The mechanism of action of MTHF when administered in combination with 5-fluorouracil
Intracellular reduced folates exist as a pool of at least six interconvertible forms. One of them, MTHF, is the essential one-carbon donor and reduced folate substrate for the enzyme TS. TS catalyzes the dUMP to deoxythymidine-5-dTMP. This enzymatic pathway is critical as it provides one of the four necessary nucleotide substrates for DNA synthesis. For this reason, TS has been an important target for cancer chemotherapy.