Overexpression of the orotate phosphoribosyl-transferase gene enhances the effect of 5-fluorouracil on gastric cancer cell lines.

OBJECTIVE

Orotate phosphoribosyl-transferase (OPRT) is the initial enzyme of the 5-fluorouracil (5-FU) metabolic pathway, converting 5-FU into 5-fluorouridinemonophosphate, which is the most important mechanism of 5-FU activation. We therefore investigated whether overexpression of the OPRT gene enhances sensitivity to 5-FU.

METHODS

An expression vector of the OPRT gene (pTARGET-OPRT) was transfected into two gastric cancer cell lines, TMK-1 and MKN-45, with low baseline expression levels of OPRT. The sensitivity to and anti-tumor activity of 5-FU were then investigated in vitro and in vivo in these two transfected clones (TMK-OPRT and MKN-OPRT).

RESULTS

Although cell growth was unaltered compared to parent cells, overexpression of the OPRT gene was confirmed by Western blotting in both the TMK-OPRT and MKN-OPRT cells. OPRT enzyme activity increased 38-fold in TMK-OPRT cells and 8.0 fold in MKN-OPRT cells compared to their parent cells. Interestingly, although the sensitivity to Adriamycin, cis-platinum, mitomycin C and paclitaxel was unaltered in the transfected clones, the sensitivity to 5-FU was increased 14.2- and 6.0-fold in TMK-OPRT and MKN-OPRT cells, respectively, compared to their parent cells. Moreover, enhanced sensitivity was also confirmed in the in vivo study.

CONCLUSION

The results indicate that overexpression of the OPRT gene plays an important role in the antiproliferative effect of 5-FU and might therefore be a predictive factor of response to 5-FU in gastric cancer patients.