The 27th Scientific Conference of the Society on NeuroImmune Pharmacology: New Delhi, India, March 15-18, 2023

The 27th Scientific Conference of the Society on Neuroimmune Pharmacology (SNIP) in New Delhi, India, on March 15-18, 2023 is a historic summit of experts from around the world. The four day conference provides insights into the latest and most advanced science in the intersecting areas of neuroscience, immunology, pharmacology, and its translational aspects, in particular, HIV and drug abuse. Abstracts are ordered in three major groups: (1) Symposium speakers (S1-S64), (2) Investigator Posters (I1-I18), and (3) Trainee Poster (T1-T28).

The 26th Scientific Conference of the Society on NeuroImmune Pharmacology: College of Pharmacy, University of Tennessee Health Science Center, Memphis, TN, June 1-3, 2022

The 26^th Scientific Conference of the Society on NeuroImmune Pharmacology (SNIP) at the University of Tennessee Health Science Center in Memphis, Tennessee, June 1-3, 2022, is SNIP’s first full-fledged meeting in person since the onset of the coronavirus disease-19 pandemic. The three-day meeting encompasses a variety of activities that include a pre-conference session, many scientific sessions (eight symposia and two plenary lectures), two special talks, a poster session, oral talks, a mentoring session for early career investigators, a diversity and inclusion SNIP committee session, a business meeting, and an award session. A conference summary, detailed program agenda, accepted poster abstracts, and presentation abstracts are included in this brief report published in advance of the meeting.

Mice with high FGF21 serum levels had a reduced preference for morphine and an attenuated development of acute antinociceptive tolerance and physical dependence

Because of increased opioid misuse, there is a need to identify new targets for minimizing opioid tolerance, and physical and psychological dependence. Previous studies showed that fibroblast growth factor 21 (FGF21) decreased alcohol and sweet preference in mice. In this study, FGF21-transgenic (FGF21-Tg) mice, expressing high FGF21 serum levels, and wildtype (WT) C57BL/6J littermates were treated with morphine and saline to determine if differences exist in their physiological and behavioral responses to opioids. FGF21-Tg mice displayed reduced preference for morphine in the conditioned place preference assay compared to WT littermates. Similarly, FGF21-Tg mice had an attenuation of the magnitude and rate of acute morphine antinociceptive tolerance development, and acute and chronic morphine physical dependence, but exhibited no change in chronic morphine antinociceptive tolerance. The ED50 values for morphine-induced antinociception in the 55 °C hot plate and the 55 °C warm-water tail withdrawal assays were similar in both strains of mice. Likewise, FGF21-Tg and WT littermates had comparable responses to morphine-induced respiratory depression. Overall, FGF21-Tg mice had a decrease in the development of acute analgesic tolerance, and the development of physical dependence, and morphine preference. FGF21 and its receptor have therapeutic potential for reducing opioid withdrawal symptoms and craving, and augmenting opioid therapeutics for acute pain patients to minimize tolerance development.

The COVID-19 Pandemic: Reflections of Science, Person, and Challenge in Academic Research Settings

In spring of 2021, the Society on NeuroImmune Pharmacology (SNIP) organized a virtual workshop on the coronavirus disease 2019 (COVID-19). The daylong event's fourth and final symposium, "Well-being and reflections," offered a glimpse at the pandemic's impact on the lives of our scientists and educators. This manuscript includes a brief summary of the symposium, a transcription of our incoming president Dr. Santosh Kumar's lecture, titled "Intervention and improved well-being of basic science researchers during the COVID-19 era: a case study," and the panel discussion that followed, "Reflection and sharing," featuring Drs. Jean M. Bidlack, Sylvia Fitting, Santhi Gorantla, Maria Cecilia G. Marcondes, Loyda M. Melendez, and Ilker K. Sariyer. The conclusion of this manuscript includes comments from SNIP's president Dr. Sulie L. Chang and our Chief Editor, Dr. Howard E. Gendelman. Drs. Sowmya Yelamanchili and Jeymohan Joseph co-chaired the symposium.

The Delta-Specific Opioid Glycopeptide BBI-11008: CNS Penetration and Behavioral Analysis in a Preclinical Model of Levodopa-Induced Dyskinesia

In previous work we evaluated an opioid glycopeptide with mixed μ/δ-opioid receptor agonism that was a congener of leu-enkephalin, MMP-2200. The glycopeptide analogue showed penetration of the blood-brain barrier (BBB) after systemic administration to rats, as well as profound central effects in models of Parkinson's disease (PD) and levodopa (L-DOPA)-induced dyskinesia (LID). In the present study, we tested the glycopeptide BBI-11008 with selective δ-opioid receptor agonism, an analogue of deltorphin, a peptide secreted from the skin of frogs (genus Phyllomedusa). We tested BBI-11008 for BBB-penetration after intraperitoneal (i.p.) injection and evaluated effects in LID rats. BBI-11008 (10 mg/kg) demonstrated good CNS-penetrance as shown by microdialysis and mass spectrometric analysis, with peak concentration levels of 150 pM in the striatum. While BBI-11008 at both 10 and 20 mg/kg produced no effect on levodopa-induced limb, axial and oral (LAO) abnormal involuntary movements (AIMs), it reduced the levodopa-induced locomotor AIMs by 50% after systemic injection. The N-methyl-D-aspartate receptor antagonist MK-801 reduced levodopa-induced LAO AIMs, but worsened PD symptoms in this model. Co-administration of MMP-2200 had been shown prior to block the MK-801-induced pro-Parkinsonian activity. Interestingly, BBI-11008 was not able to block the pro-Parkinsonian effect of MK-801 in the LID model, further indicating that a balance of mu- and delta-opioid agonism is required for this modulation. In summary, this study illustrates another example of meaningful BBB-penetration of a glycopeptide analogue of a peptide to achieve a central behavioral effect, providing additional evidence for the glycosylation technique as a method to harness therapeutic potential of peptides.

Unique Pharmacological Properties of the Kappa Opioid Receptor Signaling Through Gαz as Shown with Bioluminescence Resonance Energy Tranfer

Opioid receptors (ORs) convert extracellular messages to signaling events by coupling to the heterotrimeric G proteins, Gα•βγ Classic pharmacological methods, such as [³⁵S]GTPγS binding and inhibition of cyclic AMP production, allow for general opioid characterization, but they are subject to the varying endogenous Gα proteins in a given cell type. Bioluminescence resonance energy transfer (BRET) technology offers new insight by allowing the direct observation of Gα subunit-specific effects on opioid pharmacology. Using a Venus-tagged Gβγ and nanoluciferase-tagged truncated G protein receptor kinase 3, an increase in BRET signal correlated with OR activation mediated by a specific Gα protein. The magnitude of the BRET signal was normalized to the maximum response obtained with 10 µM 2-(3,4-dichlorophenyl)-N-methyl-N-[(1R,2R)-2-pyrrolidin-1-ylcyclohexyl]acetamide (U50,488) for the kappa OR (KOR). Opioids reached equilibrium with the KOR, and concentration-response curves were generated. Although the full agonists U50,488, salvinorin A, nalfurafine, and dynorphin peptides were equally efficacious regardless of the Gα subunit present, the concentration-response curves were leftward shifted when the KOR was signaling through Gαz compared with other Gαi/o subunits. In contrast, the Gα subunit distinctly affected both the efficacy and potency of partial kappa agonists, such as the benzomorphans, and the classic mu opioid antagonists, naloxone, naltrexone, and nalmefene. For example, (-)pentazocine had EC₅₀ values of 7.3 and 110 nM and maximal stimulation values of 79% and 35% when the KOR signaled through Gαz and Gαi1, respectively. Together, these observations suggest KOR pharmacology varies based on the specific Gα subunit coupled to the KOR. SIGNIFICANCE STATEMENT: Opioid receptors couple to various heterotrimeric Gαβγ proteins to convert extracellular cues to precise intracellular events. This paper focuses on how the various inhibitory Gα subunits influence the pharmacology of full and partial agonists at the kappa opioid receptor. Using a bioluminescent assay, the efficacy and potency of kappa opioids was determined. Opioid signaling was more potent through Gαz compared with other Gα proteins. These observations suggest that Gαz may impact opioid pharmacology and cellular physiology more than previously thought.

Behavioral pharmacology of the mixed-action delta-selective opioid receptor agonist BBI-11008: studies on acute, inflammatory and neuropathic pain, respiration, and drug self-administration

RATIONALE AND OBJECTIVES

The present study characterized the behavioral pharmacology of a novel, mixed-action delta-selective (78:1) opioid receptor agonist, BBI-11008. This glycopeptide drug candidate was tested in assays assessing antinociception (acute, inflammatory, and neuropathic pain-like conditions) and side-effect endpoints (respiratory depression and drug self-administration).

RESULTS

BBI-11008 had a 78-fold greater affinity for the delta opioid receptor than the mu receptor, and there was no binding to the kappa opioid receptor. BBI-11008 (3.2-100; 10-32 mg kg-1, i.v.) and morphine (1-10; 1-3.2 mg kg-1, i.v.) produced antinociceptive and anti-allodynic effects in assays of acute thermal nociception and complete Freund's adjuvant (CFA)-induced inflammatory pain, with BBI-11008 being less potent than morphine in both assays. BBI-11008 (1-18 mg kg-1, i.v.) had similar efficacy to gabapentin (10-56 mg kg-1, i.v.) in a spinal nerve ligation (SNL) model of neuropathic pain. In the respiration assay, with increasing %CO2 exposure, BBI-11008 produced an initial increase (32 mg kg-1, s.c.) and then decrease (56 mg kg-1, s.c.) in minute volume (MV) whereas morphine (3.2-32 mg kg-1, s.c.) produced dose-dependent decreases in MV. In the drug self-administration procedure, BBI-11008 did not maintain self-administration at any dose tested.

CONCLUSIONS

These results suggest that the glycopeptide drug candidate possesses broad-spectrum antinociceptive and anti-allodynic activity across a range of pain-like conditions. Relative to morphine or fentanyl, the profile for BBI-11008 in the respiration and drug self-administration assays suggests that BBI-11008 may have less pronounced deleterious side effects. Continued assessment of this compound is warranted.

Noradrenergic signaling in the wakeful state inhibits microglial surveillance and synaptic plasticity in the mouse visual cortex

Microglia are the brain's resident innate immune cells and also have a role in synaptic plasticity. Microglial processes continuously survey the brain parenchyma, interact with synaptic elements and maintain tissue homeostasis. However, the mechanisms that control surveillance and its role in synaptic plasticity are poorly understood. Microglial dynamics in vivo have been primarily studied in anesthetized animals. Here we report that microglial surveillance and injury response are reduced in awake mice as compared to anesthetized mice, suggesting that arousal state modulates microglial function. Pharmacologic stimulation of β₂-adrenergic receptors recapitulated these observations and disrupted experience-dependent plasticity, and these effects required the presence of β₂-adrenergic receptors in microglia. These results indicate that microglial roles in surveillance and synaptic plasticity in the mouse brain are modulated by noradrenergic tone fluctuations between arousal states and emphasize the need to understand the effect of disruptions of adrenergic signaling in neurodevelopment and neuropathology.

In Vitro Pharmacological Characterization of Buprenorphine, Samidorphan, and Combinations Being Developed as an Adjunctive Treatment of Major Depressive Disorder

A combination of buprenorphine (BUP) and samidorphan (SAM) at a 1:1 (mg/mg) fixed-ratio dose is being investigated as an adjunctive treatment of major depressive disorder (BUP/SAM, ALKS 5461). Both [³H]BUP and [³H]SAM bound to the μ-, κ-, and δ-opioid receptors (MOR, KOR, and DOR, respectively) with K_d values of 3 nM or less. [³H]BUP dissociated from the MOR more slowly than [³H]SAM did. In the [³⁵S]GTPγS assay, BUP was a partial agonist at the MOR, KOR, and DOR. SAM was an antagonist at the MOR and a partial agonist at the KOR and DOR. The pharmacology of the combination of SAM and BUP was characterized at ratios like the molar ratios of both compounds at steady state in humans. In all assessments, SAM reduced the efficacy of BUP at the MOR without altering its potency. At the KOR, SAM had no significant effect on the activity of BUP. In bioluminescent resonance energy transfer assays, SAM, naltrexone, and naloxone were partial agonists when the MOR was coupled to the Gα _oB and Gα _z, and were antagonists when coupled to Gα _i At the KOR, SAM was a partial agonist activating Gα _oA and Gα _oB and a full agonist in stimulating Gα _z SAM inhibited BUP's recruitment of β-arrestin to the MOR, suggesting an attenuation of BUP's efficacy in activating G proteins correlated with an inhibition of β-arrestin recruitment. The collective data suggest that SAM attenuates the efficacy of BUP under all conditions tested at the MOR and DOR but had little effect on BUP activity at the KOR.

Structural Requirements for CNS Active Opioid Glycopeptides

Glycopeptides related to β-endorphin penetrate the blood-brain barrier (BBB) of mice to produce antinociception. Two series of glycopeptides were assessed for opioid receptor binding affinity. Attempts to alter the mu-selectivity of [D-Ala(2),N-MePhe(4),Gly-ol(5)]enkephalin (DAMGO)-related glycopeptides by altering the charged residues of the amphipathic helical address were unsuccessful. A series of pan-agonists was evaluated for antinociceptive activity (55 °C tail flick) in mice. A flexible linker was required to maintain antinociceptive activity. Circular dichroism (CD) in H2O, trifluoroethanol (TFE), and SDS micelles confirmed the importance of the amphipathic helices (11s → 11sG → 11) for antinociception. The glycosylated analogues showed only nascent helices and random coil conformations in H2O. Chemical shift indices (CSI) and nuclear Overhauser effects (NOE) with 600 MHz NMR and CD confirmed helical structures in micelles, which were rationalized by molecular dynamics calculations. Antinociceptive studies with mice confirm that these glycosylated endorphin analogues are potential drug candidates that penetrate the BBB to produce potent central effects.

Can amphipathic helices influence the CNS antinociceptive activity of glycopeptides related to β-endorphin?

Glycosylated β-endorphin analogues of various amphipathicity were studied in vitro and in vivo in mice. Opioid binding affinities of the O-linked glycopeptides (mono- or disaccharides) and unglycosylated peptide controls were measured in human receptors expressed in CHO cells. All were pan-agonists, binding to μ-, δ-, or κ-opioid receptors in the low nanomolar range (2.2-35 nM K(i)'s). The glycoside moiety was required for intravenous (i.v.) but not for intracerebroventricular (i.c.v.) activity. Circular dichroism and NMR indicated the degree of helicity in H2O, aqueous trifluoroethanol, or micelles. Glycosylation was essential for activity after i.v. administration. It was possible to manipulate the degree of helicity by the alteration of only two amino acid residues in the helical address region of the β-endorphin analogues without destroying μ-, δ-, or κ-agonism, but the antinociceptive activity after i.v. administration could not be directly correlated to the degree of helicity in micelles.

Preliminary pharmacological evaluation of enantiomeric morphinans

A series of levo- and dextromorphinan pairs have been synthesized and evaluated for their affinities to the mu, kappa, and delta opioid receptors, the N-methyl-D-aspartate (NMDA) channel, and sigma 1 and 2 receptors. It was found that levo isomers tended to have higher affinities at the opioid receptors and moderate to high affinities to the NMDA and sigma receptors, while dextro isomers tended to have lower affinities to the opioid receptors but comparatively higher affinities to the NMDA and sigma receptors. This series of compounds have interesting and complex pharmacological profiles, and merit further investigation as potential therapies for drug abuse treatment.

Mixed κ/μ partial opioid agonists as potential treatments for cocaine dependence

Cocaine use activates the dopamine reward pathway, leading to the reinforcing effects of dopamine. There is no FDA-approved medication for treating cocaine dependence. Opioid agonists and antagonists have been approved for treating opioid and alcohol dependence. Agonists that activate the μ opioid receptor increase dopamine levels in the nucleus accumbens, while μ receptor antagonists decrease dopamine levels by blocking the effects of endogenous opioid peptides. Activation of the κ opioid receptor decreases dopamine levels and leads to dysphoria. In contrast, inhibition of the κ opioid receptor decreases dopamine levels in the nucleus accumbens. Antagonists acting at the κ receptor reduce stress-mediated behaviors and anxiety. Mixed partial μ/κ agonists have the potential of striking a balance between dopamine levels and attenuating relapse to cocaine. The pharmacological properties of mixed μ/κ opioid receptor agonists will be discussed and results from clinical and preclinical studies will be presented. Results from studies with some of the classical benzomorphans and morphinans will be presented as they lay the foundation for structure-activity relationships. Recent results with other partial opioid agonists, including buprenorphine derivatives and the mixed μ/κ peptide CJ-15,208, will be discussed. The behavioral effects of the mixed μ/κ MCL-741, an aminothiazolomorphinan, in attenuating cocaine-induced locomotor activity will be presented. While not a mixed μ/κ opioid, results obtained with GSK1521498, a μ receptor inverse agonist, will be discussed. Preclinical strategies and successes will lay the groundwork for the further development of mixed μ/κ opioid receptor agonists to treat cocaine dependence.

Synthesis and pharmacological evaluation of aminothiazolomorphinans at the mu and kappa opioid receptors

Previous studies with aminothiazolomorphinans suggested that this class of opioid ligands may be useful as a potential pharmacotherapeutic to decrease drug abuse. Novel aminothiazole derivatives of cyclorphan were prepared to evaluate a series of aminothiazolomorphinans with varying pharmacological properties at the κ opioid receptor (KOR) and μ opioid receptor (MOR). This study was focused on exploring the regioisomeric analogs with the aminothiazole on the C-ring of the morphinan skeleton. Receptor binding and [(35)S]GTPγS binding assays were used to characterize the affinity and pharmacological properties of the aminothiazolomorphinans. Intracranial self-stimulation (ICSS) was used to compare the effects of a representative aminothiazolomorphinan with the morphinan mixed-KOR/MOR agonist butorphan (MCL-101) on brain-stimulation reward.

Redefining the structure-activity relationships of 2,6-methano-3-benzazocines. Part 9: Synthesis, characterization and molecular modeling of pyridinyl isosteres of N-BPE-8-CAC (1), a high affinity ligand for opioid receptors

Derivatives of the lead compound N-BPE-8-CAC (1) where each CH of the biphenyl group was individually replaced by N were prepared in hopes of identifying high affinity ligands with improved aqueous solubility. Compared to 1, binding affinities of the five possible pyridinyl derivatives for the μ opioid receptor were between threefold lower to fivefold higher with the Ki of the most potent compound being 0.064 nM. Docking of 8-CAC (2) into the unliganded binding site of the mouse μ opioid receptor (pdb: 4DKL) revealed that 8-CAC and β-FNA (from 4DKL) make nearly identical interactions with the receptor. However, for 1 and the new pyridinyl derivatives 4-8, binding is not tolerated in the 8-CAC binding mode due to the steric constraints of the large N-substituents. Either an alternative binding mode or rearrangement of the protein to accommodate these modifications may account for their high binding affinity.

Redefining the structure-activity relationships of 2,6-methano-3-benzazocines. Part 8. High affinity ligands for opioid receptors in the picomolar Ki range: oxygenated N-(2-[1,1'-biphenyl]-4-ylethyl) analogues of 8-CAC

N-[2-(4'-methoxy[1,1'-biphenyl]-4-yl)ethyl]-8-CAC (1) is a high affinity (K(i)=0.084 nM) ligand for the μ opioid receptor and served as the lead compound for this study. Analogues of 1 were made in hopes of identifying an SAR within a series of oxygenated (distal) phenyl derivatives. A number of new analogues were made having single-digit pM affinity for the μ receptor. The most potent was the 3',4'-methylenedioxy analogue 18 (K(i)=1.6 pM).

Synthesis, binding affinity, and functional in vitro activity of 3-benzylaminomorphinan and 3-benzylaminomorphine ligands at opioid receptors

A series of 3-benzylamino-3-desoxymorphinan (I) and 3-benzylamino-3-desoxymorphine (II) derivatives were synthesized and evaluated for their binding affinities, and functional activity data are presented at MOR, KOR, and DOR. Some of these ligands were found to have high binding affinity at MOR and KOR and displayed increased selectivity at MOR over KOR and DOR compared to butorphan or cyclorphan. The most selective compound, 3-(3'-hydroxybenzyl)amino-17-methylmorphinan (4g) (24-fold MOR to KOR and 1700-fold MOR to DOR) also showed high binding affinity (0.42 nM to MOR) and was a full agonist in the [(35)S]GTPγS binding assay. 2-(3'-Hydroxybenzyl)amino-17-cyclopropylmethylmorphinan (17) was found to be a KOR-selective ligand (150-fold over MOR and >10000-fold over the DORs). Most 3-benzylaminomorphinan derivatives were partial agonists at MOR and full agonists at KOR in the [(35)S]GTPγS binding assay.

Effects of oral loperamide on efficacy of naltrexone, baclofen and AM-251 in blocking ethanol self-administration in rats

Naltrexone is a μ-opioid receptor antagonist that has been extensively studied for its ability to block the rewarding effects of ethanol. Opioid receptors are widely distributed within the gastrointestinal tract (GIT). Typically, naltrexone is administered by parenteral routes in nonclinical studies. We initially tested if opioid receptors within the GIT would influence the ability of oral naltrexone to inhibit ethanol oral self-administration in rats using the co-administration of oral loperamide, a peripherally restricted opioid agonist. As expected, oral naltrexone only had modest effects on ethanol intake, and the response was not dose-dependent. However in rats, treatment with loperamide prior to the administration of naltrexone resulted in a suppression of ethanol intake which approached that observed with naltrexone given by the subcutaneous (SC) route. Importantly, administration of loperamide prior to administration of naltrexone did not alter blood concentrations of naltrexone. We then evaluated if oral loperamide would enhance effects of baclofen (a GABA(B) receptor agonist) and AM-251 (a CB-1 receptor antagonist) and found that pre-treatment with loperamide did potentiate the action of both drugs to reduce ethanol self-administration. Finally, the specific opioid receptor type involved was investigated using selective μ- and κ-receptor antagonists to determine if these would affect the ability of the AM-251 and loperamide combination to block ethanol drinking behavior. The effect of loperamide was blocked by ALKS 37, a peripherally restricted μ-receptor antagonist. These data suggest an important role for opioid receptors within the GIT in modulating central reward pathways and may provide new insights into strategies for treating reward disorders, including drug dependency.

Phosphorylation of enkephalins: NMR and CD studies in aqueous and membrane-mimicking environments

Phosphorylation of l-serine-containing enkephalin analogs has been explored as an alternative to glycosylation in an effort to increase blood-brain barrier permeability and CNS bioavailability of peptide pharmacophores. Two enkephalin-based peptides were modified for these studies, a set related to DTLES, a mixed μ/δ-agonist, and one related to DAMGO, a highly selective μ-agonist. Each unglycosylated peptide was compared to its phosphate, its mono-benzylphosphate ester, and its β-d-glucoside. Binding was characterized in membrane preparations from Chinese hamster ovary cells expressing human μ, δ and κ-opiate receptors. Antinociception was measured in mice using the 55 °C tail-flick assay. To estimate bioavailability, the antinociceptive effect of each opioid agonist was evaluated after intracerebroventricular (i.c.v.) or intravenous administration (i.v.) of the peptides. Circular dichroism methods and high-field nuclear magnetic resonance were used in the presence and absence of sodium dodecylsulfate to understand how the presence of a membrane might influence the peptide conformations.

Brain P450 epoxygenase activity is required for the antinociceptive effects of improgan, a nonopioid analgesic

The search for the mechanism of action of improgan (a nonopioid analgesic) led to the recent discovery of CC12, a compound that blocks improgan antinociception. Because CC12 is a cytochrome P450 inhibitor, and brain P450 mechanisms were recently shown to be required in opioid analgesic signaling, pharmacological and transgenic studies were performed in rodents to test the hypothesis that improgan antinociception requires brain P450 epoxygenase activity. Intracerebroventricular (i.c.v.) administration of the P450 inhibitors miconazole and fluconazole, and the arachidonic acid (AA) epoxygenase inhibitor N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide (MS-PPOH) potently inhibited improgan antinociception in rats at doses that were inactive alone. MW06-25, a new P450 inhibitor that combines chemical features of CC12 and miconazole, also potently blocked improgan antinociception. Although miconazole and CC12 were weakly active at opioid and histamine H(3) receptors, MW06-25 showed no activity at these sites, yet retained potent P450-inhibiting properties. The P450 hypothesis was also tested in Cpr(low) mice, a viable knock-in model with dramatically reduced brain P450 activity. Improgan (145 nmol, i.c.v.) antinociception was reduced by 37% to 59% in Cpr(low) mice, as compared with control mice. Moreover, CC12 pretreatment (200 nmol, i.c.v.) abolished improgan action (70% to 91%) in control mice, but had no significant effect in Cpr(low) mice. Thus, improgan's activation of bulbospinal nonopioid analgesic circuits requires brain P450 epoxygenase activity. A model is proposed in which (1) improgan activates an unknown receptor to trigger downstream P450 activity, and (2) brainstem epoxygenase activity is a point of convergence for opioid and nonopioid analgesic signaling.

Synthesis and binding affinity of novel mono- and bivalent morphinan ligands for κ, μ, and δ opioid receptors

A novel series of homo- and heterodimeric ligands containing κ/μ agonist and μ agonist/antagonist pharmacophores joined by a 10-carbon ester linker chain were synthesized and evaluated for their in vitro binding affinity at κ, μ, and δ opioid receptors, and their functional activities were determined at κ and μ receptors in [(35)S]GTPγS functional assays. Most of these compounds had high binding affinity at μ and κ receptors (K(i) values less than 1nM). Compound 15b, which contains butorphan (1) at one end of linking chain and butorphanol (5) at the other end, was the most potent ligand in this series with binding affinity K(i) values of 0.089nM at the μ receptor and 0.073nM at the κ receptor. All of the morphinan-derived ligands were found to be partial κ and μ agonists; ATPM-derived ligands 12 and 11 were found to be full κ agonists and partial μ agonists.

Aminothiazolomorphinans with mixed κ and μ opioid activity

A series of N-substituted and N'-substituted aminothiazole-derived morphinans (5) were synthesized for expanding the structure-activity relationships of aminothiazolo-morphinans. Although their affinities were somewhat lower than their prototype aminothiazolo-N-cyclopropylmorphinan (3), 3-aminothiazole derivatives of cyclorphan (1) containing a primary amino group displayed high affinity and selectivity at the κ and μ opioid receptors. [(35)S]GTPγS binding assays showed that the aminothiazolomorphinans were κ agonists with mixed agonist and antagonist activity at the μ opioid receptor. These novel N'-monosubstituted aminothiazole-derived morphinans may be valuable for the development of drug abuse medications.

Opioid bifunctional ligands from morphine and the opioid pharmacophore Dmt-Tic

Bifunctional ligands containing an ester linkage between morphine and the δ-selective pharmacophore Dmt-Tic were synthesized, and their binding affinity and functional bioactivity at the μ, δ and κ opioid receptors determined. Bifunctional ligands containing or not a spacer of β-alanine between the two pharmacophores lose the μ agonism deriving from morphine becoming partial μ agonists 4 or μ antagonists 5. Partial κ agonism is evidenced only for compound 4. Finally, both compounds showed potent δ antagonism.

In vivo characterization of MMP-2200, a mixed δ/μ opioid agonist, in mice

We have previously reported the chemistry and antinociceptive properties of a series of glycosylated enkephalin analogs (glycopeptides) exhibiting approximately equal affinity and efficacy at δ opioid receptors (DORs) and μ opioid receptors (MORs). More detailed pharmacology of the lead glycopeptide MMP-2200 [H₂N-Tyr-D-Thr-Gly-Phe-Leu-Ser-(O-β-D-lactose)-CONH₂] is presented. MMP-2200 produced dose-related antinociception in the 55°C tail-flick assay after various routes of administration. The antinociceptive effects of MMP-2200 were blocked by pretreatment with the general opioid antagonist naloxone and partially blocked by the MOR-selective antagonist β-funaltrexamine and the DOR-selective antagonist naltrindole. The κ opioid receptor antagonist nor-binaltorphimine and the peripherally active opioid antagonist naloxone-methiodide were ineffective in blocking the antinociceptive effects of MMP-2200. At equi-antinociceptive doses, MMP-2200 produced significantly less stimulation of locomotor activity compared with morphine. Repeated administration of equivalent doses of morphine and MMP-2200 (twice daily for 3 days) produced antinociceptive tolerance (~13- and 5-fold rightward shifts, respectively). In acute and chronic physical dependence assays, naloxone precipitated a more severe withdrawal in mice receiving morphine compared with equivalent doses of the glycopeptide. Both morphine and MMP-2200 inhibited respiration and gastrointestinal transit. In summary, MMP-2200 acts as a mixed DOR/MOR agonist in vivo, which may in part account for its high antinociceptive potency after systemic administration, as well as its decreased propensity to produce locomotor stimulation, tolerance, and physical dependence in mice, compared with the MOR-selective agonist morphine. For other measures (e.g., gastrointestinal transit and respiration), the significant MOR component may not allow differentiation from morphine.

Evolution of the Bifunctional Lead μ Agonist / δ Antagonist Containing the Dmt-Tic Opioid Pharmacophore

Based on a renewed importance recently attributed to bi- or multifunctional opioids, we report the synthesis and pharmacological evaluation of some analogues derived from our lead μ agonist / δ antagonist, H-Dmt-Tic-Gly-NH-Bzl. Our previous studies focused on the importance of the C-teminal benzyl function in the induction of such bifunctional activity. The introduction of some substituents in the para position of the phenyl ring (-Cl, -CH(3), partially -NO(2), inactive -NH(2)) was found to give a more potent μ agonist / antagonist effect associated with a relatively unmodified δ antagonist activity (pA(2) = 8.28-9.02). Increasing the steric hindrance of the benzyl group (using diphenylmethyl and tetrahydroisoquinoline functionalities) substantially maintained the μ agonist and δ antagonist activities of the lead compound. Finally and quite unexpectedly D-Tic2, considered as a wrong opioid message now; inserted into the reference compound in lieu of L-Tic, provided a μ agonist / δ agonist better than our reference ligand (H-Dmt-Tic-Gly-NH-Ph) and was endowed with the same pharmacological profile.

Effect of linker substitution on the binding of butorphan univalent and bivalent ligands to opioid receptors

A series of bivalent hydroxy ether butorphan ligands were prepared and their binding affinities at the opioid receptors determined. Addition of a hydroxy group to a hydrocarbon chain can potentiate binding affinity up to 27- and 86-fold at the mu and kappa opioid receptors, respectively. Two bivalent ligands with sub-nanomolar binding affinity at the mu and kappa opioid receptors were discovered.

Synthesis and opioid receptor binding affinities of 2-substituted and 3-aminomorphinans: ligands for mu, kappa, and delta opioid receptors

The phenolic group of the potent mu and kappa opioid morphinan agonist/antagonists cyclorphan and butorphan was replaced by phenylamino and benzylamino groups including compounds with para-substituents in the benzene ring. These compounds are highly potent mu and kappa ligands, e.g., p-methoxyphenylaminocyclorphan showing a K(i) of 0.026 nM at the mu receptor and a K(i) of 0.03 nM at the kappa receptor. Phenyl carbamates and phenylureas were synthesized and investigated. Selective o-formylation of butorphan and levorphanol was achieved. This reaction opened the way to a large set of 2-substituted 3-hydroxymorphinans, including 2-hydroxymethyl-, 2-aminomethyl-, and N-substituted 2-aminomethyl-3-hydroxymorphinans. Bivalent ligands bridged in the 2-position were also synthesized and connected with secondary and tertiary aminomethyl groups, amide bonds, and hydroxymethylene groups, respectively. Although most of the 2-substituted morphinans showed considerably lower affinities compared to their parent compounds, the bivalent ligand approach led to significantly higher affinities compared to the univalent 2-substituted morphinans.

Univalent and bivalent ligands of butorphan: characteristics of the linking chain determine the affinity and potency of such opioid ligands

Bivalent morphinan compounds containing ester linkers were synthesized and their binding affinities at the mu, delta, and kappa opioid receptors determined. Addition of methyl groups adjacent to the hydrolytically labile ester linkage increased stability while only partially affecting binding affinity. The resulting bivalent ligands with optimized spacer length and structure show potent binding profiles with the most potent compound (4b), having K(i) values of 0.47 nM for both the mu and kappa opioid receptors, and 4a, having K(i) values of 0.95 and 0.62 nM for the mu and kappa receptors, respectively. Both 4a and 4b were partial agonists at the kappa and micro receptors in the [(35)S]GTPgammaS binding assay.

Syntheses of novel high affinity ligands for opioid receptors

A series of novel high affinity opioid receptor ligands have been made whereby the phenolic-OH group of nalbuphine, naltrexone methiodide, 6-desoxonaltrexone, hydromorphone and naltrindole was replaced by a carboxamido group and the furan ring was opened to the corresponding 4-OH derivatives. These furan ring 'open' derivatives display very high affinity for mu and kappa receptors and much less affinity for delta. The observation that these target compounds have much higher receptor affinity than the corresponding ring 'closed' carboxamides significantly strengthens our underlying pharmacophore hypothesis concerning the bioactive conformation of the carboxamide group.

Redefining the structure-activity relationships of 2,6-methano-3-benzazocines. Part 7: syntheses and opioid receptor properties of cyclic variants of cyclazocine

A series of 7,8- and 8,9-fused triazole and imidazole analogues of cyclazocine have been made and characterized in opioid receptor binding and [(35)S]GTPgammaS assays. Target compounds were designed to explore the SAR surrounding our lead molecule for this study, namely the 8,9-fused pyrrolo analogue 2 of cyclazocine. Compared to 2, many of the new compounds in this study displayed very high affinity for opioid receptors.

Syntheses and opioid receptor binding properties of carboxamido-substituted opioids

A series of 15 novel opioid derivatives were made where the prototypic phenolic-OH group of traditional opioids was replaced by a carboxamido (CONH(2)) group. For 2,6-methano-3-benzazocines and morphinans similar or, in a few instances, enhanced affinity for mu, delta and kappa opioid receptors was observed when the OH-->CONH(2) switch was applied. For 4,5alpha-epoxymorphinans, binding affinities for the corresponding carboxamide derivatives were much lower than the OH partner consistent with our pharmacophore hypothesis concerning carboxamide bioactive conformation. The active metabolite of tramadol and its carboxamide counterpart had comparable affinities for the three receptors.

Phenobarbital withdrawal seizures may occur over several weeks before remitting: human data and hypothetical mechanism

This case is the first report of a patient who had phenobarbital (PB) withdrawal seizures after having been seizure-free for 3 years following temporal lobe surgery. The patient had been taking PB for 14 years when a gradual taper of PB was started. When PB was at 60 mg/d, a titration of lamotrigine (LTG) was started. However, typical complex seizures occurred when the patient was on PB 60 mg/d, along with LTG 25mg/d. PB was increased back to 90 mg/d and levetiracetam (LEV) was titrated. Seizures appeared when the patient was on PB 30 mg/d and LEV 750 mg BID and continued for 3 weeks after PB was stopped and the patient was on LEV 1,000 mg BID. For the following 6 months, her aura frequency remained elevated in comparison to her baseline aura of two auras per month for the previous year before the start of the PB taper. She was followed for 24 months after her last PB withdrawal seizure. During the last 8 months, her aura frequency returned to her baseline. As suggested by animal studies, the PB withdrawal seizures and increase in aura frequency in this patient may be explained by changes in her levels of GABA(A) receptor subunits.

Synthesis and pharmacological evaluation of hydrophobic esters and ethers of butorphanol at opioid receptors

We synthesized several hydrophobic esters and ethers of butorphanol and assessed their affinities at opioid receptors in CHO cell membranes. Tested compounds displayed moderate to high affinities to the mu and kappa receptors. The findings accord with previous evidence of a lipophilic binding pocket in the opioid receptors that can be accessed to afford good binding affinity without the need for a phenolic hydrogen-bond donor group. The most potent (K(i)=61 pM at mu and 48 pM at kappa) novel agent was (-)-N-cyclobutylmethylmorphinan-3-yl-14-ol phenoxyacetate (4d).

In vivo characterization of (-)(-)MCL-144 and (+)(-)MCL-193: isomeric, bivalent ligands with mu/kappa agonist properties

Once opioid receptor dimers were postulated, a goal has been to synthesize and screen novel opioids, with the hope of furthering our knowledge of the structure-activity relationship of opioid ligands with the opioid receptors. The aim of the current study was to address whether two isomeric bivalent ligands would have pharmacological differences after central administration, in vivo. The two compounds, (-) bis(N-cyclobutylmethyl-morphinan-3-yl) sebacoylate dihydrochloride (MCL-144) and 1-((+)N-cyclobutylmethylmorphinan-3-yl)-10-((-) N-cyclobutylmethylmorphinan-3-yl)sebacolyate (MCL-193) are each linked by a 10-carbon chain ester. The active (-) enantiomer for both ligands is 3-hydroxy-N-cyclobutylmethyl morphinan ((-)MCL-101), a N-cyclobutylmethyl analogue of cyclorphan (J Med Chem 43:114-122, 2000). MCL-144 contains two active levo rotatory (-)(-) pharmacophores, while MCL-193 contains one active (-) and one inactive (+) pharmacophore of MCL-101. In vitro analysis demonstrated that all three compounds, (-)(-)MCL-144, (+)(-)MCL-193 and (-)MCL-101 were kappa agonists and mu partial agonists. (-)(-)MCL-144 and (-)MCL-101 had much higher affinity for both the mu and kappa opioid receptors compared to (+)(-)MCL-193. In vivo, (-)(-)MCL-144 and (+)(-)MCL-193 produced full dose-response curves, in the 55 degrees C tail-flick test, with each compound having an ED(50) value of 3.0 nmol after intracerebroventricular (i.c.v.) administration. The analgesic properties of both compounds were antagonized by the mu-selective antagonist, beta-funaltrexamine and the kappa-selective antagonist nor-binaltorphimine. Concomitant, i.c.v., administration of either (-)(-)MCL-144 or (+)(-)MCL-193 with morphine, did not significantly antagonize morphine-induced antinociception at any dose tested. In antinociceptive tests, (-)(-)MCL-144 and (+)(-)MCL-193 had the same pharmacological properties, demonstrating that having two active pharmacophores separated by a 10-carbon spacer group did not increase the antinociceptive efficacy of the compound. Additionally, it was also of interest to compare (-)(-)MCL-145 and (-)(-)MCL-144, as the only difference between these bivalent ligands is the spacer region connecting the two pharmacophores, yet (-)(-)MCL-145 produced an ED(50) value 10-fold lower than (-)(-)MCL-144 (ED(50) values = 0.3 nmol and 3.0 nmol, respectively).

Extracellular biotransformation of beta-endorphin in rat striatum and cerebrospinal fluid

Numerous studies have investigated the behavioural effects of beta-endorphin, both endogenous and exogenously applied. However, the potential for biotransformation of beta-endorphin in the extracellular space of the brain has not been previously directly addressed in vivo. Utilising microinfusion/microdialysis and matrix-assisted laser desorption/ionisation mass spectrometry, we investigated beta-endorphin biotransformation in the striatum of rats. We infused 1.0 nmol beta-endorphin into the striatum of adult male Fischer rats and observed rapid cleavage resulting in beta-endorphin 1-18, as well as several fragments resulting from further N-terminal degradation. In vitro studies with incubation of full-length beta-endorphin, with and without protease inhibitors, in the incubation fluid of isolated striatal slices indicate that beta-endorphin is initially cleaved predominantly at the Phe(18)-Lys(19), position, as well as at the Leu(17)-Phe(18) position. Investigations of cerebrospinal fluid revealed similar enzymatic cleavage of beta-endorphin. The observed pattern of cleavage sites (Phe(18)-Lys(19) and Leu(17)-Phe(18)) is consistent with published in vitro studies of purified insulin-degrading enzyme cleavage of beta-endorphin. The binding affinities of full-length beta-endorphin, as well as previously identified beta-endorphin fragments alpha-endorphin (beta-endorphin 1-16) and gamma-endorphin (beta-endorphin 1-17), and the fragment identified in the present study, beta-endorphin 1-18, at heterologously expressed mu, delta and kappa-opioid receptors, respectively, were determined; the affinity of the truncation fragments is reduced at each of the receptors compared to the affinity of full length beta-endorphin.

Redefining the structure-activity relationships of 2,6-methano-3-benzazocines. 5. Opioid receptor binding properties of N-((4'-phenyl)-phenethyl) analogues of 8-CAC

A series of aryl-containing N-monosubstituted analogues of the lead compound 8-[N-((4'-phenyl)-phenethyl)]-carboxamidocyclazocine were synthesized and evaluated to probe a putative hydrophobic binding pocket of opioid receptors. Very high binding affinity to the mu opioid receptor was achieved though the N-(2-(4'-methoxybiphenyl-4-yl)ethyl) analogue of 8-CAC. High binding affinity to mu and very high binding affinity to kappa opioid receptors was observed for the N-(3-bromophenethyl) analogue of 8-CAC. High binding affinity to all three opioid receptors were observed for the N-(2-naphthylethyl) analogue of 8-CAC.

Synthesis and pharmacological evaluation of 6,7-indolo/thiazolo-morphinans--further SAR of levorphanol

To further extend the structure-activity relationships of levorphanol, two series of novel morphinans were prepared by incorporation of an indole or aminothiazole fragment to the hexyl ring (ring C) in levorphanol. Such morphinans differed from previously reported ligands in that such indole- or aminothiazole-containing morphinans displayed enhanced binding affinity to the delta opioid receptor, while the affinity to kappa and micro receptors was slightly reduced.

Pharmacological properties of bivalent ligands containing butorphan linked to nalbuphine, naltrexone, and naloxone at mu, delta, and kappa opioid receptors

Our investigation of bivalent ligands at mu, delta, and kappa opioid receptors is focused on the preparation of ligands containing kappa agonist and mu agonist/antagonist pharmacophores at one end joined by a chain containing the mu antagonist pharmacophores (naltrexone, naloxone, or nalbuphine) at the other end. These ligands were evaluated in vitro by their binding affinity at mu, delta, and kappa opioid receptors and their relative efficacy in the [35S]GTPgammaS assay.

In-vitro investigation of oxazol and urea analogues of morphinan at opioid receptors

A series of 2-amino-oxazole (7 and 8) analogs and 2-one-oxazole analogs (9 and 10) were synthesized from cyclorphan (1) or butorphan (2) and evaluated in-vitro by their binding affinity at mu, delta, and kappa opioid receptors and compared with their 2-aminothiozole analogs 5 and 6. Ligands 7-10 showed decreased affinities at kappa and mu receptors. Urea analogs (11-14) were also prepared from 2-aminocyclorphan (3) or 2-aminobutorphan (4) and evaluated in-vitro by their binding affinity at mu, delta, and kappa opioid receptors. The urea derived opioids retained their affinities at mu receptors while showing increased affinities at delta receptors and decreased affinities at kappa receptors. Functional activities of these compounds were measured in the [35S]GTPgammaS binding assay, illustrating that all of these ligands were kappa agonists. At the mu receptor, compounds 11 and 12 were mu agonist/antagonists.

Glycosylation Improves the Central Effects of DAMGO

A series of mu-agonist DAMGO analogs were synthesized and pharmacologically characterized to test the 'biousian' hypothesis of membrane hopping. DAMGO was altered by incorporating moieties of increasing water solubility into the C-terminus via carboxamide and simple glycoside additions. The hydrophilic C-terminal moieties were varied from glycinol in DAMGO (1) to l-serine amide (2), l-serine amide beta-d-xyloside (3), l-serine amide beta-d-glucoside (4), and finally to l-serine amide beta-lactoside (5). Opioid binding and mouse tail-flick studies were performed. Antinociceptive potency (intravenous) increased, passing through a maximum (A(50) approximately 0.2 micromol/kg) for 2 and 3 as membrane affinity versus water solubility became optimal, and dropped off (A(50) approximately 1.0 micromol/kg) for 4 and 5 as water solubility dominated molecular behavior. Intravenous A(50) values were plotted versus hydrodynamic values (glucose units, g.u.) for the glycoside moieties, or the hydrophilic/hydrophobic Connolly surface areas (A(50) versus e(-Awater/Alipid)), and provided either a V-shaped or a U-shaped curve, as predicted by the 'biousian' hypothesis. The mu-selective receptor profile was maintained (K(i)'s = 0.66-1.3 nm) upon modifications at the C-terminus. The optimal 'degree of glycosylation' for the DAMGO peptide message appears to be between 1.25 and 1.75 g.u. (hydrodynamic g.u.), or 0.75 and 0.90 in terms of the surface-derived amphipathicity values.

New opioid designed multiple ligand from Dmt-Tic and morphinan pharmacophores

Here, we report the synthesis of a designed multi-pharmacophore ligand derived from the linkage of a delta selective peptide antagonist (Dmt-Tic) and a mu/kappa morphinan agonist butorphan (MCL 101) through a two methylene spacer. The new compound MCL 450 maintains the same characteristics as those the two reference compounds. MCL 450 represents a useful starting point for the synthesis of other multiple opioid ligands endowed with analgesic properties with low tolerance and dependence.

Redefining the structure-activity relationships of 2,6-methano-3-benzazocines. 4. Opioid receptor binding properties of 8-[N-(4'-phenyl)-phenethyl)carboxamido] analogues of cyclazocine and ethylketocycalzocine

The synthesis and evaluation of a series of aryl-containing N-monosubstituted analogues of the lead compound 8-carboxamidocyclazocine were performed to probe a putative hydrophobic binding pocket of opioid receptors. High binding affinity to mu, kappa, and delta opioid receptors was observed for the 8-[N-(4'-phenyl)-phenethyl)carboxamido] analogue.

Opioid receptors and signaling on cells from the immune system

This review discusses the criteria for determining whether a binding site or functional response is directly mediated by either the mu, delta, or kappa opioid receptors. In 1988, Sibinga and Goldstein published the first review that addressed whether cells from the immune system express opioid receptors. The criteria that they used, namely, structure-activity relationships, stereoselectivity, dose- and concentration-dependence, and saturability are still relevant criteria today for determining if an immunological response is mediated by either the mu, delta or kappa opioid receptors. Radioligand receptor binding studies and functional studies that clearly show the presence of an opioid receptor on immunocytes are presented. Selective agonists and antagonists for the mu, delta, and kappa opioid receptors are discussed, and the need for their use in experiments is emphasized. Conditions used in functional assays are very important. Receptor desensitization and downregulation occur within minutes after the application of an agonist. However, many immunological assays are applying an agonist for days before measuring an immunological effect. The results obtained may reflect changes that are results of receptor desensitization and/or downregulation instead of changes that are observed with acute activation of the receptor. The future of receptor pharmacology lies in the crosstalk and dimerization of G protein-coupled receptors. In transfected systems, opioid receptors have been shown to dimerize with chemokine and cannabinoid receptors, resulting in crosstalk between different types of receptors.

The expression of prodynorphin gene is down-regulated by activation with lipopolysaccharide in U-937 macrophage cells

Dynorphins are endogenous kappa opioid peptides widely distributed in the central nervous system. A number of recent reports have established their roles in modulating immunological functions. In this study, we investigated the expression of prodynorphin (PDYN) gene, which encodes the precursor of dynorphin peptides, in human macrophage U-937 cell line. PDYN mRNA was expressed at a detectable level, measured with a standard RT-PCR method in U-937 cells, but not in Jurkat and Raji cells, which are human T and B lymphocytes, respectively. Further analyses with RT-PCR assays by using primers covering each exon of the PDYN gene showed that U-937 cells expressed the adult brain-type PDYN mRNA. Most interestingly, activation of U-937 cells with lipopolysaccharide (LPS) led to a decrease in PDYN mRNA levels. This decrease was dependent on both the concentration of LPS and the duration of LPS treatment. In order to test the role of transcription in LPS-mediated down-regulation of PDYN gene expression in U937 cells, the proximal PDYN gene promoter with a length of either approximately 300 base pairs or approximately 900 base pairs was cloned and inserted upstream of luciferase reporter gene. Results from transient transfections and dual luciferase assays showed that PDYN gene promoter activity was decreased by LPS treatment. Taken together, our results suggested the U-937 cells expressed adult brain-type PDYN mRNA which was down-regulated by activation of the cells with LPS due to an inhibition of PDYN gene transcription.

Differential Targeting of G -Subunit Signaling with Small Molecules

G protein betagamma subunits have potential as a target for therapeutic treatment of a number of diseases. We performed virtual docking of a small-molecule library to a site on Gbetagamma subunits that mediates protein interactions. We hypothesized that differential targeting of this surface could allow for selective modulation of Gbetagamma subunit functions. Several compounds bound to Gbetagamma subunits with affinities from 0.1 to 60 muM and selectively modulated functional Gbetagamma-protein-protein interactions in vitro, chemotactic peptide signaling pathways in HL-60 leukocytes, and opioid receptor-dependent analgesia in vivo. These data demonstrate an approach for modulation of G protein-coupled receptor signaling that may represent an important therapeutic strategy.

Reduction of lipopolysaccharide-induced interleukin-6 production by the kappa opioid U50,488 in a mouse monocyte-like cell line

Several studies demonstrate that opioids modulate the immune response via opioid receptors expressed directly on the immune cells themselves. Recently, it has been suggested that the kappa opioid system has a modulatory role in various inflammatory diseases including rheumatoid arthritis. This modulation may occur via changes in cytokine secretion by monocyte-derived cells. To further study this opioid-immune relationship, we stimulated P388D1 cells, a mouse monocyte-like cell line, with lipopolysaccharide (LPS) in the presence or absence of the kappa opioid-selective ligand, U50,488. Pretreatment with U50,488 significantly reduced LPS-stimulated interleukin-6 (IL-6) production as measured by ELISA. This effect was mediated by the kappa opioid receptor, because nor-binaltorphimine (nor-BNI), a kappa-selective antagonist, blocked this inhibition. It is likely that this reduction of IL-6 protein by U50,488 treatment is attributed to decreases in IL-6 mRNA. RT-PCR experiments demonstrated that U50,488 treatment significantly reduced the LPS-mediated increase in IL-6 mRNA and that this effect was also blocked by nor-BNI. Understanding the mechanism behind the reduction of proinflammatory cytokine production by opioids may lead to the development of more effective therapeutics for inflammatory diseases.

Synthesis and Preliminary In vitro Investigation of Bivalent Ligands Containing Homo- and Heterodimeric Pharmacophores at μ, δ, and κ Opioid Receptors

A series of homo- and heterodimeric ligands containing kappa agonist and mu agonist/antagonist pharmacophores joined by a linker chain of varying lengths was synthesized and evaluated in vitro by their binding affinity at mu, delta, and kappa opioid receptors. The functional activities of these compounds were measured in the [(35)S]GTPgammaS binding assay. The data suggest that the stereochemistry of the pharmacophores, the N-substituents of the pharmacophore, ester linkages, and the spacer length were crucial factors for optimum interactions of such ligands at opioid receptor binding sites. These novel ligands as well as their pharmacological properties will serve as the basis for our continuing investigation of such bivalent ligands as probes of the opioid receptor oligomerization phenomena and for in vivo studies as analgesics.

Nalmefene induced elevation in serum prolactin in normal human volunteers: partial kappa opioid agonist activity?

In humans, mu- and kappa-opioid receptor agonists lower tuberoinfundibular dopamine, which tonically inhibits prolactin release. Serum prolactin is, therefore, a useful biomarker for tuberoinfundibular dopamine. The current study evaluated the unexpected finding that the relative mu- and kappa-opioid receptor selective antagonist nalmefene increases serum prolactin, indicating possible kappa-opioid receptor agonist activity. In all, 33 healthy human volunteers (14 female) with no history of psychiatric or substance use disorders received placebo, nalmefene 3 mg, and nalmefene 10 mg in a double-blind manner. Drugs were administered between 0900 and 1000 on separate days via 2-min intravenous infusion. Serial blood specimens were analyzed for serum levels of prolactin. Additional in vitro studies of nalmefene binding to cloned human kappa-opioid receptors transfected into Chinese hamster ovary cells were performed. Compared to placebo, both doses of nalmefene caused significant elevations in serum prolactin (p<0.002 for nalmefene 3 mg and p<0.0005 for nalmefene 10 mg). There was no difference in prolactin response between the 3 and 10 mg doses. Binding assays confirmed nalmefene's affinity at kappa-opioid receptors and antagonism of mu-opioid receptors. [(35)S]GTPgammaS binding studies demonstrated that nalmefene is a full antagonist at mu-opioid receptors and has partial agonist properties at kappa-opioid receptors. Elevations in serum prolactin following nalmefene are consistent with this partial agonist effect at kappa-opioid receptors. As kappa-opioid receptor activation can lower dopamine in brain regions important to the persistence of alcohol and cocaine dependence, the partial kappa agonist effect of nalmefene may enhance its therapeutic efficacy in selected addictive diseases.

Redefining the structure-activity relationships of 2,6-methano-3-benzazocines. Part 3: 8-Thiocarboxamido and 8-thioformamido derivatives of cyclazocine

8-Position variants of cyclazocine have been made where the phenolic 8-OH was replaced by thioamide, amidine, guanidine, urea and thiourea groups. High affinity for opioid receptors was observed for the 8-CSNH2 and 8-NHCHS analogues indicating that these groups are isosteric with not only the 8-OH but with the previously synthesized 8-CONH2 and 8-NHCHO cyclazocine derivatives.

The human herpesvirus 6 G protein-coupled receptor homolog U51 positively regulates virus replication and enhances cell-cell fusion in vitro

Human herpesvirus 6 (HHV-6) is a ubiquitous T-lymphotropic betaherpesvirus that encodes two G protein-coupled receptor homologs, U12 and U51. HHV-6A U51 has been reported to bind to CC chemokines including RANTES, but the biological function of U51 remains uncertain. In this report, we stably expressed short interfering RNAs (siRNAs) specific for U51 in human T cells and then infected these cells with HHV-6. Viral DNA replication was reduced 50-fold by the U51 siRNA, and virally induced cytopathic effects were also inhibited. In contrast, viral replication and syncytium formation were unaltered in cells that expressed a scrambled derivative of the siRNA or an irrelevant siRNA and were restored to normal when a human codon-optimized derivative of U51 was introduced into cells containing the U51 siRNA. To examine the mechanism whereby U51 might contribute to viral replication, we explored the signaling characteristics of U51. None of the chemokines and opioids tested was able to induce G protein coupling by U51, and no evidence for opioid ligand binding by U51 was obtained. The effect of U51 on cell-cell fusion was also evaluated; these studies showed that U51 enhanced cell fusion mediated by the G protein of vesicular stomatitis virus. However, a U51-specific antiserum had no virus-neutralizing activity, suggesting that U51 may not be involved in the initial interaction between the virus particle and host cell. Overall, these studies suggest that HHV-6 U51 is a positive regulator of virus replication in vitro, perhaps because it may promote membrane fusion and facilitates cell-cell spread of this highly cell-associated virus.