Abstract 878: A new SOX2/OCT4 stem cell biosensor reveals the mechanism of cancer stem cell dissemination in human breast cancer

Abstract

Abstract There is increasing consensus that cancer stem cells (CSC) play an important role during metastatic progression of breast cancer. Previous studies have shown that stem cells display a pro-invasive phenotype in breast cancer. However, the phenotypes specific to breast cancer stem cells have not been evaluated at single cell resolution in vivo. Here, we employ high-resolution intravital two-photon microscopy in both orthotopic xenograft tumors, and their metastases, formed from human breast cancer cell lines expressing a previously characterized SOX2/OCT4 transcription-based fluorescent stem cell biosensor (SORE6). Using this high resolution imaging technology we found that SORE6+ stem cells: (a) constitute a minority population of the primary mammary tumors, (b) move approximately ten times slower than non-stem breast cancer cells (0.1 vs 1.1 µm/min, respectively), (c) are migratory toward blood vessels and, (d) compared to non-stem cells, they are enriched for invasive cellular protrusions called invadopodia. This is important because we have shown that these phenotypes are specifically associated with the disseminating population of tumor cells in the primary tumor site and, in addition, invadopodia are required for transendothelial migration during intravasation. Stem cells also have a three-fold higher incidence of direct contact with macrophages compared to non-stem cells. In fact, stem cells were frequently seen to be part of the tripartite macrophage-tumor cell- endothelial cell complex called TMEM, which was previously shown to be the doorway for intravasation of tumor cells in primary mammary tumors and is validated as a prognostic of metastasis in human breast cancer patients. Furthermore, we followed breast cancer stem cell dissemination to the lung by using a novel lung window for high resolution imaging of the lung (WHRIL), which allows visualization of the same lung tissue in a single mouse, serially, over days to weeks. Using WHRIL, in combination with intravital multiphoton microscopy and the above biosensor, we visualized the arrival, extravasation and outgrowth of spontaneously arriving breast tumor cells in the lung. We report here for the first time, the kinetics and stemness state of the spontaneously metastasizing tumor cells and, the record at single cell resolution, of their fate and metastatic outgrowth in the lung over time. Citation Format: Ved P. Sharma, Sonia Voiculescu, Yarong Wang, George S. Karagiannis, Binwu Tang, Lalage Wakefield, David Entenberg, Sumanta Goswami, Maja Oktay, John Condeelis. A new SOX2/OCT4 stem cell biosensor reveals the mechanism of cancer stem cell dissemination in human breast cancer [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 878. doi:10.1158/1538-7445.AM2017-878