Project Summary Background: The metastasis of cancerous cells to distant and vital organs is responsible for in excess of 90% of cancer mortalities. Given this extraordinarily high mortality rate, there is a significant need for the development of novel therapeutic approaches that either eliminate metastatic cancer cells or eradicate incipient cancer cells prior to metastatic dissemination. An important barrier to tumor progression and metastasis is anoikis, a caspase- dependent cell death program induced by loss of integrin-mediated attachment to extracellular matrix (ECM). However, it has become clear that ECM-detachment can induce anoikis-independent mechanisms that can compromise cell viability. More specifically, we have discovered that detachment of non-cancerous epithelial cells from ECM triggers a significant elevation in the levels of reactive oxygen species (ROS) which compromises cell survival in an anoikis-independent fashion. The understanding of the cellular changes that contribute to the elevation of ROS during ECM-detachment remains rudimentary and the strategies utilized by cancer cells to combat ROS during ECM-detachment are insufficiently explored. Therefore, these points represent significant knowledge gaps that this grant proposal aims to address. Discernment of mechanistic information regarding the links between ECM-detachment, ROS, and cell survival could provide targets for the design of the therapeutic approaches aimed at specifically eliminating ECM-detached cancer cells; an outcome that may have significant impact for patients with metastatic disease. Objective/hypothesis: In aggregate, our preliminary studies have unveiled a novel cell death mechanism (with a tumor suppressive function) that compromises the viability of ECM-detached cells: the induction of mitophagy as consequence of RIPK1 signaling. As such, these data have motivated our central hypothesis that RIPK1- mediated mitophagy during ECM-detachment functions as a barrier to breast cancer progression. Specific Aim I: To elucidate the molecular mechanism by which ECM-detachment promotes RIPK1-dependent mitophagy and initiates cell death. Specific Aim II: To assess the capacity of RIPK1-mediated mitophagy to antagonize tumor formation in vivo and to evaluate antioxidant inhibition as a novel strategy to limit tumorigenesis in cancers that are deficient in RIPK1-mediated mitophagy Anticipated Outcomes: Following the completion of these studies, we will have accumulated significant mechanistic knowledge regarding the relationship between ECM-detachment, RIPK1 mitophagy, and cell death. Thus, the completion of these studies will unveil fundamental biological insights regarding cancer cell survival during ECM-detachment that may ultimately lead to the development of therapeutic approaches to limit the dissemination of breast cancer cells.