title: The novel poly(ADP-Ribose) polymerase inhibitor, AG14361, sensitizes cells to topoisomerase I poisons by increasing the persistence of DNA strand breaks.
abstract: Poly(ADP-ribose) polymerase (PARP) inhibitors enhance DNA topoisomerase I (topo I) poison-induced cytotoxicity and antitumor activity in vitro and in vivo, but the mechanism has not been defined. We investigated the role of PARP-1 in the response to topo I poisons using PARP-1-/- and PARP-1+/+ mouse embryonic fibroblasts and the potent PARP-1 inhibitor, AG14361 (Ki < 5 nmol/L). PARP-1-/- mouse embryonic fibroblasts were 3-fold more sensitive to topotecan than PARP-1+/+ mouse embryonic fibroblasts (GI50, 21 and 65 nmol/L, respectively). AG14361 caused a >3-fold sensitization of PARP-1+/+ cells to topotecan compared with a <1.4-fold sensitization in PARP-1-/- cells. In human leukemia K562 cells, AG14361 caused a 2-fold sensitization to camptothecin-induced cytotoxicity. AG14361 did not affect the cellular activity of topo I as determined by measurement of cleavable complexes and topo I relaxation activity, showing that sensitization was not due to topo I activation. In contrast, repair of DNA following camptothecin removal, normally very rapid, was significantly retarded by AG14361, resulting in a 62% inhibition of repair 10 minutes after camptothecin removal. This led to a 20% increase in the net accumulation of camptothecin-induced DNA strand break levels in cells coexposed to AG14361 for 16 hours. We investigated the DNA repair mechanism involved using a panel of DNA repair-deficient Chinese hamster ovary cells. AG14361 significantly potentiated camptothecin-mediated cytotoxicity in all cells, except the base excision repair-deficient EM9 cells. Therefore, the most likely mechanism for the potentiation of topo I poison-mediated cytotoxicity by AG14361 is via PARP-1-dependent base excision repair.
authors.affiliation: Northern Institute for Cancer Research and Institute for Cell and Molecular Biosciences, Medical School, University of Newcastle upon Tyne, Newcastle upon Tyne, United Kingdom.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Smith
authors.forename: Elaine
authors.initials: E
authors.lastname: Willmore
authors.forename: Caroline A
authors.initials: CA
authors.lastname: Austin
authors.forename: Nicola J
authors.initials: NJ
authors.lastname: Curtin
mesh_terms: D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D052176:Azulenes; D001569:Benzodiazepines / Q000494:pharmacology*; D016466:CHO Cells / Q000187:drug effects; D002166:Camptothecin / Q000633:toxicity*; D006224:Cricetinae; D004249:DNA Damage / Q000187:drug effects*; D004260:DNA Repair / Q000187:drug effects; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D005347:Fibroblasts / Q000187:drug effects / Q000201:enzymology; D006801:Humans; D020014:K562 Cells / Q000187:drug effects; D051379:Mice; D018345:Mice, Knockout; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D059004:Topoisomerase I Inhibitors; D019772:Topotecan / Q000633:toxicity*; D014410:Tumor Stem Cell Assay
chemical_list: C479234:1-(4-dimethylaminomethylphenyl)-8,9-dihydro-7H-2,7,9a-benzo(cd)azulen-6-one; D000972:Antineoplastic Agents, Phytogenic; D052176:Azulenes; D004791:Enzyme Inhibitors; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D059004:Topoisomerase I Inhibitors; D001569:Benzodiazepines; D019772:Topotecan; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin