Quantitative Measurement of Thymidylate Synthase and Dihydropyrimidine Dehydrogenase mRNA Level in Gastric Cancer by Real‐time RT‐PCR

We used real‐time reverse‐transcription polymerase chain reaction (RT‐PCR) to assay expression of the mRNA of thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD) in gastric cancer tissue with the objective of establishing a system to measure TS and DPD in ultra‐low‐volume samples. Nude mouse xenografts of 5 human gastric cancer cell lines and 85 clinical samples were used as the specimens in this study. Sensitivity to 5‐fluorouracil (5‐FU) was determined on the basis of the relative tumor proliferation rate in mice and the results of ATP assay using serum‐free cultures of the clinical samples. mRNA expression was measured in tumor tissue by real‐tune RT‐ PCR using the ABI PRISM 7700 system. The values for expression of the mRNA for TS and DPD were corrected according to the level of glyceraldehyde‐3‐phosphate dehydrogenase mRNA expression. The xenografts yielded correlations between TS and DPD mRNA expression and the activity of the enzymes (TS: r(s)=0.700, DPD: r(s)=0.900), and an inverse correlation was noted between the mRNA levels and sensitivity to 5‐FU (TS: r(s)=‐0.900, DPD: r(s)=‐0.800). The clinical samples showed an inverse correlation between 5‐FU sensitivity and mRNA expression (TS: r(s)=‐0.518, DPD: r(s)=‐0.564). Sensitivity to 5‐FU was noted only in cases in which TS mRNA expression and DPD mRNA expression were both low. Real‐time RT‐PCR can provide a highly sensitive assessment of TS and DPD mRNA expression in gastric cancer, and it was useful for predicting 5‐FU sensitivity.