thymoquinone could increase the efficacy of tamoxifen induced apoptosis in human breast cancer cells: an in vitro study

objective: thymoquinone (tq), as the main component of nigella sativa plant, shows anticancer properties. this study was aimed to evaluate the combined effect of tq and tamoxifen (tam) on viability and apoptosis of human breast cancer cell lines. materials and methods: in this experimental study, estrogen positive mcf-7 and estrogen negative mda-mb-231 human breast cancer cell lines were induced by tam (2 μm) or different doses of tq (50, 75, 100, 150 μm), individually or in combination. cell viability and apoptosis were investigated by mtt assay and tdt-mediated deoxy-uracil nick end labeling (tunel) assay; acridine orange (ao)/ethidium bromide (eb) staining respectively. data were analyzed by one way anova and p<0.05 was considered significant. results: in 24 hours treatment, tam and all doses of tq, solely or in combination, significantly reduced cell viability of both cell lines, except in mcf-7 cells treated with 50 μm tq, and mda-mb-231 cells treated with 50 or 75 μm tq (p<0.01). after 48 hours treatment, cell viability of both cell lines was reduced in all treated groups (p<0.05). remarkable apoptotic index was observed in combination treatment of mcf-7 or mda-mb-231 cell lines with tam and tq (p<0.001). conclusion: the synergistic effect of tq and tam on human breast cancer cell lines showed cell viability reduction as well as apoptosis induction, independent to estrogen.