An insight into the anticancer mechanism of Tribulus terrestris extracts on human breast cancer cells

Tribulus terrestris (TT), a herb belonging to Zygophyllaceae family is widely used due to its medicinal properties. This study was undertaken to elucidate the anticancer mechanism of TT on MCF-7 breast cancer cells. Cytotoxic effect of the herb was assessed by 3-(4,5-diethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Apoptotic potential was assessed through DNA fragmentation, TUNEL and caspase 3 activity assays. Expressions of genes regulating the apoptotic pathway were examined by RT-PCR and expression of proteins was analyzed by immunocytochemistry. The result of MTT assay revealed that methanolic and saponin extracts from leaves and seeds of TT were cytotoxic to MCF-7 cells. Cytotoxicity studies on peripheral blood mononuclear cells (PBMC) proved that TT extracts were non-toxic to non-malignant cells. Treatment of human breast cancer MCF-7 cells with seed and leaf methanol and saponin extracts of TT resulted in fragmentation of DNA and induction of apoptosis. This was evident by agarose gel electrophoresis of DNA and TUNNEL assay. The extracts of TT also caused a significant increase in caspase 3 activity in MCF-7 cells. TT extracts caused an induction of intrinsic apoptotic pathway which was evident by the upregulation in the expression of Bax and p53 genes and downregulation in the expression of Bcl-2. FADD, AIF and caspase 8 genes were also upregulated indicating the possible induction of extrinsic apoptotic pathway. Therefore, our results suggest that the Tribulus terrestris (TT) extracts may exert their anticancer activity by both extrinsic and intrinsic apoptotic pathways.