NOTCH3 Blockade Inhibits Cancer Cell Plasticity through a NOTCH3/PD-L1 Oncogenic Axis in Triple Negative Breast Cancer

Triple negative breast cancer (TNBC) accounts for 15-20% of all breast cancers and mainly affects pre-menopausal and minority women. Therapeutic options are yet limited, in part because of acquisition of tumor cells with cancer stem cell (CSC) properties, leading to intrinsic resistance to chemotherapeutic agents and immune evasion capacity. Dysregulated Notch signaling has been linked to breast cancer and in this study, we demonstrate the pivotal role of NOTCH3 in inducing the enrichment of chemoresistant ALDHhigh CSCs. Significantly, selective targeting of NOTCH3 with AV-353, a novel humanized monoclonal antibody, or by shRNA-mediated knockdown, impaired the enrichment of ALDHhigh CSCs with high self-renewal capacity, induced apoptosis and enhanced chemosensitivity. AV-353 treatment similarly reduced growth of xenografted tumors in vivo. Moreover, blocking NOTCH3 by AV-353 or shRNA reduced PD-L1 expression in TNBC cells, which was linked to the inhibition of tumor growth and enhancement of CD8+ T-cell infiltration. Taken together, these findings provide preclinical evidence for NOTCH3 as a novel therapeutic target in TNBC and reveal a novel NOTCH3/PD-L1 oncogenic axis as a platform for the betterment of TNBC therapy. Overall design: Briefly, several breast cancer cell lines were subjected to different treatments, i.e. lentiviral mediated knockdown of Notch3, PD-L1 or treatment with a N3 blocking antibody. Untreated samples serves as control. Samples were then further processed for RNA-sequencing. Transcriptomes of each condition have been recorded in three independent biological samples.