Regulation of Dihydropyrimidine Dehydrogenase and Pyrimidine Nucleoside Phosphorylase Activities by Growth Factors and Subsequent Effects on 5‐Fluorouracil Sensitivity in Tumor Cells

Abstract

Dihydropyrimidine dehydrogenase (DPD) and pyrimidine nucleoside phosphorylase (PyNPase) are the first and rate-limiting enzymes that regulate 5-fluorouracil (5-FU) metabolism, and tumoral DPD activity appears to be a promising predictor of 5-FU sensitivity. However, the regulatory mechanisms determining these enzyme activities have not been fully understood. We investigated the biological effects of epidermal growth factor (EGF) and transforming growth factor (TGF)-α α α α Key words: Dihydropyrimidine dehydrogenase -Pyrimidine nucleoside phosphorylase -Growth factor -5-Fluorouracil sensitivity -Cervical cancer 5-Fluorouracil (5-FU) has been widely used in the treatment of a variety of neoplastic diseases, particularly cancers of the breast and digestive organs, and is given either alone or in combination with other cytostatics. We have demonstrated that 5-FU-based chemotherapy is also useful for the treatment of uterine cervical cancer.1, 2) Two main modes of action have been proposed for 5-FU through its active metabolites, 5-fluoro-dUMP (FdUMP) and 5-fluoro-UTP. FdUMP suppresses thymidylate synthetase (TS) by forming a covalent ternary complex with 5,10-methylenetetrahydrofolate, which inhibits DNA synthesis.3) 5-Fluoro-UTP is incorporated into cellular RNA, resulting in RNA dysfunction. 4) 5-FU is initially anabolized by pyrimidine nucleoside phosphorylase (PyNPase) in both pathways. Thymidine phosphorylase (ThdPase) converts 5-FU to 5-fluorodeoxyuridine (FUdR), a precursor of FdUMP. Uridine phosphorylase (UrdPase) converts 5-FU to 5-fluorouridine (FUR), a precursor of 5-fluoro-UMP, which is finally metabolized to 5-fluoro-UTP. The former enzyme is identical to platelet-derived endothelial cell growth factor (PD-ECGF) 5) and is closely associated with tumor angiogenesis.5, 6) 5-FU is initially catabolized to 5-fluorodihydrouracil (DHFU) by dihydropyrimidine dehydrogenase (DPD), mainly in the liver, then dihydropyrimidinase and β-ureido-propionase catalyze the formation of 2-fluoro-β-alanine. Several recent studies 7-10) concerned with 5-FU antitumor effects have demonstrated that tumoral DPD activity may influence 5-FU sensitivity. Thus, DPD and PyNPase are considered to be the first and rate-limiting enzymes in the chain of reactions that regulate 5-FU metabolism.Determination of tumoral DPD has become of clinical interest because elevated intratumoral DPD can influence the tumor response to 5-FU therapy as a result of increased inactivation. Etienne et al. 8) evaluated DPD activity in tumor biopsy specimens from head and neck cancer patients before administration of 5-FU and found that the tumoral/non-tumoral DPD activity ratio was higher in the non-responding patients than in those with a partial or complete response. Moreover, certain biochemical modulations to enhance the antitumor activity of 5-FU by inhibiting intratumoral DPD activity have been attempted. 11,12) The underlying differences in tumoral DPD activity result in a variable 5-FU degradation prior to 5-FU

Enzymatic activities of uridine and thymidine phosphorylase in normal and cancerous uterine cervical tissues

“…However, since the effect of 5FU is also influenced by the dihydropyrimidine dehydrogenase (DPD) activity, as well as epidermal growth factor and TGF-alpha, the enzymatic activities of TP, DPD and other environmental tumor factors should be studied concurrently. 16 Tokumo et al reported that the TP expression was higher in squamous cell carcinoma than in adenocarcinoma or adenosquamous cell carcinoma of the cervix. 14 However, in our present study, no significant difference in the TP enzymatic activity was found between squamous cell carcinoma and adenocarcinoma/adenosquamous cell carcinoma, although the TP activity had a tendency to be a little higher in the former.…”

“…On the other hand, from a viewpoint of 5FU activation, which, other than as an angiogenic factor, is one of primary roles of TP, the enzymatic activity of TP in the whole cancer tissues can become an index to estimate the effect of 5FU‐based chemotherapy. However, since the effect of 5FU is also influenced by the dihydropyrimidine dehydrogenase (DPD) activity, as well as epidermal growth factor and TGF‐alpha, the enzymatic activities of TP, DPD and other environmental tumor factors should be studied concurrently 16 …”

Analysis of the DPYD gene implicated in 5-fluorouracil catabolism in Chinese cancer patients

“…Various reports have clearly shown that DPD activity closely correlates with mRNA levels, indicating that the DPD phenotype is controlled by some transcriptional or post‐transcriptional mechanisms in both normal and cancer cells (18, 40, 41). It has been shown that several factors, including circadian rhythm (15, 28), gender (35), treatment with 5‐FU (42), tegafur (43), epidermal growth factor and transforming growth factor‐α (44, 45), methylation of the DPYD promoter region (46), activator protein‐1 (47), may alter DPYD expression. In this study, we ruled out the possibilities of impact on DPD activity with regard to circadian rhythm and treatment factors.…”

Effect of 5‐fluorouracil and epidermal growth factor on cell growth and dihydropyrimidine dehydrogenase regulation in human uterine cervical carcinoma SKG‐IIIb cells

“…8) We also reported that these growth factors suppress tumoral DPD activity, increase pyrimidine nucleoside phosphorylase activity, and make tumor cells more sensitive to 5-FU. 9) In the present study, we investigated the biological effects of 5-FU on tumoral DPD activity in the presence or absence of EGF and studied the regulation of DPD activity by 5-FU and EGF.…”