title: Iniparib nonselectively modifies cysteine-containing proteins in tumor cells and is not a bona fide PARP inhibitor.
abstract: OBJECTIVE
  PARP inhibitors are being developed as therapeutic agents for cancer. More than six compounds have entered clinical trials. The majority of these compounds are β-nicotinamide adenine dinucleotide (NAD(+))-competitive inhibitors. One exception is iniparib, which has been proposed to be a noncompetitive PARP inhibitor. In this study, we compare the biologic activities of two different structural classes of NAD(+)-competitive compounds with iniparib and its C-nitroso metabolite.
  
  
  METHODS
  Two chemical series of NAD(+)-competitive PARP inhibitors, iniparib and its C-nitroso metabolite, were analyzed in enzymatic and cellular assays. Viability assays were carried out in MDA-MB-436 (BRCA1-deficient) and DLD1(-/-) (BRCA2-deficient) cells together with BRCA-proficient MDA-MB-231 and DLD1(+/+) cells. Capan-1 and B16F10 xenograft models were used to compare iniparib and veliparib in vivo. Mass spectrometry and the (3)H-labeling method were used to monitor the covalent modification of proteins.
  
  
  RESULTS
  All NAD(+)-competitive inhibitors show robust activity in a PARP cellular assay, strongly potentiate the activity of temozolomide, and elicit robust cell killing in BRCA-deficient tumor cells in vitro and in vivo. Cell killing was associated with an induction of DNA damage. In contrast, neither iniparib nor its C-nitroso metabolite inhibited PARP enzymatic or cellular activity, potentiated temozolomide, or showed activity in a BRCA-deficient setting. We find that the nitroso metabolite of iniparib forms adducts with many cysteine-containing proteins. Furthermore, both iniparib and its nitroso metabolite form protein adducts nonspecifically in tumor cells.
  
  
  CONCLUSIONS
  Iniparib nonselectively modifies cysteine-containing proteins in tumor cells, and the primary mechanism of action for iniparib is likely not via inhibition of PARP activity.
authors: Cancer Research, Advanced Technology, and Process R&D, Abbott Laboratories, Abbott Park, IL 60064, USA.
authors: Xuesong
authors: X
authors: Liu
authors: Yan
authors: Y
authors: Shi
authors: David X
authors: DX
authors: Maag
authors: Joann P
authors: JP
authors: Palma
authors: Melanie J
authors: MJ
authors: Patterson
authors: Paul A
authors: PA
authors: Ellis
authors: Bruce W
authors: BW
authors: Surber
authors: Damien B
authors: DB
authors: Ready
authors: Niru B
authors: NB
authors: Soni
authors: Uri S
authors: US
authors: Ladror
authors: Allison J
authors: AJ
authors: Xu
authors: Ramesh
authors: R
authors: Iyer
authors: John E
authors: JE
authors: Harlan
authors: Larry R
authors: LR
authors: Solomon
authors: Cherrie K
authors: CK
authors: Donawho
authors: Thomas D
authors: TD
authors: Penning
authors: Eric F
authors: EF
authors: Johnson
authors: Alexander R
authors: AR
authors: Shoemaker
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000737:chemistry / Q000494:pharmacology* / Q000627:therapeutic use; D024682:BRCA2 Protein / Q000172:deficiency / Q000235:genetics; D001549:Benzamides / Q000737:chemistry / Q000494:pharmacology* / Q000627:therapeutic use; D001562:Benzimidazoles / Q000737:chemistry / Q000494:pharmacology / Q000627:therapeutic use; D045744:Cell Line, Tumor; D003545:Cysteine / Q000737:chemistry*; D004260:DNA Repair / Q000187:drug effects; D003606:Dacarbazine / Q000031:analogs & derivatives / Q000494:pharmacology / Q000627:therapeutic use; D004357:Drug Synergism; D005260:Female; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D016513:Mice, SCID; D009374:Neoplasms, Experimental / Q000188:drug therapy / Q000473:pathology; D000071137:Poly (ADP-Ribose) Polymerase-1; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011065:Poly(ADP-ribose) Polymerases / Q000737:chemistry / Q000378:metabolism; D000077204:Temozolomide; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; D024682:BRCA2 Protein; C551750:BRCA2 protein, human; D001549:Benzamides; D001562:Benzimidazoles; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; C521013:veliparib; C090712:iniparib; D003606:Dacarbazine; C499320:PARP1 protein, human; C483041:PARP2 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; D003545:Cysteine; D000077204:Temozolomide