Thymidylate synthase and dihydropyrimidine dehydrogenase mRNA expression after administration of 5‐fluorouracil to patients with colorectal cancer

Abstract

This study explores the effect of 5-fluorouracil (5FU) exposure on mRNA levels of its target enzyme thymidylate synthase (TS) and the rate-limiting catabolic enzyme dihydropyrimidine dehydrogenase (DPD) in tumors of colorectal cancer patients. TS and DPD mRNA levels were determined in primary tumor and liver metastasis samples from patients who were either not pretreated (n 5 29) or given one presurgery bolus of 5FU (n 5 67). In both groups a wide variation in TS mRNA levels was observed. Median TS mRNA expression in 17 primary tumors of exposed patients was 3.0-fold higher than in 19 primary tumors of unexposed patients (p 5 0.015). TS mRNA expression in liver metastasis samples of exposed patients (n 5 16) was also higher (5.2-fold) than that of unexposed patients (n 5 48; p < 0.001). Also DPD mRNA expression displayed a large degree of interpatient variation. No difference in DPD expression in liver metastasis samples was observed between exposed and unexposed patients. However, median DPD mRNA expression in 15 primary tumors of exposed patients was 3.2-fold lower than in 18 primary tumors of unexposed patients (p 5 0.027). In conclusion, administration of 5FU in vivo influences the gene expression of TS and DPD. ' 2007 Wiley-Liss, Inc.Key words: 5-fluorouracil; colorectal carcinoma; thymidylate synthase; dihydropyrimidine dehydrogenase; RT-PCR The antimetabolite 5-fluorouracil (5FU) has been included in the standard treatment of patients with advanced colorectal cancer for over 40 years.1,2 Several studies have indicated that 2 important enzymes in 5FU metabolism, thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD), are potential markers for response to 5FU-based therapy.3-8 TS is the main target for 5FU, while DPD plays a major role in 5FU degradation.TS is a key enzyme in the de novo synthesis of dTMP and dTTP, a precursor for DNA. TS catalyses the methylation of dUMP to dTMP for which 5,10-methylene-tetrahydrofolate (CH 2 -THF) is the methyl donor. The main mechanism for the action of 5FU is considered to be an inhibitor of TS. 5-Fluoro-dUMP (FdUMP) is an active metabolite of 5FU and it inhibits TS by the formation of a covalent ternary complex between FdUMP, TS and CH 2 -THF, resulting in depletion of dTTP, which can lead to thymine-less death because of inhibition of DNA synthesis. 9,10 Several groups have noted in preclinical models, both cell lines and animal models, an induction of TS activity or TS-FdUMPbinding 4-24 hr after administration of 5FU.11,12 Interestingly, this increase in TS protein after 5FU exposure in vitro is not accompanied by an increase in TS mRNA expression. This observation has led to the hypothesis that this TS induction in vitro by 5FU (or other TS inhibitors) occurs because of disruption of the translational repression caused by the binding of TS to its own mRNA. 11,13 Another explanation that has been proposed is that 5FU exposure results in stabilization of the TS protein because of decreased degradation of the ternary complex.

Molecular Mechanisms Underlying the Synergistic Interaction of Erlotinib, an Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitor, with the Multitargeted Antifolate Pemetrexed in Non-Small-Cell Lung Cancer Cells

“…In agreement with this hypothesis and with the observed increase in TS mRNA expression, as detected previously with pemetrexed and 5-FU Mauritz et al, 2007), TS protein expression and catalytic activity in cell extracts were enhanced after pemetrexed exposure.…”

Molecular pathways involved in the synergistic interaction of the PKCβ inhibitor enzastaurin with the antifolate pemetrexed in non-small cell lung cancer cells

“…TS, as an RNA-binding protein, also regulates its own synthesis by impairing the translation of its mRNA, whereas the binding to a specific inhibitor leads to upregulation of TS protein (Chu et al, 1991). In agreement with this hypothesis, as well as with the observed increase in TS mRNA expression, as previously detected with pemetrexed and 5-fluorouracil (5-FU) (Peters et al, 2002;Mauritz et al, 2007), TS protein expression in cell extracts was enhanced after pemetrexed exposure. However, this study also shows that enzastaurinpemetrexed combination significantly inhibited the activity of TS, potentially leading to synergistic drug interaction.…”

Liver-only metastatic colorectal cancer patients and thymidylate synthase polymorphisms for predicting response to 5-fluorouracil-based chemotherapy

“…methylenetetrahydrofolate reductase gene polymorphisms). In addition to the fact that TS is the target enzyme of 5-fluorouracil, it has been observed that TS levels may be dynamic, with upregulation after fluoropyrimidine exposure (Uchida et al, 2004a, b;Mauritz et al, 2007). In particular, this effect was described in liver metastases from colorectal cancer in patients who received bolus 5-fluorouracil (Mauritz et al, 2007).…”

“…In addition to the fact that TS is the target enzyme of 5-fluorouracil, it has been observed that TS levels may be dynamic, with upregulation after fluoropyrimidine exposure (Uchida et al, 2004a, b;Mauritz et al, 2007). In particular, this effect was described in liver metastases from colorectal cancer in patients who received bolus 5-fluorouracil (Mauritz et al, 2007). Therefore, TS polymorphisms may influence the outcome to 5-fluorouracil chemotherapy, not only for their role in determining different baseline levels of TS activity (Marsh, 2005), but also for modulating the enhancement of TS levels in response to 5-fluorouracil.…”