title: Histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA), enhances anti-tumor effects of the poly (ADP-ribose) polymerase (PARP) inhibitor olaparib in triple-negative breast cancer cells.
abstract: BACKGROUND
  Olaparib, a poly (ADP-ribose) polymerase (PARP) inhibitor, has been found to have therapeutic potential for treating cancers associated with impaired DNA repair capabilities, particularly those with deficiencies in the homologous recombination repair (HRR) pathway. Histone deacetylases (HDACs) are important for enabling functional HRR of DNA by regulating the expression of HRR-related genes and promoting the accurate assembly of HRR-directed sub-nuclear foci. Thus, HDAC inhibitors have recently emerged as a therapeutic agent for treating cancer by inhibiting DNA repair. Based on this, HDAC inhibition could be predicted to enhance the anti-tumor effect of PARP inhibitors in cancer cells by blocking the HRR pathway.
  
  
  METHODS
  We determined whether suberoylanilide hydroxamic acid (SAHA), a HDAC inhibitor, could enhance the anti-tumor effects of olaparib on breast cancer cell lines using a cytotoxic assay, cell cycle analysis, and Western blotting. We evaluated how exposure to SAHA affects the expression of HRR-associated genes. The accumulation of DNA double strand breaks (DSBs) induced by combination treatment was assessed. Induction of autophagy was monitored by imaging green fluorescent protein-tagged microtubule-associated protein 1A/1B-light chain 3 (LC3) expression following co-treatment with olaparib and SAHA. These in vitro data were validated in vivo using a human breast cancer xenograft model.
  
  
  RESULTS
  Triple-negative breast cancer cell (TNBC) lines showed heterogeneous responses to the PARP and HDAC inhibitors. Co-administration of olaparib and SAHA synergistically inhibited the growth of TNBC cells that expressed functional Phosphatase and tensin homolog (PTEN). This effect was associated with down-regulation of the proliferative signaling pathway, increased apoptotic and autophagic cell death, and accumulation of DNA damage. The combined anti-tumor effect of olaparib and SAHA was also observed in a xenograft model. These data suggest that PTEN expression in TNBC cells can sensitize the cell response to simultaneous inhibition of PARP and HDAC both in vitro and in vivo.
  
  
  CONCLUSIONS
  Our findings suggest that expression of functional PTEN may serve as a biomarker for selecting TNBC patients that would favorably respond to a combination of olaparib with SAHA. This provides a strong rationale for treating TNBC patients with PTEN expression with a combination therapy consisting of olaparib and SAHA.
authors.affiliation: Cancer Research Institute, Seoul National University College of Medicine, Seoul, 110-799, Korea. mar6716@snu.ac.kr.|Biomedical Research Institute, Seoul National University Hospital, Seoul, 110-799, Korea. mar6716@snu.ac.kr.
authors.forename: Ahrum
authors.initials: A
authors.lastname: Min
authors.affiliation: Cancer Research Institute, Seoul National University College of Medicine, Seoul, 110-799, Korea. moisa@snu.ac.kr.|Department of Internal Medicine, Seoul National University College of Medicine, Seoul, 110-799, Korea. moisa@snu.ac.kr.|Biomedical Research Institute, Seoul National University Hospital, Seoul, 110-799, Korea. moisa@snu.ac.kr.
authors.forename: Seock-Ah
authors.initials: SA
authors.lastname: Im
authors.affiliation: Seoul International School, Seongnam, 461-830, Korea. deborak.98@gmail.com.
authors.forename: Debora Keunyoung
authors.initials: DK
authors.lastname: Kim
authors.affiliation: Cancer Research Institute, Seoul National University College of Medicine, Seoul, 110-799, Korea. song1030@snu.ac.kr.
authors.forename: Sang-Hyun
authors.initials: SH
authors.lastname: Song
authors.affiliation: Cancer Research Institute, Seoul National University College of Medicine, Seoul, 110-799, Korea. heejun.dino11@gmail.com.|Department of Internal Medicine, Chung Ang University College of Medicine, Seoul, 156-755, Korea. heejun.dino11@gmail.com.
authors.forename: Hee-Jun
authors.initials: HJ
authors.lastname: Kim
authors.affiliation: Cancer Research Institute, Seoul National University College of Medicine, Seoul, 110-799, Korea. drleekh@gmail.com.|Department of Internal Medicine, Seoul National University College of Medicine, Seoul, 110-799, Korea. drleekh@gmail.com.|Biomedical Research Institute, Seoul National University Hospital, Seoul, 110-799, Korea. drleekh@gmail.com.
authors.forename: Kyung-Hun
authors.initials: KH
authors.lastname: Lee
authors.affiliation: Cancer Research Institute, Seoul National University College of Medicine, Seoul, 110-799, Korea. ktyongmd@gmail.com.|Department of Internal Medicine, Seoul National University College of Medicine, Seoul, 110-799, Korea. ktyongmd@gmail.com.|Biomedical Research Institute, Seoul National University Hospital, Seoul, 110-799, Korea. ktyongmd@gmail.com.
authors.forename: Tae-Yong
authors.initials: TY
authors.lastname: Kim
authors.affiliation: Cancer Research Institute, Seoul National University College of Medicine, Seoul, 110-799, Korea. saewon1@snu.ac.kr.|Department of Internal Medicine, Seoul National University College of Medicine, Seoul, 110-799, Korea. saewon1@snu.ac.kr.|Biomedical Research Institute, Seoul National University Hospital, Seoul, 110-799, Korea. saewon1@snu.ac.kr.
authors.forename: Sae-Won
authors.initials: SW
authors.lastname: Han
authors.affiliation: Cancer Research Institute, Seoul National University College of Medicine, Seoul, 110-799, Korea. ohdoyoun@snu.ac.kr.|Department of Internal Medicine, Seoul National University College of Medicine, Seoul, 110-799, Korea. ohdoyoun@snu.ac.kr.|Biomedical Research Institute, Seoul National University Hospital, Seoul, 110-799, Korea. ohdoyoun@snu.ac.kr.
authors.forename: Do-Youn
authors.initials: DY
authors.lastname: Oh
authors.affiliation: Cancer Research Institute, Seoul National University College of Medicine, Seoul, 110-799, Korea. kimty@snu.ac.kr.|Department of Internal Medicine, Seoul National University College of Medicine, Seoul, 110-799, Korea. kimty@snu.ac.kr.|Biomedical Research Institute, Seoul National University Hospital, Seoul, 110-799, Korea. kimty@snu.ac.kr.
authors.forename: Tae-You
authors.initials: TY
authors.lastname: Kim
authors.affiliation: AstraZeneca UK Ltd, Macclesfield, Cheshire, SK10 2NA, UK. mark.j.occonnor@astrazeneca.com.
authors.forename: Mark J
authors.initials: MJ
authors.lastname: O'Connor
authors.affiliation: Cancer Research Institute, Seoul National University College of Medicine, Seoul, 110-799, Korea. bangyj@snu.ac.kr.|Department of Internal Medicine, Seoul National University College of Medicine, Seoul, 110-799, Korea. bangyj@snu.ac.kr.|Biomedical Research Institute, Seoul National University Hospital, Seoul, 110-799, Korea. bangyj@snu.ac.kr.
authors.forename: Yung-Jue
authors.initials: YJ
authors.lastname: Bang
mesh_terms: D000818:Animals; D017209:Apoptosis; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D004357:Drug Synergism; D005260:Female; D015870:Gene Expression; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology*; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology*; D051379:Mice; D010793:Phthalazines / Q000494:pharmacology*; D010879:Piperazines / Q000494:pharmacology*; D000067856:Poly(ADP-ribose) Polymerase Inhibitors / Q000494:pharmacology*; D011065:Poly(ADP-ribose) Polymerases / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics; D064726:Triple Negative Breast Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism; D000077337:Vorinostat; D023041:Xenograft Model Antitumor Assays
chemical_list: D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids; D010793:Phthalazines; D010879:Piperazines; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D034741:RNA, Small Interfering; D000077337:Vorinostat; D011065:Poly(ADP-ribose) Polymerases; C531550:olaparib