S1PR1 activation by CYM5442 modulates platelet aggregation and activation

Introduction Various mediators can affect platelet function, thereby influencing physiological and pathophysiological mechanisms of hemostasis [ 1 ]. The lipid mediator sphingosine-1-phosphate (S1P) is produced and stored within platelets and released in large quantities upon activation [ 2 ]. S1P exerts its effects by autocrine and paracrine binding to a family of five G-protein-coupled receptors (S1PR1-5). However, its specific effects are still under debate [ 3 ]. Therefore, the present study aims to elucidate the functional effects of S1P and S1PR1 engagement for platelet activation. Method Platelet-rich plasma (PRP) was generated from blood of healthy volunteers. The effects of S1PR1 activation on platelet function were tested using the specific S1PR1 agonist CYM5442 (final concentration of 10 µM; with 10 minutes of short-term and 90 minutes of long-term incubation). The impact on platelet aggregation was evaluated by light transmission aggregometry (LTA), while platelet activation (CD62P and CD63 expression, PAC-1 binding as well as Annexin-V staining) was determined by flow cytometry (FC). Platelet function was tested either without or with co-stimulation of the activator ADP (final concentration 2-3 µM, following CYM5442 incubation). Platelet activation and pore formation were visualized using scanning electron microscopy (SEM). Results Short-term incubation of PRP with CYM5442 alone does not induce platelet aggregation, whereas co-stimulation with ADP maintains the time-dependent extent of platelet aggregation. We also observed a significant decrease in the primary aggregation wave, triggered in response to ADP after 90 minutes of PRP incubation with CYM5442. Flow cytometry analysis revealed a diminished expression of platelet CD62P and reduced PAC-1 binding following short-term stimulation with CYM5442 and ADP. Long-term stimulation preserved the decreased GPIIb/IIIa activation, while the expression of CD62P and CD63 significantly increased. Meanwhile, phosphatidylserine exposure measured by Annexin-V binding was not affected by CYM5442. Furthermore, SEM analysis showed no abnormalities regarding membrane effects due to CYM5442 incubation. In both the CYM5442-treated and control samples, no structural damage was observed. Conclusion S1PR1 activation by the selective agonist CYM5442 can modulate platelet activation. In our study, short-term incubation decreased ADP-induced platelet activation. This, in turn, may lead to a "platelet-stabilizing" effect, resulting in sustained maximum platelet aggregation ex vivo over time. Intriguingly, long-term activation diminished the activation of the GPIIb/IIIa receptor while CD62P expression was significantly increased. In conclusion, platelet S1PR1 plays an important role in fine-tuning processes of hemostasis. Activation of S1PR1 with CYM5442 initially leads to reduced platelet activation. Consequently, modulating the S1P-S1PR1 pathway in platelets may provide a novel therapeutic target for cardiovascular diseases. Publication History Article published online: 17 February 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany