title: Heat shock protein 90 inhibitor 17-allylamino-17-demethoxygeldanamycin potentiates the radiation response of tumor cells grown as monolayer cultures and spheroids by inducing apoptosis.
abstract: Activation of the PI3K-Akt pathway is known to induce tumor radioresistance. In the current study, we examined the ability of 17AAG, which decreases the levels of Hsp90 client proteins including components of the PI3K-Akt pathway, to sensitize radioresistant human squamous cell carcinoma cells to X-irradiation. Human squamous cell carcinoma cell lines (SQ20B, SCC61 and SCC13) were incubated for 16 h at 37 degrees C in medium containing 17AAG. Radiation sensitivity was determined by clonogenic assays, and protein levels were examined by western blotting. Apoptosis was determined in monolayer cells by AO/EB double staining and in spheroids using the TdT-mediated dUTP nick end labeling assay. 17AAG (0.2 microM) enhanced the radiosensitivity more effectively in radioresistant SQ20B and SCC13 cells than in radiosensitive SCC61 cells. However, in all three cell lines, 17AAG increased radiation-induced apoptosis by reducing the expression of EGFR and ErbB-2 and inhibiting the phosphorylation of Akt. Furthermore, 17AAG (1 microM) sensitized SQ20B spheroids to radiation, and inhibition of Akt activation by 17AAG increased radiation-induced apoptosis in spheroids. The findings suggest that 17AAG effectively sensitizes radioresistant cells to radiation by inhibiting the PI3K-Akt pathway. Targeting the PI3K-Akt pathway with 17AAG could be a useful strategy for radiosensitization of carcinomas.
authors.affiliation: Department of Radiological Sciences, Ibaraki Prefectural University of Health Sciences, 4669-2 Ami, Amimachi, Inashiki-gun, Ibaraki 300-0394, Japan.
authors.forename: Hikaru
authors.initials: H
authors.lastname: Machida
authors.forename: Syuichi
authors.initials: S
authors.lastname: Nakajima
authors.forename: Naoto
authors.initials: N
authors.lastname: Shikano
authors.forename: Junko
authors.initials: J
authors.lastname: Nishio
authors.forename: Shinobu
authors.initials: S
authors.lastname: Okada
authors.forename: Munehiko
authors.initials: M
authors.lastname: Asayama
authors.forename: Makoto
authors.initials: M
authors.lastname: Shirai
authors.forename: Nobuo
authors.initials: N
authors.lastname: Kubota
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D016227:Benzoquinones; D002294:Carcinoma, Squamous Cell; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors*; D006801:Humans; D047029:Lactams, Macrocyclic; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology; D017828:Rifabutin / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D016227:Benzoquinones; D018841:HSP90 Heat-Shock Proteins; D047029:Lactams, Macrocyclic; D011838:Radiation-Sensitizing Agents; D017828:Rifabutin; C112765:tanespimycin