17-allylamino-17-demethoxygeldanamycin enhances the cytotoxicity of tumor cells irradiated with carbon ions

17-アリラミノ-17-デメトキシゲルダナマイシンは炭素線による癌細胞殺傷効果を増強する

野口 実穂; 平山 亮一*; 岡安 隆一*

Noguchi, Miho; Hirayama, Ryoichi*; Okayasu, Ryuichi*

Hsp90阻害剤17-AAGは単独でも抗腫瘍効果を持ち、放射線や他の化学療法剤と組合せることでさらに高い抗腫瘍効果が報告されている薬剤である。われわれ17-AAGはHIMAC炭素イオン線の細胞殺傷効果に影響を与えるかどうかを検討した。細胞は前立腺癌DU145,ヒト胎児肺線維芽細胞HFLIIIを用いた。17-AAGは照射前に24時間、100nMを投与した。また炭素線は炭素線治療に用いられているLET70keV/umを用いて実験を行った。17-AAGはDU145細胞において10%生存率で2.13倍の増感効果を示した。しかし、正常細胞では17-AAGの増感は現れなかった。DU145細胞において17-AAGの炭素線増感に対するDNA二本鎖切断(DSB)修復への影響を定電圧電気泳動法にて調べた。炭素線はX線と異なり炭素線単独でも非常にDSB修復が悪く、17-AAGを投与しても全く影響は見られなかった。しかし、Rad51フォーカス形成は炭素線単独と17-AAGと炭素線を併用したときとでは大きな違いが見られた。しかし、この薬剤による相同組換え修復経路の阻害は炭素線増感に大きな可能性が示唆される。

We investigated radiosensitization effect and its mechanism of Hsp90 inhibitor 17-AAG in human tumor cell lines irradiated with high LET carbon ions. Human tumor cell lines, DU145 derived from prostate carcinoma and normal human fibroblasts HFL III were incubated for 24 h in the presence of 17-AAG at concentration of 100nM. The cells were then irradiated with carbon ions (290MeV/nucleon, LET70keV/um) and several biological endpoints were compared. Cellular radiation sensitivity was determined by clonogenic assay and DNA double strand break (DSB) repair kinetics were examined by constant field gel electrophoresis. DU145 cells showed an increase in carbon ions-induced cell death when pre-treated with 17-AAG. The radiosensitivity enhancement ratios measured at a survival rate of 10% were 2.13 for DU145 cells. In contrast to the tumor cell lines, normal human fibroblasts with carbon irradiation showed no radiosensitization with 17-AAG pre-treatment. Our constant field gel electrophoresis studies indicated that 17-AAG had almost no effect on carbon ion-induced DSB repair in DU145 cells. On the other hand, radiation induced Rad51 foci formation showed different kinetics between the carbon ion alone and the combined treatment with 17-AAG and carbon ions in DU145 cells. Our findings suggest that mechanisms other than inhibition of DSB repair could be involved with the radiosensitization by 17-AAG in tumor cells irradiated with carbon ions. However, limited inhibition of homologous recombination by this agent may still be a possibility.