Functional screening of G protein-coupled receptors by measuring intracellular calcium with a fluorescence microplate reader

Synthesis, structure-activity relationships and biological evaluation of benzimidazole derived sulfonylurea analogues as a new class of antagonists of P2Y1 receptor

The P2Y receptors are responsible for the regulation of various physiological processes including neurotransmission and inflammatory responses. These receptors are also considered as novel potential therapeutic targets for prevention and treatment of thrombosis, neurological disorders, pain, cardiac diseases and cancer. Previously, number of P2Y receptor antagonists has been investigated but they are less potent and non-selective with poor solubility profile. Herein, we present the synthesis of new class of benzimidazole derived sulfonylureas (1a-y) as potent antagonists of P2Y receptors, with the specific aim to explore selective antagonists of P2Y1 receptors. The efficacy and selectivity of the synthesized derivatives 1) against four P2Y receptors i.e., t-P2Y1, h-P2Y2, h-P2Y4, and r-P2Y6Rs was carried out by calcium mobilization assay. The results revealed that except 1b, 1d, 1l, 1m, 1o, 1u, 1v, 1w, and 1y, rest of the synthesized derivatives exhibited moderate to excellent inhibitory potential against P2Y1 receptors. Among the potent antagonists, derivative 1h depicted the maximum inhibition of P2Y1 receptor in calcium signalling assay, with an IC₅₀ value of 0.19 ± 0.04 µM. The potential of inhibition was validated by computational investigations where bonding and non-bonding interactions between ligand and targeted receptor further strengthen the study. The best identified derivative 1h revealed the same binding mechanism as that of already reported selective antagonist of P2Y1 receptor i.e (1-(2- (2-tert-butyl-phenoxy) pyridin-3-yl)-3-4-(trifluoromethoxy) phenylurea but the newly synthesized derivative exhibited better solubility profile. Hence, this derivative can be used as lead candidate for the synthesis of more potential antagonist with much better solubility profile and medicinal importance.

Synthesis of Sulfonamide Tethered (Hetero)aryl ethylidenes as Potential Inhibitors of P2X Receptors: A Promising Way for the Treatment of Pain and Inflammation

P2X receptors have the ability to regulate various physiological functions like neurotransmission, inflammatory responses, and pain sensation. Such physiological properties make these receptors a new target for the treatment of pain and inflammation. Several antagonists of P2X receptors have been studied for the treatment of neuropathic pain and neurodegenerative disorders but potency and selectivity are the major issues with these known inhibitors. Sulfonamide derivatives were reported to be potent inhibitors of P2X receptors. In this study, sulfonamide carrying precursor hydrazide was synthesized by a facile method that was subsequently condensed with methyl (hetero)arylketones to obtain a series of new (hetero)aryl ethylidenes. These compounds were screened for inhibitory potential against h-P2X2, h-P2X4, h-P2X5, and h-P2X7 receptors to find their potency and selectivity. Computational studies were performed to confirm the mode of inhibition as well as type of interaction between ligand and target site. In calcium signaling experiments, compound 6h was found to be the most potent and selective inhibitor of h-P2X2 and h-P2X7 receptors with IC₅₀ ± standard error of the mean (SEM) values of 0.32 ± 0.01 and 1.10 ± 0.21 μM, respectively. Compounds 6a and 6c exhibited selective inhibition for h-P2X7 receptor, whereas 6e, 7a, and 7b expressed selective inhibitions toward h-P2X2 receptor that were comparable to the positive control suramin and pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS).

Profiling of a suramin-derived compound library at recombinant human P2Y receptors identifies NF272 as a competitive but non-selective P2Y2 receptor antagonist

Extracellular nucleotides mediate multiple physiological effects such as proliferation, differentiation, or induction of apoptosis through G protein-coupled P2Y receptors or P2X ion channels. Evaluation of the complete physiological role of nucleotides has long been hampered by a lack of potent and selective ligands for all P2 subtypes. Meanwhile, for most of the P2 receptors, selective ligands are available, but only a few potent and selective P2Y₂ receptor antagonists are described. This limits the understanding of the role of P2Y₂ receptors. The purpose of this study was to search for P2Y₂ receptor antagonists by a combinatorial screening of a library of around 415 suramin-derived compounds. Calcium fluorescence measurements at P2Y₂ receptors recombinantly expressed in human 1321N1 astrocytoma cells identified NF272 [8-(4-methyl-3-(3-phenoxycarbonylimino-benzamido)benzamido)-naphthalene-1,3,5-trisulfonic acid trisodium salt] as a competitive P2Y₂ receptor antagonist with a K_i of 19 μM which is 14-fold more potent than suramin at this receptor subtype. The SCHILD analysis of competitive inhibition resulted in a pA₂ value of 5.03 ± 0.22 (mean ± SEM) with a slope not significantly different from unity. Among uracil-nucleotide-preferring P2Y receptors, NF272 shows a moderate selectivity over P2Y₄ (3.6-fold) and P2Y₆ (5.7-fold). However, NF272 is equipotent at P2Y₁, and even more potent at P2Y₁₁ and P2Y₁₂ receptors. Up to 250 μM, NF272 showed no cytotoxicity in MTT cell viability assays in 1321N1, HEK293, and OVCAR-3 cells. Further, NF272 was able to inhibit the ATP-induced calcium signal in OVCAR-3 cells demonstrated to express P2Y₂ receptors. In conclusion, NF272 is a competitive but non-selective P2Y₂ receptor antagonist with 14-fold higher potency than suramin lacking cytotoxic effects. Therefore, NF272 may serve as a lead structure for further development of P2Y₂ receptor antagonists.

A comparison of assay performance between the calcium mobilization and the dynamic mass redistribution technologies for the human urotensin receptor

The popular screening method for urotensin (UT) receptor antagonists is to measure the intracellular calcium concentration with a calcium-sensitive fluorescent dye. This assay format has an inherent limitation on the problem related to the fluorescence interference as it involves fluorescent dyes. In the present study, a label-free assay for the screening of UT receptor antagonists was developed by using dynamic mass redistribution (DMR) assay based on label-free optical biosensor. The addition of urotensin II (UII) stimulated a DMR profile to HEK293 cells stably expressing the human UT receptor (HEK293UT cells) but not on parental cells. The EC50 value of UII in label-free assay was 4.58 nM, which is very similar to that in conventional calcium mobilization assay (4.15 nM). Compared with the calcium mobilization assay for UII (Z' factor, 0.77), the current label-free assay presented improved Z' factor (0.81), with a relatively similar S/B ratio (28.0 and 25.6, respectively). The known high-affinity UT receptor antagonists, SB657510, GSK562590, and urantide, exhibited comparable IC50 values but rather less potent in the DMR assay than in calcium mobilization. Our DMR assay was able to present various functional responses, including inverse agonism in SB657510 and GSK1562590 as well as partial agonism in urantide. Moreover, the DMR assay exerted the stable antagonist window upon the minimal agonist stimulus. These results suggest that the label-free cell-based UT receptor assay can be applicable to evaluate the various functional activities of UT receptor-related drug candidates.

In vitro and mouse in vivo characterization of the potent free fatty acid 1 receptor agonist TUG-469

Activation of the G protein-coupled free fatty acid receptor 1 (FFA1; formerly known as GPR40) leads to an enhancement of glucose-stimulated insulin secretion from pancreatic β-cells. TUG-469 has previously been reported as a potent FFA1 agonist. This study was performed to confirm the higher in vitro potency of TUG-469 compared to the reference FFA1 agonist GW9508 and to prove in vivo activity in a pre-diabetic mouse model. The in vitro pharmacology of TUG-469 was studied using Ca(2+)-, cAMP-, and impedance-based assays at recombinant FFA1 and free fatty acid receptor 4, formerly known as GPR120 (FFA4) expressing 1321N1 cells and the rat insulinoma cell line INS-1. Furthermore, we investigated the systemic effect of TUG-469 on glucose tolerance in pre-diabetic New Zealand obese (NZO) mice performing a glucose tolerance test after intraperitoneal administration of 5 mg/kg TUG-469. In comparison to GW9508, TUG-469 showed a 1.7- to 3.0-times higher potency in vitro at 1321N1 cells recombinantly expressing FFA1. Both compounds increased insulin secretion from rat insulinoma INS-1 cells. TUG-469 is > 200-fold selective for FFA1 over FFA4. Finally, a single dose of 5 mg/kg TUG-469 significantly improved glucose tolerance in pre-diabetic NZO mice. TUG-469 turned out as a promising candidate for further drug development of FFA1 agonists for treatment of type 2 diabetes mellitus.

NF546 [4,4'-(carbonylbis(imino-3,1-phenylene-carbonylimino-3,1-(4-methyl-phenylene)-carbonylimino))-bis(1,3-xylene-alpha,alpha'-diphosphonic acid) tetrasodium salt] is a non-nucleotide P2Y11 agonist and stimulates release of interleukin-8 from human monocyte-derived dendritic cells

The G protein-coupled P2Y(11) receptor is involved in immune system modulation. In-depth physiological evaluation is hampered, however, by a lack of selective and potent ligands. By screening a library of sulfonic and phosphonic acid derivatives at P2Y(11) receptors recombinantly expressed in human 1321N1 astrocytoma cells (calcium and cAMP assays), the selective non-nucleotide P2Y(11) agonist NF546 [4,4'-(carbonylbis(imino-3,1-phenylene-carbonylimino-3,1-(4-methyl-phenylene)carbonylimino))-bis(1,3-xylene-alpha,alpha'-diphosphonic acid) tetrasodium salt] was identified. NF546 had a pEC(50) of 6.27 and is relatively selective for P2Y(11) over P2Y(1), P2Y(2), P2Y(4), P2Y(6), P2Y(12), P2X(1), P2X(2), and P2X(2)-X(3). Adenosine-5'-O-(3-thio)triphosphate (ATPgammaS), a nonhydrolyzable analog of the physiological P2Y(11) agonist ATP, and NF546 use a common binding site as suggested by molecular modeling studies and their competitive behavior toward the nanomolar potency antagonist NF340 [4,4'-(carbonylbis(imino-3,1-(4-methyl-phenylene)carbonylimino))bis(naphthalene-2,6-disulfonic acid) tetrasodium salt] in Schild analysis. The pA(2) of NF340 was 8.02 against ATPgammaS and 8.04 against NF546 (calcium assays). NF546 was further tested for P2Y(11)-mediated effects in monocyte-derived dendritic cells. Similarly to ATPgammaS, NF546 led to thrombospondin-1 secretion and inhibition of lipopolysaccharide-stimulated interleukin-12 release, whereas NF340 inhibited these effects. Further, for the first time, it was shown that ATPgammaS or NF546 stimulation promotes interleukin 8 (IL-8) release from dendritic cells, which could be inhibited by NF340. In conclusion, we have described the first selective, non-nucleotide agonist NF546 for P2Y(11) receptors in both recombinant and physiological expression systems and could show a P2Y(11)-stimulated IL-8 release, further supporting the immunomodulatory role of P2Y(11) receptors.

Chemical calcium indicators

Our understanding of the underlying mechanisms of Ca2+ signaling as well as our appreciation for its ubiquitous role in cellular processes has been rapidly advanced, in large part, due to the development of fluorescent Ca2+ indicators. In this chapter, we discuss some of the most common chemical Ca2+ indicators that are widely used for the investigation of intracellular Ca2+ signaling. Advantages, limitations and relevant procedures will be presented for each dye including their spectral qualities, dissociation constants, chemical forms, loading methods and equipment for optimal imaging. Chemical indicators now available allow for intracellular Ca2+ detection over a very large range (<50 nM to >50 microM). High affinity indicators can be used to quantify Ca2+ levels in the cytosol while lower affinity indicators can be optimized for measuring Ca2+ in subcellular compartments with higher concentrations. Indicators can be classified into either single wavelength or ratiometric dyes. Both classes require specific lasers, filters, and/or detection methods that are dependent upon their spectral properties and both classes have advantages and limitations. Single wavelength indicators are generally very bright and optimal for Ca2+ detection when more than one fluorophore is being imaged. Ratiometric indicators can be calibrated very precisely and they minimize the most common problems associated with chemical Ca2+ indicators including uneven dye loading, leakage, photobleaching, and changes in cell volume. Recent technical advances that permit in vivo Ca2+ measurements will also be discussed.

Selective nucleoside triphosphate diphosphohydrolase-2 (NTPDase2) inhibitors: nucleotide mimetics derived from uridine-5'-carboxamide

Ecto-nucleoside triphosphate diphosphohydrolases (E-NTPDases, subtypes 1, 2, 3, 8 of NTPDases) dephosphorylate nucleoside tri- and diphosphates to the corresponding di- and monophosphates. In the present study we synthesized adenine and uracil nucleotide mimetics, in which the phosphate residues were replaced by phosphonic acid esters attached to the nucleoside at the 5'-position by amide linkers. Among the synthesized uridine derivatives, we identified the first potent and selective inhibitors of human NTPDase2. The most potent compound was 19a (PSB-6426), which was a competitive inhibitor of NTPDase2 exhibiting a K i value of 8.2 microM and selectivity versus other NTPDases. It was inactive toward uracil nucleotide-activated P2Y 2, P2Y 4, and P2Y 6 receptor subtypes. Compound 19a was chemically and metabolically highly stable. In contrast to the few known (unselective) NTPDase inhibitors, 19a is an uncharged molecule and may be perorally bioavailable. NTPDase2 inhibitors have potential as novel cardioprotective drugs for the treatment of stroke and for cancer therapy.

Small mouse cholangiocytes proliferate in response to H1 histamine receptor stimulation by activation of the IP3/CaMK I/CREB pathway

Cholangiopathies are characterized by the heterogeneous proliferation of different-sized cholangiocytes. Large cholangiocytes proliferate by a cAMP-dependent mechanism. The function of small cholangiocytes may depend on the activation of inositol trisphosphate (IP(3))/Ca(2+)-dependent signaling pathways; however, data supporting this speculation are lacking. Four histamine receptors exist (HRH1, HRH2, HRH3, and HRH4). In several cells: 1) activation of HRH1 increases intracellular Ca(2+) concentration levels; and 2) increased [Ca(2+)](i) levels are coupled with calmodulin-dependent stimulation of calmodulin-dependent protein kinase (CaMK) and activation of cAMP-response element binding protein (CREB). HRH1 agonists modulate small cholangiocyte proliferation by activation of IP(3)/Ca(2+)-dependent CaMK/CREB. We evaluated HRH1 expression in cholangiocytes. Small and large cholangiocytes were stimulated with histamine trifluoromethyl toluidide (HTMT dimaleate; HRH1 agonist) for 24-48 h with/without terfenadine, BAPTA/AM, or W7 before measuring proliferation. Expression of CaMK I, II, and IV was evaluated in small and large cholangiocytes. We measured IP(3), Ca(2+) and cAMP levels, phosphorylation of CaMK I, and activation of CREB (in the absence/presence of W7) in small cholangiocytes treated with HTMT dimaleate. CaMK I knockdown was performed in small cholangiocytes stimulated with HTMT dimaleate before measurement of proliferation and CREB activity. Small and large cholangiocytes express HRH1, CaMK I, and CaMK II. Small (but not large) cholangiocytes proliferate in response to HTMT dimaleate and are blocked by terfenadine (HRH1 antagonist), BAPTA/AM, and W7. In small cholangiocytes, HTMT dimaleate increased IP(3)/Ca(2+) levels, CaMK I phosphorylation, and CREB activity. Gene knockdown of CaMK I ablated the effects of HTMT dimaleate on small cholangiocyte proliferation and CREB activation. The IP(3)/Ca(2+)/CaMK I/CREB pathway is important in the regulation of small cholangiocyte function.

Prolactin stimulates the proliferation of normal female cholangiocytes by differential regulation of Ca2+-dependent PKC isoforms

Background

Prolactin promotes proliferation of several cells. Prolactin receptor exists as two isoforms: long and short, which activate different transduction pathways including the Ca²⁺-dependent PKC-signaling. No information exists on the role of prolactin in the regulation of the growth of female cholangiocytes. The rationale for using cholangiocytes from female rats is based on the fact that women are preferentially affected by specific cholangiopathies including primary biliary cirrhosis. We propose to evaluate the role and mechanisms of action by which prolactin regulates the growth of female cholangiocytes.

Results

Normal cholangiocytes express both isoforms (long and short) of prolactin receptors, whose expression increased following BDL. The administration of prolactin to normal female rats increased cholangiocyte proliferation. In purified normal female cholangiocytes, prolactin stimulated cholangiocyte proliferation, which was associated with increased [Ca²⁺]_i levels and PKCβ-I phosphorylation but decreased PKCα phosphorylation. Administration of an anti-prolactin antibody to BDL female rats decreased cholangiocyte proliferation. Normal female cholangiocytes express and secrete prolactin, which was increased in BDL rats. The data show that prolactin stimulates normal cholangiocyte growth by an autocrine mechanism involving phosphorylation of PKCβ-I and dephosphorylation of PKCα.

Conclusion

We suggest that in female rats: (i) prolactin has a trophic effect on the growth of normal cholangiocytes by phosphorylation of PKCβ-I and dephosphorylation of PKCα; and (iii) cholangiocytes express and secrete prolactin, which by an autocrine mechanism participate in regulation of cholangiocyte proliferation. Prolactin may be an important therapeutic approach for the management of cholangiopathies affecting female patients.

Dibenzazecine compounds with a novel dopamine/5HT2A receptor profile and 3D-QSAR analysis

Background

Antipsychotics are divided into typical and atypical compounds based on clinical efficacy and side effects. The purpose of this study was to characterize in vitro a series of novel azecine-type compounds at human dopamine D₁-D₅ and 5HT_2A receptors and to assign them to different classes according to their dopamine/5HT_2A receptor profile.

Results

Regardless of using affinity data (pK_i values at D₁-D₅ and 5HT_2A) or selectivity data (15 log (K_i ratios)), principal component analysis with azecine-type compounds, haloperidol, and clozapine revealed three groups of dopamine/5HT_2A ligands: 1) haloperidol; 2) clozapine plus four azecine-type compounds; 3) two hydroxylated dibenzazecines. Reducing the number of K_i ratios used for principal component analysis from 15 to two (the D₁/D₂ and D₂/5HT_2A K_i ratios) obtained the same three groups of compounds. The most potent dibenzazecine clustering in the same group as clozapine was the non-hydroxylated LE410 which shows a slightly different D₂-like receptor profile (D_2L > D₃ > D_4.4) than clozapine (D_4.4 > D_2L > D₃). The monohydroxylated dibenzacezine LE404 clusters in a separate group from clozapine/LE410 and from haloperidol and shows increased D₁ selectivity.

Conclusion

In conclusion, two compounds with a novel dopamine/5HT_2A receptor profile, LE404 and LE410, with some differences in their respective D₁/D₂ receptor affinities including a validated pharmacophore-based 3D-QSAR model for D₁ antagonists are presented.

Establishment of ELISA on 384-well microplate for AFP, CEA, CA 19-9, CA 15-3, CA 125, and PSA-ACT: higher sensitivity and lower reagent cost

The 384-well microplate contains four times as many wells as the regular 96-well microplate. Establishing enzyme linked immunosorbent assay (ELISA) on 384-well microplate should lead to savings in reagents and specimens. To determine that ELISAs on 384-well microplate have acceptable assay precision, ELISAs for tumor markers, including AFP, PSA-ACT, CEA, CA 125, CA 15-3, and CA 19-9, were compared to the same ELISAs established on 96-well microplate. We found that ELISAs established on 384-well microplate had similar sensitivity and covered similar concentration ranges as ELISAs on 96-well microplate. All within-day and day-to-day precisions for the 384-ELISA had %CV less than 10%. Compared to ELISA on 96-well microplate, 384-ELISA used less reagents, less specimen, and exhibited approximately a two-fold increase in sensitivity. Overall cost of the 384-384-ELISA was also greatly reduced. Our results suggest that 384-ELISA is suitable for use in routine clinical laboratories.

Quantitative comparison of functional screening by measuring intracellular Ca2+ with radioligand binding at recombinant human dopamine receptors

The purpose of this study was to test whether screening at dopamine receptors performed with a recently described functional assay for G-protein coupled receptors (GPCRs) provides data that correlate significantly with radioligand binding data in the literature, thus possibly allowing researchers to replace radioligand binding with nonradioactive functional screening. Human dopamine receptors hD1 and hD2L (representing Gs [hD1] or Gi [hD2L] coupled GPCRs) were recombinantly expressed in human embryonic kidney (HEK293) cells. Cells were loaded with Oregon Green 488 BAPTA-1/AM and evenly distributed in 384 well plates. Seventeen test compounds were screened for agonistic activity by injection into the cell suspension and monitoringH of intracellular Ca2+ with a fluorescence microplate reader. Then, standard agonists (100nM SKF38393 for hD1, 30nM quinpirole for hD2L) were injected into wells preincubated with test compounds (screening for antagonism). Injection of various agonists resulted in a concentration-dependent increase in fluorescence. Further, preincubation of antagonists with dopamine receptor expressing cells inhibits concentration-dependent the agonist-induced increase in fluorescence. Calculated apparent functional Ki values correlate with radioligand binding data in the literature (r2 = 0.7796 for D1, r2 = 0.7743 for D2). The correlation between apparent functional Ki values and radioligand binding data for the 17 tested compounds suggests that screening of test compounds at dopamine receptors with the functional Ca2+ assay can replace radioligand binding studies. Furthermore, besides apparent Ki values, information about agonistic or antagonistic properties of a test compound can be obtained with the functional Ca2+ assay.