Downregulation of midkine induces cisplatin resistance in human oral squamous cell carcinoma.

The presence of drug-resistant cancer cells has been associated with poor clinical outcomes. Cisplatin is one of the most effective chemotherapeutic agents commonly used for several malignancies including oral squamous cell carcinoma (OSCC). Although cisplatin resistance is a major obstacle in cancer treatment, mechanisms by which it develops are not well understood. Midkine (MK), a heparin-binding growth factor, has various cancer-related functions. In this study, we investigated whether MK is involved in cisplatin resistance in OSCC. We demonstrated that the Sa-3R cell line, which is OSCC cisplatin-resistant, exhibited lower MK expression with slow growth compared with its parent, Sa-3 cells. In Sa-3 cells, downregulation of MK expression significantly reduced cisplatin sensitivity, cell growth, and the expression of cyclin D1 and cyclin E1. MK knockdown suppressed cellular cisplatin accumulation via induction of ATP-binding cassette efflux transporters. These data suggest that MK may play important roles in cisplatin resistance in OSCC by modulating both cell growth and intracellular cisplatin accumulation.