Pathway-selective antagonism of proteinase activated receptor 2

Genome editing of PAR2 through targeted delivery of CRISPR-Cas9 system for alleviating acute lung inflammation via ERK/NLRP3/IL-1β and NO/iNOS signalling

Excessive and uncontrollable inflammatory responses in alveoli can dramatically exacerbate pulmonary disease progressions through vigorous cytokine releases, immune cell infiltration and protease-driven tissue damages. It is an urgent need to explore potential drug strategies for mitigating lung inflammation. Protease-activated receptor 2 (PAR2) as a vital molecular target principally participates in various inflammatory diseases via intracellular signal transduction. However, it has been rarely reported about the role of PAR2 in lung inflammation. This study applied CRISPR-Cas9 system encoding Cas9 and sgRNA (pCas9-PAR2) for PAR2 knockout and fabricated an anionic human serum albumin-based nanoparticles to deliver pCas9-PAR2 with superior inflammation-targeting efficiency and stability (TAP/pCas9-PAR2). TAP/pCas9-PAR2 robustly facilitated pCas9-PAR2 to enter and transfect inflammatory cells, eliciting precise gene editing of PAR2 in vitro and in vivo. Importantly, PAR2 deficiency by TAP/pCas9-PAR2 effectively and safely promoted macrophage polarization, suppressed pro-inflammatory cytokine releases and alleviated acute lung inflammation, uncovering a novel value of PAR2. It also revealed that PAR2-mediated pulmonary inflammation prevented by TAP/pCas9-PAR2 was mainly dependent on ERK-mediated NLRP3/IL-1β and NO/iNOS signalling. Therefore, this work indicated PAR2 as a novel target for lung inflammation and provided a potential nanodrug strategy for PAR2 deficiency in treating inflammatory diseases.

New insight into the agonism of protease-activated receptors as an immunotherapeutic strategy

The activation and mobilization of immune cells play a crucial role in immunotherapy. Existing therapeutic interventions, such as cytokines administration, aim to enhance immune cell activity. However, these approaches usually result in modest effectiveness and toxic side effects, thereby restricting their clinical application. Protease-activated receptors (PARs), a subfamily of G protein-coupled receptors, actively participate in the immune system by directly activating immune cells. The activation of PARs by proteases or synthetic ligands can modulate immune cell behavior, signaling, and responses to treat immune-related diseases, suggesting the significance of PARs agonism in immunotherapy. However, the agonism of PARs in therapeutical applications remains rarely discussed, since it has been traditionally considered that PARs activation facilitates disease progressions. This review aims to comprehensively summarize the activation, rather than inhibition, of PARs in immune-related physiological responses and diseases. Additionally, we will discuss the emerging immunotherapeutic potential of PARs agonism, providing a new strategic direction for PARs-mediated immunotherapy.

Protease-activated receptor 2 attenuates doxorubicin-induced apoptosis in colon cancer cells

Drug resistance represents a major problem in cancer treatment. Doxorubicin (adriamycin) is an injectable DNA intercalating drug that halts cancer cell growth by inhibiting topoisomerase 2, but its long-term effectiveness is compromised by onset of resistance. This study demonstrates that expression of the PAR2 gene in human colon adenocarcinoma tissue samples was the highest among 32 different cancer types (n = 10,989), and higher in colon adenocarcinoma tissues (n = 331) than normal colon tissues (n = 308), revealing an association between PAR2 expression and human colon cancer. HT29 cells are a human colorectal adenocarcinoma cell line that is sensitive to the chemotherapeutic drug doxorubicin and also expresses PAR2. We find that PAR2 activation in HT29 cells, either by an endogenous protease agonist (trypsin) or an exogenous peptide agonist (2f-LIGRL-NH2), significantly reduces doxorubicin-induced cell death, reactive oxygen species production, caspase 3/7 activity and cleavage of caspase-8 and caspase-3. Moreover, PAR2-mediated MEK1/2-ERK1/2 pathway induced by 2f-LIGRL-NH2 leads to upregulated anti-apoptotic MCL-1 and Bcl-xL proteins that promote cellular survival. These findings suggest that activation of PAR2 compromises efficacy of doxorubicin in colon cancer. Further support for this conclusion came from experiments with human colon cancer HT29 cells, either with the PAR2 gene deleted or in the presence of a pharmacological antagonist of PAR2, which showed full restoration of all doxorubicin-mediated effects. Together, these findings reveal a strong link between PAR2 activation and signalling in human colon cancer cells and increased survival against doxorubicin-induced cell death. They support PAR2 antagonism as a possible new strategy for enhancing doxorubicin therapy.

Tissue factor (coagulation factor III): a potential double-edge molecule to be targeted and re-targeted toward cancer

Tissue factor (TF) is a protein that plays a critical role in blood clotting, but recent research has also shown its involvement in cancer development and progression. Herein, we provide an overview of the structure of TF and its involvement in signaling pathways that promote cancer cell proliferation and survival, such as the PI3K/AKT and MAPK pathways. TF overexpression is associated with increased tumor aggressiveness and poor prognosis in various cancers. The review also explores TF's role in promoting cancer cell metastasis, angiogenesis, and venous thromboembolism (VTE). Of note, various TF-targeted therapies, including monoclonal antibodies, small molecule inhibitors, and immunotherapies have been developed, and preclinical and clinical studies demonstrating the efficacy of these therapies in various cancer types are now being evaluated. The potential for re-targeting TF toward cancer cells using TF-conjugated nanoparticles, which have shown promising results in preclinical studies is another intriguing approach in the path of cancer treatment. Although there are still many challenges, TF could possibly be a potential molecule to be used for further cancer therapy as some TF-targeted therapies like Seagen and Genmab's tisotumab vedotin have gained FDA approval for treatment of cervical cancer. Overall, based on the overviewed studies, this review article provides an in-depth overview of the crucial role that TF plays in cancer development and progression, and emphasizes the potential of TF-targeted and re-targeted therapies as potential approaches for the treatment of cancer.

C781, a β-Arrestin Biased Antagonist at Protease-Activated Receptor-2 (PAR2), Displays in vivo Efficacy Against Protease-Induced Pain in Mice

Given the limited options and often harmful side effects of current analgesics and the suffering caused by the opioid crisis, new classes of pain therapeutics are needed. Protease-activated receptors (PARs), particularly PAR2, are implicated in a variety of pathologies, including pain. Since the discovery of the role of PAR2 in pain, development of potent and specific antagonists has been slow. In this study, we describe the in vivo characterization of a novel small molecule/peptidomimetic hybrid compound, C781, as a β-arrestin-biased PAR2 antagonist. In vivo behavioral studies were done in mice using von Frey filaments and the Mouse Grimace Scale. Pharmacokinetic studies were done to assess pharmacokinetic/pharmacodynamic relationship in vivo. We used both prevention and reversal paradigms with protease treatment to determine whether C781 could attenuate protease-evoked pain. C781 effectively prevented and reversed mechanical and spontaneous nociceptive behaviors in response to small molecule PAR2 agonists, mast cell activators, and neutrophil elastase. The ED50 of C781 (intraperitoneal dosing) for inhibition of PAR2 agonist (20.9 ng 2-AT)-evoked nociception was 6.3 mg/kg. C781 was not efficacious in the carrageenan inflammation model. Pharmacokinetic studies indicated limited long-term systemic bioavailability for C781 suggesting that optimizing pharmacokinetic properties could improve in vivo efficacy. Our work demonstrates in vivo efficacy of a biased PAR2 antagonist that selectively inhibits β-arrestin/MAPK signaling downstream of PAR2. Given the importance of this signaling pathway in PAR2-evoked nociception, C781 exemplifies a key pharmacophore for PAR2 that can be optimized for clinical development. PERSPECTIVE: Our work provides evidence that PAR2 antagonists that only block certain aspects of signaling by the receptor can be effective for blocking protease-evoked pain in mice. This is important because it creates a rationale for developing safer PAR2-targeting approaches for pain treatment.

Protease-activated receptors in health and disease

Proteases are signaling molecules that specifically control cellular functions by cleaving protease-activated receptors (PARs). The four known PARs are members of the large family of G protein-coupled receptors. These transmembrane receptors control most physiological and pathological processes and are the target of a large proportion of therapeutic drugs. Signaling proteases include enzymes from the circulation; from immune, inflammatory epithelial, and cancer cells; as well as from commensal and pathogenic bacteria. Advances in our understanding of the structure and function of PARs provide insights into how diverse proteases activate these receptors to regulate physiological and pathological processes in most tissues and organ systems. The realization that proteases and PARs are key mediators of disease, coupled with advances in understanding the atomic level structure of PARs and their mechanisms of signaling in subcellular microdomains, has spurred the development of antagonists, some of which have advanced to the clinic. Herein we review the discovery, structure, and function of this receptor system, highlight the contribution of PARs to homeostatic control, and discuss the potential of PAR antagonists for the treatment of major diseases.

PARs in the inflammation-cancer transformation of CRC

Colorectal cancer (CRC) is one of the common malignancies with a global trend of increasing incidence and mortality. There is an urgent need to identify new predictive markers and therapeutic targets for the treatment of CRC. Protease-activated receptors (PARs) are a class of G-protein-coupled receptors, with currently identified subtypes including PAR1, PAR2, PAR3 and PAR4. Increasingly, studies suggest that PARs play an important role in the growth and metastasis of CRC. By targeting multiple signaling pathways may contribute to the pathogenesis of CRC. In this review, we first describe recent studies on the role of PARs in CRC inflammation-cancer transformation, focusing on the important role of PARs in signaling pathways associated with inflammation-cancer transformation, and summarize the progress of research on PARs-targeted drugs.

GB83, an Agonist of PAR2 with a Unique Mechanism of Action Distinct from Trypsin and PAR2-AP

Protease-activated receptor 2 (PAR2) is a G-protein-coupled receptor (GPCR) activated by proteolytic cleavage of its N-terminal domain. Once activated, PAR2 is rapidly desensitized and internalized by phosphorylation and β-arrestin recruitment. Due to its irreversible activation mechanism, some agonists that rapidly desensitized PAR2 have been misconceived as antagonists, and this has impeded a better understanding of the pathophysiological role of PAR2. In the present study, we found that GB83, initially identified as a PAR2 antagonist, is a bona fide agonist of PAR2 that induces unique cellular signaling, distinct from trypsin and PAR2-activating peptide (AP). Activation of PAR2 by GB83 markedly elicited an increase in intracellular calcium levels and phosphorylation of MAPKs, but in a delayed and sustained manner compared to the rapid and transient signals induced by trypsin and PAR2-AP. Interestingly, unlike PAR2-AP, GB83 and trypsin induced sustained receptor endocytosis and PAR2 colocalization with β-arrestin. Moreover, the recovery of the localization and function of PAR2 was significantly delayed after stimulation by GB83, which may be the reason why GB83 is recognized as an antagonist of PAR2. Our results revealed that GB83 is a bona fide agonist of PAR2 that uniquely modulates PAR2-mediated cellular signaling and is a useful pharmacological tool for studying the pathophysiological role of PAR2.

Antagonism of Protease Activated Receptor-2 by GB88 Reduces Inflammation Triggered by Protease Allergen Tyr-p3

The occurrence of allergic diseases induced by aeroallergens has increased in the past decades. Among inhalant allergens, mites remain the important causal agent of allergic diseases. Storage mites- Tyrophagus putrescentiae are found in stored products or domestic environments. Major allergen Tyr-p3 plays a significant role in triggering IgE-mediated hypersensitivity. However, its effects on pulmonary inflammation, internalization, and activation in human epithelium remain elusive. Protease-activated receptors (PARs) are activated upon cleavage by proteases. A549 cells were used as an epithelial model to examine the PAR activation by Tyr-p3 and therapeutic potential of PAR-2 antagonist (GB88) in allergic responses. Enzymatic properties and allergen localization of Tyr-p3 were performed. The release of inflammatory mediators, phosphorylation of mitogen-activated protein kinase (MAPK), and cell junction disruptions were evaluated after Tyr-p3 challenge. Enzymatic properties determined by substrate digestion and protease inhibitors indicated that Tyr-p3 processes a trypsin-like serine protease activity. The PAR-2 mRNA levels were significantly increased by nTyr-p3 but inhibited by protease inhibitors or GB88. Protease allergen of nTyr-p3 significantly increased the levels of pro-inflammatory cytokines (IL-6 and TNF-α), chemokine (IL-8), and IL-1β in epithelial cells. nTyr-p3 markedly increased phosphorylation of extracellular signal-regulated kinase (ERK)1/2 and MAP kinase. When cells were pretreated with GB88 then added nTyr-p3, the phosphorylated ERK1/2 did not inhibit by GB88. GB88 increased ERK1/2 phosphorylation in human epithelium cells. GB88 is able to block PAR-2-mediated calcium signaling which inhibits the nTyr-p3-induced Ca²⁺ release. Among the pharmacologic inhibitors, the most effective inhibitor of the nTyr-p3 in the induction of IL-8 or IL-1β levels was GB88 followed by SBTI, MAPK/ERK, ERK, and p38 inhibitors. Levels of inflammatory mediators, including GM-CSF, VEGF, COX-2, TSLP, and IL-33 were reduced by treatment of GB88 or SBTI. Further, GB88 treatment down-regulated the nTyr-p3-induced PAR-2 expression in allergic patients with asthma or rhinitis. Tight junction and adherens junction were disrupted in epithelial cells by nTyr-p3 exposure; however, this effect was avoided by GB88. Immunostaining with frozen sections of the mite body showed the presence of Tyr-p3 throughout the intestinal digestive system, especially in the hindgut around the excretion site. In conclusion, our findings suggest that Tyr-p3 from domestic mites leads to disruption of the airway epithelial barrier after inhalation. Proteolytic activity of Tyr-p3 causes the PAR-2 mRNA expression, thus leading to the release of numerous inflammatory mediators. Antagonism of PAR2 activity suggests GB88 as the therapeutic potential for anti-inflammation medicine, especially in allergy development triggered by protease allergens.

The development of proteinase-activated receptor-2 modulators and the challenges involved

Protease-activated receptor-2 (PAR2) has been extensively studied since its discovery in the mid-1990. Despite the advances in understanding PAR2 pharmacology, it has taken almost 25 years for the first inhibitor to reach clinical trials, and so far, no PAR2 antagonist has been approved for human use. Research has employed classical approaches to develop a wide array of PAR2 agonists and antagonists, consisting of peptides, peptoids and antibodies to name a few, with a surge in patent applications over this period. Recent breakthroughs in PAR2 structure determination has provided a unique insight into proposed PAR2 ligand binding sites. Publication of the first crystal structures of PAR2 resolved in complex with two novel non-peptide small molecule antagonists (AZ8838 and AZ3451) revealed two distinct binding pockets, originally presumed to be allosteric sites, with a PAR2 antibody (Fab3949) used to block tethered ligand engagement with the peptide-binding domain of the receptor. Further studies have proposed orthosteric site occupancy for AZ8838 as a competitive antagonist. One company has taken the first PAR2 antibody (MEDI0618) into phase I clinical trial (NCT04198558). While this first-in-human trial is at the early stages of the assessment of safety, other research into the structural characterisation of PAR2 is still ongoing in an attempt to identify new ways to target receptor activity. This review will focus on the development of novel PAR2 modulators developed to date, with an emphasis placed upon the advances made in the pharmacological targeting of PAR2 activity as a strategy to limit chronic inflammatory disease.

PAR2-Induced Tissue Factor Synthesis by Primary Cultures of Human Kidney Tubular Epithelial Cells Is Modified by Glucose Availability

Coagulopathies common to patients with diabetes and chronic kidney disease (CKD) are not fully understood. Fibrin deposits in the kidney suggest the local presence of clotting factors including tissue factor (TF). In this study, we investigated the effect of glucose availability on the synthesis of TF by cultured human kidney tubular epithelial cells (HTECs) in response to activation of protease-activated receptor 2 (PAR2). PAR2 activation by peptide 2f-LIGRLO-NH₂ (2F, 2 µM) enhanced the synthesis and secretion of active TF (~45 kDa) which was blocked by a PAR2 antagonist (I-191). Treatment with 2F also significantly increased the consumption of glucose from the cell medium and lactate secretion. Culturing HTECs in 25 mM glucose enhanced TF synthesis and secretion over 5 mM glucose, while addition of 5 mM 2-deoxyglucose (2DOG) significantly decreased TF synthesis and reduced its molecular weight (~40 kDa). Blocking glycosylation with tunicamycin also reduced 2F-induced TF synthesis while reducing its molecular weight (~36 kDa). In conclusion, PAR2-induced TF synthesis in HTECs is enhanced by culture in high concentrations of glucose and suppressed by inhibiting either PAR2 activation (I-191), glycolysis (2DOG) or glycosylation (tunicamycin). These results may help explain how elevated concentrations of glucose promote clotting abnormities in diabetic kidney disease. The application of PAR2 antagonists to treat CKD should be investigated further.

PAR2 Activation on Human Kidney Tubular Epithelial Cells Induces Tissue Factor Synthesis, That Enhances Blood Clotting

Coagulation abnormalities and increased risk of atherothrombosis are common in patients with chronic kidney diseases (CKD). Mechanisms that alter renal hemostasis and lead to thrombotic events are not fully understood. Here we show that activation of protease activated receptor-2 (PAR2) on human kidney tubular epithelial cells (HTECs), induces tissue factor (TF) synthesis and secretion that enhances blood clotting. PAR-activating coagulation-associated protease (thrombin), as well as specific PAR2 activators (matriptase, trypsin, or synthetic agonist 2f-LIGRLO-NH₂ (2F), induced TF synthesis and secretion that were potently inhibited by PAR2 antagonist, I-191. Thrombin-induced TF was also inhibited by a PAR1 antagonist, Vorapaxar. Peptide activators of PAR1, PAR3, and PAR4 failed to induce TF synthesis. Differential centrifugation of the 2F-conditoned medium sedimented the secreted TF, together with the exosome marker ALG-2 interacting protein X (ALIX), indicating that secreted TF was associated with extracellular vesicles. 2F-treated HTEC conditioned medium significantly enhanced blood clotting, which was prevented by pre-incubating this medium with an antibody for TF. In summary, activation of PAR2 on HTEC stimulates synthesis and secretion of TF that induces blood clotting, and this is attenuated by PAR2 antagonism. Thrombin-induced TF synthesis is at least partly mediated by PAR1 transactivation of PAR2. These findings reveal how underlying hemostatic imbalances might increase thrombosis risk and subsequent chronic fibrin deposition in the kidneys of patients with CKD and suggest PAR2 antagonism as a potential therapeutic strategy for intervening in CKD progression.

Protease-activated receptor-2 ligands reveal orthosteric and allosteric mechanisms of receptor inhibition

Protease-activated receptor-2 (PAR2) has been implicated in multiple pathophysiologies but drug discovery is challenging due to low small molecule tractability and a complex activation mechanism. Here we report the pharmacological profiling of a potent new agonist, suggested by molecular modelling to bind in the putative orthosteric site, and two novel PAR2 antagonists with distinctly different mechanisms of inhibition. We identify coupling between different PAR2 binding sites. One antagonist is a competitive inhibitor that binds to the orthosteric site, while a second antagonist is a negative allosteric modulator that binds at a remote site. The allosteric modulator shows probe dependence, more effectively inhibiting peptide than protease activation of PAR2 signalling. Importantly, both antagonists are active in vivo, inhibiting PAR2 agonist-induced acute paw inflammation in rats and preventing activation of mast cells and neutrophils. These results highlight two distinct mechanisms of inhibition that potentially could be targeted for future development of drugs that modulate PAR2.

Kennedy et al. report the pharmacological and in vivo profiling of two small molecule PAR2 inhibitors and an agonist. They conclude that while the small molecule agonist and one of the inhibitors bind to the orthosteric PAR2 binding site, the other inhibitor is a negative allosteric modulator, highlighting two distinct mechanisms of inhibition that could be targeted for future development of drugs that modulate PAR2.

The PAR2 inhibitor I-287 selectively targets Gαq and Gα12/13 signaling and has anti-inflammatory effects

Protease-activated receptor-2 (PAR2) is involved in inflammatory responses and pain, therefore representing a promising therapeutic target for the treatment of immune-mediated inflammatory diseases. However, as for other GPCRs, PAR2 can activate multiple signaling pathways and those involved in inflammatory responses remain poorly defined. Here, we describe a new selective and potent PAR2 inhibitor (I-287) that shows functional selectivity by acting as a negative allosteric regulator on Gα_q and Gα_12/13 activity and their downstream effectors, while having no effect on G_i/o signaling and βarrestin2 engagement. Such selective inhibition of only a subset of the pathways engaged by PAR2 was found to be sufficient to block inflammation in vivo. In addition to unraveling the PAR2 signaling pathways involved in the pro-inflammatory response, our study opens the path toward the development of new functionally selective drugs with reduced liabilities that could arise from blocking all the signaling activities controlled by the receptor.

Avet et al. characterize I-287, an inhibitor to protease-activated receptor 2 using BRET-assays. They find that I-287 selectively inhibits Gα_q and Gα_12/13 without affecting the activation of G_i/o or the recruitment of βarrestin2 and that it blocks inflammation in vitro and in vivo.

Legumain Induces Oral Cancer Pain by Biased Agonism of Protease-Activated Receptor-2

Oral squamous cell carcinoma (OSCC) is one of the most painful cancers, which interferes with orofacial function including talking and eating. We report that legumain (Lgmn) cleaves protease-activated receptor-2 (PAR₂) in the acidic OSCC microenvironment to cause pain. Lgmn is a cysteine protease of late endosomes and lysosomes that can be secreted; it exhibits maximal activity in acidic environments. The role of Lgmn in PAR₂-dependent cancer pain is unknown. We studied Lgmn activation in human oral cancers and oral cancer mouse models. Lgmn was activated in OSCC patient tumors, compared with matched normal oral tissue. After intraplantar, facial or lingual injection, Lgmn evoked nociception in wild-type (WT) female mice but not in female mice lacking PAR₂ in Na_V1.8-positive neurons (Par₂Na_v1.8), nor in female mice treated with a Lgmn inhibitor, LI-1. Inoculation of an OSCC cell line caused mechanical and thermal hyperalgesia that was reversed by LI-1. Par₂Na_v1.8 and Lgmn deletion attenuated mechanical allodynia in female mice with carcinogen-induced OSCC. Lgmn caused PAR₂-dependent hyperexcitability of trigeminal neurons from WT female mice. Par₂ deletion, LI-1, and inhibitors of adenylyl cyclase or protein kinase A (PKA) prevented the effects of Lgmn. Under acidified conditions, Lgmn cleaved within the extracellular N terminus of PAR₂ at Asn³⁰↓Arg³¹, proximal to the canonical trypsin activation site. Lgmn activated PAR₂ by biased mechanisms in HEK293 cells to induce Ca²⁺ mobilization, cAMP formation, and PKA/protein kinase D (PKD) activation, but not β-arrestin recruitment or PAR₂ endocytosis. Thus, in the acidified OSCC microenvironment, Lgmn activates PAR₂ by biased mechanisms that evoke cancer pain.SIGNIFICANCE STATEMENT Oral squamous cell carcinoma (OSCC) is one of the most painful cancers. We report that legumain (Lgmn), which exhibits maximal activity in acidic environments, cleaves protease-activated receptor-2 (PAR₂) on neurons to produce OSCC pain. Active Lgmn was elevated in OSCC patient tumors, compared with matched normal oral tissue. Lgmn evokes pain-like behavior through PAR₂ Exposure of pain-sensing neurons to Lgmn decreased the current required to generate an action potential through PAR₂ Inhibitors of adenylyl cyclase and protein kinase A (PKA) prevented the effects of Lgmn. Lgmn activated PAR₂ to induce calcium mobilization, cAMP formation, and activation of protein kinase D (PKD) and PKA, but not β-arrestin recruitment or PAR₂ endocytosis. Thus, Lgmn is a biased agonist of PAR₂ that evokes cancer pain.

Activation of protease-activated receptor 2 is associated with blood pressure regulation and proteinuria reduction in metabolic syndrome

Metabolic syndrome (MetS) increases the risk of kidney disease. In SHRSP.Z-Lepr^fa /IzmDmcr (SHRSP.ZF) rats with MetS, protease-activated receptor 2 (PAR2)-mediated vasorelaxation is preserved in the aorta at 20 weeks of age (weeks) via enhancement of nitric oxide production but impaired at 30 weeks by oxidative stress. However, impairment of PAR2-mediated vasorelaxation of renal arteries and its possible implications for kidney disease are unclear. We used organ baths to assess PAR2-mediated vasorelaxation of isolated renal arteries, colorimetric methods to measure urinary protein levels as an index of renal function, and western blot to determine expression of PAR2 and nephrin proteins in the kidneys of SHRSP.ZF rats at 10, 20, and 30 weeks. We assessed renal arteries and kidney function for effects of orally administered GB88, a pathway-dependent PAR2 antagonist, from 10 to 18 weeks, and azilsartan, an angiotensin II type 1 receptor blocker, from 13 to 23 weeks. PAR2-mediated vasorelaxation was slightly lower at 20 weeks and attenuated significantly at 30 weeks compared with those at 10 weeks. Urinary protein levels were increased at 20 and 30 weeks. Decreased protein expression of PAR2 and nephrin in the kidney were observed at 30 weeks. Administration of GB88 increased blood pressure (BP) and proteinuria. Azilsartan reduced the high BP and the impaired PAR2-mediated vasorelaxation, but did not restore the increase in urinary protein levels and decreased PAR2 and nephrin protein expression in the kidney. PAR2 activation in the kidney may be associated with maintenance of BP and urinary protein excretion in MetS.

Synthesis and initial pharmacology of dual-targeting ligands for putative complexes of integrin αVβ3 and PAR2

Unpublished data from our labs led us to hypothesize that activated protein C (aPC) may initiate an anti-inflammatory signal in endothelial cells by modulating both the integrin αVβ3 and protease-activated receptor 2 (PAR2), which may exist in close proximity on the cellular surface. To test this hypothesis and to probe the possible inflammation-related pathway, we designed and synthesized dual-targeting ligands composed of modified versions of two αVβ3 ligands and two agonists of PAR2. These novel ligands were connected via copper-catalyzed alkyne-azide cycloadditions with polyethylene glycol (PEG) spacers of variable length. Initial in vitro pharmacology with EA.hy926 and HUVEC endothelial cells indicated that these ligands are effective binders of αVβ3 and potent agonists of PAR2. These were also used in preliminary studies investigating their effects on PAR2 signaling in the presence of inflammatory agents, and represent the first examples of ligands targeting both PARs and integrins, though concurrent binding to αVβ3 and PAR2 has not yet been demonstrated.

Potent Thiophene Antagonists of Human Complement C3a Receptor with Anti-Inflammatory Activity

Structure-activity relationships for a series of small-molecule thiophenes resulted in potent and selective antagonism of human Complement C3a receptor. The compounds are about 100-fold more potent than the most reported antagonist SB290157. A new compound JR14a was among the most potent of the new antagonists in vitro, assessed by (a) inhibition of intracellular calcium release (IC₅₀ 10 nM) induced in human monocyte-derived macrophages by 100 nM C3a, (b) inhibition of β-hexosaminidase secretion (IC₅₀ 8 nM) from human LAD2 mast cells degranulated by 100 nM C3a, and (c) selectivity for human C3aR over C5aR. JR14a was metabolically stable in rat plasma and in rat liver microsomes and efficacious in rats when given orally to suppress rat paw inflammation, macrophage and mast cell activation, and histopathology induced by intraplantar paw administration of a C3aR agonist. Potent C3aR antagonists are now available for interrogating C3a receptor activation and suppressing C3aR-mediated inflammation in mammalian physiology and disease.

Activated clotting factor X mediates mitochondrial alterations and inflammatory responses via protease-activated receptor signaling in alveolar epithelial cells

There is growing evidence for the contribution of the activated coagulation factor X (FXa) in the development of chronic inflammatory lung diseases. Therefore, we aimed to investigate effects of exogenous FXa on mitochondrial and metabolic function as well as the induction of inflammatory molecules in type II alveolar epithelial cells. Effects of FXa on epithelial cells were investigated in A549 cell line. Activation of extracellular signal-regulated kinase (ERK) and induction of inflammatory molecules were examined by immunoblot and gene expression analysis. Mitochondrial function was assessed by the measurement of oxygen consumption during maximal oxidative phosphorylation and quantitative determination of cardiolipin oxidation. Apoptosis was tested using a caspase 3 antibody. Metabolic activity and lactate dehydrogenase assay were applied for the detection of cellular viability. FXa activated ERK1/2 and induced an increase in the expression of pro-inflammatory cytokines, which was prevented by an inhibitor of FXa, edoxaban, or an inhibitor of protease-activated receptor 1, vorapaxar. Exposure to FXa caused mitochondrial alteration with restricted capacity for ATP generation, which was effectively prevented by edoxaban, vorapaxar and GB83 (inhibitor of protease-activated receptor 2). Of note, exposure to FXa did not initiate apoptosis in epithelial cells. FXa-dependent pro-inflammatory state and impairment of mitochondria did not reach the level of significance in lung epithelial cells. However, these effects might limit regenerative potency of lung epithelial cells, particular under clinical circumstances where lung injury causes exposure to clotting factors.

Protease-activated receptor 2 does not contribute to renal inflammation or fibrosis in the obstructed kidney

AIM

Protease-activated receptor 2 (PAR2) has been implicated in the development of renal inflammation and fibrosis. In particular, activation of PAR2 in cultured tubular epithelial cells induces extracellular signal-regulated kinase signalling and secretion of fibronectin, C-C Motif Chemokine Ligand 2 (CCL2) and transforming growth factor-β1 (TGF-β1), suggesting a role in tubulointerstitial inflammation and fibrosis. We tested this hypothesis in unilateral ureteric obstruction (UUO) in which ongoing tubular epithelial cell damage drives tubulointerstitial inflammation and fibrosis.

METHODS

Unilateral ureteric obstruction surgery was performed in groups (n = 9/10) of Par2-/- and wild type (WT) littermate mice which were killed 7 days later. Non-experimental mice were controls.

RESULTS

Wild type mice exhibited a 5-fold increase in Par2 messenger RNA (mRNA) levels in the UUO kidney. In situ hybridization localized Par2 mRNA expression to tubular epithelial cells in normal kidney, with a marked increase in Par2 mRNA expression by tubular cells, including damaged tubular cells, in WT UUO kidney. Tubular damage (tubular dilation, increased KIM-1 and decreased α-Klotho expression) and tubular signalling (extracellular signal-regulated kinase phosphorylation) seen in WT UUO were not altered in Par2-/- UUO. In addition, macrophage infiltration, up-regulation of M1 (NOS2) and M2 (CD206) macrophage markers, and up-regulation of pro-inflammatory molecules (tumour necrosis factor, CCL2, interleukin-36α) in WT UUO kidney were unchanged in Par2-/- UUO. Finally, the accumulation of α-SMA+ myofibroblasts, deposition of collagen IV and expression of pro-fibrotic factors (CTGF, TGF-β1) were not different between WT and Par2-/- UUO mice.

CONCLUSION

Protease-activated receptor 2 expression is substantially up-regulated in tubular epithelial cells in the obstructed kidney, but this does not contribute to the development of tubular damage, renal inflammation or fibrosis.

Pharmacological inhibition of protease-activated receptor-2 reduces crescent formation in rat nephrotoxic serum nephritis

Glomerular crescent formation is a hallmark of rapidly progressive forms of glomerulonephritis. Thrombosis and macrophage infiltration are features of crescent formation in human and experimental kidney disease. Protease-activated receptor-2 (PAR-2) is a G-protein coupled receptor that links coagulation and inflammation. This study investigated whether pharmacological inhibition of PAR-2 can suppress glomerular crescent formation in rat nephrotoxic serum nephritis (NTN). Disease was induced in Wistar Kyoto rats by immunisation with sheep IgG followed by administration of sheep nephrotoxic serum. Rats (n = 8/group) received the PAR-2 antagonist (GB88, 10 mg/kg/p.o.), vehicle or no treatment starting 3 days before nephrotoxic serum injection and continuing until day 14. Vehicle and untreated rats developed thrombosis and macrophage infiltration in the glomerular tuft and Bowman's space in conjunction with prominent crescent formation. Activation of JNK signalling and proliferation in parietal epithelial cells was associated with crescent formation. GB88 treatment significantly reduced crescent formation with a substantial reduction in glomerular thrombosis, reduced macrophage infiltration in Bowman's space, and reduced activation of parietal epithelial cells. However, GB88 did not protect against the development of proteinuria, renal function impairment, inflammation or tubular cell damage in the NTN model. In conclusion, PAR-2 plays a specific role in glomerular crescent formation by promoting glomerular thrombosis, macrophage accumulation in Bowman's space and activation of parietal epithelial cells.

Protease-activated receptor-2 signaling through β-arrestin-2 mediates Alternaria alkaline serine protease-induced airway inflammation

Alternaria alternata is a fungal allergen associated with severe asthma and asthma exacerbations. Similarly to other asthma-associated allergens, Alternaria secretes a serine-like trypsin protease(s) that is thought to act through the G protein-coupled receptor protease-activated receptor-2 (PAR2) to induce asthma symptoms. However, specific mechanisms underlying Alternaria-induced PAR2 activation and signaling remain ill-defined. We sought to determine whether Alternaria-induced PAR2 signaling contributed to asthma symptoms via a PAR2/β-arrestin signaling axis, identify the protease activity responsible for PAR2 signaling, and determine whether protease activity was sufficient for Alternaria-induced asthma symptoms in animal models. We initially used in vitro models to demonstrate Alternaria-induced PAR2/β-arrestin-2 signaling. Alternaria filtrates were then used to sensitize and challenge wild-type, PAR2-/- and β-arrestin-2-/- mice in vivo. Intranasal administration of Alternaria filtrate resulted in a protease-dependent increase of airway inflammation and mucin production in wild-type but not PAR2-/- or β-arrestin-2-/- mice. Protease was isolated from Alternaria preparations, and select in vitro and in vivo experiments were repeated to evaluate sufficiency of the isolated Alternaria protease to induce asthma phenotype. Administration of a single isolated serine protease from Alternaria, Alternaria alkaline serine protease (AASP), was sufficient to fully activate PAR2 signaling and induce β-arrestin-2-/--dependent eosinophil and lymphocyte recruitment in vivo. In conclusion, Alternaria filtrates induce airway inflammation and mucus hyperplasia largely via AASP using the PAR2/β-arrestin signaling axis. Thus, β-arrestin-biased PAR2 antagonists represent novel therapeutic targets for treating aeroallergen-induced asthma.

The Role of PAR2 in TGF-β1-Induced ERK Activation and Cell Motility

Background: Recently, the expression of proteinase-activated receptor 2 (PAR2) has been shown to be essential for activin receptor-like kinase 5 (ALK5)/SMAD-mediated signaling and cell migration by transforming growth factor (TGF)-β1. However, it is not known whether activation of non-SMAD TGF-β signaling (e.g., RAS–RAF–MEK–extracellular signal-regulated kinase (ERK) signaling) is required for cell migration and whether it is also dependent on PAR2. Methods: RNA interference was used to deplete cells of PAR2, followed by xCELLigence technology to measure cell migration, phospho-immunoblotting to assess ERK1/2 activation, and co-immunoprecipitation to detect a PAR2–ALK5 physical interaction. Results: Inhibition of ERK signaling with the MEK inhibitor U0126 blunted the ability of TGF-β1 to induce migration in pancreatic cancer Panc1 cells. ERK activation in response to PAR2 agonistic peptide (PAR2–AP) was strong and rapid, while it was moderate and delayed in response to TGF-β1. Basal and TGF-β1-dependent ERK, but not SMAD activation, was blocked by U0126 in Panc1 and other cell types indicating that ERK activation is downstream or independent of SMAD signaling. Moreover, cellular depletion of PAR2 in HaCaT cells strongly inhibited TGF-β1-induced ERK activation, while the biased PAR2 agonist GB88 at 10 and 100 µM potentiated TGF-β1-dependent ERK activation and cell migration. Finally, we provide evidence for a physical interaction between PAR2 and ALK5. Our data show that both PAR2–AP- and TGF-β1-induced cell migration depend on ERK activation, that PAR2 expression is crucial for TGF-β1-induced ERK activation, and that the functional cooperation of PAR2 and TGF-β1 involves a physical interaction between PAR2 and ALK5.

A Potent Antagonist of Protease-Activated Receptor 2 That Inhibits Multiple Signaling Functions in Human Cancer Cells

Protease-activated receptor 2 (PAR2) is a cell surface protein linked to G-protein dependent and independent intracellular signaling pathways that produce a wide range of physiological responses, including those related to metabolism, inflammation, pain, and cancer. Certain proteases, peptides, and nonpeptides are known to potently activate PAR2. However, no effective potent PAR2 antagonists have been reported yet despite their anticipated therapeutic potential. This study investigates antagonism of key PAR2-dependent signaling properties and functions by the imidazopyridazine compound I-191 (4-(8-(tert-butyl)-6-(4-fluorophenyl)imidazo[1,2-b]pyridazine-2-carbonyl)-3,3-dimethylpiperazin-2-one) in cancer cells. At nanomolar concentrations, I-191 inhibited PAR2 binding of and activation by structurally distinct PAR2 agonists (trypsin, peptide, nonpeptide) in a concentration-dependent manner in cells of the human colon adenocarcinoma grade II cell line (HT29). I-191 potently attenuated multiple PAR2-mediated intracellular signaling pathways leading to Ca²⁺ release, extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation, Ras homologue gene family, member A (RhoA) activation, and inhibition of forskolin-induced cAMP accumulation. The mechanism of action of I-191 was investigated using binding and calcium mobilization studies in HT29 cells where I-191 was shown to be noncompetitive and a negative allosteric modulator of the agonist 2f-LIGRL-NH₂ The compound alone did not activate these PAR2-mediated pathways, even at high micromolar concentrations, indicating no bias in these signaling properties. I-191 also potently inhibited PAR2-mediated downstream functional responses, including expression and secretion of inflammatory cytokines and cell apoptosis and migration, in human colon adenocarcinoma grade II cell line (HT29) and human breast adenocarcinoma cells (MDA-MB-231). These findings indicate that I-191 is a potent PAR2 antagonist that inhibits multiple PAR2-induced signaling pathways and functional responses. I-191 may be a valuable tool for characterizing PAR2 functions in cancer and in other cellular, physiological, and disease settings.

Protease activated receptor 2 controls myelin development, resiliency and repair

Oligodendrocytes are essential regulators of axonal energy homeostasis and electrical conduction and emerging target cells for restoration of neurological function. Here we investigate the role of protease activated receptor 2 (PAR2), a unique protease activated G protein-coupled receptor, in myelin development and repair using the spinal cord as a model. Results demonstrate that genetic deletion of PAR2 accelerates myelin production, including higher proteolipid protein (PLP) levels in the spinal cord at birth and higher levels of myelin basic protein and thickened myelin sheaths in adulthood. Enhancements in spinal cord myelin with PAR2 loss-of-function were accompanied by increased numbers of Olig2- and CC1-positive oligodendrocytes, as well as in levels of cyclic adenosine monophosphate (cAMP), and extracellular signal related kinase 1/2 (ERK1/2) signaling. Parallel promyelinating effects were observed after blocking PAR2 expression in purified oligodendrocyte cultures, whereas inhibiting adenylate cyclase reversed these effects. Conversely, PAR2 activation reduced PLP expression and this effect was prevented by brain derived neurotrophic factor (BDNF), a promyelinating growth factor that signals through cAMP. PAR2 knockout mice also showed improved myelin resiliency after traumatic spinal cord injury and an accelerated pattern of myelin regeneration after focal demyelination. These findings suggest that PAR2 is an important controller of myelin production and regeneration, both in the developing and adult spinal cord.

Distinct Signaling Patterns of Allosteric Antagonism at the P2Y1 Receptor

Traditionally, G protein-coupled receptor antagonists are classified as competitive or noncompetitive and surmountable or insurmountable based on functional antagonism. P2Y₁ receptor (P2Y₁R) structures showed two antagonists binding to two spatially distinct sites: nucleotide MRS2500 (orthosteric, contacting the helical bundle) and urea BPTU (allosteric, on the external receptor surface). However, the nature of their P2Y₁R antagonism has not been characterized. Here we characterized BPTU antagonism at various signaling pathways activated by structurally diverse agonists. BPTU rightward shifted the concentration-response curves of both 2-methylthioadenosine 5'-diphosphate trisodium salt and MRS2365 (5'-diphosphates) in some signaling events, such as extracellular signal-regulated kinase 1/2 and label free, in a parallel manner without affecting the maximum agonist effect (E_max) but antagonized insurmountably (suppressed agonist E_max) in signaling events such as guanosine 5'-3-O-(thio)triphosphate binding and β-arrestin2 recruitment. However, with dinucleotide Ap4A as an agonist, BPTU suppressed the E_max insurmountably in all signaling pathways. By comparison, MRS2500 behaved as surmountable antagonist rightward-shifting concentration-response curves of all three agonists in a parallel manner for all signaling pathways measured. Thus, we demonstrated a previously undocumented phenomenon that P2Y₁R antagonism patterns could vary in different signaling pathways, which could be related to conformational selection, signaling amplification, and probe dependence. This phenomenon may apply generally to other receptors considering that antagonism by a specific ligand is often not compared at multiple signaling pathways. Thus, antagonism can be surmountable or insurmountable depending on the signaling pathways measured and the agonists used, which should be of broad relevance to drug discovery and disease treatment.

Tryptase potentiates enteric nerve activation by histamine and serotonin: Relevance for the effects of mucosal biopsy supernatants from irritable bowel syndrome patients

BACKGROUND

We previously showed that mucosal biopsy supernatants from irritable bowel syndrome patients activated neurons despite low concentrations of tryptase, histamine, and serotonin which individually would not cause spike discharge. We studied the potentiating responses between these mediators on excitability of enteric neurons.

METHODS

Calcium-imaging was performed using the calcium-sensitive dye Fluo-4 AM in human submucous plexus preparations from 45 individuals. Histamine, serotonin, and tryptase were applied alone and in combinations to evaluate nerve activation which was assessed by analyzing increase in intracellular Ca²⁺ ([Ca²⁺ ]_i ), the proportion of responding neurons and the product of both defined as Ca-neuroindex (NI). Protease activated receptor (PAR) 2 activating peptide, PAR2 antagonist and the serine protease-inhibitor FUT-175 were used to particularly investigate the role of proteases.

KEY RESULTS

Histamine or serotonin (1 μmol/L each) evoked only few small responses (median NI [25%/75%]: 0 [0/148]; 85 [0/705] respectively). Their combined application evoked statistically similar responses (216 [21/651]). Addition of the PAR2 activator tryptase induced a significantly higher Ca-NI (1401 [867/4075]) compared to individual application of tryptase or to coapplied histamine and serotonin. This synergistic potentiation was neither mimicked by PAR2 activating peptide nor reversed by the PAR2 antagonist GB83, but abolished by FUT-175.

CONCLUSIONS & INFERENCES

We observed synergistic potentiation between histamine, serotonin, and tryptase in enteric neurons, which is mediated by proteolytic activity rather than PAR2 activation. This explained neuronal activation by a cocktail of these mediators despite their low concentrations and despite a relatively small PAR2-mediated response in human submucous neurons.

Homeostatic effects of coagulation protease-dependent signaling and protease activated receptors

A homeostatic function of the coagulation system in regard to hemostasis is well established. Homeostasis of blood coagulation depends partially on protease activated receptor (PAR)-signaling. Beyond coagulation proteases, numerous other soluble and cell-bound proteases convey cellular effects via PAR signaling. As we learn more about the mechanisms underlying cell-, tissue-, and context-specific PAR signaling, we concurrently gain new insights into physiological and pathophysiological functions of PARs. In this regard, regulation of cell and tissue homeostasis by PAR signaling is an evolving scheme. Akin to the control of blood clotting per se (the fibrin-platelet interaction) coagulation proteases coordinately regulate cell- and tissue-specific functions. This review summarizes recent insights into homeostatic regulation through PAR signaling, focusing on blood coagulation proteases. Considering the common use of drugs altering coagulation protease activity through either broad or targeted inhibitory activities, and the advent of PAR modulating drugs, an in-depth understanding of the mechanisms through which coagulation proteases and PAR signaling regulate not only hemostasis, but also cell and tissue homeostasis is required.

Inhibitory effect of FSLLRY-NH2 on inflammatory responses induced by hydrogen peroxide in HepG2 cells

Proteinase activated receptor 2 (PAR2), which is localized in the GI tract, the respiratory system, and the kidney tubules is a G protein-coupled receptor associated with inflammation, metabolism, and disease. The aim of this study was to explore the role of PAR2 in hydrogen peroxide (H₂O₂)-induced HepG2 cells by using FSLLRY-NH₂ a PAR2 antagonist. H₂O₂ treatment resulted in induction of PAR2 in esophageal, gastric, and liver cells, with the most robust response being in HepG2 cells. Furthermore, this effect was dose-dependent in HepG2 cells. Treatment with H₂O₂ at concentrations above 400 μM for 24 h also reduced HepG2 cell viability. H₂O₂ treatment increased both the protein and mRNA levels of IL-1β, IL-8, and TNF-α, as well as those of SAPK/JNK. The increased levels of these pro-inflammatory genes and SAPK/JNK induced by H₂O₂ were attenuated in a dose-dependent manner when cells were co-treated with H₂O₂ and FSLLRY-NH2. In summary, the PAR2 antagonist peptide, FSLLRY-NH2, reduces the level of the pro-inflammatory genes IL-8, IL-1β, and TNF-α induced by H₂O₂, through the SAPK/JNK pathways in HepG2 cells. These data suggest that a PAR2 antagonist could be an anti-inflammatory agent in HepG2 cells.

Biased Signaling by Agonists of Protease Activated Receptor 2

Protease activated receptor 2 (PAR2) is associated with metabolism, obesity, inflammatory, respiratory and gastrointestinal disorders, pain, cancer, and other diseases. The extracellular N-terminus of PAR2 is a common target for multiple proteases, which cleave it at different sites to generate different N-termini that activate different PAR2-mediated intracellular signaling pathways. There are no synthetic PAR2 ligands that reproduce the same signaling profiles and potencies as proteases. Structure-activity relationships here for 26 compounds spanned a signaling bias over 3 log units, culminating in three small ligands as biased agonist tools for interrogating PAR2 functions. DF253 (2f-LAAAAI-NH₂) triggered PAR2-mediated calcium release (EC₅₀ 2 μM) but not ERK1/2 phosphorylation (EC₅₀ > 100 μM) in CHO cells transfected with hPAR2. AY77 (Isox-Cha-Chg-NH₂) was a more potent calcium-biased agonist (EC₅₀ 40 nM, Ca²⁺; EC₅₀ 2 μM, ERK1/2), while its analogue AY254 (Isox-Cha-Chg-A-R-NH₂) was an ERK-biased agonist (EC₅₀ 2 nM, ERK1/2; EC₅₀ 80 nM, Ca²⁺). Signaling bias led to different functional responses in human colorectal carcinoma cells (HT29). AY254, but not AY77 or DF253, attenuated cytokine-induced caspase 3/8 activation, promoted scratch-wound healing, and induced IL-8 secretion, all via PAR2-ERK1/2 signaling. Different ligand components were responsible for different PAR2 signaling and functions, clues that can potentially lead to drugs that modulate different pathway-selective cellular and physiological responses.

Don't stress about CRF: assessing the translational failures of CRF1antagonists

BACKGROUND

Dr. Athina Markou sought treatments for a common neural substrate shared by depression and drug dependence. Antagonists of corticotropin-releasing factor (CRF) receptors, a target of interest to her, have not reached the clinic despite strong preclinical rationale and sustained translational efforts.

METHODS

We explore potential causes for the failure of CRF1 antagonists and review recent findings concerning CRF-CRF1 systems in psychopathology.

RESULTS

Potential causes for negative outcomes include (1) poor safety and efficacy of initial drug candidates due to bad pharmacokinetic and physicochemical properties, (2) specificity problems with preclinical screens, (3) the acute nature of screens vs. late-presenting patients, (4) positive preclinical results limited to certain models and conditions with dynamic CRF-CRF1 activation not homologous to tested patients, (5) repeated CRF1 activation-induced plasticity that reduces the importance of ongoing CRF1 agonist stimulation, and (6) therapeutic silencing which may need to address CRF2 receptor or CRF-binding protein molecules, constitutive CRF1 activity, or molecules that influence agonist-independent activity or to target structural regions other than the allosteric site bound by all drug candidates. We describe potential markers of activation towards individualized treatment, human genetic, and functional data that still implicate CRF1 systems in emotional disturbance, sex differences, and suggestive clinical findings for CRF1 antagonists in food craving and CRF-driven HPA-axis overactivation.

CONCLUSION

The therapeutic scope of selective CRF1 antagonists now appears narrower than had been hoped. Yet, much remains to be learned about CRF's role in the neurobiology of dysphoria and addiction and the potential for novel anti-CRF therapies therein.

PAR2 Modulators Derived from GB88

PAR2 antagonists have potential for treating inflammatory, respiratory, gastrointestinal, neurological, and metabolic disorders, but few antagonists are known. Derivatives of GB88 (3) suggest that all four of its components bind at distinct PAR2 sites with the isoxazole, cyclohexylalanine, and isoleucine determining affinity and selectivity, while the C-terminal substituent determines agonist/antagonist function. Here we report structurally similar PAR2 ligands with opposing functions (agonist vs antagonist) upon binding to PAR2. A biased ligand AY117 (65) was found to antagonize calcium release induced by PAR2 agonists trypsin and hexapeptide 2f-LIGRLO-NH₂ (IC₅₀ 2.2 and 0.7 μM, HT29 cells), but it was a selective PAR2 agonist in inhibiting cAMP stimulation and activating ERK1/2 phosphorylation. It showed anti-inflammatory properties both in vitro and in vivo.

Antagonism of the proinflammatory and pronociceptive actions of canonical and biased agonists of protease-activated receptor-2

BACKGROUND AND PURPOSE

Diverse proteases cleave protease-activated receptor-2 (PAR2) on primary sensory neurons and epithelial cells to evoke pain and inflammation. Trypsin and tryptase activate PAR2 by a canonical mechanism that entails cleavage within the extracellular N-terminus revealing a tethered ligand that activates the cleaved receptor. Cathepsin-S and elastase are biased agonists that cleave PAR2 at different sites to activate distinct signalling pathways. Although PAR2 is a therapeutic target for inflammatory and painful diseases, the divergent mechanisms of proteolytic activation complicate the development of therapeutically useful antagonists.

EXPERIMENTAL APPROACH

We investigated whether the PAR2 antagonist GB88 inhibits protease-evoked activation of nociceptors and protease-stimulated oedema and hyperalgesia in rodents.

KEY RESULTS

Intraplantar injection of trypsin, cathespsin-S or elastase stimulated mechanical and thermal hyperalgesia and oedema in mice. Oral GB88 or par2 deletion inhibited the algesic and proinflammatory actions of all three proteases, but did not affect basal responses. GB88 also prevented pronociceptive and proinflammatory effects of the PAR2-selective agonists 2-furoyl-LIGRLO-NH2 and AC264613. GB88 did not affect capsaicin-evoked hyperalgesia or inflammation. Trypsin, cathepsin-S and elastase increased [Ca(2+) ]i in rat nociceptors, which expressed PAR2. GB88 inhibited this activation of nociceptors by all three proteases, but did not affect capsaicin-evoked activation of nociceptors or inhibit the catalytic activity of the three proteases.

CONCLUSIONS AND IMPLICATIONS

GB88 inhibits the capacity of canonical and biased protease agonists of PAR2 to cause nociception and inflammation.

Teleocidin A2 inhibits human proteinase-activated receptor 2 signaling in tumor cells

Enhanced expression of the proteinase‐activated receptor 2 (PAR2) is linked to cell proliferation and migration in many cancer cell types. The role of PAR2 in cancer progression strongly illustrates the need for PAR2‐inhibiting compounds. However, to date, potent and selective PAR2 antagonists have not been reported. The natural product teleocidin A2 was characterized against PAR2‐activating peptide SLIGKV‐NH₂, and trypsin‐induced PAR2‐dependent intracellular Ca²⁺ mobilization in tumor and in primary endothelial or epithelial cells. Further biochemical and cell‐based studies were conducted to evaluate teleocidin specificity. The antagonizing effect of teleocidin A2 was confirmed in PAR2‐dependent cell migration and rearrangement of actin cytoskeleton of human breast adenocarcinoma cell line (MDA‐MB 231) breast cancer cells. Teleocidin A2 antagonizes PAR2‐dependent intracellular Ca²⁺ mobilization induced by either SLIGKV‐NH₂ or trypsin with IC₅₀ values from 15 to 25 nmol/L in MDA‐MB 231, lung carcinoma cell line, and human umbilical vein endothelial cell. Half maximal inhibition of either PAR1 or P2Y receptor‐dependent Ca²⁺ release is only achieved with 10‐ to 20‐fold higher concentrations of teleocidin A2. In low nanomolar concentrations, teleocidin A2 reverses both SLIGKV‐NH₂ and trypsin‐mediated PAR2‐dependent migration of MDA‐MB 231 cells, and has no effect itself on cell migration and no effect on cell viability. Teleocidin A2 further controls PAR2‐induced actin cytoskeleton rearrangement of MDA‐MB 231 cells. Thus, for the first time, the small molecule natural product teleocidin A2 exhibiting PAR2 antagonism in the low nanomolar range with potent antimigratory activity is described.

The role of protease-activated receptor type 2 in nociceptive signaling and pain

Protease-activated receptors (PARs) belong to the G-protein-coupled receptor family, that are expressed in many body tissues especially in different epithelial cells, mast cells and also in neurons and astrocytes. PARs play different physiological roles according to the location of their expression. Increased evidence supports the importance of PARs activation during nociceptive signaling and in the development of chronic pain states. This short review focuses on the role of PAR2 receptors in nociceptive transmission with the emphasis on the modulation at the spinal cord level. PAR2 are cleaved and subsequently activated by endogenous proteases such as tryptase and trypsin. In vivo, peripheral and intrathecal administration of PAR2 agonists induces thermal and mechanical hypersensitivity that is thought to be mediated by PAR2-induced release of pronociceptive neuropeptides and modulation of different receptors. PAR2 activation leads also to sensitization of transient receptor potential channels (TRP) that are crucial for nociceptive signaling and modulation. PAR2 receptors may play an important modulatory role in the development and maintenance of different pathological pain states and could represent a potential target for new analgesic treatments.

Protease activated receptor 2 (PAR2) modulators: a patent review (2010-2015)

INTRODUCTION

Protease activated receptor 2 (PAR2) is a self-activated G protein-coupled receptor that has been implicated in several diseases, including inflammatory, gastrointestinal, respiratory, metabolic diseases, cancers and others, making it an important prospective drug target. No known endogenous ligands are available for PAR2, so having potent exogenous agonists and antagonists can be helpful for studying physiological functions of PAR2.

AREAS COVERED

This review covers agonist-, antagonist-, antibody- and pepducin-based modulators of PAR2 reported in patent applications between 2010-2015, along with their available structure-activity relationships, biological activities and potential uses for studying PAR2.

EXPERT OPINION

In the last six years, substantial efforts were made towards developing PAR2 modulators, but most lack potency or selectivity or have poor pharmacokinetic profiles. Many PAR2 modulators were assessed by measuring Gαq protein-mediated calcium release in cells. This may be insufficient to fully characterize ligand function, since different ligands signal through PAR2 via multiple signaling pathways. It may be feasible to develop biased ligands as drugs that can selectively modulate one or more specific signaling pathways linking PAR2 to a specific diseased state. Accordingly, potent, orally bioavailable, pathway- and receptor-selective PAR2 modulators may be an achievable goal to realizing effective drugs that can treat PAR2-mediated diseases.

Characterization and Functions of Protease-Activated Receptor 2 in Obesity, Diabetes, and Metabolic Syndrome: A Systematic Review

Proteinase-activated receptor 2 (PAR2) is a cell surface receptor activated by serine proteinases or specific synthetic compounds. Interest in PAR2 as a pharmaceutical target for various diseases is increasing. Here we asked two questions relevant to endothelial dysfunction and diabetes: How is PAR2 function affected in blood vessels? What role does PAR2 have in promoting obesity, diabetes, and/or metabolic syndrome, specifically via the endothelium and adipose tissues? We conducted a systematic review of the published literature in PubMed and Scopus (July 2015; search terms: par2, par-2, f2lr1, adipose, obesity, diabetes, and metabolic syndrome). Seven studies focused on PAR2 and vascular function. The obesity, diabetes, or metabolic syndrome animal models differed amongst studies, but each reported that PAR2-mediated vasodilator actions were preserved in the face of endothelial dysfunction. The remaining studies focused on nonvascular functions and provided evidence supporting the concept that PAR2 activation promoted obesity. Key studies showed that PAR2 activation regulated cellular metabolism, and PAR2 antagonists inhibited adipose gain and metabolic dysfunction in rats. We conclude that PAR2 antagonists for treatment of obesity indeed show early promise as a therapeutic strategy; however, endothelial-specific PAR2 functions, which may offset mechanisms that produce vascular dysfunction in diabetes, warrant additional study.

Protease-activated Receptor-2 (PAR-2)-mediated Nf-κB Activation Suppresses Inflammation-associated Tumor Suppressor MicroRNAs in Oral Squamous Cell Carcinoma

Oral cancer is the sixth most common cause of death from cancer with an estimated 400,000 deaths worldwide and a low (50%) 5-year survival rate. The most common form of oral cancer is oral squamous cell carcinoma (OSCC). OSCC is highly inflammatory and invasive, and the degree of inflammation correlates with tumor aggressiveness. The G protein-coupled receptor protease-activated receptor-2 (PAR-2) plays a key role in inflammation. PAR-2 is activated via proteolytic cleavage by trypsin-like serine proteases, including kallikrein-5 (KLK5), or by treatment with activating peptides. PAR-2 activation induces G protein-α-mediated signaling, mobilizing intracellular calcium and Nf-κB signaling, leading to the increased expression of pro-inflammatory mRNAs. Little is known, however, about PAR-2 regulation of inflammation-related microRNAs. Here, we assess PAR-2 expression and function in OSCC cell lines and tissues. Stimulation of PAR-2 activates Nf-κB signaling, resulting in RelA nuclear translocation and enhanced expression of pro-inflammatory mRNAs. Concomitantly, suppression of the anti-inflammatory tumor suppressor microRNAs let-7d, miR-23b, and miR-200c was observed following PAR-2 stimulation. Analysis of orthotopic oral tumors generated by cells with reduced KLK5 expression showed smaller, less aggressive lesions with reduced inflammatory infiltrate relative to tumors generated by KLK5-expressing control cells. Together, these data support a model wherein KLK5-mediated PAR-2 activation regulates the expression of inflammation-associated mRNAs and microRNAs, thereby modulating progression of oral tumors.

Potent Small Agonists of Protease Activated Receptor 2

Many proteases cut the PAR2 N-terminus resulting in conformational changes that activate cells. Synthetic peptides corresponding to newly exposed N-terminal sequences of PAR2 also activate the receptor at micromolar concentrations. PAR2-selective small molecules reported here induce PAR2-mediated intracellular calcium signaling at nanomolar concentrations (EC50 = 15-100 nM, iCa(2+), CHO-hPAR2 cells). These are the most potent and efficient small molecule ligands to activate PAR2-mediated calcium release and chemotaxis, including for human breast and prostate cancer cells.

The novel PAR2 ligand C391 blocks multiple PAR2 signalling pathways in vitro and in vivo

BACKGROUND AND PURPOSE

Proteinase-activated receptor-2 (PAR2) is a GPCR linked to diverse pathologies, including acute and chronic pain. PAR2 is one of the four PARs that are activated by proteolytic cleavage of the extracellular amino terminus, resulting in an exposed, tethered peptide agonist. Several peptide and peptidomimetic agonists, with high potency and efficacy, have been developed to probe the functions of PAR2, in vitro and in vivo. However, few similarly potent and effective antagonists have been described.

EXPERIMENTAL APPROACH

We modified the peptidomimetic PAR2 agonist, 2-furoyl-LIGRLO-NH₂ , to create a novel PAR2 peptidomimetic ligand, C391. C391 was evaluated for PAR2 agonist/antagonist activity to PAR2 across G_q signalling pathways using the naturally expressing PAR2 cell line 16HBE14o-. For antagonist studies, a highly potent and specific peptidomimetic agonist (2-aminothiazo-4-yl-LIGRL-NH₂ ) and proteinase agonist (trypsin) were used to activate PAR2. C391 was also evaluated in vivo for reduction of thermal hyperalgesia, mediated by mast cell degranulation, in mice.

KEY RESULTS

C391 is a potent and specific peptidomimetic antagonist, blocking multiple signalling pathways (G_q -dependent Ca²⁺ , MAPK) induced following peptidomimetic or proteinase activation of human PAR2. In a PAR2-dependent behavioural assay in mice, C391 dose-dependently (75 μg maximum effect) blocked the thermal hyperalgesia, mediated by mast cell degranulation.

CONCLUSIONS AND IMPLICATIONS

C391 is the first low MW antagonist to block both PAR2 Ca²⁺ and MAPK signalling pathways activated by peptidomimetics and/or proteinase activation. C391 represents a new molecular structure for PAR2 antagonism and can serve as a basis for further development for this important therapeutic target.

Three Homology Models of PAR2 Derived from Different Templates: Application to Antagonist Discovery

Protease activated receptor 2 (PAR2) is an unusual G-protein coupled receptor (GPCR) involved in inflammation and metabolism. It is activated through cleavage of its N-terminus by proteases. The new N-terminus functions as a tethered ligand that folds back and intramolecularly activates PAR2, initiating multiple downstream signaling pathways. The only compounds reported to date to inhibit PAR2 activation are of moderate potency. Three structural models for PAR2 have been constructed based on sequence homology with known crystal structures for bovine rhodopsin, human ORL-1 (also called nociceptin/orphanin FQ receptor), and human PAR1. The three PAR2 model structures were compared and used to predict potential interactions with ligands. Virtual screening for ligands using the Chembridge database, and either ORL-1 or PAR1 derived PAR2 models led to identification of eight new small molecule PAR2 antagonists (IC50 10-100 μM). Notably, the most potent compound 1 (IC50 11 μM) was derived from the less homologous template protein, human ORL-1. The results suggest that virtual screening against multiple homology models of the same GPCR can produce structurally diverse antagonists and that this may be desirable even when some models have less sequence homology with the target protein.