Dynamic mechanisms of non-classical antagonism by competitive AT1 receptor antagonists

Lew, Michael J.; Ziogas, James; Christopoulos, Arthur

doi:10.1016/s0165-6147(00)01523-6

Cited by 41 publications

(37 citation statements)

References 24 publications

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“…To determine which receptors were involved in the adenosine-mediated calcium flux, dose-response curves were obtained in the presence of several concentrations of antagonists selective for the various adenosine receptors. It has now been well documented that high-affinity competitive antagonists tend to depress the dose-response functions obtained from calcium flux assays; therefore, traditional null methods for characterizing receptors cannot be applied (Kukkonen et al, 1998;Christopoulos et al, 1999;Lew et al, 2000). Nevertheless, use of multiple fixed concentrations of selective antagonists against dose-response curves still can provide a clear picture of the receptors involved in the calcium response.…”

Section: Resultsmentioning

confidence: 99%

Pharmacological Analysis of Calcium Responses Mediated by the Human A3 Adenosine Receptor in Monocyte-Derived Dendritic Cells and Recombinant Cells

Fossetta¹,

Jackson²,

Deno³

et al. 2003

Mol Pharmacol

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Extensive characterization of adenosine receptors expressed by human monocyte-derived dendritic cells (MDDCs) was performed with quantitative polymerase chain reaction, radioligand binding, and calcium signaling. Transcript for the A3 adenosine receptor was elevated more than 100-fold in immature MDDCs compared with monocyte precursors. A3 receptor transcript was substantially diminished, and A2A receptor transcript increased, by lipopolysaccharide maturation of MDDCs. Saturation binding of N Pretreatment with 100 nM 2Cl-IB-MECA eliminated responses to CGS21680 but not to monocyte inhibitory protein-1␣. For comparison, dose-response functions were obtained from doublerecombinant human embryonic kidney 293 cells expressing the human A3 receptor and a chimeric G␣q-i3 protein, which was required to establish A3-mediated calcium signaling. The pharmacological profile of calcium signaling elicited by adenosine-related agonists in the double-recombinant cells was essentially identical to that obtained from immature MDDCs. Our results provide an extensive analysis of A3-mediated calcium signaling and unequivocally identify immature MDDCs as native expressers of the human A3 receptor.

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Section: Resultsmentioning

confidence: 99%

Pharmacological Analysis of Calcium Responses Mediated by the Human A3 Adenosine Receptor in Monocyte-Derived Dendritic Cells and Recombinant Cells

Fossetta¹,

Jackson²,

Deno³

et al. 2003

Mol Pharmacol

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“…Desensitization of the receptor by the agonist also has been shown to lead to depression of maximal responses. A plateau depression of the maximal response due to hemi-equilibria has been described by Lew et al (2000) when desensitization to the agonist is operative.…”

Section: Discussionmentioning

confidence: 99%

Determining the Potency and Molecular Mechanism of Action of Insurmountable Antagonists

Kenakin¹,

Jenkinson²,

Watson³

2006

J Pharmacol Exp Ther

162

138

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Insurmountable antagonism (maximal response to the agonist depressed) can result from a temporal inequilibrium involving a slow offset orthosteric antagonist or be the result of an allosteric modulation of the receptor. The former mechanism is operative when the antagonist, agonist, and receptors cannot come to proper equilibrium during the time allotted for collection of agonist response (hemi-equilibrium conditions). Allosteric effects (changes in the conformation of the receptor through binding of the allosteric modulator to a separate site) can preclude the agonist-induced production of response, leading to depression of maximal responses. In these cases, the effects on receptor affinity can be observed as well. The first premise of this article is that system-independent estimates of insurmountable antagonist potency can be made with no prior knowledge of molecular mechanism through the use of pA 2 (Ϫlog molar concentration of antagonist producing a 2-fold shift of the concentration response curve) measurements The relationship between the pA 2 and antagonist pK B (Ϫlog equilibrium dissociation constant of the antagonist-receptor complex) is described; the former is an extremely close approximation of the latter in most cases. The second premise is that specially designed experiments are required to differentiate orthosteric versus allosteric mechanisms; simply fitting of data to orthosteric or allosteric theoretical models can lead to ambiguous results. A strategy to determine whether the observed antagonism is orthosteric (agonist and antagonist competing for the same binding site on the receptor) or allosteric in nature is described that involves the detection of the hallmarks of allosteric response, namely saturation and probe dependence of effect.Two major considerations in a drug discovery program for antagonists are the need for 1) system-independent estimates of potency and 2) knowledge of the molecular mechanism of action. The former enables systematic study of structure and activity and subsequent optimization of activity, whereas the latter allows prediction of the properties of the antagonist in the therapeutic situation. The major premise of this study is that knowledge of the mechanism of action of insurmountable antagonists is not required for the systemindependent measure of antagonist potency. In fact, verisimilitude of data to specific theoretical models is an unreliable way to determine mechanism of action (vide infra). It will be proposed that specifically designed experiments are required to do so.By definition, antagonists interfere with the ability of agonists to produce pharmacological response. The way they express this interference varies but generally involves changing the location parameter (EC 50 ; molar concentration proArticle, publication date, and citation information can be found at

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“…Adapted from Woolf and Linderman (2000). more realistic mechanisms for understanding biological behavior under such circumstances (Christopoulos et al, 1999;Lew et al, 2000;Woolf and Linderman, 2000). Indeed, it may be that it is timely to bring nonlinear dynamic approaches into the receptor pharmacology arena.…”

Section: Impact On Research and Training The Impact Of Functional Selmentioning

confidence: 99%

Functional Selectivity and Classical Concepts of Quantitative Pharmacology

Urban¹,

Clarke

Zastrow

et al. 2006

J Pharmacol Exp Ther

Self Cite

992

910

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The concept of intrinsic efficacy has been enshrined in pharmacology for half of a century, yet recent data have revealed that many ligands can differentially activate signaling pathways mediated via a single G protein-coupled receptor in a manner that challenges the traditional definition of intrinsic efficacy. Some terms for this phenomenon include functional selectivity, agonist-directed trafficking, and biased agonism. At the extreme, functionally selective ligands may be both agonists and antagonists at different functions mediated by the same receptor. Data illustrating this phenomenon are presented from serotonin, opioid, dopamine, vasopressin, and adrenergic receptor systems. A variety of mechanisms may influence this apparently ubiquitous phenomenon. It may be initiated by differences in ligand-induced intermediate conformational states, as shown for the ␤ 2 -adrenergic receptor. Subsequent mechanisms that may play a role include diversity of G proteins, scaffolding and signaling partners, and receptor oligomers. Clearly, expanded research is needed to elucidate the proximal (e.g., how functionally selective ligands cause conformational changes that initiate differential signaling), intermediate (mechanisms that translate conformation changes into differential signaling), and distal mechanisms (differential effects on target tissue or organism). Besides the heuristically interesting nature of functional selectivity, there is a clear impact on drug discovery, because this mechanism raises the possibility of selecting or designing novel ligands that differentially activate only a subset of functions of a single receptor, thereby optimizing therapeutic action. It also may be timely to revise classic concepts in quantitative pharmacology and relevant pharmacological conventions to incorporate these new concepts. Receptor Pharmacology for the New MillenniumFor the last half-century, pharmacological theory has posited that ligands could be characterized by the nature of the functional effects elicited by their interaction with their tar-

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Dynamic mechanisms of non-classical antagonism by competitive AT1 receptor antagonists

Cited by 41 publications

References 24 publications

Pharmacological Analysis of Calcium Responses Mediated by the Human A3 Adenosine Receptor in Monocyte-Derived Dendritic Cells and Recombinant Cells

Pharmacological Analysis of Calcium Responses Mediated by the Human A3 Adenosine Receptor in Monocyte-Derived Dendritic Cells and Recombinant Cells

Determining the Potency and Molecular Mechanism of Action of Insurmountable Antagonists

Functional Selectivity and Classical Concepts of Quantitative Pharmacology

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