Abstract A014: Transcriptional regulation of basal leader cell identity 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. 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 presence of these K14+ cells promote metastasis and predict poor prognosis. The molecular mechanisms regulating K14+ leader cell identity and the methods for targeted depletion of these cells 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 through correlation with K14 expression and invasive strand formation we classified one of the states as leader cells. Having confirmed the leader cell cluster markers spatially localize to the invasive front, we next asked which transcription factors were enriched, reasoning that transcription factors could be master regulators of leader cell fate. Three different shRNAs targeting ten genes were systematically evaluated for their effects on collective invasion and keratin-14 transcription. Each transcription factor was designated as either an invasion promoter or invasion suppressor depending on the correlation between transcription factor expression and organoid invasion. Studies are ongoing investigating the impact of invasion-promoting and invasion-suppressing transcription factors on cellular transcriptional states and metastatic dissemination in-vivo. We propose that targeting invasion-suppressing pathways could be combined with therapies that specifically target and eliminate K14+ invasive cells. To this end, we have identified multiple candidate druggable targets and specific surface markers expressed in K14+ invasive cells. Citation Format: Andrea E. Doak, Rose Qu, Kevin J. Cheung. Transcriptional regulation of basal leader cell identity during collective breast cancer invasion [abstract]. In: Proceedings of the AACR Special Conference: Cancer Metastasis; 2022 Nov 14-17; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_2):Abstract nr A014.