Elizabeth R. Lawlor

EWS-FLI1 fusion transcript structure is an independent determinant of prognosis in Ewing's sarcoma.

PURPOSE More than 90% of Ewings sarcomas (ES) contain a fusion of the EWS and FLI1 genes, due to the t(11;22)(q24;q12) translocation. At the molecular level, the EWS-FLI1 rearrangements show great diversity. Specifically, many different combinations of exons from EWS and FLI1 encode in-frame fusion transcripts and result in differences in the length and composition of the chimeric protein, which functions as an oncogenic aberrant transcription factor. In the most common fusion type (type 1), EWS exon 7 is linked in frame with exon 6 of FLI1. As the fundamental pathogenetic lesion in ES, the molecular heterogeneity of these fusion transcripts may have functional and clinical significance. PATIENTS AND METHODS We performed a clinical and pathologic analysis of 112 patients with ES in which EWS-FLI1 fusion transcripts were identified by reverse-transcriptase polymerase chain reaction (RT-PCR). Adequate treatment and follow-up data were available in 99 patients treated with curative intent. Median follow-up in these 99 patients was 26 months (range, 1 to 140 months). Univariate and multivariate survival analyses were performed that included other prognostic factors, such as age, tumor location, size, and stage. RESULTS Among the 99 patients suitable for survival analysis, the tumors in 64 patients contained the type 1 fusion and in 35 patients contained less common fusion types. Stage at presentation was localized in 74 patients and metastatic in 25. Metastases (relative risk [RR] = 2.6; P = .008), and type 1 EWS-FLI1 fusion (RR = 0.37; P = .014) were, respectively, independent negative and positive prognostic factors for overall survival by multivariate analysis. Among 74 patients with localized tumors, the type 1 EWS-FLI1 fusion was also a significant positive predictor of overall survival (RR = 0.32; P = .034) by multivariate analysis. CONCLUSION EWS-FLI1 fusion type appears to be prognostically relevant in ES, independent of tumor site, stage, and size. Further studies are needed to clarify the biologic basis of this phenomenon.

Mast cells are required for angiogenesis and macroscopic expansion of Myc-induced pancreatic islet tumors

An association between inflammation and cancer has long been recognized, but the cause and effect relationship linking the two remains unclear. Myc is a pleiotropic transcription factor that is overexpressed in many human cancers and instructs many extracellular aspects of the tumor tissue phenotype, including remodeling of tumor stroma and angiogenesis. Here we show in a β-cell tumor model that activation of Myc in vivo triggers rapid recruitment of mast cells to the tumor site—a recruitment that is absolutely required for macroscopic tumor expansion. In addition, treatment of established β-cell tumors with a mast cell inhibitor rapidly triggers hypoxia and cell death of tumor and endothelial cells. Inhibitors of mast cell function may therefore prove therapeutically useful in restraining expansion and survival of pancreatic and other cancers.

Temporal dissection of p53 function in vitro and in vivo

To investigate the functions of the p53 tumor suppressor, we created a new knock-in gene replacement mouse model in which the endogenous Trp53 gene is substituted by one encoding p53ERTAM, a p53 fusion protein whose function is completely dependent on ectopic provision of 4-hydroxytamoxifen. We show here that both tissues in vivo and cells in vitro derived from such mice can be rapidly toggled between wild-type and p53 knockout states. Using this rapid perturbation model, we define the kinetics, dependence, persistence and reversibility of p53-mediated responses to DNA damage in tissues in vivo and to activation of the Ras oncoprotein and stress in vitro. This is the first example to our knowledge of a new class of genetic model that allows the specific, rapid and reversible perturbation of the function of a single endogenous gene in vivo.

Isolation and characterization of neural crest stem cells derived from in vitro-differentiated human embryonic stem cells

The neural crest is a transient structure of vertebrate embryos that initially generates neural crest stem cells (NCSCs) which then migrate throughout the body to produce a diverse array of mature tissue types. Due to the rarity of adult NCSCs as well as ethical and technical issues surrounding isolation of early embryonic tissues, biologic studies of human NCSCs are extremely challenging. Thus, much of what is known about human neural crest development has been inferred from model organisms. In this study, we report that functional NCSCs can be rapidly generated and isolated from in vitro-differentiated human embryonic stem cells (hESCs). Using the stromal-derived inducing activity (SDIA) of PA6 fibroblast co-culture we have induced hESCs to differentiate into neural crest. Within 1 week, migrating cells that express the early neural crest markers p75 and HNK1 as well as numerous other genes associated with neural crest induction such as SNAIL, SLUG, and SOX10 are detectable. Fluorescence-activated cell sorting (FACS)-based isolation of the p75-positive population enriches for cells with genetic, phenotypic, and functional characteristics of NCSCs. These p75-enriched cells readily form neurospheres in suspension culture, self-renew to form secondary spheres, and give rise under differentiation conditions to multiple neural crest lineages including peripheral nerves, glial, and myofibroblastic cells. Importantly, these cells differentiate into neural crest derivatives when transplanted into developing chick embryos in vivo. Thus, this SDIA protocol can be used to successfully and efficiently isolate early human NCSCs from hESCs in vitro. This renewable source of NCSCs provides an invaluable source of cells for studies of both normal and disordered human neural crest development.

Imaging guidelines for children with Ewing sarcoma and osteosarcoma: A report from the Children's Oncology Group Bone Tumor Committee

The Childrens Oncology Group (COG) is a multi‐institutional cooperative group dedicated to childhood cancer research that has helped to increase the survival of children with cancer through clinical trials. These clinical trials include a standardized regimen of imaging examinations performed prior to, during, and following therapy. This article presents imaging guidelines developed by a multidisciplinary group from the COG Bone Tumor Committee. These guidelines provide both required and recommended studies. Recommended examinations may become required in the future. These guidelines should be considered a work in progress that will evolve with advances in imaging and childhood cancer research. Pediatr Blood Cancer 2008;51:163–170.

Current Treatment Protocols Have Eliminated the Prognostic Advantage of Type 1 Fusions in Ewing Sarcoma: A Report From the Children's Oncology Group

PURPOSE Ewing sarcoma family tumors (ESFTs) exhibit chromosomal translocations that lead to the creation of chimeric fusion oncogenes. Combinatorial diversity among chromosomal breakpoints produces varying fusions. The type 1 EWS-FLI1 transcript is created as a result of fusion between exons 7 of EWS and 6 of FLI1, and retrospective studies have reported that type 1 tumors are associated with an improved outcome. We have re-examined this association in a prospective cohort of patients with ESFT treated according to current Childrens Oncology Group (COG) treatment protocols. METHODS Frozen tumor tissue was prospectively obtained from patients diagnosed with ESFT, and reverse transcriptase polymerase chain reaction (RT-PCR) was used to determine translocation status. Analysis was confined to patients with localized tumors who were diagnosed after 1994 and treated according to COG protocols. Translocation status was correlated with disease characteristics, event-free survival (EFS), and overall survival (OS). Results RT-PCR identified chimeric fusion oncogenes in 119 of 132 ESFTs. Eighty-nine percent of identified transcripts were EWS-FLI1, and of these, 58.8% were type 1. Five-year EFS and OS rates for patients with type 1 and non-type 1 fusions diagnosed between 2001 and 2005 were equivalent (type 1: EFS, 63% +/- 7%; OS, 83% +/- 6%; non-type 1: EFS, 71% +/- 9%; OS, 79% +/- 8%). CONCLUSION Current intensive treatment protocols for localized ESFT have erased the clinical disadvantage that was formerly observed in patients with non-type 1 EWS-FLI1 fusions.

BMI-1 Promotes Ewing Sarcoma Tumorigenicity Independent of CDKN2A Repression

Deregulation of the polycomb group gene BMI-1 is implicated in the pathogenesis of many human cancers. In this study, we have investigated if the Ewing sarcoma family of tumors (ESFT) expresses BMI-1 and whether it functions as an oncogene in this highly aggressive group of bone and soft tissue tumors. Our data show that BMI-1 is highly expressed by ESFT cells and that, although it does not significantly affect proliferation or survival, BMI-1 actively promotes anchorage-independent growth in vitro and tumorigenicity in vivo. Moreover, we find that BMI-1 promotes the tumorigenicity of both p16 wild-type and p16-null cell lines, demonstrating that the mechanism of BMI-1 oncogenic function in ESFT is, at least in part, independent of CDKN2A repression. Expression profiling studies of ESFT cells following BMI-1 knockdown reveal that BMI-1 regulates the expression of hundreds of downstream target genes including, in particular, genes involved in both differentiation and development as well as cell-cell and cell-matrix adhesion. Gain and loss of function assays confirm that BMI-1 represses the expression of the adhesion-associated basement membrane protein nidogen 1. In addition, although BMI-1 promotes ESFT adhesion, nidogen 1 inhibits cellular adhesion in vitro. Together, these data support a pivotal role for BMI-1 ESFT pathogenesis and suggest that its oncogenic function in these tumors is in part mediated through modulation of adhesion pathways.

Modeling Initiation of Ewing Sarcoma in Human Neural Crest Cells

Ewing sarcoma family tumors (ESFT) are aggressive bone and soft tissue tumors that express EWS-ETS fusion genes as driver mutations. Although the histogenesis of ESFT is controversial, mesenchymal (MSC) and/or neural crest (NCSC) stem cells have been implicated as cells of origin. For the current study we evaluated the consequences of EWS-FLI1 expression in human embryonic stem cell-derived NCSC (hNCSC). Ectopic expression of EWS-FLI1 in undifferentiated hNCSC and their neuro-mesenchymal stem cell (hNC-MSC) progeny was readily tolerated and led to altered expression of both well established as well as novel EWS-FLI1 target genes. Importantly, whole genome expression profiling studies revealed that the molecular signature of established ESFT is more similar to hNCSC than any other normal tissue, including MSC, indicating that maintenance or reactivation of the NCSC program is a feature of ESFT pathogenesis. Consistent with this hypothesis, EWS-FLI1 induced hNCSC genes as well as the polycomb proteins BMI-1 and EZH2 in hNC-MSC. In addition, up-regulation of BMI-1 was associated with avoidance of cellular senescence and reversible silencing of p16. Together these studies confirm that, unlike terminally differentiated cells but consistent with bone marrow-derived MSC, NCSC tolerate expression of EWS-FLI1 and ectopic expression of the oncogene initiates transition to an ESFT-like state. In addition, to our knowledge this is the first demonstration that EWS-FLI1-mediated induction of BMI-1 and epigenetic silencing of p16 might be critical early initiating events in ESFT tumorigenesis.

Reversible Kinetic Analysis of Myc Targets In vivo Provides Novel Insights into Myc-Mediated Tumorigenesis

Deregulated expression of the Myc transcription factor is a frequent causal mutation in human cancer. Thousands of putative Myc target genes have been identified in in vitro studies, indicating that Myc exerts highly pleiotropic effects within cells and tissues. However, the complexity and diversity of Myc gene targets has confounded attempts at identifying which of these genes are the critical targets mediating Myc-driven tumorigenesis in vivo. Acute activation of Myc in a reversibly switchable transgenic model of Myc-mediated beta cell tumorigenesis induces rapid tumor onset, whereas subsequent Myc deactivation triggers equally rapid tumor regression. Thus, sustained Myc activity is required for tumor maintenance. We have used this reversibly switchable kinetic tumor model in combination with high-density oligonucleotide microarrays to develop an unbiased strategy for identifying candidate Myc-regulated genes responsible for maintenance of Myc-dependent tumors. Consistent with known Myc functions, some Myc-regulated genes are involved in cell growth, cycle, and proliferation. In addition, however, many Myc-regulated genes are specific to beta cells, indicating that a significant component of Myc action is cell type specific. Finally, we identify a very restricted cadre of genes with expression that is inversely regulated upon Myc activation-induced tumor progression and deactivation-induced tumor regression. By definition, such genes are candidates for tumor maintenance functions. Combining reversibly switchable, transgenic models of tumor formation and regression with genomic profiling offers a novel strategy with which to deconvolute the complexities of oncogenic signaling pathways in vivo.

Anchorage-independent multi-cellular spheroids as an in vitro model of growth signaling in Ewing tumors

Little is known about the growth-signaling pathways that govern the proliferation of Ewing tumor (ET) cells either in vitro or in vivo. We have studied signal transduction pathways in ET cell lines and compared kinase expression levels and proliferation rates with primary tumors. Cell lines were studied both as conventional adherent monolayers and as anchorage-independent multi-cellular spheroids. Importantly, we observed significant differences between these in vitro models and found that ET spheroids were more closely related to primary tumors with respect to cell morphology, cell–cell junctions, proliferative index and kinase activation. Monolayer ET cells demonstrated serum-dependent phosphorylation of ERK1/2 and AKT and constitutively high serum-independent cyclin D1 protein expression. However, when ET cells were placed in suspension culture, there was immediate serum-independent activation of ERK1/2 and AKT. In addition, cyclin D1 protein expression was completely blocked until stable multi-cellular spheroids had formed, indicating that cell–cell adhesion is necessary for the proliferation of anchorage independent ET cells. This reduction in cyclin D1 expression was post-transcriptional and could be mimicked in monolayer cells by treatment with phosphatidyl inositol-3 kinase (PI3K) inhibitors. Moreover, PI3K inhibition significantly reduced ET cell proliferation and, in primary ET samples, cyclin D1 expression correlated with expression of activated AKT. Thus, the PI3K–AKT pathway appears to be critical for the proliferation of ET cells both in vitro and in vivo and tumor cell growth in vivo may be better represented by the study of anchorage-independent multi-cellular spheroids.