Background:

Tipiracil is an inhibitor of Thymidine phosphorylase (TP).

Thymidine phosphorylase (TP)is a key enzyme in the pyrimidine nucleoside salvage pathway. It catalyses the reversible phosphorylation of thymidine, and thereby generate thymine and 2-deoxy-D-ribose-1-phosphate.

Tipiracil (TPI) and trifluridine (FTD) are active components of TAS-102 at a molecular ratio of 1:0.5, which is a novel oral nucleoside antitumor agent in clinical trials. Oral administered TPI and FTD co-treatment may differ from that of i.v. administration of FTD alone. [1] When FTD is administered orally, it is rapidly degraded to its inactive form in the intestines and the liver (first-pass effect) [2], but the combination with TPI helps to maintain adequate FTD plasma concentrations [3]. TPI thus, potentiates the antitumor activity of FTD, and the optimal molecular ratio of FTD to TPI has been proven to be 1:0.5. [3]

参考文献:
1. Tsukihara H1, Nakagawa F2, Sakamoto K et al.  Efficacy of combination chemotherapy using a novel oral chemotherapeutic agent, TAS-102, together with bevacizumab, cetuximab, or panitumumab on human colorectal cancer xenografts. Oncol Rep. 2015 May;33(5):2135-42.
2.  Dexter DL, Wolberg WH, Ansfield FJ, Helson L and Heidelberger C: The clinical pharmacology of 5-trifluoro-methyl-2'-deoxyuridine. Cancer Res 32: 247-253, 1972.
3.  Fukushima M, Suzuki N, Emura T et al. Structure and activity of specific inhibitors of thymidine phosphorylase to potentiate the function of antitumor 2'-deoxyribonucleosides. biochem Pharmacol 59: 1227-1236, 2000.