High-resolution crystal structure of human protease-activated receptor 1

The U.S. FDA approved cardiovascular drugs from 2011 to 2023: A medicinal chemistry perspective

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality worldwide. A total of 28 new molecular entities (NMEs) were approved by the U.S. Food and Drug Administration (FDA) for the treatment of cardiovascular diseases from 2011 to 2023. Approximately 25 % of the medications were sanctioned for the management of diverse vascular disorders. The other major therapeutic areas of focus included antilipemic agents (15 %), blood pressure disease (11 %), heart failure, hyperkalemia, and cardiomyopathy (7-8% each). Among all the approved drugs, there are a total of 22 new chemical entities (NCEs), including inhibitors, agonists, polymers, and inorganic compounds. In addition to NCEs, 6 biological agents (BLAs), including monoclonal antibodies, small interfering RNAs (siRNAs), and antisense oligonucleotides, have also obtained approval for the treatment of cardiovascular diseases. From this perspective, approved NCEs are itemized and discussed based on their disease, targets, chemical classes, major drug metabolites, and biochemical and pharmacological properties. Systematic analysis has been conducted to examine the binding modes of these approved drugs with their targets using cocrystal structure information or docking studies to provide valuable insights for designing next-generation agents. Furthermore, the synthetic approaches employed in the creation of these drug molecules have been emphasized, aiming to inspire the development of novel, efficient, and applicable synthetic methodologies. Generally, the primary objective of this review is to provide a comprehensive examination of the clinical applications, pharmacology, binding modes, and synthetic methodologies employed in small-molecule drugs approved for treating CVD. This will facilitate the development of more potent and innovative therapeutics for effectively managing cardiovascular diseases.

Differential Behavior of Conformational Dynamics in Active and Inactive States of Cannabinoid Receptor 1

The cannabinoid receptor CB1 is a G protein-coupled receptor that regulates critical physiological processes including pain, appetite, and cognition. Understanding the conformational dynamics of CB1 associated with transitions between inactive and active signaling states is imperative for developing targeted modulators. Using microsecond-level all-atom molecular dynamics simulations, we identified marked differences in the conformational ensembles of inactive and active CB1 states in apo conditions. The inactive state exhibited substantially increased structural heterogeneity and plasticity compared to the more rigidified active state in the absence of stabilizing ligands. Transmembrane helices TM3 and TM7 were identified as distinguishing factors modulating the state-dependent dynamics. TM7 displayed amplified fluctuations selectively in the inactive state simulations attributed to disruption of conserved electrostatic contacts anchoring it to surrounding helices in the active state. Additionally, we identified significant reorganization of key salt bridge and hydrogen bond networks known to control CB1 activation between states. For instance, a conserved D213-Y224 hydrogen bond and D184-K192 salt bridge interactions showed marked rearrangements between the states. Collectively, these findings reveal the specialized role of TM7 in directing state-dependent CB1 dynamics through electrostatic switch mechanisms. By elucidating the intrinsic enhanced flexibility of inactive CB1, this study provides valuable insights into the conformational landscape enabling functional transitions. Our perspective advances understanding of CB1 activation mechanisms and offers opportunities for structure-based drug discovery targeting the state-specific conformational dynamics of this receptor.

Calcium-Driven In Silico Inactivation of a Human Olfactory Receptor

Conformational changes as well as molecular determinants related to the activation and inactivation of olfactory receptors are still poorly understood due to the intrinsic difficulties in the structural determination of this GPCR family. Here, we perform, for the first time, the in silico inactivation of human olfactory receptor OR51E2, highlighting the possible role of calcium in this receptor state transition. Using molecular dynamics simulations, we show that a divalent ion in the ion binding site, coordinated by two acidic residues at positions 2.50 and 3.39 conserved across most ORs, stabilizes the receptor in its inactive state. In contrast, protonation of the same two acidic residues is not sufficient to drive inactivation within the microsecond timescale of our simulations. Our findings suggest a novel molecular mechanism for OR inactivation, potentially guiding experimental validation and offering insights into the possible broader role of divalent ions in GPCR signaling.

Therapeutic Effect of Proteinase-Activated Receptor-1 Antagonist on Colitis-Associated Carcinogenesis

BACKGROUND & AIMS

Inflammatory bowel disease is associated with carcinogenesis, which limits the prognosis of the patients. The local expression of proteinases and proteinase-activated receptor 1 (PAR1) increases in inflammatory bowel disease. The present study investigated the therapeutic effects of PAR1 antagonism on colitis-associated carcinogenesis.

METHODS

A colitis-associated carcinogenesis model was prepared in mice by treatment with azoxymethane (AOM) and dextran sulfate sodium (DSS). PAR1 antagonist E5555 was administered in long- and short-term protocol, starting on the day of AOM injection and 1 week after completing AOM/DSS treatment, respectively. The fecal samples were collected for metagenome analysis of gut microbiota. The intestinal myofibroblasts of the Crohn's disease patients were used to elucidate underlying cellular mechanisms. Caco-2 cells were used to investigate a possible source of PAR1 agonist proteinases.

RESULTS

AOM/DSS model showed weight loss, diarrhea, tumor development, inflammation, fibrosis, and increased production of inflammatory cytokines. The β-diversity, but not α-diversity, of microbiota significantly differed between AOM/DSS and control mice. E5555 alleviated these pathological changes and altered the microbiota β-diversity in AOM/DSS mice. The thrombin expression was up-regulated in tumor and non-tumor areas, whereas PAR1 mRNA expression was higher in tumor areas compared with non-tumor areas. E5555 inhibited thrombin-triggered elevation of cytosolic Ca2+ concentration and ERK1/2 phosphorylation, as well as IL6-induced signal transducer and activator of transcription 3 (STAT3) phosphorylation in intestinal myofibroblasts. Caco-2 cell-conditioned medium contained immunoreactive thrombin, which cleaved the recombinant protein containing the extracellular domain of PAR1 at the thrombin cleavage site.

CONCLUSIONS

PAR1 antagonism is proposed to be a novel therapeutic strategy for treatment of inflammatory bowel disease and its associated carcinogenesis.

Discovery of Protease-Activated Receptor 4 (PAR4)-Tethered Ligand Antagonists Using Ultralarge Virtual Screening

Here, we demonstrate a structure-based small molecule virtual screening and lead optimization pipeline using a homology model of a difficult-to-drug G-protein-coupled receptor (GPCR) target. Protease-activated receptor 4 (PAR4) is activated by thrombin cleavage, revealing a tethered ligand that activates the receptor, making PAR4 a challenging target. A virtual screen of a make-on-demand chemical library yielded a one-hit compound. From the single-hit compound, we developed a novel series of PAR4 antagonists. Subsequent lead optimization via simultaneous virtual library searches and structure-based rational design efforts led to potent antagonists of thrombin-induced activation. Interestingly, this series of antagonists was active against PAR4 activation by the native protease thrombin cleavage but not the synthetic PAR4 agonist peptide AYPGKF.

Exploring biased activation characteristics by molecular dynamics simulation and machine learning for the μ-opioid receptor

Biased ligands selectively activating specific downstream signaling pathways (termed as biased activation) exhibit significant therapeutic potential. However, the conformational characteristics revealed are very limited for the biased activation, which is not conducive to biased drug development. Motivated by the issue, we combine extensive accelerated molecular dynamics simulations and an interpretable deep learning model to probe the biased activation features for two complex systems constructed by the inactive μOR and two different biased agonists (G-protein-biased agonist TRV130 and β-arrestin-biased agonist endomorphin2). The results indicate that TRV130 binds deeper into the receptor core compared to endomorphin2, located between W2936.48 and D1142.50, and forms hydrogen bonding with D1142.50, while endomorphin2 binds above W2936.48. The G protein-biased agonist induces greater outward movements of the TM6 intracellular end, forming a typical active conformation, while the β-arrestin-biased agonist leads to a smaller extent of outward movements of TM6. Compared with TRV130, endomorphin2 causes more pronounced inward movements of the TM7 intracellular end and more complex conformational changes of H8 and ICL1. In addition, important residues determining the two different biased activation states were further identified by using an interpretable deep learning classification model, including some common biased activation residues across Class A GPCRs like some key residues on the TM2 extracellular end, ECL2, TM5 intracellular end, TM6 intracellular end, and TM7 intracellular end, and some specific important residues of ICL3 for μOR. The observations will provide valuable information for understanding the biased activation mechanism for GPCRs.

A comprehensive review of the ten main platelet receptors involved in platelet activity and cardiovascular disease

Cardiovascular disease (CVD) is a major cause of death worldwide. Although there are many variables that contribute to the development of this disease, it is predominantly the activity of platelets that provides the mechanisms by which this disease prevails. While there are numerous platelet receptors expressed on the surface of platelets, it is largely the consensus that there are 10 main platelet receptors that contribute to a majority of platelet function. Understanding these key platelet receptors is vitally important for patients suffering from myocardial infarction, CVD, and many other diseases that arise due to overactivation or mutations of these receptors. The goal of this manuscript is to review the main platelet receptors that contribute most to platelet activity.

Structural insights into ligand recognition and selectivity of the human hydroxycarboxylic acid receptor HCAR2

Hydroxycarboxylic acid receptor 2 (HCAR2) belongs to the family of class A G protein-coupled receptors with key roles in regulating lipolysis and free fatty acid formation in humans. It is deeply involved in many pathophysiological processes and serves as an attractive target for the treatment of cardiovascular, neoplastic, autoimmune, neurodegenerative, inflammatory, and metabolic diseases. Here, we report four cryo-EM structures of human HCAR2-Gi1 complexes with or without agonists, including the drugs niacin (2.69 Å) and acipimox (3.23 Å), the highly subtype-specific agonist MK-6892 (3.25 Å), and apo form (3.28 Å). Combined with molecular dynamics simulation and functional analysis, we have revealed the recognition mechanism of HCAR2 for different agonists and summarized the general pharmacophore features of HCAR2 agonists, which are based on three key residues R1113.36, S17945.52, and Y2847.43. Notably, the MK-6892-HCAR2 structure shows an extended binding pocket relative to other agonist-bound HCAR2 complexes. In addition, the key residues that determine the ligand selectivity between the HCAR2 and HCAR3 are also illuminated. Our findings provide structural insights into the ligand recognition, selectivity, activation, and G protein coupling mechanism of HCAR2, which shed light on the design of new HCAR2-targeting drugs for greater efficacy, higher selectivity, and fewer or no side effects.

IUPHAR themed review: Opioid efficacy, bias, and selectivity

Drugs acting at the opioid receptor family are clinically used to treat chronic and acute pain, though they represent the second line of treatment behind GABA analogs, antidepressants and SSRI's. Within the opioid family mu and kappa opioid receptor are commonly targeted. However, activation of the mu opioid receptor has side effects of constipation, tolerance, dependence, euphoria, and respiratory depression; activation of the kappa opioid receptor leads to dysphoria and sedation. The side effects of mu opioid receptor activation have led to mu receptor drugs being widely abused with great overdose risk. For these reasons, newer safer opioid analgesics are in high demand. For many years a focus within the opioid field was finding drugs that activated the G protein pathway at mu opioid receptor, without activating the β-arrestin pathway, known as biased agonism. Recent advances have shown that this may not be the way forward to develop safer analgesics at mu opioid receptor, though there is still some promise at the kappa opioid receptor. Here we discuss recent novel approaches to develop safer opioid drugs including efficacy vs bias and fine-tuning receptor activation by targeting sub-pockets in the orthosteric site, we explore recent works on the structural basis of bias, and we put forward the suggestion that Gα subtype selectivity may be an exciting new area of interest.

Cryo-EM structures of human GPR34 enable the identification of selective antagonists

GPR34 is a functional G-protein-coupled receptor of Lysophosphatidylserine (LysoPS), and has pathogenic roles in numerous diseases, yet remains poorly targeted. We herein report a cryo-electron microscopy (cryo-EM) structure of GPR34 bound with LysoPS (18:1) and Gi protein, revealing a unique ligand recognition mode with the negatively charged head group of LysoPS occupying a polar cavity formed by TM3, 6 and 7, and the hydrophobic tail of LysoPS residing in a lateral open hydrophobic groove formed by TM3-5. Virtual screening and subsequent structural optimization led to the identification of a highly potent and selective antagonist (YL-365). Design of fusion proteins allowed successful determination of the challenging cryo-EM structure of the inactive GPR34 complexed with YL-365, which revealed the competitive binding of YL-365 in a portion of the orthosteric binding pocket of GPR34 and the antagonist-binding-induced allostery in the receptor, implicating the inhibition mechanism of YL-365. Moreover, YL-365 displayed excellent activity in a neuropathic pain model without obvious toxicity. Collectively, this study offers mechanistic insights into the endogenous agonist recognition and antagonist inhibition of GPR34, and provides proof of concept that targeting GPR34 represents a promising strategy for disease treatment.

Structural basis of hydroxycarboxylic acid receptor signaling mechanisms through ligand binding

Hydroxycarboxylic acid receptors (HCA) are expressed in various tissues and immune cells. HCA2 and its agonist are thus important targets for treating inflammatory and metabolic disorders. Only limited information is available, however, on the active-state binding of HCAs with agonists. Here, we present cryo-EM structures of human HCA2-Gi and HCA3-Gi signaling complexes binding with multiple compounds bound. Agonists were revealed to form a salt bridge with arginine, which is conserved in the HCA family, to activate these receptors. Extracellular regions of the receptors form a lid-like structure that covers the ligand-binding pocket. Although transmembrane (TM) 6 in HCAs undergoes dynamic conformational changes, ligands do not directly interact with amino acids in TM6, suggesting that indirect signaling induces a slight shift in TM6 to activate Gi proteins. Structural analyses of agonist-bound HCA2 and HCA3 together with mutagenesis and molecular dynamics simulation provide molecular insights into HCA ligand recognition and activation mechanisms.

Chiral recognition of neutral guests by chiral naphthotubes with a bis-thiourea endo-functionalized cavity

Developing chiral receptors with an endo-functionalized cavity for chiral recognition is of great significance in the field of molecular recognition. This study presents two pairs of chiral naphthotubes containing a bis-thiourea endo-functionalized cavity. Each chiral naphthotube has two homochiral centers which were fixed adjacent to the thiourea groups, causing the skeleton and thiourea groups to twist enantiomerically through chiral transfer. These chiral naphthotubes are highly effective at enantiomerically recognizing various neutral chiral molecules with an enantioselectivity up to 17.0. Furthermore, the mechanism of the chiral recognition has been revealed to be originated from differences in multiple non-covalent interactions. Various factors, such as the shape of cavities, substituents of guests, flexibility of host and binding modes are demonstrated to contribute to creating differences in the non-covalent interactions. Additionally, the driving force behind enantioselectivity is mainly attributed to enthalpic differences, and enthalpy -entropy compensation has also been observed to influence enantioselectivity.

Protons taken hostage: Dynamic H-bond networks of the pH-sensing GPR68

Proton-sensing G Protein Coupled Receptors (GPCRs) sense changes in the extracellular pH to effect cell signaling for cellular homeostasis. They tend to be overexpressed in solid tumors associated with acidic extracellular pH, and are of direct interest as drug targets. How proton-sensing GPCRs sense extracellular acidification and activate upon protonation change is important to understand, because it may guide the design of therapeutics. Lack of publicly available experimental structures make it challenging to discriminate between conflicting mechanisms proposed for proton-binding, as main roles have been assigned to either an extracellular histidine cluster or to an internal carboxylic triad. Here we present a protocol to derive and evaluate structural models of the proton-sensing GPR68. This approach integrates state-of-the-art homology modeling with microsecond-timescale atomistic simulations, and with a detailed assessment of the compatibility of the structural models with known structural features of class A GPCRs. To decipher structural elements of potential interest for protonation-coupled conformational changes of GPR68, we used the best-compatible model as a starting point for independent atomistic simulations of GPR68 with different protonation states, and graph computations to characterize the response of GPR68 to changes in protonation. We found that GPR68 hosts an extended hydrogen-bond network that inter-connects the extracellular histidine cluster to the internal carboxylic triad, and which can even reach groups at the cytoplasmic G-protein binding site. Taken together, results suggest that GPR68 relies on dynamic, hydrogen-bond networks to inter-connect extracellular and internal proton-binding sites, and to elicit conformational changes at the cytoplasmic G-protein binding site.

Targeting biased signaling by PAR1: function and molecular mechanism of parmodulins

The G protein-coupled receptor (GPCR) protease-activated receptor 1 (PAR1) is a therapeutic target that was originally pursued with the aim of restricting platelet activation and the burden of cardiovascular diseases. In clinical studies, the use of orthosteric PAR1 inhibitors was associated with an increased risk of hemorrhage, including intracranial hemorrhage. Because (1) PAR1 is expressed by various cell types, including endothelial cells, (2) conveys in mice a physiological indispensable function for vascular development during embryogenesis, and (3) is subject to biased signaling dependent on the activating proteases, orthosteric PAR1 inhibition may be associated with unwanted side effects. Alternatively, the protease-activated protein C (aPC) and its variants can promote valuable anti-inflammatory signaling via PAR1. Most recently, small molecule allosteric modulators of PAR1 signaling, called parmodulins, have been developed. Parmodulins inhibit coagulation and platelet activation yet maintain cytoprotective effects typically provoked by PAR1 signaling upon the activation by aPC. In this study, we review the discovery of parmodulins and their preclinical data, summarize the current knowledge about their mode of action, and compare the structural interaction of parmodulin and PAR1 with that of other intracellularly binding allosteric GPCR modulators. Thus, we highlight the pharmaceutical potential and challenges associated with the future development of parmodulins.

Topical application of aerial portion of Acalypha indica Linn ameliorates psoriasis in rodents: Evidences from in vivo and in silico studies

ETHANOPHARMACOLOGICAL RELEVANCE

Acalypha indica Linn. is a weed, used traditionally for different skin diseases such as eczema and dermatitis in various parts of India. There are no previous in vivo studies reported on the antipsoriatic potential of this medicinal plant.

AIM

The aim of this study was to investigate antipsoriatic activity of coconut oil dispersion of aerial portion of Acalypha indica Linn. Few lipid-soluble phytoconstituents of this plantwere subjected to molecular docking studies on different targets to determine phytoconstituent responsible for antipsoriatic activity.

METHODS

Virgin coconut oil dispersion of aerial portion of the plant was prepared by mixing three parts of coconut oil and one part of powdered aerial portion. The acute dermal toxicity was determined according to OECD guidelines. Mouse tail model was used to evaluate the antipsoriatic activity. Molecular docking of phytoconstituents was carried out using Biovia Discovery Studio.

RESULTS

In acute dermal toxicity study,the coconut oil dispersion was found to be safe up to the dose of 20000 mg/kg. The dispersion exhibited significant antipsoriatic activity (p < 0.01) at the dose of 250 mg/kg; at 500 mg/kg dose, the activity was similar that of 250 mg/kg dose. In the docking study of the phytoconstituents, 2-methyl anthraquinone was found to be responsible for antipsoriatic activity.

CONCLUSION

This study provides new evidence of Acalypha indica Linn as antipsoriatic plant and justifies its traditional use. Computational studies also endorse the results obtained via acute dermal toxicity study and mouse tail model for evaluation of antipsoriatic potential.

Species Differences in Platelet Protease-Activated Receptors

Protease-activated receptors (PARs) are a class of integral membrane proteins that are cleaved by a variety of proteases, most notably thrombin, to reveal a tethered ligand and promote activation. PARs are critical mediators of platelet function in hemostasis and thrombosis, and therefore are attractive targets for anti-platelet therapies. Animal models studying platelet PAR physiology have relied heavily on genetically modified mouse strains, which have provided ample insight but have some inherent limitations. The current review aims to summarize the notable PAR expression and functional differences between the mouse and human, in addition to highlighting some recently developed tools to further study human physiology in mouse models.

Counterion at an atypical position: Investigating the mechanism of photoisomerization in jellyfish rhodopsin

The position of the counterion in animal rhodopsins plays a crucial role in maintaining visible light sensitivity and facilitating the photoisomerization of their retinal chromophore. The counterion displacement is thought to be closely related to the evolution of rhodopsins, with different positions found in invertebrates and vertebrates. Interestingly, box jellyfish rhodopsin (JelRh) acquired the counterion in transmembrane 2 (TM2) independently. This is a unique feature, as in most animal rhodopsins, the counterion is found in a different location. In this study, we used Fourier Transform Infrared spectroscopy to examine the structural changes that occur in the early photointermediate state of JelRh. We aimed to determine whether the photochemistry of JelRh is similar to that of other animal rhodopsins by comparing its spectra to those of vertebrate bovine rhodopsin (BovRh) and invertebrate squid rhodopsin (SquRh). We observed that the N-D stretching band of the retinal Schiff base was similar to that of BovRh, indicating the interaction between the Schiff base and the counterion is similar in both rhodopsins, despite their different counterion positions. Furthermore, we found that the chemical structure of the retinal in JelRh is similar to that in BovRh, including the changes in the hydrogen-out-of-plane band that indicates a retinal distortion. Overall, the protein conformational changes induced by the photoisomerization of JelRh yielded spectra that resemble an intermediate between BovRh and SquRh, suggesting a unique spectral property of JelRh, and making it the only animal rhodopsin with a counterion in TM2 and an ability to activate G_s protein.

Integrated LC-MS/MS and network pharmacology approach for predictingactive ingredients and pharmacological mechanisms of Tribulus terrestris L. against cardiac diseases

Tribulus terrestris L. (Gokshura) is a medicinal herb used for treating cardiac diseases and several other diseases. However, the active ingredients and the possible mechanism of action for treating cardiac diseases remain unclear. Hence, the study was designed to identify the active ingredients and to explore the potential mechanism of action of Tribulus terrestris L. for treating cardiac diseases by an integrated approach of metabolomics and network pharmacology. We performed HPLC-QTOF-MS/MS analysis to identify putative compounds and network pharmacology approach for predictive key targets and pathways. Using molecular docking and molecular dynamics simulation, we identified the active ingredients in Tribulus terrestris L. that can act as putative lead compounds to treat cardiac diseases. A total of 55 putative compounds were identified using methanolic extract of Tribulus terrestris L. using HPLC-QTOF-MS/MS analysis. Network pharmacology analysis predicted 32 human protein targets from 25 secondary metabolites, which have shown direct interaction with cardiac diseases. Based on the degrees of interaction, the hub targets such as TACR1, F2, F2R, ADRA1B, CHRM5, ADRA1A, ADRA1D, HTR2B, and AVPR1A were identified. In silico molecular docking and simulation resulted in the identification of active ingredients such as Kaempferol 3-rutinoside 7-glucuronide, Keioside, rutin, moupinamide, aurantiamide, quercetin-3-o-α-rhamnoside, tribuloside, and 3'',6''- Di-O-p-coumaroyltrifolin against hub protein targets. Hence, these compounds could be potential lead compounds for treating cardiac diseases. A further assessment of its efficacy can be made based on in vivo and in vitro studies for better understanding and strong assertion.Communicated by Ramaswamy H. Sarma.

Three-Dimensional Structural Insights Have Revealed the Distinct Binding Interactions of Agonists, Partial Agonists, and Antagonists with the µ Opioid Receptor

The United States is experiencing the most profound and devastating opioid crisis in history, with the number of deaths involving opioids, including prescription and illegal opioids, continuing to climb over the past two decades. This severe public health issue is difficult to combat as opioids remain a crucial treatment for pain, and at the same time, they are also highly addictive. Opioids act on the opioid receptor, which in turn activates its downstream signaling pathway that eventually leads to an analgesic effect. Among the four types of opioid receptors, the µ subtype is primarily responsible for the analgesic cascade. This review describes available 3D structures of the µ opioid receptor in the protein data bank and provides structural insights for the binding of agonists and antagonists to the receptor. Comparative analysis on the atomic details of the binding site in these structures was conducted and distinct binding interactions for agonists, partial agonists, and antagonists were observed. The findings in this article deepen our understanding of the ligand binding activity and shed some light on the development of novel opioid analgesics which may improve the risk benefit balance of existing opioids.

Structural insights into the human niacin receptor HCA2-Gi signalling complex

The hydroxycarboxylic acid receptor 2 (HCA2) agonist niacin has been used as treatment for dyslipidemia for several decades albeit with skin flushing as a common side-effect in treated individuals. Extensive efforts have been made to identify HCA2 targeting lipid lowering agents with fewer adverse effects, despite little being known about the molecular basis of HCA2 mediated signalling. Here, we report the cryo-electron microscopy structure of the HCA2-G_i signalling complex with the potent agonist MK-6892, along with crystal structures of HCA2 in inactive state. These structures, together with comprehensive pharmacological analysis, reveal the ligand binding mode and activation and signalling mechanisms of HCA2. This study elucidates the structural determinants essential for HCA2 mediated signalling and provides insights into ligand discovery for HCA2 and related receptors.

Oligosaccharide Blocks PAR1 (Proteinase-Activated Receptor 1)-PAR4-Mediated Platelet Activation by Binding to Thrombin Exosite II and Impairs Thrombosis

BACKGROUND

Inappropriate activation and aggregation of platelets can lead to arterial thrombosis. Thrombin is the most potent platelet agonist that activates human platelets via two PARs (proteinase-activated receptors), PAR1 and PAR4. The aim is to study the activity and mechanism of an oligosaccharide HS-11 (the undecasaccharide, derived from sea cucumber Holothuria fuscopunctata) in inhibiting thrombin-mediated platelet activation and aggregation and to evaluate its antithrombotic activity.

METHODS

Platelet activation was analyzed by detecting CD62P/P-selectin expression using flow cytometry. The HS-11-thrombin interaction and the binding site were studied by biolayer interferometry. Intracellular Ca²⁺ mobilization of platelets was measured by FLIPR Tetra System using Fluo-4 AM (Fluo-4 acetoxymethyl). Platelet aggregation, thrombus formation, and bleeding Assay were assessed.

RESULTS

An oligosaccharide HS-11, depolymerized from fucosylated glycosaminoglycan from sea cucumber Holothuria fuscopunctata blocks the interaction of thrombin with PAR1 and PAR4 complex by directly binding to thrombin exosite II, and completely inhibits platelet signal transduction, including intracellular Ca²⁺ mobilization and protein phosphorylation. Furthermore, HS-11 potently inhibits thrombin-PARs-mediated platelet aggregation and reduces thrombus formation in a model of ex vivo thrombosis.

CONCLUSIONS

The study firstly report that the fucosylated glycosaminoglycan oligosaccharide has antiplatelet activity by binding to thrombin exosite II, and demonstrates that thrombin exosite II plays an important role in the simultaneous activation of PAR1 and PAR4, which may be a potential antithrombotic target for effective treatment of arterial thrombosis.

Protein Design Strategies for the Structural–Functional Studies of G Protein-Coupled Receptors

G protein-coupled receptors (GPCRs) are an important family of membrane proteins responsible for many physiological functions in human body. High resolution GPCR structures are required to understand their molecular mechanisms and perform rational drug design, as GPCRs play a crucial role in a variety of diseases. That is difficult to obtain for the wild-type proteins because of their low stability. In this review, we discuss how this problem can be solved by using protein design strategies developed to obtain homogeneous stabilized GPCR samples for crystallization and cryoelectron microscopy.

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.

Insights into divalent cation regulation and G13-coupling of orphan receptor GPR35

Endogenous ions play important roles in the function and pharmacology of G protein-coupled receptors (GPCRs) with limited atomic evidence. In addition, compared with G protein subtypes G_s, G_i/o, and G_q/11, insufficient structural evidence is accessible to understand the coupling mechanism of G_12/13 protein by GPCRs. Orphan receptor GPR35, which is predominantly expressed in the gastrointestinal tract and is closely related to inflammatory bowel diseases (IBDs), stands out as a prototypical receptor for investigating ionic modulation and G₁₃ coupling. Here we report a cryo-electron microscopy structure of G₁₃-coupled GPR35 bound to an anti-allergic drug, lodoxamide. This structure reveals a novel divalent cation coordination site and a unique ionic regulatory mode of GPR35 and also presents a highly positively charged binding pocket and the complementary electrostatic ligand recognition mode, which explain the promiscuity of acidic ligand binding by GPR35. Structural comparison of the GPR35-G₁₃ complex with other G protein subtypes-coupled GPCRs reveals a notable movement of the C-terminus of α5 helix of the Gα₁₃ subunit towards the receptor core and the least outward displacement of the cytoplasmic end of GPR35 TM6. A featured 'methionine pocket' contributes to the G₁₃ coupling by GPR35. Together, our findings provide a structural basis for divalent cation modulation, ligand recognition, and subsequent G₁₃ protein coupling of GPR35 and offer a new opportunity for designing GPR35-targeted drugs for the treatment of IBDs.

Integrate thermostabilized fusion protein apocytochrome b562RIL and N-glycosylation mutations: A novel approach to heterologous expression of human UDP-glucuronosyltransferase (UGT) 2B7

Human UDP-glucuronosyltransferase (UGT) 2B7 is a crucial phase II metabolic enzyme that transfers glucuronic acid from UDP-glucuronic acid (UDPGA) to endobiotic and xenobiotic substrates. Biophysical and biochemical investigations of UGT2B7 are hampered by the challenge of the integral membrane protein purification. This study focused on the expression and purification of recombinant UGT2B7 by optimizing the insertion sites for the thermostabilized fusion protein apocytochrome b₅₆₂RIL (BRIL) and various mutations to improve the protein yields and homogeneity. Preparation of the recombinant proteins with high purity accelerated the measurement of pharmacokinetic parameters of UGT2B7. The dissociation constants (K_D) of two classical substrates (zidovudine and androsterone) and two inhibitors (schisanhenol and hesperetin) of UGT2B7 were determined using the surface plasmon resonance spectroscopy (SPR) for the first time. Using negative-staining transmission electron microscopy (TEM), UGT2B7 protein particles were characterized, which could be useful for further exploring its three-dimensional structure. The methods described in this study could be broadly applied to other UGTs and are expected to provide the basis for the exploration of metabolic enzyme kinetics, the mechanisms of drug metabolisms and drug interactions, changes in pharmacokinetics, and pharmacodynamics studies in vitro.

Exogenous human α-Synuclein acts in vitro as a mild platelet antiaggregant inhibiting α-thrombin-induced platelet activation

α-Synuclein (αSyn) is a small disordered protein, highly conserved in vertebrates and involved in the pathogenesis of Parkinson’s disease (PD). Indeed, αSyn amyloid aggregates are present in the brain of patients with PD. Although the pathogenic role of αSyn is widely accepted, the physiological function of this protein remains elusive. Beyond the central nervous system, αSyn is expressed in hematopoietic tissue and blood, where platelets are a major cellular host of αSyn. Platelets play a key role in hemostasis and are potently activated by thrombin (αT) through the cleavage of protease-activated receptors. Furthermore, both αT and αSyn could be found in the same spatial environment, i.e. the platelet membrane, as αT binds to and activates platelets that can release αSyn from α-granules and microvesicles. Here, we investigated the possibility that exogenous αSyn could interfere with platelet activation induced by different agonists in vitro. Data obtained from distinct experimental techniques (i.e. multiple electrode aggregometry, rotational thromboelastometry, immunofluorescence microscopy, surface plasmon resonance, and steady-state fluorescence spectroscopy) on whole blood and platelet-rich plasma indicate that exogenous αSyn has mild platelet antiaggregating properties in vitro, acting as a negative regulator of αT-mediated platelet activation by preferentially inhibiting P-selectin expression on platelet surface. We have also shown that both exogenous and endogenous (i.e. cytoplasmic) αSyn preferentially bind to the outer surface of activated platelets. Starting from these findings, a coherent model of the antiplatelet function of αSyn is proposed.

Allosteric Modulation of Adenosine A2A Receptors as a New Therapeutic Avenue

The therapeutic potential of targeting adenosine A_2A receptors (A_2ARs) is immense due to their broad expression in the body and central nervous system. The role of A_2ARs in cardiovascular function, inflammation, sleep/wake behaviors, cognition, and other primary nervous system functions has been extensively studied. Numerous A_2AR agonist and antagonist molecules are reported, many of which are currently in clinical trials or have already been approved for treatment. Allosteric modulators can selectively elicit a physiologic response only where and when the orthosteric ligand is released, which reduces the risk of an adverse effect resulting from A_2AR activation. Thus, these allosteric modulators have a potential therapeutic advantage over classical agonist and antagonist molecules. This review focuses on the recent developments regarding allosteric A_2AR modulation, which is a promising area for future pharmaceutical research because the list of existing allosteric A_2AR modulators and their physiologic effects is still short.

Predicting the Activities of Drug Excipients on Biological Targets using One-Shot Learning

Excipients are major components of drugs and are used to improve drug attributes such as stability and appearance. Excipients approved by the U.S. Food and Drug Administration (FDA) are regarded as safe for humans in allowed concentrations, but their potential interactions with drug targets have not been investigated systematically, which might influence a drug's efficacy. Deep learning models have been used for the identification of ligands that could bind to the drug targets. However, due to the limited available data, it is challenging to reliably estimate the likelihood of a ligand-protein interaction. One-shot learning techniques provide a potential approach to address this low data problem as these techniques require only one or a few examples to classify the new data. In this study, we apply one-shot learning models to data sets that include ligands binding to G-protein-coupled receptors (GPCRs) and kinases. The predicted results suggest that one-shot learning could be used for predicting ligand-protein interactions, and the models attain better performance when protein targets contain conserved binding pockets. The trained models are also used to predict interactions between excipients and drug targets, which provides a potential efficient strategy to explore the activities of drug excipients. We find that a large number of drug excipients could interact with biological targets and influence their function. The results demonstrate how one-shot learning can be used to make accurate predictions for excipient-protein interactions, and these methods could be used for selecting excipients with limited drug-protein interactions.

Mapping the binding sites of UDP and prostaglandin E2 glyceryl ester in the nucleotide receptor P2Y6

Cyclooxygenase‐2 catalyzes the biosynthesis of prostaglandins from arachidonic acid and the biosynthesis of prostaglandin glycerol esters (PG‐Gs) from 2‐arachidonoylglycerol. PG‐Gs are mediators of several biological actions such as macrophage activation, hyperalgesia, synaptic plasticity, and intraocular pressure. Recently, the human UDP receptor P2Y₆ was identified as a target for the prostaglandin E2 glycerol ester (PGE₂‐G). Here, we show that UDP and PGE₂‐G are evolutionary conserved endogenous agonists at vertebrate P2Y₆ orthologs. Using sequence comparison of P2Y₆ orthologs, homology modeling, and ligand docking studies, we proposed several receptor positions participating in agonist binding. Site‐directed mutagenesis and functional analysis of these P2Y₆ mutants revealed that both UDP and PGE₂‐G share in parts one ligand‐binding site. Thus, the convergent signaling of these two chemically very different agonists has already been manifested in the evolutionary design of the ligand‐binding pocket.

The Structural Basis of Peptide Binding at Class A G Protein-Coupled Receptors

G protein-coupled receptors (GPCRs) represent the largest membrane protein family and a significant target class for therapeutics. Receptors from GPCRs’ largest class, class A, influence virtually every aspect of human physiology. About 45% of the members of this family endogenously bind flexible peptides or peptides segments within larger protein ligands. While many of these peptides have been structurally characterized in their solution state, the few studies of peptides in their receptor-bound state suggest that these peptides interact with a shared set of residues and undergo significant conformational changes. For the purpose of understanding binding dynamics and the development of peptidomimetic drug compounds, further studies should investigate the peptide ligands that are complexed to their cognate receptor.

High glucose upregulates PAR-1 in SH-SY5Y cells via deficiency of miR-20a and miR-190a

Thrombin activity enhancement and its receptor protease-activated receptor 1 (PAR-1) activation play vital roles in neurologic deficits in the central nervous system. Our recent study showed that PAR-1 upregulation stimulated by chronic high glucose (HG) caused central neuron injury through neuroinflammation; however, the molecular mechanisms are far from clear. In the present study, we found that HG resulted in neuronal injury of SH-SY5Y cells as evidenced by decreased cell viability and increased lactate dehydrogenase release and elevated the mRNA level of PAR-1. Moreover, we predicted and determined several potential microRNAs (miRs) combining with the 3'-UTR of PAR-1 mRNA, finding that miR-20a-5p, miR-93-5p, and miR-190a-5p were significantly decreased in HG-cultured SH-SY5Y cells compared with control. Further, SH-SY5Y cells stably transfected with miR-20a-5p or miR-190a-5p mimic were established, and overexpression efficiency were confirmed. It was found that miR-20a-5p or miR-190a-5p overexpression markedly decreased PAR-1 mRNA level and protein expression in SH-SY5Y cells cultured with HG and normal glucose, indicating that miR-20a or miR-19a deficiency contributed to HG-induced PAR-1 upregulation. Together, our findings demonstrated that PAR-1 upregulation mediated HG-induced neuronal damage in central neurons, which was achieved through miR-20a or miR-190a deficiency.

Direct evidence of edge-to-face CH/π interaction for PAR-1 thrombin receptor activation

Heptapeptide SFLLRNP is a receptor-tethered ligand of protease-activated receptor 1 (PAR-1), and its Phe at position 2 is essential for the aggregation of human platelets. To validate the structural elements of the Phe-phenyl group in receptor activation, we have synthesized a complete set of S/Phe/LLRNP peptides comprising different series of fluorophenylalanine isomers (F_n)Phe, where n = 1, 2, 3, and 5. Phe-2-phenyl was strongly suggested to be involved in the edge-to-face CH/π interaction with the receptor aromatic group. In the present study, to prove this receptor interaction definitively, we synthesized another series of peptide analogs containing (F₄)Phe-isomers, with the phenyl group of each isomer possessing only one hydrogen atom at the ortho, meta, or para position. When the peptides were assayed for their platelet aggregation activity, S/(2,3,4,6-F₄)Phe/LLRNP and S/(2,3,4,5-F₄)Phe/LLRNP exhibited noticeable activity (34% and 6% intensities of the native peptide, respectively), whereas S/(2,3,5,6-F₄)Phe/LLRNP was completely inactive. The results indicated that, at the ortho and meta positions but not at the para position, benzene-hydrogen atoms are required for the CH/π interaction to activate the receptor. The results provided a decisive evidence of the molecular recognition property of Phe, the phenyl benzene-hydrogen atom of which participates directly in the interaction with the receptor aromatic π plane.

The Evolving Concept of Neuro-Thromboinflammation for Neurodegenerative Disorders and Neurotrauma: A Rationale for PAR1-Targeting Therapies

Interest in the role of coagulation and fibrinolysis in the nervous system was active in several laboratories dating back before cloning of the functional thrombin receptor in 1991. As one of those, our attention was initially on thrombin and plasminogen activators in synapse formation and elimination in the neuromuscular system, with orientation towards diseases such as amyotrophic lateral sclerosis (ALS) and how clotting and fibrinolytic pathways fit into its pathogenesis. This perspective is on neuro-thromboinflammation, emphasizing this emerging concept from studies and reports over more than three decades. It underscores how it may lead to novel therapeutic approaches to treat the ravages of neurotrauma and neurodegenerative diseases, with a focus on PAR1, ALS, and parmodulins.

Protease-Activated Receptor-1 Antagonist Protects Against Lung Ischemia/Reperfusion Injury

Protease-activated receptor (PAR)-1 is a thrombin-activated receptor that plays an essential role in ischemia/reperfusion (IR)-induced acute inflammation. PAR-1 antagonists have been shown to alleviate injuries in various IR models. However, the effect of PAR-1 antagonists on IR-induced acute lung injury (ALI) has not yet been elucidated. This study aimed to investigate whether PAR-1 inhibition could attenuate lung IR injury. Lung IR was induced in an isolated perfused rat lung model. Male rats were treated with the specific PAR-1 antagonist SCH530348 (vorapaxar) or vehicle, followed by ischemia for 40 min and reperfusion for 60 min. To examine the role of PAR-1 and the mechanism of SCH530348 in lung IR injury, western blotting and immunohistochemical analysis of lung tissue were performed. In vitro, mouse lung epithelial cells (MLE-12) were treated with SCH530348 or vehicle and subjected to hypoxia-reoxygenation (HR). We found that SCH530348 decreased lung edema and neutrophil infiltration, attenuated thrombin production, reduced inflammatory factors, including cytokine-induced neutrophil chemoattractant-1, interleukin-6 and tumor necrosis factor-α, mitigated lung cell apoptosis, and downregulated the phosphoinositide 3-kinase (PI3K), nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) pathways in IR-injured lungs. In addition, SCH530348 prevented HR-induced NF-κB activation and inflammatory chemokine production in MLE12 cells. Our results demonstrate that SCH530348 exerts protective effects by blocking PAR-1 expression and modulating the downstream PI3K, NF-κB and MAPK pathways. These findings indicate that the PAR-1 antagonist protects against IR-induced ALI and is a potential therapeutic candidate for lung protection following IR injury.

The Antagonist pGlu-βGlu-Pro-NH2 Binds to an Allosteric Site of the Thyrotropin-Releasing Hormone Receptor

After we identified pGlu-βGlu-Pro-NH2 as the first functional antagonist of the cholinergic central actions of the thyrotropin-releasing hormone (TRH, pGlu-His-Pro-NH2), we became interested in finding the receptor-associated mechanism responsible for this antagonism. By utilizing a human TRH receptor (hTRH-R) homology model, we first refined the active binding site within the transmembrane bundle of this receptor to enhance TRH's binding affinity. However, this binding site did not accommodate the TRH antagonist. This directed us to consider a potential allosteric binding site in the extracellular domain (ECD). Searches for ECD binding pockets prompted the remodeling of the extracellular loops and the N-terminus. We found that different trajectories of ECDs produced novel binding cavities that were then systematically probed with TRH, as well as its antagonist. This led us to establish not only a surface-recognition binding site for TRH, but also an allosteric site that exhibited a selective and high-affinity binding for pGlu-βGlu-Pro-NH2. The allosteric binding of this TRH antagonist is more robust than TRH's binding to its own active site. The findings reported here may shed light on the mechanisms and the multimodal roles by which the ECD of a TRH receptor is involved in agonist and/or antagonist actions.

Switching Lysophosphatidylserine G Protein-Coupled Receptor Agonists to Antagonists by Acylation of the Hydrophilic Serine Amine

Three human G protein-coupled receptors (GPCRs)-GPR34/LPS₁, P2Y10/LPS₂, and GPR174/LPS₃-are activated specifically by lysophosphatidylserine (LysoPS), an endogenous hydrolysis product of a cell membrane component, phosphatidylserine (PS). LysoPS consists of l-serine, glycerol, and fatty acid moieties connected by phosphodiester and ester linkages. We previously generated potent and selective GPCR agonists by modification of the three modules and the ester linkage. Here, we show that a novel modification of the hydrophilic serine moiety, that is, N-acylations of the serine amine, converted a GPR174 agonist to potent GPR174 antagonists. Structural exploration of the amide functionality provided access to a range of activities from agonist to partial agonist to antagonist. The present study would provide a new strategy for the development of lysophospholipid receptor antagonists.

Uncovering Membrane-Bound Models of Coagulation Factors by Combined Experimental and Computational Approaches

In the life sciences, including hemostasis and thrombosis, methods of structural biology have become indispensable tools for shedding light on underlying mechanisms that govern complex biological processes. Advancements of the relatively young field of computational biology have matured to a point where it is increasingly recognized as trustworthy and useful, in part due to their high space–time resolution that is unparalleled by most experimental techniques to date. In concert with biochemical and biophysical approaches, computational studies have therefore proven time and again in recent years to be key assets in building or suggesting structural models for membrane-bound forms of coagulation factors and their supramolecular complexes on membrane surfaces where they are activated. Such endeavors and the proposed models arising from them are of fundamental importance in describing and understanding the molecular basis of hemostasis under both health and disease conditions. We summarize the body of work done in this important area of research to drive forward both experimental and computational studies toward new discoveries and potential future therapeutic strategies.

Human GPR17 missense variants identified in metabolic disease patients have distinct downstream signaling profiles

GPR17 is a G-protein-coupled receptor (GPCR) implicated in the regulation of glucose metabolism and energy homeostasis. Such evidence is primarily drawn from mouse knockout studies and suggests GPR17 as a potential novel therapeutic target for the treatment of metabolic diseases. However, links between human GPR17 genetic variants, downstream cellular signaling, and metabolic diseases have yet to be reported. Here, we analyzed GPR17 coding sequences from control and disease cohorts consisting of individuals with adverse clinical metabolic deficits including severe insulin resistance, hypercholesterolemia, and obesity. We identified 18 nonsynonymous GPR17 variants, including eight variants that were exclusive to the disease cohort. We characterized the protein expression levels, membrane localization, and downstream signaling profiles of nine GPR17 variants (F43L, V96M, V103M, D105N, A131T, G136S, R248Q, R301H, and G354V). These nine GPR17 variants had similar protein expression and subcellular localization as wild-type GPR17; however, they showed diverse downstream signaling profiles. GPR17-G136S lost the capacity for agonist-mediated cAMP, Ca²⁺, and β-arrestin signaling. GPR17-V96M retained cAMP inhibition similar to GPR17-WT, but showed impaired Ca²⁺ and β-arrestin signaling. GPR17-D105N displayed impaired cAMP and Ca²⁺ signaling, but unaffected agonist-stimulated β-arrestin recruitment. The identification and functional profiling of naturally occurring human GPR17 variants from individuals with metabolic diseases revealed receptor variants with diverse signaling profiles, including differential signaling perturbations that resulted in GPCR signaling bias. Our findings provide a framework for structure–function relationship studies of GPR17 signaling and metabolic disease.

Bias-inducing allosteric binding site in mu-opioid receptor signaling

Abstract

G-protein-biased agonism of the mu-opioid receptor (μ-OR) is emerging as a promising strategy in analgesia. A deep understanding of how biased agonists modulate and differentiate G-protein-coupled receptors (GPCR) signaling pathways and how this is transferred into the cell are open questions. Here, using extensive all-atom molecular dynamics simulations, we analyzed the binding recognition process and signaling effects of three prototype μ-OR agonists. Our suggested structural mechanism of biased signaling in μ-OR involves an allosteric sodium ion site, water networks, conformational rearrangements in conserved motifs and collective motions of loops and transmembrane helices. These analyses led us to highlight the relevance of a bias-inducing allosteric binding site in the understanding of μ-OR’s G-protein-biased signaling. These results also suggest a competitive equilibrium between the agonists and the allosteric sodium ion, where the bias-inducing allosteric binding site can be modulated by this ion or an agonist such as herkinorin. Notably, herkinorin arises as the archetype modulator of μ-OR and its interactive pattern could be used for screening efforts via protein–ligand interaction fingerprint (PLIF) studies.

Article highlights

Correlated Motions of Conserved Polar Motifs Lay out a Plausible Mechanism of G Protein-Coupled Receptor Activation

Recent advancements in the field of experimental structural biology have provided high-resolution structures of active and inactive state G protein-coupled receptors (GPCRs), a highly important pharmaceutical target family, but the process of transition between these states is poorly understood. According to the current theory, GPCRs exist in structurally distinct, dynamically interconverting functional states of which populations are shifted upon binding of ligands and intracellular signaling proteins. However, explanation of the activation mechanism, on an entirely structural basis, gets complicated when multiple activation pathways and active receptor states are considered. Our unbiased, atomistic molecular dynamics simulations of the μ opioid receptor (MOP) revealed that transmission of external stimulus to the intracellular surface of the receptor is accompanied by subtle, concerted movements of highly conserved polar amino acid side chains along the 7th transmembrane helix. This may entail the rearrangement of polar species and the shift of macroscopic polarization in the transmembrane domain, triggered by agonist binding. Based on our observations and numerous independent indications, we suggest amending the widely accepted theory that the initiation event of GPCR activation is the shift of macroscopic polarization between the ortho- and allosteric binding pockets and the intracellular G protein-binding interface.

Structure-Activity Relationship Studies on Oxazolo[3,4-a]pyrazine Derivatives Leading to the Discovery of a Novel Neuropeptide S Receptor Antagonist with Potent In Vivo Activity

Neuropeptide S modulates important neurobiological functions including locomotion, anxiety, and drug abuse through interaction with its G protein-coupled receptor known as neuropeptide S receptor (NPSR). NPSR antagonists are potentially useful for the treatment of substance abuse disorders against which there is an urgent need for new effective therapeutic approaches. Potent NPSR antagonists in vitro have been discovered which, however, require further optimization of their in vivo pharmacological profile. This work describes a new series of NPSR antagonists of the oxazolo[3,4-a]pyrazine class. The guanidine derivative 16 exhibited nanomolar activity in vitro and 5-fold improved potency in vivo compared to SHA-68, a reference pharmacological tool in this field. Compound 16 can be considered a new tool for research studies on the translational potential of the NPSergic system. An in-depth molecular modeling investigation was also performed to gain new insights into the observed structure-activity relationships and provide an updated model of ligand/NPSR interactions.

Site-specific epitope insertion into recombinant proteins using the MAP tag system

The MAP tag system comprises a 14-residue peptide derived from mouse podoplanin and its high-affinity monoclonal antibody PMab-1. We determined the crystal structure of PMab-1 complexed with the MAP tag peptide and found that the recognition required only the N-terminal 8 residues of MAP tag sequence, enabling the shortening of the tag length without losing the affinity for PMab-1. Furthermore, the structure illustrated that the MAP tag adopts a U-shaped conformation when bound by PMab-1, suggesting that loop-inserted MAP tag would assume conformation compatible with the PMab-1 binding. We inserted the 8-residue MAP tag into multiple loop regions in various proteins including fibronectin type III domain and G-protein-coupled receptors and tested if they maintain PMab-1 reactivity. Despite the conformational restraints forced by the insertion position, all MAP-inserted mutants were expressed well in mammalian cells at levels comparable to the non-tagged proteins. Furthermore, the binding by PMab-1 was fully maintained even for the mutant where MAP tag was inserted at a structurally restricted β-hairpin, indicating that the MAP tag system has unique feature that allows placement in the middle of protein domain at desired locations. Our results indicate the versatile utility of the MAP tag system in 'site-specific epitope insertion' application.

Doxycycline Inhibits Cancer Stem Cell-Like Properties via PAR1/FAK/PI3K/AKT Pathway in Pancreatic Cancer

Pancreatic cancer stem cells (CSCs) play an important role in the promotion of invasion and metastasis of pancreatic cancer. Protease activation receptor 1 (PAR1) is closely related to malignant progression of tumors, however, its effects on pancreatic cancer stem cell-like (CSC-like) properties formation have not been reported. In this work, the effects of PAR1 on pancreatic cancer stem cell-like (CSC-like) properties formation were studied. PAR1 overexpression can induce CSC-like properties in Aspc-1 cells, whereas interference of PAR1 in Panc-1 cells showed the contrary results. Data on patients with pancreatic cancer obtained from TCGA showed that high PAR1 expression and focal adhesion kinase (FAK) protein considerably affect the prognosis of patients. Further experiments showed that PAR1 could regulate FAK, PI3K, and AKT phosphorylation and the epithelial-mesenchymal transformation (EMT) in Aspc-1 and Panc-1 cells. Doxycycline, as a PAR1 inhibitor, could effectively inhibit the CSC-like properties of pancreatic cancer cells and the FAK/PI3K/AKT pathway activation. Doxycycline inhibits the growth of pancreatic cancer and enhances the treatment effect of 5-fluorouracil (5-FU) in Panc-1 xenograft mouse model. In conclusion, PAR1 promotes the CSC-like properties and EMT of pancreatic cancer cells via the FAK/PI3K/AKT pathway. Doxycycline inhibits the pancreatic cancer through the PAR1/FAK/PI3K/AKT pathway and enhances the therapeutic effect of 5-FU.