title: Radiosensitization with combined use of olaparib and PI-103 in triple-negative breast cancer.
abstract: BACKGROUND
  Triple-negative breast cancer (TNBC) shows aggressive clinical behavior, but the treatment options are limited due to lack of a specific target. TNBC shares many clinical and pathological similarities with BRCA-deficient breast cancer, for which poly(ADP-ribose) polymerase (PARP) inhibitor is effective, but PARP inhibitor alone failed to show clinical effects in patients with sporadic TNBC. Radiation induces DNA double-strand breaks, and the phosphoinositide 3-kinase (PI3K) signaling pathway has been known to regulate steady-state levels of homologous recombination. A recent preclinical study showed that PI3K inhibition impairs BRCA1/2 expression and sensitizes BRCA-proficient TNBC to PARP inhibition. Therefore, we assessed the radiosensitizing effect, and the underlying mechanism of combination treatment with PARP inhibitor olaparib and PI3K inhibitor PI-103 in BRCA-proficient TNBC cells.
  
  
  METHODS
  MDA-MB-435S cells were divided into four treatment groups, irradiation (IR) alone, olaparib plus IR, PI-103 plus IR, and olaparib plus PI-103 plus IR. Cells were exposed to the drugs for 2 hours prior to irradiation, and the cell survival curve was obtained using a clonogenic assay. Western blotting and immunofluorescent detection of γH2AX foci were performed. Xenograft and bioluminescence imaging were carried out to assess in vivo radiosensitivity.
  
  
  RESULTS
  Combined use of olaparib and PI-103 enhanced radiation-induced death of MDA-MB-435S (sensitizer enhancement ratio[SER]0.05,1.7) and MDA-MB-231-BR (SER0.05,2.1) cells and significantly reduced tumor volume in a xenograft models (P < 0.001). Treatment with PI-103 showed persistent γH2AX foci, indicating delayed repair of DNA strand breaks. PI-103 alone increased levels of poly(ADP-ribose) and phosphorylated extracellular signal-regulated kinase, and downregulated BRCA1.
  
  
  CONCLUSIONS
  Combined use of olaparib and PI-103 enhanced radiation-induced cell death in BRCA-proficient MDA-MB-435S and MDA-MB-231-BR cells and xenografts. TNBC patients have high incidences of locoregional relapse and distant metastasis, and radiation therapy targets both locoregional control and treatment of distant recurrences such as brain metastasis or other oligometastasis. Targeting of the PI3K signaling pathway combined with PARP inhibition maybe a feasible approach to enhance effects of radiation in BRCA-proficient TNBC.
authors.affiliation: Department of Radiation Oncology, Graduate School of Medicine, Seoul National University, Seoul, Korea. mumuki79@gmail.com.|Department of Radiation Oncology, Veterans Health Service Medical Center, Seoul, Korea. mumuki79@gmail.com.
authors.forename: Na Young
authors.initials: NY
authors.lastname: Jang
authors.affiliation: Medical Science Research Institute, Seoul National University Bundang Hospital, Seongnam, Korea. danhyo@hanmail.net.
authors.forename: Dan Hyo
authors.initials: DH
authors.lastname: Kim
authors.affiliation: Medical Science Research Institute, Seoul National University Bundang Hospital, Seongnam, Korea. bongjun.cho@gmail.com.
authors.forename: Bong Jun
authors.initials: BJ
authors.lastname: Cho
authors.affiliation: Medical Science Research Institute, Seoul National University Bundang Hospital, Seongnam, Korea. epio78@hanmail.net.
authors.forename: Eun Jung
authors.initials: EJ
authors.lastname: Choi
authors.affiliation: Department of Life Science, College of Natural Sciences, Ajou University, Suwon, Korea. jsjlee@ajou.ac.kr.
authors.forename: Jong-Soo
authors.initials: JS
authors.lastname: Lee
authors.affiliation: Department of Radiation Oncology, Seoul National University, Seoul, Korea. wuhg@snu.ac.kr.
authors.forename: Hong-Gyun
authors.initials: HG
authors.lastname: Wu
authors.affiliation: Department of Radiation Oncology, Seoul National University, Seoul, Korea. ekchie93@snu.ac.kr.
authors.forename: Eui Kyu
authors.initials: EK
authors.lastname: Chie
authors.affiliation: Medical Science Research Institute, Seoul National University Bundang Hospital, Seongnam, Korea. inah228@snu.ac.kr.|Department of Radiation Oncology, Seoul National University, Seoul, Korea. inah228@snu.ac.kr.|Cancer Research Institute, Seoul National University, Seoul, Korea. inah228@snu.ac.kr.
authors.forename: In Ah
authors.initials: IA
authors.lastname: Kim
mesh_terms: D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000008:administration & dosage* / Q000494:pharmacology; D019313:BRCA1 Protein / Q000378:metabolism; D016923:Cell Death; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects / Q000528:radiation effects; D005260:Female; D005663:Furans / Q000008:administration & dosage* / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D051379:Mice; D010793:Phthalazines / Q000008:administration & dosage* / Q000494:pharmacology; D010879:Piperazines / Q000008:administration & dosage* / Q000494:pharmacology; D011725:Pyridines / Q000008:administration & dosage* / Q000494:pharmacology; D011743:Pyrimidines / Q000008:administration & dosage* / Q000494:pharmacology; D011838:Radiation-Sensitizing Agents / Q000008:administration & dosage* / Q000494:pharmacology; D064726:Triple Negative Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000532:radiotherapy*; D023041:Xenograft Model Antitumor Assays
chemical_list: D019313:BRCA1 Protein; D005663:Furans; C522973:PI103; D010793:Phthalazines; D010879:Piperazines; D011725:Pyridines; D011743:Pyrimidines; D011838:Radiation-Sensitizing Agents; C531550:olaparib