Downregulation of miR-21 increases cisplatin sensitivity of non–small-cell lung cancer

Recent studies have shown that plasma miR-21 is a biomarker of chemotherapeutic response in lung cancer, but the influence of miR-21 on the sensitivity of non–small-cell lung cancer (NSCLC) to cisplatin (DDP) has not been confirmed. The aim of this study was to evaluate the role of miR-21 in NSCLC sensitivity to DDP in vitro and in vivo. Real-time quantitative PCR was used to detect miR-21 expression in lung cancer cell lines. Synthesized locked nucleic acid (LNA) anti–miR-21 was transiently transfected into A549 cells and pre–miR-21 was transfected into SK-MES-1 cells. We also investigated the effects of miR-21 downregulation and upregulation on growth and colony formation in DDP-treated cells. Finally, the effect of miR-21 downregulation on in vivo sensitivity of A549 cells to DDP was determined in BALB/c nude mice. miR-21 expression was significantly higher in A549 than in other lung cancer cell lines. LNA-based knockdown of miR-21 significantly inhibited growth and induced death in A549 cells, possibly via apoptotic signaling. Pre–miR-21 significantly promoted growth and inhibited death in SK-MES-1 cells. Moreover, ectopic suppression of miR-21 sensitized A549 cells to DDP in vivo. Our findings demonstrate that miR-21 suppression enhances the sensitivity of lung cancer cells to DDP in vitro and in vivo.