Naturally Occurring Sesquiterpene Lactone-Santonin, Exerts Anticancer Effects in Multi-Drug Resistant Breast Cancer Cells by Inducing Mitochondrial Mediated Apoptosis, Caspase Activation, Cell Cycle Arrest, and by Targeting Ras/Raf/MEK/ERK Signaling Pathway

BACKGROUND: Sesquiterpene lactones have gained tremendous attention owing to their potent anticancer properties. The main focus of this study was to evaluate the anticancer effects of a naturally occurring sesquiterpene lactone, santonin, against human breast cancer SK-BR-3 cells. MATERIAL/METHODS: Cell counting kit 8 assay was used for the determination of cell viability. Apoptosis was detected by DAPI (4′,6-diamidino-2-phenylindole) and annexin V/propidium iodide (IP) staining. Flow cytometry was used for cell cycle analysis and western blotting was used for the estimation of protein expression. RESULTS: Results showed that santonin exerts significant anti-proliferative effects on the SK-BR-3 breast cancer cells in a concentration dependent manner. Santonin showed an IC(50) of 16 μM against SK-BR-3 cells. DAPI staining showed that santonin caused DNA fragmentation in the SK-BR-3 cells, which is indicative of apoptosis. Annexin V/PI staining showed that apoptotic cell percentage increased up to 34.32% at 32 μM concentration of santonin. Santonin also caused an increase in the expression of Bax, caspase-3, and caspase-9, and a decrease in the expression of Bcl-2. Santonin also caused the arrest of the SK-BR-3 cells at the G2/M phase of the cell cycle and suppressed the expression of cyclin A and B1. Finally, santonin could also block the Raf/MEK/ERK pathway in breast cancer cells. CONCLUSIONS: The findings of this study suggest the potential for the naturally occurring sesquiterpene lactone santonin in breast cancer treatment and also suggest that it could be developed as a promising anticancer agent.