title: Amplification of DNA damage by a γH2AX-targeted radiopharmaceutical.
abstract: (111)In-DTPA-anti-γH2AX-Tat, which combines an anti-γH2AX antibody with a cell-penetrating peptide, Tat, and the Auger electron-emitting radioisotope, (111)In, targets the DNA damage signalling protein, γH2AX, and has potential as a probe for imaging DNA damage in vivo. The goal of this study was to investigate whether (111)In-DTPA-anti-γH2AX-Tat labelled to high specific activity (6MBq/μg) can amplify treatment-related DNA damage for therapeutic gain.
  
  
  METHODS
  MDA-MB-468 and MDA-MB-231/H2N (231-H2N) breast cancer cells were incubated with (111)In-DTPA-anti-γH2AX-Tat (3MBq, 6MBq/μg) or a control radioimmunoconjugate, (111)In-DTPA-mIgG-Tat, and exposed to IR or bleomycin. DNA damage was studied by counting γH2AX foci and by neutral comet assay. Cytotoxicity was evaluated using clonogenic assays. (111)In-DTPA-anti-γH2AX-Tat was administered intravenously to 231-H2N-xenograft-bearing Balb/c nu/nu mice in tumor growth inhibition studies.
  
  
  RESULTS
  The number of γH2AX foci was greater after exposure of cells to IR (10Gy) plus (111)In-DTPA-anti-γH2AX-Tat compared to IR alone (20.6±2.5 versus 10.4±2.3 foci/cell; P<.001).(111)In-DTPA-anti-γH2AX-Tat resulted in a reduced surviving fraction in cells co-treated with IR (4Gy) versus IR alone (5.2%±0.9% versus 47.8%±2.8%; P<.001). Similarly, bleomycin (25-200μg/mL) plus (111)In-DTPA-anti-γH2AX-Tat resulted in a lower SF compared to bleomycin alone. The combination of a single exposure to IR (10Gy) plus (111)In-DTPA-anti-γH2AX-Tat significantly decreased the growth rate of 231-H2N xenografts in vivo compared to either (111)In-DTPA-anti-γH2AX-Tat or IR alone (-0.002±0.004 versus 0.036±0.011 and 0.031±0.014mm(3)/day, respectively, P<.001).
  
  
  CONCLUSIONS
  (111)In-DTPA-anti-γH2AX-Tat amplifies anticancer treatment-related DNA damage in vitro and has a potent anti-tumor effect when combined with IR in vivo.
authors: Department of Oncology, CR-UK/MRC Gray Institute for Radiation Oncology and Biology, University of Oxford, OX3 7LJ Oxford, UK.
authors: Bart
authors: B
authors: Cornelissen
authors: Sonali
authors: S
authors: Darbar
authors: Veerle
authors: V
authors: Kersemans
authors: Danny
authors: D
authors: Allen
authors: Nadia
authors: N
authors: Falzone
authors: Jody
authors: J
authors: Barbeau
authors: Sean
authors: S
authors: Smart
authors: Katherine A
authors: KA
authors: Vallis
mesh_terms: D000818:Animals; D001761:Bleomycin / Q000494:pharmacology / Q000627:therapeutic use; D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000473:pathology / Q000532:radiotherapy; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic; D053903:DNA Breaks, Double-Stranded / Q000187:drug effects / Q000528:radiation effects; D004249:DNA Damage; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006657:Histones / Q000235:genetics*; D006801:Humans; D018796:Immunoconjugates / Q000737:chemistry / Q000627:therapeutic use; D007205:Indium Radioisotopes / Q000627:therapeutic use; D051379:Mice; D058990:Molecular Targeted Therapy / Q000379:methods*; D004369:Pentetic Acid / Q000737:chemistry; D010446:Peptide Fragments / Q000737:chemistry; D011874:Radiometry; D019275:Radiopharmaceuticals / Q000737:chemistry* / Q000627:therapeutic use*; D054322:tat Gene Products, Human Immunodeficiency Virus / Q000737:chemistry
chemical_list: C468783:H2AX protein, human; D006657:Histones; D018796:Immunoconjugates; D007205:Indium Radioisotopes; D010446:Peptide Fragments; D019275:Radiopharmaceuticals; D054322:tat Gene Products, Human Immunodeficiency Virus; D001761:Bleomycin; D004369:Pentetic Acid