Improved Ligand Binding by Antibody–Aptamer Pincers

To increase the affinities of antibodies or aptamers for their targets, we designed antibody–aptamer pincers (AAPs) or heterodimers for thrombin or human epidermal growth factor 2 (HER2) as a model system. For this purpose, we first conjugated a 15-mer or 29-mer anti-thrombin aptamer, which are well-known to bind to thrombin in two specific epitopes, with an anti-thrombin antibody to enable each binding part of the AAP to simultaneously recognize a different part of the thrombin molecule. The AAP comprising a 15-mer aptamer and an anti-thrombin antibody has an apparent dissociation constant (Kdapp) value of 567 pM, and this value is approximately 1/100 of that of the antibody alone or 1/35 of that of the aptamer monomer alone. The AAP comprising a 29-mer aptamer and an anti-thrombin antibody has a much lower Kdapp value than that of 15-mer aptamer-conjugated antibody. Furthermore, this concept of the AAP system was employed to HER2-targeted drug delivery system (DDS) based on both antibody and drug-loaded...