A) Serum ammonia or B) T cell proliferation was assessed in wildtype mice treated with ammonium acetate diet for 7 days or cotreated with ammonium acetate and daily intraperitoneal injection of 10 mM ornithine (n=3). C, D) Syngeneic tumor study in C57BL/6J or E) athymic nude mice with CRC-derived MC38 cells following ornithine treatment (10 mM ornithine intraperitoneally (n=8–10). Representative IHC F) image and G) quantitation of Ki67 in MC38 tumors treated with ornithine. H) Quantification of ammonia in MC38 tumors treated with ornithine. I) Serum ammonia levels in healthy, CRC, or metastatic CRC patients. J) Gene expression analysis for OTC and HNF4α in normal livers or livers with metastatic lesions K) Ammonia quantification from normal livers or metastatic tumors (n=3). L) Representative images and M) tumor weights of in the liver metastasis model treated with vehicle and intraperitoneal ornithine (n=8–10). N) Ammonia concentration in ornithine treated liver metastasis livers (n=3). *p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001 unless otherwise indicated. Data is presented as mean ± SEM. All experiments were performed in triplicates at least three times.