Selectivity of pharmacological tools: implications for use in cell physiology. A Review in the Theme: Cell Signaling: Proteins, Pathways and Mechanisms

Abstract

Pharmacological inhibitors are frequently used to identify the receptors, receptor subtypes, and associated signaling pathways involved in physiological cell responses. Based on the effects of such inhibitors conclusions are drawn about the involvement of their assumed target or lack thereof. While such inhibitors can be useful tools for a better physiological understanding, their uncritical use can lead to incorrect conclusions. This article reviews the concept of inhibitor selectivity and its implication for cell physiology. Specifically, we discuss the implications of using inhibitor vs. activator approaches, issues of direct vs. indirect pathway modulation, implications of inverse agonism and biased signaling, and those of orthosteric vs. allosteric, competitive vs. noncompetitive, and reversible vs. irreversible inhibition. Additional problems can result from inconsistent estimates of inhibitor potency and differences in potency between cell-free systems and intact cells. These concepts are illustrated by several examples of inhibitors displaying affinity for related but distinct targets or even unrelated targets. Of note, many of the issues being addressed are also applicable to genetic inhibition strategies. The main practical conclusion following from these concepts is that investigators should be critical in the choice of inhibitor, its concentrations, and its mode of application. When this advice is adhered to, small-molecule pharmacological inhibitors can be important experimental tools in the hand of physiologists.

Effects of 39 Compounds on Calmodulin-Regulated Adenylyl Cyclases AC1 and Bacillus anthracis Edema Factor

“…CDZ is highly prone to off-target effects. A review on the critical use of pharmacological inhibitors has been recently published [ 84 ].…”

Agonist‐induced desensitisation of β3‐adrenoceptors: Where, when, and how?

“…Most investigators try to limit the impact by including PDE inhibitors such as IBMX in their assays. However, how well such inhibitors prevent cAMP degradation and whether they may have other effects, for example, by acting on adenosine receptors, is not well understood for most model systems (Michel & Seifert, 2015). Moreover, accumulating cAMP can leave cells, making intracellular concentrations lower than they should be and concomitantly act on adenosine receptors to inhibit cAMP formation (Pacini, Sanders-Silveira, & Godinho, 2018).…”

β-Adrenoceptor-mediated Relaxation of Urinary Bladder Muscle in β2-Adrenoceptor Knockout Mice

“…Constitutive systemic knockout of a particular receptor subtype may cause compensatory changes in expression of other receptors or proteins ( Michel and Seifert, 2015 ). Therefore, the expression of all β-AR subtypes in detrusor tissue from WT and transgenic mice was checked using RT- PCR and quantitative real-time PCR.…”

“…Although, small molecule inhibitors have been valuable tools to characterize receptor subtypes in pharmacological studies, the interpretation of such results is complicated because the compounds may exhibit non-anticipated receptor-activation patterns or lack of selectivity ( Michel and Seifert, 2015 ). In our previous work, we concluded that the relaxing effect of (-)-isoprenaline in murine detrusor was mediated via β 2 -ARs, because only ICI 118,551 (50 nM) shifted the CRCs for (-)-isoprenaline to the right, whereas the β 1 -AR blocker CGP 20712A (300 nM) and the β 3 -AR blocker L748,337 (100 nM) were without effect ( Wuest et al, 2009 ; Propping et al, 2015a ).…”