PB0895 - Platelet activation and aggregation assays in Non-Human Primates for the evaluation of potential effects of new drugs in the context of non-clinical studies.

Background: In vitro and ex-vivo platelet assays are performed at different stages of the development of new drug candidates. Non-human primate (NHP) platelet reactivity is different from Human and not all assays available in clinical settings can be translated in this species.

Aims: The purpose of this study was to qualify in vitro testing of NHP (Cynomolgus monkeys) platelet function in whole blood and platelet rich plasma (PRP).

Methods: NHP platelet aggregation was measured by electrical impedance in whole blood samples with a Chrono-Log Aggregometer 700CA and at high shear rate with a PFA-100 system, and by optical transmission in PRP samples with a PAP-8E aggregometer. Platelet activation, defined by the percentage of platelet activation markers CD62P (P-Selectin) and GIIBIIIa on CD61 expressing platelets, was measured by flow cytometry. Platelet reactivity assayed with different concentrations of agonists (Chronolog Corp (CC) or BioData (BD)): collagen (Col), epinephrine (Epi), arachidonic acid (AA) or adenosine diphosphate (ADP).

Results: Platelet aggregation in NHP whole blood was optimal with AA (60 µM-1 mM, CC), moderate with Col (0.5- 4 µg/ml CC), while variable with thrombin (up to 0.2 U/ml CC) and ristocetin (1.25 mg/ml CC) and was insufficient with ADP (up to 20 µM) and Epi (up to 15 µM CC). In PRP, it was optimal with AA (0.5 mM), ADP (5-20 µM BD), Col (2 to 5 µg/ml CC) but insufficient with Epi (up to 15 µM), and it could be induced by addition of calcium chloride. Platelet activation was optimal in whole blood with ADP (10-20 µM). NHP platelet closure time on PFA200 was optimal with Col/ADP (46-66 sec) and variable with Col/Epi (94-202 sec).

Conclusion(s): Particular NHP platelet reactivity to different agonists should be considered in the context of nonclinical studies for the evaluation of drug candidates.