CD117 and Stro-1 Identify Osteosarcoma Tumor-Initiating Cells Associated with Metastasis and Drug Resistance

Abstract

Emerging evidence indicates the presence of tumor-initiating cells (TIC) or cancer stem cells (CSCs) in osteosarcoma. However, no study has demonstrated specific markers to identify osteosarcoma TICs with in vivo tumor formation ability. Additionally, there has been a lack of investigations gauging the contribution of osteosarcoma TICs to metastatic and drug-resistant properties. In this study, we have identified mouse and human osteosarcoma TICs using mesenchymal stem cell (MSC) markers CD117 and Stro-1. These markers were preferentially expressed in spheres and doxorubicin-resistant cells. Both mouse and human cells expressing these markers were sorted and analyzed for their abilities of tumor formation with as few as 200 cells, self-renewability, multipotency, drug resistance, metastatic potential, and enrichment of a metastasis-associated marker CXCR4 and a drug-resistance marker ABCG2. CD117+Stro-1+ cells efficiently formed serially transplantable tumors, whereas CD117−Stro-1− cells rarely initiated tumors. Upon orthotopic injections, CD117+Stro-1+ cell-derived tumors metastasized at a high frequency. Further, CD117+Stro-1+ cells showed high invasive and drug-resistant properties and were efficiently enriched for CXCR4 (20–90%) and ABCG2 (60–90%). These results suggest possible mechanisms for the high metastatic and drug-resistant properties of osteosarcoma TICs. In summary, CD117 and Stro-1 identify osteosarcoma TICs associated with the most lethal characteristics of the disease - metastasis and drug resistance - and these markers offer candidates for TIC-targeted drug delivery aimed at eradicating osteosarcoma.

Immunotherapy targeting HER2 with genetically modified T cells eliminates tumor-initiating cells in osteosarcoma

“…[4][5][6][7]13 Their enhanced capacity to form sarcospheres is a surrogate of their self-renewal property regardless of the method used to characterize and isolate this cell subpopulation from Targeting tumor-initiating cells in osteosarcoma N Rainusso et al the tumor bulk. Sarcospheres have previously been shown to be resistant to doxorubicin, cisplatin and vincristine, 8,9 and we now show they are also resistant to methotrexate.…”

“…OS TICs have been found to express genes involved in the processes of cell migration and metastasis. 4,13 Therefore, targeting this tumor cell compartment may impair the ability of OS cells to metastasize.…”

“…3 TICs have been identified in OS by the expression of certain surface markers or as a 'side population' through the exclusion of the vital dye Hoechst 33342. [4][5][6] In addition, OS TICs can be grown in culture as sphere-like structures (sarcospheres) under serum starvation, 7 a property that allows functional testing of different anti-neoplastic agents against this tumor cell compartment. Furthermore, OS TICs have been reported to be resistant to chemotherapy.…”

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].…”