Targeting ammonia metabolism to enhance immunotherapy response in colorectal cancer 2776

Abstract Description Advanced colorectal cancer (CRC) is notably resistant to immunotherapy, yet the underlying metabolic mechanisms driving this resistance remain unclear. Using genetically engineered mouse models with Apc, Tp53, and Kras mutations, we identified significant ammonia accumulation in tumors, resulting from dysregulated urea cycle metabolism via HNF4α/OTC downregulation. Ammonia exposure impaired T cell proliferation, increased exhaustion markers (PD-1, CTLA-4), and reduced interferon-gamma production. Enhancing ammonia clearance through ornithine supplementation restored T cell activity and improved the response to anti-PD-L1 therapy. Analysis of CRC patient samples revealed elevated serum ammonia levels, which correlated with poor survival and diminished immunotherapy efficacy. Mechanistically, high ammonia levels impaired T cell function by disrupting the transsulfuration pathway, increasing oxidative stress, and exacerbating T cell exhaustion. To further investigate the mechanisms of ammonia-mediated immunosuppression, we will conduct genome-wide CRISPR screens in T cells under ammonia stress in vitro, followed by validation of key hits using targeted CRISPR deletions in mouse models. Additionally, an in vivo CRISPR screen will identify metabolic regulators of ammonia production in tumor cells. This work aims to uncover novel therapeutic targets and generate innovative combination strategies to enhance immunotherapy outcomes in CRC patients. Funding Sources NIH grants: R01CA148828, R01CA245546, R01DK095201, R37CA237421, R01CA248160, R01CA244931, UMCCC Core Grant P30CA046592, R35GM130183 Topic Categories Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)