Abstracts Category : Other

Defining the Transcriptomic Profile of Dormant Breast Cancer Cells in the Skeleton

by Nancy Mourad

Breast cancer cells disseminate to the skeleton where they can reside in a dormant state for prolonged periods. These dormant disseminated tumour cells (DTCs) are thought to play a pivotal role in driving tumour growth in bone and are likely responsible for disease recurrence following chemotherapy. Currently, the molecular pathways regulating cancer cell dormancy remain to be determined. DTCs have very low abundance in bone and are, therefore, difficult to detect and study. This thesis aimed to develop approaches to identify and study rare dormant cancer cells in bone and to address the hypothesis that; dormant cancer cells in bone express a unique transcriptional profile that differs from proliferating cancer cells.Through the administration of MDA-MB-231 cells via the intracardiac route, we established a breast cancer bone colonisation model that enabled tracking of temporal tumour development within the skeleton. Detected in the early and late stages of disease, discrete single cells were identified histologically amongst growing colonies suggesting that not all tumour cells that colonise bone activate to form colonies. Retention of the fluorescent membrane dye, DiD, was used to discriminate proliferating from non-proliferating cells in vitro and in vivo. In vitro, less than 0.1% of cells retained DiD after 14 days suggesting that the majority of cells had proliferated. In contrast, rare solitary, dormant cells were visualised in-vivo using. Two-photon imaging of explanted bones from mice 28 days following injection of DiD labelled MDA-MB-231 cells. DiD retaining dormant cells isolated from mice using flow activated cell sorting re-activated upon in vitro culture confirming their ability to grow and eliminating the possibility that they were senescent or non-viable cells. In agreement with our hypothesis, single cell transcriptomic profiling analysis of dormant breast cancer cells from bone revealed a distinct transcriptomic profile when compared to proliferating cancer cells, with over 2,000 differentially expressed genes. Using gene ontology and NMF clustering analyses, we identified novel pathways and genes which may play a role in regulating tumour cell dormancy and activation. These findings will facilitate advances in understanding dormant cancer cell biology which may uncover new therapeutic targets to ultimately prevent disease, progression and, importantly, recurrence.Advisors/Committee Members: Croucher, Peter, Garvan Institute of Medical Research, Faculty of Medicine, UNSW, McDonald, Michelle, Garvan Institute of Medical Research, Faculty of Medicine, UNSW.