Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Anatomy and Cell Biology

Supervisor

Dr. Trevor Shepherd

2nd Supervisor

Dr. Gabriel DiMattia

Joint Supervisor

Abstract

High-grade serous (HGS) carcinoma, the most prevalent and most deadly subtype of epithelial ovarian cancer (EOC), presents unique therapeutic challenges since the majority of cases are diagnosed at advanced, metastatic stage. At this point widespread intraperitoneal metastatic lesions are numerous, which is why models that recapitulate disease dissemination are critical to uncover novel therapeutic targets. One of the initiating events in ovarian cancer metastasis is shedding from the primary tumour into the peritoneal cavity where cells must survive in suspension in order to seed secondary tumours. This non-adherent population of cells exists as multicellular aggregates, or spheroids; data from our lab has demonstrated that cells within spheroids are dormant, yet are readily alter their phenotype upon reattachment to an adherent substratum. To further explore the pathobiology of ovarian cancer spheroids, my thesis work describes the functional characterization of two different signalling pathways— bone morphogenetic protein (BMP), and the liver kinase B1 (LKB1)/AMP-activated protein kinase (AMPK)—which mediate distinct and important aspects of spheroid formation and reattachment. Activated BMP signalling resulted in smaller, loosely-aggregated spheroids, which were more readily able to reattach and disperse. These phenotypic alterations observed as a result of active BMP signalling were mediated, at least in part, by cooperation with the AKT signalling pathway. These studies implicate inhibition of BMP and AKT signalling as potential strategies for therapeutic targeting of reattaching spheroids, which is critical for the formation of secondary metastatic lesions. Other work in our lab implicated the downregulation of AKT signalling in spheroid formation-induced dormancy. In an attempt to uncover additional pathways promoting the dormant phenotype of ovarian cancer spheroids, I investigated the LKB1/AMPK signalling cascade given its ability to alter cellular metabolism in response to nutrient and energy availability. Despite a dramatic enhancement in AMPK activity observed in ovarian cancer spheroids, targeted knockdown had no effect on viability of cells in this context. However, knockdown of its upstream kinase, LKB1, revealed a dramatic decrease in ovarian cancer spheroid viability, suggesting a role for this kinase in mediating anoikis-resistance in an AMPK-independent manner. Taken together, my results have uncovered two distinct and important signalling pathways that regulate unique aspects of spheroid formation, cell survival, and reattachment. By understanding the molecular mechanisms used by ovarian cancer spheroids to survive during dissemination and promote secondary metastasis, my work has uncovered additional therapeutic targets for the potential treatment of advanced-stage ovarian cancer.

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