title: Tumor selective delivery of 5-fluorouracil by capecitabine, a new oral fluoropyrimidine carbamate, in human cancer xenografts.
abstract: Capecitabine (N4-pentyloxycarbonyl-5'-deoxy-5-fluorocytidine) is a novel fluoropyrimidine carbamate that is converted to 5-fluorouracil (5-FUra) by three enzymes located in the liver and tumors; the final step is the conversion of 5'-deoxy-5-fluorouridine (5'-dFUrd) to 5-FUra by thymidine phosphorylase in tumors. The present study compared the efficacy of capecitabine and 5-FUra at their maximum tolerated doses in CXF280, HCT116, COLO205, and WiDr human colon cancer xenograft models, and measured subsequent 5-FUra and 5'-dFUrd levels in tumors and in the plasma and muscle. Capecitabine was effective in the first three models, whereas 5-FUra was effective only in CXF280, which is a cell line highly susceptible to fluoropyrimidines. In the three susceptible models, 5-FUra AUCs in tumors after capecitabine administration were 210 to 303 nmol x hr/g, whereas those after 5-FUra administration were 8.54 to 13.1 nmol x hr/g. In addition, capecitabine gave higher levels of 5-FUra AUC in tumors than in plasma (114- to 209-fold higher) and muscle (21.6-fold higher), whereas 5-FUra was not selectively distributed to tumors. In the refractory model, WiDr, 5-FUra AUC in tumors after capecitabine administration was only 62.8 nmol x hr/g, although the level of the intermediate metabolite 5'-dFUrd was high (AUC: 695 nmol x hr/g). The ratio of 5-FUra/5'-dFUrd levels in the WiDr tumors was 0.09, which was 23.8-fold lower than that in the HCT116 tumors. The mechanism of resistance would be the inefficient conversion of 5'-dFUrd to 5-FUra by thymidine phosphorylase in tumors. Thus, capecitabine might show its high efficacy as a result of delivering high levels of 5-FUra selectively to the tumors.
authors.affiliation: Cytostatics Group, Nippon Roche Research Center, Kamakura-City, Kanagawa, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Ishikawa
authors.forename: M
authors.initials: M
authors.lastname: Utoh
authors.forename: N
authors.initials: N
authors.lastname: Sawada
authors.forename: M
authors.initials: M
authors.lastname: Nishida
authors.forename: Y
authors.initials: Y
authors.lastname: Fukase
authors.forename: F
authors.initials: F
authors.lastname: Sekiguchi
authors.forename: H
authors.initials: H
authors.lastname: Ishitsuka
mesh_terms: D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D000069287:Capecitabine; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology; D005260:Female; D005472:Fluorouracil / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology*; D006207:Half-Life; D006801:Humans; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D009368:Neoplasm Transplantation; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured
chemical_list: D000964:Antimetabolites, Antineoplastic; D000970:Antineoplastic Agents; D003841:Deoxycytidine; D000069287:Capecitabine; D005472:Fluorouracil