title: Highly constrained cyclic (S,S) -CXaaC- peptides as inhibitors of fibrinogen binding to platelets.
abstract: The Arg-Gly-Asp RGD motif of adhesive proteins is recognized by the activated platelet integrin alpha(IIb)beta3. Binding of fibrinogen (Fg) to activated alpha(IIb)beta3 causes platelet aggregation and thrombus formation. Highly constraint cyclic (S,S) -CXaaC- containing peptides incorporating the (S,S) -CDC- and (S,S) -CRC- motifs were tested for their ability to inhibit platelet aggregation and Fg binding. Our results suggest that the above cyclic scaffolds stabilize a favorable structure for the antiaggregatory activity (IC50-values ranged from 1.7 to 570 microm). The peptides inhibited Fg binding with IC50-values up to 30-fold lower than those determined for the inhibition of the adenosine diphosphate (ADP)-induced platelet aggregation. Importantly, peptides (S,S) PSRCDCR-NH2 (peptide 11) and (S,S) PRCDCK-NH2 (peptide 10) did not inhibit PAC-1 binding to the activated platelets at a concentration in which they completely inhibited Fg binding. Moreover, (S,S) PSRCDCR-NH(2) (peptide 11), one of the more active peptides, inhibited ADP-induced P-selectin exposure. By contrast, peptide (S,S) Ac-RWDCRC-NH2, incorporating the inverse (S,S) -DCRC- sequence (peptide 16), failed to inhibit P-selectin exposure whereas at the same concentration, it effectively inhibited PAC-1 and Fg binding. It is concluded that peptides containing the (S,S) -CDC- as well the (S,S) -CRC- sequences, exhibit a broad range of activities toward platelets, and could be helpful tools for elucidating the structural interaction of Fg with the integrin receptor alpha(IIb)beta3, in its activated form. Furthermore, the (S,S) -RCDC- sequence can be used as a scaffold for developing potent non-RGD-like Fg-binding inhibitors.
authors.affiliation: Department of Chemistry, Section of Organic Chemistry and Biochemistry, University of Ioannina, Ioannina, Greece.
authors.forename: A
authors.initials: A
authors.lastname: Kouki
authors.forename: J V
authors.initials: JV
authors.lastname: Mitsios
authors.forename: M
authors.initials: M
authors.lastname: Sakarellos-Daitsiotis
authors.forename: C
authors.initials: C
authors.lastname: Sakarellos
authors.forename: A D
authors.initials: AD
authors.lastname: Tselepis
authors.forename: V
authors.initials: V
authors.lastname: Tsikaris
authors.forename: D C
authors.initials: DC
authors.lastname: Tsoukatos
mesh_terms: D000595:Amino Acid Sequence; D001792:Blood Platelets / Q000378:metabolism*; D054641:Dual Specificity Phosphatase 2; D005340:Fibrinogen / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006801:Humans; D020128:Inhibitory Concentration 50; D008968:Molecular Conformation; D019007:P-Selectin; D010456:Peptides, Cyclic / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology*; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000737:chemistry; D011485:Protein Binding / Q000187:drug effects; D054648:Protein Phosphatase 2; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: D019007:P-Selectin; D010456:Peptides, Cyclic; D010975:Platelet Aggregation Inhibitors; D005340:Fibrinogen; D054648:Protein Phosphatase 2; C517032:DUSP2 protein, human; D054641:Dual Specificity Phosphatase 2; D017027:Protein Tyrosine Phosphatases