Ovarian cancer (OC) is the most lethal form of gynaecological cancer, with high- grade serous ovarian carcinoma (HGSOC) being the most common and the deadliest subtype. Non-coding RNAs are a recently discovered species of RNAs that do not code for proteins, yet play a crucial role in both normal physiology and disease. The overall goal of this thesis was to apply the power of non-coding RNAs to OC with the following aims: (1) to identify novel small non-coding RNAs present in serum that could separate patients with HGSOC from healthy women as well as predict their surgical outcome, (2) to assess the role of long non-coding RNAs (lncRNAs) in promoting cisplatin resistance in cell line models of OC, and (3) to study the effects of mutant-p53 on mRNAs and lncRNAs using a small compound known as APR-246 as well as investigating the drug’s mechanisms of action. Firstly, the lethality of OC could partially be attributed to the lack of specific symptoms, leading this disease to be termed the ‘silent killer’, as well as low inci- dence rate of 9.4 cases per 100,000 individuals, both requiring a highly accurate test for population screening that remains an ongoing challenge. Measuring the levels of small non-coding RNAs, known as microRNAs, in serum, experiments described in this thesis aimed to identify novel microRNAs that could separate pa- tients with HGSOC from healthy women as well as predict their surgical outcome, one of the most important factors influencing overall patient survival. Because serum microRNAs can be affected by pre-analytical factors such as haemolysis, the sensitivity of four methodologies to detect low levels of haemolysis was first determined. This work is published in Plos One. The work described in this thesis identified a novel serum microRNA, miR-375, that could improve the accuracy of CA-125, a routinely used biomarker in diagnosing OC, in separating patients with HGSOC from healthy women. Next, serum microRNA miR-34a-5p was found to predict the surgical outcome of patients with HGSOC. In fact, miR-34a-5p was found to be superior to CA-125 for this purpose. Although the standard therapy for treating OC consists of surgical removal of the tumour followed by chemotherapy containing platinum/taxane agents, this regimen may be too aggressive for a sub- set of patients who might benefit from neoadjuvant chemotherapy, i.e. chemother- apy followed by the surgery. A pre-operative expectation of the the surgical out- come could help surgeons decide on optimal timing for surgery. Both miR-375 and miR-34a-5p were also unaffected by haemolysis. Secondly, although OC is initially sensitive to chemotherapy, most patients develop resistance within two years, resulting in recurrent disease that is difficult to treat. To identify novel lncRNAs that could promote drug resistance, expression of ninety lncRNAs was profiled in cell line models of cisplatin resistance. Five lncRNAs were found to have the potential to promote cisplatin resistance in vitro, and lncRNA Urothelial Cancer Associated 1 (UCA1) was selected for further investigations. Despite its role in promoting cisplatin resistance in bladder cancer, UCA1 was not found to promote cisplatin resistance in cell line models of OC. Lastly, the tumour suppressor TP53 plays a central role in the biology of cancer and it is almost universally mutated in HGSOC. Recent evidence suggests that p53, the protein encoded by TP53, can significantly influence the expression of both small and long non-coding RNAs. Experiments described in this thesis aimed to investigate the effect of mutant-p53 on protein-coding and non-coding RNAs by using a small compound known as APR-246 which has been reported to restore wild-type p53 activities in multiple cancers by stabilising the structure of mutant- p53. Despite currently undergoing a phase Ib/II clinical trial for potential treatment of recurrent HGSOC, the ability of APR-246 to restore wild-type p53 activities in HGSOC has not been tested. A global transcriptomic analysis conducted in this thesis discovered that p53-responsive mRNAs and lncRNAs were not robustly induced following APR-246 treatment in two cell line models of HGSOC, but indicated that APR-246 could function by inducing high levels of reactive oxidative species (ROS). Overall, data presented in this thesis demonstrated the utility of small non- coding RNAs in identifying patients with HGSOC from healthy women as well as predicting their surgical outcome. This thesis also implicated that lncRNAs, in general, could have a role in promoting cisplatin resistance in OC as well as suggested that APR-246 could, based on evidence obtained from the expression of p53-responsive mRNAs and lncRNAs, act independently of mutant-p53. Together, this research raises novel ways for clinical management of patients with HGSOC and addresses the challenge of drug resistance using non-coding RNAs, as well as questions the assumed mechanisms of action of the ‘p53-activating’ drug APR- 246
