Withaferin A (WA) is a promising cancer chemopreventive constituent of a traditional Indian medicine (Ayurvedic medicine) plant, Withania somnifera. This plant has been safely used for centuries in India for the treatment of different ailments. We have shown previously that WA treatment suppresses the growth of cultured (MCF-7 and MDA-MB-231) as well as xenografted (MDA-MB-231) human breast cancer cells by causing apoptosis but the mechanism of cell death is not fully understood. The inhibitor of apoptosis (IAP) family proteins, including X-linked Inhibitor of Apoptosis (XIAP), Survivin, cIAP1, and cIAP2, have emerged as critical regulators of apoptosis by functioning as inhibitors of caspases. The IAP family proteins are also implicated in adaptive response to cellular stress and immune responses. The present study was designed to determine the role of IAP family proteins in execution of WA-induced apoptosis. Exposure of MCF-7 and MDA-MB-231 cells to WA resulted in downregulation of XIAP, Survivin, cIAP1, and cIAP2 proteins as judged by western blotting and immunocytochemical analysis. The WA-mediated downregulation of cIAP2 and Survivin proteins was attributable to their transcriptional repression. On the other hand, WA treatment promoted proteasomal degradation of XIAP and cIAP1 proteins. Overexpression of XIAP, Survivin, and cIAP2 in MCF-7 and MDA-MB-231 cells conferred significant resistance towards WA-induced apoptosis. Moreover, WA-mediated inhibition of MDA-MB-231 xenograft growth in vivo was accompanied by statistically significant decrease in Survivin protein expression in the tumor. The WA treatment caused activation of intrinsic and extrinsic caspase pathways. Furthermore, the WA-induced apoptosis was significantly attenuated in the presence of caspase inhibitors. In conclusion, the present study indicates that WA-induced apoptosis in human breast cancer cells is mediated by downregulation of IAP family proteins. This investigation was supported by the US PHS grant CA142604 awarded by the National Cancer Institute.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 567. doi:1538-7445.AM2012-567