IL-6 strengthens chemoresistance to DDP/ADR in osteosarcoma cells. (A) hFOB 1.19, U2OS/MG-63, and T98G cells were pretreated with or without IL-6, then cultured with 0, 0.3, 3, or 30 µg/ml DDP for 48 h. Cell proliferation was determined by MTT assay. *P < 0.05 vs. DDP group alone. (B) hFOB 1.19, U2OS/MG-63-CSC, and T98G cells were precultured with or without IL-6, then cultured with 0, 0.06, 0.6, or 6 µg/ml ADR for 48 h. Cell proliferation was determined by MTT assay. *P < 0.05 vs. ADR group alone. (C) U2OS/MG-63 cells were precultured with or without si-IL-6, then cultured with 0, 0.3, 3, or 30 µg/ml DDP for 48 h. Cell proliferation was determined by MTT assay. *P < 0.05 vs. DDP + si-control group. (D) U2OS/MG-63 cells were precultured with or without si-IL-6, then cultured with 0, 0.06, 0.6, or 6 µg/ml ADR for 48 h. Cell proliferation was determined by MTT assay. *P < 0.05 vs. ADR + si-control group.