209P - Deoxyuridine monophosphate reverses resistance to 5FU in 5FU-resistant gastric cancer

Date 19 December 2015
Event ESMO Asia 2015 Congress
Session Poster presentation 1
Topics Gastric Cancer
Translational Research
Presenter Ryutaro Mori
Citation Annals of Oncology (2015) 26 (suppl_9): 42-70. 10.1093/annonc/mdv523
Authors R. Mori, T. Tanahashi, N. Okumura, K. Yamaguchi, M. Futamura, K. Yoshida
  • Surgical Oncology, Gifu University, Graduate School of Medicine, 5011194 - Gifu/JP

Abstract

Aim/Background

5FU is a pyrimidine analogue that inhibits DNA synthesis. The present study investigated the influence of nucleosides and nucleotides on 5FU-resistance in gastric cancer cells.

Methods

MKN45 cells (parental cells) and 5FU-resistant MKN45/F2R cells (resistant cells) were treated with 5FU, fluorodeoxyuridine monophosphate (FdUMP), and trifluorothymidine (TFT), which are inhibitors of thymidylate synthase (TS). Deoxyuridine monophosphate (dUMP), thymidine monophosphate (dTMP) and thymidine (dT) were combined with these drugs. The expression levels of TS and orotate phosphoribosyltransferase (OPRT) were determined by Western blotting. The viability of the cell lines was calculated by an MTT assay.

Results

The resistant cells exhibited resistance to 5FU (93-fold), FdUMP (45-fold) and TFT (79-fold) and expressed decreased OPRT (0.74-fold) and increased TS (2.4-fold) levels in comparison to the parental cells. While dUMP alone was not cytotoxic to either of the cells, it decreased the IC50 for 5FU (88.2 µM to 31.2 µM) and FdUMP (51.2 µM to 5.6 µM) in the resistant cells and increased the IC50 for TFT in the parental cells (0.6 µM to 3.15 µM). Low concentrations (<10 µM) of dTMP and dT reversed the cytotoxicity of TFT, while high concentrations were cytotoxic. A Western blotting analysis revealed that dUMP enhanced the upper band of TS after treatment with 5FU and FdUMP, which presented an increase in the ternary complex composed of FdUMP, folic acid and TS.

Conclusions

The increase in the ternary complex after treatment with 5FU with dUMP in resistant cells suggests that dUMP increased the level of FdUMP that was metabolized from 5FU. Furthermore, treatment with FdUMP (instead of 5FU) revealed similar result, indicating that the resistant cells had the ability to reduce the amount of intracellular FdUMP and that dUMP inhibited this ability because the decrease in OPRT and the increase in TS cannot explain these results.

Clinical trial identification

Disclosure

All authors have declared no conflicts of interest.