Avidity and positive allosteric modulation/cooperativity act hand in hand to increase the residence time of bivalent receptor ligands. doi: 10.1111/fcp.12052

Bivalent ligands bear two target-binding pharmacophores. Their simultaneous binding increases their affinity (avidity) and residence time. They become "bitopic" when the pharmacophores exert allosteric modulation of each other's affinity and/or activity.
Present simulations reveal that positive cooperativity exacerbates these phenomena whereas negative cooperativity curtails them, irrespective of whether the association- or dissociation rate of the individual pharmacophores is affected. Positive cooperativity delays the attainment of equilibrium binding, yielding "hemi-equilibrium" conditions and only apparent affinity constants under usual experimental conditions. Monovalent ligands that bind to one of the target sites decrease the bitopic ligand's residence time concentration-wise; their potency depends on their association rate and thereon acting cooperativity rather than on affinity. This stems from the repetitive, very fast reformation of fully-bound ligand-target complexes by rebinding of freshly dissociated pharmacophores.
These studies deal with kinetic binding properties (of increasing interest in pharmacology) of bitopic ligands (a promising avenue in medicinal chemistry).

Publication year:2014

Keywords:bivalent, bitopic, avidity, residence time, cooperativity, simulations