title: Platelet-derived endothelial cell growth factor/thymidine phosphorylase inhibitor augments radiotherapeutic efficacy in experimental colorectal cancer.
abstract: OBJECTIVE
  A lot of radiosensitizers have been developed. However, there are few to be available in the clinical setting. Thymidine phosphorylase inhibitor (TPI) regulates the phosphorolysis of thymidine to thymine and 2-deoxy-d-ribose-1-phosphate which is essential for tumor angiogenesis. The aim of this study is to evaluate whether TPI augments the radiotherapy for colorectal cancer in vitro and in vivo studies.
  
  
  METHODS
  The cytotoxicity of TPI with irradiation on HT29 and HCT116 cells was examined using MTT- and colony formation assay. At 10days post-inoculation, HT29 bearing orthotopic model mice (n=28) were divided into four groups and orally treated with TPI- (50mg/kg/day for 2weeks), radiation (RT, 2Gy×4: Total 8Gy), their combination or the vehicle. The mechanisms underlying the efficacy were assessed genomically and immunohistochemically.
  
  
  RESULTS
  Compared to each single treatment, the combination of TPI and RT synergistically inhibited the cell viability in a time- and dose-dependent manner. In the HT-29 bearing mice, the combination of TPI and RT reduced the tumor growth compared with RT alone. Notably, the mRNA levels of VEGF, TGF-β and, Rad51 and the protein expressions of VEGF and CD34 were significantly lower in the combination than the others. Furthermore, the combination markedly increased the TUNEL-positive cells, suggesting that TPI augments the cancer cell death through inhibition of angiogenesis and DNA repair system in the radiotherapy.
  
  
  CONCLUSIONS
  Our study first demonstrated that the combination of TPI and irradiation was effective in colon cancer. TPI would provide a promising therapeutic strategy as a radiosensitizer.
authors.affiliation: Department of Surgery, Institute of Health Biosciences, The University of Tokushima Graduate School, Kuramoto, Tokushima, Japan. tmiyatani@clin.med.tokushima-u.ac.jp
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Miyatani
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Kurita
authors.forename: Tohru
authors.initials: T
authors.lastname: Utsunomiya
authors.forename: Takashi
authors.initials: T
authors.lastname: Iwata
authors.forename: Masanori
authors.initials: M
authors.lastname: Nishioka
authors.forename: Kozo
authors.initials: K
authors.lastname: Yoshikawa
authors.forename: Jun
authors.initials: J
authors.lastname: Higashijima
authors.forename: Hideya
authors.initials: H
authors.lastname: Kashihara
authors.forename: Chie
authors.initials: C
authors.lastname: Takasu
authors.forename: Masakazu
authors.initials: M
authors.lastname: Fukushima
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Shimada
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000532:radiotherapy*; D003131:Combined Modality Therapy; D004260:DNA Repair; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D007150:Immunohistochemistry; D051379:Mice; D013939:Thymidine Phosphorylase / Q000037:antagonists & inhibitors* / Q000494:pharmacology*
chemical_list: D004791:Enzyme Inhibitors; D013939:Thymidine Phosphorylase