title: The Hsp90 inhibitor NVP-AUY922-AG inhibits NF-κB signaling, overcomes microenvironmental cytoprotection and is highly synergistic with fludarabine in primary CLL cells.
abstract: Heat shock protein 90 (Hsp90) is a molecular chaperone required for the stability and function of multiple over-expressed signaling proteins that promote growth and survival in cancer cells. Chronic lymphocytic leukaemia (CLL) is characterized by increased expression of several Hsp90 client proteins making it a potentially susceptible to Hsp90 inhibition. In this study we showed that the novel Hsp90 inhibitor NVP-AUY922-AG was cytotoxic to primary CLL cells in vitro (LD50=0.18μM±0.20). Importantly, its toxicity was preserved under cytoprotective co-culture conditions that rendered fludarabine ineffective. At the molecular level, NVP-AUY922-AG depleted the expression of multiple Hsp90 client proteins including Akt and activators of NF- κB, IKKα and IKKβ. Consistent with this inhibition profile, NVP-AUY922-AG resulted in decreased transcription of the NF-B target genes MCL1, CFLAR, BIRC5. In contrast, fludarabine significantly induced the transcription of MCL1 and BIRC5. Given the anti-apoptotic nature of these genes and the role they play in fludarabine resistance, we considered that the combination of NVP-AUY922-AG with fludarabine might resensitize CLL cells to the effects of fludarabine. In keeping with this hypothesis, the combination of NVP-AUY922-AG and fludarabine was highly synergistic (mean CI=0.110.06) and this synergy was enhanced in co-culture (mean CI=0.06±0.08). Furthermore, the combination maintained the decrease in MCL1, CFLAR and BIRC5 transcription suggesting that the ability of NVP-AUY922-AG to modulate expression of these genes may contribute to the efficacy of this drug under cytoprotective co-culture conditions and for its remarkable synergy with fludarabine. Taken together these findings indicate that Hsp90 inhibition is an attractive therapeutic strategy in CLL.
authors.affiliation: Department of Haematology, Institute of Cancer and Genetics, Cardiff University, School of Medicine, Heath Park, Cardiff, UK. walsbyej@cf.ac.uk
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Walsby
authors.forename: Lawrence
authors.initials: L
authors.lastname: Pearce
authors.forename: Alan K
authors.initials: AK
authors.lastname: Burnett
authors.forename: Chris
authors.initials: C
authors.lastname: Fegan
authors.forename: Chris
authors.initials: C
authors.lastname: Pepper
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D019610:Cytoprotection / Q000187:drug effects; D004357:Drug Synergism; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors*; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins / Q000235:genetics / Q000378:metabolism; D007555:Isoxazoles / Q000008:administration & dosage / Q000494:pharmacology*; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000188:drug therapy* / Q000473:pathology; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D016328:NF-kappa B / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D012118:Resorcinols / Q000008:administration & dosage / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects; D000077022:Survivin; D059016:Tumor Microenvironment; D014740:Vidarabine / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: C528044:5-(2,4-dihydroxy-5-isopropylphenyl)-4-(4-morpholin-4-ylmethylphenyl)isoxazole-3-carboxylic acid ethylamide; C107489:BIRC5 protein, human; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D018841:HSP90 Heat-Shock Proteins; D051034:Inhibitor of Apoptosis Proteins; D007555:Isoxazoles; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D016328:NF-kappa B; D019253:Proto-Oncogene Proteins c-bcl-2; D012118:Resorcinols; D000077022:Survivin; D014740:Vidarabine; C024352:fludarabine