Potentially lethal damage repair and its inhibitory effect of caffeine in two yolk sac tumor cell lines with different radiosensitivities.
OBJECTIVE
In order to investigate the role of potentially lethal damage repair (PLDR) in cellular radiosensitivity, PLDR and its inhibitory effect by caffeine was examined. In addition, cell cycle distribution was also examined.


METHODS
Two rat yolk sac tumor cell lines, NMT-1 and NMT-1R, with different radiosensitivities in vitro were used. The capacity for PLDR was examined using confluent-phase cells, and evaluated by calculating the recovery ratio. Inhibitory effect of caffeine on PLDR was examined with doses of 1, 5 and 10 mM.


RESULTS
The capacity of PLDR in two cell lines reflected radiosensitivity. The recovery ratio after irradiation of 5 Gy was 2.8 in the radiosensitive NMT-1 and 5.2 in the radioresistant NMT-1R, and recovery reached its peak level at 6 h in both cell lines. The degree of inhibition of PLDR was weaker in NMT-1R than that in NMT-1 at the same dose level, and was correlated with reduction of G2-arrested cells by caffeine.


CONCLUSIONS
The results of this study suggest that the capacity of PLDR may be one of the determinant factors for radiosensitivity in the two cell lines used, and the inhibitory effect of caffeine on PLDR was in part attributable to the modification of the cell cycle progression.
Akimoto
T
T
Department of Radiology and Radiation Oncology, Gunma University School of Medicine, Maebashi, Japan. takimoto@sb.gunma-u.ab.jp
Mitsuhashi
N
N
Matsumoto
H
H
Sakurai
H
H
Maebayashi
K
K
Higuchi
K
K
Nozaki
M
M
Niibe
H
H
D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D004260:DNA Repair / Q000187:drug effects* / Q000528:radiation effects*; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D018240:Endodermal Sinus Tumor / Q000378:metabolism* / Q000473:pathology / Q000532:radiotherapy; D011836:Radiation Tolerance / Q000187:drug effects*; D051381:Rats; D013997:Time Factors; D014407:Tumor Cells, Cultured
D002110:Caffeine