Identification of Cancer Stem Cells in Ewing's Sarcoma

Abstract

Cancer stem cells that display tumor-initiating properties have recently been identified in several distinct types of malignancies, holding promise for more effective therapeutic strategies. However, evidence of such cells in sarcomas, which include some of the most aggressive and therapy-resistant tumors, has not been shown to date. Here, we identify and characterize cancer stem cells in Ewing's sarcoma family tumors (ESFT), a highly aggressive pediatric malignancy believed to be of mesenchymal stem cell (MSC) origin. Using magnetic bead cell separation of primary ESFT, we have isolated a subpopulation of CD133+ tumor cells that display the capacity to initiate and sustain tumor growth through serial transplantation in nonobese diabetic/severe combined immunodeficiency mice, re-establishing at each in vivo passage the parental tumor phenotype and hierarchical cell organization. Consistent with the plasticity of MSCs, in vitro differentiation assays showed that the CD133+ cell population retained the ability to differentiate along adipogenic, osteogenic, and chondrogenic lineages. Quantitative real-time PCR analysis of genes implicated in stem cell maintenance revealed that CD133+ ESFT cells express significantly higher levels of OCT4 and NANOG than their CD133À counterparts. Taken together, our observations provide the first identification of ESFT cancer stem cells and demonstration of their MSC properties, a critical step towards a better biological understanding and rational therapeutic targeting of these tumors.

Modeling sarcomagenesis using multipotent mesenchymal stem cells

“…CSCs that display tumor re-initiating properties have been recently identified in osteosarcoma [81][82][83], chondrosarcoma [82], Ewing's sarcoma [61] and synovial sarcoma [79]. The identification of these sarcoma-initiating cells was based on both their ability to form spherical, clonal expanding colonies (called sarcospheres) in anchorage-independent and serum-starved conditions and the expression of stem cell markers [61,79,[81][82][83][84].…”

“…All of these CSCs are characterized by the expression of the pluripotent stem cell markers OCT3/4, NANOG and SOX2 and are able to self-renew and to sustain the tumor in serial transplantation experiments. More importantly, many of these sarcoma-initiating cells express MSC markers [79,[81][82][83] and retain MSC in vitro differentiation properties, giving rise to adipogenic, chondrogenic and osteogenic lineages [61,79,82]. In addition, these MSC-like CSCs are associated with drug resistance and metastasis [81,84] and therefore, they may be responsible for the frequent relapses observed in sarcomas [85].…”

“…The second model is supported by many studies reporting sarcoma formation from spontaneous or mutation-induced transformation of human or mouse primitive MSCs. Likewise, several types of CSCs presenting MSC properties have been reported [61,79,82] and moreover, sarcoma cells of certain subtypes can also differentiate into multiple mesenchymal lineages in vitro [30,31,42]. Existing sarcoma mouse models also provide arguments in favor of this theory.…”

“…For instance, treatment of Ewing's tumor cell lines with specific EWS-FLI1 short hairpin RNAs shifted their gene expression profile towards that of normal MSCs [60]. In addition, CSCs displaying MSC properties have been identified in Ewing's sarcoma [61]. In a follow-up study, these authors showed that human pediatric, but not adult, MSCs expressing EWS-FLI-1 display in vitro features of Ewing's sarcoma CSCs [62].…”

Poorly Differentiated Uterine or Cervical Sarcoma in a Young Dog

“…[8]. Likewise, it is unclear whether the primitive nature of these tumors represents dedifferentiation or lack of/arrested differentiation of an undifferentiated cell type; however, research in the area of cancer stem cells implicates arrested differentiation as a mechanism in some primitive tumors [9][10][11].…”