β-elemene reverses the drug resistance of lung cancer A549/DDP cells via the mitochondrial apoptosis pathway

beta-elemene (beta-ELE) is a new anticancer drug extracted from Curcuma zedoaria Roscoe and has been widely used to treat malignant tumors. Recent studies have demonstrated that beta-ELE reverses the drug resistance of tumor cells. To explore the possible mechanisms of action of beta-ELE, we investigated its effects on cisplatin-resistant human lung adenocarcinoma A549/DDP cells. The effects of beta-ELE on the growth of A549/DDP cells in vitro were determined by MTT assay. Apoptosis was assessed by fluorescence microscopy with Hoechst 33258 staining and flow cytometry with Annexin V-FITC/PI double staining. Mitochondrial membrane potential was assessed using JC-1 fluorescence probe and laser confocal scanning microscopy, and intracellular reactive oxygen species levels were measured by 2',7'-dichlorofluorescein-diacetate staining and flow cytometry. Cytosolic glutathione content was determined using GSH kits. The expression of cytochrome c, caspase-3, procaspase-3 and the Bcl-2 family proteins was assessed by western blotting. The results demonstrated that beta-ELE inhibited the proliferation of A549/DDP cells in a time-and dose-dependent manner. Furthermore, beta-ELE enhanced the sensitivity of A549/DDP cells to cisplatin and reversed the drug resistance of A549/DDP cells. Consistent with a role in activating apoptosis, beta-ELE decreased mitochondrial membrane potential, increased intracellular reactive oxygen species concentration and decreased the cytoplasmic glutathione levels in a time-and dose-dependent manner. The combination of beta-ELE and cisplatin enhanced the protein expression of cytochrome c, caspase-3 and Bad, and reduced protein levels of Bcl-2 and procaspase-3 in the A549/DDP lung cancer cells. These results define a pathway of procaspase-3-beta-ELE function that involves decreased mitochondrial membrane potential, leading to apoptosis triggered by the release of cytochrome c into the cytoplasm and the modulation of apoptosis-related genes. The reversal of drug resistance of the A549/DDP cell line by beta-ELE may be derived from its effect in inducing apoptosis.