0.004). CONCLUSION: The percentage of CD44(+)CD24(lo) CSC in the BM is higher in PBC patients with high risk tumour features. The selection or enrichment of Aldefluor(+) epithelial cells by NACT may represent an opportunity to target these cells with novel therapies. View Publication

BACKGROUND: Cancer stem cells (CSCs) have been shown to be a small stem cell-like cell population which appears to drive tumorigenesis,tumor recurrence and metastasis. Thus,identification and characterization of CSCs may be critical to defining effective anticancer therapies. In prostate cancer (PCa),the CD44(+) cell population appears to have stem cell-like properties including being tumorigenic. The enzyme aldehyde dehydrogenase (ALDH) has been found to identify hematopoietic stem cells and our aim was to determine the utility of ALDH activity and CD44 in identifying PCa stem cell-like cells in PCa cell lines. MATERIALS AND METHODS: LNCaP cells and PC-3 cells were sorted based on their expression of CD44 and ALDH activity. The cell populations were investigated using colony-forming assays,invasion assays,sphere formation experiments in a non-adherent environment and 3-D Matrigel matrix culture to observe the in vitro stem-cell like properties. Different sorted cell populations were injected subcutaneously into NOD/SCID mice to determine the corresponding tumorigenic capacities. RESULTS: ALDH(hi) CD44(+) cells exhibit a higher proliferative,clonogenic and metastatic capacity in vitro and demonstrate higher tumorigenicity capacity in vivo than did ALDH(lo) CD44(-) cells. The tumors recapitulated the population of the original cell line. However,ALDHlo CD44(-) cells were able to develop tumors,albeit with longer latency periods. CONCLUSION: ALDH activity and CD44 do not appear to identify PCa stem cells; however,they do indicate increased tumorigenic and metastatic potential,indicating their potential importance for further exploration. View Publication

Retinoic acid (RA) is used to treat leukemia and other cancers through its ability to promote cancer cell differentiation. Strategies to enhance the anticancer effects of RA could deepen and broaden its beneficial therapeutic applications. In this study,we describe a receptor cross-talk system that addresses this issue. RA effects are mediated by RAR/RXR receptors that we show are modified by interactions with the aryl hydrocarbon receptor (AhR),a protein functioning both as a transcription factor and a ligand-dependent adaptor in an ubiquitin ligase complex. RAR/RXR and AhR pathways cross-talk at the levels of ligand-receptor and also receptor-promoter interactions. Here,we assessed the role of AhR during RA-induced differentiation and a hypothesized convergence at Oct4,a transcription factor believed to maintain stem cell characteristics. RA upregulated AhR and downregulated Oct4 during differentiation of HL-60 promyelocytic leukemia cells. AhR overexpression in stable transfectants downregulated Oct4 and also decreased ALDH1 activity,another stem cell-associated factor,enhancing RA-induced differentiation as indicated by cell differentiation markers associated with early (CD38 and CD11b) and late (neutrophilic respiratory burst) responses. AhR overexpression also increased levels of activated Raf1,which is known to help propel RA-induced differentiation. RNA interference-mediated knockdown of Oct4 enhanced RA-induced differentiation and G(0) cell-cycle arrest relative to parental cells. Consistent with the hypothesized importance of Oct4 downregulation for differentiation,parental cells rendered resistant to RA by biweekly high RA exposure displayed elevated Oct4 levels that failed to be downregulated. Together,our results suggested that therapeutic effects of RA-induced leukemia differentiation depend on AhR and its ability to downregulate the stem cell factor Oct4. View Publication

We have used in vitro and mouse xenograft models to examine the interaction between breast cancer stem cells (CSC) and bone marrow-derived mesenchymal stem cells (MSC). We show that both of these cell populations are organized in a cellular hierarchy in which primitive aldehyde dehydrogenase expressing mesenchymal cells regulate breast CSCs through cytokine loops involving IL6 and CXCL7. In NOD/SCID mice,labeled MSCs introduced into the tibia traffic to sites of growing breast tumor xenografts where they accelerated tumor growth by increasing the breast CSC population. With immunochemistry,we identified MSC-CSC niches in these tumor xenografts as well as in frozen sections from primary human breast cancers. Bone marrow-derived MSCs may accelerate human breast tumor growth by generating cytokine networks that regulate the CSC population. View Publication

Current treatment options for advanced and hormone refractory prostate cancer are limited and responses to commonly used androgen pathway inhibitors are often unsatisfactory. Our recent results indicated that sodium ionophore monensin is one of the most potent and cancer-specific inhibitors in a systematic sensitivity testing of most known drugs and drug-like molecules in a panel of prostate cancer cell models. Because monensin has been extensively used in veterinary applications to build muscle mass in cattle,the link to prostate cancer and androgen signaling was particularly interesting. Here,we showed that monensin effects at nanomolar concentrations are linked to induction of apoptosis and potent reduction of androgen receptor mRNA and protein in prostate cancer cells. Monensin also elevated intracellular oxidative stress in prostate cancer cells as evidenced by increased generation of intracellular reactive oxygen species and by induction of a transcriptional profile characteristic of an oxidative stress response. Importantly,the antiproliferative effects of monensin were potentiated by combinatorial treatment with the antiandrogens and antagonized by antioxidant vitamin C. Taken together,our results suggest monensin as a potential well-tolerated,in vivo compatible drug with strong proapoptotic effects in prostate cancer cells,and synergistic effects with antiandrogens. Moreover,our data suggest a general strategy by which the effects of antiandrogens could be enhanced by combinatorial administration with agents that increase oxidative stress in prostate cancer cells. View Publication

Normal stem cells and cancer stem cells (CSCs) share similar properties,in that both have the capacity to self-renew and differentiate into multiple cell types. In both the normal stem cell and cancer stem cell fields,there has been a great need for a universal marker that can effectively identify and isolate these rare populations of cells in order to characterize them and use this information for research and therapeutic purposes. Currently,it would appear that certain isoenzymes of the aldehyde dehydrogenase (ALDH) superfamily may be able to fulfill this role as a marker for both normal and cancer stem cells. ALDH has been identified as an important enzyme in the protection of normal hematopoietic stem cells,and is now also widely used as a marker to identify and isolate various types of normal stem cells and CSCs. In addition,emerging evidence suggests that ALDH1 is not only a marker for stem cells,but may also play important functional roles related to self-protection,differentiation,and expansion. This comprehensive review discusses the role that ALDH plays in normal stem cells and CSCs,with focus on ALDH1 and ALDH3A1. Discrepancies in the functional themes between cell types and future perspectives for therapeutic applications will also be discussed. View Publication

The expression of an enzyme,GnT-V,that catalyzes a specific posttranslational modification of a family of glycoproteins,namely a branched N-glycan,is transcriptionally up-regulated during breast carcinoma oncogenesis. To determine the molecular basis of how early events in breast carcinoma formation are regulated by GnT-V,we studied both the early stages of mammary tumor formation by using 3D cell culture and a her-2 transgenic mouse mammary tumor model. Overexpression of GnT-V in MCF-10A mammary epithelial cells in 3D culture disrupted acinar morphogenesis with impaired hollow lumen formation,an early characteristic of mammary neoplastic transformation. The disrupted acinar morphogenesis of mammary tumor cells in 3D culture caused by her-2 expression was reversed in tumors that lacked GnT-V expression. Moreover,her-2-induced mammary tumor onset was significantly delayed in the GnT-V null tumors,evidence that the lack of the posttranslational modification catalyzed by GnT-V attenuated tumor formation. Inhibited activation of both PKB and ERK signaling pathways was observed in GnT-V null tumor cells. The proportion of tumor-initiating cells (TICs) in the mammary tumors from GnT-V null mice was significantly reduced compared with controls,and GnT-V null TICs displayed a reduced ability to form secondary tumors in NOD/SCID mice. These results demonstrate that GnT-V expression and its branched glycan products effectively modulate her-2-mediated signaling pathways that,in turn,regulate the relative proportion of tumor initiating cells and the latency of her-2-driven tumor onset. View Publication

Cancer stem cells (CSC) are rare drug-resistant cancer cell subsets proposed to be responsible for the maintenance and recurrence of cancer and metastasis. Telomerase is constitutively active in both bulk tumor cell and CSC populations but has only limited expression in normal tissues. Thus,inhibition of telomerase has been shown to be a viable approach in controlling cancer growth in nonclinical studies and is currently in phase II clinical trials. In this study,we investigated the effects of imetelstat (GRN163L),a potent telomerase inhibitor,on both the bulk cancer cells and putative CSCs. When breast and pancreatic cancer cell lines were treated with imetelstat in vitro,telomerase activity in the bulk tumor cells and CSC subpopulations were inhibited. Additionally,imetelstat treatment reduced the CSC fractions present in the breast and pancreatic cell lines. In vitro treatment with imetelstat,but not control oligonucleotides,also reduced the proliferation and self-renewal potential of MCF7 mammospheres and resulted in cell death after textless4 weeks of treatment. In vitro treatment of PANC1 cells showed reduced tumor engraftment in nude mice,concomitant with a reduction in the CSC levels. Differences between telomerase activity expression levels or telomere length of CSCs and bulk tumor cells in these cell lines did not correlate with the increased sensitivity of CSCs to imetelstat,suggesting a mechanism of action independent of telomere shortening for the effects of imetelstat on the CSC subpopulations. Our results suggest that imetelstat-mediated depletion of CSCs may offer an alternative mechanism by which telomerase inhibition may be exploited for cancer therapy. View Publication

A relatively rare aldehyde dehydrogenase 1 (ALDH1)-positive stem cell-like" subpopulation of tumor cells has the unique ability to initiate and perpetuate tumor growth; moreover� View Publication

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