Saturable Binding Research Articles

Fluorescent H2 Receptor Squaramide-Type Antagonists: Synthesis, Characterization, and Applications.

Fluorescence labeled ligands have been gaining importance as molecular tools, enabling receptor-ligand-binding studies by various fluorescence-based techniques. Aiming at red-emitting fluorescent ligands for the hH2R, a series of squaramides labeled with pyridinium or cyanine fluorophores (19-27) was synthesized and characterized. The highest hH2R affinities in radioligand competition binding assays were obtained in the case of pyridinium labeled antagonists 19-21 (pK i: 7.71-7.76) and cyanine labeled antagonists 23 and 25 (pK i: 7.67, 7.11). These fluorescent ligands proved to be useful tools for binding studies (saturation and competition binding as well as kinetic experiments), using confocal microscopy, flow cytometry, and high content imaging. Saturation binding experiments revealed pK d values comparable to the pK i values. The fluorescent probes 21, 23, and 25 could be used to localize H2 receptors in HEK cells and to determine the binding affinities of unlabeled compounds.

Incorporating nonlinear kinetics to improve predictive performance of population pharmacokinetic models for ciclosporin in adult renal transplant recipients: A comparison of modelling strategies

BackgroundCiclosporin has been shown to follow nonlinear pharmacokinetics (PK) in renal transplant recipients who received ciclosporin (NeoralⓇ, Novartis)-based triple immunosuppressive therapy. Some of these nonlinear properties have not been fully considered in population PK (popPK) analysis. Therefore, the aim of this study was to determine the potential influence of nonlinearity and the functional forms of covariates on model predictability as well as to analyse multiple nonlinear factors in the in vivo process. MethodsA total of 2969 ciclosporin whole-blood measurements, including 1328 pre-dose and 1641 2-h post-dose concentrations, were collected from 173 patients who underwent their first renal transplantation. Four popPK models based on different modelling strategies were developed to investigate the discrepancy between empirical and theory-based, linear and nonlinear compartmental kinetic models and empirical formulae on model predictability. Prediction and simulation-based diagnostics (prediction-corrected visual predictive checks) were performed to determine the stability and predictive performance of these four models. ResultsModel predictability improved when nonlinearity was considered. The theory-based nonlinear model which incorporated nonlinear property based on known theoretical relationships performed better than the other two compartmental models. The nonlinear Michaelis-Menten model showed a remarkable improvement in predictive performance compared to the other three compartmental models. The saturated binding of ciclosporin to erythrocytes, auto-inhibition induced by the inhibitory effects of ciclosporin on cytochrome P450 3A4/P-glycoprotein may have contributed to the nonlinearity. Ciclosporin-prednisolone drug interaction should be given serious consideration in clinical settings. ConclusionsIncorporation of nonlinear properties is likely to be a promising approach for improving ciclosporin model predictability. Theory-based modelling is helpful to improve model predictability. However, ciclosporin nonlinear kinetics resources need further investigation.

18F-SMBT-1: A Selective and Reversible PET Tracer for Monoamine Oxidase-B Imaging.

Reactive astrocytes play a key role in the pathogenesis of various neurodegenerative diseases. Monoamine oxidase-B (MAO-B) is one of the promising targets for the imaging of astrogliosis in the human brain. A novel selective and reversible MAO-B tracer, (S)-(2-methylpyrid-5-yl)-6-[(3-18F-fluoro-2-hydroxy)propoxy]quinoline (18F-SMBT-1), was successfully developed via lead optimization from the first-generation tau PET tracer 18F-THK-5351. Methods: SMBT-1 was radiolabeled with 18F using the corresponding precursor. The binding affinity of radiolabeled compounds to MAO-B was assessed using saturation and competitive binding assays. The binding selectivity of 18F-SMBT-1 to MAO-B was evaluated by autoradiography of frozen human brain tissues. The pharmacokinetics and metabolism were assessed in normal mice after intravenous administration of 18F-SMBT-1. A 14-d toxicity study after the intravenous administration of 18F-SMBT-1 was performed using rats and mice. Results: In vitro binding assays demonstrated a high binding affinity of 18F-SMBT-1 to MAO-B (dissociation constant, 3.7 nM). In contrast, it showed low binding affinity to MAO-A and protein aggregates such as amyloid-β and tau fibrils. Autoradiographic analysis showed higher amounts of 18F-SMBT-1 binding in the Alzheimer disease brain sections than in the control brain sections. 18F-SMBT-1 binding was completely displaced with the reversible MAO-B inhibitor lazabemide, demonstrating the high selectivity of 18F-SMBT-1 for MAO-B. Furthermore, 18F-SMBT-1 showed a high uptake by brain, rapid washout, and no radiolabeled metabolites in the brain of normal mice. 18F-SMBT-1 showed no significant binding to various receptors, ion channels, or transporters, and no toxic effects related to its administration were observed in mice and rats. Conclusion:18F-SMBT-1 is a promising and selective MAO-B PET tracer candidate, which would be useful for quantitative monitoring of astrogliosis in the human brain.

Binding affinities of oxytocin, vasopressin and Manning compound at oxytocin and V1a receptors in male Syrian hamster brains.

Oxytocin (OT) and arginine vasopressin (AVP), as well as synthetic ligands targeting their receptors (OTR, V1aR), are used in a wide variety of research contexts, although their pharmacological properties are determined in only a few species. Syrian hamsters (Mesocricetus auratus) have a long history of use as a behavioural and biomedical model for the study of OT and AVP and, more recently, hamsters have been used to investigate behavioural consequences of OT-mediated activation of V1aR. We aimed to determine the binding affinities of OT, AVP and the selective V1aR antagonist, Manning compound, for OTR and V1aR in hamster brains. We performed saturation binding assays to determine the Kd values for the selective OTR and V1aR radioligands, [125 I]ornithine vasotocin analogue and [125 I]linear vasopressin antagonist. We then performed competition binding assays to determine Ki values for OT, AVP and Manning compound at both the OTR and V1aR. We found that OT and AVP each had the highest affinity for their canonical receptors (OT-OTR Ki=4.28 [95% confidence interval (CI)=2.9-6.3]nmolL-1 ; AVP-V1ar Ki=4.70 [95% CI=1.5-14.1]nmolL-1 ) and had the lowest affinity for their non-canonical ligands (OT-V1aR=495.2 [95% CI=198.5-1276]nmolL-1 ; AVP-OTR Ki=36.1 [95% CI=12.4-97.0]nmolL-1 ). Manning compound had the highest affinity for the V1aR (MC-V1aR Ki=6.87 [95% CI=4.0-11.9]nmolL-1 ; MC-OTR Ki=213.8 [95% CI=117.3-392.7]nmolL-1 ), although Manning compound was not as selective for the V1aR in hamsters as has been reported for the receptor in rats. When comparing these data with previously published work, we found that the promiscuity of the V1aR in hamsters with respect to OT and AVP binding is more similar to the promiscuity of the human V1aR than to the rat V1aR receptor. Moreover, the selectivity of OT at hamster receptors is more similar to the selectivity of OT at human receptors than the selectivity of OT at rat receptors. These data highlight the importance of determining the pharmacological properties of behaviourally relevant compounds in diverse model species.

Evaluating the Number of Ligand Binding Sites on Protein from Tryptophan Fluorescence Quenching under Typical Experimental Conditions

Fluorescence quenching technique is extensively applied for the characterization of intermolecular interactions in the solution that is one of the major problems in biochemistry and pharmacology. Using the Stern-Volmer equation, one can obtain a measure of binding affinity calculated under the assumption of static quenching, while the possibility to determine other binding parameters is under discussion. Several mathematical approaches are known, which allow determining the number of binding sites from fluorescence quenching curves. However, they usually require high concentrations of the ligand to obtain saturating binding curves that could be complicated in a number of experimental conditions. In this paper, we present a simple algorithm, which allows to prove that the number of binding sites in the system is equal to one or not and to verify that the quantum yield of the complex is zero. The advantage of the suggested approach is its applicability at typical conditions used in tryptophan fluorescence quenching experiments for the protein-ligand binding. A web interface for automated processing of fluorescence quenching experiments based on the suggested approach is presented.

Development and validation of a mass spectrometry binding assay for mGlu5 receptor.

Mass spectrometry (MS) binding assays are a label-free alternative to radioligand or fluorescence binding assays, so the readout is based on direct mass spectrometric detection of the test ligand. The study presented here describes the development and validation of a highly sensitive, rapid, and robust MS binding assay for the quantification of the binding of the metabotropic glutamate 5 (mGlu5) negative allosteric modulator (NAM), MPEP (2-methyl-6-phenylethynylpyridine) at the mGlu5 allosteric binding site. The LC-ESI-MS/MS (liquid chromatography-electrospray ionization-tandem mass spectrometric) analytical method was established and validated with a deuterated analogue of MPEP as an internal standard. The developed MS binding assay described here allowed for the determination of MS binding affinity estimates that were in agreement with affinity estimates obtained from a tritiated MPEP radioligand saturation binding assay, indicating the suitability of this methodology for determining affinity estimates for compounds that target mGlu5 allosteric binding sites. Graphical abstract.

Pharmacological Properties of δ-Opioid Receptor-Mediated Behaviors: Agonist Efficacy and Receptor Reserve.

δ-Opioid receptor (δ-receptor) agonists produce antihyperalgesia, antidepressant-like effects, and convulsions in animals. However, the role of agonist efficacy in generating different δ-receptor-mediated behaviors has not been thoroughly investigated. To this end, efficacy requirements for δ-receptor-mediated antihyperalgesia, antidepressant-like effects, and convulsions were evaluated by comparing the effects of the partial agonist BU48 and the full agonist SNC80 and changes in the potency of SNC80 after δ-receptor elimination. Antihyperalgesia was measured in a nitroglycerin-induced thermal hyperalgesia assay. An antidepressant-like effect was evaluated in the forced swim test. Mice were observed for convulsions after treatment with SNC80 or the δ-opioid receptor partial agonist BU48. Ligand-induced G protein activation was measured by [35S]guanosine 5'-O-[γ-thio]triphosphate binding in mouse forebrain tissue, and δ-receptor number was measured by [3H]D-Pen2,5-enkephalin saturation binding. BU48 produced antidepressant-like effects and convulsions but antagonized SNC80-induced antihyperalgesia and G protein activation. The potency of SNC80 was shifted to the right in δ-receptor heterozygous knockout mice and naltrindole-5'-isothiocyanate-treated mice, and the magnitude of potency shift differed across assays, with the largest shift occurring in the thermal hyperalgesia assay, followed by the forced swim test and then convulsion observation. Naltrindole antagonized these SNC80-induced behaviors with similar potencies, suggesting that these effects are mediated by the same type of δ-receptor. These data suggest that δ-receptor-mediated behaviors display a rank order of efficacy requirement, with antihyperalgesia having the highest requirement, followed by antidepressant-like effects and then convulsions. These findings further our understanding of the pharmacological mechanisms mediating the in vivo effects of δ-opioid receptor agonists. SIGNIFICANCE STATEMENT: δ-Opioid receptor (δ-receptor) agonists produce antihyperalgesia, antidepressant-like effects, and convulsions in animal models. This study evaluates pharmacological properties, specifically the role of agonist efficacy and receptor reserve, underlying these δ-receptor-mediated behaviors. These data suggest that δ-receptor-mediated behaviors display a rank order of efficacy requirement, with antihyperalgesia having the highest requirement, followed by antidepressant-like effects and then convulsions.

Long-term systemic administration of kynurenic acid brain region specifically elevates the abundance of functional CB1 receptors in rats

Kynurenic acid (KYNA) is one of the most significant metabolite of the kynurenine pathway both in terms of functional and potential therapeutic value. It is an N-methyl-D-aspartate (NMDA) receptor antagonist, but it can also activate the G-protein coupled receptor 35 (GPR35), which shares several structural and functional properties with cannabinoid receptors. Previously our group demonstrated that systemic chronic KYNA treatment altered opioid receptor G-protein activity. Opioid receptors also overlap in many features with cannabinoid receptors. Thus, our aim was to examine the direct in vitro and systemic, chronic in vivo effect of KYNA on type 1 cannabinoid receptor (CB1R) binding and G-protein activity.Based on competition and [35S]GTPγS G-protein binding assays in rat brain, KYNA alone did not show significant binding towards the CB1R, nor did it alter CB1R ligand binding and agonist activity in vitro. When rats were chronically treated with KYNA (single daily, i.p., 128 mg/kg for 9 days), the KYNA plasma and cerebrospinal fluid levels significantly increased compared to vehicle treated group. Furthermore, in G-protein binding assays, in the whole brain the amount of G-proteins in basal and in maximum activity coupled to the CB1R also increased due to the treatment. At the same time, the overall stimulatory properties of the receptor remained unaltered in vehicle and KYNA treated samples. Similar observations were made in rat hippocampus, but not in the cortex and brainstem. In saturation binding assays the density of CB1Rs in rat whole brain and hippocampus were also significantly enhanced after the same treatment, without significantly affecting ligand binding affinity.Thus, KYNA indirectly and brain region specifically increases the abundance of functional CB1Rs, without modifying the overall binding and activity of the receptor. Supposedly, this can be a compensatory mechanism on the part of the endocannabinoid system induced by the long-term KYNA exposure.

Copper complex formed with pyridine rings grafted on cellulose nanofibrous membranes for highly efficient lysozyme adsorption

The development of separation and purification materials with high adsorption performance and large processing throughput is of great importance. Regenerated cellulose nanofibers membranes (RC-NFM) with average fiber diameter 300 nm were fabricated and functionalized via grafting 4-vinyl pyridine (4-VP) on the cellulose (RC-VP) using a chemically immobilized photo-initiator. The pyridines in RC-VP form complex nanofibrous membranes with Cu(II) to form RC-VP-Cu(II) which enhances selectivity for lysozyme adsorption. The RC-VP-Cu(II) NFM showed superb static adsorption capacity of 800 mg·g−1 and a high saturated dynamic protein binding capacity of 700 mg·g−1 toward lysozyme. Besides, benefiting from its stable physical and chemical structures, after 5 cycles of reuses, RC-VP-Cu(II) still showed promising efficiency for lysozyme separation from egg-white samples with lysozyme activity 80% of a synthetic one. The successful synthesis of such intriguing and economic RC-VP-Cu(II) NFM may serve as a promising candidate for the next generation of rapid, massive, and cost-effective separation and purification of proteins.

EFEKTIFITAS EKSTRAK DAUN KELOR (Moringa oleifera lam) DALAM MEMPERBAIKI PROFIL SERUM IRON, SATURASI TRANSFERIN, DAN TOTAL IRON BINDING CAPACITY TIKUS PUTIH JANTAN DIET RENDAH ZAT BESI

Background : Iron deficinecy can cause anemia which affect health and work productivity. Moringa oleifera leaves contain a lot of iron and vitamin C, are thought to increase serum iron levels, transferin saturation, and improve total iron binding capacity.Objectives : To determine the effectiveness of Moringa oleifera lam. leaf extract on serum iron levels, transferin saturation, and total iron binding capacity in white rats (Rattus novergicus strain wistar) given a diet low in iron (Fe).Materials and methods : true experimental research using post test only control group design. The object of theis study was thirty male white mice (Rattus novergicus strain wistar) who were given a low iron diet. The study was divided into negative control group, positive control, treatment groups with a dose of Moringa leaf extract 400 mg/kg BW, 800 mg/kgBW, 1,600 mg/kg/BW, an the ferro fumaras control group (FF) 175 mg/200 BW.Results and discussion : Multivariate manova serum iron 0.001 (p<0.05), TBC 0.19 (P>0.05), and transferin saturation 0.001(p<0.05). In the post Hoc Tukey the mean serum iron and transferin saturation appeared to differ significant in the negative control group with all the other treatment groups, but did not show a significant diffrence beetwen the positive control group, FF Group, and the treatment groups.Conclusion : The adminstration of Moringa oleifera leaf extractwas less significant in improving serum iron levels, transferin saturation, and total iron binding capacity of male white mice induced by a low iron diet.

Adenosinergic System Involvement in Ischemic Stroke Patients' Lymphocytes.

Adenosine modulates many physiological processes through the interaction with adenosine receptors (ARs) named as A1, A2A, A2B, and A3ARs. During ischemic stroke, adenosine mediates neuroprotective and anti-inflammatory effects through ARs activation. One of the dominant pathways generating extracellular adenosine involves the dephosphorylation of ATP by ecto-nucleotidases CD39 and CD73, which efficiently hydrolyze extracellular ATP to adenosine. The aim of the study is to assess the presence of ARs in lymphocytes from ischemic stroke patients compared to healthy subjects and to analyze changes in CD39 and CD73 expression in CD4+ and CD8+ lymphocytes. Saturation binding experiments revealed that A2AARs affinity and density were significantly increased in ischemic stroke patients whilst no differences were found in A1, A2B, and A3ARs. These results were also confirmed in reverse transcription (RT)-polymerase chain reaction (PCR) assays where A2AAR mRNA levels of ischemic stroke patients were higher than in control subjects. In flow cytometry experiments, the percentage of CD73+ cells was significantly decreased in lymphocytes and in T-lymphocyte subclasses CD4+ and CD8+ obtained from ischemic stroke patients in comparison with healthy individuals. These data corroborate the importance of the adenosinergic system in ischemic stroke and could open the way to more targeted therapeutic approaches and biomarker development for ischemic stroke.

Selective molecularly imprinted polymer nanofiber sorbent for the extraction of bisphenol A in a water sample

AbstractNovel molecularly imprinted polymer nanofibers (MIP‐NFs) were prepared for the adsorption of bisphenol A (BPA) in a water sample using the sol–gel process and the electrospinning technique. The effects of a number of synthesis parameters on the adsorption efficiency were investigated. The successful removal of BPA from MIP‐NFs was studied using UV–visible spectroscopy. The prepared MIP‐NFs were characterized by Fourier transform infrared, field emission SEM, TEM and energy dispersive X‐ray analysis. The results showed that the required molar ratio of 3‐aminopropyltriethoxysilane (APTES) to BPA was 15:1, which indicates a good performance in the rebinding test. Likewise, the molar ratio of APTES:acid:water was 1:2:9. The nylon 6 polymer solution, with a concentration of 12 wt%, showed a maximum adsorption capacity for BPA due to a decrease in the nanofiber diameter and an increase in the accessible sites. Furthermore, the maximum adsorption capacity of BPA was achieved at pH 7. Concerning the binding of BPA on MIP‐NFs, the experimental data matched well with the pseudo‐second‐order kinetics data and the Sips isotherm model. The saturated binding capacity for MIP‐NFs was predicted to be 115.1 mg g−1, which was more than twice as high as that for non‐imprinted polymer nanofibers (46.82 mg g−1). The results obtained in this study confirmed that the prepared MIP‐NFs showed considerable binding specificity for BPA in comparison with similar structural compounds such as phenol, naphthol and Naphthol AS, in aqueous solution. The binding capacity of MIP‐NFs remained almost constant after five cycles of reuse. The real sample analysis indicated that MIP‐NFs could be utilized as a useful sorbent material for the extraction of BPA from a water sample.

Physiologically Based Pharmacokinetic Model of the DPP-4 Inhibitor Linagliptin to Describe its Nonlinear Pharmacokinetics in Humans

Linagliptin, a dipeptidyl peptidase (DPP)-4 inhibitor, for type 2 diabetes exhibits nonlinear plasma protein binding in the therapeutic concentration range due to its high affinity binding to the pharmacological target DPP-4, and its pharmacokinetics both in plasma and urine is also nonlinear. The purpose of the present study was to explain the nonlinear pharmacokinetic profiles using a physiologically based pharmacokinetic (PBPK) model with saturable binding of linagliptin to soluble and membrane-bound DPP-4 in blood and organs including kidneys. The model was first fitted to previously reported full-scale plasma concentrations and urinary excretion data at 4 intravenous (iv) dose levels. Additional fitting to the data from 4 oral (po) dose levels was then performed to yield the final iv-po based model including gastrointestinal absorption-associated parameters. Data from [14C]linagliptin mass balance study were also used for optimizing parameters related to enterohepatic circulation. The PBPK model was thus constructed and well describes the nonlinear pharmacokinetic profiles of linagliptin in both plasma and urine, demonstrating that the nonlinear pharmacokinetics are fully explained by its specific binding to target protein. The present study thus introduces the involvement of target-mediated disposition for linagliptin in humans.

Red-Emitting Dibenzodiazepinone Derivatives as Fluorescent Dualsteric Probes for the Muscarinic Acetylcholine M2 Receptor

Fluorescently labeled dibenzodiazepinone-type muscarinic acetylcholine receptor (MR) antagonists, including dimeric ligands, were prepared using red-emitting cyanine dyes. Probes containing a fluorophore with negative charge showed high M2R affinities (pKi (radioligand competition binding): 9.10-9.59). Binding studies at M1 and M3-M5 receptors indicated a M2R preference. Flow cytometric and high-content imaging saturation and competition binding (M1R, M2R, and M4R) confirmed occupation of the orthosteric site. Confocal microscopy revealed that fluorescence was located mainly at the cell membrane (CHO-hM2R cells). Results from dissociation and saturation binding experiments (M2R) in the presence of allosteric M2R modulators (dissociation: W84, LY2119620, and alcuronium; saturation binding: W84) were consistent with a competitive mode of action between the fluorescent probes and the allosteric ligands. Taken together, these lines of evidence indicate that these ligands are useful fluorescent molecular tools to label the M2R in imaging and binding studies and suggest that they have a dualsteric mode of action.

Tritiated JNJ‐63514230 is a novel GluN2B‐selective radioligand with no affinity to sigma receptors

IntroductionCommonly used GluN2B radioligands exhibit limited selectivity towards GluN2B receptors as they interact with sigma and other off‐target receptors. Here we describe development and characterization of [3H] JNJ‐63514230, a novel radioligand selective for GluN2B‐containing NMDA receptors.MethodsThe selectivity JNJ 63514230 was determined using functional assays and CEREP panel. Saturation binding and competitive radioligand binding experiments were used to characterize [3H]‐JNJ 63514230 properties. We have also tested utility of [3H]‐JNJ 63514230 as a tracer for ex‐vivo autoradiography in rat brain.ResultsWe confirmed that widely used tracers [3H] Ifenprodil and [3H] Ro 25‐6981 have substantial affinity to sigma receptors as measured in radioligand competition experiments (CEREP). In contrast, new tracer [3H] JNJ‐63514230 exhibits no affinity to sigma 1 and sigma 2 receptors in CEREP assays. Saturation binding in rat brain membranes yielded a Kd value of 2.53 nM and Bmax of 2531 fmol/mg. Association constant Kon, dissociation constant Koff, and calculated equilibrium binding constant (Kon/Koff) were 0.0067±0.001 min−1 nM‐1, 0.021±0.0002 min−1, and 3.28±0.61 nM, respectively (average of 3 individual experiments each ± SD). Enhanced selectivity for GluN2B‐containing receptors translates to reduced non‐specific binding and better signal to noise ratio in both in vitro radioligand binding assays and ex vivo autoradiography.ConclusionsWe showed that new radioligand [3H] JNJ 63514230 is superior to previous previously described GluN2B tracers as it permits accurate measurement of affinity to GluN2B‐containing receptors (Ki) without using additional blockers to mask native sigma receptors.Support or Funding InformationAuthors are full time employees of Janssen Research & Development, LLC. The research was funded by the company.

125‐I‐Sarcosine(1), D‐Alanine(8) Angiotensin II as a Biased Radioligand for AT1 Angiotensin II Receptors

The concept of biased agonism of G protein‐coupled receptors arose from studies of the AT1 subtype of angiotensin (Ang) II receptor. A putative antagonist ligand, sarcosine1, isoleucine4, isoleucine8 Ang II (SII) showed negligible ability to activate G protein signaling pathways of the AT1 receptor, but was able to cause AT1 receptor internalization and mitogen activated protein (MAP) kinase activation at micromolar concentrations. Subsequently, a different Ang II congener; sarcosine1, D‐alanine8 Ang II was developed as a potential therapeutic (TRV‐027; TRV120027) for treatment of acute heart failure. While clinical trials did not support a therapeutic benefit of sarcosine1, D‐alanine8 Ang II for treatment of heart failure, it still promises to be a better biased agonist than SII, which acts only at micromolar concentrations. To assess the potential use of sarcosine1, D‐alanine8 Ang II as a radioligand for quantification of Ang II receptor binding, we radiolabeled sarcosine1, D‐alanine8 Ang II with 125iodine and compared its binding to that of 125I‐sarcosine1 isoleucine8 Ang II in rat liver membranes, which express high levels of AT1 receptors and negligible levels of AT2 receptors. At concentrations up to 5.6 nM, 125I‐sarcosine1, D‐alanine8 Ang II showed little evidence of saturable binding to AT1 receptors, in contrast to 125I‐sarcosine1 isoleucine8 Ang II, which showed a KD of 0.6 nM. At 5.6 nM 125I‐sarcosine1 isoleucine8 Ang II binding to AT1 receptors was 8.5 times greater than 125I‐sarcosine1, D‐alanine8 Ang II. To verify that sarcosine1, D‐alanine8 Ang II binds to liver membrane AT1 receptors, we compared the ability of sarcosine1, D‐alanine8 Ang II and Ang II to compete for 125I‐sarcosine1 isoleucine8 Ang II binding. Sarcosine1 isoleucine8 Ang II and Ang II were similar in their ability to compete for AT1 receptor binding: 6.7±0.7 nM and 15.6±0.8 nM and 84.3±1.1 and 86.7±0.3 % of total binding (IC50, n=2±SD), respectively. This suggests that iodination of tyr4 of sarcosine1, D‐alanine8 Ang II alters its ability to bind to AT1 receptors and potentially act as a biased agonist. Continuing studies will examine the ability of higher concentrations of 125/127I‐sarcosine1, D‐alanine8 Ang II to interact with Ang II receptors.Support or Funding InformationNova Southeastern University President’s Faculty Research Development Grant, Cardiovascular Neuroscience Research Fund

A MiniG Protein Recruitment Assay for the Histamine Receptor Family to Functionally Characterize Histamine Receptor Ligands

In addition to the determination of binding affinities, the functional characterization of biologically active compounds is a prerequisite in drug discovery in order to identify lead structures and to optimize potential scaffolds regarding their mode of action and potency. Therefore, our aim was to develop a high‐throughput screening (HTS) compatible assay procedure yielding functional parameters of histamine receptor ligands at a proximal level avoiding signal amplification.For this purpose, we applied the NanoLuc split‐luciferase technology [1] to the histamine receptor subtypes H1, H2, H3 and H4 and the corresponding G protein surrogates miniGq, miniGs and miniGi [2]. The small fragment of the NanoLuc (NlucC) was fused to the C‐terminus of the respective receptor to retain the integrity of the receptors regarding binding affinities and intracellular signalling, whereas the large fragment of the NanoLuc (NlucN) was N‐terminally fused to the miniG proteins (see fig. 1). Upon activation by a ligand the corresponding miniG protein is recruited to the receptor which then leads to the formation of a functional NanoLuc enzyme enabling the registration of a concentration dependent luminescence signal (see fig. 1).Compared to reported data, standard ligands for histamine receptors provide appropriate potencies, intrinsic activities and modes of action.By radioligand saturation binding experiments it could be shown that there was no alteration in the binding affinities of the radioligands due to the minor receptor modification by the C‐terminally fused NlucC. Additionally, this assay principle should be appropriate for HTS assessed by the investigation of the Z′ factor, which was in an excellent range for all histamine receptor subtypes (0.5 < Z′ < 1).From these results we conclude that the application of the presented methodology is an excellent approach to be implemented in routine and detailed functional characterisation of putative histamine receptor ligands synthesized in our group. Moreover, the assay offers an opportunity to draw conclusions on biased signalling of investigated ligands in combination with the results obtained in β‐arrestin recruitment assays [3].Support or Funding InformationThis project is funded by the DFG research training group GRK1910.Schematic illustration of the assay principle.Two complementing NanoLuc fragments fused to the receptor and the mini G protein form a functional NanoLuc upon activation of the GPCR.Figure 1

Investigating the Binding of Albumin and C‐peptide to Red Blood Cells

The pancreatic β‐cells of healthy individuals secrete insulin and C‐peptide, a 31‐amino acid peptide, in a 1:1 mole ratio. However, the β‐cells of people with type 1 diabetes (T1D) are damaged or destroyed. Therefore, exogenous insulin is required for people with T1D to survive. Even with regular insulin treatments, patients develop complications such as retinopathy, neuropathy, and nephropathy. Research from our group demonstrates that C‐peptide increases microvascular blood flow, therefore, it could be a useful tool to decrease these complications due to poor blood flow. However, the unknown C‐peptide receptor and mechanism has been a major roadblock in utilizing C‐peptide as a therapeutic. Utilizing ELISA, our group has demonstrated that approximately 1,800 C‐peptide molecules bind per red blood cell (RBC) in the presence of albumin. Without albumin, there was no detectable C‐peptide binding per RBC. Rather than C‐peptide solely binding to a RBC receptor, we hypothesize that C‐peptide binds to RBCs through an albumin/C‐peptide complex receptor. Bovine serum albumin (BSA) binding per RBC was detectable through an attached gamma decay radiolabel (99mTc). A binding saturation experiment was conducted to examine the specific binding of BSA to RBCs with and without C‐peptide. The specific binding curves revealed that albumin saturates at 14,021 ± 1489 BSA molecules/RBC with a Kd of 1.07 (±0.19) × 10−7 M and a Bmax of 1.94 (±0.06) × 10−8 M, or 13,900 receptor molecules/RBC. Whereas, in the presence of C‐peptide and zinc, albumin saturates at 16,696 ± 1479 BSA molecules/RBC with a Kd of 1.91 (±0.09) × 10−7 M and a Bmax of 2.50 (±0.03) × 10−8 M, or 17,900 receptor molecules/RBC. At saturation, the additional 2,700 BSA molecules binding per RBC in the presence of C‐peptide and zinc indicates that an albumin receptor exists on RBCs as well as a separate albumin/C‐peptide complex receptor.Support or Funding InformationNIH

Hazards of Using Masking Protocols When Performing Ligand Binding Assays: Lessons From the Sigma-1 and Sigma-2 Receptors.

Sigma-1 and sigma-2 receptors are emerging therapeutic targets. Although the molecular identity of the sigma-2 receptor has recently been determined, receptor quantitation has used, and continues to use, the sigma-1 selective agents (+) pentazocine or dextrallorphan to mask the sigma-1 receptor in radioligand binding assays. Here, we have assessed the suitability of currently established saturation and competition binding isotherm assays that are used to quantify parameters of the sigma-2 receptor. We show that whilst the sigma-1 receptor mask (+) pentazocine has low affinity for the sigma-2 receptor (Ki 406 nM), it can effectively compete at this site with [³H] di-O-tolyl guanidine (DTG) at the concentrations frequently used to mask the sigma-1 receptor (100 nM and 1 µM). This competition influences the apparent affinity of DTG and other ligands tested in this system. A more troublesome issue is that DTG can displace (+) pentazocine from the sigma-1 receptor, rendering it partly unmasked. Indeed, commonly used concentrations of (+) pentazocine, 100 nM and 1 µM, allowed 37 and 11% respectively of sigma-1 receptors to be bound by DTG (300 nM), which could result in an overestimation of sigma-2 receptor numbers in assays where sigma-1 receptors are also present. Similarly, modelled data for 1 µM dextrallorphan show that only 71–86% of sigma-1 receptors would be masked in the presence of 300 nM DTG. Therefore, the use of dextrallorphan as a masking agent would also lead to the overestimation of sigma-2 receptors in systems where sigma-1 receptors are present. These data highlight the dangers of using masking agents in radioligand binding studies and we strongly recommend that currently used masking protocols are not used in the study of sigma-2 receptors. In order to overcome these problems, we recommend the use of a cell line apparently devoid of sigma-1 receptors [e.g., MCF7 (ATCC HTB-22)] in the absence of any masking agent when determining the affinity of agents for the sigma-2 receptor. In addition, assessing the relative levels of sigma-1 and sigma-2 receptors can be achieved using [³H] DTG saturation binding followed by two-site analysis of (+) pentazocine competition binding with [³H] DTG.

Primary Preclinical and Clinical Evaluation of 68Ga-DOTA-TMVP1 as a Novel VEGFR-3 PET Imaging Radiotracer in Gynecological Cancer.

Tumor periphery and lymph nodes of tumor-induced lymphangiogenesis often abundantly express VEGFR-3. In our previous study, we identified a 5-amino acid peptide named TMVP1, which binds specifically to VEGFR-3. The objective of this study was to develop a novel 68Ga-labeled TMVP1 for VEGFR-3 PET imaging and to investigate its safety, biodistribution, and tumor-localizing efficacy in xenograft tumor models and a small cohort of patients with recurrent ovarian and cervical cancer. The DOTA-conjugated TMVP1 peptide was labeled with radionuclide 68Ga. SPR and saturation binding assays were used for the receptor-binding studies. Gynecologic xenograft tumors were employed for small-animal PET imaging and biodistribution of 68Ga-DOTA-TMVP1 in vivo. In the clinical study, 5 healthy volunteers and 8 patients with gynecologic cancer underwent whole-body PET/CT after being injected with 68Ga-DOTA-TMVP1. DOTA-TMVP1 was successfully labeled with 68Ga. LECs showed higher binding capacity with 68Ga-DOTA-TMVP1 than LEC(shVEGFR-3) and human umbilical vein endothelial cells. In mice with subcutaneous C33-A and SKOV-3 xenografts, the tracer was rapidly eliminated through the kidney to the bladder, and the small-animal PET/CT helped to clearly visualize the tumors. In patients with recurrent ovarian cancer and cervical cancer, tracer accumulation well above the background level was demonstrated in most identified sites of disease; especially with recurrent endodermal sinus tumors, the diagnostic value of 68Ga-DOTA-TMVP1 was comparable with that of 18F-FDG PET/CT. 68Ga-DOTA-TMVP1 is a potential PET tracer for imaging VEGFR-3 with favorable pharmacokinetics.