title: The epidermal growth factor receptor tyrosine kinase inhibitor gefitinib sensitizes colon cancer cells to irinotecan.
abstract: Epidermal growth factor receptor (EGFR) overactivity plays a significant role in colon cancer biology and has been associated with poor clinical prognosis. Early clinical trials reported efficacy of receptor-targeted compounds, including modulation of clinical irinotecan resistance. We investigated the effects of the EGFR tyrosine kinase inhibitor gefitinib on cellular determinants of irinotecan resistance in human colon cancer cells. At non-cytotoxic concentrations, gefitinib sensitized colon cancer cells to SN-38, the active metabolite of irinotecan. Gefitinib increased the SN-38-mediated induction of protein-linked DNA single-strand breaks in a dose-dependent manner, with no alteration of topoisomerase (Topo) I protein expression or enzymatic activity. Whereas Topo IIbeta protein expression was not affected by gefitinib, significant time- and concentration-dependent downregulation of Topo IIalpha protein and inhibition of its enzymatic function were observed, corresponding to a G1 phase cell cycle arrest. Gefitinib significantly inhibited EGFR-associated signaling molecules, including phospho-mitogen-activated protein kinase or protein kinase C, which may account for decreases in proliferation or topoisomerase activity, respectively. Although a dose-dependent decrease of the BCRP/MXR/ABCP half-transporter was observed under gefitinib, cellular pharmacokinetics revealed no significant differences in accumulation or retention of the active SN-38 lactone using reverse-phase HPLC analysis. This study delineates mechanisms that may contribute to the synergism observed between irinotecan and EGFR inhibitors.
authors.affiliation: Department of Internal Medicine (Cancer Research), West German Cancer Center, Essen, Germany. ada.h.braun@vanderbilt.edu
authors.forename: Ada Henrike
authors.initials: AH
authors.lastname: Braun
authors.forename: Katrin
authors.initials: K
authors.lastname: Stark
authors.forename: Olaf
authors.initials: O
authors.lastname: Dirsch
authors.forename: Ralf Axel
authors.initials: RA
authors.lastname: Hilger
authors.forename: Siegfried
authors.initials: S
authors.lastname: Seeber
authors.forename: Udo
authors.initials: U
authors.lastname: Vanhoefer
mesh_terms: D000951:Antigens, Neoplasm / Q000235:genetics / Q000378:metabolism; D000970:Antineoplastic Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000201:enzymology* / Q000378:metabolism; D019927:Cyclin E / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D066246:ErbB Receptors / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000077156:Gefitinib; D006801:Humans; D000077146:Irinotecan; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011799:Quinazolines / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D000951:Antigens, Neoplasm; D000970:Antineoplastic Agents; D019927:Cyclin E; D004268:DNA-Binding Proteins; D047428:Protein Kinase Inhibitors; D011799:Quinazolines; D000077146:Irinotecan; D066246:ErbB Receptors; D004250:DNA Topoisomerases, Type II; D000077156:Gefitinib; D002166:Camptothecin