title: PARP-1 Expression Quantified by [18F]FluorThanatrace: A Biomarker of Response to PARP Inhibition Adjuvant to Radiation Therapy.
abstract: BACKGROUND
  Poly (ADP-ribose) polymerase 1 (PARP-1) is the major target of clinical PARP inhibitors and is a potential predictive biomarker for response to therapy. Due to the limited success of PARP inhibitors as monotherapy, investigators have shifted the clinical role of PARP inhibitors to the adjuvant setting. In this study, we evaluate the radiotracer [18F]FluorThanatrace ([18F]FTT) as a marker of PARP expression in vitro and the associated biological implications of PARP-1 expression in PARP inhibitor treatment adjuvant to radiation therapy.
  
  
  METHODS
  SNU-251 (BRCA1-mutant) and SKOV3 (BRCA1-WT) cell lines were evaluated in vitro by using the radiotracer [18F]FTT. Pharmacological binding assays were performed at baseline and were correlated with PARP-1 protein expression measured by Western blot protein analysis. Cell viability and clonogenic assays were used to characterize in vitro cytotoxicity for treatments, including: PARP inhibitors alone, radiation alone, and PARP inhibitor adjuvant to radiation. Western blot protein analysis was used to assess response to treatment by using γH2AX to measure DNA damage and PAR to measure the catalytic inhibition of PARP.
  
  
  RESULTS
  [18F]FTT was capable of measuring PARP-1 protein expression in vitro and corresponded to Western blot protein analysis at baseline. The addition of a PARP inhibitor enhanced radiation effects in both cell lines; however, a greater synergy was observed in the SNU-251 cell line that expresses a BRCA1 mutation and homologous recombination deficiency. Western blot protein analysis showed that the addition of a PARP inhibitor adjuvant to radiation increases DNA damage in both cell lines and reduces PARP enzymatic activity as measured by PAR.
  
  
  CONCLUSIONS
  In this work, we found that PARP-1 expression positively corresponds in vitro to the response of PARP inhibitors in combination with radiation therapy in ovarian cancer.
authors.affiliation: 1 Division of Nuclear Medicine and Clinical Molecular Imaging, Department of Radiology, University of Pennsylvania Perelman School of Medicine , Philadelphia, Pennsylvania.
authors.forename: Samuel
authors.initials: S
authors.lastname: Sander Effron
authors.affiliation: 1 Division of Nuclear Medicine and Clinical Molecular Imaging, Department of Radiology, University of Pennsylvania Perelman School of Medicine , Philadelphia, Pennsylvania.
authors.forename: Mehran
authors.initials: M
authors.lastname: Makvandi
authors.affiliation: 2 Department of Radiation Oncology, University of Pennsylvania Perelman School of Medicine , Philadelphia, Pennsylvania.
authors.forename: Lilie
authors.initials: L
authors.lastname: Lin
authors.affiliation: 1 Division of Nuclear Medicine and Clinical Molecular Imaging, Department of Radiology, University of Pennsylvania Perelman School of Medicine , Philadelphia, Pennsylvania.
authors.forename: Kuiying
authors.initials: K
authors.lastname: Xu
authors.affiliation: 1 Division of Nuclear Medicine and Clinical Molecular Imaging, Department of Radiology, University of Pennsylvania Perelman School of Medicine , Philadelphia, Pennsylvania.
authors.forename: Shihong
authors.initials: S
authors.lastname: Li
authors.affiliation: 1 Division of Nuclear Medicine and Clinical Molecular Imaging, Department of Radiology, University of Pennsylvania Perelman School of Medicine , Philadelphia, Pennsylvania.
authors.forename: Hsiaoju
authors.initials: H
authors.lastname: Lee
authors.affiliation: 1 Division of Nuclear Medicine and Clinical Molecular Imaging, Department of Radiology, University of Pennsylvania Perelman School of Medicine , Philadelphia, Pennsylvania.
authors.forename: Catherine
authors.initials: C
authors.lastname: Hou
authors.affiliation: 1 Division of Nuclear Medicine and Clinical Molecular Imaging, Department of Radiology, University of Pennsylvania Perelman School of Medicine , Philadelphia, Pennsylvania.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Pryma
authors.affiliation: 2 Department of Radiation Oncology, University of Pennsylvania Perelman School of Medicine , Philadelphia, Pennsylvania.
authors.forename: Cameron
authors.initials: C
authors.lastname: Koch
authors.affiliation: 1 Division of Nuclear Medicine and Clinical Molecular Imaging, Department of Radiology, University of Pennsylvania Perelman School of Medicine , Philadelphia, Pennsylvania.
authors.forename: Robert H
authors.initials: RH
authors.lastname: Mach
mesh_terms: D054316:Biomarkers, Pharmacological / Q000378:metabolism*; D045744:Cell Line, Tumor; D002470:Cell Survival; D017024:Chemotherapy, Adjuvant; D004249:DNA Damage / Q000187:drug effects; D005260:Female; D005462:Fluorine Radioisotopes; D006801:Humans; D010051:Ovarian Neoplasms / Q000188:drug therapy / Q000532:radiotherapy / Q000628:therapy*; D000071137:Poly (ADP-Ribose) Polymerase-1 / Q000378:metabolism*; D000067856:Poly(ADP-ribose) Polymerase Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use
chemical_list: D054316:Biomarkers, Pharmacological; D005462:Fluorine Radioisotopes; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; C499320:PARP1 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1
keywords: BRCA1; DNA damage; PARP inhibitor; PARP-1; ovarian cancer