The dual H3/4R antagonist thioperamide does not fully mimic the effects of the 'standard' H4R antagonist JNJ 7777120 in experimental murine asthma

Opportunities and challenges in the therapeutic exploitation of histamine and histamine receptor pharmacology in inflammation-driven disorders

Inflammation-driven diseases encompass a wide array of pathological conditions characterised by immune system dysregulation leading to tissue damage and dysfunction. Among the myriad of mediators involved in the regulation of inflammation, histamine has emerged as a key modulatory player. Histamine elicits its actions through four rhodopsin-like G-protein-coupled receptors (GPCRs), named chronologically in order of discovery as histamine H1, H2, H3 and H4 receptors (H1-4R). The relatively low affinity H1R and H2R play pivotal roles in mediating allergic inflammation and gastric acid secretion, respectively, whereas the high affinity H3R and H4R are primarily linked to neurotransmission and immunomodulation, respectively. Importantly, however, besides the H4R, both H1R and H2R are also crucial in driving immune responses, the H2R tending to promote yet ill-defined and unexploited suppressive, protective and/or resolving processes. The modulatory action of histamine via its receptors on inflammatory cells is described in detail. The potential therapeutic value of the most recently discovered H4R in inflammatory disorders is illustrated via a selection of preclinical models. The clinical trials with antagonists of this receptor are discussed and possible reasons for their lack of success described.

Mechanisms of unconventional CD8 Tc2 lymphocyte induction in allergic contact dermatitis: Role of H3/H4 histamine receptors

Histamine (HA) is a potent mediator that plays a central role in inflammation and allergy, acting through four G-protein-coupled receptors (i.e. H₁–H₄). HA is an accepted promoter of type 2 immunity in CD4⁺ T cells during hypersensitivity. Previously, we demonstrated that HA can promote antigen cross-presentation, inducing the activation of antigen-specific CD8⁺ T cells in an asthmatic murine model. Non-classical CD8+ T-cell profiles, such as Tc2 or Tc17, are associated with allergic disease persistence and chronicity. In this paper, we focus on the role of the H₃ receptor (H₃R) and the H₄ receptor (H₄R) in the development of allergic contact dermatitis. We were able to show that induction of the type 2 profiles associated with interleukin 13 production, both by CD4 and CD8 lymphocytes, depend on the interaction of HA with H₃R and H₄R. Blocking both receptors using the selective H₃/H₄ receptor antagonist thioperamide or the selective H₄R ligand JNJ777120 reduces the inflammatory response, inducing an immunosuppressive profile associated with the increased proportion of FOXp3⁺ regulatory T lymphocytes and CD11b⁺Gr-1⁺ myeloid suppressor cells. Interestingly, in dendritic cells, only H₄R blockade, and not H₃R blockade, is capable of modulating most of the inflammatory effects observed in our model.

Histamine via histamine H1 receptor enhances the muscarinic receptor-induced calcium response to acetylcholine in an enterochromaffin cell model

As a prerequisite for serotonin secretion, the P‐STS ileal enterochromaffin cell line responds to acetylcholine (ACh) stimulation with an increase in intracellular calcium mediated by the muscarinic ACh receptor M3 (M3R). Histamine increases intracellular calcium via histamine H1 receptor (H1R) in P‐STS cells and pre‐incubation with histamine specifically augments the response to ACh but not to epinephrine or nicotine. We aimed to elucidate whether histamine receptors are involved in this synergism. Astonishingly, HEK‐293 T cells—known to express M3R, but only a very low amount of histamine receptor messenger RNA—showed a similar enhancement of the calcium response to ACh by pre‐incubation with histamine. Despite the much lower level of H1R protein detected in HEK‐293 T cells as compared to P‐STS cells, in both cell lines pre‐treatment with H1R antagonists inhibited the synergism between histamine and ACh. No indication for an involvement of histamine H2 or H4 receptors in the synergism was found. Furthermore, pre‐incubation with the cAMP‐inducing compound forskolin had no influence on the intracellular calcium response to ACh. Serotonin secretion from P‐STS cells was increased after challenge with ACh and histamine added simultaneously compared to ACh alone, suggesting that histamine increases ACh‐induced serotonin secretion from enterochromaffin cells. In conclusion, our data suggest that histamine enhances the M3R‐mediated intracellular calcium response to ACh via activation of H1R. This probably increases serotonin secretion from enterochromaffin cells and thereby affects intestinal motility in histamine intolerance, food allergies and irritable bowel syndrome.

Chemical Probes for Histamine Receptor Subtypes

Ligands with different properties and different selectivity are highly needed for in vitro and in vivo studies on the (patho)physiological influence of the chemical mediator histamine and its receptor subtypes. A selection of well-described ligands for the different receptor subtypes and different studies is shown with a particular focus on affinity and selectivity. In addition, compounds with radioactive or fluorescence elements will be presented with their beneficial use for other species or different investigations.

Combined Treatment With H1 and H4 Receptor Antagonists Improves Th2 Inflammatory Responses in the Nasal Mucosa of Allergic Rhinitis Rats

BACKGROUND

Histamine H1 receptor (H1R) antagonists are the first-line drugs for the treatment of allergic rhinitis (AR) at present. Emerging evidence supports an important role of histamine H4 receptor (H4R) in allergic diseases. However, information regarding the effects of combined treatment with H1 and H4 receptor antagonists in AR is limited.

OBJECTIVES

We aimed to assess the effects of combined treatment with H1R and H4R antagonists on Th2 inflammatory responses in the nasal mucosa of AR rats.

METHODS

Sprague Dawley rats were sensitized with ovalbumin and treated with H1R antagonist desloratadine or/and H4R antagonist JNJ7777120. Western blotting was used to assay the phenotypic markers of mature dendritic cells in the nasal mucosa, including major histocompatibility complex class II (MHC-II) and co-stimulatory molecules CD80, CD86 and OX40 ligand (OX40L). Th2 inflammatory cytokines including interleukin-4, 5 and 13 in nasal lavage fluids were determined by using enzyme-linked immunoassay.

RESULTS

The treatment with desloratadine alone down-regulated the CD86 expression, and decreased the production of Th2 cytokines, but had no impact on the expression of MHC-II, CD80 and OX40L. The administration of NJ7777120 alone reduced the levels of CD86, OX40L and Th2 cytokines, whereas MHC-II and CD80 expression was unaffected. The combination of desloratadine and JNJ7777120 showed more significant synergistic therapeutic effects than monotherapy.

CONCLUSION

H4R antagonist acted synergistically with H1R antagonist to reduce Th2 inflammatory responses by down-regulating CD86 and OX40L expression in the nasal mucosa of AR rats. The combination with H1R and H4R antagonists might be a new strategy for AR treatment.

Histamine pharmacology: from Sir Henry Dale to the 21st century

Histamine has been one of the most studied substances in medicine, playing a major role in diverse (patho)physiological processes. It elicits its multifaceted modulatory functions by activating four types of GPCRs, designated as H_1-4 . Despite the heterogeneity and the complexity of histamine receptor pharmacology, many discoveries over the past 100 years resulted in the development of H₁ antihistamines and H₂ -targeting 'blockbuster' therapeutics for the management of allergies and gastrointestinal disorders respectively. Recently, a first-in-class H₃ inverse agonist was approved for the treatment of narcolepsy, whereas H₄ antagonists are under clinical evaluation for their potential therapeutic exploitation in immune-related diseases. This review critically presents the past successes and drawbacks in histamine research, complemented by the modern conceptual innovations in molecular and receptor pharmacology. It targets both young and experienced researchers in an ongoing effort to stimulate novel insights for the dissection of the translational potential of histamine pharmacology. LINKED ARTICLES: This article is part of a themed section on New Uses for 21st Century. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.3/issuetoc.

Effects of indole alkaloids from leaf of Alstonia scholaris on post-infectious cough in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Leaf of Alstonia scholaris (L.) R. Br. (Apocynaceae), a wide used ethic-medicine in many Asia and Africa counties, has also been recorded as the common traditional Chinese medicine for treatment of illnesses in respiratory system by Dai people.

AIM OF THE STUDY

To provide experimental data of clinical adaption of total indole alkaloids (TA) from leaf of A. scholaris for treating post-infectious cough in phase II clinical trial.

MATERIALS AND METHODS

To model post-infectious cough, all animals except control group were instilled intra-tracheal with lipopolysaccharide (LPS) (80 μg/50 µL/mouse), followed by subsequent exposure to cigarette smoke (CS) for 30 min per day for a total of 30 days. Mice were orally given TA at dose of 10, 25, 50 mg/kg, and four main alkaloids (Sch: scholaricine, Epi: 19-epischolaricine, Val: vallesamine, Pic: picrinine) once daily. Cellular infiltration was assessed in the broncho-alveolar lavage fluid (BALF). Expression of interleukin-6 (IL-6) and C-reactive protein (CRP) in the serum was determined, the superoxide dismutase (SOD) activity as well as malondialdehyde (MDA) content in the serum and homogenate were examined. Finally, histopathological examination in the lungs was assessed by H. E. staining.

RESULTS

After administration of TA and four major alkaloids respectively, the symptoms of cough in mice were obviously attenuated. Total white blood cells (WBC) and neutrophils (NEU) amounts in BALF were reduced obviously and the pathological damage of lung was also attenuated. There was also significant reduction in IL-6, CRP, MDA and a marked improvement in SOD.

CONCLUSIONS

The efficacy of indole alkaloids against post-infectious cough (PIC) was shown in the down-regulation of inflammatory cells, cytokines, and the balance of antioxidants. What's more, the pharmacological effects of TA were better than single indole alkaloid, which might be related to the synergic effect of four major alkaloids.

Pharmacological Characterization of 5-Substituted 1-[(2,3-dihydro-1-benzofuran-2-yl)methyl]piperazines: Novel Antagonists for the Histamine H3 and H4 Receptors with Anti-inflammatory Potential

The histamine receptors (HRs) are traditional G protein-coupled receptors of extensive therapeutic interest. Recently, H₃R and H₄R subtypes have been targeted in drug discovery projects for inflammation, asthma, pain, cancer, Parkinson’s, and Alzheimer’s diseases, which includes searches for dual acting H₃R/H₄R ligands. In the present work, nine 1-[(2,3-dihydro-1-benzofuran-2-yl)methyl]piperazine (LINS01 series) molecules were synthesized and evaluated as H₃R and H₄R ligands. Our data show that the N-allyl-substituted compound LINS01004 bears the highest affinity for H₃R (pK_i 6.40), while the chlorinated compound LINS01007 has moderate affinity for H₄R (pK_i 6.06). In addition, BRET assays to assess the functional activity of G_i1 coupling indicate that all compounds have no intrinsic activity and act as antagonists of these receptors. Drug-likeness assessment indicated these molecules are promising leads for further improvements. In vivo evaluation of compounds LINS01005 and LINS01007 in a mouse model of asthma showed a better anti-inflammatory activity of LINS01007 (3 g/kg) than the previously tested compound LINS01005. This is the first report with functional data of these compounds in HRs, and our results also show the potential of their applications as anti-inflammatory.

Role of the Histamine H4-Receptor in Bronchial Asthma

Histamine is a pro-inflammatory mediator with a prominent role in allergic diseases. Antagonists at the histamine receptor subtype 1 are central in anti-allergic therapies, with the exception of allergic asthma, where they are clinically without effect. The latest identified histamine receptor subtype 4, which is expressed mainly in hematopoietic cells, now provides a reasonable target for new therapeutic strategies inhibiting histamine function. The pathophysiology of allergy, esp. allergic asthma, and in its context the effects of antagonists at the histamine receptor subtype 4 in preclinical and clinical settings are discussed in this chapter.

Airways antiallergic effect and pharmacokinetics of alkaloids from Alstonia scholaris

BACKGROUND

Alstonia scholaris (L.) R. Br. (Apocynaceae), an important herbal medicine, has been widely used to treat respiratory tract diseases, such as cough, asthma, phlegm, and chronic obstructive pulmonary disease.

PURPOSE

To evaluate pharmacological effect of alkaloids from A. scholaris on ovalbumin induced airways allergic inflammatory model, and explore whether the dosing frequency is related to pharmacokinetics.

STUDY DESIGN

After oral administration of total alkaloids, the pharmacokinetic study of it was investigated. In addition, anti-allergic studies were carried out on ovalbumin-sensitized airways allergic inflammatory model of mice.

METHODS

The pharmacokinetics of total alkaloids (TA) was investigated in SD rat plasma by a fully-validated LC-MS/MS method. Then, an ovalbumin (OVA)-sensitized airways allergic inflammatory model was established, in which mice were intra-gastrically administrated by 3 times a day (8.3 and 16.7mg/kg) based on the pharmacokinetic behavior of TA) and single (25, 50mg/kg) treatment regimen. Dexamethasone was used as a positive control for corticosteroid drugs. Cellular infiltration was assessed in the broncho-alveolar lavage fluid (BALF). Expressions of interleukin-4 (IL-4) and interleukin-10 (IL-10) in the BALF were determined, levels of immunoglobulin E (IgE) and eotaxin in serum were measured, and superoxide dismutase (SOD) activities as well as malondialdehyde (MDA) content in the serum and BALF were examined. Finally, histopathological examination in the lung was assessed by H. E. staining.

RESULTS

The time course of plasma concentration of 4 bioactive indole alkaloids fitted an open two-compartment model after oral administration of total alkaloids at doses of 10, 25, and 50mg/kg. The area under the curve and the maximum concentration values of four major alkaloids increased dose-dependently, and half-life suggested a short-lasting pharmacological effect. Then, an ovalbumin-provoked airways allergic inflammatory model indicated that the pharmacological effect of administration of total alkaloids 3 times a day was a little better than that of single dose daily. The percentage of eosinophils in BALF was reduced obviously and the pathological damage of lung was also attenuated. There was also a significant reduction in IL-4 and promotion in IL-10 in the BALF. Serum IgE and eotaxin expression also significantly decreased in treated animals. Furthermore, the activity of SOD elevated remarkably and lipid peroxidation product (MDA) decreased in the administrated mice.

CONCLUSION

The pharmacological effects administrated for 3 times a day had precedence over single dose daily, which was related to the prolonged retention time and the maintained plasma concentration. Moreover, scholaricine and vallesamine might be responsible for the treatment of allergic asthma, mainly in total alkaloids.

1-[(2,3-Dihydro-1-benzofuran-2-yl) methyl]piperazines as novel anti-inflammatory compounds: Synthesis and evaluation on H3 R/H4 R

The histamine receptors (HRs) are members of G-protein-coupled receptor superfamily and traditional targets of huge therapeutic interests. Recently, H₃ R and H₄ R have been explored as targets for drug discovery, including in the search for dual-acting H₃ R/H₄ R ligands. The H₄ R, the most recent histamine receptor, is a promising target for novel anti-inflammatory agents in several conditions such as asthma and other chronic inflammatory diseases. Due to similarity with previously reported ligands of HRs, a set of 1-[(2,3-dihydro-1-benzofuran-2-yl)methyl]piperazines were synthesized and evaluated in competitive binding assays as H₃ R/H₄ R ligands herein. The results showed the compounds presented affinity (K_i ) for H₃ R/H₄ R in micromolar range, and they are more selective to H₃ R. All the compounds showed no important cytotoxicity to mammalian cells. The phenyl-substituted compound LINS01005 has shown the higher affinity of the set for H₄ R, but no considerable selectivity toward this receptor over H₃ R. LINS01005 showed interesting anti-inflammatory activity in murine asthma model, reducing the eosinophil counts in bronchoalveolar lavage fluid, as well as the COX-2 expression. The presented compounds are valuable prototypes for further improvements to achieve better anti-inflammatory agents.

Molecularly targeted therapies for asthma: Current development, challenges and potential clinical translation

Extensive research into the therapeutics of asthma has yielded numerous effective interventions over the past few decades. However, adverse effects and ineffectiveness of most of these medications especially in the management of steroid resistant severe asthma necessitate the development of better medications. Numerous drug targets with inherent airway smooth muscle tone modulatory role have been identified for asthma therapy. This article reviews the latest understanding of underlying molecular aetiology of asthma towards design and development of better antiasthma drugs. New drug candidates with their putative targets that have shown promising results in the preclinical and/or clinical trials are summarised. Examples of these interventions include restoration of Th1/Th2 balance by the use of newly developed immunomodulators such as toll-like receptor-9 activators (CYT003-QbG10 and QAX-935). Clinical trials revealed the safety and effectiveness of chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) antagonists such as OC0000459, BI-671800 and ARRY-502 in the restoration of Th1/Th2 balance. Regulation of cytokine activity by the use of newly developed biologics such as benralizumab, reslizumab, mepolizumab, lebrikizumab, tralokinumab, dupilumab and brodalumab are at the stage of clinical development. Transcription factors are potential targets for asthma therapy, for example SB010, a GATA-3 DNAzyme is at its early stage of clinical trial. Other candidates such as inhibitors of Rho kinases (Fasudil and Y-27632), phosphodiesterase inhibitors (GSK256066, CHF 6001, roflumilast, RPL 554) and proteinase of activated receptor-2 (ENMD-1068) are also discussed. Preclinical results of blockade of calcium sensing receptor by the use of calcilytics such as calcitriol abrogates cardinal signs of asthma. Nevertheless, successful translation of promising preclinical data into clinically viable interventions remains a major challenge to the development of novel anti-asthmatics.

Multiple Targeting Approaches on Histamine H3 Receptor Antagonists

With the very recent market approval of pitolisant (Wakix®), the interest in clinical applications of novel multifunctional histamine H₃ receptor antagonists has clearly increased. Since histamine H₃ receptor antagonists in clinical development have been tested for a variety of different indications, the combination of pharmacological properties in one molecule for improved pharmacological effects and reduced unwanted side-effects is rationally based on the increasing knowledge on the complex neurotransmitter regulations. The polypharmacological approaches on histamine H₃ receptor antagonists on different G-protein coupled receptors, transporters, enzymes as well as on NO-signaling mechanism are described, supported with some lead structures.

International Union of Basic and Clinical Pharmacology. XCVIII. Histamine Receptors

Histamine is a developmentally highly conserved autacoid found in most vertebrate tissues. Its physiological functions are mediated by four 7-transmembrane G protein-coupled receptors (H1R, H2R, H3R, H4R) that are all targets of pharmacological intervention. The receptors display molecular heterogeneity and constitutive activity. H1R antagonists are long known antiallergic and sedating drugs, whereas the H2R was identified in the 1970s and led to the development of H2R-antagonists that revolutionized stomach ulcer treatment. The crystal structure of ligand-bound H1R has rendered it possible to design new ligands with novel properties. The H3R is an autoreceptor and heteroreceptor providing negative feedback on histaminergic and inhibition on other neurons. A block of these actions promotes waking. The H4R occurs on immuncompetent cells and the development of anti-inflammatory drugs is anticipated.

Cherry-picked ligands at histamine receptor subtypes

Histamine, a biogenic amine, is considered as a principle mediator of multiple physiological effects through binding to its H1, H2, H3, and H4 receptors (H1-H4Rs). Currently, the HRs have gained attention as important targets for the treatment of several diseases and disorders ranging from allergy to Alzheimer's disease and immune deficiency. Accordingly, medicinal chemistry studies exploring histamine-like molecules and their physicochemical properties by binding and interacting with the four HRs has led to the development of a diversity of agonists and antagonists that display selectivity for each HR subtype. An overview on H1-R4Rs and developed ligands representing some key steps in development is provided here combined with a short description of structure-activity relationships for each class. Main chemical diversities, pharmacophores, and pharmacological profiles of most innovative H1-H4R agonists and antagonists are highlighted. Therefore, this overview should support the rational choice for the optimal ligand selection based on affinity, selectivity and efficacy data in biochemical and pharmacological studies. This article is part of the Special Issue entitled 'Histamine Receptors'.

Biased signalling: the instinctive skill of the cell in the selection of appropriate signalling pathways

GPCRs (G-protein-coupled receptors) are members of a family of proteins which are generally regarded as the largest group of therapeutic drug targets. Ligands of GPCRs do not usually activate all cellular signalling pathways linked to a particular seven-transmembrane receptor in a uniform manner. The fundamental idea behind this concept is that each ligand has its own ability, while interacting with the receptor, to activate different signalling pathways (or a particular set of signalling pathways) and it is this concept which is known as biased signalling. The importance of biased signalling is that it may selectively activate biological responses to favour therapeutically beneficial signalling pathways and to avoid adverse effects. There are two levels of biased signalling. First, bias can arise from the ability of GPCRs to couple to a subset of the available G-protein subtypes: Gαs, Gαq/11, Gαi/o or Gα12/13. These subtypes produce the diverse effects of GPCRs by targeting different effectors. Secondly, biased GPCRs may differentially activate G-proteins or β-arrestins. β-Arrestins are ubiquitously expressed and function to terminate or inhibit classic G-protein signalling and initiate distinct β-arrestin-mediated signalling processes. The interplay of G-protein and β-arrestin signalling largely determines the cellular consequences of the administration of GPCR-targeted drugs. In the present review, we highlight the particular functionalities of biased signalling and discuss its biological effects subsequent to GPCR activation. We consider that biased signalling is potentially allowing a choice between signalling through ‘beneficial’ pathways and the avoidance of ‘harmful’ ones.

The effect of selective antagonist of H4 receptor JNJ7777120 on nasal symptoms, cough, airway reactivity and inflammation in guinea pigs

The efficacy of H4R antagonist JNJ7777120 on nasal symptoms, cough, airway resistance (Raw), inflammatory cell count in bronchoalveolar lavage (BAL) and blood in ovalbumin (OVA) induced allergic rhinitis (AR) was studied in guinea pigs. Animals (n=8) were sensitized by i.p. OVA and were repeatedly challenged with nasal OVA to induce rhinitis, seven animals were not sensitized. Animals were pre-treated with JNJ7777120 2.5 and 5mg/kg i.p. 30 min prior OVA. Cough was induced by inhalation of citric acid, Raw was measured in vivo by Pennock's method as baseline, during AR and after JNJ7777120 treatment. Leucocyte count in BAL and blood was analyzed. JNJ7777120 (5mg/kg) significantly suppressed nasal symptoms and the number of coughs. This compound significantly inhibited airway reactivity to histamine, but not methacholine. Pre-treatment with JNJ7777120 5mg/kg did not influence significantly the leucocyte count in BAL and blood except for a significant decrease in monocyte count in blood compared to the control group (p<0.05). We conclude that the antitussive action of JNJ7777120 is peripheral. The primary effect of the compound is anti-inflammatory, and the suppression of cough is a consequence of reduced airway inflammation.

The histamine H4 receptor: from orphan to the clinic

The histamine H4 receptor (H4R) was first noted as a sequence in genomic databases that had features of a class A G-protein coupled receptor. This putative receptor was found to bind histamine consistent with its homology to other histamine receptors and thus became the fourth member of the histamine receptor family. Due to the previous success of drugs that target the H1 and H2 receptors, an effort was made to understand the function of this new receptor and determine if it represented a viable drug target. Taking advantage of the vast literature on the function of histamine, a search for histamine activity that did not appear to be mediated by the other three histamine receptors was undertaken. From this asthma and pruritus emerged as areas of particular interest. Histamine has long been suspected to play a role in the pathogenesis of asthma, but antihistamines that target the H1 and H2 receptors have not been shown to be effective for this condition. The use of selective ligands in animal models of asthma has now potentially filled this gap by showing a role for the H4R in mediating lung function and inflammation. A similar story exists for chronic pruritus associated with conditions such as atopic dermatitis. Antihistamines that target the H1 receptor are effective in reducing acute pruritus, but are ineffective in pruritus experienced by patients with atopic dermatitis. As for asthma, animal models have now suggested a role for the H4R in mediating pruritic responses, with antagonists of the H4R reducing pruritus in a number of different conditions. The anti-pruritic effect of H4R antagonists has recently been shown in human clinical studies, validating the preclinical findings in the animal models. A selective H4R antagonist inhibited histamine-induced pruritus in health volunteers and reduced pruritus in patients with atopic dermatitis. The history to date of the H4R provides an excellent example of the deorphanization of a novel receptor and the translation of this into clinical efficacy in humans.

Functional selectivity of G-protein-coupled receptors: from recombinant systems to native human cells

In the mid 1990s, it was assumed that a two-state model, postulating an inactive (R) state and an active (R*) state provides the molecular basis for GPCR activation. However, it became clear that this model could not accommodate many experimental observations. Accordingly, the two-state model was superseded by a multi-state model according to which any given ligand stabilizes a unique receptor conformation with distinct capabilities of activating down-stream G-proteins and β-arrestin. Much of this research was conducted with the β2-adrenoceptor in recombinant systems. At the molecular level, there is now no doubt anymore that ligand-specific receptor conformations, also referred to as functional selectivity, exist. This concept holds great potential for drug discovery in terms of developing drugs with higher selectivity for specific cells and/or cell functions and fewer side effects. A major challenge is the analysis for functional selectivity in native cells. Here, I discuss our current knowledge on functional selectivity of three representative GPCRs, the β2-adrenoceptor and the histamine H2- and H4-receptors, in recombinant systems and native human cells. Studies with human neutrophils and eosinophils support the concept of functional selectivity. A major strategy for the analysis of functional selectivity in native cells is to generate complete concentration/response curves with a large set of structurally diverse ligands for multiple parameters. Next, correlations of potencies and efficacies are analyzed, and deviations of the correlations from linearity are indicative for functional selectivity. Additionally, pharmacological inhibitors are used to dissect cell functions from each other.