Abstract 4782: Transforming growth factor-beta regulation of cancer stem cell dynamics at different stages of breast cancer progression

Cancer stem cells (CSCs) are a subpopulation of tumor cells that are uniquely capable of initiating and sustaining tumorigenesis, and they have also been implicated in driving disease recurrence after cancer therapy. We have previously developed a novel lentiviral-based reporter system for direct visualization, quantitation and isolation of cells with CSC properties. The construct consists of a tandemly-repeated composite SOX2-OCT4 response element (“SORE6”) driving expression of a destabilized fluorescent protein reporter (Tang et al. Stem Cell Reports, 2015). TGF-βs are pleiotropic regulatory factors with complex roles in tumorigenesis. We and others have hypothesized that TGF-β can regulate the CSC population in breast cancer with stimulatory or inhibitory effects depending the model and stage of cancer development. Using the MCF10Ca1h and MCF7 breast cancer models, which retain tumor suppressor responses to TGF-β, here we show that TGF-β treatment significantly reduces the size of the CSC population in vitro. Although TGF-β had relatively little effect on invasion and migration of the bulk population in these models, it clearly inhibited migration and invasion of the CSCs, suggesting that biological responses to TGF-β can vary depending on the position of the cell in the differentiation hierarchy. Combining our stem cell reporter with a TGF-β pathway reporter, we further show that CSCs in the MCF10Ca1h model have higher endogenous activation of the TGF-β pathway than does the bulk tumor cell population, and by time-lapse video microscopy we find that CSCs with active TGF-β signaling are relatively quiescent. Furthermore, neutralization of TGF-β in vivo leads to an increased representation of CSCs in MCF10Ca1h and MCF7 tumors. Thus our preliminary results suggest that in breast cancer models where TGF-β acts as a tumor suppressor, TGF-β signaling is preferentially activated in the CSC compartment and keeps a subpopulation of CSCs in a quiescent and stationary state. These findings have important implications for the clinical use of TGF-β pathway antagonists. In contrast, in the metastatic breast cancer MDA-MB231 model, in which TGF-β acts as a pro-progression factor, we show that TGF-β can increase the size of the CSC population and enhance invasion. In this model, the CSCs are enriched for the ability to form macroscopic lung metastases when compared with non-CSCs, and we show that this effect is due in part to a selective survival advantage of the CSCs in the first 24 hours after arrival at the metastatic site. The role of TGF-β in this process is currently under investigation. Citation Format: Binwu Tang, George Baker, Joshua Zent, Yuval Raviv, Lalage Wakefield. Transforming growth factor-beta regulation of cancer stem cell dynamics at different stages of breast cancer progression [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 4782. doi:10.1158/1538-7445.AM2017-4782