title: Combination of 5-fluorouracil and irinotecan on modulation of thymidylate synthase and topoisomerase I expression and cell cycle regulation in human colon cancer LoVo cells: clinical relevance.
abstract: This study was designed to explore the possible interaction of 5-fluorouracil (5-FU) and 7-ethyl-10-hydroxycamptothecin (SN-38) in vitro. Human colon cancer LoVo cells were treated in both a dose- and time-dependent manner using clinically relevant concentrations of and exposure to 5-FU and/or SN-38. The expression of thymidylate synthase (TS), topoisomerase I, and cell cycle kinetics were evaluated by Western blot analysis and flow cytometry, respectively. Cytotoxicity was evaluated by MTT (3-[4,5-dimethylthiazol-2yl]-2,5-diphenyl tetrazolium bromide) assay. The cytotoxic effects of combination treatment were determined by median effect analysis. Topoisomerase I expression was downregulated following 12 hours of exposure to treatment, and topoisomerase I expression recovered 8 hours after SN-38 was removed. The TS expression was decreased following 24 hours of 5-FU and it remained at reduced levels for > 24 hours after removal of 5-FU. SN-38 induced an arrest at S/G2/M phase, reaching its maximum effect at 12 hours. This cell cycle arrest was reversed 24 hours after SN-38 was removed. 5-FU induced an arrest at the S phase, and maximum arrest occurred at 12 hours and lasted for > 48 hours. After 12 hours of sequential SN-38, LoVo cells were arrested in S phase, thereby potentiating the effect of 5-FU. Cytotoxicity studies confirmed the synergistic interaction between 5-FU and irinotecan. These findings suggest that the proper sequencing of 5-FU/irinotecan depends on regulation of topoisomerase I, and cell cycle kinetics
authors.affiliation: Beijing 307 Hospital Cancer Center, China.
authors.forename: Jian-Ming
authors.initials: JM
authors.lastname: Xu
authors.forename: Amalia
authors.initials: A
authors.lastname: Azzariti
authors.forename: Stefania
authors.initials: S
authors.lastname: Tommasi
authors.forename: Rosanna
authors.initials: R
authors.lastname: Lacalamita
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Colucci
authors.forename: Patrick G
authors.initials: PG
authors.lastname: Johnston
authors.forename: Stewart W
authors.initials: SW
authors.lastname: Church
authors.forename: Angelo
authors.initials: A
authors.lastname: Paradiso
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology / Q000627:therapeutic use*; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use*; D002453:Cell Cycle / Q000187:drug effects*; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005472:Fluorouracil / Q000494:pharmacology / Q000627:therapeutic use*; D006801:Humans; D066298:In Vitro Techniques; D000077146:Irinotecan; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors*; D059004:Topoisomerase I Inhibitors; D014407:Tumor Cells, Cultured
chemical_list: D059004:Topoisomerase I Inhibitors; D000077146:Irinotecan; D013940:Thymidylate Synthase; D005472:Fluorouracil; D002166:Camptothecin