The inhibition of thymidine phosphorylase can reverse acquired 5FU-resistance in gastric cancer cells

Abstract

Background 5FU can be converted to its active metabolite fluoro-deoxyuridine monophosphate (FdUMP) through two pathways: the orotate phosphoribosyl transferase–ribonucleotide reductase (OPRT–RR) pathway and the thymidine phosphorylase–thymidine kinase (TP–TK) pathway. We investigated the mechanism underlying 5FU-resistance, focusing on the changes in the 5FU metabolisms. Methods MKN45 and 5FU-resistant MKN45/F2R cells were treated with 5FU or fluoro-deoxyuridine (FdU) in combination with hydroxyurea (HU) or tipiracil (TPI). The amount of FdUMP was determined by the density of the upper band of thymidylate synthase on Western blotting. Results The MKN45/F2R cells exhibited 5FU resistance (37.1-fold) and showed decreased OPRT and increased TP levels. In both cells, the FdUMP after treatment with 5FU was decreased when RR was inhibited by HU but not when TP was inhibited by TPI. A metabolome analysis revealed the loss of intracellular deoxyribose 1-phosphate (dR1P) in both cells, indicating that FdUMP was synthesized from 5FU only through the OPRT–RR pathway because of the loss of dR1P. After the knockdown of TK, the FdUMP after treatment with FdU was decreased in MKN45 cells. However, it was not changed in MKN45/F2R cells. Furthermore, TP inhibition caused an increase in FdUMP after treatment with 5FU or FdU and reversed the 5FU resistance in MKN45/F2R cells, indicating that FdUMP was reduced through the TP–TK pathway in MKN45/F2R cells. Conclusions In MKN45/F2R cells, the reduction of FdUMP through the TP–TK pathway caused 5FU resistance, and the inhibition of TP reversed the resistance to 5FU, suggesting that the combination of 5FU and TPI is a promising cancer therapy.

5-Fluorouracil Conversion Pathway Mutations in Gastric Cancer

“…Indeed, 5FU is actively absorbed by highly proliferating tissues, especially tumor ones, that need uracil for nucleic acid biosynthesis, and thus acts by inhibiting tumor cell division exploiting two different ways: it may inhibit the thymidylate synthase (TYMS), forming a covalent ternary complex with 5,10-methylenetetrahydrofolate, suppressing in that way the DNA synthesis, or it might be incorporated into RNA molecules blocking gene expression [ 3 ]. Once internalized into tumor cells, 5FU is converted to fluorouridine monophosphate (FUMP) by the orotate phosphoribosyltransferase (OPRT) and then converted to fluorodeoxyuridine monophosphate (FdUMP) by the ribosyl reductase complexes (RRM1/2), a biochemical process better known as the “OPRT–RR pathway” [ 4 ]. While FdUMP inhibits DNA synthesis through its inhibitory action on TYMS, FUMP is largely responsible for the inhibition of gene expression through its incorporation into mRNAs.…”

A 3D View of Colorectal Cancer Models in Predicting Therapeutic Responses and Resistance

“…5-FU functions by inhibiting thymidylate synthase through replacement of thymidine in DNA with fluorinated nucleotides, which in turn inhibits DNA replication causing cell death [ 165 ]. The success of 5-FU in triggering cell death is highly dependent on expression of a number of enzymes including thymidine phosphorylase and dihydro-pyrimidine dehydrogenase, which contribute to the degradation and metabolism of 5-FU, leading to drug resistance [ 166 , 167 ]. Other mechanisms contributing to resistance to 5-FU include an increased level of DNA repair [ 165 ].…”

Targeting Cancer Metabolism to Resensitize Chemotherapy: Potential Development of Cancer Chemosensitizers from Traditional Chinese Medicines

“…It was reported that PRPS1 was highly and specifically expressed in cisplatin-resistant human breast cancer cell lines, which could be a therapeutic approach to enhance drug responsiveness [92]. Mori et al suggested that the suppression of thymidine phosphorylase could enhance the drug responsiveness of gastric cancer cells to 5-fluorouracil [93]. Mitochondrial methylenetetrahydrofolate dehydrogenase 2 and its downstream purine synthesis pathway played an important role in the chemoresistance of lung cancer cells to gefitinib [94].…”