title: Inhibition of PARP1-dependent end-joining contributes to Olaparib-mediated radiosensitization in tumor cells.
abstract: Poly-ADP-ribose-polymerase inhibitors (PARPi) are considered to be optimal tools for specifically enhancing radiosensitivity. This effect has been shown to be replication-dependent and more profound in HR-deficient tumors. Here, we present a new mode of PARPi-mediated radiosensitization which was observed in four out of six HR-proficient tumor cell lines (responders) investigated, but not in normal cells. This effect is replication-independent, as the radiosensitization remained unaffected following the inhibition of replication using aphidicolin. We showed that responders are radiosensitized by Olaparib because their DSB-repair is switched to PARP1-dependent end-joining (PARP1-EJ), as evident by (i) the significant increase in the number of residual γH2AX foci following irradiation with 3Gy and treatment with Olaparib, (ii) the enhanced enrichment of PARP1 at the chromatin after 3Gy and (iii) the inhibition of end-joining activity measured by a specific reporter substrate upon Olaparib treatment. This is the first study which directly demonstrates the switch to PARP1-EJ in tumor cells and its contribution to the response to Olaparib as a radiosensitizer, findings which could widen the scope of application of PARPi in tumor therapy.
authors.affiliation: Laboratory of Radiobiology & Experimental Radiooncology, University Medical Center Hamburg-Eppendorf, Hamburg 20246, Germany.
authors.forename: Annika
authors.initials: A
authors.lastname: Kötter
authors.affiliation: Institute of Bone Marrow Transplantation, University Medical Center Hamburg-Eppendorf, Hamburg 20246, Germany.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Cornils
authors.affiliation: Laboratory of Radiobiology & Experimental Radiooncology, University Medical Center Hamburg-Eppendorf, Hamburg 20246, Germany.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Borgmann
authors.affiliation: Laboratory of Radiobiology & Experimental Radiooncology, University Medical Center Hamburg-Eppendorf, Hamburg 20246, Germany.
authors.forename: Jochen
authors.initials: J
authors.lastname: Dahm-Daphi
authors.affiliation: Department of Radiotherapy & Radiooncology, University Medical Center Hamburg-Eppendorf, Hamburg 20246, Germany.
authors.forename: Cordula
authors.initials: C
authors.lastname: Petersen
authors.affiliation: Laboratory of Radiobiology & Experimental Radiooncology, University Medical Center Hamburg-Eppendorf, Hamburg 20246, Germany.
authors.forename: Ekkehard
authors.initials: E
authors.lastname: Dikomey
authors.affiliation: Laboratory of Radiobiology & Experimental Radiooncology, University Medical Center Hamburg-Eppendorf, Hamburg 20246, Germany; Tumor Biology Department, National Cancer Institute, Cairo University, Egypt. Electronic address: wmansour@uke.uni-hamburg.de.
authors.forename: Wael Y
authors.initials: WY
authors.lastname: Mansour
mesh_terms: D015153:Blotting, Western; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D053903:DNA Breaks, Double-Stranded / Q000187:drug effects; D004260:DNA Repair / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005455:Fluorescent Antibody Technique; D006801:Humans; D010793:Phthalazines / Q000494:pharmacology*; D010879:Piperazines / Q000494:pharmacology*; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*
chemical_list: D004791:Enzyme Inhibitors; D010793:Phthalazines; D010879:Piperazines; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011838:Radiation-Sensitizing Agents; C531550:olaparib
keywords: DSB repair; Non-homologous end-joining; Olaparib; PARP1-dependent end-joining; Radiosensitivity