Ovarian cancer is the 5th leading cause of cancer-related death. The disease responds initially to treatment which is most often surgical cytoreduction followed by chemotherapy. The primary response rates to chemotherapy are approximately 80%. Unfortunately, most patients relapse and eventually tumours become refractory to frontline therapy. The lack of widely effective therapies at this points leads to a low 5-year survival. Therefore, new therapeutic agents or treatment strategies are required. It has been reported previously that gain of function mutations of p53 which upregulate the mevalonate pathway in breast cancer. TP53 is commonly altered in high grade serous ovarian cancer which might suggest that the mevalonate pathway may also be deregulated in ovarian cancer. The result reported in this thesis indicate that p53 upregulate the expression of key enzymes of the mevalonate pathway in ovarian cancer cell lines. In particular, it was found that 3-Hydroxy-3-Methylglutaryl-CoA Reductase (HMGCR), the rate limiting enzymes of the pathway, geranylgeranyl transferase-I (GGTI), GGTII and farnesyltransferase are upregulated in number of ovarian cancer cell lines. These observations suggest that pharmaceutical inhibition of the mevalonate pathway may be a promising therapeutic approach. Pitavastatin, a member of statin family of HMGCR inhibitors, has been found to have significant activity against ovarian cancer cells and induce regression of ovarian cancer xenografts in mice in previously published result from our laboratory. Although repurposing statins for use in oncology is an attractive strategy, there are legitimate concerns about the potential for the drug to cause myopathy. Therefore, other pharmacological agents which inhibit the mevalonate pathway were evaluated to test the hypothesis that dual inhibition of the mevalonate pathway would synergistically cause ovarian cancer cell death. Bisphosphonates, such as zolendronic acid, are inhibitors of farnesyl diphosphate synthase. Zolendronic acid, and to lesser extends risedronate, potentiated the activity of pitavastatin in several assays assessing the growth and viability of ovarian cancer cells. In contrast, the geranylgeranyl transferase I inhibitor, GGTI-2133, antagonised the activity of pitavastatin. Similarly, knockdown of either GGTI-β or GGTII-β by RNAi failed to potentiate the activity of pitavastatin. However, combined knockdown of both geranylgeranyl transferases potentiated the activity of pitavastatin. To identify further drugs which could interact synergistically with pitavastatin, a library of 100 off-patent drugs was screened in combination with pitavastatin in cell growth assays. Several compounds were identified which potentiated the activity of pitavastatin and/or had notable activity as single agents. The most striking hit from this screen was prednisolone, a synthetic glucocorticoid. Subsequent studies confirmed the synergistic interaction between prednisolone and pitavastatin in several cell growth and viability assays. To evaluate the mechanism underlying this synergistic interaction, publically-available expression data were interrogated to identify mevalonate pathway enzymes whose expression was regulated by prednisolone. The effect of these candidate genes was then tested in ovarian cancer cells and levels of HMGCR, farnesyl diphosphate synthase and geranylgeranyl transferase II were found to be reduced. These data suggest that drug combinations inhibiting multiple points in the mevalonate pathway may increase the therapeutic window for pitavastatin and offer a potential treatment for ovarian cancer.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:739438 |
| Date | January 2018 |
| Creators | Abdullah, Marwan Ibrahim |
| Publisher | Keele University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://eprints.keele.ac.uk/4579/ |
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