title: Enhancement of 5-fluorouracil-induced in vitro and in vivo radiosensitization with MEK inhibition.
abstract: OBJECTIVE
  Gastrointestinal cancers frequently exhibit mutational activation of the Ras/MAPK pathway, which is implicated in resistance to ionizing radiation (IR) and chemotherapy. Concurrent radiotherapy and 5-fluorouracil (5-FU) based chemotherapy is commonly used for treatment of gastrointestinal malignancies. We previously reported radiosensitization with selumetinib, an inhibitor of MEK1/2. The purpose of the current study was to evaluate if selumetinib could enhance radiosensitivity induced by 5-FU.
  
  
  METHODS
  Clonogenic survival assays were carried out with the HT29 (colorectal), HCT116 (colorectal), and MiaPaca-2 (pancreatic) cell lines using pre-IR treatment with selumetinib, 5-FU and 5-FU+selumetinib. Cell proliferation was determined using a tetrazolium conversion assay. Mitotic catastrophe and DNA repair were analyzed using immunocytochemistry. Flow cytometry was used to analyze cell cycle and apoptosis. Growth delay was used to determine effects of 5-FU+selumetinib on in vivo tumor radiosensitivity.
  
  
  RESULTS
  Pre-IR treatment with 5-FU+selumetinib significantly decreased clonogenic survival compared with either agent alone. Dose modifying factors at a surviving fraction of 0.1 for 5-FU+selumetinib was 1.78, 1.52, and 1.3 for HT29, HCT116, and MiaPaca-2, respectively. Cell proliferation was decreased by treatment with selumetinib+5-FU as compared with single agent treatment regardless of treatment sequencing. Enhancement of 5-FU cytotoxicity and 5-FU mediated radiosensitization with selumetinib treatment was accompanied by an increase in mitotic catastrophe and apoptosis, and reductions in Stat3 phosphorylation and survivin expression. In vivo, an additive growth delay was observed with 5-FU+selumetinib+3Gy versus 5-FU+3Gy and selumetinib alone.
  
  
  CONCLUSIONS
  These data suggest that selumetinib can be used with 5-FU to augment radiation response.
authors.affiliation: Radiation Oncology Branch and Radiation Biology Branch, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Mary Ellen
authors.initials: ME
authors.lastname: Urick
authors.forename: Eun Joo
authors.initials: EJ
authors.lastname: Chung
authors.forename: William P
authors.initials: WP
authors.lastname: Shield
authors.forename: Naamit
authors.initials: N
authors.lastname: Gerber
authors.forename: Ayla
authors.initials: A
authors.lastname: White
authors.forename: Anastasia
authors.initials: A
authors.lastname: Sowers
authors.forename: Angela
authors.initials: A
authors.lastname: Thetford
authors.forename: Kevin
authors.initials: K
authors.lastname: Camphausen
authors.forename: James
authors.initials: J
authors.lastname: Mitchell
authors.forename: Deborah E
authors.initials: DE
authors.lastname: Citrin
mesh_terms: D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology*; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000188:drug therapy; D019610:Cytoprotection / Q000187:drug effects; D004260:DNA Repair; D004359:Drug Therapy, Combination; D005260:Female; D005472:Fluorouracil / Q000494:pharmacology*; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors*; D010190:Pancreatic Neoplasms / Q000188:drug therapy; D011836:Radiation Tolerance / Q000187:drug effects; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*
chemical_list: C517975:AZD 6244; D001562:Benzimidazoles; D011838:Radiation-Sensitizing Agents; D020929:Mitogen-Activated Protein Kinase Kinases; D005472:Fluorouracil