Interaction of radiation and etoposide on two cell lines with different radiosensitivities in vitro.
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.
Takahashi
Takeo
T
Department of Radiology, Saitama Medical Center, Saitama Medical School 1981, Kamodatsujido-cho, Kawagoe, Saitama 350-8550, Japan. taketaka@saitama-med.ac.jp
Mitsuhashi
Norio
N
Akimoto
Tetsuo
T
Matsumoto
Hiroko
H
Ishikawa
Hitoshi
H
Saito
Yoshihiro
Y
Niibe
Hideo
H
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
D000972:Antineoplastic Agents, Phytogenic; D005047:Etoposide