Diallyl disulfide (DADS), an organosulfur compound in garlic, has been reported to be effective in inhibiting the growth of several human tumor cell lines. The aim of this study was to determine whether DADS induced growth inhibition in MCF-7 breast cancer cell lines and to understand the molecular mechanism by which DADS acts.

MCF-7 cell lines were incubated with various concentrations of DADS for various time intervals and the cytotoxicity was determined by MTT assay. We examined the changes of intracellular proteins related to apoptosis, such as bcl-2, bax and PARP in cells treated with DADS. To study the expression level of bcl-2 and bax, which serve as modulators of apoptosis, we performed RT-PCR and western blot analysis.

MCF-7 cells treated with DADS led to the suppression of viability and proliferation in both a time and concentration dependent manner. Microscopic observation revealed typical features of apoptosis in the DADS-treated cells, further verified in nuclear DAPI staining. Flow cytometry analysis with FITC-annexinV and propidium iodide (PI) demonstrated that the apoptotic cell population with AnnexinV+/PI- increased dramatically from ~0.8% to ~75% after 24h exposure to 500,µM DADS in MCF-7 cells. Cell cycle analysis demonstrated that the number of apoptotic cells increased with the increasing time of the DADS treatment. Additionally, thermore, we investigated the effects of DADS on apoptosis related gene expression in MCF-7 cells. PARP cleavage was markedly increased in the DADS treated cells with time. This result indicated that DADS induced the caspase-dependent apoptotic pathway. We also found down-regulation of bcl-2, however no significant change of Bax expression was observed after DADS treatment.

Taken together, these results indicate that DADS induces apoptosis by activating a caspase pathway involving the activation of BcI-2 but not of Bax. Our findings suggest chemotherapeutic potentials of DADS in human breast cancer.