Background: Ovarian cancer (OC) is the leading cause of death from gynaecological cancers among women. Vague clinical manifestation attributes to late-stage diagnosis in approximately 75% of OC patients. Surgical debulking and chemotherapy offers marginal benefit to improve clinical outcomes. As OC progresses, ascites (peritoneal malignant tumour fluid) containing detached tumour cells, cancer stem cells (CSC) and pro-oncogenic components accumulate and facilitate tumour spread and survival. We previously reported CSCs-like phenotypes including enrichment of metabolic pathways and distinct immune surveillance process in the ascites-derived tumour cells of OC patients after (chemoresistant, CR) but not before (chemo-naïve, CN) chemotherapy. We hypothesise that extracellular solutes in ascites contribute to chemoresistance and promote survival of residual CSCs leading to recurrence. The aim of this study is thus to identify the proteome signature of the ascites unique to chemotherapy-resistant OC patients.
Methods: Ascites were collected from advanced-stage CN (n=5) and CR (n=5) serous OC patients. All samples were processed with filter-aided sample preparation (FASP) protocol. Peptides were fragmented and analysed using Thermo liquid chromatography (LC)-Orbitrap EliteTM electron transfer dissociation (ETD) mass spectrometer. Raw data were processed using MaxQuant (v184.108.40.206) and Perseus (v220.127.116.11) workflow and searched against the human UniProt Swiss-Prot database (December 2018, 20,412 protein sequences). Label-free quantification intensities were calculated and fold changes were determined between CN and CR samples. Gene enrichment analysis was performed using FunRich (v3.1).
Results: We have identified a total of 324 proteins, 207 of which are commonly found in both CN and CR ascites. Alpha-1-antitrypsin (SERPINA1) was upregulated by 2-fold in CN compared to CR samples (p<0.001). Gene ontology (GO) analysis revealed an overrepresentation of proteins associated with the regulation of complement activation (GO:0030449), cellular protein metabolic process (GO:0044267) and innate immune response (GO:0045087).
Conclusion: Proteins identified in ascites highlight the existence of metabolic and immune regulatory signatures in the tumour microenvironement that nurtures OC. Further functional analyses need to be performed to determine the importance of the reduced SERPINA1 expression in the development of chemoresistance in OC patients.