319 Factors that govern the cell death response induced by inhibition of the molecular chaperone heat shock protein 90

Abstract

The ginger rhizome is rich in bioactive compounds, including [6]-gingerol, [8]-gingerol, and [10]-gingerol; however, to date, most research on the anti-cancer activities of gingerols have focused on [6]-gingerol. In this study, we compared [10]-gingerol with [8]-gingerol and [6]-gingerol in terms of their ability to inhibit the growth of human and mouse mammary carcinoma cells. A colorimetric assay based on the enzymatic reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide revealed that [10]-gingerol was more potent than [6]-gingerol and at least as potent as [8]-gingerol for the inhibition of triple-negative human (MDA-MB-231, MDA-MB-468) and mouse (4T1, E0771) mammary carcinoma cell growth. Further investigation of [10]-gingerol showed that it suppressed the growth of estrogen receptor-bearing (MCF-7, T47D) and HER2-overexpressing (SKBR3) breast cancer cells. The inhibitory effect of [10]-gingerol on the growth of MDA-MB-231 cells was associated with a reduction in the number of rounds of cell division and evidence of S phase-cell cycle arrest, as well as induction of apoptosis due to mitochondrial outer membrane permeabilization and the release of proapoptotic mitochondrial cytochrome c and SMAC/DIABLO into the cytoplasm. Surprisingly, killing of MDA-MB-231 cells by [10]-gingerol was not affected by a pan-caspase inhibitor (zVAD-fmk) or an anti-oxidant (N-acetylcysteine), suggesting that the cytotoxic effect of [10]-gingerol did not require caspase activation or the accumulation of reactive oxygen species. These findings suggest that further investigation of [10]-gingerol is warranted for its possible use in the treatment of breast cancer.