The CD49d+/high subpopulation from isolated human breast sarcoma spheres possesses tumor-initiating ability

Abstract

Primary breast sarcomas that arise from mammary stroma are very rare, highly aggressive tumors with a heterogeneous phenotype and are associated with high risk of recurrence and poor prognosis. Despite significant advances in medical and surgical management, these tumors have no suitable therapeutic modalities. Tumor-initiating cells (TICs) or cancer stem cells (CSCs) have been recently implicated in the pathogenesis of other heterogeneous, highly malignant tumors. I demonstrate here the existence of a small subpopulation of self-renewing primary breast sarcoma cells that are capable of forming suspended spherical, also called sarcospheres (designated NDY-1 sarcospheres), in anchorage-independent, serum-starved conditions from primary breast sarcoma tissue. Sarcospheres able to initiate and sustain tumor growth in immune-deficient NOD/SCID mice, to express stemness genes, including Notch 4, Bmi-1 and ABCG2, and to differentiate into mesenchymal lineages, such as osteoblasts and adipocytes. In addition, I observed a distribution of ALDH+ stem-like cells activity NDY-1 sarcospheres compared to the adherent cells. Through the screening for various markers and analysis of gene expression profiles in both sarcospheres and adherent cells, revealed a marked decrease in CD49d expression in corresponding adherent cells from NDY-1 sarcospheres. The CD49d+/high subpopulation sorted from NDY-1 spheres displayed higher cell viability and sphere-forming ability than CD49d-/low population in vitro. Moreover, the CD49d+/high population displayed high tumor initiating ability in limiting dilution transplantation to NOD/SCID mice, and the xenotransplanted CD49dhigh/+ population recapitulated the complexity of the original primary tumors. Moreover, greater doxorubicin resistance was exhibited by the CD49d+/high population, compared with the CD49d-/low population. Therefore, my results support the extension of the CSCs hypothesis to include tumors of mesenchymal lineage, breast sarcoma and highlight CD49d as a pivotal marker for identification of these cells. This is the first study to identify CSCs from primary breast sarcoma and this may be of primary importance in the development of new therapeutic strategies and new prognostic procedures against highly aggressive breast sarcoma.