Abstract A008: DNA methyltransferase 3A promotes inflammation-associated gastric cancer growth and presents a therapy target for gastric cancer

Gastric cancer (GC) remains the third leading cause of cancer-related death worldwide. While inflammation is a well-established driver of gastric tumorigenesis, only a small subset of GC patients responds to immunotherapy. One proposed mechanism of immune escape is silencing tumor-antigen expression, and thereby avoiding immune recognition. DNA methyltransferases (DNMTs) are the enzymes responsible for DNA methylation and hence, for the epigenetic silencing of gene expression of tumor-antigens and other immune-related molecules. Interestingly, they are often overexpressed in solid tumors. Epigenetic drugs inhibiting these DNMTs have shown anti-tumor effects in combination with immune checkpoint inhibitors. Here we are studying the role of DNMTs, specifically DNMT3A, in GC mouse models and the possibility of combining DNMT inhibitors with immunotherapy for the treatment of GC. This project utilises various mouse models of GC. We established a Dnmt3a-overexpressing inflammation-driven GC mouse model (gp130FF, A33Dnmt3a). In a second mouse model, mutant Kras, Pi3kca and Tp53 expression results in highly advanced invasive gastric carcinoma formation (KPT model). We successfully established GC organoids of one of these triple mutant tumors, which can be injected subcutaneously into wild type mice and result in allograft tumor formation. DNMT3A overexpression was detected in human GC specimen and associated with bad overall survival of patients. Gastric adenomas of our gp130FF, A33Dnmt3a mouse model have a 10-fold elevated Dnmt3a expression. Importantly, tumor-specific Dnmt3a overexpression significantly increased gastric tumor burden. We have conducted DNA methylation and gene expression analyses to identify differently methylated and expressed genes between gp130FF and gp130FF, A33Dnmt3a gastric adenoma cells. Treatment with the DNMT inhibitor decitabine reduced tumor growth in the inflammation-driven gp130FF gastric adenoma mouse model. In the KPT model, we have identified DNMT3A as being highly expressed in the invasive front of tumors, their liver metastases as well as in the allograft tumors established by the KPT organoids. In this model of advanced GC, treatment with the DNMT inhibitor decitabine significantly decreased tumor growth and we are currently investigating the efficacy of decitabine in combination with anti-PD-1 and/or anti-CTLA-4 immunotherapy. Taken together, we provide evidence for a driver function of Dnmt3a in gastric tumorigenesis and gastric tumor growth. In addition, our findings encourage further studies to investigate the potential of DNMT inhibitors for the treatment of GC. Citation Format: Anne Huber, Christine Dijkstra, Yuba Bhandari, Hariharan Easwaran, Stephen Baylin, Matthias Ernst, Moritz Eissmann. DNA methyltransferase 3A promotes inflammation-associated gastric cancer growth and presents a therapy target for gastric cancer. [abstract]. In: Proceedings of the AACR Special Conference: Cancer Epigenomics; 2022 Oct 6-8; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2022;82(23 Suppl_2):Abstract nr A008.