title: Nonhomologous end joining is essential for cellular resistance to the novel antitumor agent, beta-lapachone.
abstract: Commonly used antitumor agents, such as DNA topoisomerase I/II poisons, kill cancer cells by creating nonrepairable DNA double-strand breaks (DSBs). To repair DSBs, error-free homologous recombination (HR), and/or error-prone nonhomologous end joining (NHEJ) are activated. These processes involve the phosphatidylinositol 3'-kinase-related kinase family of serine/threonine enzymes: ataxia telangiectasia mutated (ATM), ATM- and Rad3-related for HR, and DNA-dependent protein kinase catalytic subunit (DNA-PKcs) for NHEJ. Alterations in these repair processes can cause drug/radiation resistance and increased genomic instability. beta-Lapachone (beta-lap; also known as ARQ 501), currently in phase II clinical trials for the treatment of pancreatic cancer, causes a novel caspase- and p53-independent cell death in cancer cells overexpressing NAD(P)H:quinone oxidoreductase-1 (NQO1). NQO1 catalyzes a futile oxidoreduction of beta-lap leading to reactive oxygen species generation, DNA breaks, gamma-H2AX foci formation, and hyperactivation of poly(ADP-ribose) polymerase-1, which is required for cell death. Here, we report that beta-lap exposure results in NQO1-dependent activation of the MRE11-Rad50-Nbs-1 complex. In addition, ATM serine 1981, DNA-PKcs threonine 2609, and Chk1 serine 345 phosphorylation were noted; indicative of simultaneous HR and NHEJ activation. However, inhibition of NHEJ, but not HR, by genetic or chemical means potentiated beta-lap lethality. These studies give insight into the mechanism by which beta-lap radiosensitizes cancer cells and suggest that NHEJ is a potent target for enhancing the therapeutic efficacy of beta-lap alone or in combination with other agents in cancer cells that express elevated NQO1 levels.
authors.affiliation: Department of Pharmacology, Case Western Reserve University, Cleveland, OH, USA.
authors.forename: Melissa S
authors.initials: MS
authors.lastname: Bentle
authors.forename: Kathryn E
authors.initials: KE
authors.lastname: Reinicke
authors.forename: Ying
authors.initials: Y
authors.lastname: Dong
authors.forename: Erik A
authors.initials: EA
authors.lastname: Bey
authors.forename: David A
authors.initials: DA
authors.lastname: Boothman
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002470:Cell Survival; D020552:Comet Assay; D053960:DNA Breaks; D004249:DNA Damage; D004260:DNA Repair; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008954:Models, Biological; D009285:Naphthoquinones / Q000494:pharmacology*; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D018894:Reverse Transcriptase Inhibitors / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D000970:Antineoplastic Agents; D009285:Naphthoquinones; D018894:Reverse Transcriptase Inhibitors; C014638:beta-lapachone; C499320:PARP1 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases