Figure 5.

Mode of action of TAS-102. α,α,α-Trifluorothymidine (FTD) is converted by TK to its monophosphate form. F₃dTMP is further phosphorylated to its triphosphate form, F₃dTTP, which is well incorporated into DNA. TAS-102 exerts antitumor activity primarily via FTD incorporation into DNA. Thymidine phosphorylase inhibitor (TPI) inhibits the degradation of FTD, which is catalyzed by thymidine phosphorylase (TP) to FTY (trifluorothymine).