title: Potentiation of chemotherapeutics by the Hsp90 antagonist geldanamycin requires a steady serum condition.
abstract: Inhibition of Hsp90 potentiates diverse chemotherapeutics, but it is not clear if this applies only to specific agents, tumor types or conditions. The aim of this report is to determine the effect of serum starvation (SS) on potentiation. SUIT2 cells were cultured with and without the presence of serum and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assays were carried out at time intervals. Cytotoxic agents were added individually or in combination. Immunohistochemistry of tumor samples and immunofluorescence of cultured cells were used to examine Hsp90 localization. In the presence of serum an at least additive effect of combining the Hsp90 inhibitor geldanamycin (GA) with 5-fluorouracil (5FU) was demonstrated. Following pretreatment with GA, 5FU and GA were synergistic. However, during SS GA was protective against 5FU. Geldanamycin also protected cells from 12-O-tetradecanoylphorbol-13-acetate (TPA) during SS. Protection of cells is transitory, as after 24 h of SS GA again has an at least additive negative effect on vitality with 5FU or TPA. Serum starvation of pancreatic cancer cell lines causes normally largely cytoplasmic Hsp90 to become predominantly nuclear localized. Hsp90 nuclear localization was observed in pancreatic and prostate tumors. Hsp90 binding to a pro-apoptotic client could explain the transitory protection of cells by Hsp90 inhibition during SS. Although potentiation of chemotherapeutics by Hsp90 inhibition is probably a general phenomenon, design of clinical trials should take into account that continuous co-administration may be ineffective because of a balance of synergy of the drugs in some cells and mutual inhibition of the two drug activities in other cells.
authors.affiliation: Division of Gastroenterology, Liverpool University, Liverpool, United Kingdom.
authors.forename: Michael
authors.initials: M
authors.lastname: Burkitt
authors.forename: Conor
authors.initials: C
authors.lastname: Magee
authors.forename: David
authors.initials: D
authors.lastname: O'Connor
authors.forename: Fiona
authors.initials: F
authors.lastname: Campbell
authors.forename: Philip
authors.initials: P
authors.lastname: Cornford
authors.forename: William
authors.initials: W
authors.lastname: Greenhalf
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D053477:Apoptotic Protease-Activating Factor 1 / Q000378:metabolism; D016227:Benzoquinones / Q000008:administration & dosage*; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D002469:Cell Separation; D003593:Cytoplasm / Q000378:metabolism; D004357:Drug Synergism; D005472:Fluorouracil / Q000494:pharmacology; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors*; D006801:Humans; D047029:Lactams, Macrocyclic / Q000008:administration & dosage*; D008297:Male; D010179:Pancreas / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000188:drug therapy; D044967:Serum / Q000187:drug effects / Q000378:metabolism*
chemical_list: C506592:APAF1 protein, human; D000970:Antineoplastic Agents; D053477:Apoptotic Protease-Activating Factor 1; D016227:Benzoquinones; D018841:HSP90 Heat-Shock Proteins; D047029:Lactams, Macrocyclic; D005472:Fluorouracil; C001277:geldanamycin