Figure 1.

CXCR4 is implicated in the regulation of osteosarcoma doxorubicin resistance. (A) CXCR4 was downregulated in CXCR4-positive LM8 cells by small interfering RNA and upregulated in CXCR4-negative Dunn cells by lentiviral transfection. LM8 and Dunn cells were treated with various concentrations of doxorubicin (0, 0.2, 0.4, 0.8, 1 and 10 µg/ml) for 48 h, and cell viability was measured by Cell Counting Kit-8 assay. Dose-response curves were generated with GraphPad Prism 8.0 software, and half maximal inhibitory concentrations of doxorubicin were obtained for each group. (B) LM8 and Dunn cells were cultured in the presence of 0.2 µg/ml doxorubicin (with or without CXCR4 knockdown/overexpression) for 48 h, and the expression levels of the apoptosis-related protein cleaved caspase 3, caspase 3 and the drug resistant-related protein P-glycoprotein were then determined by western blotting. The protein bands were quantified and subjected to statistical analysis. (C) LM8 and Dunn cells were cultured with 0.2 µg/ml doxorubicin (with or without CXCR4 knockdown/overexpression) for 48 h, and the apoptosis ratios for each group (percentage of Annexin V⁺ cells) were determined by flow cytometry. ^*P<0.05, ^**P<0.01, ^***P<0.001, ^****P<0.0001. CXCR4, C-X-C motif chemokine receptor 4.