Targeting GPVI with glenzocimab in COVID-19 patients: Results from a randomized clinical trial.

BACKGROUND: Glenzocimab is a novel antithrombotic agent which targets platelet glycoprotein VI (GPVI) and does not induce haemorrhage. SARS-CoV-2 triggers a prothrombotic state and lung injury whose mechanisms include coagulopathy, endothelial dysfunction, and inflammation with dysregulated platelets. METHODS AND PATIENTS: GARDEN was a randomised double-blind, exploratory phase II study of glenzocimab in SARS-CoV-2 respiratory failure (NCT04659109). PCR+ adults in Brazil and France (7 centres) were randomized to standard-of-care (SOC) plus glenzocimab (1000 mg/dayx3 days) or placebo, followed for 40 days. Primary efficacy endpoint was clinical progression at Day 4. All analyses concerned the intention-to-treat population. RESULTS: Between December 2020 and August 2021, 61 patients received at least one dose (30 glenzocimab vs 32 placebo) and 58 completed the study (29 vs 29). Clinical progression of COVID-19 ARDS was not statistically different between glenzocimab and placebo arms (43.3% and 29.0%, respectively; p = 0.245). Decrease in the NEWS-2 category at D4 was statistically significant (p = 0.0290) in the glenzocimab arm vs placebo. No Serious Adverse Event (SAE) was deemed related to study drug; bleeding related events were reported in 6 patients (7 events) and 4 patients (4 events) in glenzocimab and placebo arms, respectively. CONCLUSIONS: Therapeutic GPVI inhibition assessment during COVID-19 was conducted in response to a Public Health emergency. Glenzocimab in coagulopathic patients under therapeutic heparin was neither associated with increased bleeding, nor SAE. Clinical impact of glenzocimab on COVID-19 ARDS was not demonstrated. A potential role for GPVI inhibition in other types of ARDS deserves further experimentation. Glenzocimab is currently studied in stroke (ACTISAVE: NCT05070260) and cardiovascular indications.

Does Yogurt Enriched with Platelet-Activating Factor Inhibitors from Olive Oil By-Products Affect Gut Microbiota and Faecal Metabolites in Healthy Overweight Subjects? (A randomized, parallel, three arm trial.).

OBJECTIVE: The effect of the daily consumption of a low-fat yogurt (150 g) enriched with Platelet-Activating Factor receptor (PAF-R) antagonists, or the plain one, on gut microbiota and faecal metabolites was investigated in healthy overweight subjects. METHODS: A randomized, three-arm, double-blind, placebo-controlled, parallel-group study was performed that lasted 8 weeks. Blood and stools were collected and analyzed before and after the intervention. RESULTS: Our findings revealed that the intake of the enriched yogurt resulted in a significant increase in the levels of Bifidobacterium spp., Clostridium perfringens group and Firmicutes-to-Bacteroidetes (F/B) ratio. On the other hand, a significant increase in the levels of Lactobacillus and C. perfringens group was detected after the intake of the plain yogurt. The increase in the levels of C. perfringens group was inversely associated with the plasma catabolic enzyme of PAF, namely LpPLA2 (lipoprotein-associated phospholipase A2), a cardiovascular risk marker that has been linked with inflammation and atherosclerosis. Moreover, in the enriched with PAF-R antagonists yogurt group, the increased levels of C. perfringens group were also associated with lower PAF action assessed as ex vivo human platelet-rich plasma (PRP) aggregation. Additionally, a higher % increase in molar ratio of Branched Short Chain Fatty Acids (BSCFAs) was detected for both yogurt groups after the 8 week-intervention compared to control. The consumption of the enriched yogurt also resulted in a significant drop in faecal caproic levels and a trend for lower ratio of butyrate to total volatile fatty acids (VFAs) compared to baseline levels. CONCLUSION: Yogurt consumption seems to favorably affect gut microbiota while its enrichment with PAF-R antagonists from olive oil by-products, may provide further benefits in healthy overweight subjects. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov (NCT02259205).

Antagonism of the Platelet-Activating Factor Pathway Mitigates Inflammatory Adverse Events Driven by Anti-erythrocyte Antibody Therapy in Mice.

Immune thrombocytopenia (ITP) is an autoimmune disease characterized by low platelet counts primarily due to antiplatelet autoantibodies. Anti-D is a donor-derived polyclonal Ab against the rhesus D Ag on erythrocytes used to treat ITP. Unfortunately, adverse inflammatory/hypersensitivity reactions and a Food and Drug Administration-issued black box warning have limited its clinical use. This underscores the imperative to understand the inflammatory pathway associated with anti-erythrocyte Ab-based therapies. TER119 is an erythrocyte-specific Ab with anti-D-like therapeutic activity in murine ITP, while also exhibiting a distinct inflammatory signature involving production of CCL2, CCL5, and CXCL9 but not IFN-γ. Therefore, TER119 has been used to elucidate the potential mechanism underlying the adverse inflammatory activity associated with anti-erythrocyte Ab therapy in murine ITP. Prior work has demonstrated that TER119 administration is associated with a dramatic decrease in body temperature and inflammatory cytokine/chemokine production. The work presented in the current study demonstrates that inhibiting the highly inflammatory platelet-activating factor (PAF) pathway with PAF receptor antagonists prevents TER119-driven changes in body temperature and inhibits the production of the CCL2, CCL5, and CXCL9 inflammatory cytokines in CD-1 mice. Phagocytic cells and a functional TER119 Fc region were found to be necessary for TER119-induced body temperature changes and increases in CXCL9 and CCL2. Taken together, this work reveals the novel requirement of the PAF pathway in causing adverse inflammatory activity associated with anti-erythrocyte Ab therapy in a murine model and provides a strategy of mitigating these potential reactions without altering therapeutic activity.

GPVI inhibition: Advancing antithrombotic therapy in cardiovascular disease.

Glycoprotein (GP) VI (GPVI) plays a major role in thrombosis but not haemostasis, making it a promising antithrombotic target. The primary role of GPVI on the surface of platelets is a signalling receptor for collagen, which is one of the most potent thrombotic sub-endothelial components that is exposed by atherosclerotic plaque rupture. Inhibition of GPVI has therefore been investigated as a strategy for treatment and prevention of atherothrombosis, such as during stroke and acute coronary syndromes. A range of specific GPVI inhibitors have been characterized, and two of these inhibitors, glenzocimab and revacept, have completed Phase II clinical trials in ischaemic stroke. In this review, we summarize mechanisms of GPVI activation and the latest progress of clinically tested GPVI inhibitors, including their mechanisms of action. By focusing on what is known about GPVI activation, we also discuss whether alternate strategies could be used to target GPVI.

Antagonizing astrocytic platelet activating factor receptor-neuroinflammation for total flavone of epimedium in response to cuprizone demyelination.

Demyelinating diseases of the central nervous system are characterized by recurrent demyelination and progressive neurodegeneration, but there are no clinical drugs targeting myelin regeneration or improving functional disability in the treatment of multiple sclerosis. Total flavone of Epimedium (TFE) is the main active components of Epimedium, which exhibits the beneficial biological activities in the treatment of diseases, but there is no report in the treatment of demyelinating disorder. The purpose of this study was to explore the therapeutic potential and possible mechanism of TFE in the treatment of demyelination. The results showed that TFE efficiently improved the behavioural performance and histological demyelination in cuprizone (CPZ)-induced demyelinating model. In terms of action, TFE increased astrocytes enrichment in corpus callosum, striatum and cortex, and promoted astrocytes to express neurotrophic factors. Furthermore, the expression of platelet-activating factor receptor (PAFR) in astrocytes was induced by CPZ feeding and LPS stimulation, accompanied by the increase of inflammatory cytokines TNF-α,IL-6 and IL-1ß. TFE declined the expression of PAFR, and inhibited inflammatory response. At the same time, TFE also antagonized PAFR activation and inflammatory response triggered by PAF, which further confirmed that TFE, as a new PAFR antagonist, inhibited the astrocyte-derived inflammatory response by antagonizing PAFR-neuroinflammation axis, thus contributing to myelin protection and regeneration.

The Platelet-Activating Factor Receptor's Association with the Outcome of Ovarian Cancer Patients and Its Experimental Inhibition by Rupatadine.

The platelet-activating factor receptor (PAFR) and its ligand (PAF) are important inflammatory mediators that are overexpressed in ovarian cancer. The receptor is an important player in ovarian cancer development. In this study, we aimed to evaluate the prognostic value of PAFR in epithelial ovarian cancer (EOC) and the potential use of its antagonist, rupatadine, as an experimental treatment. Tissue microarrays of ovarian cancer patients, most markedly those with a non-mucinous subtype, immunohistochemically overexpressed PAFR. Elevated cytoplasmic PAFR expression was found to significantly and independently impair patients' overall and recurrence-free survival (OS: median 83.48 vs. 155.03 months; p = 0.022; RFS: median 164.46 vs. 78.03 months; p = 0.015). In vitro, the serous ovarian cancer subtypes especially displayed an elevated PAFR gene and protein expression. siRNA knockdown of PAFR decreased cell proliferation significantly, thus confirming the receptor's protumorigenic effect on ovarian cancer cells. The clinically approved PAFR antagonist rupatadine effectively inhibited in vitro cell proliferation and migration of ovarian cancer cells. PAFR is a prognostic marker in ovarian cancer patients and its inhibition through rupatadine may have important therapeutic implications in the therapy of ovarian cancer patients.

PAF Receptor Inhibition Attenuates Neuronal Pyroptosis in Cerebral Ischemia/Reperfusion Injury.

Ischemic stroke is an inflammation-related disease, during which process activation of NLRP3 inflammasome and subsequent pyroptosis play crucial roles. Platelet-activating factor (PAF) is a potent phospholipid regulator of inflammation which exerts its effect via binding specific PAF receptor (PAFR). However, whether PAFR contributes to pyroptosis during ischemia/reperfusion (I/R) injury remains to be elucidated. To explore the underlying effect of PAFR on ischemic stroke from the perspective of pyroptosis, mice were subjected to middle cerebral artery occlusion/reperfusion (MCAO/R) injury and primary cultures of mice cerebral cortical neurons were exposed to oxygen-glucose deprivation/reoxygenation (OGD/R) injury to mimic I/R in vivo and in vitro, after which indexes associated with pyroptosis were analyzed. Intriguingly, our results indicated that inhibition of PAFR with its inhibitor XQ-1H or PAFR siRNA exerted a neuroprotective effect against I/R injury both in vivo and in vitro. Furthermore, inflammasome activation and pyroptosis after ischemic challenge were attenuated by XQ-1H or PAFR siRNA. Besides, the protection of XQ-1H was abolished by PAF stimulaiton to some extent. Moreover, XQ-1H or PAFR siRNA alleviated the neuronal pyroptosis induced by LPS and nigericin (an NLRP3 activator) in cortical neurons. Taken together, this study firstly demonstrates that PAFR is involved in neuronal pyroptosis after I/R injury, and XQ-1H, a specific PAFR inhibitor, has a promising prospect in attenuating I/R injury from the perspective of anti-pyroptosis.

Platelet GPVI (Glycoprotein VI) and Thrombotic Complications in the Venous System.

The immunoglobulin receptor GPVI (glycoprotein VI) is selectively expressed on megakaryocytes and platelets and is currently recognized as a receptor for not only collagen but also a variety of plasma and vascular proteins, including fibrin, fibrinogen, laminin, fibronectin, and galectin-3. Deficiency of GPVI is protective in mouse models of experimental thrombosis, pulmonary thromboembolism as well as in thromboinflammation, suggesting a role of GPVI in arterial and venous thrombus formation. In humans, platelet GPVI deficiency is associated with a mild bleeding phenotype, whereas a common variant rs1613662 in the GP6 gene is considered a risk factor for venous thromboembolism. However, preclinical studies on the inhibition of GPVI-ligand interactions are focused on arterial thrombotic complications. In this review we discuss the emerging evidence for GPVI in venous thrombus formation and leukocyte-dependent thromboinflammation, extending to venous thromboembolism, pulmonary thromboembolism, and cancer metastasis. We also recapitulate indications for circulating soluble GPVI as a biomarker of thrombosis-related complications. Collectively, we conclude that the current evidence suggests that platelet GPVI is also a suitable cotarget in the prevention of venous thrombosis due to its role in thrombus consolidation and platelet-leukocyte complex formation.

Targeting platelet glycoprotein VI attenuates progressive ischemic brain damage before recanalization during middle cerebral artery occlusion in mice.

In acute ischemic stroke due to large vessel occlusion (LVO) infarcts rapidly grow into the penumbra, which represents dysfunctional, but still viable brain tissue amenable to rescue by vessel recanalization. However, infarct progression and/or delayed patient presentation are serious and frequent limitations of this so far only acute therapy. Thus, a major goal of translational research is to "freeze" the penumbra already during LVO (before opening the vessel) and thereby extend individual time windows for non-futile recanalization. We used the filament occlusion model of the middle cerebral artery (MCAO) in mice and assessed progressive infarction under occlusion at 2, 3, and 4 h after onset. We show that blocking the activatory platelet receptor glycoprotein (GP)VI substantially delayed progressive neocortical infarction compared to isotype control antibody treated mice. Moreover, the local vascular recruitment of infiltrating neutrophils and T-cells was mitigated. In conclusion, our experimental data support ongoing clinical trials blocking platelet GPVI in acute ischemic stroke.

Efficacy and Safety of Revacept, a Novel Lesion-Directed Competitive Antagonist to Platelet Glycoprotein VI, in Patients Undergoing Elective Percutaneous Coronary Intervention for Stable Ischemic Heart Disease: The Randomized, Double-blind, Placebo-Controlled ISAR-PLASTER Phase 2 Trial.

Importance: The assessment of new antithrombotic agents with a favorable safety profile is clinically relevant. Objective: To test the efficacy and safety of revacept, a novel, lesion-directed antithrombotic drug, acting as a competitive antagonist to platelet glycoprotein VI. Design, Setting, and Participants: A phase 2 randomized clinical trial; patients were enrolled from 9 centers in Germany from November 20, 2017, to February 27, 2020; follow-up ended on March 27, 2020. The study included patients with stable ischemic heart disease (SIHD) undergoing elective percutaneous coronary intervention (PCI). Interventions: Single intravenous infusion of revacept, 160 mg, revacept, 80 mg, or placebo prior to the start of PCI on top of standard antithrombotic therapy. Main Outcomes and Measures: The primary end point was the composite of death or myocardial injury, defined as an increase in high-sensitivity cardiac troponin to at least 5 times the upper limit of normal within 48 hours from randomization. The safety end point was bleeding type 2 to 5 according to the Bleeding Academic Research Consortium criteria at 30 days. Results: Of 334 participants (median age, 67.4 years; interquartile range, 60-75.1 years; 253 men [75.7%]; and 330 White participants [98.8%]), 120 were allocated to receive the 160-mg dose of revacept, 121 were allocated to receive the 80-mg dose, and 93 received placebo. The primary end point showed no significant differences between the revacept and placebo groups: 24.4%, 25.0%, and 23.3% in the revacept, 160 mg, revacept, 80 mg, and placebo groups, respectively (P = .98). The high dose of revacept was associated with a small but significant reduction of high-concentration collagen-induced platelet aggregation, with a median 26.5 AU × min (interquartile range, 0.5-62.2 AU × min) in the revacept, 160 mg, group; 43.5 AU × min (interquartile range, 22.8-99.5 AU × min) in the revacept, 80 mg, group; and 41.0 AU × min (interquartile range, 31.2-101.0 AU × min) in the placebo group (P = .02), while adenosine 5'-diphosphate-induced aggregation was not affected. Revacept did not increase Bleeding Academic Research Consortium type 2 or higher bleeding at 30 days compared with placebo: 5.0%, 5.9%, and 8.6% in the revacept, 160 mg, revacept, 80 mg, and placebo groups, respectively (P = .36). Conclusions and Relevance: Revacept did not reduce myocardial injury in patients with stable ischemic heart disease undergoing percutaneous coronary intervention. There were few bleeding events and no significant differences between treatment arms. Trial Registration: ClinicalTrials.gov Identifier: NCT03312855.

Overcoming challenges in developing small molecule inhibitors for GPVI and CLEC-2.

GPVI and CLEC-2 have emerged as promising targets for long-term prevention of both arterial thrombosis and thrombo-inflammation with a decreased bleeding risk relative to current drugs. However, while there are potent blocking antibodies of both receptors, their protein nature comes with decreased bioavailability, making formulation for oral medication challenging. Small molecules are able to overcome these limitations, but there are many challenges in developing antagonists of nanomolar potency, which is necessary when considering the structural features that underlie the interaction of CLEC-2 and GPVI with their protein ligands. In this review, we describe current small-molecule inhibitors for both receptors and strategies to overcome such limitations, including considerations when it comes to in silico drug design and the importance of complex compound library selection.

GSK669, a NOD2 receptor antagonist, inhibits thrombosis and oxidative stress via targeting platelet GPVI.

BACKGROUND AND PURPOSE: Previously, we discovered that the activation of nucleotide-binding oligomerization domain 2 (NOD2) enhances platelet activation. We here investigated the antiplatelet and antithrombotic potential of GSK669, a NOD2 antagonist. EXPERIMENTAL APPROACH: Effects of GSK669 on platelet functions, reactive oxygen species (ROS) and proinflammatory cytokine generation were detected. NOD2-/- platelets were used to confirm GSK669 target. The interaction between GSK669 and glycoprotein VI (GPVI) was detected using surface plasmon resonance (SPR) spectroscopy. GPVI downstream signaling was examined by Western blot. The antithrombotic and antioxidative effects were investigated using mouse mesenteric arteriole thrombosis model and pulmonary embolism model. KEY RESULTS: GSK669 significantly inhibits platelet proinflammatory cytokine release induced by muramyl dipeptide, platelet aggregation, ATP release, and ROS generation induced by collagen and collagen related peptide (CRP). Platelet spreading and clot retraction are also inhibited. GSK669 also decreases collagen-induced phosphorylation of Src, Syk, PLCγ2, and Akt. The antiplatelet effect of GSK669 is NOD2-independent and mediated by GPVI antagonism. Consistent with its antiplatelet activity as a GPVI antagonist, GSK669 inhibits platelet adhesion on collagen in flow condition. Notably, GSK669 inhibits mouse mesenteric arteriole thrombosis similarly to aspirin without bleeding. The antithrombotic effect of GSK669 is further confirmed in the pulmonary embolism model; decreased malonaldehyde (MDA) and increased superoxide dismutase (SOD) levels in mouse plasma reveal a significant antioxidant effect of GSK669. CONCLUSION AND IMPLICATIONS: Beyond its anti-inflammatory effect as a NOD2 antagonist, GSK669 is also an efficient and safe antiplatelet agent combined with antioxidant effect by targeting GPVI. An antiplatelet agent bearing antioxidative and anti-inflammatory activities without bleeding risk may have therapeutic advantage over current antiplatelet drugs for atherothrombosis.

Glycoprotein VI - novel target in antiplatelet medication.

Subendothelial collagen exposed to platelets after rupture of atherosclerotic plaques is the main trigger of platelet activation und acute arterial thrombotic occlusion leading to myocardial infarction or ischemic stroke. An efficacious antiplatelet therapy is essential to prevent atherothrombotic events. However, increasing potency of antiplatelet treatment is associated with an increased risk of bleeding limiting the clinical benefit for the patient since current antiplatelet strategies concomitantly affect hemostasis. Therefore, an unmet clinical need remains to develop antiplatelet strategies that selectively inhibit atherothrombosis without interfering with control of bleeding. Platelet glycoprotein VI (GPVI) plays a crucial role in collagen-induced activation and aggregation of platelets. Since GPVI is platelet-specific and strongly involved in the pathogenesis of arterial thrombosis without great impact on normal hemostasis, GPVI moved into the focus of novel approaches of antithrombotic therapy strategies. This review summarizes ligands, properties, function and downstream signaling of GPVI and discusses the potential of GPVI as target for novel therapeutic strategies in thrombotic and inflammatory diseases on the basis of recent scientific findings and currently ongoing clinical phase I and phase II trials.

Biomechanical thrombosis: the dark side of force and dawn of mechano-medicine.

Arterial thrombosis is in part contributed by excessive platelet aggregation, which can lead to blood clotting and subsequent heart attack and stroke. Platelets are sensitive to the haemodynamic environment. Rapid haemodynamcis and disturbed blood flow, which occur in vessels with growing thrombi and atherosclerotic plaques or is caused by medical device implantation and intervention, promotes platelet aggregation and thrombus formation. In such situations, conventional antiplatelet drugs often have suboptimal efficacy and a serious side effect of excessive bleeding. Investigating the mechanisms of platelet biomechanical activation provides insights distinct from the classic views of agonist-stimulated platelet thrombus formation. In this work, we review the recent discoveries underlying haemodynamic force-reinforced platelet binding and mechanosensing primarily mediated by three platelet receptors: glycoprotein Ib (GPIb), glycoprotein IIb/IIIa (GPIIb/IIIa) and glycoprotein VI (GPVI), and their implications for development of antithrombotic 'mechano-medicine' .

Pharmacological Blockade of Glycoprotein VI Promotes Thrombus Disaggregation in the Absence of Thrombin.

OBJECTIVE: Atherothrombosis occurs upon rupture of an atherosclerotic plaque and leads to the formation of a mural thrombus. Computational fluid dynamics and numerical models indicated that the mechanical stress applied to a thrombus increases dramatically as a thrombus grows, and that strong inter-platelet interactions are essential to maintain its stability. We investigated whether GPVI (glycoprotein VI)-mediated platelet activation helps to maintain thrombus stability by using real-time video-microscopy. Approach and Results: We showed that GPVI blockade with 2 distinct Fab fragments promoted efficient disaggregation of human thrombi preformed on collagen or on human atherosclerotic plaque material in the absence of thrombin. ACT017-induced disaggregation was achieved under arterial blood flow conditions, and its effect increased with wall shear rate. GPVI regulated platelet activation within a growing thrombus as evidenced by the loss in thrombus contraction when GPVI was blocked, and the absence of the disaggregating effect of an anti-GPVI agent when the thrombi were fully activated with soluble agonists. The GPVI-dependent thrombus stabilizing effect was further supported by the fact that inhibition of any of the 4 key immunoreceptor tyrosine-based motif signalling molecules, src-kinases, Syk, PI3Kß, or phospholipase C, resulted in kinetics of thrombus disaggregation similar to ACT017. The absence of ACT017-induced disaggregation of thrombi from 2 afibrinogenemic patients suggests that the role of GPVI requires interaction with fibrinogen. Finally, platelet disaggregation of fibrin-rich thrombi was also promoted by ACT017 in combination with r-tPA (recombinant tissue plasminogen activator). CONCLUSIONS: This work identifies an unrecognized role for GPVI in maintaining thrombus stability and suggests that targeting GPVI could dissolve platelet aggregates with a poor fibrin content.

Glycoprotein VI is not a Functional Platelet Receptor for Fibrin Formed in Plasma or Blood.

Glycoprotein VI (GPVI), a platelet collagen receptor, is crucial in mediating atherothrombosis. Besides collagen, injured plaques expose tissue factor (TF) that triggers fibrin formation. Previous studies reported that GPVI also is a platelet receptor for fibrinogen and fibrin. We studied the effect of anti-GPVI antibodies and inhibitors of GPVI signaling kinases (Syk and Btk) on platelet adhesion and aggregate formation onto immobilized fibrinogen and different types of fibrin under arterial flow conditions. Fibrin was prepared from isolated fibrinogen ("pure fibrin"), recombinant fibrinogen ("recombinant fibrin"), or generated more physiologically from endogenous fibrinogen in plasma ("plasma fibrin") or by exposing TF-coated surfaces to flowing blood ("blood fibrin"). Inhibition of GPVI and Syk did not inhibit platelet adhesion and aggregate formation onto fibrinogen. In contrast anti-GPVI antibodies, inhibitors of Syk and Btk and the anti-GPIb antibody 6B4 inhibited platelet aggregate formation onto pure and recombinant fibrin. However, inhibition of GPVI and GPVI signaling did not significantly reduce platelet coverage of plasma fibrin and blood fibrin. Plasma fibrin contained many proteins incorporated during clot formation. Advanced optical imaging revealed plasma fibrin as a spongiform cushion with thicker, knotty, and long fibers and little activation of adhering platelets. Albumin intercalated in plasma fibrin fibers left only little space for platelet attachment. Pure fibrin was different showing a dense mesh of thin fibers with strongly activated platelets. We conclude that fibrin formed in plasma and blood contains plasma proteins shielding GPVI-activating epitopes. Our findings do not support a role of GPVI for platelet activation by physiologic fibrin.

Population Pharmacokinetic/Pharmacodynamic Modeling of Glenzocimab (ACT017) a Glycoprotein VI Inhibitor of Collagen-Induced Platelet Aggregation.

Glenzocimab (ACT017) is a humanized monoclonal antigen-binding fragment (Fab) directed against the human platelet glycoprotein VI, a key receptor for collagen and fibrin that plays a major role in thrombus growth and stability. Glenzocimab is being developed as an antiplatelet agent to treat the acute phase of ischemic stroke. During a phase I study in healthy volunteers, the population pharmacokinetics (PK) and pharmacodynamics (PD) of glenzocimab were modeled using Monolix software. The PK/PD model thus described glenzocimab plasma concentrations and its effects on ex vivo collagen-induced platelet aggregation. Glenzocimab was found to have dose-proportional, 2-compartmental PK with a central distribution volume of 4.1 L, and first and second half-lives of 0.84 and 9.6 hours. Interindividual variability in clearance in healthy volunteers was mainly explained by its dependence on body weight. The glenzocimab effect was described using an immediate effect model with a dose-dependent half maximal inhibitory concentration: Larger doses resulted in a stronger effect at the same glenzocimab plasma concentration. The mechanism of the overproportional concentration effect at higher doses remained unexplained. PK/PD simulations predicted that 1000-mg glenzocimab given as a 6-hour infusion reduced platelet aggregation to 20% in 100% of subjects at 6 hours and in 60% of subjects at 12 hours after dosing. Simulations revealed a limited impact of creatinine clearance on exposure, suggesting that no dose adjustments were required with respect to renal function. Future studies in patients with ischemic stroke are now needed to establish the relationship between ex vivo platelet aggregation and the clinical effect.

Treatment with a platelet-activating factor receptor antagonist improves hemodynamics and reduces epinephrine requirements, in a lethal rodent model of anaphylactic shock.

BACKGROUND: In some cases, anaphylactic shock (AS) is still lethal, despite rapid use of epinephrine. High doses of epinephrine are associated with severe complications. Platelet-activating factor (PAF) is secreted in massive amounts during AS, and a high plasma level is correlated with increased AS severity. OBJECTIVE: To assess the effect of ABT-491, a PAF-receptor antagonist and possible adjunct treatment, alone or in combination with epinephrine during AS. METHODS: AS was induced by intravenous injection of 1 mg ovalbumin into ovalbumin-sensitized rats. Rats were then randomly assigned to 5 groups (n = 10 per group): SHAM (vehicle only), SHOCK (no treatment), ABT (ABT-491 1 mg/kg), EPI (epinephrine 5 µg as a bolus then 10 µg kg-1  min-1 by continuous infusion, followed by a reducing protocol) and EPI-ABT (both treatments). RESULTS: Ovalbumin injection resulted in a severe decrease in mean arterial pressure, left ventricular inotropy (max dP/dt) and left ventricular shortening fraction (LVSF). All rats from the ABT group survived until the end of the experiment. ABT-491 prevented the LVSF decrease observed in the SHOCK group (at T15: ABT 50% ± 11% vs SHOCK 36% ± 9%, P = .01), significantly reduced the dose of epinephrine needed to treat anaphylactic shock (EPI-ABT 314 ± 67 µg/kg vs EPI 475 ± 69 µg/kg, P < .001) and reduced the time to restore basal MAP (ABT 23 ± 7 minutes vs EPI-ABT 13 ± 5 minutes, P < .01). CONCLUSIONS AND CLINICAL RELEVANCE: AS was characterized by early cardiac dysfunction in our model. Treatment with ABT-491 allowed survival until the end of the experiment and reduced cardiac dysfunction. Use of the PAF-R antagonist had a synergistic effect with epinephrine and allowed a significant reduction in epinephrine consumption. Use of PAF-R antagonists during AS could reduce epinephrine-related complications and improve the treatment of epinephrine refractory cases.

Comparison of the GPVI inhibitors losartan and honokiol.

Losartan and honokiol are small molecules which have been described to inhibit aggregation of platelets by collagen. Losartan has been proposed to block clustering of GPVI but not to affect binding of collagen. Honokiol has been reported to bind directly to GPVI but only at a concentration that is three orders of magnitude higher than that needed for inhibition of aggregation. The mechanism of action of both inhibitors is so far unclear. In the present study, we confirm the inhibitory effects of both agents on platelet aggregation by collagen and show that both also block the aggregation induced by the activation of CLEC-2 or the low affinity immune receptor FcγRIIa at similar concentrations. For GPVI and CLEC-2, this inhibition is associated with a reduction in protein tyrosine phosphorylation of multiple proteins including Syk. In contrast, on a collagen surface, spreading of platelets and clustering of GPVI (measured by single molecule localisation microscopy) was not altered by losartan or honokiol. Furthermore, in flow whole-blood, both inhibitors suppressed the formation of multi-layered platelet thrombi at arteriolar shear rates at concentrations that hardly affect collagen-induced platelet aggregation in platelet rich plasma. Together, these results demonstrate that losartan and honokiol have multiple effects on platelets which should be considered in the use of these compounds as anti-platelet agents.