HSP90 inhibitor, DMAG, synergizes with radiation of lung cancer cells by interfering with base excision and ATM-mediated DNA repair

Abstract

Inhibition of heat shock protein 90 (HSP90) leads to inappropriate processing of proteins involved in cell survival pathways. We found that HSP90 inhibitor, 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (DMAG), is synergistic with radiation for non-small cell lung cancer cell lines, NCI-H460 and A549. To establish the optimal schedule for this combination, cells were radiated before, after, or simultaneously with DMAG, and survival was scored by clonogenic assay. The sequence of DMAG administration was critical for synergy with radiation, and pretreatment for 16 h led to maximal synergy. Similar radiosensitization was observed in isogenic cells in which expression of wild-type p53 was silenced by RNA interference, although p53 loss rendered cells overall less radiosensitive. The mechanistic basis for synergy was studied by Western blotting, cell cycle analysis, alkaline comet assay, and direct measurement of the activities of key base excision repair enzymes. Regardless of schedule of administration, DMAG led to degradation of proteins involved in activation of cell survival pathways after radiation, which did not explain the differences in the schedule of administration observed in clonogenic assays. In addition to previously reported decrease in activation of ATM, pretreatment with DMAG blocked activation of base excision repair machinery and activity of key enzymes, apurinic/apyrimidinic endonuclease, and DNA polymerase-B.Similarly, pretreatment with specific apurinic/apyrimidinic endonuclease inhibitor, CRT0044876, reproduced the effects of DMAG. Thus, administration of HSP90 inhibitors before radiation is critical for optimizing their use as radiosensitizers. [Mol Cancer Ther 2008;7(7):1985 -92]

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

“…Functional tumour suppressor protein p53 was apparently not essential for the radiosensitising action of NVP-AUY922 and NVP-BEP800, because both drugs radiosensitised all tested cell lines, independent of their p53 status (Figures 2 and 3). This finding is consistent with the recent data for two non-small-cell lung cancer cell lines, NCI-H460 and A549 (Koll et al, 2008), but it conflicts with the results for squamous carcinoma cell lines (Shintani et al, 2006), indicating that the Hsp90 inhibitor 17-AAG is a more efficient radiosensitiser in a cell line with p53 wild type compared with four p53-mutated cell lines.…”

“…For that reason, the drugs were used at the same concentration of 200 nM in subsequent experiments. Besides this, the selected drug concentration is consistent with the previously reported 100 nM for 17-DMAG (Robles et al, 2006;Koll et al, 2008).…”

Strong antitumor synergy between DNA crosslinking and HSP90 inhibition causes massive premitotic DNA fragmentation in ovarian cancer 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 cells were processed as in Figure 4a and representative images are shown.…”

Radiosensitizing effects of miR‐18a‐5p on lung cancer stem‐like cells via downregulating both ATM and HIF‐1α

“…DNA damage activates ATM through intermolecular autophosphorylation (phospho S1981) and dimer dissociation 40. Inhibition of ATM or pATM (phospho S1981) could radiosensitize cancer cells 20, 41, 42, 43. The present study showed that upregulated miR‐18a‐5p inhibited the expressions of ATM and pATM (phospho S1981) and then enhanced the radiosensitivity of A549 cells and CD133 + stem‐like cells.…”