Abstract PO2-24-06: Cancer-Associated Fibroblasts Promote Tumor Stemness in Aggressive Breast Cancers via NDRG1

Abstract Background: Inflammatory breast cancer (IBC) and triple negative breast cancer (TNBC) have the lowest 5-year survival rates among breast cancers: 40% for IBC and 77% for TNBC. Effective treatments for these aggressive tumors are urgently needed. To develop better treatments, it is crucial to understand the underlying mechanisms driving their aggressive biology. Our recent research has identified N-myc downstream regulated gene 1 (NDRG1) as a crucial driver of tumor progression and metastasis in aggressive breast cancers. We have also found that NDRG1 expression in tumors is correlated with poorer outcomes in IBC patients. Additionally, we have observed that cancer-associated fibroblasts (CAFs), derived from breast cancer biopsies, stimulate NDRG1 expression and phosphorylation as well as tumor stemness. Based on these findings, we hypothesize that NDRG1 is a key regulator of tumor stemness and progression, and secreted stromal factors regulate tumor stemness through NDRG1. Methods: To assess tumor stemness, we conducted in vitro experiments by quantifying the CD44+/CD24- subpopulation and performing mammosphere assays in NDRG1 control and depleted cells (SUM149, BCX010, MDA-IBC3). In vivo, we employed a limiting dilution transplantation assay, where NDRG1 control and knockdown SUM149 cells were transplanted into the mammary fat pad at different dilutions. We treated NDRG1 control and knockdown breast cancer cells with different patient-derived CAF-conditioned media (CAFs-CM, 50%, 24h) or control medium. The expression of NDRG1/pNDRG1 and CD44+/CD24- cells was evaluated by immunoblotting and flow cytometry. qPCR array was performed to evaluate tumor stemness markers. Results: NDRG1 depletion significantly reduced the CD44+/CD24- subpopulation (p 0.001) and the efficiency of mammosphere formation (p=0.001). In vivo limiting dilution experiments demonstrated a substantial reduction in the frequency of breast cancer stem cells in NDRG1 knockdown cells (p= 1 x 10-12). Treatment of IBC cells with CAF-CM derived from breast cancer patients stimulated the cancer stem cell subpopulation CD44+/CD24-: Control medium (43.1 ± 0.1) vs CAF-CM (55.1 ± 0.7); p=0.004 and increased NDRG1 and phospho-NDRG1 expression. However, the stimulation of NDRG1 knockdown cells with CAF-CM did not significantly alter the cancer stem cell population (0.2 ± 0.2 in Control medium versus 0.4 ± 0.3 in CAF-CM) and the expression of NDRG1/phospho-NDRG1. Additionally, qPCR array analysis revealed the upregulation of several cancer stem cell and self-renewal markers in CAF-CM stimulated cells compared to control-medium treated cells. Conclusions: Our data strongly support the role of NDRG1 as a critical regulator of tumor stemness. Moreover, we have discovered that conditioned media from patient-derived CAFs induces tumor stemness in breast cancer cells, and this effect is dependent on the expression NDRG1. Citation Format: Emilly Villodre, Jenny M Hogstrom, Xiaoding Hu, Nina Kozlova, Debu Tripathy, Taru Muranen, Bisrat Debeb. Cancer-Associated Fibroblasts Promote Tumor Stemness in Aggressive Breast Cancers via NDRG1 abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-24-06.