title: Enhanced tumor cell radiosensitivity and abrogation of G2 and S phase arrest by the Hsp90 inhibitor 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin.
abstract: 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.
authors.affiliation: Molecular Radiation Therapeutics Branch, Radiation Oncology Branch, Developmental Therapeutics Program, National Cancer Institute, Bethesda, Maryland, USA.
authors.forename: Elizabeth E A
authors.initials: EE
authors.lastname: Bull
authors.forename: Hideaki
authors.initials: H
authors.lastname: Dote
authors.forename: Kristin J
authors.initials: KJ
authors.lastname: Brady
authors.forename: William E
authors.initials: WE
authors.lastname: Burgan
authors.forename: Donna J
authors.initials: DJ
authors.lastname: Carter
authors.forename: Michael A
authors.initials: MA
authors.lastname: Cerra
authors.forename: Kelli A
authors.initials: KA
authors.lastname: Oswald
authors.forename: Melinda G
authors.initials: MG
authors.lastname: Hollingshead
authors.forename: Kevin
authors.initials: K
authors.lastname: Camphausen
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Tofilon
mesh_terms: 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
chemical_list: 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