title: Irinotecan overcomes the resistance to 5-fluorouracil in human colon cancer xenografts by down-regulation of intratumoral thymidylate synthase.
abstract: To clarify the molecular interaction of irinotecan (CPT-11) and oxaliplatin (l-OHP) in combination with 5-fluorouracil (5-FU), the antitumor effects of CPT-11 and l-OHP combined with the oral 5-FU prodrug, S-1 composed by tegafur, gimeracil and potassium oteracil, were investigated on human colon cancer KM12C xenografts sensitive or resistant to 5-FU in nude mice. In parental KM12C tumor xenografts, combined treatment of CPT-11 with oral S-1 significantly augmented the antitumor activity compared with those of CPT-11 and S-1 alone. Interestingly, combined therapy of CPT-11 with S-1 was markedly effective with almost 90% of inhibition of tumor growth on 5-FU-resistant tumors (KM12C/ 5-FU), and its potency likely corresponded to that in parental tumors. In contrast, combined administration of l-OHP with S-1 did not shown an effect on KM12C/5-FU tumor xenografts. To investigate why only CPT-11 potentiated the anti-tumor activity in combination with 5-FU pro-drugs against 5-FU-resistant colon tumors, the activities or expression levels of thymidylate synthase (TS), ribonucleotide reductase (RNR) and other enzymes in 5-FU-metabolism in both tumors were measured following administration of CPT-11 and/or l-OHP. CPT-11, but not l-OHP, induced a decrease in activities and protein levels of TS and an increase in those of RNR in KM12C/5-FU tumors only, which was likely related to decreased expressions of several proteins in G1/S phase of the cells including CDK4, pRB, and E2F1 in these tumors. These findings suggest that CPT-11, but not l-OHP, would overcome the resistance to 5-FU in combination with 5-FU pro-drugs on 5-FU-resistant colon tumors.
authors.affiliation: Tokushima Research Center, Taiho Pharmaceutical Co., Ltd., Kawauchi, Tokushima 771-0194, Japan. fukusima@taiho.co.jp
authors.forename: Masakazu
authors.initials: M
authors.lastname: Fukushima
authors.forename: Kazuki
authors.initials: K
authors.lastname: Sakamoto
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Ohshimo
authors.forename: Fumio
authors.initials: F
authors.lastname: Nakagawa
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Taguchi
mesh_terms: D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000008:administration & dosage; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D015153:Blotting, Western; D002166:Camptothecin / Q000008:administration & dosage / Q000031:analogs & derivatives*; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000201:enzymology; D015536:Down-Regulation; D004338:Drug Combinations; D019008:Drug Resistance, Neoplasm / Q000502:physiology*; D005472:Fluorouracil; D006801:Humans; D000077146:Irinotecan; D051379:Mice; D008819:Mice, Nude; D009944:Organoplatinum Compounds / Q000008:administration & dosage; D000077150:Oxaliplatin; D010094:Oxonic Acid / Q000008:administration & dosage; D011355:Prodrugs / Q000008:administration & dosage; D005641:Tegafur / Q000008:administration & dosage; D013940:Thymidylate Synthase / Q000187:drug effects / Q000378:metabolism*; D023041:Xenograft Model Antitumor Assays
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D004338:Drug Combinations; D009944:Organoplatinum Compounds; D011355:Prodrugs; D000077150:Oxaliplatin; C079198:S 1 (combination); D005641:Tegafur; D010094:Oxonic Acid; D000077146:Irinotecan; D013940:Thymidylate Synthase; D005472:Fluorouracil; D002166:Camptothecin