Submitted August 6, 2007
Accepted October 24, 2007
Application of high throughput screening to identify a novel 
IIb-specific small molecule inhibitor of IIb
3-mediated platelet interaction with fibrinogen
Robert Blue, Marta Murcia, Charles Karan, Marketa Jirouskova, and Barry S. Coller*
Laboratory of Blood and Vascular Biology, Rockefeller University, New York, NY
Department of Physiology and Biophysics, Weill Cornell Medical College, New York, NY
High Throughput Screening Resource Center, Rockefeller University, New York, NY
* Corresponding author; email: collerb{at}rockefeller.edu.
Small molecule 
IIb
3 antagonists competitively block ligand binding by spanning between the D224 in IIb and the MIDAS metal ion in 3. They variably induce conformational changes in the receptor, which may have undesirable consequences. To identify IIb3 antagonists with novel structures, we tested 33,264 small molecules for their ability to inhibit the adhesion of washed platelets to immobilized fibrinogen at 16 µM. A total of 102 compounds demonstrated 
50% inhibition, and one of these (compound 1, 265 g/mol) inhibited ADP-induced platelet aggregation (IC50 13 ± 5 µM), the binding of soluble fibrinogen to platelets induced by mAb AP5, and the binding of soluble fibrinogen and a cyclic RGD peptide to purified IIb3. Compound 1 did not affect the function of GPIb, 21, or the other 3 family receptor V3. Molecular docking simulations suggest that compound 1 interacts with IIb, but not 3. Compound 1 induced partial exposure of an IIb ligand induced binding site (LIBS), but did not induce exposure of 2 3 LIBS. Transient exposure of purified IIb3 to eptifibatide, but not compound 1, enhanced fibrinogen binding ("priming"). Compound 1 provides a prototype for small molecule selective inhibition of IIb3, without receptor priming, via targeting IIb.
