Folitixorin is a reduced form of folate and cofactor for thymidylate synthetase, the enzyme that catalyzes the methylation of deoxyuridine monophosphate (dUMP) to deoxythymidine monophosphate (dTMP).^1,2It forms a ternary complex with thymidylate synthetase and fluorodeoxyuridylate (FdUMP), the active metabolite of 5-fluorouracil , that inhibits thymidylate synthetase activity and DNA synthesis.^3,2Folitixorin has synergistic or additive cytotoxic effects against LS 174 or HT-29 human colon cancer cells, respectively, when used in combination with 5-fluorouracil.⁴In vivo, folitixorin (0.6 mg/animal) increases survival and reduces tumor growth in an HT-29 mouse xenograft model when administered in combination with 5-fluorouracil.⁵

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