Molecular profile of 5-fluorouracil pathway genes in colorectal carcinoma

Background: Colorectal carcinoma (CRC) is the third most frequent malignancy worldwide. Over 30 years, the core therapy of CRC remains 5-fluorouracil (5-FU). Only 1–3% of administered 5-FU is converted into its active form – fluorodeoxyuridine monophosphate. Several studies indicate potential prognostic and predictive role of 5-FU metabolizing enzymes in resistance of CRC. This study focused on involvement of fifteen 5-FU pathway genes in the prognosis of CRC patients.

Material and Methods: Testing set and two validation sets consist of paired tumor and non-neoplastic control tissue samples from 154 CRC patients and were used for transcript and methylation profiling. Gene expression of 15 genes was performed using quantitative real-time PCR and methylation profiling was performed using high resolution melting analysis. These molecular profiles were then correlated with clinical data of patients. Further, most relevant candidate markers were chosen and their protein profile was assessed by immunoblotting.

Results: In testing and validation sets, higher transcript level of DPYD and lower levels of PPAT, UMPS, RRM2, and SLC29A1 were established in tumors compared to paired adjacent mucosa tissues. RRM2 downregulation significantly associated with poor response of patients to the first-line palliative treatment by 5-FU in testing set and this was confirmed by survival analysis of the validation set. Strong methylation of UPP2, but no transcript levels were found in both tumor and control tissues. DPYS was significantly more methylated in tumors in comparison with adjacent mucosas of testing and validation sets. Low intratumoral UPB1 methylation levels predicted poor disease-free interval in both sets of patients. Most of the investigated 5-FU pathway genes showed no methylation in either tumor or adjacent mucosa tissues.

Conclusions: The observed upregulation of a certain 5-FU activating genes and downregulation of DPYD, which inactivates 5-FU, indicate a favorable gene expression profile for 5-FU therapy in chemotherapy-naive colorectal tumors. Furthermore, low RRM2 transcript levels and UPB1 hypomethylation represent individual poor prognostic markers for colorectal carcinoma patients and therefore should be further examined in greater detail.

Study was supported by projects no.: NT14329–3 (Internal Grant Agency), P301/12/1585 (Czech Science Foundation), 75010330 (MH CZ – DRO, NIPH), CZ.1.05/2.1.00/03.0076 (European Regional Development Fund) and 1200314 (Grant Agency of Charles University).

No conflict of interest.