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Stable expansion of high-grade serous ovarian cancer organoids requires a low Wnt environment

ABSTRACT: High-grade serous ovarian cancer (HGSOC) likely originates from the fallopian tube (FT) epithelium. Here, we established 15 organoid lines from HGSOC primary tumor deposits that closely match the mutational profile and phenotype of the parental tumor. We found that Wnt pathway activation leads to growth arrest of these cancer organoids. Moreover, active BMP signaling is almost always required for generation of HGSOC organoids, while healthy fallopian tube organoids depend on BMP suppression by Noggin. Fallopian tube organoids modified by stable shRNA knockdown of p53, PTEN, and retinoblastoma protein (RB), also require a low-Wnt environment for long-term growth, while fallopian tube organoid medium triggers growth arrest. Thus, early changes in the stem cell niche environment are needed to support outgrowth of these genetically-altered cells. Indeed, comparative analysis of gene expression pattern and phenotypes of normal vs. loss-of-function organoids confirmed that depletion of tumor suppressors triggers changes in the regulation of stemness and differentiation.

SUBMITTER: Karen Hoffmann

PROVIDER: S-SCDT-EMBOJ-2019-104013 | biostudies-other |

REPOSITORIES: biostudies-other

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Project description: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). These pathways are known to be disrupted in the vast majority of HGSOC patients (>95%, 45% and 67% of cases, respectively as reported by TCGA consortium). Unexpectedly, combined loss of function of the three tumor suppressor proteins, p53, PTEN and Rb, led to a growth arrest and loss of stemness if organoids are cultured in medium optimized for healthy FT epithelium, which maintains high Wnt signaling and BMP pathway inhibition. This designates a requirement for alterations in the exogenous signaling cues to facilitate transformation. Indeed, we show that successful expansion of patient-derived HGSOC organoids from solid tumor deposits depends on the absence of exogenous Wnt3A in the medium. Using a combinatorial screening approach of different medium compositions, we have established 15 organoid lines, which closely resemble the parental tumor tissue and express hallmarks of HGSOC phenotype as revealed by histology and global gene expression profiles. Strikingly, the medium optimized for ovarian cancer organoids also rescued 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. Likewise, surface expression of the stemness marker CD133 was strongly increased in triple KD organoids in the absence of Wnt3A/Rspo1. Complementary to this finding, the addition of Wnt agonists to cancer organoids led to rapid growth arrest and a sharp drop in stemness, as evidenced by cell viability assay and the number of CD133 positive cells, respectively. Taken together, our data reveal that critical changes in the paracrine environment constitute early events during HGSOC development.

Project description: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.

Project description:Ovarian tumors of low malignant potential and low-grade ovarian serous carcinomas are thought to represent different stages on a tumorigenic continuum and to develop along pathways distinct from high-grade ovarian serous carcinoma. We performed gene expression profiling on three normal human ovarian surface epithelia samples, and 10 low-grade and 10 high-grade ovarian serous carcinomas. Analysis of gene expression profiles of these samples has identified 80 genes upregulated and 232 genes downregulated in low-grade ovarian serous carcinomas. PAX2 was found to be one of the most upregulated genes in low-grade ovarian serous carcinoma. The upregulation of PAX2 was validated by real-time quantitative RT-PCR, western blot and immunohistochemical analyses. Real-time RT-PCR showed a statistically significant difference in PAX2 mRNA expression (expressed as fold change in comparison to normal human ovarian surface epithelia) among ovarian tumors of low malignant potential (1837.38, N=8), low-grade (183.12, N=17), and high-grade (3.72, N=23) carcinoma samples (P=0.015). Western blot analysis revealed strong PAX2 expression in ovarian tumors of low malignant potential (67%, N=3) and low-grade carcinoma samples (50%, N=10) but no PAX2 protein expression in high-grade carcinomas (0%, N=10). Using immunohistochemistry, tumors of low malignant potential (59%, N=17) and low-grade carcinoma (63%, N=16) samples expressed significantly stronger nuclear staining than high-grade ovarian carcinoma samples (9.1%, N=263). Furthermore, consistent with earlier immunohistochemical findings, PAX2 expression was expressed in the epithelial cells of fallopian tubes but not in normal ovarian surface epithelial cells. Our findings further support the two-tiered hypothesis that tumors of low malignant potential and low-grade ovarian serous carcinoma are on a continuum and are distinct from high-grade ovarian carcinomas. In addition, the absence of PAX2 expression in normal ovarian epithelia but expression in fallopian tube fimbria and ciliated epithelial inclusions would suggest the potential development of tumors of low malignant potential and of low-grade ovarian serous carcinomas from secondary Müllerian structures.

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Stable expansion of high-grade serous ovarian cancer organoids requires a low Wnt environment

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