Radiosensitization of Normoxic and Hypoxic H1339 Lung Tumor Cells by Heat Shock Protein 90 Inhibition Is Independent of Hypoxia Inducible Factor-1α

Abstract

BackgroundIonizing irradiation is a commonly accepted treatment modality for lung cancer patients. However, the clinical outcome is hampered by normal tissue toxicity and tumor hypoxia. Since tumors often have higher levels of active heat shock protein 90 (Hsp90) than normal tissues, targeting of Hsp90 might provide a promising strategy to sensitize tumors towards irradiation. Hsp90 client proteins include oncogenic signaling proteins, cell cycle activators, growth factor receptors and hypoxia inducible factor-1α (HIF-1α). Overexpression of HIF-1α is assumed to promote malignant transformation and tumor progression and thus might reduce the accessibility to radiotherapy.Methodology/Principal FindingsHerein, we describe the effects of the novel Hsp90 inhibitor NVP-AUY922 and 17-allylamino-17-demethoxygeldanamycin (17-AAG), as a control, on HIF-1α levels and radiosensitivity of lung carcinoma cells under normoxic and hypoxic conditions. NVP-AUY922 exhibited a similar biological activity to that of 17-AAG, but at only 1/10 of the dose. As expected, both inhibitors reduced basal and hypoxia-induced HIF-1α levels in EPLC-272H lung carcinoma cells. However, despite a down-regulation of HIF-1α upon Hsp90 inhibition, sensitivity towards irradiation remained unaltered in EPLC-272H cells under normoxic and hypoxic conditions. In contrast, treatment of H1339 lung carcinoma cells with NVP-AUY922 and 17-AAG resulted in a significant up-regulation of their initially high HIF-1α levels and a concomitant increase in radiosensitivity.Conclusions/SignificanceIn summary, our data show a HIF-1α-independent radiosensitization of normoxic and hypoxic H1339 lung cancer cells by Hsp90 inhibition.

A novel HSP90 inhibitor with reduced hepatotoxicity synergizes with radiotherapy to induce apoptosis, abrogate clonogenic survival, and improve tumor control in models of colorectal cancer

“…Figure 1A-1C), thus confirming its function as a potent HSP90 inhibitor. Apart from client protein degradation, upregulation of the heat shock response has been described as a central feature of HSP90 inhibition [15, 30]. Therefore, we next examined, whether this upregulation could also be observed in case of NW457.…”

Sensitizing tumor cells to radiation by targeting the heat shock response

“…The human lung (H1339 and EPLC-272H) and breast (MDA-MB-231 and T47D) cancer cell lines and human fetal lung fibroblasts (HFL) (kindly provided by Prof. Rodemann) were cultured as described previously [15,21,22]. The authenticity of the tumor cell lines was tested by the DSMZ (German Collection of Microorganisms and Cell Cultures).…”

“…To measure the radiosensitivity, clonogenic assays were performed as described previously [15]. The cells were seeded in 12-well plates, one day later treated with NZ28/NVP-AUY922 and 24 h later irradiated using the RS225A irradiation device (Gulmay Medical Ltd) at a dose rate of 1 Gy/min (70 keV).…”

“…We have previously shown that a continuous treatment of H1339 cells with the Hsp90 inhibitor NVP-AUY922 can enhance the radiosensitivity but also increases the expression of Hsp70 [15]. Herein, we investigated whether NZ28 can inhibit the NVP-AUY922-induced activation of HSF1 and the expression of Hsp70 to increase the NVP-AUY922-mediated radiosensitization.…”

“…Several Hsp90 inhibitors are currently tested in clinical trials. By a simultaneous degradation of multiple oncogenic client proteins, Hsp90 inhibitors reduce tumor cell proliferation and enhance the radiosensitivity of tumor cells [15,16]. However, a negative side effect of Hsp90 inhibition is the activation of HSF1 and subsequently the induction of Hsp70.…”