Exploring avidity: understanding the potential gains in functional affinity and target residence time of bivalent and heterobivalent ligands

Abstract

Bivalent ligands are increasingly important therapeutic agents. Although the naturally occurring antibodies are predominant, it is becoming more common to combine different antibody fragments or even low molecular weight compounds to generate heterobivalent ligands. Such ligands exhibit markedly increased affinity (i.e. avidity) and target residence time when both pharmacophores can bind simultaneously to their target sites. This is because binding of one pharmacophore forces the second tethered one to stay close to its corresponding site. This 'forced proximity' favours its binding and rebinding (once dissociated) to that site. However, rebinding will also take place when the diffusion of freshly dissociated ligands is merely slowed down. The present differential equation-based simulations explore the way both situations affect ligand binding. Both delay the attainment of binding equilibrium (resulting in steep saturation curves) and also increase the target residence time. Competitive ligands are able to interfere in a concentration-dependent manner, although much higher concentrations are required in the 'forced proximity' situation. Also, it is only in that situation that the ligand shows increased affinity. These simulations shed light on two practical consequences. Depending on the pharmacokinetic half-life of the bivalent ligand in the body, it may not have sufficient time to achieve equilibrium with the target. This will result in lower potency than expected, although it would have significant advantages in terms of residence time. In in vitro experiments, the manifestation of steep saturation curves and of accelerated dissociation in the presence of competitive ligands could mistakenly be interpreted as evidence for non-competitive, allosteric interactions. Abbreviations2D, 3D, two-and three-dimensional; (a and c), aa, ab, monovalent, homobivalent and heterobivalent ligands; A, B, target sites (ligand-bound species are named in Schemes 1 and 2); [L], f, local concentration of unbound pharmacophore of ab, handicap factor for its binding; r, maximal distance between a and b in ab

Potent and Efficacious Inhibition of CXCR2 Signaling by Biparatopic Nanobodies Combining Two Distinct Modes of Action

“…This pK B value is a log order of magnitude lower in potency than the biparatopic nanobody, suggesting that when linked, the binding of one monomer forces the second tethered one to stay close to its corresponding binding site. This forced proximity favors the binding and rebinding (once dissociated) of each nanobody to their discreet epitopes and hence leads to the increased potency/ affinity that we observe with the biparatopic constructs (Vauquelin and Charlton, 2013). Finally, the biparatopic nanobody showed inverse agonist effects on basal […”

“…The two classes of nanobody also behaved very differently when bivalent constructs were generated; for the class 1 nanobodies, this resulted in large increases in potency compared with the monovalent molecules, suggesting simultaneous binding of the linked monomers to epitopes that are close enough together to allow this to occur (model 1 as described by Vauquelin and Charlton (2013)). In contrast, the class 2 nanobodies did not show any strong increase in potency as bivalent constructs, suggesting that the two building blocks do not bind simultaneously as the epitopes are too far apart (model 2, as described by Vauquelin and Charlton, 2013).…”

Cell membranes… and how long drugs may exert beneficial pharmacological activity in vivo

“…micro-compartments with little convective stirring, such as synapses and other interstitial spaces -and (C) interactions with membrane components that promote the 2D diffusion of drugs at the surface or deeper within the hydrocarbon core of the membrane. (D) The most extreme form of rebinding applies to bivalent ligands because binding of one of their domains/pharmacophores (red circles) to the target 'forces' the second, tethered pharmacophore to remain close to its cognate binding pocket at the target for bivalent ligand-target interactions [61][62][63] is that, as long as one of the ligand's binding domains/pharmacophores is bound, the second, tethered pharmacophore is forced to remain close to its cognate target site ( Figure 3D). The resultant high 'local' concentration of this second pharmacophore will boost its association rate and, as a result, both pharmacophores will experience multiple unbinding and rebinding events before the bivalent ligand drifts away [64].…”

Ligand Residence Time at G-protein–Coupled Receptors—Why We Should Take Our Time To Study It

“…Within the last 10 years several excellent reviews have appeared on the general topic of drug-target residence time, each covering the topic from a different perspective (Copeland et al, 2006;Tummino and Copeland, 2008;Lu and Tonge, 2010;Dahl andAkerud, 2013, Vauquelin andCharlton, 2013;Guo et al, 2014 to name a few), and have highlighted this parameter for drug discovery. To keep this minireview focused, we will refer the reader to those articles or the recently published book Thermodynamics and Kinetics of Drug Binding (Keserü and Swinney, 2015) for an in-depth discussion, and we will focus on the concept of residence time at GPCRs.…”