PAR-1 inhibitors: a novel class of antiplatelet agents for the treatment of patients with atherothrombosis

Safety, Tolerability, and Pharmacodynamics of AZD3366 (Optimized Human CD39L3 Apyrase) Alone and in Combination With Ticagrelor and Acetylsalicylic Acid: A Phase 1, Randomized, Placebo-Controlled Study

BACKGROUND

ADP and ATP are importantly involved in vascular and thrombotic homeostasis, via multiple receptor pathways. Blockade of ADP P2Y12 receptors inhibits platelet aggregation and represents an effective cardiovascular disease prevention strategy. AZD3366 (APT102), a long-acting recombinant form of an optimized CD39L3 human apyrase, has effectively reduced ATP, ADP, and platelet aggregation and provided tissue protection in preclinical models, features that could be very beneficial in treating patients with cardiovascular disease.

METHODS AND RESULTS

We conducted this phase 1, first-in-human study of single ascending doses of intravenous AZD3366 or placebo, including doses added to dual antiplatelet therapy with ticagrelor and acetylsalicylic acid. The primary objective was safety and tolerability; secondary and exploratory objectives included pharmacokinetics, pharmacodynamics (measured as inhibition of platelet aggregation), adenosine diphosphatase (ADPase) activity, and ATP/ADP metabolism. In total, 104 participants were randomized. AZD3366 was generally well tolerated, with no major safety concerns observed. ADPase activity increased in a dose-dependent manner with a strong correlation to AZD3366 exposure. Inhibition of ADP-stimulated platelet aggregation was immediate, substantial, and durable. In addition, there was a prompt decrease in systemic ATP concentration and an increase in adenosine monophosphate concentrations, whereas ADP concentration appeared generally unaltered. At higher doses, there was a prolongation of capillary bleeding time without detectable changes in the ex vivo thromboelastometric parameters.

CONCLUSIONS

AZD3366 was well tolerated in healthy participants and demonstrated substantial and durable inhibition of platelet aggregation after single dosing. Higher doses prolonged capillary bleeding time without detectable changes in ex vivo thromboelastometric parameters.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique Identifier: NCT04588727.

Using PAR4 Inhibition as an Anti-Thrombotic Approach: Why, How, and When?

Protease-activated receptors (PARs) are a family of four GPCRs with a variety of cellular functions, yet the only advanced clinical endeavours to target these receptors for therapeutic gain to date relates to the impairment of platelet function for anti-thrombotic therapy. The only approved PAR antagonist is the PAR1 inhibitor, vorapaxar—the sole anti-platelet drug against a new target approved in the past 20 years. However, there are two PARs on human platelets, PAR1 and PAR4, and more recent efforts have focused on the development of the first PAR4 antagonists, with first-in-class agents recently beginning clinical trial. Here, we review the rationale for this approach, outline the various modes of PAR4 inhibition, and speculate on the specific therapeutic potential of targeting PAR4 for the prevention of thrombotic conditions.

Evaluation of the Total Thrombus-Formation System (T-TAS): application to human and mouse blood analysis

The Total Thrombus-formation Analyser System (T-TAS) is a whole blood flow chamber system for the measurement of in vitro thrombus formation under variable shear stress conditions. Our current study sought to evaluate the potential utility of the T-TAS for the measurement of thrombus formation within human and mouse whole blood. T-TAS microchips (collagen, PL chip; collagen/tissue thromboplastin, AR chip) were used to analyze platelet (PL) or fibrin-rich thrombus formation, respectively. Blood samples from humans (healthy and patients with mild bleeding disorders) and wild-type (WT), mice were tested. Light transmission lumi-aggregometer (lumi-LTA) was performed in PRP using several concentrations of ADP, adrenaline, arachidonic acid, collagen, PAR-1 peptide and ristocetin. Thrombus growth (N = 22) increased with shear within PL (4:40 ± 1.11, 3:25 ± 0.43 and 3:12 ± 0.48 mins [1000, 1500 and 2000s-1]) and AR chips (3:55 ± 0.42 and 1:49 ± 0.19 [240s-1 and 600s-1]). The area under the curve (AUC) on the PL chip was also reduced at 1000s-1 compared to 1500/2000s-1 (260 ± 51.7, 317 ± 55.4 and 301 ± 66.2, respectively). In contrast, no differences in the AUC between 240s-1 and 600s-1 were observed in the AR chip (1593 ± 122 and 1591 ± 158). The intra-assay coefficient of variation (CV) (n = 10) in the PL chip (1000s-1) and AR chip (240s-1) were T1014.1%, T6016.7%, T10-6022.8% and AUC1024.4% or T10 9.03%, T808.64%, T10-8023.8% and AUC305.1%. AR chip thrombus formation was inhibited by rivaroxaban (1 µM), but not with ticagrelor (10 µM). In contrast, PL chip thrombus formation was totally inhibited by ticagrelor. T-TAS shows an overall agreement with lumi-LTA in 87% of patients (n = 30) with normal PL counts recruited into the genotyping and phenotyping of platelet (GAPP) study and suspected to have a PL function defect. The onset (T10) of thrombus formation in WT mice (N = 4) was shorter when compared to humans e.g. PL chip (1000s-1) T10 were 02:02 ± 00:23 and 03:30 ± 0:45, respectively). T-TAS measures in vitro thrombus formation and can be used for monitoring antithrombotic therapy, investigating patients with suspected PL function defects and monitoring PL function within mice.

Oral anticoagulants in coronary heart disease (Section IV). Position paper of the ESC Working Group on Thrombosis - Task Force on Anticoagulants in Heart Disease

Until recently, vitamin K antagonists (VKAs) were the only available oral anticoagulants evaluated for long-term treatment of patients with coronary heart disease (CHD), particularly after an acute coronary syndrome (ACS). Despite efficacy in this setting, VKAs are rarely used because they are cumbersome to administer. Instead, the more readily manageable antiplatelet agents are the mainstay of prevention in ACS patients. This situation has the potential to change with the introduction of non-VKA oral anticoagulants (NOACs), which are easier to administer than VKAs because they can be given in fixed doses without routine coagulation monitoring. The NOACs include dabigatran, which inhibits thrombin, and apixaban, rivaroxaban and edoxaban, which inhibit factor Xa. Apixaban and rivaroxaban were evaluated in phase III trials for prevention of recurrent ischaemia in ACS patients, most of whom were also receiving dual antiplatelet therapy with aspirin and clopidogrel. Although at the doses tested rivaroxaban was effective and apixaban was not, both agents increased major bleeding. The role for the NOACs in ACS management, although promising, is therefore complicated, because it is uncertain how they compare with newer antiplatelet agents, such as prasugrel, ticagrelor or vorapaxar, and because their safety in combination with these other drugs is unknown. Ongoing studies are also now evaluating the use of NOACs in non-valvular atrial fibrillation patients, where their role is established, with coexistent ACS or coronary stenting. Focusing on CHD, we review the results of clinical trials with the NOACs and provide a perspective on their future incorporation into clinical practice.

Combined upregulation of matrix metalloproteinase-1 and proteinase-activated receptor-1 predicts unfavorable prognosis in human nasopharyngeal carcinoma

Background

The upregulation of matrix metalloproteinase-1 (MMP-1) has been demonstrated to be correlated with lymph node metastasis of nasopharyngeal carcinoma (NPC), while the activation of protease-activated receptor-1 (PAR-1) mediates proliferation and invasion of NPC cells. The present study investigated the clinical significance of the coexpression of MMP-1 and PAR-1 in NPC patients in determining the prognosis.

Methods

Immunohistochemistry was performed to detect the expression of MMP-1 and PAR-1 in tumor tissue samples from 266 NPC patients.

Results

Overexpression of MMP-1 and PAR-1 proteins were, respectively, detected in 190 (71.43%) and 182 (68.42%) of the 266 NPC patients. In addition, the combined MMP-1 and PAR-1 expression was significantly associated with advanced T-stage (P = 0.01), advanced clinical stage (P = 0.002), positive recurrence (P = 0.01), and metastatic status (P = 0.01) of NPC. Moreover, the overall survival in NPC patients with MMP-1 and PAR-1 dual overexpression was significantly shorter than in those with dual low expression (P < 0.001). Furthermore, the multivariate analyses indicated that the combined MMP-1 and PAR-1 overexpression was an independent prognostic factor for overall survival (P = 0.001) in NPC patients, but the upregulation of MMP-1 and PAR-1 alone was, in each case, not an independent prognostic factor for this disease.

Conclusion

Our data provide convincing evidence, for the first time, that the activation of the MMP-1 and PAR-1 axis may be involved in the tumorigenesis and progression of NPC. The upregulation of MMP-1 in combination with PAR-1 overexpression is an unfavorable prognostic marker for NPC and might offer the possibility of future therapeutic targets.