Simultaneous targeting of two ligand-binding sites on VEGFR2 using biparatopic Affibody molecules results in dramatically improved affinity

Angiogenesis plays an important role in cancer and ophthalmic disorders such as age-related macular degeneration and diabetic retinopathy. The vascular endothelial growth factor (VEGF) family and corresponding receptors are regulators of angiogenesis and have been much investigated as therapeutic targets. The aim of this work was to generate antagonistic VEGFR2-specific affinity proteins having adjustable pharmacokinetic properties allowing for either therapy or molecular imaging. Two antagonistic Affibody molecules that were cross-reactive for human and murine VEGFR2 were selected by phage and bacterial display. Surprisingly, although both binders independently blocked VEGF-A binding, competition assays revealed interaction with non-overlapping epitopes on the receptor. Biparatopic molecules, comprising the two Affibody domains, were hence engineered to potentially increase affinity even further through avidity. Moreover, an albumin-binding domain was included for half-life extension in future in vivo experiments. The best-performing of the biparatopic constructs demonstrated up to 180-fold slower dissociation than the monomers. The new Affibody constructs were also able to specifically target VEGFR2 on human cells, while simultaneously binding to albumin, as well as inhibit VEGF-induced signaling. In summary, we have generated small antagonistic biparatopic Affibody molecules with high affinity for VEGFR2, which have potential for both future therapeutic and diagnostic purposes in angiogenesis-related diseases.