title: Rad51 Degradation: Role in Oncolytic Virus-Poly(ADP-Ribose) Polymerase Inhibitor Combination Therapy in Glioblastoma.
abstract: Clinical success of poly(ADP-ribose) polymerase inhibitors (PARP i ) has been limited to repair-deficient cancers and by resistance. Oncolytic herpes simplex viruses (oHSVs) selectively kill cancer cells, irrespective of mutation, and manipulate DNA damage responses (DDR). Here, we explore potential synthetic lethal-like interactions between oHSV and PARP i .
  
  
  
  The efficacy of combining PARP i , oHSV MG18L, and G47Δ in killing patient-derived glioblastoma stem cells (GSCs) was assessed using cell viability assays and Chou-Talalay synergy analysis. Effects on DDR pathways, apoptosis, and cell cycle after manipulation with pharmacological inhibitors and lentivirus-mediated knockdown or overexpression were examined by immunoblotting and FACS. In vivo efficacy was evaluated in two GSC-derived orthotopic xenograft models (n = 7-8 per group). All statistical tests were two-sided.
  
  
  
  GSCs are differentially sensitive to PARP i despite uniform inhibition of PARP activity. oHSV sensitized GSCs to PARP i , irrespective of their PARP i sensitivity through selective proteasomal degradation of key DDR proteins; Rad51, mediating the combination effects; and Chk1. Rad51 degradation required HSV DNA replication. This synthetic lethal-like interaction increased DNA damage, apoptosis, and cell death in vitro and in vivo. Combined treatment of mice bearing PARP i -sensitive or -resistant GSC-derived brain tumors greatly extended median survival compared to either agent alone (vs olaparib: P ≤.001; vs MG18L: P  = .005; median survival for sensitive of 83 [95% CI = 77 to 86], 94 [95% CI = 75 to 107], 102 [95% CI = 85 to 110], and 131 [95% CI = 108 to 170] days and for resistant of 54 [95% CI = 52 to 58], 56 [95% CI = 52 to 61], 62 [95% CI = 56 to 72], and 75 [95% CI = 64 to 90] days for mock, PARPi, oHSV, and combination, respectively).
  
  
  
  The unique oHSV property to target multiple components of DDR generates cancer selective sensitivity to PARP i . This combination of oHSV with PARP i is a new anticancer strategy that overcomes the clinical barriers of PARP i resistance and DNA repair proficiency and is applicable not only to glioblastoma, an invariably lethal tumor, but also to other tumor types.
authors.affiliation: Molecular Neurosurgery Laboratory, Brain Tumor Research Center, Massachusetts General Hospital, Boston, MA, USA.|Department of Neurosurgery, Harvard Medical School, Boston, MA, USA.
authors.forename: Jianfang
authors.initials: J
authors.lastname: Ning
authors.affiliation: Molecular Neurosurgery Laboratory, Brain Tumor Research Center, Massachusetts General Hospital, Boston, MA, USA.|Department of Neurosurgery, Harvard Medical School, Boston, MA, USA.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Wakimoto
authors.affiliation: Molecular Neurosurgery Laboratory, Brain Tumor Research Center, Massachusetts General Hospital, Boston, MA, USA.|Program in Virology, Harvard Medical School, Boston, MA, USA.
authors.forename: Cole
authors.initials: C
authors.lastname: Peters
authors.affiliation: Molecular Neurosurgery Laboratory, Brain Tumor Research Center, Massachusetts General Hospital, Boston, MA, USA.|Department of Neurosurgery, Harvard Medical School, Boston, MA, USA.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Martuza
authors.affiliation: Molecular Neurosurgery Laboratory, Brain Tumor Research Center, Massachusetts General Hospital, Boston, MA, USA.|Department of Neurosurgery, Harvard Medical School, Boston, MA, USA.|Program in Virology, Harvard Medical School, Boston, MA, USA.
authors.forename: Samuel D
authors.initials: SD
authors.lastname: Rabkin
mesh_terms: D000818:Animals; D017209:Apoptosis; D001932:Brain Neoplasms / Q000201:enzymology / Q000628:therapy*; D002453:Cell Cycle; D002470:Cell Survival / Q000187:drug effects; D000071877:Checkpoint Kinase 1 / Q000378:metabolism; D003131:Combined Modality Therapy; D004260:DNA Repair; D004261:DNA Replication; D004279:DNA, Viral / Q000096:biosynthesis*; D019008:Drug Resistance, Neoplasm; D005260:Female; D005909:Glioblastoma / Q000201:enzymology / Q000628:therapy*; D006801:Humans; D051379:Mice; D009368:Neoplasm Transplantation; D014411:Neoplastic Stem Cells; D050130:Oncolytic Virotherapy; D050504:Oncolytic Viruses / Q000502:physiology; D010793:Phthalazines / Q000494:pharmacology / Q000627:therapeutic use*; D010879:Piperazines / Q000494:pharmacology / Q000627:therapeutic use*; D000067856:Poly(ADP-ribose) Polymerase Inhibitors / Q000494:pharmacology / Q000627:therapeutic use*; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D051135:Rad51 Recombinase / Q000378:metabolism*; D015398:Signal Transduction; D018139:Simplexvirus / Q000502:physiology*; D014407:Tumor Cells, Cultured; D014410:Tumor Stem Cell Assay
chemical_list: D004279:DNA, Viral; D010793:Phthalazines; D010879:Piperazines; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011065:Poly(ADP-ribose) Polymerases; D000071877:Checkpoint Kinase 1; D051135:Rad51 Recombinase; C531550:olaparib