title: Interaction of radiation and etoposide on two cell lines with different radiosensitivities in vitro.
abstract: OBJECTIVE
  To investigate the differences between two rat yolk sac tumor cell lines with different radiosensitivities in etoposide sensitivity and in the sensitizing effect of etoposide in combination with irradiation.
  
  
  METHODS
  NMT-1 is a parent radiosensitive cell line and NMT-1R is a variant radioresistant cell line. The effects were assessed by clonogenic assay. Apoptosis was evaluated by DNA fragmentation to investigate the mechanism of cell death.
  
  
  RESULTS
  Etoposide potentiation of radiation sensitivity was manifested by elimination of the initial shoulder of the cell survival curve in radioresistant NMT-1R cells. However, there was no enhancement effect in radiosensitive NMT-1 cells. The incidence of apoptosis was elevated in NMT-1R cells treated with etoposide and radiation.
  
  
  CONCLUSIONS
  Etoposide had a supra-additive effect in combination with irradiation for radioresistant NMT-1R cells due to the induction of apoptosis. However, a suppra-additive effect was not seen in radiosensitive NMT-1 cells.
authors.affiliation: Department of Radiology, Saitama Medical Center, Saitama Medical School 1981, Kamodatsujido-cho, Kawagoe, Saitama 350-8550, Japan. taketaka@saitama-med.ac.jp
authors.forename: Takeo
authors.initials: T
authors.lastname: Takahashi
authors.forename: Norio
authors.initials: N
authors.lastname: Mitsuhashi
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Akimoto
authors.forename: Hiroko
authors.initials: H
authors.lastname: Matsumoto
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Ishikawa
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Saito
authors.forename: Hideo
authors.initials: H
authors.lastname: Niibe
mesh_terms: D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D003131:Combined Modality Therapy; D004307:Dose-Response Relationship, Radiation; D004334:Drug Administration Schedule; D018240:Endodermal Sinus Tumor / Q000188:drug therapy* / Q000532:radiotherapy*; D005047:Etoposide / Q000494:pharmacology*; D011836:Radiation Tolerance / Q000187:drug effects*; D051381:Rats; D014407:Tumor Cells, Cultured
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D005047:Etoposide