Combined xanthorrhizol-curcumin exhibits synergistic growth inhibitory activity via apoptosis induction in human breast cancer cells MDA-MB-231

Isobole analysis revealed that substances interaction was synergistic when xanthorrhizol and curcumin were added concurrently to the cultures but merely additive when they were added sequentially. The synergistic combination treatment was then applied to the cultures to investigate the mode of cell death induced by the treatment. Immunofluorescence staining using antibody MitoCapture？ revealed the possibility of altered mitochondrial transmembrane potential, which is one of the hallmark of apoptosis. Hoechst 33258 nuclear staining assay showed the rate of apoptosis of MDA-MB-231 cells to increase in response to the treatment. Apoptotic cell death was further confirmed by DNA fragmentation assay, where internucleosomal excision of DNA was induced upon treatment with xanthorrhizol-curcumin.This is the first time the combined cytotoxic effect of xanthorrhizol and curcumin on MDA-MB-231 cells has been documented and our findings provide experimental support to the hypothesis that combined xanthorrhizol-curcumin showed synergistic growth inhibitory activity on MDA-MB-231 cells via apoptosis induction.Drug discovery from medicinal plants continues to provide an important source of new drug leads [1]. Previous studies have reported the ability of xanthorrhizol and curcumin in killing various cancer cell lines [2-7]. Our previous report on the cytotoxicity of xanthorrhizol on human breast carcinoma MCF-7 has proved that xanthorrhizol was able to induced apoptotic cell death [3]. From the study, we suggested that xanthorrhizol may be able to disrupt the cell plasma membrane as the late apoptotic event was happened in a huge magnitude during a short exposure time according to the flow cytometry analysis [3]. The ability of an antiproliferative agent to disrupt the cell plasma membrane was reported to have involved in the cell protein membrane redox homeostasis and thus, facilitates the induction of apoptosis event [8]. Most recently, curcumin was discovered to have membrane-t