title: Identification and characterization of a small inhibitory peptide that can target DNA-PKcs autophosphorylation and increase tumor radiosensitivity.
abstract: OBJECTIVE
  The DNA protein kinase catalytic subunit (DNA-PKcs) is one of the critical elements involved in the DNA damage repair process. Inhibition of DNA-PKcs results in hypersensitivity to ionizing radiation (IR); therefore, this approach has been explored to develop molecular targeted radiosensitizers. Here, we aimed to develop small inhibitory peptides that could specifically target DNA-PKcs autophosphorylation, a critical step for the enzymatic activation of the kinase in response to IR.
  
  
  METHODS
  We generated several small fusion peptides consisting of 2 functional domains, 1 an internalization domain and the other a DNA-PKcs autophosphorylation inhibitory domain. We characterized the internalization, toxicity, and radiosensitization activities of the fusion peptides. Furthermore, we studied the mechanisms of the inhibitory peptides on DNA-PKcs autophosphorylation and DNA repair.
  
  
  RESULTS
  We found that among several peptides, the biotin-labeled peptide 3 (BTW3) peptide, which targets DNA-PKcs threonine 2647 autophosphorylation, can abrogate IR-induced DNA-PKcs activation and cause prolonged γ-H2AX focus formation. We demonstrated that BTW3 exposure led to hypersensitivity to IR in DNA-PKcs-proficient cells but not in DNA-PKcs-deficient cells.
  
  
  CONCLUSIONS
  The small inhibitory peptide BTW3 can specifically target DNA-PKcs autophosphorylation and enhance radiosensitivity; therefore, it can be further developed as a novel class of radiosensitizer.
authors.affiliation: Department of Radiation Oncology, Sir Run Run Shaw Hospital, Sir Run Run Shaw Institute of Clinical Medicine of Zhejiang University, Hangzhou, China.
authors.forename: Xiaonan
authors.initials: X
authors.lastname: Sun
authors.forename: Chunying
authors.initials: C
authors.lastname: Yang
authors.forename: Hai
authors.initials: H
authors.lastname: Liu
authors.forename: Qi
authors.initials: Q
authors.lastname: Wang
authors.forename: Shi-Xiu
authors.initials: SX
authors.lastname: Wu
authors.forename: Xia
authors.initials: X
authors.lastname: Li
authors.forename: Tian
authors.initials: T
authors.lastname: Xie
authors.forename: Kathryn L
authors.initials: KL
authors.lastname: Brinkman
authors.forename: Bin S
authors.initials: BS
authors.lastname: Teh
authors.forename: E Brian
authors.initials: EB
authors.lastname: Butler
authors.forename: Bo
authors.initials: B
authors.lastname: Xu
authors.forename: Shu
authors.initials: S
authors.lastname: Zheng
mesh_terms: D000595:Amino Acid Sequence; D001710:Biotin / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000494:pharmacology; D059766:DNA End-Joining Repair; D051747:DNA-Activated Protein Kinase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D004354:Drug Screening Assays, Antitumor / Q000379:methods; D004789:Enzyme Activation / Q000187:drug effects; D006657:Histones / Q000096:biosynthesis; D006801:Humans; D058990:Molecular Targeted Therapy / Q000379:methods*; D010455:Peptides / Q000138:chemical synthesis / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D011836:Radiation Tolerance / Q000187:drug effects*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000494:pharmacology; D013912:Threonine / Q000037:antagonists & inhibitors
chemical_list: C577324:BTW3 peptide; C468783:H2AX protein, human; D006657:Histones; D010455:Peptides; D047428:Protein Kinase Inhibitors; D011993:Recombinant Fusion Proteins; D013912:Threonine; D001710:Biotin; D051747:DNA-Activated Protein Kinase