156P - Targeting HSP90 in irradiated cancer cells blocks DNA-reparative, antiapoptotic and angiogenic pathways

Date 30 September 2012
Event ESMO Congress 2012
Session Poster presentation II
Topics Basic Science
Presenter Vladimir Kudryavtsev
Authors V. Kudryavtsev1, A. Demidkina2, A. Kabakov2
  • 1Medical Radiological Research Center, 249020 - Obninsk/RU
  • 2Department Of Radiotherapy, Medical Radiology Research Center, 249020 - Obninsk/RU

Abstract

Introduction

Human tumors are often resistant to radiotherapy; therefore, radiosensitization of them is of importance. We explored how 17-N-allilamino-17-demethoxygeldanamycin (17AAG), an inhibitor of the heat shock protein 90 (Hsp90) chaperone activity, affects radiation response of breast cancer cells. In addition, we examined effects of 17AAG on the angiogenic signaling because tumor-stimulated angiogenesis is a factor decreasing the efficacy of radiotherapy.

Methods

MCF-7 cells cultured from human breast carcinoma were exposed to clinically relevant doses (2-5 Gy) of gamma-radiation, while some samples were co-treated with 10-500 nM 17AAG. The cell death/survival was assessed in annexin-V staining and clonogenic assays. Certain cell death-, DNA repair- and angiogenesis-related proteins were probed by immunoblotting. The p53 and ATM patterns were visualized by immunofluorescence.

Results

In the breast cancer cells, 40-150 nM 17AAG inhibited the Hsp90 chaperone function and down-regulated the Akt, survivin, HIF-1alpha, VEGF and Bcl-2 levels. The phosphorylation of Akt and its down-stream targets such as Bad, XIAP, GSK-3 or MDM2 became impaired. Enhanced activation of p53 and its longer up-regulation together with the inhibition of phosphorylation and nuclear translocation of ATM were found in the cells irradiated at 2-5 Gy after incubation with 40-150 nM 17AAG. The cells co-treated by such a way exhibited massive apoptosis and sharply decreased clonogenicity, whereas the same irradiation without 17AAG induced the less cytotoxicity. This radiosensitization seems to be due to (i) down-regulation or inactivation of antiapoptotic proteins (Akt, Bcl-2, survivin, XIAP), (ii) activation of pro-apoptotic proteins (Bad, GSK-3) and (iii) switching the MDM2/p53/ATM-mediated DNA damage response from DNA repair to apoptosis. Besides the enhancement of radiation-induced killing of the cancer cells, 40-150 nM 17AAG impaired their angiogenic potential that was revealed on down-regulation of HIF-1alpha and VEGF.

Conclusion

Clinically achievable concentrations of 17AAG allow to enhance the radiation response of human breast tumors and to suppress the tumor-stimulated angiogenesis.

Disclosure

All authors have declared no conflicts of interest.