Enhanced tumor cell radiosensitivity and abrogation of G2 and S phase arrest by the Hsp90 inhibitor 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin.
OBJECTIVE
Because of the potential for affecting multiple signaling pathways, inhibition of Hsp90 may provide a strategy for enhancing tumor cell radiosensitivity. Therefore, we have investigated the effects of the orally bioavailable Hsp90 inhibitor 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17-DMAG) on the radiosensitivity of human tumor cells in vitro and grown as tumor xenografts.


METHODS
The effect of 17-DMAG on the levels of three proteins (Raf-1, ErbB2, and Akt) previously implicated in the regulation of radiosensitivity was determined in three human solid tumor cell lines. A clonogenic assay was then used to evaluate cell survival after exposure to 17-DMAG followed by irradiation. For mechanistic insight, the G(2)- and S-phase checkpoints were evaluated in 17-DMAG-treated cells. Finally, the effect of in vivo administration of 17-DMAG in combination with radiation on the growth rate of xenograft tumors was determined.


RESULTS
17-DMAG exposure reduced the levels of the three radiosensitivity-associated proteins in a cell line-specific manner with ErbB2 being the most susceptible. Corresponding concentrations of 17-DMAG enhanced the radiosensitivity of each of the tumor cell lines. This sensitization seemed to be the result of a 17-DMAG-mediated abrogation of the G(2)- and S-phase cell cycle checkpoints. The oral administration of 17-DMAG to mice bearing tumor xenografts followed by irradiation resulted in a greater than additive increase in tumor growth delay.


CONCLUSIONS
These data indicate that 17-DMAG enhances the in vitro and in vivo radiosensitivity of human tumor cells. The mechanism responsible seems to involve the abrogation of radiation-induced G(2)- and S-phase arrest.
Bull
Elizabeth E A
EE
Molecular Radiation Therapeutics Branch, Radiation Oncology Branch, Developmental Therapeutics Program, National Cancer Institute, Bethesda, Maryland, USA.
Dote
Hideaki
H
Brady
Kristin J
KJ
Burgan
William E
WE
Carter
Donna J
DJ
Cerra
Michael A
MA
Oswald
Kelli A
KA
Hollingshead
Melinda G
MG
Camphausen
Kevin
K
Tofilon
Philip J
PJ
D000284:Administration, Oral; D000818:Animals; D016227:Benzoquinones; D001943:Breast Neoplasms / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D003131:Combined Modality Therapy; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D005260:Female; D016195:G2 Phase / Q000187:drug effects / Q000528:radiation effects; D005910:Glioma / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors*; D006801:Humans; D015151:Immunoblotting; D047029:Lactams, Macrocyclic; D008297:Male; D051379:Mice; D008819:Mice, Nude; D011471:Prostatic Neoplasms / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D011809:Quinones / Q000008:administration & dosage / Q000494:pharmacology*; D011836:Radiation Tolerance; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism; D016196:S Phase / Q000187:drug effects / Q000528:radiation effects; D013936:Thymidine / Q000378:metabolism; D014183:Transplantation, Heterologous; D014410:Tumor Stem Cell Assay
D016227:Benzoquinones; D018841:HSP90 Heat-Shock Proteins; D047029:Lactams, Macrocyclic; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf; D011809:Quinones; D018719:Erb-b2 Receptor Tyrosine Kinases; D013936:Thymidine; C448659:17-(dimethylaminoethylamino)-17-demethoxygeldanamycin; C494918:AKT1 protein, human