Synthesis and Evaluation of a Mitochondria-Targeting Poly(ADP-ribose) Polymerase-1 Inhibitor

Abstract

The poly(ADP-ribose) polymerase (PARP) family of enzymes plays a crucial role in cellular and molecular processes including DNA damage detection and repair and transcription; indeed, PARP inhibitors are under clinical evaluation as chemotherapeutic adjuncts given their capacity to impede genomic DNA repair in tumor cells. Conversely, overactivation of PARP can lead to NAD depletion, mitochondrial energy failure, and cell death. Since PARP activation facilitates genomic but impedes mitochondrial DNA repair, nonselective PARP inhibitors are likely to have opposing effects in these cellular compartments. Herein, we describe the synthesis and evaluation of the mitochondria-targeting PARP inhibitor, XJB-veliparib. Attachment of the hemigramicidin S pentapeptide isostere for mitochondrial targeting using a flexible linker at the primary amide site of veliparib did not disrupt PARP affinity or inhibition. XJB-veliparib was effective at low nanomolar concentrations (10-100 nM) and more potent than veliparib in protection from oxygen-glucose deprivation (OGD) in primary cortical neurons. Both XJB-veliparib and veliparib (10 nM) preserved mitochondrial NAD after OGD; however, only XJB-veliparib prevented release of NAD into cytosol. XJB-veliparib (10 nM) appeared to inhibit poly(ADP-ribose) polymer formation in mitochondria and preserve mitochondrial cytoarchitecture after OGD in primary cortical neurons. After 10 nM exposure, XJB-veliparib was detected by LC-MS in mitochondria but not nuclear-enriched fractions in neurons and was observed in mitoplasts stripped of the outer mitochondrial membrane obtained from HT22 cells. XJB-veliparib was also effective at preventing glutamate-induced HT22 cell death at micromolar concentrations. Importantly, in HT22 cells exposed to HO to produce DNA damage, XJB-veliparib (10 μM) had no effect on nuclear DNA repair, in contrast to veliparib (10 μM) where DNA repair was retarded. XJB-veliparib and analogous mitochondria-targeting PARP inhibitors warrant further evaluation in vitro and in vivo, particularly in conditions where PARP overactivation leads to mitochondrial energy failure and maintenance of genomic DNA integrity is desirable, e.g., ischemia, oxidative stress, and radiation exposure.

The PARP inhibitor olaparib exerts beneficial effects in mice subjected to cecal ligature and puncture and in cells subjected to oxidative stress without impairing DNA integrity: A potential opportunity for repurposing a clinically used oncological drug for the experimental therapy of sepsis

“…This latter finding may be related to effects on the mitochondrial isoform of PARP, which has a qualitatively different role in the regulation of mitochondrial DNA repair than its nuclear counterpart [36]. At the lower levels of oxidative stress -in line with prior observations [36][37][38] -the H 2 0 rinduced DNA damage was preferential to mitochondrial, as opposed to nuclear DNA (Fig. 30B).…”

Poly(ADP-ribose) polymerase 1 regulates mitochondrial DNA repair in an NAD-dependent manner

“…Additionally, perhaps preventing PARP1 transport into mitochondria via inhibition of the Mitofilin/PARP1 interaction could overcome certain PARP1 side-effects in treatment of cardiovascular disorders. As mitochondria-specific PARP1 inhibitors have been synthesized ( 56 ), they can be used to further tease out PARP1’s function in mitochondria and nucleus.…”

Mitochondrial Protection by PARP Inhibition

“…As it was demonstrated in a number of in vitro, ex vivo and in vivo experiments, nuclear PARP inhibition achieved either by pharmacological means or by gene silencing, activates Akt [92,95,96]. This activation could become so substantial that it significantly contributes to the mitochondria-and cytoprotective effects of PARP inhibitors in experimental or pathological oxidative stress situations [97][98][99][100][101]. Recently, we presented a mechanism ( Figure 1) for PARP inhibition-induced Akt activation [102].…”