UMPS and cancer: Uric acid can directly inhibit uridine monophosphate synthase (UMPS) and reduce the sensitivity of cancer cells to the chemotherapy drug 5-fluorouracil [41]; however, the concentration of uric acid in mouse plasma is one-tenth that of human plasma, and therefore the mouse plasma environment shows little effect on UMPS activity or 5-fluorouracil-induced resistance of cancer cells [41].