Abstract BS2-1: Collective invasion in breast cancer is led by specialized cancer cells with basal gene expression

Abstract

Abstract Metastasis is the major driver of mortality and morbidity from breast cancer. Unfortunately, there are very few therapies that are effective in the metastatic setting. The overall hypothesis guiding our work is that a deeper biological understanding of the cellular and molecular mechanisms driving metastatic progression would facilitate the development of novel therapeutic concepts. A major barrier to achieving this goal is that the essential cellular steps occur deep within the body over a period of months to years. To overcome this barrier, we developed a novel organoid invasion assay that enables us to prospectively identify the most invasive cells within primary breast tumors. We initially explanted organoids from advanced tumors derived from the MMTV-PyMT transgenic mouse model of luminal B breast cancer. Surprisingly, we discovered that the cells that lead invasion into the extracellular matrix express basal epithelial genes, such as keratin-14, p63, and P-cadherin, both in 3D culture and in vivo. We next demonstrated that the cells leading invasion in mouse models of Her2 overexpressing (MMTV-Neu) and basal breast cancer (C3(1)-Tag) also expressed basal epithelial markers. We then adapted our organoid invasion assay to study primary human breast tumors in real-time and found that keratin-14+ cells lead collective invasion across diverse molecular subtypes of breast cancer, both in 3D culture and in vivo. With these correlations firmly established, we returned to the MMTV-PyMT mouse model to dissect the mechanisms underlying collective invasion. Using a keratin-14 reporter line we revealed that the basal invasion program can be induced in luminal phenotype cancer cells and that these newly keratin-14+ cells can lead collective invasion. We then identified shRNA constructs to knockdown keratin-14 and demonstrated that it is required for collective invasion in 3D culture and in vivo. Our current work focuses on using next generation sequencing to identify targetable genes required for the invasive process and using in vivo lineage analysis to study the relationship between collective invasion and distant metastasis. Citation Format: Andrew J Ewald. Collective invasion in breast cancer is led by specialized cancer cells with basal gene expression [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr BS2-1.