text: << Thymidylate synthase >> (TS) continues to be a critical target for 5-fluorouracil (5-FU) and its prodrugs, UFT/LV (Orzel), capecitabine (Xeloda), and S-1, primarily because this enzyme is essential for the synthesis of [[ 2-deoxythymidine-5-monophosphate ]], a precursor for DNA synthesis.