Inhibition of Hsp90 Compromises the DNA Damage Response to Radiation

Abstract

Inhibitors of the molecular chaperone Hsp90 have been shown to enhance tumor cell radiosensitivity. To begin to address the mechanism responsible, we have determined the effect of the Hsp90 inhibitor 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17DMAG) on the DNA damage response to radiation. Exposure of MiaPaCa tumor cells to 17DMAG, which results in radiosensitization, inhibited the repair of DNA double-strand breaks according to ;H2AX foci dispersal and the neutral comet assay. This repair inhibition was associated with reduced DNA-PK catalytic subunit (DNA-PKcs) phosphorylation after irradiation and a disruption of DNA-PKcs/ ErbB1 interaction. These data suggest that the previously established 17DMAG-mediated reduction in ErbB1 activity reduces its interaction with DNA-PKcs and thus accounts for the attenuation of radiation-induced DNA-PK activation. 17DMAG was also found to abrogate the activation of the G 2 -and S-phase cell cycle checkpoints. Associated with these events was a reduction in radiation-induced ataxia-telangiectasia mutated (ATM) activation and foci formation in 17DMAG-treated cells. Although no interaction between ATM and Hsp90 was detected, Hsp90 was found to interact with the MRE11/Rad50/NBS1 (MRN) complex. 17DMAG exposure reduced the ability of the MRN components to form nuclear foci after irradiation. Moreover, 17DMAG exposure reduced the interaction between NBS1 and ATM, although no degradation of the MRN complex was detected. These results suggest that the diminished radiation-induced activation of ATM in 17DMAG-treated cells was the result of a compromise in the function of the MRN complex. These data indicate that Hsp90 can contribute to the DNA damage response to radiation affecting both DNA repair and cell cycle checkpoint activation. (Cancer Res 2006; 66(18): 9211-20)

Novel HSP90 inhibitors, NVP-AUY922 and NVP-BEP800, radiosensitise tumour cells through cell-cycle impairment, increased DNA damage and repair protraction

“…Moreover, the repair of DNA DSBs induced by combined treatment occurred much more slowly than after irradiation alone ( Figure 6 and Supplementary Figure S3). These data are in accordance with the delayed dispersal of histone gH2AX in the MiaPaCa pancreas carcinoma cell line, which received the combined 17DMAG/radiation treatment (Dote et al, 2006). The authors suggest that 17DMAG inhibits the repair of DNA DSBs induced by radiation (Dote et al, 2006), Similarly, an inhibition of homologous DNA recombination repair, that is, degradation of BRCA2 and alteration of Rad51 by 17-AAG, causes the radiosensitisation of prostate carcinoma DU145 and lung squamous carcinoma SQ-5 cell lines (Noguchi et al, 2006).…”

“…Previous studies have shown that inhibition of Hsp90 enhances the radiation response of several cell lines derived from a variety of human tumour entities (Bisht et al, 2003;Enmon et al, 2003;Machida et al, 2003;Russell et al, 2003;Bull et al, 2004;Harashima et al, 2005;Dote et al, 2006). These findings validate the molecular chaperone Hsp90 as a clinically relevant target for tumour radiosensitisation.…”

“…Indeed, a number of studies have already explored Hsp90 as a potential molecular target for radiosensitisation of tumour cells (Bisht et al, 2003;Machida et al, 2003;Russell et al, 2003;Bull et al, 2004;Harashima et al, 2005;Dote et al, 2006;Kabakov et al, 2008;Wu et al, 2009). Thus, the inhibitor of Hsp90, geldanamycin, and its derivatives significantly enhance the radiosensitivity of tumour cell lines derived from a variety of histologies, including glioma, prostate, pancreas and cervix (Bisht et al, 2003;Enmon et al, 2003;Machida et al, 2003;Russell et al, 2003;Bull et al, 2004;Harashima et al, 2005;Dote et al, 2006). However, geldanamycins have several limitations, including poor solubility, formulation difficulties, hepatotoxicity and extensive metabolism by polymorphic enzymes, along with drug efflux by P-glycoprotein (Kelland et al, 1999;Eiseman et al, 2005;Brough et al, 2008;Eccles et al, 2008).…”

Strong antitumor synergy between DNA crosslinking and HSP90 inhibition causes massive premitotic DNA fragmentation in ovarian cancer cells

“…Homologous recombination repair of double-stranded DNA breaks, as well as non-homologous end joining, are impaired by HSP90 inhibitors, enhancing radiosensitivity of tumor cells. [34][35][36][37] Moreover, HSP90 inhibitors interfere with DNA damage signaling by degrading ATR, Chk1 and Rad51. [38][39][40] Table S1) in the presence of 20 μM zVAD.…”

The HSP90 inhibitor alvespimycin enhances the potency of telomerase inhibition by imetelstat in human osteosarcoma

“…5,6,39 HSP90 inhibition has been shown to act as a radiosensitizer by delaying DNA repair. 40 Cells treated with an HSP90 inhibitor followed by ionizing radiation (IR) had delayed resolution of gH2AX foci compared to cells treated with ionizing radiation alone. 40 Likewise, cells treated with the combination of imetelstat and alvespimycin had increased levels of gH2AX compared to treatment with either agent alone (Fig.…”