Abstract 1314: Pharmacological Targeting of Rac1 GTPase in Platelets: A Novel Approach for Developing Antithrombotic Agents
Blood platelets play a critical role in initiation and progression of arterial thrombosis leading to myocardial infarction and/or stroke. Anti-platelet agents are drugs of choice for prevention and management of thrombosis in patients with coronary artery disease and transient cerebral ischemia. Rac1 GTPase, a member of the Ras related Rho GTPase family, has been implicated in platelet lamellipodia formation as well as in the stability of the platelet aggregates under sheer stress. We hypothesized that if Rac1 GTPase plays a critical role in platelet activation then NSC23766, a rationally designed Rac1 GTPase specific small molecule inhibitor that specifically interferes with the Rac-GEF interaction, may inhibit platelet function. Here we report that incubation of human platelets with NSC23766 inhibited:
thrombin-induced activation of platelet Rac1 GTPase and phosphorylation of the Rac effector p21-activated kinase (PAK);
thrombin or U46619 induced expression of P-selectin and secretion of ATP;
aggregation induced by ADP, collagen, thrombin and U46619, a stable analog of thromboxane A2; and
Intraperitoneal administration of NSC23766 (2.5 mg/kg) to wild type mice inhibited ex vivo:
activation of Rac1 GTPase;
phosphorylation of PAK; and
aggregation induced by U46619 and ADP.
The in vivo effect of inhibiting Rac GTPase was assessed by monitoring the tail bleeding times in wild type mice after intraperitoneal administration of NSC23766 (2.5 mg/kg) . The bleeding times in mice administered NSC23766 (>560 sec) were significantly prolonged as compared to the mice given saline (137 sec).These results suggest that Rac1 GTPase is involved in regulation of platelet secretion and aggregation and Rac GTPase-specific small molecule inhibitors may serve as novel anti-platelet agents.