Cell-cell communication in ovarian cancer cell migration and invasion

Peritoneal carcinomatosis in late stages of high-grade serous ovarian carcinoma (HGSOC) arises from transcoelomic dissemination of ovarian cancer cells (OCC) via the malignant ascites. Human peritoneal mesothelial cells (HPMC) play a crucial role in shaping the tumor microenvironment to establish a metastatic niche. Despite their importance, the exact functional role and molecular mechanisms underlying the interaction between HPMC and OCC remain largely unclear. For this study, primary OCC, primary HPMC, and ascites derived from patients with HGSOC were used. Conditioned medium (CM) was obtained from HPMC to treat OCC in order to examine the effect on the migratory capacity of tumor cells. These findings show that HPMC from HGSOC patients could promote migration of OCC. The experimental results of this thesis indicate that this pro-migratory effect is mediated by an indirect communication mechanism, i.e. via the secretion of soluble factors. Moreover, it was found that this secretion from HPMC is promoted by malignant ascites. Transcriptome analysis of HPMC revealed several genes upregulated by exposure to ascites, however gene knockdown of the top five candidates, which are SEMA3D, PLAT, MGP, CEMIP and TNFRSF11B, did not lead to changes of the pro-migratory effects of the HPMC secretome on OCC migration. Therefore, an optimized HPMC culture protocol was established, using human serum-containing culture medium as a control instead of FCS-containing culture medium. This approach was to enhance the potential functional and clinical relevance of the applied assays. To identify the pro-migratory factors released from HPMC in response to ascites, transcriptomic and proteomic analyses were performed. Transcriptome analysis demonstrated an Interferon (IFN) type I response, which was further validated by qPCR. Proteomic analyses of the HPMC secretome was conducted using both Liquid Chromatography Mass Spectrometry-based (LC-MS) proteomics as well as Olink affinity proteomics, revealing an enrichment of gene sets associated with cell migration, motility and adhesion. To further explore the impact of HPMC-secreted proteins on OCC, a transcriptome analysis of tumor cells was conducted. The results revealed an upregulation of several genes, including FOXP1, PDE4A, and PTPN6, known as oncogenes in ovarian cancer. These findings imply these genes as potential therapeutic targets; however, additional experiments are required to investigate their functional role in cancer cell migration and metastasis. Overall, the data of this thesis strongly suggest that HPMC have an important function in the metastasis of ovarian cancer cells into peritoneal organs, and that molecules in the tumor microenvironment lead to the reprogramming of HPMC, which in turn contribute to tumor motility by secreting soluble factors.