title: Application of high-throughput screening to identify a novel alphaIIb-specific small- molecule inhibitor of alphaIIbbeta3-mediated platelet interaction with fibrinogen.
abstract: Small-molecule alphaIIbbeta3 antagonists competitively block ligand binding by spanning between the D224 in alphaIIb and the MIDAS metal ion in beta3. They variably induce conformational changes in the receptor, which may have undesirable consequences. To identify alphaIIbbeta3 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 muM. A total of 102 compounds demonstrated 50% or more inhibition, and one of these (compound 1, 265 g/mol) inhibited ADP-induced platelet aggregation (IC(50): 13+/- 5 muM), the binding of soluble fibrinogen to platelets induced by mAb AP5, and the binding of soluble fibrinogen and a cyclic RGD peptide to purified alphaIIbbeta3. Compound 1 did not affect the function of GPIb, alpha2beta1, or the other beta3 family receptor alphaVbeta3. Molecular docking simulations suggest that compound 1 interacts with alphaIIb but not beta3. Compound 1 induced partial exposure of an alphaIIb ligand-induced binding site (LIBS), but did not induce exposure of 2 beta3 LIBS. Transient exposure of purified alphaIIbbeta3 to eptifibatide, but not compound 1, enhanced fibrinogen binding ("priming"). Compound 1 provides a prototype for small molecule selective inhibition of alphaIIbbeta3, without receptor priming, via targeting alphaIIb.
authors.affiliation: Laboratory of Blood and Vascular Biology, The Rockefeller University, New York, NY 10021, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Blue
authors.forename: Marta
authors.initials: M
authors.lastname: Murcia
authors.forename: Charles
authors.initials: C
authors.lastname: Karan
authors.forename: Markéta
authors.initials: M
authors.lastname: Jirousková
authors.forename: Barry S
authors.initials: BS
authors.lastname: Coller
mesh_terms: D000906:Antibodies / Q000276:immunology; D001792:Blood Platelets / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D002448:Cell Adhesion / Q000187:drug effects; D002460:Cell Line; D003094:Collagen / Q000378:metabolism; D004353:Drug Evaluation, Preclinical; D005340:Fibrinogen / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D015394:Molecular Structure; D040201:Platelet Membrane Glycoprotein IIb / Q000737:chemistry / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D000077466:Tirofiban; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology
chemical_list: D000906:Antibodies; D040201:Platelet Membrane Glycoprotein IIb; D014443:Tyrosine; D005340:Fibrinogen; D003094:Collagen; D000077466:Tirofiban