A Novel Anti-LIBS mcAb (3C7) Is Specific for the Complex of Integrin aIIbb3 and Inhibits Platelets Aggregation and Adhesion

Abstract number: P0932

Liu J, Chen P, Sun C

Activation or ligand binding causes conformational changes in AlphaIIbBeta3, resulting in exposure of neo-epitopes named ligand induced binding sites (LIBS). We reported here a novel monoclonal antibody developed by using CHO cells expressing an activated AlphaIIbBeta3 mutant (CHO AlphaIIbBeta3-del717) as the immunogen. This IgG2bkappa named 3C7 was specific for the complex of AlphaIIbBeta3 as demonstrated by flow cytometry, immunoprecipitation and EDTA chelating. Binding of 3C7 to platelets was increased significantly with higher affinity when platelets were activated by ADP/thrombin or in the presence of RGDS peptides, fibrinogen or PAC-1, suggesting that it was an anti-LIBS antibody. The failure of 3C7 binding to the CHO cells expressing another AlphaIIbBeta3 mutant (Beta3Y178A) indicated that the C177–C184 loop of Beta3 was likely to be the epitope for 3C7. 3C7 inhibited platelets aggregation initiated by ADP or thrombin in a dose dependent manner with an IC50 of 5.6 microgram/mL and 0.05 microgram/mL, respectively. It also inhibited platelets adhesion to immobilized fibrinogen but not to fibronectin or collagen. These findings suggested that 3C7 was a potent antagonist for integrin AlphaIIbBeta3 and a potential antithrombotic agent.