GBT021601 improves red blood cell health and the pathophysiology of sickle cell disease in a murine model.

The pathophysiologic mechanism of sickle cell disease (SCD) involves polymerization of deoxygenated haemoglobin S (HbS), leading to red blood cell (RBC) sickling, decreased RBC deformability, microvascular obstruction, haemolysis, anaemia and downstream clinical complications. Pharmacological increase in the concentration of oxygenated HbS in RBCs has been shown to be a novel approach to inhibit HbS polymerization and reduce RBC sickling and haemolysis. We report that GBT021601, a small molecule that increases HbS-oxygen affinity, inhibits HbS polymerization and prevents RBC sickling in blood from patients with SCD. Moreover, in a murine model of SCD (SS mice), GBT021601 reduces RBC sickling, improves RBC deformability, prolongs RBC half-life and restores haemoglobin levels to the normal range, while improving oxygen delivery and increasing tolerance to severe hypoxia. Notably, oral dosing of GBT021601 in animals results in higher levels of Hb occupancy than voxelotor and suggests the feasibility of once-daily dosing in humans. In summary, GBT021601 improves RBC health and normalizes haemoglobin in SS mice, suggesting that it may be useful for the treatment of SCD. These data are being used as a foundation for clinical research and development of GBT021601.

Increased hemoglobin affinity for oxygen with GBT1118 improves hypoxia tolerance in sickle cell mice.

Therapeutic agents that increase the Hb affinity for oxygen (O2) could, in theory, lead to decreased O2 release from Hb and impose a hypoxic risk to tissues. In this study, GBT1118, an allosteric modifier of Hb affinity for O2, was used to assess the impact of increasing Hb affinity for O2 on brain tissue oxygenation, blood pressure, heart rate, O2 delivery, and tolerance to hypoxia in Townes transgenic sickle cell disease (SCD) mice. Brain oxygenation and O2 delivery were studied during normoxia and severe hypoxic challenges. Chronic treatment with GBT1118 increased Hb affinity for O2, reducing the Po2 for 50% HbO2 saturation (P50) in SCD mice from 31 mmHg to 18 mmHg. This treatment significantly reduced anemia, increasing hematocrit by 33%, improved cardiac output (CO), and O2 delivery and extraction. Chronically increasing Hb affinity for O2 with GBT1118 preserved cortical O2 tension during normoxia, improved cortical O2 tension during hypoxia, and increased tolerance to severe hypoxia in SCD mice. Independent of hematological changes induced by chronic treatment, a single dose of GBT1118 significantly improved tolerance to hypoxia, highlighting the benefits of increasing Hb affinity for O2 and consequently reducing sickling of RBCs in blood during hypoxia in SCD.NEW & NOTEWORTHY Chronic pharmacologically increased hemoglobin affinity for oxygen in sickle cell disease mice alleviated hematological consequences of sickle cell disease, increasing RBC half-life, hematocrit, and hemoglobin concentration, while also decreasing reticulocyte count. Additionally, chronically increased hemoglobin affinity for oxygen significantly improved survival as well as cortical tissue oxygenation in sickle cell disease mice during hypoxia, suggesting that oxygen delivery and utilization is improved by increased hemoglobin affinity for oxygen.

Pharmacokinetics and pharmacodynamics of voxelotor (GBT440) in healthy adults and patients with sickle cell disease.

AIMS: Voxelotor (previously GBT440) is a haemoglobin (Hb) modulator that increases Hb-oxygen affinity, thereby reducing Hb polymerization and sickling of red blood cells (RBCs), being developed as a once-daily oral drug to treat sickle cell disease (SCD). This first-in-human study evaluated the safety, tolerability, pharmacokinetics and pharmacodynamics of voxelotor in healthy volunteers and SCD patients. METHODS: A total of 40 healthy volunteers (100, 400, 1000, 2000 or 2800 mg) and 8 SCD patients (1000 mg) were randomly assigned to a single dose of voxelotor once daily (n = 6 per group) or placebo (n = 2 per group). Twenty-four healthy volunteers received multiple doses of voxelotor once daily for 15 days (300, 600 or 900 mg, n = 6 per group) or placebo (n = 2 per group). RESULTS: Voxelotor was well tolerated and exhibited a linear pharmacokinetic profile and a half-life ranging from 61 ± 7 h to 85 ± 7 h. High partitioning into the RBC compartment provides evidence of highly specific binding to Hb. Voxelotor exhibited a concentration-dependent left-shift of oxygen equilibrium curves. Percent Hb modification following 900 mg voxelotor for 15 days was 38 ± 9%. Terminal half-life of voxelotor in SCD patients (50 ± 3 h) was shorter than in healthy volunteers. Evaluation of erythropoietin, exercise testing, and haematologic parameters were consistent with normal oxygen delivery during both rest and exercise. CONCLUSION: This first-in-human study demonstrates voxelotor was well tolerated in SCD patients and healthy volunteers and established proof of mechanism on increasing Hb-oxygen affinity.

GBT1118, a potent allosteric modifier of hemoglobin O2 affinity, increases tolerance to severe hypoxia in mice.

Adaptation to hypoxia requires compensatory mechanisms that affect O2 transport and utilization. Decreased hemoglobin (Hb) O2 affinity is considered part of the physiological adaptive process to chronic hypoxia. However, this study explores the hypothesis that increased Hb O2 affinity can complement acute physiological responses to hypoxia by increasing O2 uptake and delivery compared with normal Hb O2 affinity during acute severe hypoxia. To test this hypothesis, Hb O2 affinity in mice was increased by oral administration of 2-hydroxy-6-{[(2S)-1-(pyridine-3-carbonyl)piperidin-2yl] methoxy}benzaldehyde (GBT1118; 70 or 140 mg/kg). Systemic and microcirculatory hemodynamics and oxygenation parameters were studied during hypoxia in awake-instrumented mice. GBT1118 increased Hb O2 affinity and decreased the Po2 at which 50% of Hb is saturated with O2 (P50) from 43 ± 1.1 to 18.3 ± 0.9 mmHg (70 mg/kg) and 7.7 ± 0.2 mmHg (140 mg/kg). In a dose-dependent fashion, GBT1118 increased arterial O2 saturation by 16% (70 mg/kg) and 40% (140 mg/kg) relative to the control group during 5% O2 hypoxia. In addition, a GBT1118-induced increase in Hb O2 affinity reduced hypoxia-induced hypotension compared with the control group. Moreover, microvascular blood flow was higher during hypoxia in GBT1118-treated groups than the control group. The increased O2 saturation and improved blood flow in GBT1118-treated groups preserved higher interstitial tissue Po2 than in the control group during 5% O2 hypoxia. In conclusion, increased Hb O2 affinity enhanced physiological tolerance to hypoxia, as evidenced by improved hemodynamics and tissue oxygenation. Therefore, pharmacologically induced increases in Hb O2 affinity become a potential therapeutic approach to improve tissue oxygenation in pulmonary diseases characterized by severe hypoxemia.NEW & NOTEWORTHY This study establishes that pharmacological modification of hemoglobin O2 affinity can be a promising and novel therapeutic strategy for the treatment of hypoxic hypoxia and paves the way for the clinical development of molecules that prevent hypoxemia.

GBT440 increases haemoglobin oxygen affinity, reduces sickling and prolongs RBC half-life in a murine model of sickle cell disease.

A major driver of the pathophysiology of sickle cell disease (SCD) is polymerization of deoxygenated haemoglobin S (HbS), which leads to sickling and destruction of red blood cells (RBCs) and end-organ damage. Pharmacologically increasing the proportion of oxygenated HbS in RBCs may inhibit polymerization, prevent sickling and provide long term disease modification. We report that GBT440, a small molecule which binds to the N-terminal α chain of Hb, increases HbS affinity for oxygen, delays in vitro HbS polymerization and prevents sickling of RBCs. Moreover, in a murine model of SCD, GBT440 extends the half-life of RBCs, reduces reticulocyte counts and prevents ex vivo RBC sickling. Importantly, oral dosing of GBT440 in animals demonstrates suitability for once daily dosing in humans and a highly selective partitioning into RBCs, which is a key therapeutic safety attribute. Thus, GBT440 has the potential for clinical use as a disease-modifying agent in sickle cell patients.

The sigma-1 receptor enhances brain plasticity and functional recovery after experimental stroke.

Stroke leads to brain damage with subsequent slow and incomplete recovery of lost brain functions. Enriched housing of stroke-injured rats provides multi-modal sensorimotor stimulation, which improves recovery, although the specific mechanisms involved have not been identified. In rats housed in an enriched environment for two weeks after permanent middle cerebral artery occlusion, we found increased sigma-1 receptor expression in peri-infarct areas. Treatment of rats subjected to permanent or transient middle cerebral artery occlusion with 1-(3,4-dimethoxyphenethyl)-4-(3-phenylpropyl)piperazine dihydrochloride, an agonist of the sigma-1 receptor, starting two days after injury, enhanced the recovery of lost sensorimotor function without decreasing infarct size. The sigma-1 receptor was found in the galactocerebroside enriched membrane microdomains of reactive astrocytes and in neurons. Sigma-1 receptor activation increased the levels of the synaptic protein neurabin and neurexin in membrane rafts in the peri-infarct area, while sigma-1 receptor silencing prevented sigma-1 receptor-mediated neurite outgrowth in primary cortical neuronal cultures. In astrocytic cultures, oxygen and glucose deprivation induced sigma-1 receptor expression and actin dependent membrane raft formation, the latter blocked by sigma-1 receptor small interfering RNA silencing and pharmacological inhibition. We conclude that sigma-1 receptor activation stimulates recovery after stroke by enhancing cellular transport of biomolecules required for brain repair, thereby stimulating brain plasticity. Pharmacological targeting of the sigma-1 receptor provides new opportunities for stroke treatment beyond the therapeutic window of neuroprotection.

Rheological Impact of GBT1118 Cessation in a Sickle Mouse Model.

In sickle cell disease (SCD), higher whole blood viscosity is a risk factor for vaso-occlusive crisis, avascular necrosis, and proliferative retinopathy. Blood viscosity is strongly impacted by hemoglobin (Hb) levels and red blood cell (RBC) deformability. Voxelotor is a hemoglobin S (HbS) polymerization inhibitor with anti-sickling properties that increases the Hb affinity for oxygen, thereby reducing HbS polymerization. In clinical trials, voxelotor increased Hb by an average of 1g/dl, creating concern that this rise in Hb could increase viscosity, particularly when the drug was cleared. To investigate this potential rebound hyperviscosity effect, we treated SCD mice with GBT1118, a voxelotor analog, and stopped the treatment to determine the effect on blood viscosity and RBC deformability under a range of oxygen concentrations. GBT1118 treatment increased Hb, improved RBC deformability by increasing the elongation index under normoxic (EImax) and hypoxic conditions (EImin), and decreased the point of sickling (PoS) without increasing blood viscosity. The anti-sickling effects and improvement of RBC deformability balanced the effect of increased Hb such that there was no increase in blood viscosity. Forty-eight hours after ceasing GBT1118, Hb declined from the rise induced by treatment, viscosity did not increase, and EImin remained elevated compared to control animals. Hb and PoS were not different from control animals, suggesting a return to native oxygen affinity and clearance of the drug. RBC deformability did not return to baseline, suggesting some residual rheological improvement. These data suggest that concerns regarding viscosity rise above pre-treatment levels upon sudden cessation of voxelotor are not warranted.

The effect of the antisickling compound GBT1118 on the permeability of red blood cells from patients with sickle cell anemia.

Sickle cell anemia (SCA) is one of the commonest severe inherited disorders. Nevertheless, effective treatments remain inadequate and novel ones are avidly sought. A promising advance has been the design of novel compounds which react with hemoglobin S (HbS) to increase oxygen (O2 ) affinity and reduce sickling. One of these, voxelotor (GBT440), is currently in advanced clinical trials. A structural analogue, GBT1118, was investigated in the current work. As RBC dehydration is important in pathogenesis of SCA, the effect of GBT1118 on RBC cation permeability was also studied. Activities of Psickle , the Gardos channel and the KCl cotransporter (KCC) were all reduced. Gardos channel and KCC activities were also inhibited in RBCs treated with Ca2+ ionophore or the thiol reagent N-ethylmaleimide, indicative of direct effects on these two transport systems. Consistent with its action on RBC membrane transporters, GBT1118 significantly increased RBC hydration. RBC hemolysis was reduced in a nonelectrolyte lysis assay. Further to its direct effects on O2 affinity, GBT1118 was therefore found to reduce RBC shrinkage and fragility. Findings reveal important effects of GBT1118 on protecting sickle cells and suggest that this is approach may represent a useful therapy for amelioration of the clinical complications of SCA.

Expression and function of striatal enriched protein tyrosine phosphatase is profoundly altered in cerebral ischemia.

Striatal enriched protein tyrosine phosphatase (STEP) acts in the central nervous system to dephosphorylate a number of important proteins involved in synaptic function including ERK and NMDA receptor subunits. These proteins are also linked to stroke, in which cerebral ischemia triggers a complex cascade of events. Here we demonstrate that STEP is regulated at both the transcriptional and the post-transcriptional levels in rat models of cerebral ischemia and that its regulation may play a role in the outcome of ischemic insults. After transient middle cerebral artery occlusion, there are profound decreases in the levels of STEP mRNA, whilst in global ischemia STEP mRNA is selectively down-regulated in areas susceptible to ischemic damage. In a neuroprotective preconditioning paradigm, and in regions of the brain that are relatively resistant to ischemic damage, STEP mRNA levels are increased. Furthermore, there is a significant processing of STEP after ischemia to generate a novel species, STEP(33), resulting in a redistribution of STEP from membrane-bound to soluble compartments. Concomitant with the cleavage of mature forms of STEP, there are changes in the phosphorylation state of ERK. We show that the cleavage of STEP leads to a catalytically active form, but this cleaved form no longer binds to and dephosphorylates its substrate pERK. Therefore, in response to ischemic insults, there are profound reductions in both the amount and the activity of STEP, its localization, as well as the activity of one of its key substrates, pERK. These changes in STEP may reflect a critical role in the outcomes of ischemic brain injury.

GBT440 reverses sickling of sickled red blood cells under hypoxic conditions in vitro.

Sickle cell disease is characterized by hemolytic anemia, vasoocclusion and early mortality. Polymerization of hemoglobin S followed by red blood cell sickling and subsequent vascular injury are key events in the pathogenesis of sickle cell disease. Sickled red blood cells are major contributors to the abnormal blood rheology, poor microvascular blood flow and endothelial injury in sickle cell disease. Therefore, an agent that can prevent and or reverse sickling of red blood cells, may provide therapeutic benefit for the treatment of sickle cell disease. We report here that GBT440, an anti-polymerization agent being developed for the chronic treatment of sickle cell disease, increases hemoglobin oxygen affinity and reverses in vitro sickling of previously sickled red blood cells under hypoxic conditions. Our results suggest that besides preventing sickling of red blood cells, GBT440 may mitigate vasoocclusion and microvascular dysfunction by reversing sickling of circulating sickled red blood cells in vivo.

GBT440 improves red blood cell deformability and reduces viscosity of sickle cell blood under deoxygenated conditions.

BACKGROUND: In sickle cell disease (SCD), polymerization of hemoglobin S (HbS) leads to the formation of rigid, non-deformable sickled RBCs. Loss of RBC deformability, sickling and irreversible membrane damage causes abnormal blood rheology, and increases viscosity which contributes to vasoocclusion and other SCD pathophysiology. GBT440 (generic name voxelotor) is a novel anti-polymerization and anti-sickling agent currently undergoing clinical evaluation for the treatment of SCD. OBJECTIVE: The purpose of this study was to determine the effects of GBT440 on deformability of sickle RBCs (SS RBCs) and the hyperviscosity of sickle cell blood (SS blood). METHODS: The mechanical and rheological properties of GBT440-treated SS RBCs were measured using micropipette and filtration techniques. The viscosity of sickle blood was measured using a Wells-Brookfield cone/plate viscometer. RESULTS: GBT440 restored movement of deoxygenated SS RBCs through a gel filtration column and reduced the pressure required to pass SS RBCs through a polycarbonate filter. Moreover, GBT440 decreased the membrane shear elastic modulus of SS RBCs assessed via micropipette aspiration and reduced the hyperviscosity of SS blood under deoxygenated conditions. CONCLUSIONS: GBT440 maintains SS RBC deformability and improves SS blood viscosity by inhibiting HbS polymerization under deoxygenated conditions. These results further support development of GBT440 as a disease-modifying agent in SCD patients.

Development and validation of an oxygen dissociation assay, a screening platform for discovering, and characterizing hemoglobin-oxygen affinity modifiers.

INTRODUCTION: Hemoglobin (Hb) is a critical molecule necessary for all vertebrates to maintain aerobic metabolism. Hb-oxygen (O2) affinity modifiers have been studied to address various diseases including sickle cell disease, hypoxemia, tumor hypoxia, and wound healing. However, drug development of exogenous Hb modifiers has been hindered by the lack of a technique to rapidly screen compounds for their ability to alter Hb-O2 affinity. We have developed a novel screening assay based upon the spectral changes observed during Hb deoxygenation and termed it the oxygen dissociation assay (ODA). METHODOLOGY: ODA allows for the quantitation of oxygenated Hb at given time points during Hb deoxygenation on a 96-well plate. This assay was validated by comparing the ability of 500 Hb modifiers to alter the Hb-O2 affinity in the ODA vs the oxygen equilibrium curves obtained using the industry standard Hemox Analyzer instrument. RESULTS: A correlation (R2) of 0.7 indicated that the ODA has the potential to screen and identify potent exogenous Hb modifiers. In addition, it allows for concurrent comparison of compounds, concentrations, buffers, or pHs on the level of Hb oxygenation. CONCLUSION: With a cost-effective, simple, rapid, and highly adaptable assay, the ODA will allow researchers to rapidly characterize Hb-O2 affinity modifiers.

Discovery of GBT440, an Orally Bioavailable R-State Stabilizer of Sickle Cell Hemoglobin.

We report the discovery of a new potent allosteric effector of sickle cell hemoglobin, GBT440 (36), that increases the affinity of hemoglobin for oxygen and consequently inhibits its polymerization when subjected to hypoxic conditions. Unlike earlier allosteric activators that bind covalently to hemoglobin in a 2:1 stoichiometry, 36 binds with a 1:1 stoichiometry. Compound 36 is orally bioavailable and partitions highly and favorably into the red blood cell with a RBC/plasma ratio of ∼150. This partitioning onto the target protein is anticipated to allow therapeutic concentrations to be achieved in the red blood cell at low plasma concentrations. GBT440 (36) is in Phase 3 clinical trials for the treatment of sickle cell disease (NCT03036813).

GBT440 Inhibits Sickling of Sickle Cell Trait Blood Under In Vitro Conditions Mimicking Strenuous Exercise.

In sickle cell trait (SCT), hemoglobin A (HbA) and S (HbS) are co-expressed in each red blood cell (RBC). While homozygous expression of HbS (HbSS) leads to polymerization and sickling of RBCs resulting in sickle cell disease (SCD) characterized by hemolytic anemia, painful vaso-occlusive episodes and shortened life-span, SCT is considered a benign condition usually with minor or no complications related to sickling. However, physical activities that cause increased tissue oxygen demand, dehydration and/or metabolic acidosis leads to increased HbS polymerization and life-threatening complications including death. We report that GBT440, an agent being developed for the treatment of SCD, increases the affinity of oxygen for Hb and inhibits in vitro polymerization of a mixture of HbS and HbA that simulates SCT blood. Moreover, GBT440 prevents sickling of SCT blood under in vitro conditions mimicking strenuous exercise with hypoxia, dehydration and acidosis. Together, our results indicate that GBT440 may have the potential to protect SCT individuals from sickling-related complications during conditions that favor HbS polymerization.

Increased hemoglobin-oxygen affinity ameliorates bleomycin-induced hypoxemia and pulmonary fibrosis.

Although exertional dyspnea and worsening hypoxia are hallmark clinical features of idiopathic pulmonary fibrosis (IPF), no drug currently available could treat them. GBT1118 is a novel orally bioavailable small molecule that binds to hemoglobin and produces a concentration-dependent left shift of the oxygen-hemoglobin dissociation curve with subsequent increase in hemoglobin-oxygen affinity and arterial oxygen loading. To assess whether pharmacological modification of hemoglobin-oxygen affinity could ameliorate hypoxemia associated with lung fibrosis, we evaluated GBT1118 in a bleomycin-induced mouse model of hypoxemia and fibrosis. After pulmonary fibrosis and hypoxemia were induced, GBT1118 was administered for eight consecutive days. Hypoxemia was determined by monitoring arterial oxygen saturation, while the severity of pulmonary fibrosis was assessed by histopathological evaluation and determination of collagen and leukocyte levels in bronchoalveolar lavage fluid. We found that hemoglobin modification by GBT1118 had strong antihypoxemic therapeutic effects with improved arterial oxygen saturation to near normal level. Moreover, GBT1118 treatment significantly attenuated bleomycin-induced lung fibrosis, collagen accumulation, body weight loss, and leukocyte infiltration. This study is the first to suggest the beneficial effects of hemoglobin modification in fibrotic lungs and offers a promising and novel therapeutic strategy for the treatment of hypoxemia associated with chronic fibrotic lung disorders in human, including IPF.

A high-throughput turbidometric assay for screening inhibitors of protein disulfide isomerase activity.

Protein disulfide isomerase (PDI) plays a key role in protein folding by catalyzing rearrangements of disulfide bonds in substrate proteins following their synthesis in eukaryotic cells. Besides its major role in the processing and maturation of secretory proteins in the endoplasmic reticulum, this enzyme and its homologs have been implicated in multiple important cellular processes; however, they have not served as targets for the development of therapeutic agents. The authors developed a high-throughput screening assay for PDI and its homologous enzymes in 384-well microplates. The method is based on the enzyme-catalyzed reduction of insulin in the presence of dithiothreitol and measures the aggregation of reduced insulin chains at 650 nm. This kinetic assay was converted to an end-point assay by using hydrogen peroxide as a stop reagent. The feasibility of this high-throughput assay for screening chemical libraries was demonstrated in a pilot screen. The authors show that this homogenous turbidometric assay is robust and cost-effective and can be applied to identify PDI inhibitors from chemical libraries, opening this class of enzymes for therapeutic exploration.

A pharmacological screening approach for discovery of neuroprotective compounds in ischemic stroke.

With the availability and ease of small molecule production and design continuing to improve, robust, high-throughput methods for screening are increasingly necessary to find pharmacologically relevant compounds amongst the masses of potential candidates. Here, we demonstrate that a primary oxygen glucose deprivation assay in primary cortical neurons followed by secondary assays (i.e. post-treatment protocol in organotypic hippocampal slice cultures and cortical neurons) can be used as a robust screen to identify neuroprotective compounds with potential therapeutic efficacy. In our screen about 50% of the compounds in a library of pharmacologically active compounds displayed some degree of neuroprotective activity if tested in a pre-treatment toxicity assay but just a few of these compounds, including Carbenoxolone, remained active when tested in a post-treatment protocol. When further examined, Carbenoxolone also led to a significant reduction in infarction size and neuronal damage in the ischemic penumbra when administered six hours post middle cerebral artery occlusion in rats. Pharmacological testing of Carbenoxolone-related compounds, acting by inhibition of 11-ß-hydroxysteroid dehydrogenase-1 (11ß-HSD1), gave rise to similarly potent in vivo neuroprotection. This indicates that the increase of intracellular glucocorticoid levels mediated by 11ß-HSD1 may be involved in the mechanism that exacerbates ischemic neuronal cell death, and inhibiting this enzyme could have potential therapeutic value for neuroprotective therapies in ischemic stroke and other neurodegenerative disorders associated with neuronal injury.

Regulation of NMDA receptor trafficking and function by striatal-enriched tyrosine phosphatase (STEP).

Regulation of N-methyl-D-aspartate (NMDA) receptors is critical for the normal functioning of the central nervous system. There must be precise mechanisms to allow for changes in receptor function required for learning and normal synaptic transmission, but within tight constraints to prevent pathology. Tyrosine phosphorylation is a major means by which NMDA receptors are regulated through the equilibrium between activity of Src family kinases and tyrosine phosphatases. Identification of NMDA receptor phosphatases has been difficult, the best candidate being striatal-enriched tyrosine phosphatase (STEP). Here we demonstrate that STEP is a critical regulator of NMDA receptors and reveal that the action of this tyrosine phosphatase controls the constitutive trafficking of NMDA receptors and leads to changes in NMDA receptor activity at the neuronal surface. We show that STEP binds directly to NMDA receptors in the absence of other synaptic proteins. The activity of STEP selectively affects the expression of NMDA receptors at the neuronal plasma membrane. The result of STEP's action upon the NMDA receptor affects the functional properties of the receptor and its downstream signaling. These effects are evident when STEP levels are chronically reduced, indicating that there is no redundancy amongst phosphatases to compensate for altered STEP function in the CNS. STEP may have evolved specifically to fill a pivotal role as the NMDA receptor phosphatase, having a distinct and restricted localization and compartmentalization, and unique activity towards the NMDA receptor and its signaling pathway.

Death-associated protein kinase is activated by dephosphorylation in response to cerebral ischemia.

Death-associated protein kinase (DAPK) is a calcium calmodulin-regulated serine/threonine protein kinase involved in ischemic neuronal death. In situ hybridization experiments show that DAPK mRNA expression is up-regulated in brain following a global ischemic insult and down-regulated in ischemic tissues after focal ischemia. DAPK is inactive in normal brain tissues, where it is found in its phosphorylated state and becomes rapidly and persistently dephosphorylated and activated in response to ischemia in vivo. A similar dephosphorylation pattern is detected in primary cortical neurons subjected to oxygen glucose deprivation or N-methyl-D-aspartate (NMDA)-induced toxicity. Both a calcineurin inhibitor, FK506, and a selective NMDA receptor antagonist, MK-801, inhibit the dephosphorylation of DAPK after in vitro ischemia. This indicates that DAPK could be activated by NMDA receptor-mediated calcium flux, activation of calcineurin, and subsequent DAPK dephosphorylation. Moreover, concomitantly to dephosphorylation, DAPK is proteolytically processed by cathepsin after ischemia. Furthermore, a selective DAPK inhibitor is neuroprotective in both in vitro and in vivo ischemic models. These results indicate that DAPK plays a key role in mediating ischemic neuronal injury.

High-affinity thrombin receptor (PAR-1) ligands: a new generation of indole-based peptide mimetic antagonists with a basic amine at the C-terminus.

A new generation of indole-based peptide mimetics, bearing a basic amine at the C-terminus, was developed by the agency of two complementary, multistep, trityl resin-based approaches. Thus, we obtained several high-affinity thrombin receptor (PAR-1) ligands, such as 32 and 34. Compounds 32 and 34 were found to bind to PAR-1 with excellent affinity (IC(50)=25 and 35 nM, respectively) and to effectively block platelet aggregation induced by SFLLRN-NH(2) (TRAP-6) and alpha-thrombin.