title: In vitro basis for schedule-dependent interaction between gemcitabine and topoisomerase-targeted drugs in the treatment of colorectal cancer.
abstract: BACKGROUND
  While combination of gemcitabine with anti-topoisomerase poisons is routinely used in oncology, little is known on the biological interactions between these drugs.
  
  
  METHODS
  To understand the cellular basis for this association, we hypothesized an interaction of the two agents at the topoisomerase level. A real-time RT-PCR method was designed to quantify topoisomerase expression after treatment with gemcitabine (GEM) in two human colon adenocarcinoma cell lines. Efficacy of drugs as single agents and in combination was analyzed on the basis of their cytotoxic effects.
  
  
  RESULTS
  We showed that a) gemcitabine induces expression of all major eukaryotic topoisomerases (I, II alpha and beta) at definite times after drug administration; b) cytotoxicity was more relevant when cells were treated with GEM and the topoisomerase poison within a short period of time. In particular synergistic effects were found when the anti-topoisomerase II agent was given 3 h after gemcitabine or when the anti-topoisomerase I drug was delivered 3 h before or after the antimetabolite.
  
  
  CONCLUSIONS
  These findings help explaining the effectiveness of the combined therapy GEM/topoisomerase poisons and suggest a drug administration protocol for clinical treatment.
authors.affiliation: Department of Histology, Microbiology and Medical Biotechnologies, University of Padova, Italy.
authors.forename: S N
authors.initials: SN
authors.lastname: Richter
authors.forename: G
authors.initials: G
authors.lastname: Cartei
authors.forename: M
authors.initials: M
authors.lastname: Nadai
authors.forename: A
authors.initials: A
authors.lastname: Trestin
authors.forename: L
authors.initials: L
authors.lastname: Barzon
authors.forename: M
authors.initials: M
authors.lastname: Palumbo
authors.forename: G
authors.initials: G
authors.lastname: Palù
mesh_terms: D000230:Adenocarcinoma / Q000188:drug therapy* / Q000235:genetics; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000235:genetics; D026942:DNA Topoisomerases / Q000235:genetics / Q000378:metabolism; D003841:Deoxycytidine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D004334:Drug Administration Schedule; D004353:Drug Evaluation, Preclinical; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000008:administration & dosage*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D019073:HT29 Cells; D006801:Humans; D059003:Topoisomerase Inhibitors; D016896:Treatment Outcome; D000093542:Gemcitabine
chemical_list: D004791:Enzyme Inhibitors; D059003:Topoisomerase Inhibitors; D003841:Deoxycytidine; D026942:DNA Topoisomerases; D000093542:Gemcitabine