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Research Articles: Therapeutics, Targets, and Development

Benzyl isothiocyanate–induced apoptosis in human breast cancer cells is initiated by reactive oxygen species and regulated by Bax and Bak

Department of Pharmacology and University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania

Requests for reprints: Shivendra V. Singh, 2.32A Hillman Cancer Center Research Pavilion, 5117 Centre Avenue, Pittsburgh, PA 15213. Phone: 412-623-3263; Fax: 412-623-7828. E-mail: singhs{at}upmc.edu

Abstract

Epidemiologic studies have revealed an inverse correlation between dietary intake of cruciferous vegetables and the risk of breast cancer. We now show that cruciferous vegetable constituent benzyl isothiocyanate (BITC) effectively suppresses growth of cultured human breast cancer cells (MDA-MB-231 and MCF-7) by causing G₂-M phase cell cycle arrest and apoptosis induction. On the other hand, a normal mammary epithelial cell line (MCF-10A) is significantly more resistant to growth arrest and apoptosis by BITC compared with breast cancer cells. The BITC-mediated cell cycle arrest was associated with a decrease in levels of proteins involved in regulation of G₂-M transition, including cyclin B1, cyclin-dependent kinase 1, and cell division cycle 25C. The BITC-induced apoptosis correlated with induction of proapoptotic proteins Bax (MCF-7) and Bak (MDA-MB-231 and MCF-7) and down-regulation of antiapoptotic proteins Bcl-2 and Bcl-xL (MDA-MB-231). The SV40-immortalized mouse embryonic fibroblasts derived from Bax and Bak double knockout mice were significantly more resistant to BITC-induced DNA fragmentation compared with wild-type mouse embryonic fibroblasts. The BITC treatment caused rapid disruption of the mitochondrial membrane potential, leading to cytosolic release of apoptogenic molecules, which was accompanied by formation of autophagosome-like structures as revealed by transmission electron microscopy. The BITC-mediated apoptosis was associated with generation of reactive oxygen species and cleavage of caspase-9, caspase-8, and caspase-3. Apoptosis induction by BITC was significantly attenuated in the presence of a combined superoxide dismutase and catalase mimetic EUK134 as well as caspase inhibitors. In conclusion, the present study reveals a complex signaling leading to growth arrest and apoptosis induction by BITC. [Mol Cancer Ther 2006;5(11):2931–45]

Grant support: USPHS grants CA101753 and CA115498, awarded by the National Cancer Institute.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Received 7/10/06; revised 8/18/06; accepted 9/12/06.

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