(526a) The Effects of Intratumoral Heterogeneity on Metastasis of Triple-Negative Breast Cancer Cells

Metastasis is responsible for most cancer-related deaths and evaluating the risk of metastasis is essential for predicting a patient’s prognosis. Unfortunately, these predictions are challenging in the context of triple negative breast cancer (TNBC), a highly heterogeneous disease in which individual cells can undergo modifications at the genomic, epigenomic, transcriptomic, and/or proteomic levels. Over time, these modifications yield clonal subpopulations with distinct behaviors, giving rise to intratumoral heterogeneity. For instance, cells within a tumor may exhibit a spectrum of phenotypes due to the epithelial-mesenchymal transition (EMT). Our lab has derived clonal subpopulations from a mouse TNBC cell line with phenotypes that span the EMT spectrum. We have examined the behaviors of these clonal subpopulations individually and in mixtures at distinct steps along the metastatic cascade by taking advantage of engineered tumor models and an in ovo assay. Specifically, we have measured the ability of TNBC cells within engineered tumors to invade into the surrounding matrix and escape into a nearby cavity. Our data show that epithelial tumors invade and escape more slowly than mesenchymal or heterogeneous tumors do. Additionally, the presence of as few as one mesenchymal cell for every nine epithelial cells is sufficient to alter tumor morphology and increase the rate of invasion. The effects of mesenchymal cells are not due to paracrine signaling, since providing epithelial tumors with medium conditioned by mesenchymal tumors does not alter the rates of invasion or escape. To examine the metastatic capacity of the clonal subpopulations, we xenografted tumor cells onto the chick chorioallantoic membrane (CAM) and used a novel quantitative reverse transcription polymerase chain reaction-based method to detect murine cancer cells in the chick embryonic tissues. Using this engineered tumor model and in ovo model to examine the behaviors of homogeneous and heterogeneous cell populations has enhanced our understanding of the effects of intratumoral heterogeneity on metastatic potential. This understanding is necessary as physicians move towards more accurately predicting a patient’s prognosis and developing personalized treatment plans.