title: Antitumor and anticancer stem cell activity of a poly ADP-ribose polymerase inhibitor olaparib in breast cancer cells.
abstract: BACKGROUND
  Although the poly adenosine diphosphate (ADP)-ribose polymerase (PARP) inhibitor olaparib is known to have potent antitumor activity in BRCA-related breast cancer cells, a limited number of preclinical and clinical studies have shown antitumor activity of olaparib in non-BRCA-related breast cancer. We investigated antitumor activity of olaparib in breast cancer cell lines derived from patients with nonfamilial sporadic breast cancer.
  
  
  METHODS
  Effects of olaparib alone or in combination with five different chemotherapeutic agents on cell growth, cell cycle progression, apoptosis, and proportion of cancer stem cells using the mammosphere assay and CD44/CD24/ESA cell surface marker assay were investigated in a panel of six sporadic breast cancer cell lines. Extracellular-signal-regulated kinase (ERK) phosphorylation was also investigated to elucidate action mechanisms of olaparib.
  
  
  RESULTS
  Olaparib inhibited the growth of two estrogen receptor (ER)-positive and human epidermal growth factor receptor 2 (HER2)-negative breast cancer cell lines and two ER-negative and HER2-negative breast cancer cell lines (50% growth inhibitory concentrations 1.3-3.0 μM) associated with G2/M accumulation and induction of apoptosis. In contrast, two HER2-positive cell lines were resistant to olaparib. Interestingly, olaparib significantly decreased the proportion of putative cancer stem cells in either sensitive or resistant cell lines. In addition, olaparib increased expression of p-ERK. Combined treatments of olaparib with a mitogen-activated protein kinase kinase (MEK) inhibitor U0126 completely suppressed expression of p-ERK. These treatments also inhibited the G2/M accumulation and apoptosis induction by olaparib. Among five chemotherapeutic agents commonly used for breast cancer treatment, only an irinotecan metabolite SN38 showed additive antitumor activity with olaparib. Importantly, the combined treatment enhanced the increase in G2/M accumulation and apoptosis induction as well as a decrease in the proportion of cancer stem cells.
  
  
  CONCLUSIONS
  This study has indicated for the first time that the PARP inhibitor olaparib has substantial antitumor and anticancer stem cell activity in breast cancer cell lines of nonfamilial origin. Upregulation of p-ERK might explain, at least in part, antitumor and anticancer stem cell activity of olaparib. Combined treatment of olaparib with irinotecan might be effective in treatment of non-BRCA-related breast cancer.
authors.affiliation: Department of Breast and Thyroid Surgery, Kawasaki Medical School, 577 Matsushima, Kurashiki, Okayama, 701-0192, Japan.
authors.forename: Toshiro
authors.initials: T
authors.lastname: Shimo
authors.forename: Junichi
authors.initials: J
authors.lastname: Kurebayashi
authors.forename: Naoki
authors.initials: N
authors.lastname: Kanomata
authors.forename: Tetsumasa
authors.initials: T
authors.lastname: Yamashita
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kozuka
authors.forename: Takuya
authors.initials: T
authors.lastname: Moriya
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sonoo
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D002166:Camptothecin / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D006801:Humans; D000077146:Irinotecan; D014411:Neoplastic Stem Cells / Q000187:drug effects*; D010766:Phosphorylation / Q000187:drug effects; D010793:Phthalazines / Q000008:administration & dosage / Q000494:pharmacology*; D010879:Piperazines / Q000008:administration & dosage / Q000494:pharmacology*; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D002166:Camptothecin; D004791:Enzyme Inhibitors; D048049:Extracellular Signal-Regulated MAP Kinases; D000077146:Irinotecan; D010793:Phthalazines; D010879:Piperazines; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D018719:Erb-b2 Receptor Tyrosine Kinases; C508053:ERBB2 protein, human; C531550:olaparib