Gastric cancer is the second leading cause of cancer related deaths and the fifth most common malignancy worldwide. The prognosis of gastric cancer is often poor. Frequently, the lack of clinical signs lead to a delayed diagnosis with three quarters of patients presenting with non-curable advanced disease. The only curative option is surgery, supported in recent years by perioperative chemotherapy. However, known molecular alterations represent possibilities for targeted therapies to improve overall survival. Nevertheless, biomarkers to predict therapy response are missing, resulting in several failed clinical trials for targeted drugs. Organoids are a recently developed three-dimensional culture system derived from different sources, i.e. adult tissue stem cells, embryonic stem cells (ESC) or induced pluripotent stem cells (iPSC). While in ESC or iPSC derived organoids a functional niche is present that maintains stem cells, this niche is missing in adult stem cell derived organoids and needs to be replaced by a definite medium containing the relevant growth factors. Organoids have the ability of proliferation, self-renewal and self-organization. They show a comparable functionality of the organs they are derived from. In sum, organoids are valuable tools to study diseases on a patient level. In this work, we focused on the characterization of gastric cancer by using human and mouse cancer organoids. Firstly, a human gastric cancer organoid biobank was established. The patient derived organoid lines were characterized concerning their molecular profile, treated with classical chemotherapeutics and mutation specific targeting was performed. The generated human cancer organoids showed a high similarity to the tissue they were derived from and allowed a detailed analysis of observed alterations for each individual patient. However, the high number of mutations effected targeted therapies and needed to be interpreted in the whole mutation spectrum of each specific organoid line. In order to establish organoids with defined mutations for in depth analysis of pathway interference, we decided to combine inducible alleles of frequently altered signaling pathways in gastric cancer in mice and derived organoids of the stomach. These organoid lines were further analyzed by their morphology, functionality and drug response. Successful interference with activated pathways demonstrated their potential usefulness as living biomarkers for therapy response testing. In order to analyze gastric cancer in vivo a stomach specific mouse model was established. Intensive literature and database research resulted in the identification of Annexin10 (Anxa10) as potential stomach specific gene which at the same time is expressed in all different cell types of the stomach epithelium. We therefore generated an inducible Cre recombinase mouse line under the Anxa10 promotor. The Anxa10 CreERT2 line showed only stomach specific recombination events and no restriction to a specific cell type. Nevertheless, activation of Cre resulted in a patchy recombination pattern throughout the whole gland and not a uniform recombination in all cells. Due to this patchy expression, the mouse line is an optimal tool for cancer models, where a complete transformation of an organ is not desired. On the other side it is not useful, if a complete knock-out of a certain floxed allele is needed. This new stomach specific mouse line was then used to model gastric cancer subtypes in vivo. Frequently altered pathways and hotspot mutations of each gastric cancer subtype were defined based on the TCGA database. Alterations were mainly found in the following pathways: RTK/RAS, PI3K/AKT, WNT, TGF β, cell adhesion and chromatin remodelling. We generated and analyzed three different mouse models: one for the chromosomal instability (CIN) subtype and two for the genomically stable (GS) subtype. The different models mimicked very closely the histology of known human gastric cancer subtypes. The intestinal CIN model with mutations in Kras, Smad4 and Tp53 developed tumors with glandular and tubular structures showing morphologies to human intestinal type gastric cancer. The first GS model with alterations in Kras, Cdh1 and Smad4 showed cancers with a diffuse tumor cell morphology with the presence of typical signet ring cells. The second GS model with Kras, Cdh1 and Apc alterations showed similarities to the adenomatous tooth like gastric cancer subtype. Taken together, this study demonstrates that gastric cancer organoids might serve as living biomarkers to predict therapy response and resistance in individual patients. Additionally, the generated gastric cancer mouse model is to our knowledge the first model initiating tumor formation exclusively in the stomach with similar characteristics as described for human gastric cancer. This mouse represents a prime tool for further gastric cancer research.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:86087 |
| Date | 19 June 2023 |
| Creators | Seidlitz, Therese |
| Contributors | Stange, Daniel, Zeißig, Sebastian, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | 10.1136/gutjnl-2017-314549, 10.1053/j.gastro.2019.09.026 |
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