A Novel Dimeric Inhibitor That Targets Dimeric ß2GPI In ß2GPI/Anti-ß2GPI Antibody Complexes.

Abstract 1142

ß2GPI is a major antigen for autoantibodies associated with antiphospholipid syndrome, an autoimmune disease characterized by thrombosis and recurrent pregnancy loss. Only the dimeric form of ß2GPI generated by anti-ß2GPI antibodies is pathologically important, in contrast to monomeric ß2GPI which is abundant in plasma. Several cell-surface molecules including anionic phospholipids and ApoER2, a member of the lipoprotein receptor family, are implicated in the pathology of antiphospholipid syndrome.

We created a dimeric inhibitor, A1-A1, to selectively target ß2GPI in ß2GPI/antibody complexes. This inhibitor consists of two ligand-binding A1 modules from ApoER2 connected by a flexible linker. A1-A1 disrupts the binding of ß2GPI/antibody complexes with anionic phospholipids and lipoprotein receptors. We compared the potency of A1-A1 to monomeric A1 for inhibition of the binding of ß2GPI/antibody complexes to anionic phospholipids. We tested the inhibition of ß2GPI present in human serum, ß2GPI purified from human plasma and domain V of ß2GPI. We demonstrated that when ß2GPI/antibody complexes are formed, A1-A1 is more effective than A1 in inhibition of the ß2GPI binding to cardiolipin, regardless of the source of ß2GPI. Half maximum inhibition of ß2GPI in human serum in the presence of anti-ß2GPI antibodies was achieved at 9 μM of A1-A1 and 218 μM of A1. Similarly, ß2GPI purified from plasma was inhibited to 50% by 26 μM of A1-A1 and 191 μM of A1. Also, A1-A1 strongly inhibited the binding of dimerized domain V of ß2GPI to cardiolipin compared to monomeric A1. Concentration of A1-A1 and A1 at half maximum inhibition of the binding of ß2GPI domain V to cardiolipin in the presence of dimerization antibodies was 29 μM and 204 μM, respectively. In the absence of anti-ß2GPI antibodies, A1-A1 and A1 were equally inefficient in the inhibition of the binding of monomeric ß2GPI to cardiolipin. The concentration of inhibitor at half-maximum inhibition of the binding of ß2GPI in human serum to cardiolipin was 189 μM for A1-A1 and 176 μM for A1.

A novel inhibitor A1-A1 may be a starting point in the development of an effective therapeutic for antiphospholipid syndrome.