Abstract C53: Overexpression of Brachyury in human carcinoma cells drives the acquisition of resistance to anticancer therapeutics

The epithelial-mesenchymal transition (EMT) has been recognized as a process crucial to the progression of carcinomas, mediating the conversion of stationary epithelial tumor cells into mesenchymal-like, invasive tumor cells. Recent reports have also demonstrated a potential association between tumor EMT and the acquisition of resistance to cell death in carcinoma cells. We recently identified the T-box transcription factor Brachyury, a molecule prevalently expressed in human tumors but seldom found in normal adult tissues, as a novel driver of EMT in human carcinomas. Brachyury was demonstrated to induce the expression of molecules associated with the mesenchymal phenotype, tumor cell motility and invasiveness in vitro, as well as metastatic propensity in xenograft models. In the current study, we investigated whether deregulated expression of Brachyury in human lung tumor cells is also associated with acquisition of resistance to the conventional anti-cancer modalities, chemotherapy and radiation. Our results demonstrated that over-expression of Brachyury in epithelial lung tumor cells significantly improved their survival in response to treatment with various doses of Taxotere, Cisplatin, Vinorelbine, and combinations of Cisplatin plus Vinorelbine, as well as to various doses of gamma-radiation. Similarly, inhibition of Brachyury expression by using Brachyury-specific shRNA constructs in mesenchymal-like, human lung tumor cells resulted in enhanced susceptibility to the same cytotoxic agents. Analysis of clonal lines derived from single-cell isolates of human lung tumor cells expressing various amounts of Brachyury revealed an inverse relationship between Brachyury levels and tumor growth, and a positive correlation of Brachyury with the ability to resist treatment by Taxotere, Cisplatin, Vinorelbine, and Cisplatin plus Vinorelbine combinations. Detailed gene expression analysis demonstrated a positive association between Brachyury expression and markers of tumor stemness, such as the MDR1/ABCB1 transporter, and the self-renewal transcription factors Sox-2, Oct4, and Nanog. These results thus raise the possibility that in addition to being a mediator of EMT, Brachyury may also be a marker for human tumor cells bearing stem-like characteristics and resistance to conventional therapeutics. One approach that may overcome the therapeutic resistance of tumors undergoing Brachyury-mediated EMT is that of immune-mediated targeting – we have previously characterized the immunogenicity of the Brachyury protein and generated Brachyury-specific human T-cell lines that have the ability to lyse Brachyury-positive tumor cells. We hypothesize that the eradication of Brachyury-expressing tumor cells via Brachyury-based immunotherapeutic approaches could be efficient at eliminating tumor cells with metastatic propensity as well as at alleviating tumor resistance in response to conventional therapies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr C53.