Triptolide Induces Apoptosis and Synergizes with Cisplatin in Cisplatin-Resistant HNE1/DDP Nasopharyngeal Cancer Cells.

The purpose of the study was to evaluate the anti-tumour effects of triptolide (TPL) and of the combination of TPL and cisplatin (DDP) in DDPresistant HNE1/DDP nasopharyngeal cancer (NPC) cells and to reveal the possible mechanisms. HNE1/ DDP cells were treated with TPL and/or DDP. Cell proliferation was examined by 3-(4,5-dimethylthiazol-2-yl) -2,5-diphenyltetrazolium bromide (MTT) assay and colony-forming assay; the combination index of the synergism between TPL and DDP was calculated. Cell morphological changes were observed under a microscope. Reactive oxygen species (ROS) and apoptosis rate were determined by flow cytometry. 5,5',6,6'-tetrachloro-1,1',3,3'-tetrethyl benzimidalyl carbocyanine iodide (JC-1) staining was used to determine mitochondrial membrane potential (MMP). Protein expression was analysed by Western blot, including Bax, caspase-9, Bcl-2, Mcl-1. TPL had an obvious anti-tumour effect and exhibited synergistic cytotoxicity with DDP on DDP-resistant HNE1/DDP cells. TPL induced HNE1/DDP cell apoptosis via inducing ROS generation. This effect was abolished by the inhibitor of ROS, N-acetyl-L-cysteine (NAC). TPL alone or combined with DDP could lower MMP significantly. Western blot showed that TPL alone or in combination with DDP increased expression of Bax and caspase-9, but reduced expression of Bcl-2 and Mcl-1. We conclude that TPL could induce cell apoptosis and synergize with DDP by regulating ROS generation and mitochondrial pathways in HNE1/DDP cells. This indicates that TPL may be effective in DDP-resistant NPC, either alone or combined with DDP.