title: Potentiation of paclitaxel activity by the HSP90 inhibitor 17-allylamino-17-demethoxygeldanamycin in human ovarian carcinoma cell lines with high levels of activated AKT.
abstract: Activation of the phosphatidylinositol-3-kinase (PI3K)/AKT survival pathway is a mechanism of cytotoxic drug resistance in ovarian cancer, and inhibitors of this pathway can sensitize to cytotoxic drugs. The HSP90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG) depletes some proteins involved in PI3K/AKT signaling, e.g., ERBB2, epidermal growth factor receptor (EGFR), and phosphorylated AKT (p-AKT). 17-AAG and paclitaxel were combined (at a fixed 1:1 ratio of their IC(50)) in four ovarian cancer cell lines that differ in expression of p-AKT, EGFR, and ERBB2. The EGFR-overexpressing A431 and KB epidermoid cell lines were also included. Combination indices (CI) were calculated using the median-effect equation and interpreted in the context of 17-AAG-mediated inhibition of PI3K signaling. Synergy was observed in IGROV-1- and ERBB2-overexpressing SKOV-3 ovarian cancer cells that express a high level of constitutively activated p-AKT [CI at fraction unaffected (fu)(0.5) = 0.50 and 0.53, respectively]. Slight synergy was observed in A431 cells (moderate p-AKT/overexpressed EGFR; CI at fu(0.5) = 0.76) and antagonism in CH1 (moderate p-AKT), HX62 cells (low p-AKT), and KB cells (low p-AKT/overexpressed EGFR; CI at fu(50) = 3.0, 3.5, and 2.0, respectively). The observed effects correlated with changes in the rate of apoptosis induction. 17-AAG induced a decrease in HSP90 client proteins (e.g., C-RAF, ERBB2, and p-AKT) or in downstream markers of their activity (e.g., phosphorylated extracellular signal-regulated kinase or p-AKT) in SKOV-3, IGROV-1, and CH1 cells at IC(50) concentrations. A non-growth-inhibitory concentration (6 nmol/L) reduced the phosphorylation of AKT (but not extracellular signal-regulated kinase) and sensitized SKOV-3 cells to paclitaxel. In conclusion, 17-AAG may sensitize a subset of ovarian cancer to paclitaxel, particularly those tumors in which resistance is driven by ERBB2 and/or p-AKT.
authors.affiliation: The Haddow Laboratories, The Institute of Cancer Research, 15 Cotswold Road, Sutton, Surrey SM2 5NG, United Kingdom.
authors.forename: Nivedita
authors.initials: N
authors.lastname: Sain
authors.forename: Bhavani
authors.initials: B
authors.lastname: Krishnan
authors.forename: Michael G
authors.initials: MG
authors.lastname: Ormerod
authors.forename: Assunta
authors.initials: A
authors.lastname: De Rienzo
authors.forename: Wai M
authors.initials: WM
authors.lastname: Liu
authors.forename: Stanley B
authors.initials: SB
authors.lastname: Kaye
authors.forename: Paul
authors.initials: P
authors.lastname: Workman
authors.forename: Ann L
authors.initials: AL
authors.lastname: Jackman
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000378:metabolism / Q000494:pharmacology*; D016227:Benzoquinones; D016190:Carboplatin / Q000378:metabolism / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D005260:Female; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006801:Humans; D007624:KB Cells; D047029:Lactams, Macrocyclic; D010051:Ovarian Neoplasms / Q000201:enzymology / Q000378:metabolism*; D017239:Paclitaxel / Q000378:metabolism / Q000494:pharmacology*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D017828:Rifabutin / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology
chemical_list: D016227:Benzoquinones; D018841:HSP90 Heat-Shock Proteins; D047029:Lactams, Macrocyclic; D017828:Rifabutin; C112765:tanespimycin; D016190:Carboplatin; D051057:Proto-Oncogene Proteins c-akt; D017239:Paclitaxel