Σ1 Receptor Ligands Research Articles

N-Methyl-D-Aspartate and σ-Ligands Change the Production of Interleukins 8 and 10 in Lymphocytes through Modulation of the NMDA Glutamate Receptor

Human T lymphocytes express both ionotropic and metabotropic glutamate receptors that control immune responses, cell activation, maturation and death. In this study, we examined the effect of N-methyl-D-aspartate (NMDA) and σ1-receptor ligands on the secretion of the proinflammatory chemokine interleukin 8 (IL-8) and the anti-inflammatory cytokine interleukin 10 (IL-10) in human leukemia Jurkat cells and peripheral blood lymphocytes (PBLs). We have shown that NMDA increased IL-8 and decreased IL-10 secretion and that σ-ligands modulated the action of NMDA. Moreover, the effects of NMDA and σ-ligands were interrelated with the nitric oxide (NO) content, suggesting that the intracellular concentration of NO could play a major role in the synthesis of cytokines. Western blots against the NR2A and NR2B subunits of the NMDA glutamate receptor revealed that long-term (48 h) treatment of PBLs with glutamate at concentrations within normal plasma levels (1 × 10^–5M), in contrast to low concentrations (0.3 × 10^–6M), downregulates the NR2A subunit, probably by internalization. Furthermore, we found that PBLs with noninternalized NR2A secreted less IL-10 than lymphocytes with downregulated NR2A; under these conditions, the transcriptional activity of NF-κB was increased whereas the transcriptional activity of c-Fos was decreased. These findings implicate that the activities of NF-κB and c-Fos control the expression of the IL8 and IL10 genes, depending on the subunit composition of the NMDA receptor. In conclusion, we suggest that lymphocytes express an active NMDA receptor only in a low-glutamate milieu.

New N-substituted 9-azabicyclo[3.3.1]nonan-3α-yl phenylcarbamate analogs as σ2 receptor ligands: Synthesis, in vitro characterization, and evaluation as PET imaging and chemosensitization agents

A series of N-substituted 9-azabicyclo[3.3.1]nonan-3α-yl phenylcarbamate analogs were synthesized. Among them, WC-26 and WC-59 were identified as the most potent σ 2 receptor ligands ( K i = 2.58 and 0.82 nM, respectively) with high selectivity against σ 1 ( K i of σ 1/ σ 2 ratio = 557 and 2087, respectively). [ 18F] WC- 59 was radiolabeled via a nucleophilic substitution of a mesylate precursor by [ 18F]fluoride, and in vitro direct binding studies of [ 18F] WC- 59 were conducted using membrane preparations from murine EMT-6 solid breast tumors. The results indicate that [ 18F] WC-59 binds specifically to σ 2 receptors in vitro ( K d = ∼2 nM). Biodistribution studies of [ 18F] WC- 59 in EMT-6 tumor-bearing mice indicated that the tracer was a less suitable candidate for clinical imaging studies than existing F-18 labeled σ 2 receptor ligands. The ability of WC- 26 to enhance the cytotoxic effects of the chemotherapy drug, doxorubicin, was evaluated in cell culture using the mouse breast tumor EMT-6 and the human tumor MDA-MB435. WC- 26 greatly increased the ability of doxorubicin to kill these two tumor cell lines in vitro. These results indicate that WC- 26 is potentially a useful chemosensitizer for the treatment of cancer when combined with conventional chemotherapeutics.

Dual DAT/σ1 receptor ligands based on 3-(4-(3-(bis(4-fluorophenyl)amino)propyl)piperazin-1-yl)-1-phenylpropan-1-ol

Ester analogs of (±)3-(4-(3-(bis(4-fluorophenyl)amino)propyl)piperazin-1-yl)-1-phenylpropan-1-ol were synthesized and evaluated for binding at DAT, SERT, NET, and σ1 receptors, and compared to GBR 12909 and several known σ1 receptor ligands. Most of these compounds demonstrated high affinity ( K i = 4.3–51 nM) and selectivity for the DAT among the monoamine transporters. S- and R-1-(4-(3-(bis(4-fluorophenyl)amino)propyl)piperazin-1-yl)-3-phenylpropan-2-ol were also prepared wherein modest enantioselectivity was demonstrated at the DAT. However, no enantioselectivity at σ1 receptors was observed and most of the ester analogs of the more active S-enantiomer showed comparable binding affinities at both DAT and σ1 receptors with a maximal 16-fold DAT/σ1 selectivity.

An update on the development of drugs for neuropsychiatric disorders: focusing on the σ1 receptor ligand

The σ1 receptor is an intracellular molecule that shares no homology with any mammalian proteins. σ1 receptors normally localize at the endoplasmic reticulum and regulate a variety of signal transductions including intracellular Ca2+ dynamics and neurotrophic factor signaling. In the brain, σ1 receptors are known to regulate the activity of diverse ion channels via protein–protein interactions. Accumulated evidences strongly indicate that the activation/upregulation of σ1 receptors promotes the neuronal differentiation as well as a robust antiapoptotic action. In animals, σ1 receptor agonists exhibit an antidepressant-like action. Furthermore, the agonists enhanced neuronal survival eventhough they were administered several hours after a brain ischemia. Thus, primary clinical targets of σ1 receptor ligands are proposed to include stroke, neurodegenerative disorders and depression. Ligands for the σ1 receptor may constitute a new class of therapeutic drugs targeting an endoplasmic reticular protein.

IN VIVO IMAGING IN A MURINE MODEL OF GLIOBLASTOMA

To use in vivo imaging methods in mice to quantify intracranial glioma growth, to correlate images and histopathological findings, to explore tumor marker specificity, to assess effects on cortical function, and to monitor effects of chemotherapy. Mice with DBT glioma cell tumors implanted intracranially were imaged serially with a 4.7-T small-animal magnetic resonance imaging (MRI) scanner. MRI tumor volumes were measured and correlated with postmortem histological findings. Different nonspecific and specific positron emission tomography radiopharmaceuticals, [18F]2-fluoro-2-deoxy-d-glucose, [18F]3'-deoxy-3'-fluorothymidine, or [11C]RHM-I, a sigma2-receptor ligand, were visualized with microPET (CTI-Concorde MicroSystems LLC, Knoxville, TN). Intrinsic optical signals were imaged serially during contralateral whisker stimulation to study the impact of tumor growth on cortical function. Other groups of mice were imaged serially with MRI after one or two doses of the antimitotic N,N'-bis(2-chloroethyl)-N-nitrosourea (BCNU). MRI and histological tumor volumes were highly correlated (r2 = 0.85). Significant binding of [11C]RHM-I was observed in growing tumors. Over time, tumors reduced and displaced (P # 0.001) whisker-activated intrinsic optical signals but did not change intrinsic optical signals in the contralateral hemisphere. Tumor growth was delayed 7 days after a single dose of BCNU and 18 days after two doses of BCNU. Mean tumor volume 15 days after DBT implantation was significantly smaller for treated mice (1- and 2-dose BCNU) compared with controls (P = 0.0026). Mouse MRI, positron emission tomography, and optical imaging provide quantitative and qualitative in vivo assessments of intracranial tumors that correlate directly with tumor histological findings. The combined imaging approach provides powerful multimodality assessments of tumor progression, effects on brain function, and responses to therapy.

Is the σ2 Receptor a Histone Binding Protein?

Starting from the high affinity sigma(2) receptor ligand 2, (PB28), we synthesized amino derivative 4 and coupled it to an NHS-ester activated sepharose stationary phase column to elute a crude protein prepared by lysed human SK-N-SH neuroblastoma cells. We characterized the SDS-PAGE gel electrophoresis stained bands by MALDI-MS and LC-MS-MS analysis. The MASCOT MS-MS ion search program led to the identification of the protein components. The six eluted proteins had a molecular weight ranging from 13 kDa to 26 kDa and were human histone proteins. A human 40S ribosomal protein S3 (SwissProt accession number: P23396) was also identified as a comigrated band. The human histone proteins that were characterized were H3.3A histone (NCBI accession number: 51859376), H2B histone (NCBI accession number: 1568557), H2A.5 histone (NCBI accession number: 70686), H1 (NCBI accession number: 22770677), and H2.1 histone (SwissProt accession number: P16403). These results disclosed a dual hypothesis about the sigma(2) receptor, that is, that it is formed by histones or that the sigma(2) ligands also bind histone proteins.

σ1 Receptor Ligands and Related Neuroactive Steroids Interfere with the Cocaine-Induced State of Memory

The present series of experiments examined the involvement of the sigma(1) receptor and related neuroactive steroids in the memory state induced by a very low dose of cocaine. Using a modified passive avoidance procedure in mice, we examined whether cocaine induces state-dependent (StD) learning. Animals trained and tested with saline or the same dose of cocaine (0.1 or 0.3 mg/kg) showed correct retention, measured using two independent parameters: the retention latency and a ratio between the retention latency and the last training latency. Animals trained with cocaine (0.1 mg/kg) and tested with saline or cocaine (0.03, 0.3 mg/kg), or trained with saline and tested with cocaine, showed altered retention parameters, demonstrating that StD occurred. Therefore, cocaine administered before training produced a chemical state used as an endogenous cue to insure optimal retention. Since sigma(1) receptor activation is an important event during the acquisition of cocaine reward, we tested several sigma(1) ligands and related neurosteroids. The sigma(1) agonist igmesine or antagonist BD1047 failed to produce StD, but modified the cocaine state. Among neuroactive steroids, pregnanolone and allopregnanolone, positive modulators of the gamma-aminobutyric acid type A (GABA(A)) receptor, produced StD. However, steroids also acting as sigma(1) agonists, dehydroepiandrosterone (3beta-hydroxy-5alpha-androsten-17-one (DHEA)), pregnenolone, or antagonist, progesterone, failed to induce StD but modified the cocaine state. Furthermore, optimal retention was observed with mice trained with (igmesine or DHEA)+cocaine and tested with a higher dose of cocaine, or with mice trained with (BD1047 or progesterone)+cocaine and tested with vehicle. This study demonstrated that: (i) low doses of cocaine induce a chemical state/memory trace sustaining StD; (ii) modulation of the sigma(1) receptor activation, although insufficient to provoke StD, modulates the cocaine state; (iii) neuroactive steroids exert a unique role in state-dependent vs state-independent learning, via GABA(A) or sigma(1) receptor modulation, and are able to affect the cocaine-induced mnesic trace at low brain concentrations.

N‐Arylation of indoles with 4‐[18F]fluoroiodobenzene: synthesis of 18F‐labelled σ2 receptor ligands for positron emission tomography (PET)

AbstractThe palladium‐mediated N‐arylation of indoles with 4‐[18F]fluoroiodobenzene as a novel radiolabelling method has been developed. Optimized reaction conditions were elaborated by variation of different catalyst systems (CuI/1,2‐diamines and Pd2(dba)3/phosphine ligands), bases and solvents in the reaction of indole with 4‐[18F]fluoroiodobenzene. Optimized reaction conditions (Pd2(dba)3/(2‐(dicyclohexyl‐phosphino)‐2′‐(N,N‐dimethylamino)‐biphenyl, NaOBut, toluene, 100°C for 20 min) were applied for the synthesis of 18F‐labelled σ2 receptor ligands [18F]‐11 and [18F]‐13 which were obtained in 91 and 84% radiochemical yields, respectively. Copyright © 2004 John Wiley & Sons, Ltd.

Thioxanthene-derived analogs as σ1 receptor ligands

An investigation of the structure–affinity relationships for the binding of thioxanthene-related structures indicates that an intact thioxanthene ring is not required for binding at σ1 receptors, and that with the appropriate structural modifications, affinity can be enhanced to the subnanomolar level. Certain of the analogs displayed >180-fold selectivity for σ1 versus σ2 receptors.

Molecular modeling of σ1 receptor ligands: a model of binding conformational and electrostatic considerations

We have performed molecular modeling studies on several σ1 specific ligands, including PD144418, spipethiane, haloperidol, pentazocine, and others to develop a pharmacophore for σ1 receptor–ligand binding, under the assumption that all the compounds interact at the same receptor binding site. The modeling studies have investigated the conformational and electrostatic properties of the ligands. Superposition of active molecules gave the coordinates of the hypothetical 5-point σ1 pharmacophore, as follows: R1 (0.85, 7.26, 0.30); R2 (5.47, 2.40, −1.51); R3 (−2.57, 4.82, −7.10); N (−0.71, 3.29, −6.40); carbon centroid (3.16, 4.83, −0.60), where R1, R2 were constructed onto the aromatic ring of each compound to represent hydrophobic interactions with the receptor; and R3 represents a hydrogen bond between the nitrogen atom and the receptor. Additional analyses were used to describe secondary binding sites to electronegative groups such as oxygen or sulfur atom. Those coordinates are (2.34, 5.08, −4.18). The model was verified by fitting other σ1 receptor ligands. This model may be used to search conformational databases for other possibly active ligands. In conjunction with rational drug design techniques the model may be useful in design and synthesis of novel σ1 ligands of high selectivity and potency. Calculations were performed using Sybyl 6.5.

Intracellular sigma1 receptor modulates phospholipase C and protein kinase C activities in the brainstem.

Most physiological effects of sigma1 receptor ligands are sensitive to pertussis toxin, suggesting a coupling with cell membrane-bound G proteins. However, the cloning of the sigma1 receptor has allowed the identification of an intracellular protein anchored on the endoplasmic reticulum. Here, we show, using the isolated adult guinea pig brainstem preparation, that activation of the sigma1 receptor results in its translocation from the cytosol to the vicinity of the cell membrane and induces a robust and rapid decrease in hypoglossal activity, which is mediated by phospholipase C. The subsequent activation of protein kinase C beta1 and beta2 isoforms and the phosphorylation of a protein of the same molecular weight as the cloned sigma1 receptor lead to a desensitization of the sigma1 motor response. Our results indicate that the intracellular sigma1 receptor regulates several components implicated in plasma membrane-bound signal transduction. This might be an example of a mechanism by which an intracellular receptor modulates metabotropic responses.

Sigma1 (σ1) receptor agonists and neurosteroids attenuate β25–35-amyloid peptide-induced amnesia in mice through a common mechanism

The sigma1 (σ1) receptor agonists exert potent anti-amnesic effects, as they apparently block the learning impairments either induced by the muscarinic receptor antagonist scopolamine, the N-methyl-d-aspartate receptor antagonist dizocilpine or inherently due to the age-related deficits in senescence-accelerated mice. We recently described the amnesia induced by the β-amyloid-related peptide β25–35, administered centrally in an aggregated form, in mice. The deficits were sensitive to cholinomimetics or to N-methyl-d-aspartate/glycine modulatory site agonists. Herein, we examined the effects of σ1 receptor ligands on the β25–35 peptide-induced amnesia. The effects of neuro(active) steroids, which interact in vitro and in vivo with σ1 receptors were examined in parallel. Mnesic capacity was evaluated seven days after administration of aggregated β25–35 peptide (3nmol), using spontaneous alternation in the Y-maze for spatial short-term memory, or after 14 days, using the step-down type passive avoidance test for long-term memory. The σ1 receptor agonists (+)-pentazocine, PRE-084, or SA4503 attenuated, in a dose-dependent and bell-shaped manner, the β25–35 peptide-induced deficits on both tests. These effects were antagonized by haloperidol or BMY-14 802, confirming the σ1 receptor pharmacology. Pregnenolone, dehydroepiandrosterone, and their sulphate esters, but not progesterone, also dose-dependently attenuated the β25–35 peptide-induced deficits. Progesterone blocked the beneficial effects of each other neurosteroid, behaving as an antagonist. Furthermore, haloperidol blocked the effects induced by neurosteroids, whereas progesterone antagonized the effects of the non-steroidal σ1 receptor agonists, showing a clear crossed pharmacology of different drug classes.These results demonstrate that: (i) the anti-amnesic effect of σ1 receptor agonists may be of therapeutic relevance in pathological states affecting the cholinergic and/or glutamatergic systems, such as in pathological aging; (ii) neurosteroids play an important role in learning processes and may collectively constitute a therapeutic target; (iii) the interaction between σ1 systems and neurosteroids appears indeed of behavioural relevance.

SA4503, a novel cognitive enhancer, with σ1 receptor agonistic properties

We found a potent and selective sigma1 (σ1) receptor ligand, SA4503 (1-(3,4-dimethoxyphenethyl)-4-(3-phenylpropyl)piperazine dihydrochloride). This compound had a high affinity for σ1 receptor subtype (IC50=17±1.9 nM), but a low affinity for σ2 receptor subtype (IC50 = 1800 ± 310 nM). The present study examines the effect of this compound on the central cholinergic functions, since σ receptor has been reported to interact with the central cholinergic neurons. SA4503 elicited the increase in extracellular acetylcholine level in rat frontal cortex, while it did not affect the striatal acetylcholine level. On the other hand, tetrahydroaminoacridine (THA), an acetylcholinesterase (AChE) inhibitor, increased the extracellular acetylcholine level in both regions. Although both compounds had anti-amnesic effect against scopolamine-induced memory impairment, THA also induced catalepsy in rats. These results suggest that SA4503 may be a novel cognitive enhancer, with σ1 receptor agonistic properties. In addition, SA4503 does not cause striatal cholinomimetic side-effects, which is different from THA.

P-19-27 - Effect of dynorphin A (1–13) on decrease in acetylcholine release induced by carbachol in rats

The selective σ1 receptor agonist 1-(3,4-dimethoxyphenethyl)-4-(3-phenyl propyl)piperazine dihydrochloride (SA4503) was reported to reverse the amnesia induced by the muscarinic receptor antagonist scopolamine at sub-mg/kg doses. We examined its effect on the learning impairment induced in mice by the non-competitive NMDA receptor antagonist dizocilpine. Learning capacities were evaluated using spontaneous alternation in the Y-maze for spatial working memory, and step-down type passive avoidance. SA4503 (0.03–1 mg/kg s.c.) attenuated the dizocilpine (0.15 mg/kg i.p.)-induced memory deficits following a bell-shaped curve in both tests. These effects of SA4503 were blocked by haloperidol (0.05 mg/kg i.p.), implicating σ1 receptors. SA4503 also reversed the alternation deficit induced by Nω-nitro-l-arginine methyl ester (l-NAME, 100 mg/kg i.p.) at the same dosage, indicating that it acted on working memory through the nitric oxide (NO)-mediated signalling pathway. Furthermore, progesterone (2 mg/kg s.c.) blocked the SA4503 effects in the dizocilpine- and l-NAME-amnesia models, in accordance with the purported neurosteroids/σ1 receptors interaction. These results demonstrate a promising neurobehavioural profile of SA4503, a ligand equally efficient to reverse the deficit in the glutamatergic as well as in the cholinergic amnesia model. Pertinent informations on the potential mechanism of the anti-amnesic effects of σ1 receptor ligands were also obtained.