Preservation of stemness in high-grade serous ovarian cancer organoids requires low Wnt environment. Preservation of stemness in high-grade serous ovarian cancer organoids requires low Wnt environment

High-grade serous ovarian cancer (HGSOC) creates a unique clinical challenge due to late detection, limited therapeutic options and wide-spread resistance to chemotherapy, all of which lead to very low survival rates. It is now widely recognized that this cancer emerges as metastasis from the fallopian tube and the lack of suitable in vitro disease models poses a major obstacle for efforts to improve our understanding of this deadly disease. We used organoids of healthy human FT epithelium as a model for stepwise genetic modification towards malignancy, using shRNA-mediated knockdown (KD) of three major HGSOC driver genes: P53, PTEN and Retinoblastoma (RB). Moreover, we successfully established patient-derived HGSOC organoids from solid tumor deposits. After combinatorial screening approach of different media compositions we have established 15 organoid lines which depend on the absence of exogenous Wnt3a in the medium. We could show that those cultures closely resemble the parental tumor tissue and express hallmarks of HGSOC phenotype as revealed by histology and global gene expression profiles of the matching organoid and tissue samples. Expression and sequencing analysis revealed that all samples were characterized by p53 mutation and/or aberrant p53 expression. Interestingly, the addition of Wnt agonists to cancer organoids leads to rapid growth arrest and a sharp drop in stemness, as proven by cell viability assay and the number of CD133 positive cells, respectively. Complementary to this finding, we can show that the medium optimized for ovarian cancer organoids also improves the growth of the modified organoid lines, showing that changes within the niche environment are required to promote stemness upon depletion of P53/PTEN/RB. Taken together, our data reveal that critical changes in the paracrine environment are likely to represent early events during HGSOC development and provide a starting point to further analyze how specific mutations and paracrine signals influence pathways of stemness regulation and thus drive malignant transformation in ovarian carcinogenesis. Overall design: Microarray experiments were performed as single-color hybridizations on Agilent 4x44K Mouse Genome Microarrays.