Know your molecule: pharmacological characterization of drug candidates to enhance efficacy and reduce late-stage attrition

Despite advances in chemical, computational and biological sciences, the rate of attrition of drug candidates in clinical development is still high. A key point in the small-molecule discovery process that could provide opportunities to help address this challenge is the pharmacological characterization of hit and lead compounds, culminating in the selection of a drug candidate. Deeper characterization is increasingly important, because the 'quality' of drug efficacy, at least for G protein-coupled receptors (GPCRs), is now understood to be much more than activation of commonly evaluated pathways such as cAMP signalling, with many more 'efficacies' of ligands that could be harnessed therapeutically. Such characterization is being enabled by novel assays to characterize the complex behaviour of GPCRs, such as biased signalling and allosteric modulation, as well as advances in structural biology, such as cryo-electron microscopy. This article discusses key factors in the assessments of the pharmacology of hit and lead compounds in the context of GPCRs as a target class, highlighting opportunities to identify drug candidates with the potential to address limitations of current therapies and to improve the probability of them succeeding in clinical development.

Pseudoirreversible inhibition elicits persistent efficacy of a sphingosine 1-phosphate receptor 1 antagonist

Sphingosine 1-phosphate receptor 1 (S1PR1), a G protein-coupled receptor, is required for lymphocyte trafficking, and is a promising therapeutic target in inflammatory diseases. Here, we synthesize a competitive S1PR1 antagonist, KSI-6666, that effectively suppresses pathogenic inflammation. Metadynamics simulations suggest that the interaction of KSI-6666 with a methionine residue Met124 in the ligand-binding pocket of S1PR1 may inhibit the dissociation of KSI-6666 from S1PR1. Consistently, in vitro functional and mutational analyses reveal that KSI-6666 causes pseudoirreversible inhibition of S1PR1, dependent on the Met124 of the protein and substituents on the distal benzene ring of KSI-6666. Moreover, in vivo study suggests that this pseudoirreversible inhibition is responsible for the persistent activity of KSI-6666.

High-throughput kinetics in drug discovery

The importance of a drug's kinetic profile and interplay of structure-kinetic activity with PK/PD has long been appreciated in drug discovery. However, technical challenges have often limited detailed kinetic characterization of compounds to the latter stages of projects. This review highlights the advances that have been made in recent years in techniques, instrumentation, and data analysis to increase the throughput of detailed kinetic and mechanistic characterization, enabling its application earlier in the drug discovery process.

A dual role for CRTH2 in acute lung injury

Acute respiratory distress syndrome (ARDS) is a life-threatening clinical condition defined by rapid-onset respiratory failure following acute lung injury (ALI). The high mortality rate and rising incidence of ARDS due to COVID-19 make it an important research priority. Here we sought to investigate the role of chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) in ARDS. CRTH2 is a G protein-coupled receptor best studied in the context of type 2 immunity, but it also exerts effects on neutrophilic inflammation. To evaluate its role in mouse models of ARDS, we first examined its expression pattern on murine neutrophils. We found it is expressed on neutrophils, but only after extravasation into the lung. Next, we showed that CRTH2 expression on extravasated lung neutrophils promotes cell survival, as genetic deletion of CRTH2 and pharmacologic inhibition of CRTH2 using fevipiprant both led to increased apoptosis in vitro. We then evaluated the role of CRTH2 in vivo using a murine model of LPS-induced ALI. In line with the pro-inflammatory effects of CRTH2 in vitro, we observed improvement of lung injury in CRTH2-deficient mice in terms of vascular leak, weight loss and survival after LPS administration. However, neutrophilic inflammation was elevated, not suppressed in the CRTH2 KO. This finding indicated a second mechanism offsetting the pro-survival effect of CRTH2 on neutrophils. Bulk RNAseq of lung tissue indicated impairments in type 2 immune signaling in the CRTH2 KO, and qPCR and ELISA confirmed downregulation of IL-4, which is known to suppress neutrophilic inflammation. Thus, CRTH2 may play a dual role in ALI, directly promoting neutrophil cell survival, but indirectly suppressing neutrophil effector function via IL-4.

DP2 receptor activity sensor suited for antagonist screening and measurement of receptor dynamics in real-time

The DP2 receptor is a G-protein coupled receptor involved in allergic inflammation and is the target of recently developed antagonists already being tested in clinics. To get insights into DP2 receptor dynamics and to study its pharmacology on the level of the receptor, we constructed a fluorescence resonance energy transfer-based conformation sensor. The sensor reflects the selectivity profile of the DP2 receptor-wt and is suited for screening of agonists and antagonists due to its robust response. Furthermore, the sensor enables the direct measurement of DP2 receptor dynamics in real-time and revealed markedly distinct on- and off-rates of prostaglandin D2 between DP2 and DP1 receptors, suggesting a different mechanism of ligand receptor interaction.

Unraveling the Mechanism of Epichaperome Modulation by Zelavespib: Biochemical Insights on Target Occupancy and Extended Residence Time at the Site of Action

Drugs with a long residence time at their target sites are often more efficacious in disease treatment. The mechanism, however, behind prolonged retention at the site of action is often difficult to understand for non-covalent agents. In this context, we focus on epichaperome agents, such as zelavespib and icapamespib, which maintain target binding for days despite rapid plasma clearance, minimal retention in non-diseased tissues, and rapid metabolism. They have shown significant therapeutic value in cancer and neurodegenerative diseases by disassembling epichaperomes, which are assemblies of tightly bound chaperones and other factors that serve as scaffolding platforms to pathologically rewire protein-protein interactions. To investigate their impact on epichaperomes in vivo, we conducted pharmacokinetic and target occupancy measurements for zelavespib and monitored epichaperome assemblies biochemically in a mouse model. Our findings provide evidence of the intricate mechanism through which zelavespib modulates epichaperomes in vivo. Initially, zelavespib becomes trapped when epichaperomes bound, a mechanism that results in epichaperome disassembly, with no change in the expression level of epichaperome constituents. We propose that the initial trapping stage of epichaperomes is a main contributing factor to the extended on-target residence time observed for this agent in clinical settings. Zelavespib's residence time in tumors seems to be dictated by target disassembly kinetics rather than by frank drug-target unbinding kinetics. The off-rate of zelavespib from epichaperomes is, therefore, much slower than anticipated from the recorded tumor pharmacokinetic profile or as determined in vitro using diluted systems. This research sheds light on the underlying processes that make epichaperome agents effective in the treatment of certain diseases.

Indole-Based and Cyclopentenylindole-Based Analogues Containing Fluorine Group as Potential 18F-Labeled Positron Emission Tomography (PET) G-Protein Coupled Receptor 44 (GPR44) Tracers

Recently, growing evidence of the relationship between G-protein coupled receptor 44 (GPR44) and the inflammation-cancer system has garnered tremendous interest, while the exact role of GPR44 has not been fully elucidated. Currently, there is a strong and urgent need for the development of non-invasive in vivo GPR44 positron emission tomography (PET) radiotracers that can be used to aid the exploration of the relationship between inflammation and tumor biologic behavior. Accordingly, the choosing and radiolabeling of existing GPR44 antagonists containing a fluorine group could serve as a viable method to accelerate PET tracers development for in vivo imaging to this purpose. The present study aims to evaluate published (2000-present) indole-based and cyclopentenyl-indole-based analogues of the GPR44 antagonist to guide the development of fluorine-18 labeled PET tracers that can accurately detect inflammatory processes. The selected analogues contained a crucial fluorine nuclide and were characterized for various properties including binding affinity, selectivity, and pharmacokinetic and metabolic profile. Overall, 26 compounds with favorable to strong binding properties were identified. This review highlights the potential of GPR44 analogues for the development of PET tracers to study inflammation and cancer development and ultimately guide the development of targeted clinical therapies.

Pharmacodynamic model of slow reversible binding and its applications in pharmacokinetic/pharmacodynamic modeling: review and tutorial

Therapeutic responses of most drugs are initiated by the rate and degree of binding to their receptors or targets. The law of mass action describes the rate of drug-receptor complex association (k_on) and dissociation (k_off) where the ratio k_off/k_on is the equilibrium dissociation constant (K_d). Drugs with slow reversible binding (SRB) often demonstrate delayed onset and prolonged pharmacodynamic effects. This report reviews evidence for drugs with SRB features, describes previous pharmacokinetic/pharmacodynamic (PK/PD) modeling efforts of several such drugs, provides a tutorial on the mathematics and properties of SRB models, demonstrates applications of SRB models to additional compounds, and compares PK/PD fittings of SRB with other mechanistic models. We identified and summarized 52 drugs with in vitro-confirmed SRB from a PubMed literature search. Simulations with a SRB model and observed PK/PD profiles showed delayed and prolonged responses and that increasing doses/k_on or decreasing k_off led to greater expected maximum effects and a longer duration of effects. Recession slopes for return of responses to baseline after single doses were nearly linear with an inflection point that approaches a limiting value at larger doses. The SRB model newly captured literature data for the antihypertensive effects of candesartan and antiallergic effects of noberastine. Their PD profiles could also be fitted with indirect response and biophase models with minimal differences. The applicability of SRB models is probably commonplace, but underappreciated, owing to the need for in vitro confirmation of binding kinetics and the similarity of PK/PD profiles to models with other mechanistic determinants.

Long-term safety and exploratory efficacy of fevipiprant in patients with inadequately controlled asthma: the SPIRIT randomised clinical trial

BACKGROUND

The prostaglandin D₂ (PGD₂) receptor 2 (DP₂ receptor) pathway is an important regulator of the inflammatory cascade in asthma, which can be stimulated by allergic or non-allergic triggers. Fevipiprant is an oral, non-steroidal, highly selective, reversible antagonist of the DP₂ receptor that inhibits the binding of PGD₂ and its metabolites.

METHODS

SPIRIT, a 2-treatment period (52-week, double-blind and optional 104-week single-blind), randomised, placebo-controlled, multicentre, parallel-group study, assessed the long-term safety of fevipiprant (150 mg and 450 mg o.d.) added to standard of care in patients ≥ 12 years with uncontrolled asthma. Stratified block randomisation was used. Patients were randomised in an approximate ratio of 3:3:1 (fevipiprant 150 mg, fevipiprant 450 mg or placebo). Patients were either newly enrolled or had participated in a previous fevipiprant Phase 3 trial. Primary endpoints were: time-to-first treatment emergent adverse event (AE); serious AE; and AE leading to discontinuation from study treatment. Data from both treatment periods were combined for analyses. Data were collected during study site visits.

RESULTS

In total, 1093 patients were randomised to receive fevipiprant 150 mg, 1085 to fevipiprant 450 mg, and 360 to placebo. Overall, 1184 patients had ≥ 52 weeks' treatment, while 163 received ≥ 104 weeks' treatment. Both doses were well tolerated, with a safety profile similar to placebo both in new patients and in those enrolled from previous studies. In exploratory analyses, reduced rates of moderate-to-severe asthma exacerbations, increased time-to-first moderate-to-severe asthma exacerbation and improved FEV₁ were observed for both doses of fevipiprant versus placebo; these were without multiplicity adjustment and should be interpreted with caution. SPIRIT was terminated early, on 16 December 2019, by the Sponsor.

CONCLUSIONS

In patients with uncontrolled asthma, the addition of fevipiprant had a favourable long-term safety profile.

TRIAL REGISTRATION

Clinicaltrials.gov, NCT03052517, prospectively registered 23 January 2017, https://clinicaltrials.gov/ct2/show/NCT03052517 .

Prostaglandin D2 metabolites activate asthmatic patient-derived type 2 innate lymphoid cells and eosinophils via the DP2 receptor

BACKGROUND

Prostaglandin D2 (PGD2) signaling via prostaglandin D2 receptor 2 (DP2) contributes to atopic and non-atopic asthma. Inhibiting DP2 has shown therapeutic benefit in certain subsets of asthma patients, improving eosinophilic airway inflammation. PGD2 metabolites prolong the inflammatory response in asthmatic patients via DP2 signaling. The role of PGD2 metabolites on eosinophil and ILC2 activity is not fully understood.

METHODS

Eosinophils and ILC2s were isolated from peripheral blood of atopic asthmatic patients. Eosinophil shape change, ILC2 migration and IL-5/IL-13 cytokine secretion were measured after stimulation with seven PGD2 metabolites in presence or absence of the selective DP2 antagonist fevipiprant.

RESULTS

Selected metabolites induced eosinophil shape change with similar nanomolar potencies except for 9α,11β-PGF2. Maximal values in forward scatter of eosinophils were comparable between metabolites. ILC2s migrated dose-dependently in the presence of selected metabolites except for 9α,11β-PGF2 with EC50 values ranging from 17.4 to 91.7 nM. Compared to PGD2, the absolute cell migration was enhanced in the presence of Δ12-PGD2, 15-deoxy-Δ12,14-PGD2, PGJ2, Δ12-PGJ2 and 15-deoxy-Δ12,14-PGJ2. ILC2 cytokine production was dose dependent as well but with an average sixfold reduced potency compared to cell migration (IL-5 range 108.1 to 526.9 nM, IL-13 range: 125.2 to 788.3 nM). Compared to PGD2, the absolute cytokine secretion was reduced in the presence of most metabolites. Fevipiprant dose-dependently inhibited eosinophil shape change, ILC2 migration and ILC2 cytokine secretion with (sub)-nanomolar potencies.

CONCLUSION

Prostaglandin D2 metabolites initiate ILC2 migration and IL-5 and IL-13 cytokine secretion in a DP2 dependent manner. Our data indicate that metabolites may be important for in vivo eosinophil activation and ILC2 migration and to a lesser extent for ILC2 cytokine secretion.

Prostaglandin regulation of type 2 inflammation: From basic biology to therapeutic interventions

Type 2 immunity is critical for the protective and repair responses that mediate resistance to parasitic helminth infection. This immune response also drives aberrant inflammation during atopic diseases. Prostaglandins are a class of critical lipid mediators that are released during type 2 inflammation and are integral in controlling the initiation, activation, maintenance, effector functions, and resolution of Type 2 inflammation. In this review, we explore the roles of the different prostaglandin family members and the receptors they bind to during allergen‐ and helminth‐induced Type 2 inflammation and the mechanism through which prostaglandins promote or suppress Type 2 inflammation. Furthermore, we discuss the potential role of prostaglandins produced by helminth parasites in the regulation of host–pathogen interactions, and how prostaglandins may regulate the inverse relationship between helminth infection and allergy. Finally, we discuss opportunities to capitalize on our understanding of prostaglandin pathways to develop new therapeutic options for humans experiencing Type 2 inflammatory disorders that have a significant prostaglandin‐driven component including allergic rhinitis and asthma.

Efficacy and Safety of Prostaglandin D2 Receptor 2 Antagonism with Fevipiprant for Patients with Asthma: a Systematic Review and Meta-analysis of Randomized Controlled Trials

PURPOSE OF REVIEW

Accumulating evidence has shown that prostaglandin D2 (PGD2)-chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) pathway plays an important role in promoting eosinophilic airway inflammation in asthma. We aimed to assess the efficacy and safety of CRTH2 antagonist fevipiprant in patients with persistent asthma compared with placebo.

RECENT FINDINGS

We identified eligible studies by searching PubMed, EMBASE, the Cochrane Central Register of Controlled Trials and ClinicalTrials.gov. The study was registered as CRD 42020221714 ( http://www.crd.york.ac.uk/PROSPERO ). Ten randomized controlled trials with 7902 patients met our inclusion criteria. A statistically significant benefit of fevipiprant compared with placebo was shown in improving forced expiratory volume in 1 s (MD 0.05 L, 95% CI: 0.02 to 0.07; p < 0.0001), Asthma Control Questionnaire score (MD -0.10, 95% CI: -0.16 to -0.04; p = 0.001), and Asthma Quality of Life Questionnaire score (MD 0.08, 95% CI: 0.03 to 0.13; p = 0.003). Fevipiprant decreased number of patients with at least one asthma exacerbation requiring administration of systemic corticosteroids for 3 days or more (RR 0.86, 95% CI: 0.77 to 0.97; p = 0.01). Some benefits were a little more pronounced in the high eosinophil population (with an elevated blood eosinophil count or sputum eosinophil percentage) and in the 450 mg dose group. Fevipiprant was well tolerated with no safety issues compared with placebo. Fevipiprant could safely improve asthma outcomes compared to placebo. However, most of the differences didn't reach the minimal clinically important difference (MCID), thus the clinical benefits remained to be confirmed.

The Roles of Type 2 Cytotoxic T Cells in Inflammation, Tissue Remodeling, and Prostaglandin (PG) D2 Production Are Attenuated by PGD2 Receptor 2 Antagonism

Multiple proinflammatory effects of Tc2 cells are inhibited by DP2 antagonism.

Tissue-remodeling functions of Tc2 cells are attenuated by DP2 antagonism.

Autocrine/paracrine PGD₂ production in Tc2 cells is reduced by DP2 antagonism.

Human type 2 cytotoxic T (Tc2) cells are enriched in severe eosinophilic asthma and can contribute to airway eosinophilia. PGD₂ and its receptor PGD₂ receptor 2 (DP2) play important roles in Tc2 cell activation, including migration, cytokine production, and survival. In this study, we revealed novel, to our knowledge, functions of the PGD₂/DP2 axis in Tc2 cells to induce tissue-remodeling effects and IgE-independent PGD₂ autocrine production. PGD₂ upregulated the expression of tissue-remodeling genes in Tc2 cells that enhanced the fibroblast proliferation and protein production required for tissue repair and myofibroblast differentiation. PGD₂ stimulated Tc2 cells to produce PGD₂ using the routine PGD₂ synthesis pathway, which also contributed to TCR-dependent PGD₂ production in Tc2 cells. Using fevipiprant, a specific DP2 antagonist, we demonstrated that competitive inhibition of DP2 not only completely blocked the cell migration, adhesion, proinflammatory cytokine production, and survival of Tc2 cells triggered by PGD₂ but also attenuated the tissue-remodeling effects and autocrine/paracrine PGD₂ production in Tc2 induced by PGD₂ and other stimulators. These findings further confirmed the anti-inflammatory effect of fevipiprant and provided a better understanding of the role of Tc2 cells in the pathogenesis of asthma.

Efficacy and safety of fevipiprant in patients with uncontrolled asthma: Two replicate, phase 3, randomised, double-blind, placebo-controlled trials (ZEAL-1 and ZEAL-2)

BACKGROUND

These studies assessed the efficacy and safety of fevipiprant, an oral antagonist of the prostaglandin D₂ (PGD₂) receptor (DP₂), compared with placebo when added to standard-of-care (SoC) asthma therapy in patients with uncontrolled asthma.

METHODS

ZEAL-1 (NCT03215758) and ZEAL-2 (NCT03226392) are two replicate, phase 3, multicentre, randomised, double-blind, placebo-controlled, parallel-group studies in which fevipiprant 150 mg once daily (o.d.) or placebo was added to SoC asthma therapy in patients aged ≥12 years with uncontrolled asthma. Primary endpoint: change from baseline in pre-dose forced expiratory volume in 1 s (FEV₁) after 12 weeks' treatment. Key secondary endpoints: daytime asthma symptom score, short-acting β-agonist (SABA) use and Asthma Quality-of-Life Questionnaire (AQLQ+12) score after 12-weeks treatment.

FINDINGS

662 patients in ZEAL-1 and 685 patients in ZEAL-2 completed the treatment period. In ZEAL-1, the least squares (LS) mean change from baseline in pre-dose FEV₁ was 112 mL in fevipiprant vs 71 mL in placebo group (difference [∆]:41 mL; 95% CI: -6, 88; adjusted p-value 0·088). In ZEAL-2, the LS mean change in pre-dose FEV₁ was 126 mL and 157 mL in the fevipiprant and placebo groups, respectively (∆:-31 mL; 95% CI: -80, 18; adjusted p-value 0·214). For both studies, there were no statistically significant differences in the key secondary objectives between the treatment groups.

INTERPRETATION

The ZEAL studies did not demonstrate significant improvement in lung function or other clinical outcomes. These results suggest that DP₂ receptor inhibition with fevipiprant is not effective in the studied patient population.

The pharmacology of the prostaglandin D2 receptor 2 (DP2) receptor antagonist, fevipiprant

Fevipiprant is an oral, non-steroidal, highly selective, reversible antagonist of the prostaglandin D₂ (DP₂) receptor. The DP₂ receptor is a mediator of inflammation expressed on the membrane of key inflammatory cells, including eosinophils, Th2 cells, type 2 innate lymphoid cells, CD8⁺ cytotoxic T cells, basophils and monocytes, as well as airway smooth muscle and epithelial cells. The DP₂ receptor pathway regulates the allergic and non-allergic asthma inflammatory cascade and is activated by the binding of prostaglandin D₂. Fevipiprant is metabolised by several uridine 5'-diphospho glucuronosyltransferase enzymes to an inactive acyl-glucuronide (AG) metabolite, the only major human metabolite. Both fevipiprant and its AG metabolite are eliminated by urinary excretion; fevipiprant is also possibly cleared by biliary excretion. These parallel elimination pathways suggested a low risk of major drug-drug interactions (DDI), pharmacogenetic or ethnic variability for fevipiprant, which was supported by DDI and clinical studies of fevipiprant. Phase II clinical trials of fevipiprant showed reduction in sputum eosinophilia, as well as improvement in lung function, symptoms and quality of life in patients with asthma. While fevipiprant reached the most advanced state of development to date of an oral DP₂ receptor antagonist in a worldwide Phase III clinical trial programme, the demonstrated efficacy did not support further clinical development in asthma.

Population Pharmacokinetic Analysis of Fevipiprant in Healthy Subjects and Asthma Patients using a Tukey’s g-and-h Distribution

Aim The objective of this analysis was to characterize the population pharmacokinetics (PK) of fevipiprant in asthma patients and to evaluate the effect of baseline covariates on the PK of fevipiprant.

Methods PK data from 1281 healthy subjects or asthma patients were available after single or once daily dosing of fevipiprant. Population PK analysis was conducted to describe fevipiprant plasma concentration data using a non-linear mixed effect modeling approach.

Results Fevipiprant PK was described by a two-compartment model with first-order absorption and first-order elimination. Exploration of fevipiprant PK in the population from the phase III studies revealed an over-dispersed and skewed distribution. This unusual distribution was described using Tukey’s g-and-h distribution (TGH) on the between-subject variability of apparent clearance (CL/F). The model identified a significant impact of disease status on CL/F, with the value in healthy subjects being 62% higher than that in asthma patients. Bodyweight, age and renal function showed statistically significant impact on fevipiprant clearance; however, compared with a typical asthma patient, the simulated difference in steady-state exposure was at most 16%.

Conclusion Fevipiprant PK was described by a two-compartment model with first-order absorption and first-order elimination. The TGH distribution was appropriate to describe the over-dispersed and skewed PK data as observed in the current studies. Asthma patients had approximately 37% higher exposure than healthy subjects did. Other covariates changed exposure by at most 16%.

Clinical Investigation of Metabolic and Renal Clearance Pathways Contributing to the Elimination of Fevipiprant Using Probenecid as Perpetrator

Fevipiprant, an oral, nonsteroidal, highly selective, reversible, and competitive prostaglandin D₂ receptor 2 antagonist, is eliminated by glucuronidation and by direct renal excretion predominantly via organic anion transporter (OAT) 3. This study aimed to assess the effect of simultaneous UDP-glucuronosyltransferase (UGT) and OAT3 inhibition by probenecid on the pharmacokinetics of fevipiprant and its acyl glucuronide (AG) metabolite to support the dosing recommendation of fevipiprant in the presence of drugs inhibiting these pathways; however, phase III clinical trial results did not support its submission. This was a single-center, open-label, single-sequence, two-period crossover study in healthy subjects. Liquid chromatography with tandem mass spectrometry was used to measure concentrations of fevipiprant and its AG metabolite in plasma and urine. In the presence of probenecid, the mean maximum concentrations of fevipiprant increased approximately 1.7-fold, and the area under the concentration-time curve in plasma increased approximately 2.5-fold, whereas the mean apparent volume of distribution and the AG metabolite:fevipiprant ratio decreased. The apparent systemic clearance decreased by approximately 60% and the renal clearance decreased by approximately 88% in the presence of probenecid. Using these data and those from previous studies, the relative contribution of OAT and UGT inhibition to the overall effect of probenecid was estimated. Furthermore, a general disposition scheme for fevipiprant was developed, showing how a perpetrator drug such as probenecid, which interferes with two key elimination pathways of fevipiprant, causes only a moderate increase in exposure and allows estimation of the drug-drug inhibition when only one of the two pathways is inhibited. SIGNIFICANCE STATEMENT: In this drug-drug interaction (DDI) study, probenecid was used as a tool to inhibit both glucuronidation and active renal secretion of fevipiprant. The combination of plasma and urine pharmacokinetic data from this study with available data allowed the development of a quantitative scheme to describe the fate of fevipiprant in the body, illustrating why the DDI effect on fevipiprant is weak-to-moderate even if a perpetrator drug inhibits several elimination pathways.

Luciferase Complementation Approaches to Measure GPCR Signaling Kinetics and Bias

An understanding of the kinetic contributions to G protein-coupled receptor pharmacology and signaling is increasingly important in compound profiling. Nonequilibrium conditions are commonly present in vivo, for example, as the drug competes with dynamic changes in hormone or neurotransmitter concentration for the receptor. Under such conditions individual binding kinetic properties of the ligands can influence duration of action, local ligand concentration, and functional properties such as the degree of insurmountable inhibition. Mapping the kinetic patterns of GPCR signaling events elicited by agonists, rather than a peak response at a single timepoint, is often key to predicting their functional impact. This is also a path to a better understanding of the origins of ligand bias, and whether such ligands demonstrate their effects through selection of distinct GPCR conformations, or via their kinetic properties. Recent developments in complementation approaches, based on a small bright shrimp luciferase Nanoluc, provide a new route to kinetic analysis of GPCR signaling in living cells that is amenable to the throughput required for compound profiling. In the NanoBiT luciferase complementation system, GPCRs and effector proteins are tagged with Nanoluc fragments optimized for their low interacting affinity and stability. The interactions brought about by GPCR recruitment of the effector are reproduced by a rapid and reversible increase in NanoBiT luminescence, in the presence of its substrate furimazine. Here we discuss the methods for optimizing and validating the GPCR NanoBiT assays, and protocols for their application to study endpoint and kinetic aspects of agonist and antagonist pharmacology. We also describe how timecourse families of agonist concentration response curves, derived from a single NanoBiT assay experiment, can be used to evaluate the kinetic components in operational model derived parameters of ligand bias.

Effectiveness of fevipiprant in reducing exacerbations in patients with severe asthma (LUSTER-1 and LUSTER-2): two phase 3 randomised controlled trials

BACKGROUND

Fevipiprant, an oral antagonist of the prostaglandin D₂ receptor 2, reduced sputum eosinophils and improved lung function in phase 2 trials of patients with asthma. We aimed to investigate whether fevipiprant reduces asthma exacerbations in patients with severe asthma.

METHODS

LUSTER-1 and LUSTER-2 were two phase 3 randomised, double-blind, placebo-controlled, parallel-group, replicate 52-week studies; LUSTER-1 took place at 174 clinical sites in 25 countries and LUSTER 2 took place at 169 clinical sites in 19 countries. Fevipiprant or placebo was added to Global Initiative for Asthma Steps 4 and 5 therapy in adolescents and adults with severe asthma. Patients aged 12 years or older with uncontrolled asthma on dual or triple asthma therapy were randomly assigned by use of interactive response technology to one of three treatment groups (once-daily fevipiprant 150 mg, fevipiprant 450 mg, or placebo) in a 1:1:1 ratio within each of the randomisation strata: peripheral blood eosinophil counts (<250 cells per μL or ≥250 cells per μL), patient age (<18 years or ≥18 years), and use or non-use of oral corticosteroids as part of their standard of care asthma therapy. The primary efficacy endpoint was the annualised rate of moderate to severe asthma exacerbations with 150 mg or 450 mg doses of fevipiprant once daily compared with placebo over 52 weeks, in patients with high blood eosinophil counts (≥250 cells per μL) and in the overall study population. All patients who underwent randomisation and received at least one dose of study medication were included in efficacy and safety analyses. These trials are registered with ClinicalTrials.gov, NCT02555683 (LUSTER-1) and NCT02563067 (LUSTER-2), and are complete and no longer recruiting.

FINDINGS

Between Dec 11, 2015, and Oct 25, 2018, 894 patients were randomly assigned to fevipiprant 150 mg (n=301), fevipiprant 450 mg (n=295), or placebo (n=298) in LUSTER-1. Between Dec 3, 2015, and July 10, 2018, 877 patients were randomly assigned to fevipiprant 150 mg (n=296), fevipiprant 450 mg (n=294), or placebo (n=287) in LUSTER-2. In the high eosinophil population, in LUSTER-1 the annualised rate ratio of moderate to severe exacerbations compared with placebo was 1·04 (95% CI 0·77-1·41) for fevipiprant 150 mg and 0·83 (0·61-1·14) for fevipiprant 450 mg, and in LUSTER-2 it was 0·69 (0·50-0·96) for fevipiprant 150 mg and 0·72 (0·52-1·01) for fevipiprant 450 mg. In the overall population, in LUSTER-1 the annualised rate ratio of moderate to severe exacerbations compared with placebo was 0·96 (95% CI 0·75-1·22) for fevipiprant 150 mg and 0·78 (0·61-1·01) for fevipiprant 450 mg and in LUSTER-2 it was 0·82 (0·62-1·07) for fevipiprant 150 mg and 0·76 (0·58-1·00) for fevipiprant 450 mg. In the overall pooled population of both studies, serious adverse events occurred in 53 (9%) patients in the fevipiprant 150 mg group, 50 (9%) in the fevipiprant 450 mg group, and 50 (9%) in the placebo group. Adverse events leading to death occurred in two (<1%) patients in the fevipiprant 450 mg group and three (<1%) in the placebo group.

INTERPRETATION

Although neither trial showed a statistically significant reduction in asthma exacerbations after adjusting for multiple testing, consistent and modest reductions in exacerbations rates were observed in both studies with the 450 mg dose of fevipiprant.

FUNDING

Novartis.

Same Target, Different Therapeutic Outcomes: The Case of CAY10471 and Fevipiprant on CRTh2 Receptor in Treatment of Allergic Rhinitis and Asthma

OBJECTIVE

Prostaglandin 2 (PGD2) mediated signalling of Chemoattractant Receptorhomologous molecule expressed on Th2 cells (CRTh2) receptor has been implicated in the recruitment of inflammatory cells. This explains the design of highly selective compounds with innate abilities to antagonize PGD2-CRTh2 interactions and prevent pro-inflammatory allergies such as rhinitis and uncontrolled asthma. The development of PGD2-competitive CRTh2 binders; CAY10471 and Fevipiprant represent remarkable therapeutic progress even though they elicit disparate pharmacological propensities despite utilizing the same binding pocket.

METHODS & RESULTS

In this study, we seek to pinpoint the underlying phenomenon associated with differential CRTh2 therapeutic inhibition by CAY10471 and Fevipiprant using membraneembedded molecular dynamics simulation. Findings revealed that the common carboxylate group of both compounds elicited strong attractive charges with active site Arg170 and Lys210. Interestingly, a distinctive feature was the steady occurrence of high-affinity salt-bridges and an Arg170-mediated pi-cation interaction with the tetrahydrocarbozole ring of CAY10471. Further investigations into the active site motions of both ligands revealed that CAY10471 was relatively more stable. Comparative binding analyses also revealed that CAY10471 exhibited higher ΔG, indicating the cruciality of the ring stabilization role mediated by Arg170. Moreover, conformational analyses revealed that the inhibitory activity of CAY10471 was more prominent on CRTh2 compared to Fevipiprant.

CONCLUSIONS

These findings could further advance the strategic design of novel CRTh2 binders in the treatment of diseases related to pro-inflammatory allergies.

A Study of the Effect of Cyclosporine on Fevipiprant Pharmacokinetics and its Absolute Bioavailability Using an Intravenous Microdose Approach

This drug-drug interaction study determined the effect of cyclosporine, an inhibitor of organic anion transporting polypeptide (OATP) 1B3 and P-gp, on the pharmacokinetics (PK) of fevipiprant, an oral, highly selective, competitive antagonist of the prostaglandin D₂ receptor 2 and a substrate of the two transporters. The concomitant administration of an intravenous microdose of stable isotope-labeled fevipiprant provided the absolute bioavailability of fevipiprant as well as mechanistic insights into its PK and sensitivity to drug interactions. Liquid chromatography-mass spectrometry/mass spectrometry was used to measure plasma and urine concentrations. Geometric mean ratios [90% confidence interval (CI)] for oral fevipiprant with or without cyclosporine were 3.02 (2.38, 3.82) for C _max, 2.50 (2.17, 2.88) for AUC_last, and 2.35 (1.99, 2.77) for AUC_inf The geometric mean ratios (90% CI) for fevipiprant intravenous microdose with or without cyclosporine were 1.04 (0.86, 1.25) for C _max, 2.04 (1.83, 2.28) for AUC_last, and 1.95 (1.76, 2.16) for AUC_inf The absolute bioavailability for fevipiprant was approximately 0.3 to 0.4 in the absence and 0.5 in the presence of cyclosporine. The intravenous microdose allowed differentiation between systemic and presystemic effects of cyclosporine on fevipiprant, demonstrating a small (approximately 1.2-fold) presystemic effect of cyclosporine and a larger (approximately twofold) effect on systemic elimination of fevipiprant. Uptake by OATP1B3 appears to be the rate-limiting step in the hepatic elimination of fevipiprant, whereas P-gp does not have a relevant effect on oral absorption. SIGNIFICANCE STATEMENT: The drug interaction investigated here with cyclosporine, an inhibitor of several drug transporters, provides a refined quantitative understanding of the role of active transport processes in liver and intestine for the absorption and elimination of fevipiprant as well as the basis to assess the need for dose adjustment in the presence of transporter inhibitors. The applied intravenous microdose approach presents a strategy to maximize learnings from a trial, limit the number and duration of clinical trials, and enhance mechanistic drug-drug interaction understanding.

Sustained exposure to prostaglandin D2 augments the contraction induced by acetylcholine via a DP1 receptor-mediated activation of p38 in bronchial smooth muscle of naive mice

Prostaglandin D₂ (PGD₂), one of the key lipid mediators of allergic airway inflammation, is increased in the airways of asthmatics. However, the role of PGD₂ in the pathogenesis of asthma is not fully understood. In the present study, effects of PGD₂ on smooth muscle contractility of the airways were determined to elucidate its role in the development of airway hyperresponsiveness (AHR). In a murine model of allergic asthma, antigen challenge to the sensitized animals caused a sustained increase in PGD₂ levels in bronchoalveolar lavage (BAL) fluids, indicating that smooth muscle cells of the airways are continually exposed to PGD₂ after the antigen exposure. In bronchial smooth muscles (BSMs) isolated from naive mice, a prolonged incubation with PGD₂ (10⁻⁵ M, for 24 h) induced an augmentation of contraction induced by acetylcholine (ACh): the ACh concentration-response curve was significantly shifted upward by the 24-h incubation with PGD₂. Application of PGD₂ caused phosphorylation of ERK1/2 and p38 in cultured BSM cells: both of the PGD₂-induced events were abolished by laropiprant (a DP₁ receptor antagonist) but not by fevipiprant (a DP₂ receptor antagonist). In addition, the BSM hyperresponsiveness to ACh induced by the 24-h incubation with PGD₂ was significantly inhibited by co-incubation with SB203580 (a p38 inhibitor), whereas U0126 (a ERK1/2 inhibitor) had no effect on it. These findings suggest that prolonged exposure to PGD₂ causes the BSM hyperresponsiveness via the DP₁ receptor-mediated activation of p38. A sustained increase in PGD₂ in the airways might be a cause of the AHR in allergic asthmatics.

The impact of the prostaglandin D2 receptor 2 and its downstream effects on the pathophysiology of asthma

Current research suggests that the prostaglandin D₂ (PGD₂ ) receptor 2 (DP₂ ) is a principal regulator in the pathophysiology of asthma, because it stimulates and amplifies the inflammatory response in this condition. The DP₂ receptor can be activated by both allergic and nonallergic stimuli, leading to several pro-inflammatory events, including eosinophil activation and migration, release of the type 2 cytokines interleukin (IL)-4, IL-5 and IL-13 from T helper 2 (Th2) cells and innate lymphoid cells type 2 (ILCs), and increased airway smooth muscle mass via recruitment of mesenchymal progenitors to the airway smooth muscle bundle. Activation of the DP₂ receptor pathway has potential downstream effects on asthma pathophysiology, including on airway epithelial cells, mucus hypersecretion, and airway remodelling, and consequently might impact asthma symptoms and exacerbations. Given the broad distribution of DP₂ receptors on immune and structural cells involved in asthma, this receptor is being explored as a novel therapeutic target.

G Protein-Coupled Receptors in Asthma Therapy: Pharmacology and Drug Action

Asthma is a heterogeneous inflammatory disease of the airways that is associated with airway hyperresponsiveness and airflow limitation. Although asthma was once simply categorized as atopic or nonatopic, emerging analyses over the last few decades have revealed a variety of asthma endotypes that are attributed to numerous pathophysiological mechanisms. The classification of asthma by endotype is primarily routed in different profiles of airway inflammation that contribute to bronchoconstriction. Many asthma therapeutics target G protein-coupled receptors (GPCRs), which either enhance bronchodilation or prevent bronchoconstriction. Short-acting and long-acting β 2-agonists are widely used bronchodilators that signal through the activation of the β 2-adrenergic receptor. Short-acting and long-acting antagonists of muscarinic acetylcholine receptors are used to reduce bronchoconstriction by blocking the action of acetylcholine. Leukotriene antagonists that block the signaling of cysteinyl leukotriene receptor 1 are used as an add-on therapy to reduce bronchoconstriction and inflammation induced by cysteinyl leukotrienes. A number of GPCR-targeting asthma drug candidates are also in different stages of development. Among them, antagonists of prostaglandin D2 receptor 2 have advanced into phase III clinical trials. Others, including antagonists of the adenosine A2B receptor and the histamine H4 receptor, are in early stages of clinical investigation. In the past decade, significant research advancements in pharmacology, cell biology, structural biology, and molecular physiology have greatly deepened our understanding of the therapeutic roles of GPCRs in asthma and drug action on these GPCRs. This review summarizes our current understanding of GPCR signaling and pharmacology in the context of asthma treatment. SIGNIFICANCE STATEMENT: Although current treatment methods for asthma are effective for a majority of asthma patients, there are still a large number of patients with poorly controlled asthma who may experience asthma exacerbations. This review summarizes current asthma treatment methods and our understanding of signaling and pharmacology of G protein-coupled receptors (GPCRs) in asthma therapy, and discusses controversies regarding the use of GPCR drugs and new opportunities in developing GPCR-targeting therapeutics for the treatment of asthma.

New treatments for asthma: From the pathogenic role of prostaglandin D2 to the therapeutic effects of fevipiprant

Prostaglandin D₂ (PGD₂) is a pleiotropic mediator, significantly involved in the pathogenesis of type 2 (T2) asthma because of its biologic actions exerted on both immune/inflammatory and airway structural cells. In particular, the pro-inflammatory and pro-remodelling effects of PGD₂ are mainly mediated by stimulation of chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2). This receptor is the target of the oral competitive antagonist fevipiprant, which on the basis of recent phase II studies is emerging as a potential very promising anti-asthma drug. Indeed, fevipiprant appears to be safe and effective, especially in consideration of its ability to inhibit eosinophilic bronchial inflammation and improve forced expiratory volume in one second (FEV₁). Further ongoing phase III trials will definitely clarify if fevipiprant can prospectively become a valid option for an efficacious add-on treatment of moderate-to-severe T2-high asthma.

Targeting cell signaling in allergic asthma

Asthma is chronic inflammation of the airways characterized by airway hyper-responsiveness, wheezing, cough, and dyspnea. Asthma affects >350 million people worldwide. The Th2 immune response is a major contributor to the pathophysiology of asthma. Targeted therapy modulating cell signaling pathways can be a powerful strategy to design new drugs to treat asthma. The potential molecular pathways that can be targeted include IL-4-IL-13-JAK-STAT-MAP kinases, adiponectin-iNOS-NF-κB, PGD2-CRTH2, IFNs-RIG, Wnt/β-catenin-FAM13A, FOXC1-miR-PI3K/AKT, JNK-Gal-7, Nrf2-ROS, Foxp3-RORγt, CysLTR, AMP, Fas-FasL, PTHrP/PPARγ, PAI-1, FcɛRI-LAT-SLP-76, Tim-3-Gal-9, TLRs-MyD88, PAR2, and Keap1/Nrf2/ARE. Therapeutic drugs can be designed to target one or more of these pathways to treat asthma.

Investigating the Influence of Tracer Kinetics on Competition-Kinetic Association Binding Assays: Identifying the Optimal Conditions for Assessing the Kinetics of Low-Affinity Compounds

An increased appreciation of the importance of optimizing drug-binding kinetics has lead to the development of various techniques for measuring the kinetics of unlabeled compounds. One approach is the competition-association kinetic binding method first described in the 1980s. The kinetic characteristics of the tracer employed greatly affects the reliability of estimated kinetic parameters, a barrier to successfully introducing these kinetic assays earlier in the drug discovery process. Using a modeling and Monte Carlo simulation approach, we identify the optimal tracer characteristics for determining the kinetics of the range of unlabeled ligands typically encountered during the different stages of a drug discovery program (i.e., rapidly dissociating, e.g., k _off = 10 minute^-1 low-affinity "hits" through to slowly dissociating e.g., k _off = 0.01 minute^-1 high-affinity "candidates"). For more rapidly dissociating ligands (e.g., k _off = 10 minute^-1), the key to obtaining accurate kinetic parameters was to employ a tracer with a relatively fast off-rate (e.g., k _off = 1 minute^-1) or, alternatively, to increase the tracer concentration. Reductions in assay start-time ≤1second and read frequency ≤5 seconds significantly improved the reliability of curve fitting. Timing constraints are largely dictated by the method of detection, its inherent sensitivity (e.g., TR-FRET versus radiometric detection), and the ability to inject samples online. Furthermore, we include data from TR-FRET experiments that validate this simulation approach, confirming its practical utility. These insights into the optimal experimental parameters for development of competition-association assays provide a framework for identifying and testing novel tracers necessary for profiling unlabeled competitors, particularly rapidly dissociating low-affinity competitors.

GPR44 as a Target for Imaging Pancreatic Beta-Cell Mass

PURPOSE OF REVIEW

Quantitative markers for beta-cell mass (BCM) in human pancreas are currently lacking. Medical imaging using positron emission tomography (PET) markers for beta-cell restricted targets may provide an accurate and non-invasive measurement of BCM, to assist diagnosis and treatment of metabolic disease. GPR44 was recently discovered as a putative marker for beta cells and this review summarizes the developments so far.

RECENT FINDINGS

Several small molecule binders targeting GPR44 have been radiolabeled for PET imaging and evaluated in vitro and in small and large animal models. ¹¹C-AZ12204657 and ¹¹C-MK-7246 displayed a dose-dependent and GPR44-mediated binding to beta cells both in vitro and in vivo, with negligible uptake in exocrine pancreas. GPR44 represents an attractive target for visualization of BCM. Further progress in radioligand development including clinical testing is expected to clarify the role of GPR44 as a surrogate marker for BCM in humans.

Fevipiprant has a low risk of influencing co-medication pharmacokinetics: Impact on simvastatin and rosuvastatin in different SLCO1B1 genotypes

Fevipiprant, a prostaglandin D₂ receptor 2 antagonist, is in clinical development as a treatment for asthma. The goal of this study was to assess the potential of fevipiprant to cause drug-drug interactions (DDI) as a perpetrator, that is, by altering the pharmacokinetics (PK) of co-medications. In vitro drug interaction studies of clinically relevant drug metabolizing enzymes and transporters were conducted for fevipiprant and its acyl glucuronide (AG) metabolite. Comparison of K_i values with unbound systemic or portal vein steady-state plasma exposure of fevipiprant and its AG metabolite revealed the potential for inhibition of organic anion transporting polypeptide 1B1 (OATP1B1) transporters (R-value of 5.99), while other targets including cytochrome P450 enzymes were not, or only marginally, inhibited. Consequently, an open-label, two-part, two-period, single-sequence clinical study assessed the effect of fevipiprant 450 mg QD on the pharmacokinetics of simvastatin 20 mg and rosuvastatin 20 mg, two statins with different dependency in OATP1B1-mediated hepatic uptake, in healthy adult volunteers. The study also assessed the pharmacogenetics of the SLCO1B1 gene, which encodes OATP1B1. Clinically, fevipiprant 450 mg QD showed a low potential for interaction and increased the peak concentrations of simvastatin acid and rosuvastatin by 2.23- and 1.87-fold, respectively, with little or no impact on total exposure. Genotype analysis confirmed that SLCO1B1 genotype influences statin pharmacokinetics to a similar extent either with or without fevipiprant co-administration. In summary, fevipiprant at 450 mg QD has only minor liabilities as a perpetrator for DDI.

Drug-receptor kinetics and sigma-1 receptor affinity differentiate clinically evaluated histamine H3 receptor antagonists

The histamine H3 receptor is a G protein-coupled receptor (GPCR) drug target that is highly expressed in the CNS, where it acts as both an auto- and hetero-receptor to regulate neurotransmission. As such, it has been considered as a relevant target in disorders as varied as Alzheimer's disease, schizophrenia, neuropathic pain and attention deficit hyperactivity disorder. A range of competitive antagonists/inverse agonists have progressed into clinical development, with pitolisant approved for the treatment of narcolepsy. Given the breadth of compounds developed and potential therapeutic indications, we assessed the comparative pharmacology of six investigational histamine H3 agents, including pitolisant, using native tissue and recombinant cells. Whilst all of the compounds tested displayed robust histamine H3 receptor inverse agonism and did not differentiate between the main H3 receptor splice variants, they displayed a wide range of affinities and kinetic properties, and included rapidly dissociating (pitolisant, S 38093-2, ABT-239) and slowly dissociating (GSK189254, JNJ-5207852, PF-3654746) agents. S 38093-2 had the lowest histamine H3 receptor affinity (pKB values 5.7-6.2), seemingly at odds with previously reported, potent in vivo activity in models of cognition. We show here that at pro-cognitive and anti-hyperalgesic/anti-allodynic doses, S 38093-2 preferentially occupies the mouse sigma-1 receptor in vivo, only engaging the histamine H3 receptor at doses associated with wakefulness promotion and neurotransmitter (histamine, ACh) release. Furthermore, pitolisant, ABT-239 and PF-3654746 also displayed appreciable sigma-1 receptor affinity, suggesting that this property differentiates clinically evaluated histamine H3 receptor antagonists and may play a role in their efficacy.

Prostaglandin D2 receptor antagonists in allergic disorders: safety, efficacy, and future perspectives

INTRODUCTION

Prostaglandin D₂ (PGD₂) is a major cyclooxygenase mediator that is synthesized by activated human mast cells and other immune cells. The biological effects of PGD₂ are mediated by D-prostanoid (DP₁), DP₂ (CRTH2) and thromboxane prostanoid (TP) receptors that are expressed on several immune and non-immune cells involved in allergic inflammation. PGD₂ exerts various proinflammatory effects relevant to the pathophysiology of allergic disorders. Several selective, orally active, DP₂ receptor antagonists and a small number of DP₁ receptor antagonists are being developed for the treatment of allergic disorders.

AREAS COVERED

The role of DP₂ and DP₁ receptor antagonists in the treatment of asthma and allergic rhinitis.

EXPERT OPINION

Head-to-head studies that compare DP₁ antagonists with the standard treatment for allergic rhinitis are necessary to verify the role of these novel drugs as mono- or combination therapies. Further clinical trials are necessary to verify whether DP₂ antagonists as monotherapies or, more likely, as add-on therapies, will be effective for the treatment of different phenotypes of adult and childhood asthma. Long-term studies are necessary to evaluate the safety of targeted anti-PGD₂ treatments.

Prostaglandin D₂ Induces Ca2+ Sensitization of Contraction without Affecting Cytosolic Ca2+ Level in Bronchial Smooth Muscle

Prostaglandin D₂ (PGD₂) is one of the key lipid mediators of allergic airway inflammation, including bronchial asthma. However, the role of PGD₂ in the pathogenesis of asthma is not fully understood. In the present study, the effect of PGD₂ on smooth muscle contractility of the airways was determined to elucidate its role in the development of airway hyperresponsiveness (AHR). In isolated bronchial smooth muscles (BSMs) of naive mice, application of PGD₂ (10^-9⁻10^-5 M) had no effect on the baseline tension. However, when the tissues were precontracted partially with 30 mM K⁺ (in the presence of 10^-6 M atropine), PGD₂ markedly augmented the contraction induced by the high K⁺ depolarization. The PGD₂-induced augmentation of contraction was significantly inhibited both by 10^-6 M laropiprant (a selective DP₁ antagonist) and 10^-7 M Y-27632 (a Rho-kinase inhibitor), indicating that a DP₁ receptor-mediated activation of Rho-kinase is involved in the PGD₂-induced BSM hyperresponsiveness. Indeed, the GTP-RhoA pull-down assay revealed an increase in active form of RhoA in the PGD₂-treated mouse BSMs. On the other hand, in the high K⁺-depolarized cultured human BSM cells, PGD₂ caused no further increase in cytosolic Ca²⁺ concentration. These findings suggest that PGD₂ causes RhoA/Rho-kinase-mediated Ca²⁺ sensitization of BSM contraction to augment its contractility. Increased PGD₂ level in the airways might be a cause of the AHR in asthma.

The prostaglandin D2 receptor 2 pathway in asthma: a key player in airway inflammation

Asthma is characterised by chronic airway inflammation, airway obstruction and hyper-responsiveness. The inflammatory cascade in asthma comprises a complex interplay of genetic factors, the airway epithelium, and dysregulation of the immune response.Prostaglandin D2 (PGD2) is a lipid mediator, predominantly released from mast cells, but also by other immune cells such as TH2 cells and dendritic cells, which plays a significant role in the pathophysiology of asthma. PGD2 mainly exerts its biological functions via two G-protein-coupled receptors, the PGD2 receptor 1 (DP1) and 2 (DP2). The DP2 receptor is mainly expressed by the key cells involved in type 2 immune responses, including TH2 cells, type 2 innate lymphoid cells and eosinophils. The DP2 receptor pathway is a novel and important therapeutic target for asthma, because increased PGD2 production induces significant inflammatory cell chemotaxis and degranulation via its interaction with the DP2 receptor. This interaction has serious consequences in the pulmonary milieu, including the release of pro-inflammatory cytokines and harmful cationic proteases, leading to tissue remodelling, mucus production, structural damage, and compromised lung function. This review will discuss the importance of the DP2 receptor pathway and the current understanding of its role in asthma.

Structures of the Human PGD2 Receptor CRTH2 Reveal Novel Mechanisms for Ligand Recognition

The signaling of prostaglandin D₂ (PGD₂) through G-protein-coupled receptor (GPCR) CRTH2 is a major pathway in type 2 inflammation. Compelling evidence suggests the therapeutic benefits of blocking CRTH2 signaling in many inflammatory disorders. Currently, a number of CRTH2 antagonists are under clinical investigation, and one compound, fevipiprant, has advanced to phase 3 clinical trials for asthma. Here, we present the crystal structures of human CRTH2 with two antagonists, fevipiprant and CAY10471. The structures, together with docking and ligand-binding data, reveal a semi-occluded pocket covered by a well-structured amino terminus and different binding modes of chemically diverse CRTH2 antagonists. Structural analysis suggests a ligand entry port and a binding process that is facilitated by opposite charge attraction for PGD₂, which differs significantly from the binding pose and binding environment of lysophospholipids and endocannabinoids, revealing a new mechanism for lipid recognition by GPCRs.

PAM-Antagonists: A Better Way to Block Pathological Receptor Signaling?

Seven transmembrane receptor (7TMR) responses are modulated by orthosteric and allosteric ligands to great therapeutic advantage. Here we introduce a unique class of negative allosteric modulator (NAM) - the positive allosteric modulator (PAM)-antagonist - that increases the affinity of the receptor for the agonist but concomitantly decreases agonist efficacy when cobound. Notably, the reciprocation of allosteric energy causes the orthosteric agonist to increase the affinity of the receptor for the PAM-antagonist; thus, this modulator seeks out and destroys agonist-bound receptor complexes. When contrasted with standard orthosteric and allosteric antagonists it is clear that PAM-antagonists are uniquely well suited to reversing ongoing persistent agonism and provide favorable target coverage in vivo. Specifically, the therapeutic application of PAM-antagonists to reverse pathological overactivation (e.g., endothelin vasoconstriction) is emphasized.

Efficacy and safety of the CRTh2 antagonist AZD1981 as add-on therapy to inhaled corticosteroids and long-acting β2-agonists in patients with atopic asthma

Objectives

To evaluate the efficacy and safety of AZD1981, a potent, specific antagonist of the CRTh2 receptor, as add-on therapy to inhaled corticosteroids (ICS) and long-acting β₂-agonists (LABA), in patients with persistent asthma with an allergic component.

Patients and methods

In this placebo-controlled, parallel-group Phase IIb study, patients with persistent atopic asthma on ICS and LABA were randomized to receive 12 weeks of treatment with placebo or AZD1981 (80 mg daily, 200 mg daily, and 10 mg, 40 mg, 100 mg, or 400 mg twice daily [BID]). The primary end point was the mean change from baseline in predose, prebronchodilator forced expiratory volume in 1 second (FEV₁) averaged over weeks 2, 4, 8, and 12 in the AZD1981-treatment group vs the placebo group. Secondary end points included other measures of lung function, symptoms, and asthma control, as well as standard measures of safety.

Results

In total, 1,140 patients (99.7%) received study treatment. There were improvements in the primary end point across all treatment groups over 12 weeks of treatment. However, the improvement for the highest AZD1981 dose (400 mg BID) vs placebo was not statistically significant (0.02 L, P=0.58), preventing interpretation of statistical testing for the lower doses. AZD1981 was well tolerated, and the incidence of adverse events was comparable across placebo and treatment groups.

Conclusion

In patients with allergic asthma receiving ICS and LABA therapy, the addition of AZD1981 at doses up to 400 mg BID failed to produce a clinically relevant improvement in lung function or any other measured end point, but appeared to have an acceptable safety profile. This clinical study is registered with ClinicalTrials.gov (NCT01197794).

Single Step Determination of Unlabeled Compound Kinetics Using a Competition Association Binding Method Employing Time-Resolved FRET

The competition association binding method allows the characterization of the kinetics of unlabeled compounds and the calculation of receptor-drug affinity (K _d). The K _d value is defined as the ratio of the dissociation constant (or k _off) of the receptor-bound ligand to its association rate constant (or k _on) for a system at equilibrium. Traditionally, competition association binding experiments have been carried out using radiometric detection methods with limited assay throughput. Here we describe a novel method for the determination of unlabeled compound kinetics using the technique of time-resolved fluorescence resonance energy transfer (TR-FRET) performed at physiological temperature and sodium ion concentration. Based on a traditional screening format (10-point curves), up to 28 compounds can be tested on a single 384-well plate by this method.

Chemical Tools for Studying Lipid-Binding Class A G Protein-Coupled Receptors

Cannabinoid, free fatty acid, lysophosphatidic acid, sphingosine 1-phosphate, prostanoid, leukotriene, bile acid, and platelet-activating factor receptor families are class A G protein-coupled receptors with endogenous lipid ligands. Pharmacological tools are crucial for studying these receptors and addressing the many unanswered questions surrounding expression of these receptors in normal and diseased tissues. An inherent challenge for developing tools for these lipid receptors is balancing the often lipophilic requirements of the receptor-binding pharmacophore with favorable physicochemical properties to optimize highly specific binding. In this study, we review the radioligands, fluorescent ligands, covalent ligands, and antibodies that have been used to study these lipid-binding receptors. For each tool type, the characteristics and design rationale along with in vitro and in vivo applications are detailed.

Prostaglandins and Their Receptors in Eosinophil Function and As Therapeutic Targets

Of the known prostanoid receptors, human eosinophils express the prostaglandin D₂ (PGD₂) receptors DP1 [also D-type prostanoid (DP)] and DP2 (also chemoattractant receptor homologous molecule, expressed on Th2 cells), the prostaglandin E₂ receptors EP2 and EP4, and the prostacyclin (PGI₂) receptor IP. Prostanoids can bind to either one or multiple receptors, characteristically have a short half-life in vivo, and are quickly degraded into metabolites with altered affinity and specificity for a given receptor subtype. Prostanoid receptors signal mainly through G proteins and naturally activate signal transduction pathways according to the G protein subtype that they preferentially interact with. This can lead to the activation of sometimes opposing signaling pathways. In addition, prostanoid signaling is often cell-type specific and also the combination of expressed receptors can influence the outcome of the prostanoid impulse. Accordingly, it is assumed that eosinophils and their (patho-)physiological functions are governed by a sensitive prostanoid signaling network. In this review, we specifically focus on the functions of PGD₂, PGE₂, and PGI₂ and their receptors on eosinophils. We discuss their significance in allergic and non-allergic diseases and summarize potential targets for drug intervention.

Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of the Novel CRTH2 Antagonist BI 1021958 at Single Oral Doses in Healthy Men and Multiple Oral Doses in Men and Women With Well-Controlled Asthma

BI 1021958, a novel antagonist of the chemoattractant-receptor-homologous molecule (CRTH2), targets airway inflammation in asthma by inhibiting prostaglandin binding to CRTH2 receptors. Two phase 1 studies assessed BI 1021958 safety/tolerability and pharmacokinetics (PK)/pharmacodynamics (PD) following single doses in healthy men and multiple doses in men/women with well-controlled asthma. Studies 1 had 2 parts: a placebo-controlled, fixed-sequence, single-blind, single-rising-dose part (n = 56) and a randomized, 2-way crossover, open-label, repeated-dose part studying the food effect on PK/PD (n = 12). Study 2 was a placebo-controlled, single-center, double-blind multiple-rising-dose study (n = 84). Primary end points were safety/tolerability and PK/PD (both studies); secondary end points were eosinophil shape change (ESC; study 1) and dose proportionality/linearity following first dose and at steady state (study 2). BI 1021958 was adequately tolerated in both studies; adverse events were infrequent, generally mild to moderate, and occurred similarly in treatment groups. Maximum measured concentration (C_max ) was achieved in ≤2.5 hours in study 1 and ≤2.0 hours in study 2. BI 1021958 exposure increased proportionally with dose. In study 1, following a single 60-mg dose, AUC parameters and C_max were 20% and 15% lower, respectively, after a high-fat meal compared with the fasted state. After ≥60-mg single doses (study 1) and >40-mg multiple doses (study 2), >95% ESC inhibition was observed for ≥24 hours. PK/PD was similar in healthy subjects and subjects with well-controlled asthma. Data support further investigation of CRTH2 antagonists for the treatment of asthma.

Systemic immune mechanisms in atopic dermatitis and psoriasis with implications for treatment

Atopic dermatitis (AD) and psoriasis are inflammatory skin diseases that negatively affect patients' quality of life. Although distinctions exist between these diseases, both are characterized by erythematous, thickened epidermal lesions that vary in intensity and affected body surface area. Early models of aetiology attributed symptoms of both diseases to cutaneous inflammation at lesion sites, but recent studies have established that activated immune mediators in the circulation drive disease severity. Activation of T helper 2 (Th2) and Th22 cells in the circulation appears to be the principal initiator of acute AD pathology, with the emergence of Th1 and Th17/interleukin (IL)-23 pathway activation marking the transition to a chronic state. The Th17/IL-23 pathway also has an important role in psoriasis. The role of systemic inflammation in AD and psoriasis is supported by the occurrence of non-cutaneous comorbidities that affect patients, most of which intensify morbidity and disability associated with lesional skin. Atopic dermatitis is associated with allergic disorders consisting of the "atopic march," whereas psoriasis is frequently accompanied by psoriatic arthritis. Patients with both disorders are at significantly higher risk of obesity, metabolic disorders, and cardiovascular diseases, all of which feature inflammatory components in their pathology models. These insights have led to novel therapeutics aimed at addressing psoriasis by targeting tumor necrosis factor- and Th17-related cytokine pathways. The success of these agents in psoriasis management is driving new therapeutic approaches for moderate-to-severe AD, including agents targeting the Th2 and Th17/Th22 cytokine pathways.

Absorption, Distribution, Metabolism, and Excretion of the Oral Prostaglandin D2 Receptor 2 Antagonist Fevipiprant (QAW039) in Healthy Volunteers and In Vitro

Fevipiprant is a novel oral prostaglandin D₂ receptor 2 (DP₂; also known as CRTh2) antagonist, which is currently in development for the treatment of severe asthma and atopic dermatitis. We investigated the absorption, distribution, metabolism, and excretion properties of fevipiprant in healthy subjects after a single 200-mg oral dose of [¹⁴C]-radiolabeled fevipiprant. Fevipiprant and metabolites were analyzed by liquid chromatography coupled to tandem mass spectrometry and radioactivity measurements, and mechanistic in vitro studies were performed to investigate clearance pathways and covalent plasma protein binding. Biotransformation of fevipiprant involved predominantly an inactive acyl glucuronide (AG) metabolite, which was detected in plasma and excreta, representing 28% of excreted drug-related material. The AG metabolite was found to covalently bind to human plasma proteins, likely albumin; however, in vitro covalent binding to liver protein was negligible. Excretion was predominantly as unchanged fevipiprant in urine and feces, indicating clearance by renal and possibly biliary excretion. Fevipiprant was found to be a substrate of transporters organic anion transporter 3 (OAT3; renal uptake), multidrug resistance gene 1 (MDR1; possible biliary excretion), and organic anion-transporting polypeptide 1B3 (OATP1B3; hepatic uptake). Elimination of fevipiprant occurs via glucuronidation by several uridine 5'-diphospho glucuronosyltransferase (UGT) enzymes as well as direct excretion. These parallel elimination pathways result in a low risk of major drug-drug interactions or pharmacogenetic/ethnic variability for this compound.

Discovery of Fevipiprant (NVP-QAW039), a Potent and Selective DP2 Receptor Antagonist for Treatment of Asthma

Further optimization of an initial DP₂ receptor antagonist clinical candidate NVP-QAV680 led to the discovery of a follow-up molecule 2-(2-methyl-1-(4-(methylsulfonyl)-2-(trifluoromethyl)benzyl)-1H-pyrrolo[2,3-b]pyridin-3-yl)acetic acid (compound 11, NVP-QAW039, fevipiprant), which exhibits improved potency on human eosinophils and Th2 cells, together with a longer receptor residence time, and is currently in clinical trials for severe asthma.

Urolinin: The First Linear Peptidic Urotensin-II Receptor Agonist

This study investigated the role of individual U-II amino acid positions and side chain characteristics important for U-IIR activation. A complete permutation library of 209 U-II variants was studied in an activity screen that contained single substitution variants of each position with one of the other 19 proteinogenic amino acids. Receptor activation was measured using a cell-based high-throughput fluorescence calcium mobilization assay. We generated the first complete U-II substitution map for U-II receptor activation, resulting in a detailed view into the structural features required for receptor activation, accompanied by complementary information from receptor modeling and ligand docking studies. On the basis of the systematic SAR study of U-II, we created 33 further short and linear U-II variants from eight to three amino acids in length, including d- and other non-natural amino acids. We identified the first high-potency linear U-II analogues. Urolinin, a linear U-II agonist (nWWK-Tyr(3-NO₂)-Abu), shows low nanomolar potency as well as improved metabolic stability.

Investigational prostaglandin D2 receptor antagonists for airway inflammation

INTRODUCTION

By activating DP1 and DP2 receptors on immune and non-immune cells, prostaglandin D2 (PGD2), a major metabolic product of cyclo-oxygenase pathway released after IgE-mediated mast cell activation, has pro-inflammatory effects, which are relevant to the pathophysiology of allergic airway disease. At least 15 selective, orally active, DP2 receptor antagonists and one DP1 receptor antagonist (asapiprant) are under development for asthma and/or allergic rhinitis.

AREAS COVERED

In this review, the authors cover the pharmacology of PGD2 and PGD2 receptor antagonists and look at the preclinical, phase I and phase II studies with selective DP1 and DP2 receptor antagonists.

EXPERT OPINION

Future research should aim to develop once daily compounds and increase the drug clinical potency which, apart from OC000459 and ADC-3680, seems to be relatively low. Further research and development of DP2 receptor antagonists is warranted, particularly in patients with severe uncontrolled asthma, whose management is a top priority. Pediatric studies, which are not available, are required for assessing the efficacy and safety of this novel drug class in children with asthma and allergic rhinitis. Studies on the efficacy of DP2 receptor antagonists in various asthma phenotypes including: smokers, obese subjects, early vs late asthma onset, fixed vs reversible airflow limitation, are required for establishing their pharmacotherapeutic role.

Pharmacokinetics, Safety, and Tolerability of Fevipiprant (QAW039), a Novel CRTh2 Receptor Antagonist: Results From 2 Randomized, Phase 1, Placebo-Controlled Studies in Healthy Volunteers

We evaluated the pharmacokinetics (PK), safety, and tolerability of a novel oral CRTh2 antagonist, fevipiprant (QAW039), in healthy subjects. Peak concentrations of fevipiprant in plasma were observed 1‒3 hours postdosing. Concentrations declined in a multiexponential manner, followed by an apparent terminal phase (t_1/2, ∼20 hours). Steady state was achieved in 4 days with <2‐fold accumulation. Elimination was partly by renal excretion (≤30% of the dose) and glucuronidation. Food had minimal impact on the PK of fevipiprant, and it was well tolerated at single and multiple oral doses up to 500 mg/day. No dose‐dependent adverse events were observed, and all the events were mild or moderate in severity. Systemic concentrations were sufficiently high to achieve relevant target occupancy, considering in vitro pharmacology data. In summary, the data support further development as a once‐daily oral therapy for allergic diseases.