A synthetic peptide with anti‐platelet activity derived from a CDR of an anti‐GPIIb‐IIIa antibody

Abstract

A monoclonal antibody, AC7, directed against the RGD (Arg-Gly-Asp) binding site on the GpIIIa subunit of the platelet fibrinogen receptor, interacts only with activated platelet. In order to identify the regions of AC7 that interact with the receptor, cDNA sequences of AC7 immunoglobulin heavy and light chain variable regions were determined. Among the six complementarity-determining regions (CDRS) of AC7, the CDR3 heavy chain (H3) contains homology to the RGDF sequence within fibrinogen. A synthetic peptide encompassing the H3 region (H3, RQMIRGYFDV) inhibited platelet aggregation and fibrinogen binding to platelet (IC₅₀ = 700μM). The inhibitory potencies of modified H3 peptides suggest that the RGYF sequence within the H3 peptide mimic the receptor recognition sequence in fibrinogen.