Characterization of the Adenosine Pharmacology of Ticagrelor Reveals Therapeutically Relevant Inhibition of Equilibrative Nucleoside Transporter 1

Introduction: Studies have shown that ticagrelor has a further adenosine-mediated mechanism of action in addition to its potent inhibition of the P2Y 12 receptor, which may explain some of ticagrelor’s clinical characteristics. This study aimed to further characterize the adenosine pharmacology of ticagrelor, its major metabolites, and other P2Y 12 receptor antagonists. Methods: Inhibition of nucleoside transporter-mediated [ 3 H]adenosine uptake by ticagrelor, its major metabolites, and alternative P2Y 12 antagonists was examined in recombinant Madin-Darby canine kidney (MDCK) cells. The pharmacology of ticagrelor and its major metabolites at adenosine A 1 , A 2A , A 2B , and A 3 receptor subtypes was examined using in vitro radioligand binding and functional assays and ex vivo C-fiber experiments in rat and guinea pig vagus nerves. Results: Ticagrelor (and less effectively its metabolites) and the main cangrelor metabolite inhibited [ 3 H]adenosine uptake in equilibrative nucleoside transporter (ENT) 1-expressing MDCK cells, whereas cangrelor and the active metabolites of prasugrel or clopidogrel had no effect. No significant inhibitory activity was observed in MDCK cells expressing ENT2 or concentrative nucleoside transporters 2/3. Ticagrelor demonstrated high affinity (inhibition constant [K i ] = 41 nmol/L) for ENT1. In adenosine receptor-binding experiments, ticagrelor and its major circulating metabolite, AR-C124910XX, had low affinity (K i > 6 μmol/L) for each of the adenosine A 1 , A 2A , and A 2B receptors, whereas ticagrelor had a submicromolar (K i = 190 nmol/L) affinity for the adenosine A 3 receptor. However, in functional assays, at high concentrations (10 μmol/L) ticagrelor only partially inhibited 3 mmol/L adenosine-induced depolarizations in the guinea pig and rat vagus nerve preparations (by 35% and 49%, respectively). Conclusions: Ticagrelor inhibits cellular adenosine uptake selectively via ENT1 inhibition at concentrations of clinical relevance. However, the low-binding affinity and functional inhibition of adenosine receptors observed with ticagrelor or its metabolites indicate that they possess a negligible adenosine-like activity at clinically relevant concentrations.