Design and Pharmacological Characterization of a Novel Antithrombotic P2Y₁ Receptor-Based Vaccine

Platelet activation processes begin when injury to blood vessels exposes the subendothelial matrix, leading platelets to attach to it, where they become activated and exert their hemostatic function. Excessive platelet aggregation is associated with thrombotic disorders such as arterial thrombosis. To manage such diseases, medications that inhibit thrombosis are continuously sought, despite potential drawbacks that include hemorrhage. This study described the development of a novel peptide-based vaccine that targets the purinergic ADP P2Y₁ receptor (abbreviated EL2Vac) and its pharmacological characterization. Thus, we designed and developed an EL2Vac that targets the ligand-binding domain of the P2Y₁ receptor protein, which is located in its second extracellular loop (EL2). We then evaluated the vaccine's ability to trigger an immune response (antibody production) in immunized mice, modulate platelet function, its antithrombotic activity, and any effects on hemostasis, by employing a thrombosis model and the tail bleeding time assay. Results showed significant levels of antibody production in mice treated with EL2Vac, in comparison with the random peptide vaccine control (EL2rVac), which persisted at least up to six months post vaccination. Moreover, we observed significant inhibition of the ADP-induced aggregation response in platelets from EL2Vac-treated mice, relative to those from EL2rVac controls. This inhibition was selective for ADP, as other agonists, such as the thromboxane A₂ receptor (TPR) agonist U46619 or high-dose collagen, had no detectable effect on aggregation. As for its capacity to protect against thrombosis, our data showed a significant delay in the occlusion time of the EL2Vac mice when compared with the random peptide control vaccine, which was also observed (at least) six months post vaccination. Interestingly, EL2Vac did not appear to prolong the tail bleeding time, supporting the notion that it is devoid of a bleeding diathesis. As a conclusion, this study documents the design and evaluation of a novel peptide-based vaccine, EL2Vac, which appears to selectively target the P2Y₁ receptor and protect against thrombus formation without impairing hemostasis. Thus, EL2Vac may provide a promising clinical option to treat thromboembolic disorders.