Long-term protection of brain tissue from cerebral ischemia by peripherally administered peptidomimetic caspase inhibitors

Interleukin-1β converting enzyme (ICE): A comprehensive review on discovery and development of caspase-1 inhibitors

Caspase-1 is a critical mediator of the inflammatory process by activating various pro-inflammatory cytokines such as pro-IL-1β, IL-18 and IL-33. Uncontrolled activation of caspase-1 leads to various cytokines-mediated diseases. Thus, inhibition of Caspase-1 is considered therapeutically beneficial to halt the progression of such diseases. Currently, rilonacept, canakinumab and anakinra are in use for caspase-1-mediated autoinflammatory diseases. However, the poor pharmacokinetic profile of these peptides limits their use as therapeutic agents. Therefore, several peptidomimetic inhibitors have been developed, but only a few compounds (VX-740, VX-765) have advanced to clinical trials; because of their toxic profile. Several small molecule inhibitors have also been progressing based on the three-dimensional structure of caspase-1. However there is no successful candidate available clinically. In this perspective, we highlight the mechanism of caspase-1 activation, its therapeutic potential as a disease target and potential therapeutic strategies targeting caspase-1 with their limitations.

Design, synthesis, biological evaluation and docking studies of sulfonyl isatin derivatives as monoamine oxidase and caspase-3 inhibitors

Sulfonyl isatin derivatives as multifunctional agents showing monoamine oxidase and caspase-3 inhibitory activities in the low micromolar range.

Small Molecule Active Site Directed Tools for Studying Human Caspases

Caspases are proteases of clan CD and were described for the first time more than two decades ago. They play critical roles in the control of regulated cell death pathways including apoptosis and inflammation. Due to their involvement in the development of various diseases like cancer, neurodegenerative diseases, or autoimmune disorders, caspases have been intensively investigated as potential drug targets, both in academic and industrial laboratories. This review presents a thorough, deep, and systematic assessment of all technologies developed over the years for the investigation of caspase activity and specificity using substrates and inhibitors, as well as activity based probes, which in recent years have attracted considerable interest due to their usefulness in the investigation of biological functions of this family of enzymes.

Caspase inhibitors: viral, cellular and chemical

Caspases, key mediators of apoptosis, are a structurally related family of cysteine proteases that cleave their substrates at aspartic acid residues either to cause cell death or to activate cytokines as part of an immune response. They can be controlled upstream by the regulation of signals that lead to zymogen activation, or downstream by inhibitors that prevent them from reaching their substrates. This review specifically looks at caspase inhibitors as distinct from caspase regulators: those produced by the cell itself; those whose genes are carried by viruses; and artificial caspase inhibitors used for research and potentially as therapeutics.

Prevention of ischemic neuronal death by intravenous infusion of a ginseng saponin, ginsenoside Rb(1), that upregulates Bcl-x(L) expression

Almost all agents that exhibit neuroprotection when administered into the cerebral ventricles are ineffective or much less effective in rescuing damaged neurons when infused into the blood stream. Search for an intravenously infusible drug with a potent neuroprotective action is essential for the treatment of millions of patients suffering from acute brain diseases. Here, we report that postischemic intravenous infusion of a ginseng saponin, ginsenoside Rb(1) (gRb(1)) (C(54)H(92)O(23), molecular weight 1109.46) to stroke-prone spontaneously hypertensive rats with permanent occlusion of the middle cerebral artery distal to the striate branches significantly ameliorated ischemia-induced place navigation disability and caused an approximately 50% decrease in the volume of the cortical infarct lesion in comparison with vehicle-infused ischemic controls. In subsequent studies that focused on gRb(1)-induced expression of gene products responsible for neuronal death or survival, we showed that gRb(1) stimulated the expression of the mitochondrion-associated antiapoptotic factor Bcl-x(L) in vitro and in vivo. Moreover, we revealed that a Stat5 responsive element in the bcl-x promoter became active in response to gRb(1) treatment. Ginsenoside Rb(1) appears to be a promising agent not only for the treatment of cerebral stroke, but also for the treatment of other diseases involving activation of mitochondrial cell death signaling.

First-in-class pan caspase inhibitor developed for the treatment of liver disease

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.

Doxycycline reduces cleaved caspase-3 and microglial activation in an animal model of neonatal hypoxia-ischemia

Neonatal hypoxia-ischemia (HI) is a major contributor to many perinatal neurologic disorders and, thus, the search for therapies and effective treatments for the associated brain damage has become increasingly important. The tetracycline derivative, doxycycline (DOXY), has been reported to be neuroprotective in adult animal models of cerebral ischemia. To investigate the putative neuroprotective effects of DOXY in an animal model of neonatal HI, a time-course study was run such that pups received either DOXY (10 mg/kg) or VEH immediately before hypoxia, 1, 2, or 3 hours after HI (n=6). At 7 days after injury, the pups were euthanized, and the brains were removed and processed for immunohistochemical and Western blot analyses using antibodies against specific markers for neurons, apoptotic markers, microglia, oligodendrocytes, and astrocytes. Results showed that in vulnerable brain regions including the hippocampal formation, thalamus, striatum, cerebral cortex and white matter tracts, DOXY significantly decreased caspase-3 immunoreactivity (a marker of apoptosis), promoted neuronal survival, inhibited microglial activation and reduced reactive astrocytosis compared with VEH-treated HI pups. These effects were found to occur in a time-dependent manner. Taken together, these results strongly suggest that doxycycline has potential as a pharmacological treatment for mild HI in neonates.

Design, synthesis, and application of azabicyclo[X.Y.0]alkanone amino acids as constrained dipeptide surrogates and peptide mimics

Azabicyclo[X.Y.0]alkanone amino acids are challenging synthetic targets and useful tools for studying structure-activity relationships of native peptide ligands. They have been employed to increase potency and stability in conformationally rigid enzyme inhibitors and receptor ligands. Since last reviewed in 1997, activity in their synthesis and application has increased significantly and access is now available to a wider diversity of these peptide mimics. This review focuses on recent syntheses of these heterocyclic amino acids and their application in the investigation of biologically active peptides and peptide mimics.

Oxamyl dipeptide caspase inhibitors developed for the treatment of stroke

Structural modifications were made to a previously described acyl dipeptide caspase inhibitor, leading to the oxamyl dipeptide series. Subsequent SAR studies directed toward the warhead, P2, and P4 regions of this novel peptidomimetic are described herein.

Discovery of potent antagonists of the antiapoptotic protein XIAP for the treatment of cancer

Inhibitor of apoptosis (IAP) proteins are overexpressed in many cancers and have been implicated in tumor growth, pathogenesis, and resistance to chemo- or radiotherapy. On the basis of the NMR structure of a SMAC peptide complexed with the BIR3 domain of X-linked IAP (XIAP), a novel series of XIAP antagonists was discovered. The most potent compounds in this series bind to the baculovirus IAP repeat 3 (BIR3) domain of XIAP with single-digit nanomolar affinity and promote cell death in several human cancer cell lines. In a MDA-MB-231 breast cancer mouse xenograft model, these XIAP antagonists inhibited the growth of tumors. Close structural analogues that showed only weak binding to the XIAP-BIR3 domain were inactive in the cellular assays and showed only marginal in vivo activity. Our results are consistent with a mechanism in which ligands for the BIR3 domain of XIAP induce apoptosis by freeing up caspases. The present study validates the BIR3 domain of XIAP as a target and supports the use of small molecule XIAP antagonists as a potential therapy for cancers that overexpress XIAP.

Structure-activity relationships within a series of caspase inhibitors: effect of leaving group modifications

Various aryloxy methyl ketones of the 1-naphthyloxyacetyl-Val-Asp backbone have been prepared. A systematic study of their structure-activity relationship (SAR) related to caspases 1, 3, 6, and 8 is reported. Highly potent irreversible broad-spectrum caspase inhibitors have been identified. Their efficacy in cellular models of cell death and inflammation are also discussed.

MX1013, a dipeptide caspase inhibitor with potent in vivo antiapoptotic activity

1. Caspases play a critical role in apoptosis, and are considered to be key targets for the design of cytoprotective drugs. As part of our antiapoptotic drug-discovery effort, we have synthesized and characterized Z-VD-fmk, MX1013, as a potent, irreversible dipeptide caspase inhibitor. 2. MX1013 inhibits caspases 1, 3, 6, 7, 8, and 9, with IC50 values ranging from 5 to 20 nm. MX1013 is selective for caspases, and is a poor inhibitor of noncaspase proteases, such as cathepsin B, calpain I, or Factor Xa (IC50 values >10 microm). 3. In several cell culture models of apoptosis, including caspase 3 processing, PARP cleavage, and DNA fragmentation, MX1013 is more active than tetrapeptide- and tripeptide-based caspase inhibitors, and blocked apoptosis at concentrations as low as 0.5 microm. 4. MX1013 is more aqueous soluble than tripeptide-based caspase inhibitors such as Z-VAD-fmk. 5. At a dose of 1 mg kg-1 i.v., MX1013 prevented liver damage and the lethality caused by Fas death receptor activation in the anti-Fas mouse-liver apoptosis model, a widely used model of liver failure. 6. At a dose of 20 mg kg-1 (i.v. bolus) followed by i.v. infusion for 6 or 12 h, MX1013 reduced cortical damage by approximately 50% in a model of brain ischemia/reperfusion injury. 7. At a dose of 20 mg kg-1 (i.v. bolus) followed by i.v. infusion for 12 h, MX1013 reduced heart damage by approximately 50% in a model of acute myocardial infarction. 8. Based on these studies, we conclude that MX1013, a dipeptide pan-caspase inhibitor, has a good combination of in vitro and in vivo properties. It has the ability to protect cells from a variety of apoptotic insults, and is systemically active in three animal models of apoptosis, including brain ischemia.

Apoptosis and brain ischaemia

There is increasing evidence that some neuronal death after brain ischaemia is mediated by the action of cysteine-requiring aspartate-directed proteases (caspases), the proteases responsible for apoptosis in mammals, although this form of neuronal death is not always accompanied by the morphological changes that are typical of apoptosis in other tissues. Caspase-mediated neuronal death is more extensive after transient than permanent focal brain ischaemia and may contribute to delayed loss of neurons from the penumbral region of infarcts. The activation of caspases after brain ischaemia is largely consequent on the translocation of Bax, Bak, and other BH3-only members of the Bcl-2 family to the mitochondrial outer membrane and the release of cytochrome c, procaspase-9, and apoptosis activating factor-1 (Apaf-1) from the mitochondrial intermembrane space. How exactly ischaemia induces this translocation is still poorly understood. NF-kappaB, the c-jun N-terminal kinase-c-Jun pathway, p53, E2F1, and other transcription factors are probably all involved in regulating the expression of BH3-only proteins after brain ischaemia, and mitochondrial translocation of Bad from sequestering cytosolic proteins is promoted by inactivation of the serine-threonine kinase, Akt. Other processes that are probably involved in the activation of caspases after brain ischaemia include the mitochondrial release of the second mitochondrial activator of caspases (Smac) or direct inhibitor-of-apoptosis-binding protein with low pI (DIABLO), the accumulation of products of lipid peroxidation, a marked reduction in protein synthesis, and the aberrant reentry of neurons into the cell cycle. Non-caspase-mediated neuronal apoptosis may also occur, but there is little evidence to date that this makes a significant contribution to brain damage after ischaemia. The intracellular processes that contribute to caspase-mediated neuronal death after ischaemia are all potential targets for therapy. However, anti-apoptotic interventions in stroke patients will require detailed evaluation using a range of outcome measures, as some such interventions seem simply to delay neuronal death and others to preserve neurons but not neuronal function.

Apocytochrome c blocks caspase-9 activation and Bax-induced apoptosis

Complex networks of signaling pathways control the apoptotic response and, therefore, cell survival. However, these networks converge on a common machinery, of which the caspase cysteine proteases are key components. Diverse apoptotic stimuli release holocytochrome c from mitochondria, allowing holocytochrome c to bind apoptotic protease activating factor-1 (Apaf-1), which in turn binds caspase-9 both activating this caspase and forming an Apaf-1/caspase-9 holoenzyme. Cytochrome c lacking heme (the apo form) cannot support caspase activation, although the reason for this has not been studied. Here we show that apocytochrome c still binds Apaf-1 and that it can block holo-dependent caspase activation in a cell-free system. In addition we show that overexpression of apocytochrome c blocks Bax-induced apoptosis in cells. Thus it is possible to modulate cell survival by interfering with the Apaf-1/cytochrome c interaction. Given the key role played by Apaf-1/cytochrome c in the apoptotic process, and the role of apoptosis in degenerative disease, this interaction may serve as a novel therapeutic target.