Abstract A195: A novel selective estrogen receptor degrader, EC-372, inhibits tumor growth and metastasis of breast cancer cells

Abstract

Abstract Background: Breast cancer is one of the most common malignancies in women with high mortality rate worldwide. Clinical evidence suggests that antiestrogens have potential to inhibit the progression of hormone-dependent breast cancer. Here we showed that a novel selective estrogen receptor degrader (SERD), EC372, reduced estrogen receptor-α (ER-α), progesterone receptor (PR) and stabilized the expression of ER-β, which resulted in apoptosis in ER-positive breast cancer cells. Methods: We studied the effect of EC372 on DNA damage, cell cycle arrest, apoptosis, epithelial-to-mesenchymal transition (EMT), and mitochondrial membrane potential (MMP) in breast cancer cells. We also performed in vitro assays to evaluate the effect of EC372 on cell proliferation, colony formation, invasion, migration, cell adhesion in 2-dimensional (2-D) and sphere-forming abilities of tumor cells in 3-dimensional (3-D) cultures. Results: Our data show that EC372 inhibited the growth of T47D and MCF-7 human breast cancer cells. EC372 induced apoptosis in both cell lines as marked by cell shrinkage and apoptotic bodies. We found that treatment of EC372 downregulated the levels of ER-α and PR and stabilized the levels of ER-β, which subsequently resulted in cell cycle arrest, apoptosis, and suppressed the growth of breast cancer cells. We have also shown that EC372 reduced cell proliferation, colony formation, 3-D tumor spheroid size, migration, and invasive ability of breast cancer cells. Our cell cycle analysis data indicated that EC372 induced G1 arrest, as evidenced by a decrease in the protein levels of Cyclin D, phospho-Rb (S-807/811), and CDK-6 and increased Rb and p21 levels. We have further shown that EC372 induced apoptosis as evidenced by an increase in the levels of Annexin-V and by upregulation of proapoptotic molecules such as BAK, BAX, BID, cytochrome C, PARP1/cleaved PARP, and caspase 3, with a decrease in the levels of antiapoptotic molecules including BCl2, BCLxL, and survivin. In complement to our results, EC372 reduced the mitochondrial membrane potential (MMP) that triggered the activation of caspase 3 cascade, cleavage of PARP proteins, DNA damage, and subsequent cell death of breast cancer cells. Based on our in vitro results, EC372 is a unique and novel SERD, which inhibits tumor growth, migration, and invasion of breast cancer cells. Studies evaluating the potential of EC372 on in vivo tumor growth and metastasis are under way. Conclusions: This is the first comprehensive study on the mechanism by which EC372 inhibits tumor growth and promotes apoptosis of human breast cancer cells. Our collective data suggest that EC372 inhibits cell growth of ER-positive breast cancer cell lines through downregulating the levels of ER-α and PR, and stabilized the levels of ER-β. Based on our results, we suggest that EC372 is a potent SERD with anticancer effects that could be developed as a novel therapeutic agent to treat ER-positive breast cancer. Citation Format: Deepak Parashar, Anjali Geethadevi, Jyotsna Mishra, Bindu Nair, Bindu Santhamma, Klaus Nickisch, Pradeep Chaluvally-Raghavan. A novel selective estrogen receptor degrader, EC-372, inhibits tumor growth and metastasis of breast cancer cells [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A195.