Investigating lipid metabolism and gene expression in High Grade Serous Ovarian Cancer (HGSOC) disease progression and chemoresistance

HGSOC is the most common and deadly form of ovarian cancer and is characterised by vague symptoms, late diagnosis and a high level of metastasis. While most patients initially respond well to the current standard of treatment – tumour debulking surgery and platinum/taxane combination chemotherapy – patients frequently succumb to recurrent disease which is often resistant to chemotherapy. A key stage in HGSOC metastasis is the detachment of cells from the primary tumour, which requires metastatic cells to overcome anchorage dependence and avoid cell death via anoikis. Understanding the molecular drivers that underpin this stage of metastasis can highlight key effectors that could be targeted to prevent and reduce metastasis and recurrent disease after initial treatment. As most HGSOC patients eventually develop tumours that are chemoresistant, investigating the proteins and pathways that promote chemoresistance in the disease could highlight novel targets to resensitise patients to chemotherapy and improve patient outcome. Altered sphingolipid pathway signalling has been linked with anchorage-independent survival, HGSOC disease progression and chemoresistance, however, further investigation of this pathway is required to understand how the sphingolipid pathway may mediate these processes in HGSOC. To investigate the detachment phase of HGSOC disease progression, an in vitro 2D versus 3D setup using HGSOC-representative CaOV3 cells was used. Targeted analysis of sphingolipid genes, enzymes and abundance in 2D and 3D cells highlighted altered sphingolipid pathway signalling in 3D towards and increased production of ceramide and sphingosine-1-phosphate (S1P). Further analysis indicated that alkaline ceramidase 3, the enzyme which converts ceramide into sphingosine, was important for 2D and 3D CaOV3 survival and may be a promising target that may promote survival of both attached and detached HGSOC cells. Broader analysis of 2D and 3D cells using RNA sequencing highlighted a range of genes and pathways which may promote 3D survival, including increased estradiol metabolism and reduced cell proliferation and epithelial-mesenchymal transition (EMT). Further investigating how these processes mediate 3D survival could provide insight into essential mechanisms driving HGSOC cell dissemination in patients. There are many mechanisms known to promote chemoresistance in cancer. To identify which mechanisms may be most relevant in HGSOC, carboplatin-resistant, paclitaxelresistant and dual carboplatin-paclitaxel-resistant CaOV3 and OV90 (HGSOC) cell lines, along with age-matched parental controls, were subjected to RNA sequencing. Our analysis identified genes and processes that may have driven resistance in these cell lines. Of note, upregulated transcription of key genes including ABC transporters, protease inhibitor SERPINA1, sphingolipid gene A4GALT, and small heat shock protein HSPB8 was identified across all resistant cell lines and in published HGSOC patient datasets, though knockdown of SERPINA1 was not sufficient to resensitise the resistant cell lines to chemotherapy. Furthermore, an upregulation of MAPK/AP-1 signalling was identified in response to both carboplatin and paclitaxel, highlighting that this pathway may be a driver of resistance to both compounds, and may therefore be a more general target to improve sensitivity to platinum and taxane. In this thesis, I have highlighted a range of processes that appear to be important for HGSOC cell survival in 3D culture and resistance to carboplatin and paclitaxel. Notably, some signalling pathways appeared to promote both 3D survival and chemoresistance, including ABC transporters, estradiol signalling and the sphingolipid pathway.

Author dc:creator

• Jones, Nicola Sian Louisa

Advisors dc:contributor.advisor

• Pitman, Melissa
• Pitson, Stuart (University of South Australia)

• High grade serous ovarian cancer
• sphingolipids
• chemoresistance
• ascites
• anchorage-independent survival

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/2440/144838

OAI identifier oai:identifier

oai:digital.library.adelaide.edu.au:2440/144838