Sulforaphane, a naturally occurring isothiocyanate, induces cell cycle arrest and apoptosis in HT29 human colon cancer cells.

Sulforaphane is an isothiocyanate that is present naturally in widely consumed vegetables and has a particularly high concentration in broccoli. This compound has been shown to block the formation of tumors initiated by chemicals in the rat. Although sulforaphane has been proposed to modulate the metabolism of carcinogens, its mechanism of action remains poorly understood. We have previously demonstrated that sulforaphane inhibits the reinitiation of growth and decreases the cellular viability of quiescent human colon carcinoma cells (HT29). Moreover, the weak effect observed on differentiated CaCo2 cells suggests a specific anticancer activity for this compound. Here we investigated the effect of sulforaphane on the growth and viability of HT29 cells during their exponentially growing phase. We observed that sulforaphane induced a cell cycle arrest in a dose-dependent manner, followed by cell death. This sulforaphane-induced cell cycle arrest was correlated with an increased expression of cyclins A and B1. Moreover, we clearly demonstrated that sulforaphane induced cell death via an apoptotic process. Indeed, a large proportion of treated cells display the following: (a) translocation of phosphatidylserine from the inner layer to the outer layer of the plasma membrane; (b) typical chromatin condensation; and (c) ultrastructural modifications related to apoptotic cell death. We also showed that the expression of p53 was not changed in sulforaphane-treated cells. In contrast, whereas bcl-2 was not detected, we observed increased expression of the proapoptotic protein bax, the release of cytochrome c from the mitochondria to the cytosol, and the proteolytic cleavage of poly(ADP-ribose) polymerase. In conclusion, our results strongly suggest that in addition to the activation of detoxifying enzymes, induction of apoptosis is also involved in the sulforaphane-associated chemoprevention of cancer.

Selective cytostatic and cytotoxic effects of glucosinolates hydrolysis products on human colon cancer cells in vitro.

Glucosinolates hydrolysis products are attracting increasing attention since many studies have suggested that they may be involved in the anticarcinogenic property of cruciferous vegetables. In this study, we show that diindolylmethane (DIM) and sulforaphane, produced during the hydrolysis of glucobrassicin and glucoraphanin, respectively, exert a dose-dependent cytotoxicity on human colon adenocarcinoma HT29 cells. Moreover, these products are able to inhibit quiescent cells to re-enter the cell cycle. Interestingly, our results clearly show that low doses of DIM and sulforaphane, although very effective on undifferentiated intestinal HT29 cells, do not affect the viability of the differentiated CaCo2 cells. The reversibility of their effects has also been tested and is discussed.