Platelet GPIIb/IIIa binding characteristics of small molecule RGD mimetic: distinct binding profile for Roxifiban

Abstract

A number of non‐peptide orally active RGD mimetic prodrug such as Orbofiban, Sibrafiban, SR121566, Roxifiban and others entered into the clinical evaluation stage. Some of these agents were terminated and some are still in clinical trials. The present study examined the platelet GPIIb/IIIa binding profiles for the active form of Roxifiban, Sibrafiban, SR121566 and Orbofiban using 3H‐Roxifiban active form (XV459), 3H‐DMP728, 125I‐Echistatin, and 125I‐Fibrinogen. Either DMP728, Orbofiban, Sibrafiban, SR121566 or Roxifiban active form as well as other RGD mimetic bind to the same binding site (s) on human platelets as evident from the competitive inhibition of binding of each other to human platelet. Additionally, Roxifiban active form competed with FITC labeled GPIIb/IIIa antagonist cyclic RGD peptidomimetic (XL086) as demonstrated using confocal microscopy technique. Roxifiban active form (XV459) demonstrated the highest potency in inhibiting 3H‐XV459, 3H‐DMP728, 125I‐Echistatin, and 125I‐Fibrinogen binding to human platelets as compared to the others. Structure activity relationship within the isoxazoline Roxifiban series showed that substituent at the α‐carbon next to the carboxy terminal represents an exosite for the affinity binding to human platelets leading to slow platelet dissociation rate. These data indicated a distinct binding profile for Roxifiban (high affinity to both activated and resting platelets associated with a relatively slow Koff) as compared to others. These differences might determine the pharmacodynamics and pharmackokinetics of the different GPIIb/IIIa antagonists. British Journal of Pharmacology (2001) 133, 331–336; doi:

Calcium-and integrin-binding protein regulates focal adhesion kinase activity during platelet spreading on immobilized fibrinogen

“…[21][22][23][24][25][26] These mutational studies have yielded a great deal of information about platelet function, as specific sequences of these primary functional molecules are being studied as targets for therapeutic approaches. 33 FAK is widely regarded as an integral component of platelet signaling that leads to platelet spreading. 11,32 Integrin engagement with their respective ligands initiates integrin clustering.…”

Design and Structure of Peptide and Peptidomimetic Antagonists of Protein- Protein Interaction

“…Here phage display appears to have selected an interface peptide sequence from the other binding partner in the interaction which, nevertheless, inhibited the interaction. Support for this concept came from the fact that the integrin β3 chain contained a KDDLW sequence, and phage display produced a C WDDGWL C receptor interface peptide sequence which bound to fibronectin or RGD-containing fibronectin fragments [55]. Such peptides inhibited RGD-dependent cell attachment to fibronectin and vitronectin, but not to collagen.…”

Antibodies causing thrombocytopenia in patients treated with RGD-mimetic platelet inhibitors recognize ligand-specific conformers of αIIb/β3 integrin

“…32,33 A trivial explanation for this finding would be that abciximab and 7E3 dislodge drug from its binding site. However, abciximab has been shown not to compete with low-molecular-weight RGD-mimetic inhibitors for binding to the integrin 42 or to displace bound inhibitor. 43 Moreover, we found that RGD peptide induces the epitopes recognized by LIBS mAbs PMI-1, LIBS6, 319.1, 322.5, and AP5 even when abciximab is bound to the integrin (supplemental Figure 1, available on the Blood Web site; see the Supplemental Materials link at the top of the online article).…”