A cell initiating human acute myeloid leukaemia after transplantation into SCID mice

Most human acute myeloid leukaemia (AML) cells have limited proliferative capacity, suggesting that the leukaemic clone may be maintained by a rare population of stem cells. This putative leukaemic stem cell has not been characterized because the available in vitro assays can only detect progenitors with limited proliferative and replating potential. We have now identified an AML-initiating cell by transplantation into severe combined immune-deficient (SCID) mice. These cells homed to the bone marrow and proliferated extensively in response to in vivo cytokine treatment, resulting in a pattern of dissemination and leukaemic cell morphology similar to that seen in the original patients. Limiting dilution analysis showed that the frequency of these leukaemia-initiating cells in the peripheral blood of AML patients was one engraftment unit in 250,000 cells. We fractionated AML cells on the basis of cell-surface-marker expression and found that the leukaemia-initiating cells that could engraft SCID mice to produce large numbers of colony-forming progenitors were CD34+ CD38-; however, the CD34+ CD38+ and CD34- fractions contained no cells with these properties. This in vivo model replicates many aspects of human AML and defines a new leukaemia-initiating cell which is less mature than colony-forming cells.

Identification of cells initiating human melanomas

Tumour-initiating cells capable of self-renewal and differentiation, which are responsible for tumour growth, have been identified in human haematological malignancies and solid cancers. If such minority populations are associated with tumour progression in human patients, specific targeting of tumour-initiating cells could be a strategy to eradicate cancers currently resistant to systemic therapy. Here we identify a subpopulation enriched for human malignant-melanoma-initiating cells (MMIC) defined by expression of the chemoresistance mediator ABCB5 (refs 7, 8) and show that specific targeting of this tumorigenic minority population inhibits tumour growth. ABCB5+ tumour cells detected in human melanoma patients show a primitive molecular phenotype and correlate with clinical melanoma progression. In serial human-to-mouse xenotransplantation experiments, ABCB5+ melanoma cells possess greater tumorigenic capacity than ABCB5- bulk populations and re-establish clinical tumour heterogeneity. In vivo genetic lineage tracking demonstrates a specific capacity of ABCB5+ subpopulations for self-renewal and differentiation, because ABCB5+ cancer cells generate both ABCB5+ and ABCB5- progeny, whereas ABCB5- tumour populations give rise, at lower rates, exclusively to ABCB5- cells. In an initial proof-of-principle analysis, designed to test the hypothesis that MMIC are also required for growth of established tumours, systemic administration of a monoclonal antibody directed at ABCB5, shown to be capable of inducing antibody-dependent cell-mediated cytotoxicity in ABCB5+ MMIC, exerted tumour-inhibitory effects. Identification of tumour-initiating cells with enhanced abundance in more advanced disease but susceptibility to specific targeting through a defining chemoresistance determinant has important implications for cancer therapy.

Unravelling cancer stem cell potential

The maintenance and repair of many adult tissues are ensured by stem cells (SCs), which reside at the top of the cellular hierarchy of these tissues. Functional assays, such as in vitro clonogenic assays, transplantation and in vivo lineage tracing, have been used to assess the renewing and differentiation potential of normal SCs. Similar strategies have suggested that solid tumours may also be hierarchically organized and contain cancer SCs (CSCs) that sustain tumour growth and relapse after therapy. In this Opinion article, we discuss the different parallels that can be drawn between adult SCs and CSCs in solid tumours.

Human melanoma-initiating cells express neural crest nerve growth factor receptor CD271

The question of whether tumorigenic cancer stem cells exist in human melanomas has arisen in the last few years. Here we show that in melanomas, tumour stem cells (MTSCs, for melanoma tumour stem cells) can be isolated prospectively as a highly enriched CD271(+) MTSC population using a process that maximizes viable cell transplantation. The tumours sampled in this study were taken from a broad spectrum of sites and stages. High-viability cells isolated by fluorescence-activated cell sorting and re-suspended in a matrigel vehicle were implanted into T-, B- and natural-killer-deficient Rag2(-/-)gammac(-/-) mice. The CD271(+) subset of cells was the tumour-initiating population in 90% (nine out of ten) of melanomas tested. Transplantation of isolated CD271(+) melanoma cells into engrafted human skin or bone in Rag2(-/-)gammac(-/-) mice resulted in melanoma; however, melanoma did not develop after transplantation of isolated CD271(-) cells. We also show that in mice, tumours derived from transplanted human CD271(+) melanoma cells were capable of metastatsis in vivo. CD271(+) melanoma cells lacked expression of TYR, MART1 and MAGE in 86%, 69% and 68% of melanoma patients, respectively, which helps to explain why T-cell therapies directed at these antigens usually result in only temporary tumour shrinkage.

Coexistence of LMPP-like and GMP-like leukemia stem cells in acute myeloid leukemia

The relationships between normal and leukemic stem/progenitor cells are unclear. We show that in ∼80% of primary human CD34+ acute myeloid leukemia (AML), two expanded populations with hemopoietic progenitor immunophenotype coexist in most patients. Both populations have leukemic stem cell (LSC) activity and are hierarchically ordered; one LSC population gives rise to the other. Global gene expression profiling shows the LSC populations are molecularly distinct and resemble normal progenitors but not stem cells. The more mature LSC population most closely mirrors normal granulocyte-macrophage progenitors (GMP) and the immature LSC population a previously uncharacterized progenitor functionally similar to lymphoid-primed multipotential progenitors (LMPPs). This suggests that in most cases primary CD34+ AML is a progenitor disease where LSCs acquire abnormal self-renewal potential.

A hierarchy of self-renewing tumor-initiating cell types in glioblastoma

The neural stem cell marker CD133 is reported to identify cells within glioblastoma (GBM) that can initiate neurosphere growth and tumor formation; however, instances of CD133(-) cells exhibiting similar properties have also been reported. Here, we show that some PTEN-deficient GBM tumors produce a series of CD133(+) and CD133(-) self-renewing tumor-initiating cell types and provide evidence that these cell types constitute a lineage hierarchy. Our results show that the capacities for self-renewal and tumor initiation in GBM need not be restricted to a uniform population of stemlike cells, but can be shared by a lineage of self-renewing cell types expressing a range of markers of forebrain lineage.

Cancer stem cells in squamous cell carcinoma switch between two distinct phenotypes that are preferentially migratory or proliferative

Epithelial-to-mesenchymal transition (EMT) is an important driver of tumor invasion and metastasis, which causes many cancer deaths. Cancer stem cells (CSC) that maintain and initiate tumors have also been implicated in invasion and metastasis, but whether EMT is an important contributor to CSC function is unclear. In this study, we investigated whether a population of CSCs that have undergone EMT (EMT CSCs) exists in squamous cell carcinoma (SCC). We also determined whether a separate population of CSCs that retain epithelial characteristics (non-EMT CSCs) is also present. Our studies revealed that self-renewing CSCs in SCC include two biologically-distinct phenotypes. One phenotype, termed CD44(high)ESA(high), was proliferative and retained epithelial characteristics (non-EMT CSCs), whereas the other phenotype, termed CD44(high)ESA(low), was migratory and had mesenchymal traits characteristic of EMT CSCs. We found that non-EMT and EMT CSCs could switch their epithelial or mesenchymal traits to reconstitute the cellular heterogeneity which was characteristic of CSCs. However, the ability of EMT CSCs to switch to non-EMT character was restricted to cells that were also ALDH1(+), implying that only ALDH1(+) EMT cells had the ability to seed a new epithelial tumor. Taken together, our findings highlight the identification of two distinct CSC phenotypes and suggest a need to define therapeutic targets that can eradicate both of these variants to achieve effective SCC treatment.

CXCR4 regulates migration and development of human acute myelogenous leukemia stem cells in transplanted NOD/SCID mice

The chemokine stromal cell-derived factor-1 (SDF-1) and its receptor CXCR4 participate in the retention of normal hematopoietic stem cells within the bone marrow (BM) and their release into the circulation. Homing and engraftment of human stem cells in immunodeficient mice are dependent on cell surface CXCR4 expression and the production of BM SDF-1, which acts also as a survival factor for both human and murine stem cells. However, the role of SDF-1/CXCR4 interactions in the control of human acute myelogenous leukemia (AML) cell trafficking and disease progression is poorly understood. In this study, we report that although some AML cells do not express surface CXCR4, all AML cells tested express internal CXCR4 and SDF-1. Culture of AML cells with SDF-1 promoted their survival, whereas addition of neutralizing CXCR4 antibodies, SDF-1 antibodies, or AMD3100 significantly decreased it. Pretreatment of primary human AML cells with neutralizing CXCR4 antibodies blocked their homing into the BM and spleen of transplanted NOD/SCID/B2m(null) mice. Furthermore, weekly administrations of antihuman CXCR4 to mice previously engrafted with primary AML cells led to a dramatic decrease in the levels of human AML cells in the BM, blood, and spleen in a dose- and time-dependent manner. Interestingly, the same treatment did not affect significantly the levels of normal human progenitors engrafted into NOD/SCID mice. Taken together, our findings demonstrated the importance of the SDF-1/CXCR4 axis in the regulation of in vivo motility and development of human AML stem cells and identified CXCR4 neutralization as a potential treatment for AML.

GM-CSF-based cancer vaccines

The crafting of genetic and biochemical techniques to identify cancer antigens yielded the unexpected discovery that immune recognition of tumors regularly accompanies cancer development. The failure of the host to suppress tumor formation or attenuate disease progression may thus reflect the limited immunogenicity of nascent tumors. One critical determinant of host immunity is the mixture of cytokines produced in the tumor microenvironment. We have compared a large number of secreted and surface molecules for their relative abilities to augment tumor immunity following gene transfer into cancer cells. In multiple murine models, granulocyte-macrophage colony stimulating factor (GM-CSF) proved to be the most potent immunostimulatory product. Vaccination with irradiated tumor cells engineered to secrete GM-CSF involves enhanced tumor antigen presentation by recruited dendritic cells (DCs) and macrophages; the coordinated functions of CD4+ and CD8+ T cells, CD1d-restricted NKT cells and antibodies mediate protective immunity. The evaluation of this vaccination strategy in patients with advanced melanoma revealed the consistent induction of cellular and humoral antitumor responses capable of effectuating substantial necrosis of distant metastases. The formulation of simplified methods for manufacturing autologous, GM-CSF-secreting tumor cells has enabled more extensive clinical testing in diverse patient settings.

Detection, isolation, and stimulation of quiescent primitive leukemic progenitor cells from patients with acute myeloid leukemia (AML)

Although many acute myeloid leukemia (AML) colony-forming cells (CFCs) and long-term culture-initiating cells (LTC-ICs) directly isolated from patients are actively cycling, quiescent progenitors are present in most samples. In the current study, (3)H-thymidine ((3)H-Tdr) suicide assays demonstrated that most NOD/SCID mouse leukemia-initiating cells (NOD/SL-ICs) are quiescent in 6 of 7 AML samples. AML cells in G(0), G(1), and S/G(2)+M were isolated from 4 of these samples using Hoechst 33342/pyroninY staining and cell sorting. The progenitor content of each subpopulation was consistent with the (3)H-Tdr suicide results, with NOD/SL-ICs found almost exclusively among G(0) cells while the cycling status of AML CFCs and LTC-ICs was more heterogeneous. Interestingly, after 72 hours in serum-free culture with or without Steel factor (SF), Flt-3 ligand (FL), and interleukin-3 (IL-3), most G(0) AML cells entered active cell cycle (percentage of AML cells remaining in G(0) at 72 hours, 1.2% to 37%, and 0% to 7.6% in cultures without and with growth factors [GFs], respectively) while G(0) cells from normal lineage-depleted bone marrow remained quiescent in the absence of GF. All 4 AML samples showed evidence of autocrine production of 2 or more of SF, FL, IL-3, and granulocyte-macrophage colony-stimulating factor (GM-CSF). In addition, 3 of 4 samples contained an internal tandem duplication of the FLT3 gene. In summary, quiescent leukemic cells, including NOD/SL-ICs, are present in most AML patients. Their spontaneous entry into active cell cycle in short-term culture might be explained by the deregulated GF signaling present in many AMLs.

Glioma-associated cancer-initiating cells induce immunosuppression

PURPOSE

Glioblastoma multiforme is a lethal cancer that responds poorly to therapy. Glioblastoma multiforme cancer-initiating cells have been shown to mediate resistance to both chemotherapy and radiation; however, it is unknown to what extent these cells contribute to the profound immunosuppression in glioblastoma multiforme patients and if strategies that alter their differentiation state can reduce this immunosuppression.

EXPERIMENTAL DESIGN

We isolated a subpopulation of cells from glioblastoma multiforme that possessed the capacity for self-renewal, formed neurospheres in vitro, were capable of pluripotent differentiation, and could initiate tumors in vivo. The immune phenotype of these cells was characterized including the elaboration of immunosuppressive cytokines and chemokines by ELISA. Functional immunosuppressive properties were characterized based on the inhibition of T-cell proliferation and effector responses, triggering of T-cell apoptosis, and induction of FoxP3(+) regulatory T cells. On altering their differentiation state, the immunosuppressive phenotype and functional assays were reevaluated.

RESULTS

We found that the cancer-initiating cells markedly inhibited T-cell proliferation and activation, induced regulatory T cells, and triggered T-cell apoptosis that was mediated by B7-H1 and soluble Galectin-3. These immunosuppressive properties were diminished on altering the differentiation of the cancer-initiating cells.

CONCLUSION

Cancer-initiating cells contribute to tumor evasion of the immunosurveillance and approaches that alter the differentiation state may have immunotherapeutic potential.

Side population cells isolated from mesenchymal neoplasms have tumor initiating potential

Although many cancers are maintained by tumor-initiating cells, this has not been shown for mesenchymal tumors, in part due to the lack of unique surface markers that identify mesenchymal progenitors. An alternative technique to isolate stem-like cells is to isolate side population (SP) cells based on efflux of Hoechst 33342 dye. We examined 29 mesenchymal tumors ranging from benign to high-grade sarcomas and identified SP cells in all but six samples. There was a positive correlation between the percentage of SP cells and the grade of the tumor. SP cells preferentially formed tumors when grafted into immunodeficient mice, and only cells from tumors that developed from the SP cells had the ability to initiate tumor formation upon serial transplantation. Although SP cells are able to efflux rhodamine dye in addition to Hoechst 33342, we found that the ability to efflux rhodamine dye did not identify a population of cells enriched for tumor-initiating capacity. Here, we identify a subpopulation of cells within a broad range of benign and malignant mesenchymal tumors with tumor-initiating capacity. In addition, our data suggest that the proportion of SP cells could be used as a prognostic factor and that therapeutically targeting this subpopulation of cells could be used to improve patient outcome.

Concepts of human leukemic development

Two fundamental problems in cancer research are identification of the normal cell within which cancer initiates and identification of the cell type capable of sustaining the growth of the neoplastic clone. There is overwhelming evidence that virtually all cancers are clonal and represent the progeny of a single cell. What is less clear for most cancers is which cells within the tumor clone possess tumorigenic or 'cancer stem cell' (CSC) properties and are capable of maintaining tumor growth. The concept that only a subpopulation of rare CSC is responsible for maintenance of the neoplasm emerged nearly 50 years ago. Testing of this hypothesis is most advanced for the hematopoietic system due to the establishment of functional in vitro and in vivo assays for stem and progenitor cells at all stages of development. This body of work led to conclusive proof for CSC with the identification and purification of leukemic stem cells capable of repopulating NOD/SCID mice. This review will focus on the historical development of the CSC hypothesis, the mechanisms necessary to subvert normal developmental programs, and the identification of the cell in which these leukemogenic events first occur.

CD133+ liver cancer stem cells modulate radioresistance in human hepatocellular carcinoma

CD133 is a cancer stem-cell (CSC) marker associated with radioresistance and chemoresistance in various cancers. In the present study, CD133-expressing liver cancer cells following radiation exposure showed higher activation of MAPK/PI3K signaling pathway and reduction in reactive oxygen species levels compared to CD133- cells. The in vivo study with a xenograft model showed increased tumor formation in irradiated CD133+ cell-injected nude mice compared to the CD133- group, suggesting that CD133 contributes to radioresistance in HCC. Therefore, CD133-expressing liver cancer cells have anti-apoptotic and radioresistance properties that may be useful to improve anti-cancer treatments, including chemotherapy/radiotherapy of HCC.

Identification and expansion of cancer stem cells in tumor tissues and peripheral blood derived from gastric adenocarcinoma patients

Gastric cancer is the fourth most common cancer worldwide, with a high rate of death and low 5-year survival rate. To date, there is a lack of efficient therapeutic protocols for gastric cancer. Recent studies suggest that cancer stem cells (CSCs) are responsible for tumor initiation, invasion, metastasis, and resistance to anticancer therapies. Thus, therapies that target gastric CSCs are attractive. However, CSCs in human gastric adenocarcinoma (GAC) have not been described. Here, we identify CSCs in tumor tissues and peripheral blood from GAC patients. CSCs of human GAC (GCSCs) that are isolated from tumor tissues and peripheral blood of patients carried CD44 and CD54 surface markers, generated tumors that highly resemble the original human tumors when injected into immunodeficient mice, differentiated into gastric epithelial cells in vitro, and self-renewed in vivo and in vitro. Our findings suggest that effective therapeutic protocols must target GCSCs. The capture of GCSCs from the circulation of GAC patients also shows great potential for identification of a critical cell population potentially responsible for tumor metastasis, and provides an effective protocol for early diagnosis and longitudinal monitoring of gastric cancer.

Arsenic exposure transforms human epithelial stem/progenitor cells into a cancer stem-like phenotype

BACKGROUND

Inorganic arsenic is a ubiquitous environmental carcinogen affecting millions of people worldwide. Evolving theory predicts that normal stem cells (NSCs) are transformed into cancer stem cells (CSCs) that then drive oncogenesis. In humans, arsenic is carcinogenic in the urogenital system (UGS), including the bladder and potentially the prostate, whereas in mice arsenic induces multi-organ UGS cancers, indicating that UGS NSCs may represent targets for carcino-genic initiation. However, proof of emergence of CSCs induced by arsenic in a stem cell population is not available.

METHODS

We continuously exposed the human prostate epithelial stem/progenitor cell line WPE-stem to an environmentally relevant level of arsenic (5 microM) in vitro and determined the acquired cancer phenotype.

RESULTS

WPE-stem cells rapidly acquired a malignant CSC-like phenotype by 18 weeks of exposure, becoming highly invasive, losing contact inhibition, and hyper-secreting matrix metalloproteinase-9. When hetero-transplanted, these cells (designated As-CSC) formed highly pleomorphic, aggressive tumors with immature epithelial- and mesenchymal-like cells, suggesting a highly pluripotent cell of origin. Consistent with tumor-derived CSCs, As-CSCs formed abundant free-floating spheres enriched in CSC-like cells, as confirmed by molecular analysis and the fact that only these floating cells formed xeno-graft tumors. An early loss of NSC self-renewal gene expression (p63, ABCG2, BMI-1, SHH, OCT-4, NOTCH-1) during arsenite exposure was sub-sequently reversed as the tumor suppressor gene PTEN was progressively suppressed and the CSC-like phenotype acquired.

CONCLUSIONS

Arsenite transforms prostate epithelial stem/progenitor cells into CSC-like cells, indicating that it can produce CSCs from a model NSC population.

Acute myeloid leukemia stem cells

A fundamental problem in cancer research is identification of the cells within a tumor that sustain the growth of the neoplastic clone. The concept that only a subpopulation of rare cancer stem cells (CSCs) is responsible for maintenance of the neoplasm emerged nearly 50 years ago; however, conclusive proof for the existence of a CSC was obtained only relatively recently. The evidence for the existence of CSCs was first derived from the study of human acute myeloid leukemia (AML), largely because of the availability of quantitative stem cell assays for the leukemic stem cell (LSC). These studies showed that only rare cells within the leukemic clone had the capacity to initiate AML growth after transplant into NOD/SCID mice, establishing the hierarchical organization of AML. Recent clonal-tracking studies showed that the LSC compartment is composed of different classes of LSCs, which can be distinguished on the basis of self-renewal potential. These findings have important implications for our understanding of the leukemogenic process as well as the design of more effective therapies to eliminate AML based on eradication of the LSCs. These studies are briefly reviewed here.

Malignant precursor cells pre-exist in human breast DCIS and require autophagy for survival

Background

While it is accepted that a majority of invasive breast cancer progresses from a ductal carcinoma in situ (DCIS) precursor stage, very little is known about the factors that promote survival of DCIS neoplastic cells within the hypoxic, nutrient deprived intraductal microenvironment.

Methodology and Principal Findings

We examined the hypothesis that fresh human DCIS lesions contain pre-existing carcinoma precursor cells. We characterized these cells by full genome molecular cytogenetics (Illumina HumanCytoSNP profile), and signal pathway profiling (Reverse Phase Protein Microarray, 59 endpoints), and demonstrated that autophagy is required for survival and anchorage independent growth of the cytogenetically abnormal tumorigenic DCIS cells. Ex vivo organoid culture of fresh human DCIS lesions, without enzymatic treatment or sorting, induced the emergence of neoplastic epithelial cells exhibiting the following characteristics: a) spontaneous generation of hundreds of spheroids and duct-like 3-D structures in culture within 2–4 weeks; b) tumorigenicity in NOD/SCID mice; c) cytogenetically abnormal (copy number loss or gain in chromosomes including 1, 5, 6, 8, 13, 17) compared to the normal karyotype of the non-neoplastic cells in the source patient's breast tissue; d) in vitro migration and invasion of autologous breast stroma; and e) up-regulation of signal pathways linked to, and components of, cellular autophagy. Multiple autophagy markers were present in the patient's original DCIS lesion and the mouse xenograft. We tested whether autophagy was necessary for survival of cytogenetically abnormal DCIS cells. The lysosomotropic inhibitor (chloroquine phosphate) of autophagy completely suppressed the generation of DCIS spheroids/3-D structures, suppressed ex vivo invasion of autologous stroma, induced apoptosis, suppressed autophagy associated proteins including Atg5, AKT/PI3 Kinase and mTOR, eliminated cytogenetically abnormal spheroid forming cells from the organ culture, and abrogated xenograft tumor formation.

Conclusions

Cytogenetically abnormal spheroid forming, tumorigenic, and invasive neoplastic epithelial cells pre-exist in human DCIS and require cellular autophagy for survival.

The SCID-rab model: a novel in vivo system for primary human myeloma demonstrating growth of CD138-expressing malignant cells

Ethical and scientific concerns regarding the use of human fetal bones in the SCID-hu model of primary human myeloma prompted us to develop a novel system that uses rabbit bones implanted subcutaneously in unconditioned SCID mice. Immunohistochemical analysis of the implanted bone revealed that the majority of bone marrow (BM) microenvironment cells such as blood vessels, osteoclasts and osteoblasts were of rabbit origin. The implanted bones were directly injected with myeloma cells from 28 patients. Successful engraftment of unseparated BM cells from 85% of patients and CD138-selected myeloma plasma cells from 81% of patients led to the production of patients' M-protein isotypes and typical myeloma manifestations (osteolytic bone lesions and angiogenesis of rabbit origin). Myeloma cells grew exclusively in the rabbit bone, but were able to metastasize into another bone at a remote site in the same mouse. Cells from patients with extramedullary disease also grew along the outer surface of the rabbit bones. This demonstrates the ability of SCID-rab model, marked by a nonmyelomatous, nonhuman, and nonfetal microenvironment, to support the growth of CD138-expressing myeloma cells. This system can now be widely used to study the biology of myeloma and its manifestations and to develop novel therapeutic approaches for this disease.

Different subsets of primary chronic myeloid leukemia stem cells engraft immunodeficient mice and produce a model of the human disease

Xenograft models of chronic phase human chronic myeloid leukemia (CML) have been difficult to develop because of the persistence of normal hematopoietic stem cells in most chronic phase CML patients and the lack of methods to selectively isolate the rarer CML stem cells. To circumvent this problem, we first identified nine patients' samples in which the long-term culture-initiating cells were predominantly leukemic and then transplanted cells from these samples into sublethally irradiated NOD/SCID and NOD/SCID-beta2microglobulin-/- mice. This resulted in the consistent and durable (>5 months) repopulation of both host genotypes with similar numbers of BCR-ABL+/Ph+ cells. The regenerated leukemic cells included an initial, transient population derived from CD34+CD38+ cells as well as more sustained populations derived from CD34+CD38- progenitors, indicative of a hierarchy of transplantable leukemic cells. Analysis of the phenotypes produced revealed a reduced output of B-lineage cells, enhanced myelopoiesis with excessive production of erythroid and megakaropoietic cells and the generation of primitive (CD34+) leukemic cells displaying an autocrine IL-3 and G-CSF phenotype, all characteristics of primary CML cells. These findings demonstrate the validity of this xenograft model of chronic phase human CML, which should enable future investigation of disease pathogenesis and new approaches to therapy.

Lunatic fringe deficiency cooperates with the Met/Caveolin gene amplicon to induce basal-like breast cancer

Basal-like breast cancers (BLBC) express a luminal progenitor gene signature. Notch receptor signaling promotes luminal cell fate specification in the mammary gland, while suppressing stem cell self-renewal. Here we show that deletion of Lfng, a sugar transferase that prevents Notch activation by Jagged ligands, enhances stem/progenitor cell proliferation. Mammary-specific deletion of Lfng induces basal-like and claudin-low tumors with accumulation of Notch intracellular domain fragments, increased expression of proliferation-associated Notch targets, amplification of the Met/Caveolin locus, and elevated Met and Igf-1R signaling. Human BL breast tumors, commonly associated with JAGGED expression, elevated MET signaling, and CAVEOLIN accumulation, express low levels of LFNG. Thus, reduced LFNG expression facilitates JAG/NOTCH luminal progenitor signaling and cooperates with MET/CAVEOLIN basal-type signaling to promote BLBC.

Internal tandem duplications of the FLT3 gene are present in leukemia stem cells

Internal tandem duplication mutations of the FLT3 gene (FLT3/ITD mutations) are the most frequent molecular abnormality in acute myeloid leukemia (AML) and are associated with a poor overall survival. While the normal FLT3 receptor is expressed in early hematopoietic progenitor cells, it has not been determined whether FLT3 mutations are present in the leukemic stem cells. In this study, we sorted primary AML samples into stem cell-enriched CD34+/CD38- fractions and then analyzed the sorted and unsorted cells for the FLT3 mutant-wild-type ratio. In each case, the FLT3 mutant-wild-type ratio was not changed by selection of CD34+/CD38- cells, implying that the mutations are present in the leukemic stem cells. We used the stem cell-enriched fraction to engraft nonobese diabetic-severe combined immunodeficient (NOD-SCID) mice and then confirmed that the FLT3/ITD mutation was present in the resultant engrafted marrow. As a final test of the importance of FLT3/ITD signaling in this engraftment model, we used a small molecule FLT3 inhibitor, CEP-701, to inhibit engraftment of FLT3/ITD stem cells. Taken together, these experiments establish that the FLT3/ITD mutations are present in leukemia stem cells, and that FLT3 inhibitors may have activity against these cells.

Wnt3a mediated activation of Wnt/β-catenin signaling promotes tumor progression in glioblastoma

Presence of a distinct population of cells that drives tumor progression supports the hierarchical model of tumor development in Glioblastoma (GBM) and substantiates the cancer stem cell hypothesis. Amongst the various developmental signaling pathways that are aberrantly activated, we here show that activated Wnt/β-catenin signaling pathway plays a critical role in malignant transformation and tumor progression in gliomas. We demonstrate that Wnt ligands - Wnt1 and Wnt3a are expressed in a graded manner in these tumors as well as over-expressed in glioma stem cell-lines. A selective inhibition of Wnt signaling pathway by selective knock-down of its ligands Wnt1 and Wnt3a in glioma-derived stem-like cells led to decreased cell proliferation, cell migration and chemo-resistance. Furthermore, Wnt silencing in glioma cells reduced the capacity to form intra-cranial tumors in vivo. Taken together, our study indicates Wnt/β-catenin signaling pathway as an essential driver of glioma tumorigenesis, recognizing role of Wnt3a as an oncogene and thereby offering novel therapeutic strategies for management of these tumors.

Cytokine treatment or accessory cells are required to initiate engraftment of purified primitive human hematopoietic cells transplanted at limiting doses into NOD/SCID mice

Little is known about the cell types or mechanisms that underlie the engraftment process. Here, we have examined parameters affecting the engraftment of purified human Lin-CD34+CD38- normal and AML cells transplanted at limiting doses into NOD/SCID recipients. Mice transplanted with 500 to 1000 Lin-CD34+CD38- cord blood (CB) or AML cells required the co-transplantation of accessory cells (ACs) or short-term in vivo cytokine treatment for engraftment, whereas transplantation of higher doses (>5000 Lin-CD34+CD38- cells) did not show these requirements suggesting that ACs are effective for both normal and leukemic stem cell engraftment in this model. Mature Lin+CD34- and primitive Lin-CD34+CD38+ cells were capable of acting as ACs even though no repopulating cells are present. Cytokine treatment of NOD/SCID mice could partially replace the requirement for co-transplantation of AC. Furthermore, no difference was seen between the percentage of engrafted mice treated with cytokines for only the first 10 days after transplant compared to those receiving cytokines for the entire time of repopulation. Surprisingly, no engraftment was detected in mice when cytokine treatment was delayed until 10 days posttransplant. Together, these studies suggest that the engraftment process requires pluripotent stem cells plus accessory cells or cytokine treatment which act early after transplantation. The NOD/SCID xenotransplant system provides the means to further clarify the processes underlying human stem cell engraftment.