title: Geldanamycin analog 17-DMAG limits apoptosis in human peripheral blood cells by inhibition of p53 activation and its interaction with heat-shock protein 90 kDa after exposure to ionizing radiation.
abstract: Exposure to ionizing radiation induces p53, and its inhibition improves mouse survival. We tested the effect of 17-dimethylamino-ethylamino-17-demethoxygeldanamycin (17-DMAG) on p53 expression and function after radiation exposure. 17-DMAG, a heat-shock protein 90 (Hsp90) inhibitor, protects human T cells from ionizing radiation-induced apoptosis by inhibiting inducible nitric oxide synthase (iNOS) and subsequent caspase-3 activation. Using ex vivo human peripheral blood mononuclear cells, we found that ionizing radiation increased p53 accumulation, acute p53 phosphorylation, Bax expression and caspase-3/7 activation in a radiation dose- and time postirradiation-dependent manner. 17-DMAG inhibited these increases in a concentration-dependent manner (IC(50)  =  0.93 ± 0.01 µM). Using in vitro models, we determined that inhibition of p53 by genetic knockout resulted in lower levels of caspase-3/7 activity 1 day after irradiation and enhanced survival at 10 days. Analysis of p53-Hsp90 interaction in ex vivo cell lysates indicated that the binding between the two molecules occurred after irradiation but 17-DMAG prevented the binding. Taken together, these results suggest the presence of p53 phosphorylation and Hsp90-dependent p53 stabilization after acute irradiation. Hsp90 inhibitors such as 17-DMAG may prove useful with radiation-based cancer therapy as well as for general radioprotection.
authors.affiliation: Radiation Combined Injury Program, Armed Forces Radiobiology Research Institute, Bethesda, MD 20889-5603, USA.
authors.forename: Risaku
authors.initials: R
authors.lastname: Fukumoto
authors.forename: Juliann G
authors.initials: JG
authors.lastname: Kiang
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry* / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D016227:Benzoquinones / Q000737:chemistry* / Q000494:pharmacology; D001773:Blood Cells / Q000187:drug effects*; D002460:Cell Line; D005434:Flow Cytometry; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors*; D006801:Humans; D047029:Lactams, Macrocyclic / Q000737:chemistry* / Q000494:pharmacology; D011839:Radiation, Ionizing; D016159:Tumor Suppressor Protein p53 / Q000187:drug effects*
chemical_list: D000970:Antineoplastic Agents; D016227:Benzoquinones; D018841:HSP90 Heat-Shock Proteins; D047029:Lactams, Macrocyclic; D016159:Tumor Suppressor Protein p53; C001277:geldanamycin