No abstract

Two classes of quinazolinone derivatives and quinoxaline derivatives were identified as potent and selective poly-(ADP-ribose) polymerase-1 and 2 (PARP-1) and (PARP-2) inhibitors, respectively. In PARP enzyme assays using recombinant PARP-1 and PARP-2, quinazolinone derivatives displayed relatively high selectivity for PARP-1 and quinoxaline derivatives showed superior selectivity for PARP-2. SBDD analysis via a combination of X-ray structural study and homology modeling suggested distinct interactions of inhibitors with PARP-1 and PARP-2. These findings provide a new structural framework for the design of selective inhibitors for PARP-1 and PARP-2.

The massive activation of poly(ADP-ribose) polymerase-1 (PARP-1) by DNA-damaging stimuli, such as exposure to reactive oxygen species (ROS), can lead to cell injury via severe, irreversible depletion of the NAD and ATP pool, and PARP-1 inhibitors have been expected to rescue neurons from degeneration in a number of disease models. We have recently identified 2-{3-[4-(4-chlorophenyl)-1-piperazinyl] propyl}-4(3H)-quinazolinone (FR255595) as a novel and potent PARP-1 inhibitor through structure-based drug design and highthroughput screening. This compound potently inhibited PARP activity with an IC 50 value of 11 nM and was orally active and highly brain penetrable. Here, we show that prevention of PARP activation by FR255595 protects against both ROS-induced cells injury in vitro and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced nigrostriatal dopaminergic damage in an in vivo Parkinson's disease (PD) model. In cell death models in vitro, exposure of hydrogen peroxide induced cell death with PARP overactivation in PC12 cells and SH-SY5Y cells, and preand post-treatment with FR255595 (10 Ϫ9 -10 Ϫ5 M) significantly reduced PARP activation and cell death. In mouse MPTP model, MPTP (20 mg/kg i.p.) intoxication lead to PARP activation and cell damage in the nigrostriatal dopaminergic pathway, which was significantly ameliorated by oral administration of FR255595 (10 -32 mg/kg), both in the substantia nigra and in the striatum via marked reduction of PARP activation, even with delayed treatment. These findings clearly indicate that the novel PARP-1 inhibitor FR255595 exerts neuroprotective effect through its potent PARP-1 inhibitory actions in PD model, suggesting that the drug could be an attractive candidate for several neurodegenerative disorders, including PD.Poly(ADP-ribose) polymerase-1 (PARP-1) is an abundant nuclear enzyme and normally functions in DNA repair, but extensive PARP activation can promote cell death through processes involving energy depletion. It has been reported that reactive oxygen species (ROS)-mediated damage of DNA can activate PARP (Berger, 1985;Szabo and Dawson, 1998) and consumes NAD and consequently ATP, culminating in cell dysfunction or necrosis (Ha and Snyder, 1999). On the other hand, PARP plays a central role in a caspase-independent apoptosis pathway mediated by apoptosis-inducing factor (Yu et al., 2002). Translocation of apoptosis-inducing factor from the mitochondria to the nucleus is dependent on PARP activation in neurons treated with various DNA-damaging stimuli such as N-methly- NЈ-nitro-N-nitrosoguanidine, N-methyl-D-aspartate, or hydrogen peroxide (Yu et al., 2002). This cellular suicide mechanism of both necrosis and apoptosis by PARP activation has been implicated in the pathogenesis of brain injury and neurodegenerative disorders such as Parkinson's disease (PD), a chronic progressive neurologic Article, publication date, and citation information can be found at

A novel class of quinazolinone derivatives as potent poly(ADP-ribose)polymerase-1 (PARP-1) inhibitors has been discovered. Key to success was application of a rational discovery strategy involving structure-based design, combinatorial chemistry, and classical SAR for improvement of potency and bioavailability. The new inhibitors were shown to bind to the nicotinamide-ribose binding site (NI site) and the adenosine-ribose binding site (AD site) of NAD+.

The activation of poly(ADP-ribose) polymerase-1 (PARP-1) after exposure to nitric oxide or oxygen-free radicals can lead to cell injury via severe, irreversible depletion of NAD. Genetic deletion or pharmacological inhibition of PARP-1 attenuates brain injury after focal ischemia and neurotoxicity in several neurodegenerative models in animals. FR247304 (5-chloro-2-[3-(4-phenyl-3,6-dihydro-1(2H)-pyridinyl)propyl]-4(3H)-quinazolinone) is a novel PARP-1 inhibitor that has recently been identified through structure-based drug design. In an enzyme kinetic analysis, FR247304 exhibits potent and competitive inhibition of PARP-1 activity, with a K i value of 35 nM. Here, we show that prevention of PARP activation by FR247304 treatment protects against both reactive oxygen species-induced PC12 cell injury in vitro and ischemic brain injury in vivo. In cell death model, treatment with FR247304 (10 Ϫ8 -10 Ϫ5 M) significantly reduced NAD depletion by PARP-1 inhibition and attenuated cell death after hydrogen peroxide (100 M) exposure. After 90 min of middle cerebral artery occlusion in rats, poly(ADP-ribosy)lation and NAD depletion were markedly increased in the cortex and striatum from 1 h after reperfusion. The increased poly(ADPribose) immunoreactivity and NAD depletion were attenuated by FR247304 (32 mg/kg i.p.) treatment, and FR247304 significantly decreased ischemic brain damage measured at 24 h after reperfusion. Whereas other PARP inhibitors such as 3-aminobenzamide and PJ34 [N-(6-oxo-5,6-dihydro-phenanthridin-2-yl)-N,N-dimethylactamide] showed similar neuroprotective actions, they were less potent in in vitro assays and less efficacious in an in vivo model compared with FR247304. These results indicate that the novel PARP-1 inhibitor FR247304 exerts its neuroprotective efficacy in in vitro and in vivo experimental models of cerebral ischemia via potent PARP-1 inhibition and also suggest that FR247304 or its derivatives could be attractive therapeutic candidates for stroke and neurodegenerative disease.Activation of nuclear enzyme poly(ADP-ribose) polymerase (PARP) promotes cell death through processes involving energy depletion. Reactive oxygen species (ROS)-mediated damage of DNA can activate PARP (Szabo et al., 1996;Eliasson et al., 1997) and consumes NAD and consequently ATP, culminating in cell dysfunction or necrosis (Ha and Snyder, 1999). In addition, PARP plays a central role in the caspase-independent apoptosis pathway mediated by apoptosis-inducing factor. Translocation of apoptosis-inducing factor from the mitochondria to the nucleus is dependent on PARP activation in neurons treated with various DNA-damaging stimuli, including hydrogen peroxide (Yu et al., 2002). This cellular suicide mechanism of both necrosis and apoptosis by PARP activation has been implicated in the pathogenesis of ischemic brain injury and neurodegenerative disorders, and PARP inhibitors have been shown to be effective in animal models of stroke, traumatic brain injury and Parkinson's disease (Cosi et al., 1996;Endres et al...