Submitted August 18, 2008
Accepted April 23, 2009
Structural and therapeutic insights from the species specificity and in vivo antithrombotic activity of a novel 
IIb-specific IIb
3 antagonist
Robert Blue, M. Anna Kowalska, Jessica Hirsch, Marta Murcia, Christin A. Janczak, Amanda Harrington, Marketa Jirouskova, Jihong Li, Rudy Fuentes, Michael A. Thornton, Marta Filizola, Mortimer Poncz, and Barry S. Coller*
Laboratory of Blood and Vascular Biology, The Rockefeller University, New York, NY, United States
Division of Hematology, Children's Hospital of Philadelphia, Philadelphia, PA, United States
Department of Structural and Chemical Biology, Mount Sinai School of Medicine, New York, NY, United States
Department of Biology, Florida A&M University, Tallahassee, FL, United States
* Corresponding author; email: collerb{at}rockefeller.edu.
We previously reported on a novel compound (Compound 1; RUC-1) identified by high throughput screening that inhibits human 
IIb
3. RUC-1 did not inhibit V3, suggesting that it interacts with IIb, and flexible ligand/rigid protein molecular docking studies supported this speculation. We have now studied RUC-1's effects on murine and rat platelets, which are less sensitive than human to inhibition by RGD peptides due to differences in the IIb sequences contributing to the binding pocket. We found that RUC-1 was much less potent in inhibiting aggregation of murine and rat platelets. Moreover, RUC-1 potently inhibited fibrinogen binding to murine platelets expressing a hybrid IIb3 receptor composed of human IIb and murine 3 but not a hybrid receptor composed of murine IIb and human 3. Molecular docking studies of RUC-1 were consistent with the functional data. In vivo studies of RUC-1 administered intraperitoneally at a dose of 26.5 mg/kg demonstrated anti-thrombotic effects in both ferric chloride carotid artery and laser-induced microvascular injury models in mice with hybrid hIIb/m3 receptors. Collectively, these data support RUC-1's specificity for IIb, provide new insights into the IIb binding pocket, and establish RUC-1's anti-thrombotic effects in vivo.
