Abstract 1710: Xanthohumol suppresses estrogen-signaling in endocrine resistant breast cancer through the specific inhibition of BIG3-PHB2 interactions

Abstract

Abstract Estrogen-receptor-α (ERα) plays a pivotal role in the development and progression of breast cancer. The current endocrine therapies for breast cancer are mainly based on targeting ERα signaling using selective ERα modulators, ERα downregulators, and aromatase inhibitor (AI)1-3. However, tamoxifen treatment often fails, and patients succumb to recurrent, endocrine-resistant tumors. Moreover, some patients who have undergone AI treatment still relapse. The precise molecular events that determine alterations in the effectiveness of these endocrine therapies remain unknown. We previously reported that the oncoprotein brefeldin A-inhibited guanine nucleotide-exchange protein 3 (BIG3) and tumor suppressor prohibitin 2 (PHB2) complex play a pivotal role in E2 signaling modulation in ERα-positive breast cancer. Namely, BIG3 binds PHB2, thereby inhibiting the E2-dependent suppressive ability of PHB2 and resulting in constitutive ERα activation. Considering these findings, strategies utilising the tumour suppressive activity of PHB2 upon its release from BIG3 by inhibitors of protein-protein interaction may represent novel therapies for breast cancer. Accordingly, we focus on whether XN potentially binds to the tumor suppressor protein PHB2, forming a novel natural anti-tumor compound targeting the BIG3-PHB2 complex and acting as a pivotal modulator of E2 /ERα signaling in breast cancer cells. XN treatment effectively prevented the BIG3-PHB2 interaction, thereby releasing PHB2 to directly bind to both nuclear- and cytoplasmic ERα. This event led to the complete suppression of the E2-signaling pathways and ERα-positive breast cancer cell growth both in vitro and in vivo, but did not suppress the growth of normal mammary epithelial cells. Our findings suggest that XN may be a promising natural compound to suppress the growth of luminal-type breast cancers, especially endocrine resistant breast cancers. Citation Format: Toyomasa Katagiri. Xanthohumol suppresses estrogen-signaling in endocrine resistant breast cancer through the specific inhibition of BIG3-PHB2 interactions. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1710. doi:10.1158/1538-7445.AM2015-1710