Radiosensitization of human vascular endothelial cells through Hsp90 inhibition with 17-N-allilamino-17-demethoxygeldanamycin.
OBJECTIVE
In addition to invasive tumor cells, endothelial cells (ECs) of the tumor vasculature are an important target for anticancer radiotherapy. The purpose of the present work is to investigate how 17-N-allilamino-17-demethoxygeldanamycin (17AAG), known as an anticancer drug inhibiting heat shock protein 90 (Hsp90), modifies radiation responses of human vascular ECs.


METHODS
The ECs cultured from human umbilical veins were exposed to gamma-irradiation, whereas some EC samples were pretreated with growth factors and/or 17AAG. Postirradiation cell death/survival and morphogenesis were assessed by means of terminal deoxynucleotidyl transferase biotin-deoxyuridine triphosphate nick end labeling or annexin V staining and clonogenic and tube-formation assays. The 17AAG-affected expression and phosphorylation of radioresistance-related proteins were probed by means of immunoblotting. Dominant negative or constitutively activated Akt was transiently expressed in ECs to manipulate Akt activity.


RESULTS
It was found that nanomolar concentrations of 17AAG sensitize ECs to relatively low doses (2-6 Gy) of gamma-irradiation and abolish the radioprotective effects of vascular endothelial growth factor and basic fibroblast growth factor. The drug-induced radiosensitization of ECs seems to be caused by prevention of Hsp90-dependent phosphorylation (activation) of Akt that results in blocking the radioprotective phosphatidylinositol 3-kinase/Akt pathway.


CONCLUSIONS
Clinically achievable concentrations of 17AAG can decrease the radioresistance intrinsic to vascular ECs and minimize the radioprotection conferred upon them by tumor-derived growth factors. These findings characterize 17AAG as a promising radiosensitizer for the tumor vasculature.
Kabakov
Alexander E
AE
Department of Radiation Biochemistry, Medical Radiology Research Center, Obninsk, Russia. aekabakov@hotmail.com
Makarova
Yulia M
YM
Malyutina
Yana V
YV
D016227:Benzoquinones / Q000008:administration & dosage*; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects*; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors*; D006801:Humans; D047029:Lactams, Macrocyclic / Q000008:administration & dosage*; D011836:Radiation Tolerance / Q000187:drug effects / Q000502:physiology*; D011838:Radiation-Sensitizing Agents / Q000008:administration & dosage
D016227:Benzoquinones; D018841:HSP90 Heat-Shock Proteins; D047029:Lactams, Macrocyclic; D011838:Radiation-Sensitizing Agents; C112765:tanespimycin