Abstract 157: Targeting cancer stem-like cells in triple negative breast cancer

Triple Negative Breast Cancer (TNBC), an aggressive, heterogeneous subtype of breast cancer, and immunohistochemically negative for estrogen receptor α (ER-), progesterone receptor (PR-), and lacking amplification of the human epidermal growth factor receptor 2 locus (HER2-). TNBC patients have high risk of recurrence and metastasis, and current treatment options remain limited. Cancer stem-like cells (CSCs) have been linked to cancer initiation, progression and chemotherapy resistance. Therefore CSC-targeted therapies are keenly sought. There is strong evidence for the involvement of Notch signaling in TNBC. Notch1 is highly expressed in Basal-like 1 (BL1) and especially Mesenchymal-Stem-Like (MSL) TNBCs. Expression of Notch1 and its ligand Jagged1 correlates with poor prognosis. Moreover, strong evidence supports key roles of different Notch paralogs in breast CSCs. Moreover the role of non-canonical Notch signaling in TNBC remains unknown. Here, we demonstrate that Notch1 promotes cell survival in MDA-MB-231 cells, representative of MSL TNBC, in part by activating NF-κB. Notch activation by Jagged1-expressing stromal cells enhances transcription of the anti-apoptotic gene cIAP-2 (BIRC3), a known NF-κB target. This event is dependent on recruitment of NF-κB subunits, IKKα and Notch1 to the cIAP-2 promoter. Short term exposure of MDA-MB-231 cells (MSL, PTEN wild-type), but not MDA-MB-468 cells (BL1, PTEN-null) to recombinant Jagged1 leads to AKT phosphorylation. This is suppressed by dual mTORC1/2 inhibitors, AKT inhibitors and IKKα inhibitors but not Everolimus (mTORC1-selective inhibitor). These observations support a model where canonical and non-canonical mechanisms downstream of Notch1 trigger AKT phosphorylation and NF-κB activation in PTEN wild type TNBC cells. This suggests a bidirectional crosstalk between the IKKα and AKT arms of this Jagged1-activated pathway. We also demonstrate that recombinant Jagged1 increases the cellular metabolism of TNBC cells and knockdown of Notch1 or IKKα by siRNA decreases mitochondrial respiration and glycolysis. We have found that CSCs derived from MDA-MB-231 cells have increased Notch1, p-AKT, and mitochondrial respiration. AKT inhibition or NF-κB inhibition decreases both mitochondrial respiration and glycolysis of TNBC derived CSCs. Pharmacological inhibition of Notch cleavage by gamma secretase inhibitor (PF-03084014) in combination with AKT inhibitor (MK-2206) or NF-κB inhibitor (Bay11-7082) blocks CD90hi or CD44+CD24low sorted secondary mammospheres formation. These data suggest that combination treatments affecting Notch, NF-kB or AKT pathways have potential therapeutic importance in targeting CSCs of TNBC. Citation Format: Fokhrul Hossain, Ayse D Ucar Bilyeu, Claudia Sorrentino, Judy Crabtree, Antonio Pannuti, Margarite Matossian, Matthew Burow, Todd Golde, Barbara Osborne, Lucio Miele. Targeting cancer stem-like cells in triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 157.