Helicobacter pylori infection of the stomach and the resulting clinical consequences of chronic gastritis, peptic ulcer disease, and disease progression to gastric cancer remains a major health concern for Veterans. This pathogen infects half of the world?s population, and gastric cancer is the third leading cause of cancer deaths worldwide. H. pylori prevalence in Veterans is high; deployment-related infection is a problem, especially acquisition of strains associated with higher risk for carcinogenesis. The three polyamines, putrescine (Put), spermidine (Spd), and spermine (Spm), are ubiquitous molecules with many biological effects. Put is synthesized by the rate-limiting enzyme, ornithine decarboxylase (ODC), and is converted sequentially to Spd and Spm, which is back-converted to Spd by spermine oxidase (SMOX). Our Lab has had a long interest in the role of polyamines in GI inflammation and carcinogenesis, and we have the following exciting findings pertinent to this renewal grant: 1) Smox?/? mice infected with H. pylori exhibit decreased gastric inflammation, DNA damage, and chemokine expression, associated with depletion of Spd; 2) These phenotypes are recapitulated in H. pylori- infected 2D organoids from Smox?/? mice; 3) A new link between the H. pylori-induced pro-carcinogenic activation of b-catenin and SMOX, including findings that Smox?/? mice and gerbils treated with a SMOX inhibitor have loss of b-catenin activation in vivo; 4) Use of human gastric organoid cultures to demonstrate the effectiveness of a novel and potent SMOX inhibitor in blocking H. pylori-induced b-catenin activation, associated with Spd depletion; 5) Implication of a unique form of protein translation, hypusination, via the action of deoxyhypusine synthase (DHPS), a process which has been linked to carcinogenesis and appears to be attenuated by Smox deletion; 6) Demonstration of somatic genomic abnormalities by whole exome sequencing (WES) in gastritis and dysplasia tissues of INS-GAS mice, a model of H. pylori-induced carcinogenesis. We will now make effective use of important molecular tools, including valuable mutant mouse models, a key SMOX inhibitor, and advanced use of 3D and 2D gastric organoids from mice and VA patients. We hypothesize that dysregulated polyamine metabolism, due to SMOX and associated generation of Spd and hypusination, provides a molecular pathway leading to risk for gastric disease progression to carcinogenesis. Our specific aims are: 1) To directly determine the role of SMOX and Spd in gastric carcinogenesis. We will test: A) The effect of SMOX in cancer-prone INS-GAS mice, analyzing H. pylori-induced carcinogenesis, DNA damage, b-catenin activation, and GEC function in FVB/N INS-GAS Smox?/? mice +/- Spd; B) A novel, potent, second-generation SMOX inhibitor, SLH150-54, in INS-GAS mice and gerbils; C) The effect of SMOX/Spd on the formation of somatic genomic abnormalities using whole exome sequencing. 2) To determine if epithelial DHPS mediates deleterious effects of SMOX/Spd in gastric carcinogenesis. We will analyze: A) The role of SMOX in hypusination during H. pylori infection in C57BL/6 and FVB/N INS-GAS Smox?/? vs. WT mice +/- H. pylori +/- Spd; B) The effect of hypusination in gastric epithelial cells (GECs) on inflammation and carcinogenesis, using C57BL/6 and FVB/N INS-GAS mice with specific deletion of Dhps in GECs; C) the effect of DHPS/hypusination on somatic genomic instability. 3) To utilize gastric organoid reporter systems in tissues from VA patients to establish human biomarkers for carcinogenesis. H. pylori-induced DNA damage, b-catenin activation, and pathways identified in Aims 1 and 2 will be studied, related to: A) Induction and role of SMOX, using CRISPR/CAS9-mediated deletion of SMOX and SMOX inhibitors; and B) Induction and role of DHPS, using CRISPR/CAS9-mediated deletion of DHPS and the DHPS inhibitor, GC7. This research program will provide crucial new insights into H. pylori- induced inflammation and disease progression along the pathway to gastric carcinogenesis. The translation of findings from valuable animal models into robust human organoid systems is expected to facilitate the validation of new strategies for cancer risk assessment, chemoprevention, and treatment for VA patients.