Exploiting the SCF complex to identify novel therapeutic targets in high-grade serous ovarian cancer

An overarching, yet elusive goal for cancer researchers is to develop novel therapeutic strategies by identifying drug targets that will improve the lives and outcomes of cancer patients. High-grade serous ovarian cancer (HGSOC) remains the most lethal gynecological malignancy, with an estimated ~3,100 Canadians diagnosed and ~1950 succumbing to their disease each year. Unfortunately, >70% of HGSOC patients are diagnosed at stages III or IV and will eventually succumb with drug resistant disease. Therefore, new, more effective drug targets are urgently needed to address the poor morbidity and mortality associated with HGSOC. Recent genetic studies have determined that reduced expression of SKP1, CUL1 or RBX1 induces chromosome instability (CIN), or ongoing changes in chromosome complements, that is suspected to contribute to HGSOC pathogenesis. As copy-number losses of these genes occur in ~87% HGSOCs, the current study seeks to exploit these alterations using a synthetic lethal (SL) paradigm. Synthetic lethality is an innovative therapeutic strategy and is defined as the rare/lethal combination of two independently viable mutations/deletions. Accordingly, identifying SL interactors of the SCF complex (i.e., novel drug targets) would allow us to selectively exploit the aberrant genetics suspected to contribute to HGSOC pathogenesis. To identify 228 putative SL interactors of SKP1, CUL1 and RBX1, in silico and siRNA-based approaches were employed within FT secretory epithelial cellular contexts. Of these, CDK2 and PARP1 were prioritized for validation within RBX1+/- clones. To validate SL interactors, siRNAs and small-molecule inhibitors targeting PARP1 or CDK2 were combined with single-cell quantitative imaging microscopy (QuantIM) to assess SL phenotypes within RBX1+/- and NT-Control clones. QuantIM results reveal decreases in the number of RBX1+/- clones following silencing or inhibition of PARP1 or CDK2 relative to NT-Control clones, that corresponds with increases in γ-H2AX abundance, a marker of DNA DSBs. Collectively, the work presented in this thesis supports that PARP1 is a novel SL interactor of RBX1 and that CDK2 is an evolutionarily conserved SL interactor of the SCF complex. Furthermore, these findings highlight the potential clinical utility of utilizing Olaparib and/or SNS-032 for the treatment of HGSOCs exhibiting diminished expression of RBX1.

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