OTC and neoplasm: For instance, p53 protein, a tumor suppressor, represses the urea cycle by the downregulation of ARG1, carbamoyl phosphate synthetase 1 (CPS1), and Orn transcarbamylase (OTC) to decrease the capability of ammonia elimination, thus inhibiting tumor growth (Li et al., 2019); in parallel, the activity of ODC is suppressed at mRNA level to limit PA generation in human-body tissues (Li et al., 2019).