In vitro anticancer effects of levopimaric acid in cisplatin-resistant human lung carcinoma are mediated via autophagy, ROS-mediated mitochondrial dysfunction, cell apoptosis and modulation of ERK/MAPK/JNK signalling pathway.

Lung cancer is one of the deadly diseases with limited treatment options available. The main aim of the current study was to investigate the antitumor effects of levopimaric acid - a naturally occurring diterpene, against cisplatin-resistant non-small cell lung carcinoma cells A-549 and normal MRC5 cells. Effects of levopimaric acid on autophagy, reactive oxygen species (ROS), apoptosis and ERK/MAPK signalling pathways were also investigated in the current study. Proliferation rate was monitored by MTS assay. Apoptosis was detected by DAPI staining as well as western blot assay. Electron microscopy was used to investigate the autophagic effects of levopimaric acid. Effects on ROS and mitochondrial membrane potential (MMP) were evaluated by flow cytometry. Protein expression was examined by western blotting. It was found that levopimaric acid exerts potent antiproliferative effects against the cisplatin-resistant lung cancer cells and exhibited an IC50 of 15 μM. However, the toxic effects of levopimaric acid were seen to be insignificant against the normal cells. The anticancer effects of levopimaric acid were due to induction of apoptosis which was also associated with modulation of apoptosis-related proteins (Bax and Bcl-2). Levopimaric acid also induced autophagy which was also associated with alterations of autophagy-related protein expressions (LC3I, II, and p62). Levopimaric acid caused ROS-mediated alterations in the MMP. It was also found that the molecule could induce drug-resistant lung cancer cell death by activating p38 MAPK and JNK signalling pathways while inhibiting ERK pathway. The current results strongly indicate that levopimaric acid may prove to be a potential anticancer drug candidate provided further in depth studies are carried out.