title: Parmodulins inhibit thrombus formation without inducing endothelial injury caused by vorapaxar.
abstract: Protease-activated receptor-1 (PAR1) couples the coagulation cascade to platelet activation during myocardial infarction and to endothelial inflammation during sepsis. This receptor demonstrates marked signaling bias. Its activation by thrombin stimulates prothrombotic and proinflammatory signaling, whereas its activation by activated protein C (APC) stimulates cytoprotective and antiinflammatory signaling. A challenge in developing PAR1-targeted therapies is to inhibit detrimental signaling while sparing beneficial pathways. We now characterize a novel class of structurally unrelated small-molecule PAR1 antagonists, termed parmodulins, and compare the activity of these compounds to previously characterized compounds that act at the PAR1 ligand-binding site. We find that parmodulins target the cytoplasmic face of PAR1 without modifying the ligand-binding site, blocking signaling through Gαq but not Gα13 in vitro and thrombus formation in vivo. In endothelium, parmodulins inhibit prothrombotic and proinflammatory signaling without blocking APC-mediated pathways or inducing endothelial injury. In contrast, orthosteric PAR1 antagonists such as vorapaxar inhibit all signaling downstream of PAR1. Furthermore, exposure of endothelial cells to nanomolar concentrations of vorapaxar induces endothelial cell barrier dysfunction and apoptosis. These studies demonstrate how functionally selective antagonism can be achieved by targeting the cytoplasmic face of a G-protein-coupled receptor to selectively block pathologic signaling while preserving cytoprotective pathways.
authors.affiliation: Division of Hemostasis and Thrombosis, Department of Medicine, and.
authors.forename: Omozuanvbo
authors.initials: O
authors.lastname: Aisiku
authors.affiliation: Division of Hemostasis and Thrombosis, Department of Medicine, and.
authors.forename: Christian G
authors.initials: CG
authors.lastname: Peters
authors.affiliation: Division of Hemostasis and Thrombosis, Department of Medicine, and.
authors.forename: Karen
authors.initials: K
authors.lastname: De Ceunynck
authors.affiliation: Division of Nephrology and Center for Vascular Biology Research, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA; and.
authors.forename: Chandra C
authors.initials: CC
authors.lastname: Ghosh
authors.affiliation: Division of Hemostasis and Thrombosis, Department of Medicine, and.
authors.forename: James R
authors.initials: JR
authors.lastname: Dilks
authors.affiliation: Division of Hemostasis and Thrombosis, Department of Medicine, and.
authors.forename: Susanna F
authors.initials: SF
authors.lastname: Fustolo-Gunnink
authors.affiliation: Division of Hemostasis and Thrombosis, Department of Medicine, and.
authors.forename: Mingdong
authors.initials: M
authors.lastname: Huang
authors.affiliation: Department of Chemistry, Marquette University, Milwaukee, WI.
authors.forename: Chris
authors.initials: C
authors.lastname: Dockendorff
authors.affiliation: Division of Nephrology and Center for Vascular Biology Research, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA; and.
authors.forename: Samir M
authors.initials: SM
authors.lastname: Parikh
authors.affiliation: Division of Hemostasis and Thrombosis, Department of Medicine, and.
authors.forename: Robert
authors.initials: R
authors.lastname: Flaumenhaft
mesh_terms: D000818:Animals; D017209:Apoptosis; D001665:Binding Sites; D019556:COS Cells; D002522:Chlorocebus aethiops; D003593:Cytoplasm / Q000378:metabolism; D004730:Endothelium, Vascular / Q000187:drug effects / Q000293:injuries*; D005089:Exocytosis; D061307:Human Umbilical Vein Endothelial Cells; D006801:Humans; D007249:Inflammation; D007783:Lactones / Q000009:adverse effects*; D008024:Ligands; D010975:Platelet Aggregation Inhibitors / Q000737:chemistry; D011486:Protein C / Q000737:chemistry; D011725:Pyridines / Q000009:adverse effects*; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction; D013927:Thrombosis / Q000188:drug therapy* / Q000517:prevention & control*
chemical_list: D007783:Lactones; D008024:Ligands; D010975:Platelet Aggregation Inhibitors; D011486:Protein C; D011725:Pyridines; D034741:RNA, Small Interfering; C530299:vorapaxar