Targeted Ultrasound Contrast Agents
Martin G. Pomper, Juri G. Gelovani, Benjamin Tsui, Kathleen Gabrielson, Richard Wahl, S. Sam Gambhir, Jeff Bulte, Raymond Gibson, William C. Eckelman in Molecular Imaging in Oncology, 2008
Firm biocolloid adhesion is mediated by many ligandreceptor interactions and depends on the kinetics and thermodynamics of bond formation and rupture in a multivalent system. Knowing the equilibrium binding constant (affinity) of the ligand-receptor pair is not enough. Bond formation depends on the collision time, the loading force, and the intermolecular interactions (54). Bond rupture depends on the pulling force (55). These factors can be lumped into a kinetic rate constant for bond formation (kon) and rupture (koff), the ratio of which gives the bond dissociation constant (KD). In situations with high flow, such as in larger vessels, a very high kon is desired (56). In addition, firm adhesion requires that the paired bonds have sufficient strength to overcome the dislodging force. The magnitude of this force depends on the fluid shear stress and microbubble size (57,58). Multiple ligand-receptor pairs can act in concert to enhance bond stability (59), leading to firm adhesion. The use of ligand combinations, which combine a high kon with a large adhesion strength, can be used for high shear flow (60). Shells with excess area that maximize ligand-receptor contact have also been described (61).
Answers
Calver Pang, Ibraz Hussain, John Mayberry in Pre-Clinical Medicine, 2017
This question is based on drugs and receptors. Agonists are drugs that have both affinity and efficacy whereas antagonists have affinity only. The equilibrium dissociation constant (Kd) is a measure of affinity where the lower the value, the higher the affinity. The effective concentration giving 50% of the maximal response (EC50) is a measure of potency. It is often the case that EC50 is less than Kd and not all receptors are required to be occupied to get a maximal response. This is because the relationship between receptor occupancy and response is non-linear. Some tissues have more receptors than required to produce a maximum response, that is, spare receptors. These receptors increase sensitivity which allows responses at low concentrations of agonist.
Pharmacokinetic Aspects of the in Vivo, Noninvasivestudy of Neuroreceptors in Man
William C. Eckelman, Lelio G. Colombetti in Receptor-Binding Radiotracers, 2017
Although ligands which have low equilibrium dissociation constants appear to have very slow clearance rates of the receptor-bound fraction, the differential distribution of the radioligand is not the result of a process at equilibrium, but of rate processes which are driven by the time-dependent concentration of the ligand in the blood. Therefore, it is more reasonable to expect that the clearance rate of receptor-bound ligand would be determined in large part by the intrinsic dissociation rate constant for the receptor-ligand complex. Fortunately, changes in the equilibrium dissociation constant from one ligand to another are largely the result of changes in the dissociation rate constant, whereas the association rate constant remains fairly constant.13 Therefore, either the equilibrium dissociation constant or the dissociation rate constant may be used as an approximate indicator of the clearance rate of receptor-bound ligand. However, changes in these two constants do not always precisely correspond for the ligands of interest here so that one should in principle use the dissociation rate constant to predict which ligands will prove optimal for the method.14,15 As only a few ligands have been tested in vivo for the opiate and dopamine systems, it is difficult to state with certainty which parameter or parameters are most important and future investigations using a variety of ligands labeled with gamma-emitting radioisotopes should clarify this problem.
Identification and characterization of M6903, an antagonistic anti–TIM-3 monoclonal antibody
Published in OncoImmunology, 2020
Dong Zhang, Feng Jiang, Rinat Zaynagetdinov, Hui Huang, Vanita D. Sood, Hong Wang, Xinyan Zhao, Molly H. Jenkins, Qingyong Ji, Youbin Wang, David P. Nannemann, Djordje Musil, John Wesolowski, Andrea Paoletti, Tin Bartholomew, Melissa G. Derner, Qi An, Christel Iffland, Joern-Peter Halle
To determine the affinity of M6903 to TIM-3 orthologues from various species via SPR, goat anti-human-IgG Fc polyclonal antibody (Jackson Labs, 109-005-098) was immobilized on CM5 chips (GE Healthcare, BR-1006-68). Flow rate throughout was 30 μL/minute. Anti-TIM-3 antibodies were captured at 0.5 and 1.0 µg/mL for 120 seconds. TIM-3 ECD orthologues from different species were either purchased (Human Novoprotein C356, marmoset Novoprotein NP10506, murine Sino Biologicals 51152), or in the case of ECD from cynomolgus monkey, expressed in Expi293 F cells (ThermoFisher, A14527), and purified by immobilized metal affinity chromatography followed by size exclusion chromatography. ECDs were diluted from 0–100 nM. Association was measured for 180 seconds, followed by dissociation in buffer (HEPES buffered saline with EDTA and P20, GE Healthcare, BR-1006-69) for 600 or 900 seconds. Biacore T200 software version 1.0 was used to fit sensorgrams to a 1:1 Langmuir binding model to derive association (ka) and dissociation (kd) kinetic constants. The equilibrium dissociation constant (KD) was determined as the ratio of kinetic constants.
Inhibitory effects of flavonoids isolated from Sophora flavescens on indoleamine 2,3-dioxygenase 1 activity
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2019
Mincheol Kwon, Sung-Kyun Ko, Mina Jang, Gun-Hee Kim, In-Ja Ryoo, Sangkeun Son, Hyung Won Ryu, Sei-Ryang Oh, Won-Kyu Lee, Bo Yeon Kim, Jae-Hyuk Jang, Jong Seog Ahn
To determine the interaction between IDO1 and KE (6), we utilised a surface plasmon resonance (SPR) assay. Specifically, His-IDO1 was linked to the sensor chip and then incubated with successive injections of the KE (6) solution at a flow rate of 30 µL/min in PBS buffer-containing 5% DMSO. The SPR results showed that KE (6) was strongly bound to WT IDO1 with a KD value of 6.5 ± 0.1 µM (Figure 6(A)), but more slightly bound to the mutant IDO1 P314A with a KD of 8.9 ± 0.2 µM (Figure 6(B)). The equilibrium dissociation constant (KD) was calculated from the ratio of the dissociation rate constant divided by the association rate constant (KD = kd/ka). Based on this, we confirmed the direct binding of KE (6) to IDO1.
A non-clinical comparative study of IL-23 antibodies in psoriasis
Published in mAbs, 2021
Li Zhou, Yibing Wang, Qi Wan, Fei Wu, Jeffrey Barbon, Robert Dunstan, Stephen Gauld, Mark Konrad, Laura Leys, Richard McCarthy, Marian Namovic, Christine Nelson, Gary Overmeyer, Denise Perron, Zhi Su, Leyu Wang, Susan Westmoreland, Jun Zhang, Rui Zhu, Geertruida Veldman
A central mechanism of therapeutic anti-IL-23 antibodies is the neutralization of free IL-23. The binding affinity for IL-23 may therefore be a major determinant of clinical efficacy. To assess the binding kinetics of the antibodies to human IL-23, we performed surface plasmon resonance (SPR) measurements at 37°C. The antibodies were captured on the chip surface using a goat anti-human IgG Fc polyclonal antibody. Different concentrations of the analyte, either single-chain (sc) or heterodimeric human IL-23, were interacted in consecutive cycles with surface-displayed IL-23 antibodies. The individual association (ka) and dissociation (kd) rate constants and the equilibrium dissociation constant (KD) were calculated using global fitting to a 1:1 binding model. Risankizumab and guselkumab exhibited high affinity to human scIL-23 with mean KDs of 21 pM and 35 pM, respectively, whereas tildrakizumab and ustekinumab showed about a 5-fold lower affinity for scIL-23 than risankizumab with mean KDs of 136 pM for tildrakizumab and 106 pM for ustekinumab (Table 2 and Supplemental Figure S2). The affinities of the antibodies for heterodimeric IL-23 were slightly lower than for scIL-23 but followed a similar trend. The difference in KD between risankizumab and tildrakizumab/ustekinumab is mainly driven by risankizumab having an 8- to 13-fold slower dissociation rate constant (kd), indicating that risankizumab forms a more stable immune complex with IL-23.
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