Abstract 3317: Tumor microenvironment of metastasis (TMEM) in breast cancer patients represents a stem cell niche; likely mediated by the Wnt pathway

Cell surface biomarkers CD44, CD24, CD133 and intracellular biomarker ALDH1 have been used to identify breast cancer stem cells (BCSC). BCSC are clinically significant because they are resistant to chemotherapy and in very small numbers can initiate tumor growth and metastasis. Recent studies suggest that juxtacrine signaling from monocytes and macrophages support the BCSC niche. Macrophages represent one of the components of the micro-anatomical sites of hematogenous dissemination of breast cancer cells called Tumor MicroEnvironment of Metastasis (TMEM) which are predictors of metastatic outcome in patients. We hypothesize that TMEM rich tumor microenvironments support BCSCs which are a prerequisite for systemic metastatic outgrowths. We used flow cytometry to quantify CD44high/CD24low cells, as well as mRNA fluorescent in situ hybridization (FISH) and qRT-PCR to quantify CD133 and ALDH1 expression in breast cancer cells from 50 invasive ductal carcinomas obtained from patients’ cancer excisions by fine needle aspiration (FNA) before formalin fixation. Formalin-fixed paraffin embedded tissue from each sample was also analyzed for TMEM score using triple immunohistochemistry and the stem cell marker expression was compared to TMEM scores for each corresponding cancer excision. We observed very strong correlation between the percentage of CD44high/CD24low cells and TMEM scores (r = 0.91), as well as the percentage of CD133 and ALDH1 expressing cells with TMEM scores (r = 0.88 and 0.86 respectively). FISH results were validated using qRT-PCR and showed very strong correlation with TMEM scores (r = 0.76 and 0.73 for CD133 and ALDH1 respectively). Wnt/β-catenin signaling pathway is involved in stem cell generation and pathogenesis of various types of cancer. Aberrant activation of Wnt-signaling pathway in normal stem cells can promote their transformation into cancer stem cells. We hypothesize that interactions between cancer cells and macrophages, and/ or cancer cells and endothelial cells (i.e. both interactions among the cellular components of TMEM) induce cancer stemness via Wnt/-β catenin pathway. Indeed, co-culture of mouse macrophages (BAC) with MCF-7 cells, as well as human endothelial cells (HUVEC) with MCF-7, significantly increased the percentage of cells expressing stem cells markers, while salinomycin, selective inhibitor of breast cancer stem cell growth and progression, significantly reduced BAC or HUVEC induced increase in the percentage of cancer stem cells. Our findings indicate that TMEM-rich microenvironments support breast cancer stem cells likely via Wnt signaling involving juxtacrine cancer cell-macrophage and cancer cell-endothelial cell interactions. Citation Format: Gargi Bandyopadhyaya, Eli Grunblatt, Sweta Roy, Nathan Agi, Esther Adler, Joan Jones, John S. Condeelis, Maja H. Oktay, Sumanta Goswami. Tumor microenvironment of metastasis (TMEM) in breast cancer patients represents a stem cell niche; likely mediated by the Wnt pathway. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3317.