title: 5-Fluorouracil incorporation into RNA and DNA in relation to thymidylate synthase inhibition of human colorectal cancers.
abstract: BACKGROUND
  The mechanism of action of 5-fluorouracil (5-FU) has been associated with inhibition of thymidylate synthase (TS) and incorporation of 5-FU into RNA and DNA, but limited data are available in human tumor tissue for the latter. We therefore measured incorporation in human tumor biopsy specimens after administration of a test dose of 5-FU alone or with leucovorin.
  
  
  METHODS
  Patients received 5-FU (500 mg/m(2)) with or without high-dose leucovorin, low-dose leucovorin or l-leucovorin, and biopsy specimens were taken after approximately 2, 24 or 48 h. Tissues were pulverized and extracted for nucleic acids. 5-FU incorporation was measured using gas chromatography/mass spectrometry after complete degradation to bases of isolated RNA and DNA.
  
  
  RESULTS
  Maximal incorporation into RNA (1.0 pmol/micrograms RNA) and DNA (127 fmol/micrograms DNA) of 59 and 46 biopsy specimens, respectively, was found at 24 h after 5-FU administration. Incorporation into RNA but not DNA was significantly correlated with intratumoral 5-FU levels. However, DNA incorporation was significantly correlated with the RNA incorporation. Primary tumor tissue, liver metastasis and normal mucosa did not show significant differences, while leucovorin had no effect. Neither for RNA (30 patients) nor DNA (24 patients) incorporation was a significant correlation with response to 5-FU therapy found. However, in the same group of patients, response was significantly correlated to TS inhibition (mean TS in responding and non-responding groups 45 and 231 pmol/h/mg protein, respectively; P=0.001).
  
  
  CONCLUSIONS
  5-FU is incorporated at detectable levels into RNA and DNA of human tumor tissue, but no relation between the efficacy of 5-FU treatment and incorporation was found, in contrast to TS.
authors.affiliation: Department of Medical Oncology, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: P
authors.initials: P
authors.lastname: Noordhuis
authors.forename: U
authors.initials: U
authors.lastname: Holwerda
authors.forename: C L
authors.initials: CL
authors.lastname: Van der Wilt
authors.forename: C J
authors.initials: CJ
authors.lastname: Van Groeningen
authors.forename: K
authors.initials: K
authors.lastname: Smid
authors.forename: S
authors.initials: S
authors.lastname: Meijer
authors.forename: H M
authors.initials: HM
authors.lastname: Pinedo
authors.forename: G J
authors.initials: GJ
authors.lastname: Peters
mesh_terms: D000328:Adult; D000368:Aged; D000964:Antimetabolites, Antineoplastic / Q000008:administration & dosage / Q000378:metabolism / Q000627:therapeutic use; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D004273:DNA, Neoplasm / Q000378:metabolism*; D005260:Female; D005472:Fluorouracil / Q000008:administration & dosage / Q000378:metabolism / Q000627:therapeutic use*; D006499:Hepatic Artery / Q000293:injuries; D006801:Humans; D007261:Infusions, Intra-Arterial / Q000379:methods; D002955:Leucovorin / Q000008:administration & dosage; D008297:Male; D008875:Middle Aged; D012334:RNA, Neoplasm / Q000378:metabolism*; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D000964:Antimetabolites, Antineoplastic; D004273:DNA, Neoplasm; D012334:RNA, Neoplasm; D013940:Thymidylate Synthase; D002955:Leucovorin; D005472:Fluorouracil