Iniparib nonselectively modifies cysteine-containing proteins in tumor cells and is not a bona fide PARP inhibitor.

Abstract

PURPOSE:

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.

EXPERIMENTAL DESIGN:

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: Xuesong Liu, Yan Shi, David X Maag, Joann P Palma, Melanie J Patterson, Paul A Ellis, Bruce W Surber, Damien B Ready, Niru B Soni, Uri S Ladror, Allison J Xu, Ramesh Iyer, John E Harlan, Larry R Solomon, Cherrie K Donawho, Thomas D Penning, Eric F Johnson, Alexander R Shoemaker
• Journal: Clinical cancer research : an official journal of the American Association for Cancer Research (Clin Cancer Res) Vol. 18 Issue 2 Pg. 510-23 (Jan 15 2012) ISSN: 1557-3265 [Electronic] United States
• PMID: 22128301 (Publication Type: Comparative Study, Journal Article)
• Copyright: ©2011 AACR.

Chemical References

• Antineoplastic Agents
• BRCA2 Protein
• BRCA2 protein, human
• Benzamides
• Benzimidazoles
• Poly(ADP-ribose) Polymerase Inhibitors
• veliparib
• iniparib
• Dacarbazine
• PARP1 protein, human
• PARP2 protein, human
• Poly (ADP-Ribose) Polymerase-1
• Poly(ADP-ribose) Polymerases
• Cysteine
• Temozolomide

Topics

• Animals
• Antineoplastic Agents (chemistry, pharmacology, therapeutic use)
• BRCA2 Protein (deficiency, genetics)
• Benzamides (chemistry, pharmacology, therapeutic use)
• Benzimidazoles (chemistry, pharmacology, therapeutic use)
• Cell Line, Tumor
• Cysteine (chemistry)
• DNA Repair (drug effects)
• Dacarbazine (analogs & derivatives, pharmacology, therapeutic use)
• Drug Synergism
• Female
• Humans
• Mice
• Mice, Inbred C57BL
• Mice, SCID
• Neoplasms, Experimental (drug therapy, pathology)
• Poly (ADP-Ribose) Polymerase-1
• Poly(ADP-ribose) Polymerase Inhibitors
• Poly(ADP-ribose) Polymerases (chemistry, metabolism)
• Temozolomide
• Xenograft Model Antitumor Assays