Abstract 864: Repurposing FDA-approved drug bazedoxifene as a novel inhibitor of IL-6 signaling for triple-negative breast cancer
Authors: Chen Xiang , Fu Shengling , Tian Jilai , Cao Yang , Li Chenglong , Lin Jiayuh 
Published: August 2018

Abstract
Triple-negative breast cancer (TNBC) is a major cause of death among breast cancer patients and is the only subtype of breast cancer that is still lacking effective therapeutic options. IL-6 is one of the principal oncogenic mediators in breast cancer and systemic IL-6 levels correlates with poor prognosis, advanced disease, and metastases. Importantly, growth of TNBC cells are replied on autocrine cytokines including IL-6 and TNBC cells secret the highest levels of IL-6 comparing to other subtypes of breast cancer. Therefore, IL-6 signaling represents a novel approach with a potential to improve the therapeutic efficacy. To date, however, no small molecules that target IL-6 signaling are available for clinical cancer therapy. IL-6 binds to IL-6 Rα, then recruits Glycoprotein 130 (GP130) to form hexamer consisting two IL-6/IL-6 Rα/GP130 heterotrimers to trigger a signaling cascade downstream including JAK/STAT3, PI3-K/AKT/mTOR, and MEK/ERK. Therefore, it is possible to target IL-6 signaling by blocking IL-6 binds to GP130 or IL-6 Rα and thus inhibiting its signaling cascade downstream.
We have utilized a novel drug discovery approach combining Multiple Ligand Simultaneous Docking and drug repurposing to target GP130 and have identified a FDA-approved drug Bazedoxifene (for the prevention of the osteoporosis in postmenopausal women) with a novel function to inhibit IL-6 and GP130 proteinprotein interactions and thus blocking IL-6 signaling cascade downstream. In this study, we examined the therapeutic efficacy of Bazedoxifene in combination with paclitaxel on human TNBC cells and TNBC tumor model, aiming to provide experimental results of Bazedoxifene and paclitaxel combination for TNBC therapy.
Our data showed Bazedoxifene inhibited increased STAT3 phosphorylation induced by IL-6. Bazedoxifene also inhibited phosphorylation of STAT3, AKT, and ERK in TNBC cells that produced IL-6. In addition, combination of Bazedoxifene with paclitaxel exhibited more significant inhibition on cell viability and colony formation and induction of apoptosis than single agent alone in TNBC cells in vitro. Moreover, Bazedoxifene inhibits cell migration and combination of Bazedoxifene with paclitaxel more significantly inhibit cell migration than single agent alone. We also showed bazedoxifene could inhibit increased proliferation of TNBC cells induced by IL-6. The combination of Bazedoxifene with paclitaxel also showed significantly inhibition of tumor growth of TNBC in vivo furtherly supported the therapeutic effects of Bazedoxifene. The results support the significant therapeutic efficacy of Bazedoxifene and paclitaxel combination for further TNBC therapy.
Citation Format: Xiang Chen, Shengling Fu, Jilai Tian, Yang Cao, Chenglong Li, Jiayuh Lin. Repurposing FDA-approved drug bazedoxifene as a novel inhibitor of IL-6 signaling for triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 864.