title: Synergistic antitumor effect of combined 5-fluorouracil (5-FU) with 5-chloro-2,4-dihydroxypyridine on 5-FU-resistant gastric cancer cells: possible role of a dihydropyrimidine dehydrogenase-independent mechanism.
abstract: BACKGROUND
  S-1 is an oral fluorouracil antitumor drug that combines three pharmacological agents: tegafur, a prodrug of 5-fluorouracil (5-FU); 5-chloro-2,4-dihydroxypyridine (CDHP), an inhibitor of dihydropyrimidine dehydrogenase (DPD); and potassium oxonate, an agent included to reduce gastrointestinal toxicity. S-1 has a potent antitumor effect on gastric cancer, even in 5-FU-refractory cases. However, there is a lack of basic information to account for this clinical outcome. This study was performed to determine the differences in antitumor effects of combined administration of 5-FU and CDHP between NUGC-3 cells and NUGC-3/5FU/L cells, which are resistant to 5-FU (established by repeated cultures of NUGC-3 with escalating concentrations of 5-FU), and to determine the mechanisms involved.
  
  
  METHODS
  Both cell lines were incubated with various concentrations of 5-FU and/or CDHP. The antitumor effect was assessed using an MTS assay and cell counts. DPD levels were assayed by using enzyme-linked immunosorbent assay. Expression of DPD and thymidylate synthase (TS) mRNA was quantified using real-time quantitative polymerase chain reaction analysis.
  
  
  RESULTS
  The combination of 5-FU (IC15) with CDHP exerted a synergistic antitumor effect on NUGC-3/5FU/L, but not on NUGC-3, while CDHP by itself did not affect cell growth in either cell line. Expression of DPD was not detected in NUGC-3/5FU/L. In NUGC-3/5FU/L, 5-FU-enhanced expression of TS mRNA was inhibited by the addition of CDHP. In contrast, in NUGC-3, administration of 5-FU with or without CDHP did not alter TS mRNA expression.
  
  
  CONCLUSIONS
  The inhibitory mechanism of CDHP, which is independent of DPD, may in part contribute to the antitumor effect of S-1 even in 5-FU-resistant gastric cancer cases.
authors.affiliation: Department of Gastroenterology, Graduate School of Medicine, Osaka City University, 1-4-3 Asahimachi, Osaka 545-8585, Japan.
authors.forename: Eiji
authors.initials: E
authors.lastname: Sasaki
authors.forename: Kazunari
authors.initials: K
authors.lastname: Tominaga
authors.forename: Hikaru
authors.initials: H
authors.lastname: Kuwamura
authors.forename: Toshio
authors.initials: T
authors.lastname: Watanabe
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Fujiwara
authors.forename: Nobuhide
authors.initials: N
authors.lastname: Oshitani
authors.forename: Kazuhide
authors.initials: K
authors.lastname: Higuchi
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Arakawa
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D045744:Cell Line, Tumor; D042943:Dihydrouracil Dehydrogenase (NADP) / Q000187:drug effects* / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D019008:Drug Resistance, Neoplasm; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D004797:Enzyme-Linked Immunosorbent Assay; D005472:Fluorouracil / Q000008:administration & dosage / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D010094:Oxonic Acid / Q000494:pharmacology; D011725:Pyridines / Q000008:administration & dosage / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013274:Stomach Neoplasms / Q000188:drug therapy* / Q000235:genetics; D005641:Tegafur / Q000494:pharmacology; D013940:Thymidylate Synthase / Q000187:drug effects / Q000235:genetics
chemical_list: C417063:5-chlorodihydroxypyridine; D004338:Drug Combinations; D011725:Pyridines; D012333:RNA, Messenger; C079198:S 1 (combination); D005641:Tegafur; D010094:Oxonic Acid; D042943:Dihydrouracil Dehydrogenase (NADP); D013940:Thymidylate Synthase; D005472:Fluorouracil