title: Radiosensitization of HT-29 cells and xenografts by the nitric oxide donor DETANONOate.
abstract: BACKGROUND
  Mechanisms of radioresistance in rectal cancer remain unclear.
  
  
  OBJECTIVE
  To determine mechanisms of radioresistance in rectal cancer cells and to assess the role of the nitric oxide donor DETANONOate as a radiosensitizing agent.
  
  
  METHODS
  Survival was determined by clonogenic assays, apoptosis by PARP-1 cleavage, and phenotypic differences by Western blot analysis. SCID mice bearing HT-29 xenografts were treated with ionizing radiation (IR) [2.0 Gy x 5], DETANONOate [0.4 mg/kg i.p.], or combination treatment.
  
  
  RESULTS
  Colorectal cancer HT-29-p53-null cells were resistant and HCT-116-p53 wild-type cells sensitive to IR, which correlated with cleaved PARP-1. Increased levels of p21 occurred in HCT-116 cells, while Bcl-2 and survivin were elevated in HT-29 cells. Radiosensitization was achieved with a substantial elevation of cleaved PARP-1 in DETANONOate-HT-29-treated versus control cells, which was accompanied by elevation of p21, p27, and BAX, and a concomitant decrease in Bcl-2. SCID mice bearing HT-29 xenografts demonstrated a 37.6%, 51.1%, and 70.1% inhibition in tumor growth in mice receiving IR, DETANONOate, and combination treatment versus control, respectively.
  
  
  CONCLUSIONS
  Radioresistant HT-29 cells are p53-null and have substantially decreased levels of p21. DETANONOate radiosensitized HT-29 cells in vitro and in vivo by an additive effect in apoptosis.
authors.affiliation: Department of Surgery, Dallas VA Medical Center, University of Texas Southwestern, Dallas, Texas, USA.
authors.forename: Xiaohuan
authors.initials: X
authors.lastname: Gao
authors.forename: Debabrata
authors.initials: D
authors.lastname: Saha
authors.forename: Payal
authors.initials: P
authors.lastname: Kapur
authors.forename: Thomas
authors.initials: T
authors.lastname: Anthony
authors.forename: Edward H
authors.initials: EH
authors.lastname: Livingston
authors.forename: Sergio
authors.initials: S
authors.lastname: Huerta
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D045325:HCT116 Cells; D019073:HT29 Cells; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins; D051379:Mice; D016513:Mice, SCID; D008869:Microtubule-Associated Proteins / Q000502:physiology; D020030:Nitric Oxide Donors / Q000494:pharmacology*; D009603:Nitroso Compounds / Q000494:pharmacology*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D000077022:Survivin; D016159:Tumor Suppressor Protein p53 / Q000502:physiology; D023041:Xenograft Model Antitumor Assays; D051028:bcl-2-Associated X Protein / Q000032:analysis
chemical_list: C107489:BIRC5 protein, human; D051034:Inhibitor of Apoptosis Proteins; D008869:Microtubule-Associated Proteins; D020030:Nitric Oxide Donors; D009603:Nitroso Compounds; D011838:Radiation-Sensitizing Agents; D000077022:Survivin; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; C094210:2,2'-(hydroxynitrosohydrazono)bis-ethanamine