Sphere-forming stem-like cell populations with drug resistance in human sarcoma cell lines

The presence of cancer stem cells in both solid and hematopoietic malignancies, has been recently linked to their pathogenesis. Sarcomas are rare, and diversely characterized by degrees of mesenchymal differentiation. The aim of the current study was to demonstrate whether the human sarcoma cell lines, osteosarcoma MG63, Ewing's sarcoma HTB166, fibrosarcoma HT1080, possess the stem-like properties which may contribute to the drug-resistance. All cell lines possessed an ability to form spherical, clonal expanding colonies (sarcospheres) in anchorage-independent, serum-starved conditions. Sarcospheres showed the stem-like properties with the ability of self-renewal, and increased expression of the stem cell-related genes such as Nanog, OCT3/4 SOX2 and DNA repair enzyme genes, MLH1 and MSH2. Sarcospheres showed strong resistance to doxorubicin and cisplatin, and caffeine, a DNA repair inhibitor, enhanced the efficacy of those drugs, suggesting that the drug resistance in sarcosphere cells was partly related to the efficient DNA repair ability. These results indicate that human sarcoma cell lines contain stem-like cell populations with strong drug resistance, and DNA repair inhibitor could enhance the efficacy of chemo-drugs against sarcomas.