Key Points
- To investigate the pharmacological profile, antiplatelet mechanisms, and receptor specificity of R-99224, a hepatic metabolite of the thienopyridine prodrug CS-747.
- Measured in vitro aggregation in washed human and rat platelets across varying concentrations, tested persistence after washing, and assessed ex vivo aggregation after intravenous R-99224 dosing (0.1–3 mg/kg) in rats.
- Conducted competition binding assays using radioligand [3H]-2-MeS-ADP alone and alongside antagonists ARL-66096 (Gi-linked P2T) or A3P5PS (P2Y1) in human platelets.
- Assayed ADP-induced [125I]-fibrinogen binding, cyclic AMP reduction in PGE1-stimulated platelets, and intracellular calcium mobilization.
- R-99224 inhibited ADP-induced aggregation concentration-dependently in human (0.03–1 µg/ml) and rat (0.1–3 µg/ml) platelets, retained inhibitory activity after repeated washing, and caused dose-dependent ex vivo inhibition in rats.
- R-99224 selectively bound Gi-linked P2T receptors, reaching maximum [3H]-2-MeS-ADP displacement at 3 µM with no additive inhibition from ARL-66096, but achieving complete displacement when combined with A3P5PS.
- The metabolite concentration-dependently reduced ADP-induced fibrinogen binding and prevented ADP-mediated cAMP decreases, while producing no effect on ADP-induced calcium mobilization.
Structured PICO
PPopulationWashed human platelets and rat platelets/rats
IInterventionR-99224 (0.03 - 100 microM in vitro; 0.1 - 3 mg/kg intravenous in vivo)
OOutcomeInhibition of ADP-induced platelet aggregation and ADP receptor bindingsurrogate
R-99224 is a selective and irreversible antagonist of Gi-linked P2T receptors, acting as the active metabolite responsible for the in vivo antiplatelet effects of CS-747.