Activation of caspase-3 requires proteolytic processing of the inactive zymogen into p18 and p12 subunits. We generated a rabbit polyclonal antiserum, CM1, which recognizes the p18 subunit of cleaved caspase-3 but not the zymogen. CM1 demonstrated an apparent specificity for activated caspase-3 by specifically immunolabeling only apoptotic but not necrotic cortical neurons in vitro. In the embryonic mouse nervous system, CM1 immunoreactivity was detected in neurons undergoing programmed cell death and was markedly increased in Bcl-x L -deficient embryos and decreased in Bax-deficient embryos. CM1 immunoreactivity was absent in the nervous system of caspase-3-deficient mouse embryos and in neurons cultured from caspase-3-deficient mice. Along with neuronal somata, extensive neuritic staining was seen in apoptotic neurons. These studies indicate that caspase-3 is activated during apoptosis in the developing nervous system in vivo and that CM1 is a useful reagent for its in situ detection.

A series of oxamyl dipeptides were optimized for pan caspase inhibition, anti-apoptotic cellular activity and in vivo efficacy. This structure-activity relationship study focused on the P4 oxamides and warhead moieties. Primarily on the basis of in vitro data, inhibitors were selected for study in a murine model of alpha-Fas-induced liver injury. IDN-6556 (1) was further profiled in additional in vivo models and pharmacokinetic studies. This first-in-class caspase inhibitor is now the subject of two Phase II clinical trials, evaluating its safety and efficacy for use in liver disease.

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Apoptotic cell death occurs in the injured and diseased central nervous system. It is mediated by a family of caspases, which are activated by the lethal stimulus and cleave multiple protein substrates that are critical for cell viability. Previous studies demonstrated that caspase-mediated apoptotic cell death contributes to the loss of brain tissue after experimental cerebral ischemia and that peptidic caspase inhibitors can be efficacious in reducing infarct size after icv administration. Here we present the novel small molecule peptidomimetic caspase inhibitor IDN5370/CGP82630, which belongs to the structural class of oxoazepinoindoline caspase inhibitors. It is 10-100-fold more potent than current peptidic inhibitors in inhibiting multiple caspases in vitro and promoting neuronal survival. IDN5370 and a derivative, IDN7866, were tested for their ability to reduce infarct size after permanent and transient cerebral ischemia. When administered icv to rats subjected to permanent middle cerebral artery occlusion (MCAO), IDN5370 significantly reduced cortical infarct as measured by magnetic resonance imaging at 2 days after artery occlusion. Protection of brain tissue persisted for 28 days after artery occlusion. To determine whether compounds of this structural class could reduce infarct size after peripheral administration, IDN7866, which penetrates the blood-brain barrier and inhibits caspase 3 in situ in the hippocampus after kainate-induced seizures, was administered iv in both permanent and transient MCAO models. Infarct size was reduced significantly in both models 24 h after artery occlusion. These results demonstrate that peripherally administered peptidomimetic caspase inhibitors can attenuate brain injury after cerebral ischemia and confer a long-lasting protective effect on the infarcted brain tissue. Drug Dev. Res. 52:579-586, 2001.