title: A combination of trastuzumab and BAG-1 inhibition synergistically targets HER2 positive breast cancer cells.
abstract: Treatment of HER2+ breast cancer with trastuzumab is effective and combination anti-HER2 therapies have demonstrated benefit over monotherapy in the neoadjuvant and metastatic settings. This study investigated the therapeutic potential of targeting the BAG-1 protein co-chaperone in trastuzumab-responsive or -resistant cells. In the METABRIC dataset, BAG-1 mRNA was significantly elevated in HER2+ breast tumors and predicted overall survival in a multivariate analysis (HR = 0.81; p = 0.022). In a breast cell line panel, BAG-1 protein was increased in HER2+ cells and was required for optimal growth as shown by siRNA knockdown. Overexpression of BAG-1S in HER2+ SKBR3 cells blocked growth inhibition by trastuzumab, whereas overexpression of a mutant BAG-1S protein (BAG-1S H3AB), defective in binding HSC70, potentiated the effect of trastuzumab. Injection of a Tet-On SKBR3 clone, induced to overexpress myc-BAG-1S into the mammary fat pads of immunocompromised mice, resulted in 2-fold larger tumors compared to uninduced controls. Induction of myc-BAG-1S expression in two Tet-On SKBR3 clones attenuated growth inhibition by trastuzumab in vitro. Targeting endogenous BAG-1 by siRNA enhanced growth inhibition of SKBR3 and BT474 cells by trastuzumab, while BAG-1 protein-protein interaction inhibitor (Thio-S or Thio-2) plus trastuzumab combination treatment synergistically attenuated growth. In BT474 cells this reduced protein synthesis, caused G1/S cell cycle arrest and targeted the ERK and AKT signaling pathways. In a SKBR3 subpopulation with acquired resistance to trastuzumab BAG-1 targeting remained effective and either Thio-2 or BAG-1 siRNA reduced growth more compared to trastuzumab-responsive parental cells. In summary, targeting BAG-1 function in combination with anti-HER2 therapy might prove beneficial.
authors.affiliation: Cancer Research UK Centre Cancer Sciences Unit, Southampton General Hospital, Southampton, United Kingdom.
authors.forename: Emmanouil
authors.initials: E
authors.lastname: Papadakis
authors.affiliation: Cancer Research UK Centre Cancer Sciences Unit, Southampton General Hospital, Southampton, United Kingdom.
authors.forename: Natalia
authors.initials: N
authors.lastname: Robson
authors.affiliation: Cancer Research UK Centre Cancer Sciences Unit, Southampton General Hospital, Southampton, United Kingdom.
authors.forename: Alison
authors.initials: A
authors.lastname: Yeomans
authors.affiliation: Cancer Research UK Centre Cancer Sciences Unit, Southampton General Hospital, Southampton, United Kingdom.
authors.forename: Sarah
authors.initials: S
authors.lastname: Bailey
authors.affiliation: Cancer Research UK Centre Cancer Sciences Unit, Southampton General Hospital, Southampton, United Kingdom.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Laversin
authors.affiliation: Cancer Research UK Centre Cancer Sciences Unit, Southampton General Hospital, Southampton, United Kingdom.
authors.forename: Stephen
authors.initials: S
authors.lastname: Beers
authors.affiliation: Cancer Research UK Centre Cancer Sciences Unit, Southampton General Hospital, Southampton, United Kingdom.
authors.forename: A Emre
authors.initials: AE
authors.lastname: Sayan
authors.affiliation: Cancer Research UK Centre Cancer Sciences Unit, Southampton General Hospital, Southampton, United Kingdom.|University Hospital Southampton, University of Southampton Faculty of Medicine, Southampton General Hospital, Southampton, United Kingdom.
authors.forename: Margaret
authors.initials: M
authors.lastname: Ashton-Key
authors.affiliation: Institute of Pharmacy/Pharmacognosy, Center of Molecular Biosciences, University of Innsbruck, Innsbruck, Austria.
authors.forename: Stefan
authors.initials: S
authors.lastname: Schwaiger
authors.affiliation: Institute of Pharmacy/Pharmacognosy, Center of Molecular Biosciences, University of Innsbruck, Innsbruck, Austria.
authors.forename: Hermann
authors.initials: H
authors.lastname: Stuppner
authors.affiliation: Daniel Swarovski Research Laboratory, Department of Visceral, Transplant and Thoracic Surgery, Innsbruck Medical University, Innsbruck, Austria.
authors.forename: Jakob
authors.initials: J
authors.lastname: Troppmair
authors.affiliation: Cancer Research UK Centre Cancer Sciences Unit, Southampton General Hospital, Southampton, United Kingdom.
authors.forename: Graham
authors.initials: G
authors.lastname: Packham
authors.affiliation: Cancer Research UK Centre Cancer Sciences Unit, Southampton General Hospital, Southampton, United Kingdom.|University Hospital Southampton, University of Southampton Faculty of Medicine, Southampton General Hospital, Southampton, United Kingdom.
authors.forename: Ramsey
authors.initials: R
authors.lastname: Cutress
mesh_terms: D000814:Aniline Compounds / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D052160:Benzothiazoles / Q000008:administration & dosage / Q000494:pharmacology; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D049109:Cell Proliferation / Q000187:drug effects; D003131:Combined Modality Therapy; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D004357:Drug Synergism; D005260:Female; D006801:Humans; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D034741:RNA, Small Interfering / Q000008:administration & dosage / Q000235:genetics; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000096:biosynthesis*; D014157:Transcription Factors / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D000068878:Trastuzumab / Q000008:administration & dosage / Q000494:pharmacology*; D023041:Xenograft Model Antitumor Assays
chemical_list: D000814:Aniline Compounds; D052160:Benzothiazoles; D004268:DNA-Binding Proteins; D034741:RNA, Small Interfering; D018719:Erb-b2 Receptor Tyrosine Kinases; D014157:Transcription Factors; D000068878:Trastuzumab; C091732:BCL2-associated athanogene 1 protein; C000589256:N-ethyl-4-(6-methylbenzo(d)thiazol-2-yl)aniline; C508053:ERBB2 protein, human
keywords: BAG-1; HER2; breast cancer; resistance; trastuzumab