title: Inhibition of BRCT(BRCA1)-phosphoprotein interaction enhances the cytotoxic effect of olaparib in breast cancer cells: a proof of concept study for synthetic lethal therapeutic option.
abstract: Synthetic lethal therapeutic strategy using poly(adenosine diphosphate [ADP]-ribose) polymerase (PARP) inhibitor olaparib in carriers of BRCA1 or BRCA2 mutation has shown promise in clinical settings. Since <5 % of patients are BRCA1 or BRCA2 mutation carriers, small molecules that functionally mimic BRCA1 or BRCA2 mutations will extend the synthetic lethal therapeutic option for non-mutation carriers. Here we provide proof of principle for this strategy using a BRCA1 inhibitor peptide 2 that targets the BRCT(BRCA1)-phosphoprotein interaction and mimics the M177R/K BRCA1 mutation. Reciprocal immunoprecipitation and immunoblotting of BRCA1 and Abraxas was used to demonstrate inhibitor 2 targets BRCT(BRCA1)-Abraxas interface. Immunostaining of γH2AX, cell cycle analysis and homologous recombination (HR) assays were conducted to confirm that inhibitor 2 functionally mimics a chemosensitizing BRCA1 mutation. The concept of synthetic lethal therapeutic strategy with the BRCA1 inhibitor 2 and the PARP inhibitor Olaparib was explored in HeLa, MDA-MB-231, and HCC1937 cell lines. The results show that inhibition of BRCA1 by 2 sensitizes HeLa and MDA-MB-231 cells but not HCC1937 to Olaparib mediated growth inhibition and apoptosis. These results provide the basis for developing high affinity BRCT(BRCA1) inhibitors as adjuvants to treat sporadic breast and ovarian cancers.
authors.affiliation: Eppley Institute for Cancer Research, University of Nebraska Medical Center, Omaha, NE 68198, USA. zyuan@kumc.edu
authors.forename: Ziyan Yuan
authors.initials: ZY
authors.lastname: Pessetto
authors.forename: Ying
authors.initials: Y
authors.lastname: Yan
authors.forename: Tadayoshi
authors.initials: T
authors.lastname: Bessho
authors.forename: Amarnath
authors.initials: A
authors.lastname: Natarajan
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D019313:BRCA1 Protein / Q000037:antagonists & inhibitors* / Q000378:metabolism; D001943:Breast Neoplasms / Q000188:drug therapy*; D002352:Carrier Proteins / Q000378:metabolism; D045744:Cell Line, Tumor / Q000187:drug effects / Q000528:radiation effects; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D004249:DNA Damage; D004354:Drug Screening Assays, Antitumor; D005260:Female; D059565:G2 Phase Cell Cycle Checkpoints / Q000187:drug effects; D006801:Humans; D058990:Molecular Targeted Therapy; D009842:Oligopeptides / Q000494:pharmacology*; D010750:Phosphoproteins / Q000378:metabolism; D010793:Phthalazines / Q000494:pharmacology*; D010879:Piperazines / Q000494:pharmacology*; D000071137:Poly (ADP-Ribose) Polymerase-1; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*
chemical_list: C520310:ABRAXAS1 protein, human; C576357:Ac-R10G-pSPTF-CO2H; D000970:Antineoplastic Agents; D019313:BRCA1 Protein; C492913:BRCA1 protein, human; D002352:Carrier Proteins; D009842:Oligopeptides; D010750:Phosphoproteins; D010793:Phthalazines; D010879:Piperazines; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011838:Radiation-Sensitizing Agents; C499320:PARP1 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; C531550:olaparib