MK-383 (tirofiban) induces a GPIIb/IIIa receptor conformation which differs from the resting and activated receptor.
The platelet integrin alphaIIb beta3 (GPIIb/IIIa) acts as a receptor for fibrinogen, playing a critical role in platelet aggregation. GPIIb/IIIa antagonists, which block the receptor-ligand interaction, have been accused of causing occasional thrombocytopenia, probably via drug-induced platelet activation or immunogenic neoepitopes. We, therefore, analyzed the effects of the GPIIb/IIIa antagonist MK-383 (tirofiban) on platelet activation and GpIIb/IIIa conformation. At a concentration of 10(-7) mol/l, MK-383 completely inhibited fibrinogen binding to in vitro stimulated platelets. Simultaneously, the GPIIb/IIIa expression density increased, similar to that on activated platelets, but no effect on P-selectin expression or the formation of platelet-leukocyte aggregates could be observed, indicating that MK-383 binding did not induce general platelet activation. The GPIIb/IIIa receptor conformation was further analyzed by fluorescence resonance energy transfer analysis between fluorochrome-labeled antibodies against different GpIIb/IIIa epitopes. As a result, MK-383 induced a receptor conformation that differed from the resting as well as the activated receptor as induced by ADP or TRAP-6. This conformational modulation of GPIIb/IIIa presents an interesting mechanism which may be linked to receptor recruitment without inducing general platelet activation.
Institute for Clinical Chemistry and Laboratory Medicine, University of Regensburg, Germany.
Stefan
S
Barlage
Antonia
A
Wimmer
Alexandra
A
Pfeiffer
Gregor
G
Rothe
Gerd
G
Schmitz
D005434:Flow Cytometry; D031541:Fluorescence Resonance Energy Transfer; D006801:Humans; D015539:Platelet Activation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000187:drug effects; D011487:Protein Conformation / Q000187:drug effects; D000077466:Tirofiban; D014443:Tyrosine / Q000031:analogs & derivatives / Q000494:pharmacology*
D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D014443:Tyrosine; D000077466:Tirofiban