title: Resistance to therapy caused by intragenic deletion in BRCA2.
abstract: Cells with loss of BRCA2 function are defective in homologous recombination (HR) and are highly sensitive to inhibitors of poly(ADP-ribose) polymerase (PARP), which provides the basis for a new therapeutic approach. Here we show that resistance to PARP inhibition can be acquired by deletion of a mutation in BRCA2. We derived PARP-inhibitor-resistant (PIR) clones from the human CAPAN1 pancreatic cancer cell line, which carries the protein-truncating c.6174delT frameshift mutation. PIR clones could form DNA-damage-induced RAD51 nuclear foci and were able to limit genotoxin-induced genomic instability, both hallmarks of a competent HR pathway. New BRCA2 isoforms were expressed in the resistant lines as a result of intragenic deletion of the c.6174delT mutation and restoration of the open reading frame (ORF). Reconstitution of BRCA2-deficient cells with these revertant BRCA2 alleles rescued PARP inhibitor sensitivity and HR deficiency. Most of the deletions in BRCA2 were associated with small tracts of homology, and possibly arose from error-prone repair caused by BRCA2 deficiency. Similar ORF-restoring mutations were present in carboplatin-resistant ovarian tumours from c.6174delT mutation carriers. These observations have implications for understanding drug resistance in BRCA mutation carriers as well as in defining functionally important domains within BRCA2.
authors.affiliation: The Breakthrough Breast Cancer Research Centre, The Institute of Cancer Research, Fulham Road, London SW3 6JB, UK.
authors.forename: Stacey L
authors.initials: SL
authors.lastname: Edwards
authors.forename: Rachel
authors.initials: R
authors.lastname: Brough
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Lord
authors.forename: Rachael
authors.initials: R
authors.lastname: Natrajan
authors.forename: Radost
authors.initials: R
authors.lastname: Vatcheva
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Levine
authors.forename: Jeff
authors.initials: J
authors.lastname: Boyd
authors.forename: Jorge S
authors.initials: JS
authors.lastname: Reis-Filho
authors.forename: Alan
authors.initials: A
authors.lastname: Ashworth
mesh_terms: D000368:Aged; D000483:Alleles; D000595:Amino Acid Sequence; D024682:BRCA2 Protein / Q000172:deficiency / Q000235:genetics; D001483:Base Sequence; D016190:Carboplatin / Q000494:pharmacology; D045744:Cell Line, Tumor; D002869:Chromosome Aberrations / Q000139:chemically induced; D019008:Drug Resistance, Neoplasm / Q000187:drug effects* / Q000235:genetics*; D005260:Female; D005464:Fluorobenzenes / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic; D024522:Genes, BRCA2; D006801:Humans; D008875:Middle Aged; D016685:Mitomycin / Q000494:pharmacology; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D016366:Open Reading Frames / Q000235:genetics; D010051:Ovarian Neoplasms / Q000188:drug therapy / Q000235:genetics; D010190:Pancreatic Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000473:pathology; D010793:Phthalazines / Q000494:pharmacology; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011995:Recombination, Genetic / Q000235:genetics; D017384:Sequence Deletion / Q000235:genetics*
chemical_list: D024682:BRCA2 Protein; D005464:Fluorobenzenes; C506932:KU0058948; D010793:Phthalazines; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D016685:Mitomycin; D016190:Carboplatin