title: Bcl-2 inhibitors potentiate the cytotoxic effects of radiation in Bcl-2 overexpressing radioresistant tumor cells.
abstract: OBJECTIVE
  Bcl-2, an inhibitor of apoptosis frequently shows elevated expression in human tumors, thus resulting in resistance to radiation therapy. Therefore, inhibiting Bcl-2 function may enhance the radiosensitivity of tumor cells. Tetrocarcin A (TC-A) and bcl-2 antisense oligonucleotides exhibit antitumor activity by inhibiting Bcl-2 function and transcription, respectively. We investigated whether these antitumor agents would enhance the cytotoxic effects of radiation in tumor cells overexpressing Bcl-2.
  
  
  METHODS
  We used HeLa/bcl-2 cells, a stable Bcl-2-expressing cell line derived from wild-type HeLa (HeLa/wt) cells. Cells were incubated with TC-A and bcl-2 antisense oligonucleotides for 24 h after irradiation, and cell viability was then determined. Apoptotic cells were quantified by flow cytometric assay.
  
  
  RESULTS
  The HeLa/bcl-2 cells were more resistant to radiation than HeLa/wt cells. At concentrations that are not inherently cytotoxic, both TC-A and bcl-2 antisense oligonucleotides increased the cytotoxic effects of radiation in HeLa/bcl-2 cells, but not in HeLa/wt cells. However, in HeLa/bcl-2 cells, additional treatment with TC-A in combination with radiation did not significantly increase apoptosis.
  
  
  CONCLUSIONS
  The present results suggest that TC-A and bcl-2 antisense oligonucleotides reduce radioresistance of tumor cells overexpressing Bcl-2. Therefore, a combination of radiotherapy and Bcl-2 inhibitors may prove to be a useful therapeutic approach for treating tumors that overexpress Bcl-2.
authors.affiliation: Department of Radiology, Yokohama City University Graduate School of Medicine, Yokohama 236-0004, Japan.
authors.forename: Takamitsu
authors.initials: T
authors.lastname: Hara
authors.forename: Motoko
authors.initials: M
authors.lastname: Omura-Minamisawa
authors.forename: Cheng
authors.initials: C
authors.lastname: Chao
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Nakagami
authors.forename: Megumi
authors.initials: M
authors.lastname: Ito
authors.forename: Tomio
authors.initials: T
authors.lastname: Inoue
mesh_terms: D000617:Aminoglycosides / Q000494:pharmacology*; D000704:Analysis of Variance; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D006367:HeLa Cells / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D006801:Humans; D016376:Oligonucleotides, Antisense / Q000494:pharmacology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D012333:RNA, Messenger / Q000037:antagonists & inhibitors; D011836:Radiation Tolerance / Q000187:drug effects*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D014410:Tumor Stem Cell Assay
chemical_list: D000617:Aminoglycosides; D016376:Oligonucleotides, Antisense; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D011838:Radiation-Sensitizing Agents; C025518:tetrocarcin A