Manipulation of PBF/PTTG1IP phosphorylation status; a potential new therapeutic strategy for improving radioiodine uptake in thyroid and other tumors

CONTEXT

The clinical effectiveness of ablative radioiodine treatment of thyroid tumors is limited by the availability of the sodium iodide symporter (NIS) at the plasma membrane (PM) for uptake of ¹³¹I. A significant proportion of well-differentiated thyroid tumors are unable to concentrate sufficient radioiodine for effective therapy, and in other tumor models such as breast tumors, where radioiodine uptake would be an attractive therapeutic option, uptake is insufficient.

OBJECTIVE

Pituitary tumor-transforming gene-binding factor (PBF; PTTG1IP) is overexpressed in multiple cancers and significantly decreases NIS expression at the PM. The goal of this study was to identify a method by which PBF repression of NIS may be overcome in human tumors.

RESULTS

Here, we identify PBF as a tyrosine phosphoprotein that specifically binds the proto-oncogene tyrosine protein kinase Src in mass spectrometry, glutathione S-transferase pulldown and coimmunoprecipitation assays. Src induction leads to phosphorylation at PBF residue Y174. Abrogation of this residue results in PM retention and a markedly reduced ability to bind NIS. The Src inhibitor PP1 inhibits PBF phosphorylation in multiple cell lines in vitro, including human primary thyroid cells. Of direct clinical importance to the treatment of thyroid cancer, PP1 stimulates iodide uptake by transfected NIS in TPC1 thyroid carcinoma cells and entirely overcomes PBF repression of iodide uptake in human primary thyroid cells.

CONCLUSIONS

We propose that targeting PBF phosphorylation at residue Y174 via tyrosine kinase inhibitors may be a novel therapeutic strategy to enhance the efficacy of ablative radioiodine treatment in thyroid and other endocrine and endocrine-related tumors.

Fibroblast growth factor 21 mediates specific glucagon actions

Glucagon, an essential regulator of glucose homeostasis, also modulates lipid metabolism and promotes weight loss, as reflected by the wasting observed in glucagonoma patients. Recently, coagonist peptides that include glucagon agonism have emerged as promising therapeutic candidates for the treatment of obesity and diabetes. We developed a novel stable and soluble glucagon receptor (GcgR) agonist, which allowed for in vivo dissection of glucagon action. As expected, chronic GcgR agonism in mice resulted in hyperglycemia and lower body fat and plasma cholesterol. Notably, GcgR activation also raised hepatic expression and circulating levels of fibroblast growth factor 21 (FGF21). This effect was retained in isolated primary hepatocytes from wild-type (WT) mice, but not GcgR knockout mice. We confirmed this link in healthy human volunteers, where injection of natural glucagon increased plasma FGF21 within hours. Functional relevance was evidenced in mice with genetic deletion of FGF21, where GcgR activation failed to induce the body weight loss and lipid metabolism changes observed in WT mice. Taken together, these data reveal for the first time that glucagon controls glucose, energy, and lipid metabolism at least in part via FGF21-dependent pathways.

Impact of clinically relevant mutations on the pharmacoregulation and signaling bias of the calcium-sensing receptor by positive and negative allosteric modulators

Cinacalcet is predominantly used to treat secondary hyperparathyroidism due to end-stage renal failure, but, more recently, its potential clinical efficacy in treating patients with loss-of-function mutations in the calcium-sensing receptor (CaSR) has been recognized. Many clinically relevant CaSR mutations are located in the heptahelical membrane spanning and extracellular loop regions of the receptor, where allosteric modulators are predicted to bind. The aim of the present study was to investigate the impact of such mutations on the pharmacoregulation of the CaSR by the positive and negative allosteric modulators, cinacalcet and NPS-2143, respectively. Both cinacalcet and NPS-2143 effectively rescued mutants whose cell surface expression was substantially impaired, suggesting that both classes of drug can stabilize a receptor conformation that is trafficked more effectively to the cell surface. In addition, functional impairments in almost all mutant CaSRs were rescued by either cinacalcet or NPS-2143 via restoration of intracellular signaling. There was a significantly greater ability of both compounds to modulate agonist-stimulated intracellular Ca(2+) mobilization than ERK1/2 phosphorylation, indicating that the allosteric modulators engender bias in agonist-stimulated CaSR signaling to different pathways. Three mutations (G(670)R, P(748)R, and L(773)R) altered the binding affinity of allosteric modulators to the CaSR, and 3 mutations (V(817)I, L(773)R, and E(767)K) altered the cooperativity between the allosteric modulator and Ca(2+)(o). These findings have important implications for the treatment of diseases associated with CaSR mutations using allosteric CaSR modulators and for analyzing the effects of mutations on the function and pharmacoregulation of the CaSR.

Identification of endocrine disrupting chemicals activating SXR-mediated transactivation of CYP3A and CYP7A1

Endocrine disrupting chemicals (EDCs) have emerged as a major public health issue because of their potentially disruptive effects on physiological hormonal actions. SXR (steroid xenobiotic receptor), also known as NR1I2, regulates CYP3A expression in response to exogenous chemicals, such as EDCs, after binding to SXRE (SXR response element). In our study, luciferase assay showed that 14 out of 55 EDCs could enhance SXR-mediated rat or human CYP3A gene transcription nearly evenly, and could also activate rat CYP7A1 gene transcription by cross-interaction of SXR and LXRE (LXRα response element). SXR diffused in the nucleus without ligand, whereas intranuclear foci of liganded SXR were produced. Furthermore, endogenous mRNA expression of CYP3A4 gene was enhanced by the 14 positive EDCs. Our results suggested a probable mechanism of EDCs disrupting the steroid or xenobiotic metabolism homeostasis via SXR.

Regulation of GPR119 receptor activity with endocannabinoid-like lipids

The GPR119 receptor plays an important role in the secretion of incretin hormones in response to nutrient consumption. We have studied the ability of an array of naturally occurring endocannabinoid-like lipids to activate GPR119 and have identified several lipid receptor agonists. The most potent receptor agonists identified were three N-acylethanolamines: oleoylethanolamine (OEA), palmitoleoylethanolamine, and linoleylethanolamine (LEA), all of which displayed similar potency in activating GPR119. Another lipid, 2-oleoylglycerol (2-OG), also activated GPR119 receptor but with significantly lower potency. Endogenous levels of endocannabinoid-like lipids were measured in intestine in fasted and refed mice. Of the lipid GPR119 agonists studied, the intestinal levels of only OEA, LEA, and 2-OG increased significantly upon refeeding. Intestinal levels of OEA and LEA in the fasted mice were low. In the fed state, OEA levels only moderately increased, whereas LEA levels rose drastically. 2-OG was the most abundant of the three GPR119 agonists in intestine, and its levels were radically elevated in fed mice. Our data suggest that, in lean mice, 2-OG and LEA may serve as physiologically relevant endogenous GPR119 agonists that mediate receptor activation upon nutrient uptake.

SSTR2 is the functionally dominant somatostatin receptor in human pancreatic β- and α-cells

Somatostatin-14 (SST) inhibits insulin and glucagon secretion by activating G protein-coupled somatostatin receptors (SSTRs), of which five isoforms exist (SSTR1-5). In mice, the effects on pancreatic β-cells are mediated by SSTR5, whereas α-cells express SSTR2. In both cell types, SSTR activation results in membrane hyperpolarization and suppression of exocytosis. Here, we examined the mechanisms by which SST inhibits secretion from human β- and α-cells and the SSTR isoforms mediating these effects. Quantitative PCR revealed high expression of SSTR2, with lower levels of SSTR1, SSTR3, and SSTR5, in human islets. Immunohistochemistry showed expression of SSTR2 in both β- and α-cells. SST application hyperpolarized human β-cells and inhibited action potential firing. The membrane hyperpolarization was unaffected by tolbutamide but antagonized by tertiapin-Q, a blocker of G protein-gated inwardly rectifying K⁺ channels (GIRK). The effect of SST was mimicked by an SSTR2-selective agonist, whereas a SSTR5 agonist was marginally effective. SST strongly (>70%) reduced depolarization-evoked exocytosis in both β- and α-cells. A slightly weaker inhibition was observed in both cell types after SSTR2 activation. SSTR3- and SSTR1-selective agonists moderately reduced the exocytotic responses in β- and α-cells, respectively, whereas SSTR4- and SSTR5-specific agonists were ineffective. SST also reduced voltage-gated P/Q-type Ca²⁺ currents in β-cells, but normalization of Ca²⁺ influx to control levels by prolonged depolarizations only partially restored exocytosis. We conclude that SST inhibits secretion from both human β- and α-cells by activating GIRK and suppressing electrical activity, reducing P/Q-type Ca²⁺ currents, and directly inhibiting exocytosis. These effects are mediated predominantly by SSTR2 in both cell types.

α4βδ GABA(A) receptors are high-affinity targets for γ-hydroxybutyric acid (GHB)

γ-Hydroxybutyric acid (GHB) binding to brain-specific high-affinity sites is well-established and proposed to explain both physiological and pharmacological actions. However, the mechanistic links between these lines of data are unknown. To identify molecular targets for specific GHB high-affinity binding, we undertook photolinking studies combined with proteomic analyses and identified several GABA(A) receptor subunits as possible candidates. A subsequent functional screening of various recombinant GABA(A) receptors in Xenopus laevis oocytes using the two-electrode voltage clamp technique showed GHB to be a partial agonist at αβδ- but not αβγ-receptors, proving that the δ-subunit is essential for potency and efficacy. GHB showed preference for α4 over α(1,2,6)-subunits and preferably activated α4β1δ (EC(50) = 140 nM) over α4β(2/3)δ (EC(50) = 8.41/1.03 mM). Introduction of a mutation, α4F71L, in α4β1(δ)-receptors completely abolished GHB but not GABA function, indicating nonidentical binding sites. Radioligand binding studies using the specific GHB radioligand [(3)H](E,RS)-(6,7,8,9-tetrahydro-5-hydroxy-5H-benzocyclohept-6-ylidene)acetic acid showed a 39% reduction (P = 0.0056) in the number of binding sites in α4 KO brain tissue compared with WT controls, corroborating the direct involvement of the α4-subunit in high-affinity GHB binding. Our data link specific GHB forebrain binding sites with α4-containing GABA(A) receptors and postulate a role for extrasynaptic α4δ-containing GABA(A) receptors in GHB pharmacology and physiology. This finding will aid in elucidating the molecular mechanisms behind the proposed function of GHB as a neurotransmitter and its unique therapeutic effects in narcolepsy and alcoholism.

Some cannabinoid receptor ligands and their distomers are direct-acting openers of SUR1 K(ATP) channels

Here, we examined the chronic effects of two cannabinoid receptor-1 (CB1) inverse agonists, rimonabant and ibipinabant, in hyperinsulinemic Zucker rats to determine their chronic effects on insulinemia. Rimonabant and ibipinabant (10 mg·kg⁻¹·day⁻¹) elicited body weight-independent improvements in insulinemia and glycemia during 10 wk of chronic treatment. To elucidate the mechanism of insulin lowering, acute in vivo and in vitro studies were then performed. Surprisingly, chronic treatment was not required for insulin lowering. In acute in vivo and in vitro studies, the CB1 inverse agonists exhibited acute K channel opener (KCO; e.g., diazoxide and NN414)-like effects on glucose tolerance and glucose-stimulated insulin secretion (GSIS) with approximately fivefold better potency than diazoxide. Followup studies implied that these effects were inconsistent with a CB1-mediated mechanism. Thus effects of several CB1 agonists, inverse agonists, and distomers during GTTs or GSIS studies using perifused rat islets were unpredictable from their known CB1 activities. In vivo rimonabant and ibipinabant caused glucose intolerance in CB1 but not SUR1-KO mice. Electrophysiological studies indicated that, compared with diazoxide, 3 μM rimonabant and ibipinabant are partial agonists for K channel opening. Partial agonism was consistent with data from radioligand binding assays designed to detect SUR1 K(ATP) KCOs where rimonabant and ibipinabant allosterically regulated ³H-glibenclamide-specific binding in the presence of MgATP, as did diazoxide and NN414. Our findings indicate that some CB1 ligands may directly bind and allosterically regulate Kir6.2/SUR1 K(ATP) channels like other KCOs. This mechanism appears to be compatible with and may contribute to their acute and chronic effects on GSIS and insulinemia.

Click modification in the N6 region of A3 adenosine receptor-selective carbocyclic nucleosides for dendrimeric tethering that preserves pharmacophore recognition

Adenosine derivatives were modified with alkynyl groups on N(6) substituents for linkage to carriers using Cu(I)-catalyzed click chemistry. Two parallel series, both containing a rigid North-methanocarba (bicyclo[3.1.0]hexane) ring system in place of ribose, behaved as A(3) adenosine receptor (AR) agonists: (5'-methyluronamides) or partial agonists (4'-truncated). Terminal alkynyl groups on a chain at the 3 position of a N(6)-benzyl group or simply through a N(6)-propargyl group were coupled to azido derivatives, which included both small molecules and G4 (fourth-generation) multivalent poly(amidoamine) (PAMAM) dendrimers, to form 1,2,3-triazolyl linkers. The small molecular triazoles probed the tolerance in A(3)AR binding of distal, sterically bulky groups such as 1-adamantyl. Terminal 4-fluoro-3-nitrophenyl groups anticipated nucleophilic substitution for chain extension and (18)F radiolabeling. N(6)-(4-Fluoro-3-nitrophenyl)-triazolylmethyl derivative 32 displayed a K(i) of 9.1 nM at A(3)AR with ∼1000-fold subtype selectivity. Multivalent conjugates additionally containing click-linked water-solubilizing polyethylene glycol groups potently activated A(3)AR in the 5'-methyluronamide, but not 4' truncated series. N(6)-Benzyl nucleoside conjugate 43 (apparent K(i) 24 nM) maintained binding affinity of the monomer better than a N(6)-triazolylmethyl derivative. Thus, the N(6) region of 5'-methyluronamide derivatives, as modeled in receptor docking, is suitable for functionalization and tethering by click chemistry to achieve high A(3)AR agonist affinity and enhanced selectivity.

Role of lipid peroxidation and PPAR-δ in amplifying glucose-stimulated insulin secretion

OBJECTIVE

Previous studies show that polyunsaturated fatty acids (PUFAs) increase the insulin secretory capacity of pancreatic β-cells. We aimed at identifying PUFA-derived mediators and their cellular targets that are involved in the amplification of insulin release from β-cells preexposed to high glucose levels.

RESEARCH DESIGN AND METHODS

The content of fatty acids in phospholipids of INS-1E β-cells was determined by lipidomics analysis. High-performance liquid chromatography was used to identify peroxidation products in β-cell cultures. Static and dynamic glucose-stimulated insulin secretion (GSIS) assays were performed on isolated rat islets and/or INS-1E cells. The function of peroxisome proliferator-activated receptor-δ (PPAR-δ) in regulating insulin secretion was investigated using pharmacological agents and gene expression manipulations.

RESULTS

High glucose activated cPLA(2) and, subsequently, the hydrolysis of arachidonic and linoleic acid (AA and LA, respectively) from phospholipids in INS-1E cells. Glucose also increased the level of reactive oxygen species, which promoted the peroxidation of these PUFAs to generate 4-hydroxy-2E-nonenal (4-HNE). The latter mimicked the GSIS-amplifying effect of high glucose preexposure and of the PPAR-δ agonist GW501516 in INS-1E cells and isolated rat islets. These effects were blocked with GSK0660, a selective PPAR-δ antagonist, and the antioxidant N-acetylcysteine or by silencing PPAR-δ expression. High glucose, 4-HNE, and GW501516 also induced luciferase expression in a PPAR-δ-mediated transactivation assay. Cytotoxic effects of 4-HNE were observed only above the physiologically effective concentration range.

CONCLUSIONS

Elevated glucose levels augment the release of AA and LA from phospholipids and their peroxidation to 4-HNE in β-cells. This molecule is an endogenous ligand for PPAR-δ, which amplifies insulin secretion in β-cells.

Roles of affinity and lipophilicity in the slow kinetics of prostanoid receptor antagonists on isolated smooth muscle preparations

BACKGROUND AND PURPOSE

The highly lipophilic acyl-sulphonamides L-798106 and L-826266 showed surprisingly slow antagonism of the prostanoid EP₃ receptor system in guinea-pig aorta. Roles of affinity and lipophilicity in the onset kinetics of these and other prostanoid ligands were investigated.

EXPERIMENTAL APPROACH

Antagonist selectivity was assessed using a panel of human recombinant prostanoid receptor-fluorimetric imaging plate reader assays. Potencies/affinities and onset half-times of agonists and antagonists were obtained on guinea-pig-isolated aorta and vas deferens. n-Octanol-water partition coefficients were predicted.

KEY RESULTS

L-798106, L-826266 and the less lipophilic congener (DG)-3ap appear to behave as selective, competitive-reversible EP₃ antagonists. For ligands of low to moderate lipophilicity, potency increments for EP₃ and TP (thromboxane-like) agonism on guinea-pig aorta (above pEC₅₀ of 8.0) were associated with progressively longer onset half-times; similar trends were found for TP and histamine H₁ antagonism above a pA₂ limit of 8.0. In contrast, L-798106 (EP₃), L-826266 (EP₃, TP) and the lipophilic H₁ antagonists astemizole and terfenadine exhibited very slow onset rates despite their moderate affinities; (DG)-3ap (EP₃) had a faster onset. Agonism and antagonism on the vas deferens EP₃ system were overall much faster, although trends were similar.

CONCLUSIONS AND IMPLICATIONS

High affinity and high liphophilicity may contribute to the slow onsets of prostanoid ligands in some isolated smooth muscle preparations. Both relationships are explicable by tissue disposition under the limited diffusion model. EP₃ antagonists used as research tools should have moderate lipophilicity. The influence of lipophilicity on the potential clinical use of EP₃ antagonists is discussed.

Pharmacology of putative selective hBRS-3 receptor agonists for human bombesin receptors (BnR): affinities, potencies and selectivity in multiple native and BnR transfected cells

The orphan receptor, bombesin receptor subtype-3(BRS-3) is a G-protein-coupled receptor classified in the bombesin (Bn) receptor family because of its high homology (47-51%) with other members of this family [gastrin-releasing peptide receptor [GRPR] and neuromedin B receptor [NMBR]]. There is increasing interest in BRS-3, because primarily from receptor knockout studies, it seems important in energy metabolism, glucose control, insulin secretion, motility and tumor growth. Pharmacological tools to study the role of BRS-3 in physiology/pathophysiology are limited because the natural ligand is unknown and BRS-3 has low affinity for all naturally occurring Bn-related peptides. However, a few years ago a synthetic high-affinity agonist [dTyr(6),betaAla(11),Phe(13),Nle(14)]Bn-(6-14) was described but was nonselective for BRS-3 over other Bn receptors. Based on this peptide, in various studies a number of putative selective, high-potency hBRS-3 agonists were described, however the results on their selectivity are conflicting in a number of cases. The purpose of the present study was to thoroughly study the pharmacology of four of the most select/potent putative hBRS-3 agonists (#2-4, 16a). Each was studied in multiple well-characterized Bn receptor-transfected cells and native Bn receptor bearing cells, using binding studies, alterations in cellular signaling (PLC, PKD) and changes in cellular function(growth). Two peptides (#2, #3) had nM affinities/potencies for hBRS-3, peptide #4 had low affinity/potency, and peptide #16a very low (>3000 nM). Peptide#3 had the highest selectivity for hBRS-3 (100-fold), whereas #2, 4 had lower selectivity. Peptide #16a's selectivity could not be determined because of its low affinity/potencies for all hBn receptors. These results show that peptide #3 is the preferred hBRS-3 agonist for studies at present, although its selectivity of only 100-fold may limit its utility in some cases. This study underscores the importance of full pharmacological characterization of newly reported selective agonists.

Partial agonistic effect of yokukansan on human recombinant serotonin 1A receptors expressed in the membranes of Chinese hamster ovary cells

ETHNOPHARMACOLOGICAL RELEVANCE

Yokukansan (YKS) is a traditional Japanese medicine consisted of seven medicinal herbs and has been used for treatment of neurosis, insomnia, and behavioral and psychological symptoms of dementia (BPSD) in Japan.

AIM OF THE STUDY

The aim of the present study is to clarify the intrinsic activity of YKS on serotonin (5-HT)1A and 5-HT2A receptors and also to determine the constituent herbs which are responsible for the effect of YKS.

MATERIALS AND METHODS

The dry powdered extracts of YKS, seven constituent herbs, and YKS-analogues which were produced by eliminating one of the constituent herbs from YKS in the manufacturing process, were used for the evaluation. Competitive binding assays for 5-HT receptors and [(35)S]GTPgammaS binding assays for the evaluation of agonistic/antagonistic activity were performed using Chinese hamster ovary cell membranes stably expressing human recombinant 5-HT1A or 5-HT2A receptors.

RESULTS

YKS (6.25-400 microg/ml) concentration-dependently inhibited the binding of [(3)H]8-OH-DPAT to 5-HT1A receptors. The IC(50) value was estimated to be 61.2 microg/ml. In contrast, YKS failed to inhibit the binding of [(3)H]ketanserin to 5-HT2A receptors. Only Uncaria hook (3.13-50 microg/ml), of the seven constituent herbal extracts, inhibited the [(3)H]8-OH-DPAT binding to 5-HT1A receptors in a concentration-dependent manner, and the IC(50) value was estimated to be 7.42 microg/ml. The extracts of YKS or Uncaria hook increased [(35)S]GTPgammaS binding to 5-HT1A receptors to approximately 50% of that of a full agonist, 5-HT. Both the competitive binding and [(35)S]GTPgammaS binding of YKS to 5-HT1A receptors were remarkably attenuated by eliminating Uncaria hook from YKS, but it was almost unchanged when one of the other constituent herbs was eliminated from YKS.

CONCLUSION

These results suggest that YKS has a partial agonistic effect on 5-HT1A receptors, which is mainly attributed to Uncaria hook.

Differential binding of ICln in platelets to integrin-derived activating and inhibitory peptides

The capacity of platelets to form a thrombus is mediated by integrin alpha(IIb)beta(3). The cytoplasmic tail of alpha(IIb) contains a highly conserved motif, (989)KVGFFKR(995), which plays a critical role in regulating integrin activation and acts as a recognition site for various intracellular proteins, e.g. CIB1, PP1, ICln and RN181. Previously, we demonstrated that a cell-permeable integrin-derived activating (IDA) peptide, KVGFFKR, induces platelet activation, whereas an integrin-derived inhibitory (IDI) peptide, KVGAAKR, is antithrombotic. To elucidate the molecular mechanism underlying these opposite effects we investigate the affinity of known integrin alpha(IIb) binding proteins for the two immobilized peptides in dependence on the activation state of platelets by means of peptide-affinity chromatography, blotting techniques and protein:peptide docking studies. Our results provide a model for the inhibition of ICln interaction with the integrin in activated platelets by the IDI-peptide. Thus, ICln:IDI-peptide interaction profiles can have a pivotal purpose in the search for consensus pharmacophores specifically inhibiting ICln function in platelets potentially leading to the development of integrin-derived antithrombotic drugs.

Channel beta2-4 subunits fail to substitute for beta1 in sensitizing BK channels to lithocholate

Large conductance, calcium- and voltage-gated potassium (BK) channels regulate numerous physiological processes. While most basic functional characteristics of native BK channels are reproduced by BK alpha (slo1) subunit homotetramers, key biophysical and pharmacological properties are drastically modified by the presence of auxiliary beta subunits (encoded by KCNMB1-4). Numerous physiological steroids, including sex hormones, gluco- and mineralocorticoids, activate beta subunit-containing BK channels, yet these steroids appear to be sensed by different types of beta subunits, with some steroids being sensed by homomeric slo1 channels as well. We recently showed that beta1 sensitizes the BK channel to microM concentrations of lithocholate (LC). Following expression of rat cerebral artery myocyte slo1 subunits ("cbv1") with beta1, beta2, beta3 or beta4 in Xenopus laevis oocytes we now demonstrate that BK beta2, beta3 and beta4 subunits fail to substitute for beta1 in providing LC-sensitivity (150 microM) to the BK channel. These findings document for the first time a rather selective steroid activation of BK channels via a particular channel accessory subunit. In addition, LC routinely activated native BK channels in myocytes freshly isolated from rat cerebral artery smooth muscle, where BK beta1 is highly expressed, while failing to do so in skeletal (flexor digitorum brevis) muscle, where BK beta1 expression is negligible. This indicates that the native environment of the BK channel sustains the LC-sensitivity distinctly provided to the BK channel by beta1 subunits. Our study indicates that LC represents a unique tool to probe the presence of functional beta1-subunits and selectively activate BK channels in tissues that highly express KCNMB1.

Alpha9 nicotinic acetylcholine receptors and the treatment of pain

Chronic pain is a vexing worldwide problem that causes substantial disability and consumes significant medical resources. Although there are numerous analgesic medications, these work through a small set of molecular mechanisms. Even when these medications are used in combination, substantial amounts of pain often remain. It is therefore highly desirable to develop treatments that work through distinct mechanisms of action. While agonists of nicotinic acetylcholine receptors (nAChRs) have been intensively studied, new data suggest a role for selective antagonists of nAChRs. alpha-Conotoxins are small peptides used offensively by carnivorous marine snails known as Conus. A subset of these peptides known as alpha-conotoxins RgIA and Vc1.1 produces both acute and long lasting analgesia. In addition, these peptides appear to accelerate the recovery of function after nerve injury, possibly through immune mediated mechanisms. Pharmacological analysis indicates that RgIA and Vc1.1 are selective antagonists of alpha9alpha10 nAChRs. A recent study also reported that these alpha9alpha10 antagonists are also potent GABA-B agonists. In the current study, we were unable to detect RgIA or Vc1.1 binding to or action on cloned GABA-B receptors expressed in HEK cells or Xenopus oocytes. We review the background, findings and implications of use of compounds that act on alpha9* nAChRs.(1).

Synthesis and P2Y receptor activity of nucleoside 5'-phosphonate derivatives

Ribose-based nucleoside 5'-diphosphates and triphosphates and related nucleotides were compared in their potency at the P2Y receptors with the corresponding nucleoside 5'-phosphonate derivatives. Phosphonate derivatives of UTP and ATP activated the P2Y(2) receptor but were inactive or weakly active at P2Y(4) receptor. Uridine 5'-(diphospho)phosphonate was approximately as potent at the P2Y(2) receptor as at the UDP-activated P2Y(6) receptor. These results suggest that removal of the 5'-oxygen atom from nucleotide agonist derivatives reduces but does not prevent interaction with the P2Y(2) receptor. Uridine 5'-(phospho)phosphonate as well as the 5'-methylenephosphonate equivalent of UMP were inactive at the P2Y(4) receptor and exhibited maximal effects at the P2Y(2) receptor that were 50% of that of UTP suggesting novel action of these analogues.

Structure-activity relationship study on Tyr9 of urotensin-II(4-11): identification of a partial agonist of the UT receptor

Urotensin-II (U-II) activates the U-II receptor (UT) to modulate a range of biological responses at both central and peripheral sites. Previous studies have demonstrated that the sequence Trp(7)-Lys(8)-Tyr(9) of the cyclic portion of the peptide is crucial for biological activity. Here, we describe a focused structure-activity study of Tyr(9) which has been replaced with a series of non-coded amino acids in the U-II(4-11) template. Thirteen analogs were synthesized and pharmacologically tested for intracellular calcium mobilization in HEK293 cells stably expressing the rat UT receptor. The results of this study demonstrated the following Tyr(9) structure-activity features: (i) the position of the OH group of the side chain is not important for biological activity, (ii) the distance of the phenol moiety from the peptide backbone and its conformational freedom are crucial for UT receptor recognition, (iii) this position is important not only for receptor occupation but also for its activation since the 3,5-diiodoTyr(9) chemical modification generated a potent partial agonist. This pharmacological activity of [3,5-diiodoTyr(9)]U-II(4-11) was confirmed in bioassay experiments performed using the rat thoracic aorta as a U-II sensitive preparation.

Estrogen receptor-beta agonist diarylpropionitrile: biological activities of R- and S-enantiomers on behavior and hormonal response to stress

Estrogens have been shown to have positive and negative effects on anxiety and depressive-like behaviors, perhaps explained by the existence of two distinct estrogen receptor (ER) systems, ERalpha and ERbeta. The ERbeta agonist, diarylpropionitrile (DPN) has been shown to have anxiolytic properties in rats. DPN exists as a racemic mixture of two enantiomers, R-DPN and S-DPN. In this study, we compared R-DPN and S-DPN for their in vitro binding affinity, ability to activate transcription in vitro at an estrogen response element, and in vivo endocrine and behavioral responses. In vitro binding studies using recombinant rat ERbeta revealed that S-DPN has a severalfold greater relative binding affinity for ERbeta than does R-DPN. Furthermore, cotransfection of N-38 immortalized hypothalamic cells with an estrogen response element-luc reporter and ERbeta revealed that S-DPN is a potent activator of transcription in vitro, whereas R-DPN is not. Subsequently, we examined anxiety-like behaviors using the open-field test and elevated plus maze or depressive-like behaviors, using the forced swim test. Ovariectomized young adult female Sprague Dawley rats treated with racemic DPN, S-DPN, and the ERbeta agonist, WAY-200070, showed significantly decreased anxiety-like behaviors in both the open-field and elevated plus maze and significantly less depressive-like behaviors in the forced swim test compared with vehicle-, R-DPN-, or propylpyrazoletriol (ERalpha agonist)-treated animals. In concordance with the relative binding affinity and transcriptional potency, these results demonstrate that the S-enantiomer is the biologically active form of DPN. These studies also indicate that estrogen's positive effects on mood, including its anxiolytic and antidepressive actions, are due to its actions at ERbeta.

Structural basis for the activation of FGFR by NCAM

The fibroblast growth factor receptor (FGFR) can be activated through direct interaction with the neural cell adhesion molecule (NCAM). The extracellular part of the FGFR consists of three immunoglobulin-like (Ig) modules, and that of the NCAM consists of five Ig and two fibronectin type III (F3) modules. NCAM-FGFR interactions are mediated by the third FGFR Ig module and the second NCAM F3 module. Using surface plasmon resonance and nuclear magnetic resonance analyses, the present study demonstrates that the second Ig module of FGFR also is involved in binding to the NCAM. The second Ig module residues involved in binding were identified and shown to be localized on the "opposite sides" of the module, indicating that when NCAMs are clustered (e.g., due to homophilic binding), high-affinity FGFR binding sites may be formed by the neighboring NCAMs.

A mathematical approach for the transactivation of hERalpha

Several reports over the last few years have documented the dose-response curve for steroid hormone induction of gene transcription as a modulated property of a given receptor-agonist complex that varies with the changing concentration of a variety of factors including: homologous receptor, co-activators, co-repressors and selected co-factors. In each report, the dose-response curves are sigmoidal and show an excellent fit with the curve generated by Michaelis-Menten kinetics. In addition, even the overall function of human oestrogen receptors (hERs) can show a similar graph for the determination of sex versus oestrogen compounds in reptiles. Thus, the kinetic properties of the simple bimolecular reaction of A+B-->C appear, surprisingly, to be sufficient to describe the dose-response curve of the multi-step process of steroid-regulated gene induction that involves several molecules. Any advance in explaining why the dose-response curve for steroid-regulated gene expression is sigmoidal would assist in understanding what parameters are key factors of the dose-response curve and can benefit in the design of new oestrogenic substances. We have constructed and analysed a multi-step model of hER-induced gene transcription that explains the multiple forms of a simple dose-response curve in an in vitro transcription system.

A cell-based assay to assess the persistence of action of agonists acting at recombinant human beta(2) adrenoceptors

INTRODUCTION

The aim was to establish a robust, 96-well, cell-based assay to assess the potency and persistence of action of agonists acting at human recombinant beta(2) adrenoceptors expressed in CHO (Chinese Hamster Ovary) cells and to compare this with published duration of action data in guinea pig isolated trachea and human bronchus.

METHODS

Cells were treated with either: (i) beta-adrenoceptor agonist for 30 min, washed and cyclicAMP (cAMP) measured 30 min later-termed 'washed' cells or, (ii) treated with solvent for 30 min, washed, and then treated with beta-adrenoceptor agonist for 30 min and cAMP measured-termed 'unwashed' cells. The 'washed' EC(50) was divided by the 'unwashed' EC(50) to determine a rightward shift concentration ratio, which was indicative of the persistence of action at the receptor.

RESULTS

At the beta(2) adrenoceptor salmeterol, carmoterol and indacaterol were resistant to washing with a concentration ratio of <5, indicating a long persistence of action, whereas formoterol, isoprenaline and salbutamol were washed out with a ratio of 32, >294 and >800 respectively, suggesting a shorter persistence of action. At beta(1) and beta(3) adrenoceptors all compounds washed out. The persistent effects of salmeterol at beta(2) following washing could be reversed by the selective beta(2) antagonist ICI 118551, suggesting continued receptor activation.

DISCUSSION

The data presented agree well with published data assessing duration of action of beta(2) agonists in human isolated bronchus and guinea pig isolated trachea. Key features are: (a) it is a 96-well format which can be used to assess many compounds in a single experiment, (b) both potency and persistence of agonist action are assessed in the same assay, (c) any effects of concentration on the persistence of action can be highlighted, and (d) it allows triage of compounds prior to tissue bath studies thus reducing the use of animal tissue.

Identification of selective and non-selective, biostable beta-amino acid agonists of recombinant insect kinin receptors from the southern cattle tick Boophilus microplus and mosquito Aedes aegypti

The multifunctional arthropod 'insect kinins' share the evolutionarily conserved C-terminal pentapeptide motif Phe-X1-X2-Trp-Gly-NH2, where X1=His, Asn, Ser, or Tyr and X2=Ser, Pro, or Ala. Eight different analogs of the insect kinin C-terminal pentapeptide active core in which the critical residues Phe 1, Pro3 and Trp 4 are replaced with beta 3-amino acid and/or their beta2-amino acid counterparts were evaluated on recombinant insect kinin receptors from the southern cattle tick, Boophilus microplus (Canestrini) and the dengue vector, the mosquito Aedes aegypti (L.). A number of these analogs previously demonstrated enhanced resistance to degradation by peptidases. Single-replacement analog beta 2 Trp 4 and double-replacement analog [beta 3 Phe 2, beta 3 Pro 3] of the insect kinins proved to be selective agonists for the tick receptor, whereas single-replacement analog beta 3 Pro 3 and double-replacement analog [beta 3 Phe, beta 3 Pro 3] were strong agonists on both mosquito and tick receptors. These biostable analogs represent new tools for arthropod endocrinologists and potential leads in the development of selective, environmentally friendly arthropod pest control agents capable of disrupting insect kinin-regulated processes.

Cooperation of the proapoptotic receptor agonist rhApo2L/TRAIL with the CD20 antibody rituximab against non-Hodgkin lymphoma xenografts

Recombinant human rhApo2L/TRAIL selectively stimulates apoptosis in various cancer cells through its receptors DR4 and DR5, and is currently in clinical trials. Preclinical studies have established antitumor activity of rhApo2L/TRAIL in models of epithelial cancers; however, efficacy in non-Hodgkin lymphoma (NHL) models is not well studied. Of 7 NHL cell lines tested in vitro, rhApo2L/TRAIL stimulated apoptosis in BJAB, Ramos RA1, and DoHH-2 cells. Rituximab, a CD20 antibody used to treat certain types of NHL, augmented rhApo2L/TRAIL-induced caspase activation in Ramos RA1 and DoHH2 but not BJAB or SC-1 cells, through modulation of intrinsic rather than extrinsic apoptosis signaling. In vivo, rhApo2L/TRAIL and rituximab cooperated to attenuate or reverse growth of tumor xenografts of all 4 of these cell lines. Depletion of natural killer (NK) cells or serum complement substantially reduced combined efficacy against Ramos RA1 tumors, suggesting involvement of antibodydependent cell- and complement-mediated cytotoxicity. Both agents exhibited greater activity against disseminated than subcutaneous BJAB xenografts, and worked together to inhibit or abolish disseminated tumors and increase survival. Moreover, rhApo2L/TRAIL helped circumvent acquired rituximab resistance of a Ramos variant. These findings provide a strong rationale for clinical investigation of rhApo2L/TRAIL in combination with rituximab as a novel strategy for NHL therapy.

Increased hepatotoxicity of tumor necrosis factor-related apoptosis-inducing ligand in diseased human liver

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in tumor cells but not in most normal cells and has therefore been proposed as a promising antitumor agent. Recent experiments suggested that isolated primary human hepatocytes but not monkey liver cells are susceptible to certain TRAIL agonists, raising concerns about the use of TRAIL in cancer treatment. Whether TRAIL indeed exerts hepatotoxicity in vivo and how this is influenced by chemotherapeutic drugs or liver disease are completely unknown. Employing different forms of recombinant TRAIL, we found that the cytokine can induce proapoptotic caspase activity in isolated human hepatocytes. However in marked contrast, these different TRAIL preparations induced little or no cytotoxicity when incubated with tissue explants of fresh healthy liver, an experimental model that may more faithfully mimic the in vivo situation. In healthy liver, TRAIL induced apoptosis only when combined with histone deacetylase inhibitors. Strikingly, however, TRAIL alone triggered massive apoptosis accompanied by caspase activation in tissue explants from patients with liver steatosis or hepatitis C viral infection. This enhanced sensitivity of diseased liver was associated with an increased expression of TRAIL receptors and up-regulation of proapoptotic Bcl-2 proteins.

CONCLUSION

These results suggest that clinical trials should be performed with great caution when TRAIL is combined with chemotherapy or administered to patients with inflammatory liver diseases.

Synthetic studies of neoclerodane diterpenes from Salvia divinorum: exploration of the 1-position

Modification of the C-1 ketone of salvinorin A (2a) produces analogues with opioid antagonist properties. Of particular significance is the finding that 1-deoxo-1,10-dehydrosalvinorin A (11a) is a moderately potent antagonist at all three opioid receptor subtypes, and that herkinorin (2b), a mu agonist, is converted to a weak antagonist by removal of the C-1 ketone (3b and 11b). These observations suggest that the ketone of 2b is a key structural feature responsible for mu agonist activity.

Pharmacological and physiological characterization of d[Leu4, Lys8]vasopressin, the first V1b-selective agonist for rat vasopressin/oxytocin receptors

Recently, we synthesized and characterized the first selective V(1b) vasopressin (VP)/oxytocin receptor agonist, d[Cha(4)]arginine vasopressin. However, this agonist was only selective for the human receptors. We thus decided to design a selective V(1b) agonist for the rodent species. We started from previous observations showing that modifying [deamino(1),Arg(8)]VP in positions 4 and 8 altered the rat VP/oxytocin receptor selectivity. We synthesized a series of 13 [deamino(1),Arg(8)]VP analogs modified in positions 4 and 8. Among them, one seemed very promising, d[Leu(4), Lys(8)]VP. In this paper, we describe its pharmacological and physiological properties. This analog exhibited a nanomolar affinity for the rat, human, and mouse V(1b) VP receptors and a strong V(1b) selectivity for the rat species. On AtT20 cells stably transfected with the rat V(1b) receptor, d[Leu(4), Lys(8)]VP behaved as a full agonist on both phospholipase C and MAPK assays. Additional experiments revealed its ability to induce the internalization of enhanced green fluorescent protein-tagged human and mouse V(1b) receptors as expected for a full agonist. Additional physiological experiments were performed to further confirm the selectivity of this peptide. Its antidiuretic, vasopressor, and in vitro oxytocic activities were weak compared with those of VP. In contrast, used at low doses, its efficiency to stimulate adrenocorticotropin or insulin release from mouse pituitary or perfused rat pancreas, respectively, was similar to that obtained with VP. In conclusion, d[Leu(4), Lys(8)]VP is the first selective agonist available for the rat V(1b) VP receptor. It will allow a better understanding of V(1b) receptor-mediated effects in rodents.

Conformation-activity relationship of neuropeptide S and some structural mutants: helicity affects their interaction with the receptor

Neuropeptide S (NPS) is the endogenous ligand of the previously orphan G-protein coupled receptor now named NPSR. The NPS-NPSR receptor system regulates important biological functions such as sleep/waking, locomotion, anxiety and food intake. Recently, exhaustive Ala scan and d-amino acid scan studies, together with systematic N- and C-terminal truncation, led to the identification of key residues for biological activity. Because conformational preferences might also play an important role, we undertook a detailed conformational analysis of NPS and several analogues in solution. We show that helicity induced by substitution of three flexible residues in the 5-13 regulatory region abolishes biological activity. A parallel pharmacological and conformational study of single and multiple substitutions of glycines 5, 7, and 9 showed that helicity can be tolerated in the C-terminal part of the peptide but not around Gly7. The identification of hNPSR partial agonists heralds the possibility of designing pure NPS receptor antagonists.

Subunit-Specific Agonist Activity at NR2A-, NR2B-, NR2C-, and NR2D-ContainingN-Methyl-d-aspartate Glutamate Receptors

The four N-methyl-d-aspartate (NMDA) receptor NR2 subunits (NR2A-D) have different developmental, anatomical, and functional profiles that allow them to serve different roles in normal and neuropathological situations. Identification of subunit-selective NMDA receptor agonists, antagonists, or modulators could prove to be both valuable pharmacological tools as well as potential new therapeutic agents. We evaluated the potency and efficacy of a wide range of glutamate-like compounds at NR1/NR2A, NR1/NR2B, NR1/NR2C, and NR1/NR2D receptors. Twenty-five of 53 compounds examined exhibited agonist activity at the glutamate binding site of NMDA receptors. Concentration-response relationships were determined for these agonists at each NR2 subunit. We find consistently higher potency at the NR2D subunit for a wide range of dissimilar structures, with (2S,4R)-4-methylglutamate (SYM2081) showing the greatest differential potency between NR2A- and NR2D-containing receptors (46-fold). Analysis of chimeric NR2A/D receptors suggests that enhanced agonist potency for NR2D is controlled by residues in both of the domains (Domain1 and Domain2) that compose the bilobed agonist binding domain. Molecular dynamics (MD) simulations comparing a crystallography-based hydrated NR1/NR2A model with a homology-based NR1/NR2D hydrated model of the agonist binding domains suggest that glutamate exhibits a different binding mode in NR2D compared with NR2A that accommodates a 4-methyl substitution in SYM2081. Mutagenesis of functionally divergent residues supports the conclusions drawn based on the modeling studies. Despite high homology and conserved atomic contact residues within the agonist binding pocket of NR2A and NR2D, glutamate adopts a different binding orientation that could be exploited for the development of subunit selective agonists and competitive antagonists.

Fatty acyl amides of endogenous tetrahydroisoquinolines are active at the recombinant human TRPV1 receptor

The SAR of capsazepine revealed that tetrahydroisoquinoline (TIQ) moiety is a core pharmacophore of TRPV1 activity. This implied that conjugates of endogenous TIQs with fatty acids would be active at TRPV1 receptors. Six such compounds were synthesized and tested for calcium mobilization at recombinant TRPV1 receptors overexpressed in HEK293 cells. Three compounds showed partial TRPV1 agonism with EC(50) values in the low micromolar range and maximal efficacies between 25% and 55% of capsaicin.

Acetic acid opens large-conductance Ca2+-activated K+ channels in guinea pig detrusor smooth muscle cells

Acetic acid was found to have actions on urinary bladder smooth muscle in our routine ion channel screening assays. Numerous studies have examined the mechanisms of bladder irritation by acetic acid; however, the direct effect of acetic acid on ion channels in detrusor smooth muscle cells has not been evaluated. We used whole-cell patch-clamp techniques to examine the effect of acetic acid on large-conductance Ca2+-activated K+ channels (BKCa) from guinea pig detrusor smooth muscle cells and CHO cells expressing recombinant human BKCaalphabeta1 (CHO BKCaalphabeta1) and human BKCaalpha (CHO BKCaalpha). Acetic acid activated BKCa currents in a concentration-dependent (0.01% to 0.05% v/v) manner in all the cell systems studied. Acetic acid (0.05%) increased BKCa current at +30 mV by 2764+/-918% (n=8) in guinea pig detrusor smooth muscle cells. Acetic acid (0.03%) shifted the V1/2 of conductance-voltage curve by 64+/-14 (n=5), 128+/-14 (n=5), and 126+/-12 mV (n=4) in CHO BKCaalpha, CHO BKCaalphabeta1 and detrusor smooth muscle cells, respectively. This effect of acetic acid was found to be independent of pH and was also not produced by its salt form, sodium acetate. Automated patch-clamp experiments also showed similar activation of CHO BKCaalphabeta1 by acetic acid. In conclusion, acetic acid directly activates BKCa channels in detrusor smooth muscle cells. This novel study necessitates caution while interpreting the results from acetic acid bladder irritation model.

Structure-activity relationship of uridine 5'-diphosphoglucose analogues as agonists of the human P2Y14 receptor

UDP-glucose (UDPG) and derivatives are naturally occurring agonists of the Gi protein-coupled P2Y14 receptor, which occurs in the immune system. We synthesized and characterized pharmacologically novel analogues of UDPG modified on the nucleobase, ribose, and glucose moieties, as the basis for designing novel ligands in conjunction with modeling. The recombinant human P2Y14 receptor expressed in COS-7 cells was coupled to phospholipase C through an engineered Galpha-q/i protein. Most modifications of the uracil or ribose moieties abolished activity; this is among the least permissive P2Y receptors. However, a 2-thiouracil modification in 15 (EC50 49 +/- 2 nM) enhanced the potency of UDPG (but not UDP-glucuronic acid) by 7-fold. 4-Thio analogue 13 was equipotent to UDPG, but S-alkylation was detrimental. Compound 15 was docked in a rhodposin-based receptor homology model, which correctly predicted potent agonism of UDP-fructose, UDP-mannose, and UDP-inositol. The hexose moiety of UDPG interacts with multiple H-bonding and charged residues and provides a fertile region for agonist modification.

N6-methoxy-2-alkynyladenosine derivatives as highly potent and selective ligands at the human A3 adenosine receptor

A new series of N6-methoxy-2-(ar)alkynyladenosine derivatives has been synthesized and tested at the human recombinant adenosine receptors. Binding studies demonstrated that the new compounds possess high affinity and selectivity for the A3 subtype. Among them, compounds bearing an N-methylcarboxamido substituent in the 4'-position showed the highest A3 affinity and selectivity. In particular, the N6-methoxy-2-p-acetylphenylethynylMECA (40; Ki A3 = 2.5 nM, A3 selectivity versus A1 = 21 500 and A2A = 4200) results in one of the most potent and selective agonists at the human A3 adenosine receptor reported so far. Furthermore, functional assay, performed with selected new compounds, revealed that the presence of an alkylcarboxamido group in the 4'-position seems to be essential to obtain full agonists at the A3 subtype. Finally, results of molecular docking analysis were in agreement with binding and functional data and could explain the high affinity and potency of the new compounds.

A comparison of the pharmacological properties of guinea-pig and human recombinant 5-HT4 receptors

BACKGROUND AND PURPOSE

5-HT(4) receptor agonists are used therapeutically to treat disorders of reduced gastrointestinal motility. Since such compounds are evaluated in guinea-pigs, we cloned, expressed and pharmacologically characterized the guinea-pig 5-HT(4) and human 5-HT(4(b)) splice variant, which share 95% homology. The functional properties of guinea-pig 5-HT(4(b)) receptors were compared with native receptors in guinea-pig colon.

EXPERIMENTAL APPROACH

Membrane radioligand binding and whole cell cAMP accumulation assays were used to determine the affinities, potencies and intrinsic activities (IA). Contraction of the guinea-pig distal colon longitudinal muscle myenteric plexus preparation (LMMP) was monitored to evaluate functional activity.

KEY RESULTS

pK(i) values for guinea-pig and human recombinant receptors, and guinea-pig striatum 5-HT(4) receptors, were in agreement, as were the potency and IA values for guinea-pig and human 5-HT(4) receptors expressed at a similar density ( approximately 0.2 pmol mg(-1) protein). Tegaserod was a potent (pEC(50)=8.4 and 8.7, respectively), full agonist at both guinea-pig and human 5-HT(4) receptors. In contrast, in the LMMP preparation, tegaserod was a potent, partial agonist (pEC(50)=8.2; IA=66%).

CONCLUSIONS AND IMPLICATIONS

Close agreement between the pharmacological properties of guinea-pig and human 5-HT(4) receptors support the use of guinea-pig model systems for the identification of 5-HT(4) receptor therapeutics. However, the mechanisms underlying the different agonist properties of tegaserod in recombinant and isolated tissue preparations, and the extent to which these impact the clinical efficacy of tegaserod as a prokinetic agent, remain to be determined.

The cellular Toll-like receptor 4 antagonist E5531 can act as an agonist in horse whole blood

Sepsis and endotoxaemia are important causes of morbidity and mortality in humans. Research on sepsis focuses on rodent models most of which are poorly responsive to lipopolysaccharide (LPS), and thus do not mimic very well the high sensitivity of humans. Therefore, there is a need to develop more clinically relevant models. Horses suffer from a similar endotoxaemic syndrome to humans with high morbidity and mortality. LPS analogues that act as antagonists at Toll-like receptor 4 (TLR4) are being developed as novel treatments for endotoxaemia. Due to differences in recognition of ligands by TLR4 from different mammalian species, individual LPS molecules may act as agonists in some species and antagonists in others. The synthetic lipid A analogue E5531 is an antagonist at TLR4 in humans and mice, but its effects at TLR4 from other species are unknown. In the studies reported here, Escherichia coli LPS is a full agonist on equine bone marrow macrophage-like cells and its effects are antagonised by E5531. Similarly, E. coli LPS is an agonist and E5531 an antagonist on monocytes isolated from peripheral blood of healthy horses and human embryonic kidney (HEK) cells, transiently transfected to express horse TLR4 and its associated cell surface proteins MD2 and CD14. In contrast, both E. coli LPS and E5531 behave as agonists in horse whole blood by inducing production of equivalent amounts of the inflammatory mediator prostaglandin. This finding suggests that modification of E5531 may occur in whole blood, for example, deacylation, which alters its activity. This comparative study has revealed a novel pharmacological action of E5531 and emphasises the importance of extending studies of this nature beyond the normal rodent models.

Novel agonistic action of mustard oil on recombinant and endogenous porcine transient receptor potential V1 (pTRPV1) channels

Neurogenic components play a crucial role in inflammation and nociception. Mustard oil (MO) is a pungent plant extract from mustard seed, horseradish and wasabi, the main constituent of which is allylisothiocyanate. We have characterized the action of MO on transient receptor potential V1 (TRPV1), a key receptor of signal transduction pathways in the nociceptive system, using fura-2-based [Ca(2+)](i) imaging and the patch-clamp technique in a heterologous expression system and sensory neurons. In human embryonic kidney (HEK) 293 cells expressing porcine TRPV1 (pTRPV1), MO evoked increases of [Ca(2+)](i) in a concentration-dependent manner. A high concentration of MO elicited irreversible cell swelling. Capsazepine, ruthenium red and iodoresiniferatoxin dose-dependently suppressed the MO-induced [Ca(2+)](i) increase. MO elicited outward rectified currents in pTRPV1-expressing HEK 293 cells with a reversal potential similar to that of capsaicin. [Ca(2+)](i) responses to MO were completely abolished by the removal of external Ca(2+). MO simultaneously elicited an inward current and increase of [Ca(2+)](i) in the same cells, indicating that MO promoted Ca(2+) influx through TRPV1 channels. In cultured porcine dorsal root ganglion (DRG) neurons, MO elicited a [Ca(2+)](i) increase and inward current. Among DRG neurons responding to MO, 85% were also sensitive to capsaicin. The present data indicate that MO is a novel agonist of TRPV1 channels, and suggest that the action of MO in vivo may be partly mediated via TRPV1. These results provide an insight into the TRPV1-mediated effects of MO on inflammation and hyperalgesia.

The respective and combined anticoagulant effects of recombinant human activated protein C, melagatran and heparins using CAT

INTRODUCTION

Combinations of anticoagulants might be beneficial in some patients with sepsis, but most anticoagulants require specific clotting assays for monitoring. Thrombin generation assay, however, is a global function test of hemostasis.

MATERIALS AND METHODS

We performed an in vitro investigation of the respective effects of recombinant human activated protein C (rhAPC) alone and in combination with either melagatran (a new direct thrombin inhibitor), unfractionated heparin (UH) or low molecular weight heparin (LMWH) in varying concentrations on the thrombin generation (TG) using the calibrated automated thrombography.

RESULTS

RhAPC, UH, LMWH and melagatran dose-dependently prolonged the lag time and the time to peak, and significantly suppressed the endogenous thrombin potential (ETP). Combined application of rhAPC with either melagatran, UH or LMWH induced an additive prolongation of the lag time; this effect was more pronounced in a combination of rhAPC with UH or LMWH.

CONCLUSION

In our in vitro study adding either melagatran, UH or LMWH augmented the capacity of rhAPC to suppress thrombin generation in human plasma. These findings suggest that patients with severe sepsis might benefit from a treatment with combinations of anticoagulant agents.

Prophylactic treatment with recombinant Eimeria protein, alone or in combination with an agonist cocktail, protects mice from Banzi virus infection

A recombinant Eimeria protozoan protein antigen (rEA) has been shown to have antitumor and antiviral activity. The purpose of this study was to determine the effect of rEA treatment alone or in combination with an agonist cocktail consisting of granulocyte macrophage colony stimulating factor (GM-CSF), interferon gamma (IFN-gamma), interleukin 4 (IL-4), and anti CD-40 antibody, in the treatment of Banzi virus (BV) disease in BALB/c mice. Treatment with rEA resulted in a significant increase in survival, weight gain, and mean day to death in BV-infected mice and resulted in a significant decrease in brain virus titer. Treatment with rEA, in combination with a 4-agonist cocktail, improved disease parameters to a greater degree than rEA treatment alone. The effect of treatment with a reduced concentration of agonist cocktail or fewer components of the agonist cocktail, in combination with rEA, on disease outcome in BV-infected mice was also investigated. Treatment with rEA, alone or in combination with agonist cocktail, 24h after virus challenge did not improve disease. Treatment with rEA, alone or in combination with an agonist cocktail, is efficacious for the prophylaxis of BV infection in mice.

X-ray Crystal Structures of the Estrogen-related Receptor-γ Ligand Binding Domain in Three Functional States Reveal the Molecular Basis of Small Molecule Regulation

X-ray crystal structures of the ligand binding domain (LBD) of the estrogen-related receptor-gamma (ERRgamma) were determined that describe this receptor in three distinct states: unliganded, inverse agonist bound, and agonist bound. Two structures were solved for the unliganded state, the ERRgamma LBD alone, and in complex with a coregulator peptide representing a portion of receptor interacting protein 140 (RIP140). No significant differences were seen between these structures that both exhibited the conformation of ERRgamma seen in studies with other coactivators. Two structures were obtained describing the inverse agonist-bound state, the ERRgamma LBD with 4-hydroxytamoxifen (4-OHT), and the ERRgamma LBD with 4-OHT and a peptide representing a portion of the silencing mediator of retinoid and thyroid hormone action protein (SMRT). The 4-OHT structure was similar to other reported inverse agonist bound structures, showing reorientation of phenylalanine 435 and a displacement of the AF-2 helix relative to the unliganded structures with little other rearrangement occurring. No significant changes to the LBD appear to be induced by peptide binding with the addition of the SMRT peptide to the ERRgamma plus 4-OHT complex. The observed agonist-bound state contains the ERRgamma LBD, a ligand (GSK4716), and the RIP140 peptide and reveals an unexpected rearrangement of the phenol-binding residues. Thermal stability studies show that agonist binding leads to global stabilization of the ligand binding domain. In contrast to the conventional mechanism of nuclear receptor ligand activation, activation of ERRgamma by GSK4716 does not appear to involve a major rearrangement or significant stabilization of the C-terminal helix.

A small molecule agonist of an integrin, alphaLbeta2

The binding of integrin alpha(L)beta(2) to its ligand intercellular adhesion molecule-1 is required for immune responses and leukocyte trafficking. Small molecule antagonists of alpha(L)beta(2) are under intense investigation as potential anti-inflammatory drugs. We describe for the first time a small molecule integrin agonist. A previously described alpha/beta I allosteric inhibitor, compound 4, functions as an agonist of alpha(L)beta(2) in Ca(2+) and Mg(2+)and as an antagonist in Mn(2+). We have characterized the mechanism of activation and its competitive and noncompetitive inhibition by different compounds. Although it stimulates ligand binding, compound 4 nonetheless inhibits lymphocyte transendothelial migration. Agonism by compound 4 results in accumulation of alpha(L)beta(2) in the uropod, extreme uropod elongation, and defective de-adhesion. Small molecule integrin agonists open up novel therapeutic possibilities.

Molecular and cellular regulation of neurotensin receptor under acute and chronic agonist stimulation

Neurotensin is a tridecapteptide acting mostly in the brain and gastrointestinal tract. NT binds two G protein coupled receptors (GPCR), NTS1 and NTS2, and a single transmembrane domain receptor, NTS3/gp95/sortilin receptor. NTS1 mediates the majority of NT action in neurons and the periphery. Like many other GPCRs, upon agonist stimulation, NTS1 is internalized, endocytosed, and the cells are desensitized. It is tacitly acknowledged that the intensity and the lasting of cellular responses to NT are dependent on free and functional NTS1 at the cell surface. Understanding how NTS1 expression is regulated at the membrane should provide a better comprehension towards its function. This review analyzes and discusses the current cellular and molecular mechanisms affecting the expression of NTS1 at the cellular membrane upon acute and chronic NT stimulation.

Molecular activation of PPARγ by angiotensin II type 1-receptor antagonists

OBJECTIVE AND DESIGN

Elevated blood pressure and insulin resistance are strongly associated in patients. We explored the potential for the anti-hypertensive angiotensin II type 1-receptor (ATR(1)) antagonists to improve insulin sensitivity through modulation of the nuclear receptor PPARgamma, in vitro and in vivo compared to the potent insulin sensitizer, rosiglitazone.

METHODS

PPARgamma modulation by ATR(1) antagonists was measured first by direct recruitment of PGC-1, followed by trans-activation reporter assays in cells, and promotion of adipogenesis in fibroblast and pre-adipocyte cell lines. Improvement of insulin sensitivity was measured as changes in levels of glucose, insulin, and adiponectin in ob/ob mice.

RESULTS

Telmisartan, candesartan, irbesartan, and losartan (but not valsartan or olmesartan) each served as bona fide PPARgamma ligands in vitro, with EC(50) values between 3 and 5 micro mol/l. However, only telmisartan, and to a lesser extent candesartan, resulted in significant PPARgamma agonism in cells. In vivo, although rosiglitazone significantly lowered both glucose (33%, p<0.01) and insulin (61%, p<0.01) levels and increased expression of adiponectin (74%, p<0.001), sartan treatment had no effect.

CONCLUSIONS

Many members of the sartan family of ATR(1) antagonists are PPARgamma ligands in cell-free assays but their modulation of PPARgamma in cells is relatively weak. Furthermore, none appear to improve insulin sensitivity in a rodent model under conditions where other insulin sensitizers, including rosiglitazone, do. These results question whether reported effects of sartans on insulin sensitivity may be through other means, and should guide further efforts to develop dual agents to treat hypertension and insulin resistance.

IL-2 in vivo activities and antitumor efficacy enhanced by an anti-IL-2 mAb

IL-2 is a potent immunostimulant and has been tested for clinical use, including in immunotherapy for cancers and HIV infection. Here we show that a widely used neutralizing anti-murine IL-2 mAb (S4B6) exhibits unexpected activities that enhance the treatment effects of IL-2 in vivo. Coinjection of the anti-IL-2 mAb with a plasmid carrying murine IL-2 cDNA significantly increased the serum IL-2 levels and induced a substantial increase in the division of CD8+ T and NK1.1(high) cells in vivo. Injection of the mAb premixed with recombinant murine IL-2 showed the same enhanced effect. A 5-day treatment with the anti-IL-2 mAb alone gradually increased the CD44(high)CD8+ population, and the increased population was maintained for >300 days, suggesting that the mAb can gradually maintain and potentially enhance the bioactivity of endogenous IL-2 for extended periods. Furthermore, combined treatment with the anti-IL-2 mAb plus the IL-2 plasmid markedly enhanced Ag-specific CTL activity in vivo and partially protected mice from tumor metastasis to the lungs, compared with the anti-IL-2 mAb or IL-2 plasmid alone. These results demonstrated IL-2-enhancing effects of the anti-IL-2 mAb in vivo and suggest that combining a neutralizing anti-IL-2 Ab with IL-2 gene delivery might be used effectively to enhance IL-2 functions in clinical applications.

2,3,7-Trisubstituted pyrazolo[1,5-d][1,2,4]triazines: Functionally selective GABAA α3-subtype agonists

Novel synthetic routes have been devised for the preparation of previously inaccessible 2,3,7-trisubstituted pyrazolo[1,5-d][1,2,4]triazines 2. These compounds are high affinity ligands for the GABA(A) benzodiazepine binding site and some analogues show functional selectivity for agonism at alpha3-containing receptors over alpha1-containing receptors with the lead compound being 32.

Mapping the Melatonin Receptor. 7. Subtype Selective Ligands Based on β-SubstitutedN-Acyl-5-methoxytryptamines and β-SubstitutedN-Acyl-5-methoxy-1-methyltryptamines

A series of beta-substituted and beta,beta-disubstituted N-acyl 5-methoxy-1-methyltryptamines and 5-methoxytryptamines have been prepared as melatonin analogues to investigate the nature of the binding site of the melatonin receptor. The affinity of analogues was determined in a radioligand binding assay using cloned human MT(1) and MT(2) receptor subtypes expressed in NIH 3T3 cells. Agonist and antagonist potency of all analogues was measured using the pigment aggregation response of a clonal line of Xenopus laevis melanophores. beta-Methylmelatonin (17a) and beta,beta-dimethylmelatonin (17b), though showing a slight decrease in binding at human receptors, show an increase in potency on Xenopus. N-Butanoyl 5-methoxy-1-methyl-beta,beta-trimethylenetryptamine (12c) is an antagonist at human MT(1) receptors but an agonist at MT(2), while N-butanoyl 5-methoxy-1-methyl-beta,beta-tetramethylenetryptamine (13c) is an antagonist at MT(1) but had no action at MT(2) and is one of the first examples of an MT(1) selective antagonist.

Synthetic 19-nortestosterone derivatives as estrogen receptor alpha subtype-selective ligands induce similar receptor conformational changes and steroid receptor coactivator recruitment than natural estrogens

The binding of estradiol (E(2)) to estrogen receptors (ER) is followed by conformational changes resulting in coactivator or corepressor recruitment that influences gene transcription. A series of synthetic A-ring reduced 19-nortestosterone-derived progestins has the capacity to selectively bind and activate transcription through the ERalpha. Herein, the molecular mechanisms involved in ER subtype-selective interactions of these compounds as assessed by their effects upon both ERalpha and ERbeta structural conformation and their ability to induce recruitment of steroid receptor coactivator-1 (SRC-1) to ERalpha were investigated. The results demonstrated that all synthetic A-ring 3beta,5alpha-tetrahydro-reduced derivatives of 19-nortestosterone induced an ERalpha trypsin digestion pattern similar to that seen with E(2), without effects upon ERbeta. In addition, these compounds had the ability to recruit SRC-1 to the ligand-binding domain of ERalpha similar to E(2). Our data indicate that A-ring 3beta,5alpha-tetrahydro-reduced 19-nortestosterone-derived progestins behave as selective ERalpha agonists with ligand-receptor structural and functional responses similar to those induced with natural E(2).

Large-scale preparation of biologically active mouse and rat leptins and their L39A/D40A/F41A muteins which act as potent antagonists

Expression plasmids encoding mouse and rat leptins and their L39A/D40A/F41A muteins were prepared. The proteins were expressed in Escherichia coli, refolded and purified to homogeneity, yielding electrophoretically pure, over 98% monomeric protein. Circular dichroism (CD) analysis revealed that the mutations hardly affect the leptins' secondary structure, and they were similar to previously reported CD spectra for human leptin. Both mouse and rat leptins were biologically active in promoting proliferation in BAF/3 cells stably transfected with the long form of human leptin receptor. The mutations did not change the binding properties to BAF/3 cells as compared, respectively, to non-mutated mouse, rat or human leptins, or their ability to form 1:1 complexes with the leptin-binding domain of chicken leptin receptor. In contrast, their biological activity, tested in a BAF/3 proliferation assay, was abolished and both became potent antagonists. As the LDF (amino acids 39-41) sequence is preserved in all known leptins, the present results substantiate the hypothesis that this sequence plays a pivotal role in leptins' site III and that interaction of leptin with its receptors resembles the corresponding interactions of interleukin-6 and granulocyte colony-stimulating factor their receptors.

FRET-based monitoring of conformational change of the β2 adrenergic receptor in living cells

The beta(2) adrenergic receptor (beta(2)AR) is a G protein-coupled receptor that is selective to epinephrine. We demonstrate herein monitoring of an agonist-induced conformational change of beta(2)AR in living cells. The monitoring method is based on fluorescence resonance energy transfer from a cyan fluorescent protein (CFP) to a biarsenical fluorophore, FlAsH, attached to the C-terminus, and the third intracellular loop (ICL3), respectively. Recombinant beta(2)ARs exhibited agonist-induced increases in the FlAsH/CFP emission ratio, indicating that the ICL3 approached the C-terminus upon activation. Since the emission ratio changes were on a time scale of seconds, the conformational change of beta(2)AR in living cells was more rapid than that of purified beta(2)AR measured in vitro. Interestingly, the direction of the emission ratio change of beta(2)AR was opposite to that of the norepinephrine-responsive alpha(2A) adrenergic receptor reported recently. It was suggested that this discrepancy corresponds directly to the diametric biological functions, i.e., the activation or inactivation of adenylyl cyclase.

Agonist activity of naloxone benzoylhydrazone at recombinant and native opioid receptors

1. In the present study, we examined the pharmacological activity of the putative kappa3-opioid receptor agonist naloxone benzoylhydrazone (NalBzoH) at recombinant human opioid receptors individually expressed in Chinese hamster ovary (CHO) cells and native opioid receptors present in rat striatum. 2. At the mu-opioid receptor (MOR), NalBzoH stimulated guanosine-5'-O-(3-[35S]thio)triphosphate ([35S]GTPgammaS) binding (pEC50=8.59) and inhibited cyclic AMP accumulation (pEC50=8.74) with maximal effects (Emax) corresponding to 55 and 65% of those obtained with the MOR agonist DAMGO, respectively. The MOR antagonist CTAP blocked the stimulatory effects of NalBzoH and DAMGO with similar potencies. 3. At the kappa-opioid receptor (KOR), NalBzoH stimulated [35S]GTPgammaS binding (pEC50=9.70) and inhibited cyclic AMP formation (pEC50=9.45) as effectively as the selective KOR agonist (-)-U-50,488. The NalBzoH effect was blocked by the KOR antagonist nor-binaltorphimine (nor-BNI) (pKi=10.30). 4. In CHO cells expressing the delta-opioid receptor (DOR), NalBzoH increased [35S]GTPgammaS binding (pEC50=8.49) and inhibited cyclic AMP formation (pEC50=8.61) almost as effectively as the DOR agonist DPDPE. Naltrindole (NTI), a selective DOR antagonist, completely blocked the response to NalBzoH (pKi of 10.40). 5. In CHO cells expressing the nociceptin/orphanin FQ (N/OFQ) receptor (NOP), NalBzoH failed to exert agonist effects and antagonized the agonist-induced receptor activation. 6. When compared to other opioid receptor ligands, NalBzoH showed an efficacy that was lower than that of morphine at MOR, but higher at KOR and DOR. 7. In rat striatum, NalBzoH enhanced [35S]GTPgammaS binding and inhibited adenylyl cyclase activity. These effects were antagonized by either CTAP, nor-BNI or NTI, each antagonist blocking a fraction of the NalBzoH response. 8. These data demonstrate that NalBzoH displays agonist activity at MOR, DOR and KOR expressed either in a heterologous cell system or in a native environment.

Design, synthesis, and biological activity of N6-substituted-4'-thioadenosines at the human A3 adenosine receptor

A large series of N6-substituted-4'-thioadenosines were synthesized starting from D-gulonic-gamma-lactone, and structure-activity relationships were studied at the human A3 and other subtypes of adenosine receptors (ARs). 2-Chloro-substituted and 2-H analogues were compared. 2-Chloro-N6-methyl-4'-thioadenosine 19b was a highly potent and selective agonist (Ki=0.8+/-0.1 nM in binding) at the A3AR, and displayed the same relative efficacy in receptor activation as a known full agonist, Cl-IB-MECA. Most of N6-substituted-4'-thioadenosines were less potent in binding than the corresponding N6-substituted-adenosines or N6-substituted-4'-thioadenosine-5'-uronamides. N6-(3-Iodobenzyl) derivative 19g was demonstrated to be an A3AR-selective partial agonist displaying a Ki value of 3.2 nM.