Human mesenchymal stem cells promote growth of osteosarcoma: Involvement of interleukin‐6 in the interaction between human mesenchymal stem cells and Saos‐2

Our previous study showed that exogenous human mesenchymal stem cells (hMSCs) targeted established osteosarcoma and promoted its growth and pulmonary metastasis in vivo. As a follow‐up, the present study aimed to investigate how hMSCs would interact with Saos‐2 through autocrine/paracrine communication. The results showed that co‐injection of hMSCs with Saos‐2 into the proximal tibia of nude mice could promote tumor growth and progression. In vitro, the proliferation of Saos‐2 and hMSCs was promoted by each other’s conditioned medium, in which interleukin‐6 (IL‐6) played an important role. Osteogenic differentiation of hMSCs could be inhibited by conditioned medium of Saos‐2, in which IL‐6 was also involved. Furthermore, decreased IL‐6 secretion by hMSCs during its osteogenesis and increased IL‐6 secretion in response to conditioned medium of Saos‐2 were observed. Based on these data, we suggest that there was a positive feedback loop of IL‐6 in the interaction between hMSCs and Saos‐2. (Cancer Sci 2010; 101: 2554–2560)