Abstract 1908: FGFR inhibitor, AZD4547, impedes the stemness of mammary epithelial cells in the premalignant tissues of MMTV-ErbB2 transgenic mice

Abstract

Abstract The fibroblast growth factor receptor (FGFR) family (FGFR1-4) of receptor tyrosine kinases (RTKs) regulates signaling pathways involved in cell proliferation and differentiation. In particular, FGFR1 and FGFR2, which are found in the terminal end buds of developing mammary ducts, play a role in mammary development and glandular morphogenesis involving the regulation of mammary stem cells (MaSCs) in mice. As such, a number of FGFR inhibitors are being tested in preclinical studies and clinical trials for anti-tumor properties. Nevertheless, reports on FGFR inhibitor-mediated breast cancer prevention are sparse. In this study, we aimed to investigate the anti-cancer benefits of AZD4547, a small molecule inhibitor of FGFR1-3, on ErbB2-overexpressing breast cancer models. We particularly focus on the effects of AZD4547 on MaSCs and tumor-initiating cells (TICs) in the premalignant tissues of MMTV-ErbB2 transgenic mice. We first demonstrated the anti-proliferative effects of AZD4547 (1-5 µM) on human ErbB2-overexpressing breast cancer cell lines. We further showed that AZD4547 confers potent inhibition of the stemness of these breast cancer cells, as indicated by significant depletion of ALDH+ cells and impaired tumorsphere formation. To study the in vivo effects of AZD4547 on the stemness of mammary epithelial cells (MECs), MMTV-ErbB2 transgenic mice were administered AZD4547 (2-6 mg/kg/day) for 10 weeks (weeks 8-18 of age) during the ‘risk window’ for mammary tumor development. Histopathological analysis indicated that AZD4547 significantly inhibited ductal branching and MEC proliferation. To examine the effect of AZD4547 on MEC subpopulations and tissue hierarchy dynamics in the premalignant mammary tissues of this model, we performed flow cytometry analyses on the primary MECs using CD24/CD49f and CD61/CD49f cell surface markers. The results showed that AZD4547 treatment substantially reduced MaSC-derived luminal and myoepithelial cell populations. AZD4547 also selectively suppressed the CD61highCD49fhigh cell population, which is enriched with luminal progenitor cells that give rise to TICs during MMTV-ErbB2 mammary tumor development. Mammosphere and colony-forming cell (CFC) assays on primary MECs demonstrated that the stemness of these cells was also blocked by AZD4547 prior to malignant transformation. Consistently, AZD4547 inhibited the anchorage-independent growth of cells from spontaneous tumors. Moreover, we demonstrated that AZD4547 downregulated multiple pathways, including the inactivation of FGFR, EGFR, and Wnt/β-catenin signaling. Collectively, the morphogenic, MaSC/TIC, and signaling regulation associated with AZD4547 treatment provides critical evidence for AZD4547 as a breast cancer preventative and therapeutic agent, which ultimately reveals clues for more effective eradication of refractory mammary tumors. Citation Format: Qingxia Zhao, Amanda B. Parris, Erin W. Howard, Ming Zhao, Ying Xing, Zhikun Ma, Xiaohe Yang. FGFR inhibitor, AZD4547, impedes the stemness of mammary epithelial cells in the premalignant tissues of MMTV-ErbB2 transgenic mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1908. doi:10.1158/1538-7445.AM2017-1908