title: Second-Generation HSP90 Inhibitor Onalespib Blocks mRNA Splicing of Androgen Receptor Variant 7 in Prostate Cancer Cells.
abstract: Resistance to available hormone therapies in prostate cancer has been associated with alternative splicing of androgen receptor (AR) and specifically, the expression of truncated and constitutively active AR variant 7 (AR-V7). The transcriptional activity of steroid receptors, including AR, is dependent on interactions with the HSP90 chaperone machinery, but it is unclear whether HSP90 modulates the activity or expression of AR variants. Here, we investigated the effects of HSP90 inhibition on AR-V7 in prostate cancer cell lines endogenously expressing this variant. We demonstrate that AR-V7 and full-length AR (AR-FL) were depleted upon inhibition of HSP90. However, the mechanisms underlying AR-V7 depletion differed from those for AR-FL. Whereas HSP90 inhibition destabilized AR-FL and induced its proteasomal degradation, AR-V7 protein exhibited higher stability than AR-FL and did not require HSP90 chaperone activity. Instead, HSP90 inhibition resulted in the reduction of AR-V7 mRNA levels but did not affect total AR transcript levels, indicating that HSP90 inhibition disrupted AR-V7 splicing. Bioinformatic analyses of transcriptome-wide RNA sequencing data confirmed that the second-generation HSP90 inhibitor onalespib altered the splicing of at least 557 genes in prostate cancer cells, including AR. These findings indicate that the effects of HSP90 inhibition on mRNA splicing may prove beneficial in prostate cancers expressing AR-V7, supporting further clinical investigation of HSP90 inhibitors in malignancies no longer responsive to androgen deprivation. Cancer Res; 76(9); 2731-42. ©2016 AACR.
authors.affiliation: Division of Clinical Studies and Cancer Therapeutics, The Institute of Cancer Research, Sutton, Surrey, United Kingdom. Prostate Cancer Targeted Therapies Group, Royal Marsden NHS Foundation Trust, Sutton, Surrey, United Kingdom.
authors.forename: Roberta
authors.initials: R
authors.lastname: Ferraldeschi
authors.affiliation: Division of Clinical Studies and Cancer Therapeutics, The Institute of Cancer Research, Sutton, Surrey, United Kingdom.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Welti
authors.affiliation: Division of Clinical Studies and Cancer Therapeutics, The Institute of Cancer Research, Sutton, Surrey, United Kingdom.
authors.forename: Marissa V
authors.initials: MV
authors.lastname: Powers
authors.affiliation: Division of Clinical Studies and Cancer Therapeutics, The Institute of Cancer Research, Sutton, Surrey, United Kingdom.
authors.forename: Wei
authors.initials: W
authors.lastname: Yuan
authors.affiliation: Astex Pharmaceuticals, Cambridge, United Kingdom.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Smyth
authors.affiliation: Division of Clinical Studies and Cancer Therapeutics, The Institute of Cancer Research, Sutton, Surrey, United Kingdom.
authors.forename: George
authors.initials: G
authors.lastname: Seed
authors.affiliation: Division of Clinical Studies and Cancer Therapeutics, The Institute of Cancer Research, Sutton, Surrey, United Kingdom.
authors.forename: Ruth
authors.initials: R
authors.lastname: Riisnaes
authors.affiliation: Division of Clinical Studies and Cancer Therapeutics, The Institute of Cancer Research, Sutton, Surrey, United Kingdom.
authors.forename: Somaieh
authors.initials: S
authors.lastname: Hedayat
authors.affiliation: Division of Clinical Studies and Cancer Therapeutics, The Institute of Cancer Research, Sutton, Surrey, United Kingdom.
authors.forename: Hannah
authors.initials: H
authors.lastname: Wang
authors.affiliation: Division of Clinical Studies and Cancer Therapeutics, The Institute of Cancer Research, Sutton, Surrey, United Kingdom.
authors.forename: Mateus
authors.initials: M
authors.lastname: Crespo
authors.affiliation: Division of Clinical Studies and Cancer Therapeutics, The Institute of Cancer Research, Sutton, Surrey, United Kingdom.
authors.forename: Daniel
authors.initials: D
authors.lastname: Nava Rodrigues
authors.affiliation: Division of Clinical Studies and Cancer Therapeutics, The Institute of Cancer Research, Sutton, Surrey, United Kingdom.
authors.forename: Ines
authors.initials: I
authors.lastname: Figueiredo
authors.affiliation: Division of Clinical Studies and Cancer Therapeutics, The Institute of Cancer Research, Sutton, Surrey, United Kingdom.
authors.forename: Susana
authors.initials: S
authors.lastname: Miranda
authors.affiliation: Division of Clinical Studies and Cancer Therapeutics, The Institute of Cancer Research, Sutton, Surrey, United Kingdom.
authors.forename: Suzanne
authors.initials: S
authors.lastname: Carreira
authors.affiliation: Astex Pharmaceuticals, Cambridge, United Kingdom.
authors.forename: John F
authors.initials: JF
authors.lastname: Lyons
authors.affiliation: Division of Clinical Studies and Cancer Therapeutics, The Institute of Cancer Research, Sutton, Surrey, United Kingdom.
authors.forename: Swee
authors.initials: S
authors.lastname: Sharp
authors.affiliation: Department of Medicine, University of Washington School of Medicine and GRECC at VAPSHCS Seattle, Washington. Department of Urology, University of Washington School of Medicine and GRECC at VAPSHCS Seattle, Washington.
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Plymate
authors.affiliation: Division of Clinical Studies and Cancer Therapeutics, The Institute of Cancer Research, Sutton, Surrey, United Kingdom. Prostate Cancer Targeted Therapies Group, Royal Marsden NHS Foundation Trust, Sutton, Surrey, United Kingdom.
authors.forename: Gerhardt
authors.initials: G
authors.lastname: Attard
authors.affiliation: Astex Pharmaceuticals, Cambridge, United Kingdom.
authors.forename: Nicola
authors.initials: N
authors.lastname: Wallis
authors.affiliation: Division of Clinical Studies and Cancer Therapeutics, The Institute of Cancer Research, Sutton, Surrey, United Kingdom.
authors.forename: Paul
authors.initials: P
authors.lastname: Workman
authors.affiliation: Division of Clinical Studies and Cancer Therapeutics, The Institute of Cancer Research, Sutton, Surrey, United Kingdom. Prostate Cancer Targeted Therapies Group, Royal Marsden NHS Foundation Trust, Sutton, Surrey, United Kingdom. Johann.de-bono@icr.ac.uk.
authors.forename: Johann S
authors.initials: JS
authors.lastname: de Bono
mesh_terms: D000818:Animals; D001549:Benzamides / Q000494:pharmacology*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm / Q000187:drug effects* / Q000235:genetics; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors*; D006801:Humans; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D054833:Isoindoles / Q000494:pharmacology*; D008297:Male; D051379:Mice; D016133:Polymerase Chain Reaction; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D012326:RNA Splicing / Q000187:drug effects*; D012333:RNA, Messenger; D011944:Receptors, Androgen / Q000235:genetics*; D023041:Xenograft Model Antitumor Assays
chemical_list: C410798:AR protein, human; D001549:Benzamides; D018841:HSP90 Heat-Shock Proteins; D054833:Isoindoles; D012333:RNA, Messenger; D011944:Receptors, Androgen; C552103:(2,4-dihydroxy-5-isopropylphenyl)-(5-(4-methylpiperazin-1-ylmethyl)-1,3-dihydroisoindol-2-yl)methanone