Pirarubicin inhibits multidrug-resistant osteosarcoma cell proliferation through induction of G~/M phase cell cycle arrest

Aim： Pirarubicin （THP） is recently found to be effective in treating patients with advanced, relapsed or recurrent high-grade osteosarcoma. In this study, the effects of THP on the multidrug-resistant （MDR） osteosarcoma cells were assessed, and the underlying mechanisms for the disruption of cell cycle kinetics by THP were explored. Methods： Human osteosarcorna cell line MG63 and human MDR osteosarcoma cell line MG63/DOX were tested. The cytotoxicity of drugs was examined using a cell proliferation assay with the Cell Counting Kit-8 （CCK-8）. The distribution of cells across the cell cycle was determined with flow cytometry. The expression of cell cycle-regulated genes cyclin B1 and Cdc2 （CDK1）, and the phosphorylated Cdc2 and Cdc25C was examined using Western blot analyses. Results： MG63/DOX cells were highly resistant to doxorubicin （ADM） and gemcitabine （GEM）, but were sensitive or lowly resistant to THP, methotrexate （MTX） and cisplatin （DDP）. Treatment of MG63/DOX cells with THP （200-1000 ng/mL） inhibited the cell prolifera- tion in time- and concentration-dependent manners. THP （50-500 ng/mL） induced MG63/DOX cell cycle arrest at the G2/M phase in timeand concentration-dependent manners. Furthermore, the treatment of MG63/DOX cells with THP （200-1000 ng/mL） downregulated cyclin B1 expression, and decreased the phosphorylated Cdc2 at Thr161. Conversely, the treatment increased the phosphorylated Cdc2 at Thr14/Tyr1 and Cdc25C at Ser216, which led to a decrease in Cdc2-cyclin B1 activity. Conclusion： The cytotoxicity of THP to MG63/DOX cells may be in part due to its ability to arrest cell cycle progression at the G2/M phase, which supports the use of THP for managing patients with MDR osteosarcoma.