We investigated the pharmacological profiles of DR2313 [2-methyl-3,5,7,8-tetrahydrothiopyrano[4,3-d]pyrimidine-4-one], a newly synthesized poly(ADP-ribose) polymerase (PARP) inhibitor, and its neuroprotective effects on ischemic injuries in vitro and in vivo. DR2313 competitively inhibited poly(ADPribosyl)ation in nuclear extracts of rat brain in vitro (K i ϭ 0.23 M). Among several NAD ϩ -utilizing enzymes, DR2313 was specific for PARP but not selective between PARP-1 and PARP-2. DR2313 also showed excellent profiles in water solubility and rat brain penetrability. In in vitro models of cerebral ischemia, exposure to hydrogen peroxide or glutamate induced cell death with overactivation of PARP, and treatment with DR2313 reduced excessive formation of poly(ADP-ribose) and cell death. In both permanent and transient focal ischemia models in rats, pretreatment with DR2313 (10 mg/kg i.v. bolus and 10 mg/kg/h i.v. infusion for 6 h) significantly reduced the cortical infarct volume. To determine the therapeutic time window of neuroprotection by DR2313, the effect of posttreatment was examined in transient focal ischemia model and compared with that of a free radical scavenger, MCI-186 (3-methyl-1-phenyl-2-pyrazolone-5-one). Pretreatment with MCI-186 (3 mg/kg i.v. bolus and 3 mg/kg/h i.v. infusion for 6 h) significantly reduced the infarct volume, whereas the posttreatment failed to show any effects. In contrast, posttreatment with DR2313 (same regimen) delaying for 2 h after ischemia still prevented the progression of infarction. These results indicate that DR2313 exerts neuroprotective effects via its potent PARP inhibition, even when the treatment is initiated after ischemia. Thus, a PARP inhibitor like DR2313 may be more useful in treating acute stroke than a free radical scavenger.The excessive release of the excitotoxic amino acid glutamate plays a critical role in the pathogenesis of neuronal cell death following cerebral ischemia. NO produced by nNOS has been implicated in N-methyl-D-asparate (NMDA) receptor-mediated neurotoxicity of glutamate in cerebral ischemia . NMDA receptor activation causes an increase in intracellular calcium concentration leading to activation of nNOS. A part of the neurotoxicity evoked by NO is a result of the reaction of NO with superoxide anion to form a highly toxic radical, peroxynitrite Pieper et al., 1999). Postischemic injury is also exacerbated by the increased formation of hydroxyl radical, the most reactive molecule of all oxygen radicals (Chan, 2001). These reactive oxygen species (ROS) can contribute to the DNA strand breakage, which is followed by overactivation of poly(ADP-ribose) polymerase-1 (PARP-1; EC 2.4.2.30) (Szabo and Dawson, 1998;Pieper et al., 1999).PARP-1 is an abundant nuclear protein which is activated Article, publication date, and citation information can be found at