284 Differential Trapping of PARP1 and PARP2 by Clinical PARP Inhibitors

Authors' Affiliations: Laboratory of Molecular Pharmacology, Center for Cancer Research, National Clinical Target Validation Laboratory, and Division of Cancer Treatment and Diagnosis, National Cancer Institute, National Institutes of Health, Bethesda, Maryland
Cancer Research (Impact Factor: 9.33). 11/2012; 72(21):5588-99. DOI: 10.1158/0008-5472.CAN-12-2753
Source: PubMed


Small-molecule inhibitors of PARP are thought to mediate their antitumor effects as catalytic inhibitors that block repair of DNA single-strand breaks (SSB). However, the mechanism of action of PARP inhibitors with regard to their effects in cancer cells is not fully understood. In this study, we show that PARP inhibitors trap the PARP1 and PARP2 enzymes at damaged DNA. Trapped PARP-DNA complexes were more cytotoxic than unrepaired SSBs caused by PARP inactivation, arguing that PARP inhibitors act in part as poisons that trap PARP enzyme on DNA. Moreover, the potency in trapping PARP differed markedly among inhibitors with niraparib (MK-4827) > olaparib (AZD-2281) > veliparib (ABT-888), a pattern not correlated with the catalytic inhibitory properties for each drug. We also analyzed repair pathways for PARP-DNA complexes using 30 genetically altered avian DT40 cell lines with preestablished deletions in specific DNA repair genes. This analysis revealed that, in addition to homologous recombination, postreplication repair, the Fanconi anemia pathway, polymerase β, and FEN1 are critical for repairing trapped PARP-DNA complexes. In summary, our study provides a new mechanistic foundation for the rational application of PARP inhibitors in cancer therapy. Cancer Res; 72(21); 5588-99. ©2012 AACR.

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    • "a flap endonuclease involved in lagging-strand DNA synthesis [66]. Depletion of FEN1 also leads to cohesion defects and FEN1-deficient DT40 cells are sensitive to PARP inhibitor [13] [66]. These results suggests that lagging-strand synthesis might be important for sister chromatid cohesion. "
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    ABSTRACT: The encouraging response rates of BRCA1- and BRCA2-mutated cancers toward PARP inhibitors make it worthwhile to identify other potential determinants of PARP inhibitor responsiveness. Since the Fanconi anemia (FA) pathway coordinates several DNA repair pathways, including homologous recombination in which BRCA1 and BRCA2 play important roles, we investigated whether this pathway harbors other predictors of PARP inhibitor sensitivity. Lymphoblastoid cell lines derived from individuals with FA or clinically related syndromes, such as Warsaw breakage syndrome, were tested for PARP inhibitor sensitivity. Remarkably, we found a strong variability in PARP inhibitor sensitivity among different FANCD1/BRCA2-deficient lymphoblasts, suggesting that PARP inhibitor response depends on the type of FANCD1/BRCA2 mutation. We identified the DNA helicases FANCM and DDX11 as determinants of PARP inhibitor response. These results may extend the utility of PARP inhibition as effective anticancer treatment. Copyright © 2014 Elsevier B.V. All rights reserved.
    DNA Repair 12/2014; 26. DOI:10.1016/j.dnarep.2014.12.003 · 3.11 Impact Factor
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    • "Binding to damaged DNA stimulates synthesis of PAR polymers onto itself, as well as other repair proteins, and mediates recruitment of XRCC1 [10]. In the presence of an inhibitor of PARP catalytic activity, binding of PARP-1 to DNA is stabilized [11]. DNA-bound and inhibited PARP-1 protein is cytotoxic as a function of formation of replication-dependent double-strand breaks [12]. "
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    ABSTRACT: Base excision repair (BER) is a primary mechanism for repair of base lesions in DNA such as those formed by exposure to the DNA methylating agent methyl methanesulfonate (MMS). Both DNA polymerase β (pol β)- and XRCC1-deficient mouse fibroblasts are hypersensitive to MMS. This is linked to a repair deficiency as measured by accumulation of strand breaks and poly(ADP-ribose) (PAR). The interaction between pol β and XRCC1 is important for recruitment of pol β to sites of DNA damage. Endogenous DNA damage can substitute for MMS-induced damage such that BER deficiency as a result of either pol β- or XRCC1-deletion is associated with sensitivity to PARP inhibitors. Pol β shRNA was used to knock down pol β in Xrcc1(+/+) and Xrcc1(-/-) mouse fibroblasts. We determined whether pol β-mediated cellular resistance to MMS and PARP inhibitors resulted entirely from coordination with XRCC1 within the same BER sub-pathway. We find evidence for pol β-dependent cell survival independent of XRCC1 expression for both types of agents. The results suggest a role for pol β-dependent, XRCC1-independent repair. PAR immunofluorescence data are consistent with the hypothesis of a decrease in repair in both pol β knock down cell variants. Published by Elsevier B.V.
    DNA Repair 12/2014; 26. DOI:10.1016/j.dnarep.2014.11.008 · 3.11 Impact Factor
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    • "Another mode of PARP1 inhibition was unravelled in a recent study. According to the new mode of action, PARP1 inhibitors trap target proteins at the sites of DNA damage and form PARP1- protein DNA complexes, which are highly toxic to cells because they block DNA replication (Murai et al., 2012). "
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    ABSTRACT: The highly conserved abundant nuclear protein poly(ADP-ribose)polymerase1 (PARP1) functions at the centre of cellular stress responses and is mainly implied in DNA damage repairing mechanism. Apart from its involvement in DNA damage repair, it does sway multiple vital cellular processes such as cell death pathways, cell aging, insulator function, chromatin modification, transcription, and mitotic apparatus function. Since brain is the principal organ vulnerable to oxidative stress and inflammatory responses, upon stress encounters robust DNA damage can occur and intense PARP1 activation may occur that may lead to various CNS diseases. In the context of soaring interest towards PARP1 as a therapeutic target for newer pharmacological interventions, here in the present review, we are attempting to give a silhouette of the role of PARP1 in the neurological diseases and the potential of its inhibitors to enter clinical translation, along with its structural and functional aspects.
    Neurochemistry International 10/2014; 76. DOI:10.1016/j.neuint.2014.07.001 · 3.09 Impact Factor
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