Abstract
The activation of phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling and upregulation of excision repair cross complementation group 1 (ERCC1) are the two most important factors that confer resistance to cisplatin (DDP) therapy in non-small-cell lung cancer (NSCLC). Therefore, inhibition of the PI3K/Akt/mTOR signaling pathway and ERCC1 expression is a potential approach for the treatment of patients with advanced NSCLC. In the present study, whether combined treatment with DDP and BEZ235, a dual PI3K/mTOR inhibitor, could provide a synergistic antitumor effect in A549/DDP cells was investigated, and the possible mechanisms involved were explored. The half-maximal inhibitory concentration (IC50) values were calculated in A549/DDP cells. Synergistic interaction of BEZ235 and DDP was evaluated by combination index (CI) analysis. The levels of phosphorylated Akt (p-Akt), phosphorylated mTOR (p-mTOR), apoptosis-related proteins and ERCC1 were detected by western blot analysis. Apoptotic cells were quantified by flow cytometry and Hoechst 33342 staining. The migration and invasion abilities of A549/DDP cells were evaluated by wound healing and Transwell assays, respectively. It was observed that the dose reduction index (DRI) of BEZ235 was 13.82 and for DDP it was 13.58, and the CI of combination was <1 over a wide range of doses. In addition, the levels of p-Akt, p-mTOR and ERCC1 were significantly elevated by DDP treatment, and were reduced by co-administration of BEZ235 and DDP. Furthermore, the combination treatment significantly induced apoptotic cell death, decreased migration and invasion abilities compared with those treated with either BEZ235 or DDP alone. In conclusion, the combination of BEZ235 with DDP had synergistic antitumor effects in A549/DDP cells as reflected by reduced proliferation, increased apoptosis, and suppression of the migration and invasion abilities of A549/DDP cells, and the mechanism mediating these effects may be associated with the inhibition of PI3K/Akt/mTOR signaling and down-regulation of ERCC1 expression.