Abstract 5887: Experimental Model to Evaluate Human Platelet Reactivity and Related Pharmacodynamics in Mice
Introduction: In patients with symptomatic CAD, angioplasty and stenting in combination with antiplatelet therapies including aspirin, clopidogrel, and GP IIb/IIIa inhibitors are essential to ensure vessel patency. Unfortunately, not all individuals respond comparably to these drugs, which may vary in clinical effectiveness. Although platelet function tests and animal models help validate therapeutic mechanisms, their ability to predict drug efficacy can be affected by the type of agonist used and by species differences in structure of platelet receptors. Previously, we have demonstrated that substitution of histidine for arginine at position 1326 in murine von Willebrand factor (VWF1326R>H) permits human platelet hemostasis and thrombosis in mice. We now evaluate the utility of this biological platform for preclinical drug testing and assessment of drug efficacy in patients with CAD.
Methods: Optical aggregometry was performed to determine IC50 for eptifibatide and abciximab in response to ADP (20 μM) or TRAP (25 μM) activation of human or mouse platelets and the ability of aspirin (325 mg) and clopidogrel (600 mg) to prevent aggregation of platelets harvested from patients. Intravital microscopy (IVM) studies of laser-injured arterioles were utilized to evaluate human vs. mouse platelet thrombus formation in VWF1326R>H and WT animals, respectively.
Results: In ADP-induced aggregation, IC50 for eptifibatide was 25-fold greater for mouse vs. human platelets (1009±33 nM vs. 40±2.8 nM (mean± SEM), respectively), while the IC50 for abciximab was 0.67±0.01 nM for human and had no inhibitory effect on mouse platelets. A 30 – 40-fold increase in eptifibatide was needed to achieve 80% blockade with TRAP vs. ADP. Importantly, human platelet thrombus formation in VWF1326R>H mice could be reduced by >85% at standard dosing recommended for angioplasty with either drug; mouse platelet thrombus formation was diminished by < 15% in WT animals. Platelets from patients on high dose aspirin and clopidogrel were unable to support thrombus formation in IVM studies as well.
Conclusions: Results indicate that our platform can perform pharmacodynamic evaluation and may thereby expedite drug development and establish appropriate dosing regimes for clinical trials.