Abstract P6-14-05: Regulation of cellular identity and spatial organization during collective breast cancer invasion

Abstract

Abstract An early step in breast cancer progression is invasion of tumor cells into surrounding tissues. In many breast cancers, particularly ductal carcinomas, this invasion is accomplished by tumor cells migrating as a cohesive group. This often involves cells that take on heterogeneous roles as either leader or follower cells. While studies in common mouse and human breast cancer models have established that leader cells express high levels of keratin-14 (K14) and other basal epithelial markers, the molecular mechanisms regulating K14+ leader cell identity remain obscure. Here we performed time-sampled single cell RNA-sequencing in 3D type I collagen-embedded tumor organoids isolated from the MMTV-PyMT luminal B model of breast cancer. 11 distinct cellular transcriptional states were identified and correlated with K14 expression and invasive strand formation. Having identified the leader cell state we next asked what transcription factors were enriched, reasoning that transcription factors could be master regulators of leader cell fate. 30 different shRNAs targeting 10 genes were systematically evaluated for their effects on collective invasion. From this screen, suppression of Hes1, the downstream target of Notch signaling, yielded a marked switch from collective to single cell invasion. Disseminating single tumor cells maintained high expression of K14 in Hes1 knockdown organoids which was phenocopied by gamma-secretase inhibition in a human TNBC PDX model. Because K14+ tumor cells highly express the Notch ligand Jag1, these results support a model in which Notch signaling, specifically through activation of Hes1, dictates leader cell identity and spatial organization during collective invasion. Studies are ongoing investigating the impact of Hes1 dynamics on leader cell adhesion, hybrid EMT state, and preference for single versus collective metastasis. Because Notch suppression induces leader cell dissemination, we propose that Notch targeted therapy should be combined with therapies eradicating leader cells. Citation Format: Andrea E. Doak, Kevin J. Cheung. Regulation of cellular identity and spatial organization during collective breast cancer invasion. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-14-05.