Combined inhibition of extracellular signal-regulated kinases and HSP90 sensitizes human colon carcinoma cells to ionizing radiation

Shinichiro Kobayashi, Regan Nantz, Tetsuya Kitamura, Ryuji Higashikubo, Nobuo Horikoshi*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


Indomethacin, a common nonsteroidal anti-inflammatory drug, has been shown to enhance radiation-mediated cell-killing effect through the activation of p38 mitogen-activated protein kinase (MAPK). We found that indomethacin strongly reduced the basal level of extracellular signal-regulated kinases 1 and 2 (ERK1/2) in HT-29 human colon carcinoma cells. The inhibition of ERK1/2 by indomethacin was only observed in cells with high basal activities of ERK1/2 such as HT-29 cells, but not in cells with low basal activities, such as HeLa. Cell cycle analysis of HT-29 cells exposed with indomethacin showed a partial G1/S arrest and slow DNA synthesis. However, the treatment with NS398, a specific COX-1/2 inhibitor, failed to show any effect on cell cycle, indicating that the inhibition of COX-1/2 is not responsible for cell cycle arrest. Since U0126, a specific inhibitor for MEK1/2, also induced a partial G1/S arrest, the G1/S arrest induced by indomethacin is, at least in part, caused by the inhibition of ERK1/2. Cell proliferation of HT-29 was inhibited by the treatment of U0126 but not in HeLa cells, and the treatment of HT-29 cells with U0126 enhanced radiation sensitivity possibly due to the accumulation of cells in G1 phase. We found that 17-allylamino-17-demethoxygeldanamycin, a geldanamycin delivative, radiosensitized HT-29 cells at a relatively low dose of irradiation, and indomethacin and U0126 further enhanced this effect. Therefore, tumor cells with elevated ERK1/2 activity can be effectively sensitized to radiation treatment by a combinational inhibition of HSP90 and MAPK activity.

Original languageEnglish (US)
Pages (from-to)3011-3019
Number of pages9
Issue number18
StatePublished - Apr 21 2005


  • HSP90
  • MAP kinase
  • Nonsteroidal anti-inflammatory drug
  • Radiosensitization

ASJC Scopus subject areas

  • Genetics
  • Molecular Biology
  • Cancer Research


Dive into the research topics of 'Combined inhibition of extracellular signal-regulated kinases and HSP90 sensitizes human colon carcinoma cells to ionizing radiation'. Together they form a unique fingerprint.

Cite this