Abstract
Ovarian cancer is the most lethal gynaecological malignancy. Sustained response to combination carboplatin-paclitaxel chemotherapy is limited as most patients develop drug resistant disease. Our understanding of drug resistance mechanisms remains insufficient to overcome clinical failure. Previous study identified an inverse relationship of Fibroblast Growth Factor 1 (FGF1) expression with ovarian cancer patient survival. FGF1 and Fibroblast Growth Factor Receptor 2 (FGFR2) expression was induced in A2780DPP cisplatin resistant-carboplatin cross-resistant ovarian cancer cells compared to paired chemonaïve A2780 cells, and knockdown of FGF1 or FGFR2 re-sensitised A2780DPP cells to both cisplatin and carboplatin. This thesis now investigates mechanisms of FGF1-FGFR2 induced drug resistance.In A2780DPP cells, drug resistance was dependent on the DNA damage response - as knockdown or inhibition of the DNA damage regulatory kinase Ataxia Telangiectasia Mutated (ATM) re-sensitised cells to cisplatin. Activation of the homologous recombination DNA damage repair pathway was induced by FGF1, evidenced by ATM phosphorylation, Replication Protein A and gH2A.X foci formation in response to cisplatin challenge, suggesting that FGF1 induces drug resistance by directing high-fidelity DNA damage repair. Fibroblast growth factor receptor-specific inhibitor AZD4547 re- sensitised cells to cisplatin and carboplatin in A2780DPP and patient-derived ovarian cancer drug resistant cell lines.
Using Reverse Phase Protein Array (RPPA) to investigate the influence of FGF1 knockdown on candidate cancer-related protein and phospho-protein expression in A2780DPP cells, a novel FGF1-dependent phosphorylation of Heat Shock Protein 27 (HSP27) at Ser82 was identified. Knockdown of HSP27 re-sensitised A2780DPP cells to cisplatin and carboplatin. HSP27 interacted with FGF1 in response to cisplatin, where HSP27 was required for FGF1 nuclear translocation. FGF1-dependent phosphorylation of HSP27 occurred through the p38MAPK-MK2 pathway, and p38MAPK-specific inhibitors BIRB796 and SB202190 re-sensitised A2780DPP cells to cisplatin and carboplatin.
Finally, relative to epithelial-like A2780 cells, A2780DPP cells had a mesenchymal morphology coupled with induced expression of epithelial-to-mesenchymal transition (EMT)-related transcription factors including ZEB2, SNAI1 and SNAI2, and an associated induction of EMT target genes including CDH2, MMP3, MMP12, VIM, and VCAN. Epithelial morphology was restored, and EMT-related gene expression levels reduced following FGF1 or FGFR2 knockdown in A2780DPP cells, thus confirming an FGF1 and FGFR2 dependent induction of EMT in drug resistant A2780DPP ovarian cancer cells. Based on these results, the data presented in this thesis proposes novel mechanisms and associated phenotypes of FGF1-induced cisplatin and carboplatin resistance in ovarian cancer cells.
| Date of Award | 2021 |
|---|---|
| Original language | English |
| Sponsors | DC Biosciences Ltd. |
| Supervisor | Gillian Smith (Supervisor), Kevin Hiom (Supervisor) & Michelle Ferguson (Supervisor) |