Characterization of a novel bivalent morphinan possessing kappa agonist and micro agonist/antagonist properties

Previous research has shown that compounds with mixed kappa and mu activity may have utility for the treatment of cocaine abuse and dependence. The present study characterizes the pharmacological profile of a bivalent morphinan that was shown to be a kappa opioid receptor agonist and a mu opioid receptor agonist/antagonist. MCL-145 [bis(N-cyclobutylmethylmorphinan) fumarate] is related to the morphinan cyclorphan and its N-cyclobutylmethyl derivative MCL-101 [3-hydroxy-N-cyclobutylmethyl morphinan S-(+)-mandelate]. MCL-145 consists of two morphinans connected by a spacer at the 3-hydroxy position. This compound had K(i) values of 0.078 and 0.20 nM for the kappa and mu opioid receptors, respectively, using radioligand binding assays as shown by Neumeyer et al. in 2003. In the guanosine 5'-O -(3-[(35) S]thiotriphosphate) binding assay, MCL-145 produced an E(max) value of 80% for the kappa opioid receptor and 42% for the mu opioid receptor. The EC(50) values obtained for this compound were 4.3 and 3.1 nM for the kappa and mu opioid receptors, respectively. In vivo MCL-145 produced a full dose-response curve in the 55 degrees C warm water tail-flick test and was equipotent to morphine. The agonist properties of MCL-145 were antagonized by the mu-selective antagonist beta-funaltrexamine and the kappa-selective antagonist nor-binaltorphimine. MCL-145 also acted as a mu antagonist, as measured by the inhibition of morphine-induced antinociception.

Effects of the mixed-action kappa/mu opioid agonist 8-carboxamidocyclazocine on cocaine- and food-maintained responding in rhesus monkeys

The present study evaluated the effects of 8-carboxamidocyclazocine (8-CAC), a novel mixed-action kappa/mu agonist with a long duration of action, on food- and cocaine-maintained responding in rhesus monkeys to assess the potential utility of 8-CAC as a medication for the treatment of cocaine dependence. The effects of acute and chronic (10 days) 8-CAC were examined in rhesus monkeys responding under a multiple schedule for both cocaine and food reinforcement. Acute 8-CAC (0.032-0.56 mg/kg, i.m.) dose-dependently eliminated cocaine-maintained responding in all three monkeys. However, doses of 8-CAC that decreased cocaine self-administration typically also decreased food-maintained responding, and 8-CAC-induced decreases in cocaine self-administration diminished during chronic 8-CAC treatment. These results confirm that 8-CAC acutely decreases cocaine self-administration. However, non-selective effects of 8-CAC on food-maintained responding and tolerance to 8-CAC effects on cocaine self-administration may limit its potential for the treatment of cocaine dependence.

Kappa-opioid receptors are differentially labeled by arylacetamides and benzomorphans

Using Chinese Hamster Ovary cell membranes that stably expressed the human kappa-opioid receptor, we investigated the hypothesis that kappa(1)- and kappa(2)-opioid receptors, historically defined by their pharmacological selectivity for either arylacetamides or benzomorphans are, in fact, different affinity states or binding sites on the same kappa-opioid receptors. Receptor binding studies showed that GTP gamma S potently inhibited [3H](5 alpha,7 alpha,8 beta)-(+)-N-methyl-N-(7-[1-pyrrolidinyl]-1-oxaspiro [4.5]dec-8-yl)-benzeneacetamide (U69,593) binding, compared to virtually no inhibition of [3H]bremazocine binding. Saturation binding experiments showed a three-fold decrease in [3H]U69,593 affinity in the presence of GTP gamma S, but GTP gamma S had no effect on [3H]bremazocine affinity. The kappa-opioid receptor antagonist nor-binaltorphimine had a four-fold higher affinity for [3H]U69,593-labeled receptors than for [3H]bremazocine-labeled receptors. Functional selectivity studies, measuring the stimulation of [35S]GTP gamma S agonist-induced binding, showed a significantly higher U69,593-induced G protein-receptor activation in comparison to the stimulation observed with bremazocine. These results suggest that pharmacologically defined 1 kappa-opioid receptor subtypes may be different affinity states of the same receptor.

Transient overexpression of κ and μ opioid receptors using recombinant adenovirus vectors

In order to study the trafficking and signal transduction mechanisms of the multiple opioid receptors, these receptors are expressed either transiently or stably in cell lines. Often, it is difficult to express receptors at a sufficiently high density to obtain reproducible results. To achieve a high density of receptors, replication-defective adenovirus (rAd5) vectors encoding the mu (MOR) and kappa (KOR) opioid receptors, both in their native form and as fusion proteins bearing the green fluorescent protein (GFP) at their C-terminus, were constructed. These vectors efficiently and reproducibly infected Chinese hamster ovary (CHO) cells that stably express the human coxsackie-adenovirus receptor (hCAR), with up to 90% of cells becoming infected at a low multiplicity of infection (MOI). Saturation receptor binding studies using mu- and kappa-selective agonists, [3H][D-Ala2, N-Me-Phe4, Gly5-ol]enkephalin (DAMGO) and [3H](5alpha7alpha,8beta)-(-)-N-methyl-N-(7-(1-pyrrolidinyl)-1-oxaspiro(4,5)dec-8-yl)benzeneacetamide (U69,593), respectively, and a nonselective antagonist, [3H]diprenorphine, revealed that rAd5-transduced cells expressed MOR and KOR for at least 3 days, at levels which exceeded those present on widely-used CHO sublines that stably express MOR or KOR. Expression levels were highest for the vectors encoding native MOR or KOR, and slightly reduced for the GFP fusion proteins. These findings demonstrate the feasibility of using rAd5 vectors to express opioid receptors at high densities, which may facilitate opioid receptor studies.

2-aminothiazole-derived opioids. Bioisosteric replacement of phenols

A series of aminothiazole-derived morphinans, benzomorphans, and morphine were synthesized. Although their affinities were somewhat lower than their phenol prototypes, one compound (9a, ATPM) has been identified possessing high affinity and selectivity at the kappa receptor. Functional assays showed that 9a was a full kappa but partial mu agonist; the efficacy at kappa was significantly greater than at mu receptors. This novel compound may be valuable for the development of long-acting analgesics and drug abuse medication.

An investigation of the N-demethylation of 3-deoxymorphine and the affinity of the alkylation products to μ, δ, and κ receptors

The N-demethylation of 3-deoxymorphine (1) was investigated using methyl chloroformate and hydrazine. 3-Deoxynormorphine (2) was obtained in 70% yield, and 3-deoxydihydronormorphine (3) was also obtained as a side product. The mu, delta, and kappa receptor binding affinity of a series of N-substituted 3-deoxynormorphines 6 and 7 and N-substituted 3-deoxydihydronormorphines 8-11 was also determined.

10-Ketomorphinan and 3-substituted-3-desoxymorphinan analogues as mixed kappa and micro opioid ligands: synthesis and biological evaluation of their binding affinity at opioid receptors

A series of 10-ketomorphinan analogues were synthesized, and their binding affinity at all three opioid receptors was investigated. In most cases, high affinity at micro and kappa receptors, and lower affinity at delta receptor was observed, resulting in good selectivity for micro and kappa receptors. A wide range of substituents can be accommodated on the nitrogen position. The N-(S)-tetrahydrofurfuryl analogue 11 displayed the highest affinity at all three receptors. The N-cyclobutylmethyl analogue 13 gave both high affinity and selectivity at kappa receptor, and N-2-phenylethyl analogue 18 exhibited good affinity and selectivity at micro receptor. Further modifications of the 3-substituent indicated that one H-bond donor was an essential requirement for good affinity at micro and kappa receptors. Similar modifications were investigated at the 3-OH group of morphinans: levorphanol (2a), cyclorphan (2b), and MCL-101 (2c) lacking the 10-keto group. The 3-amino bioisosteric analogues (40 and 41) displayed reasonably good affinity at micro and kappa receptors. The 3-carboxamido replacement (compounds 46-48) in the morphinan subseries resulted in similar affinities comparable to their corresponding 3-OH congeners. The high affinity of these carboxamido analogues, along with their greater lipophilicity and metabolic stability, make them promising candidates for further pharmacological investigation.

Assay of G protein-coupled receptor activation of G proteins in native cell membranes using [35S]GTP gamma S binding

The interaction of a G protein-coupled receptor (GPCR) with the G protein is the first step in the transduction of receptor binding to the activation of second-messenger systems mediated by G proteins. Binding of the poorly hydroylzable GTP analog guanosine-5'-O-(3-[35S]thio)triphosphate ([35S]-GTP gamma S) to the alpha subunit of a G protein has been used as a biochemical assay to measure the efficacy of a compound. The maximal percent stimulation of [35S]GTP gamma S binding, induced by an agonist, correlates well with the efficacy of an agonist in an in vivo system. The concentration of agonist necessary to achieve 50% of the maximal stimulation is indicative of the affinity of the agonist for the receptor, under the assay conditions. The [35S]GTP gamma S binding assay, which uses membranes from either myeloma cells or endogenous tissues, is a biochemical assay to determine the efficacies of agonists for receptors that are expressed endogenously. Novel compounds that have been shown to have high affinity in radioligand receptor-binding assays are screened in the [35S]GTP gamma S binding assay to determine if they are agonists, antagonists, or partial agonists at a particular receptor.

κ-Opioid Receptor Ligands Inhibit Cocaine-Induced HIV-1 Expression in Microglial Cells

Cocaine abuse has been implicated as a cofactor in human immunodeficiency virus (HIV)-1-associated dementia (HAD). In this study, we tested the hypothesis that exposure of microglial cells, the resident macrophages of the brain, to cocaine would potentiate HIV-1 expression. Because kappa-opioid receptor (KOR) agonists have been shown to suppress neurochemical and neurobehavioral responses to cocaine and to inhibit HIV-1 expression in microglial cell cultures, we also postulated that KOR ligands would inhibit cocaine-induced potentiation of HIV-1 expression. Human microglial cells were infected with HIV-1(SF162), an R5 isolate, and viral expression was quantified by measurement of p24 antigen in culture supernatants. Treatment of microglia with the KOR agonists trans-(+/-)-3,4-dichlor-N-methyl-N-(2[1-pyrrolidnyl])benzeneacetamide methanesulfonate and 8-carboxamidocyclazocine inhibited viral expression (maximal suppression of 42 and 48%, respectively). Consistent with the hypotheses, treatment of microglia with cocaine promoted HIV-1 expression (maximal enhancement of 54%), and pretreatment of microglia with these KOR agonists as well as with the KOR-selective antagonist nor-binaltorphimine abrogated cocaine-induced potentiation of viral expression. Results of flow cytometry studies suggested that the mechanism whereby KOR ligands inhibit cocaine's stimulatory effect on viral expression involves the suppression of cocaine-induced activation of extracellular signal-regulated kinase1/2, thereby blunting cocaine-enhanced up-regulation of the HIV-1 entry chemokine coreceptor CCR5. The findings of this study suggest that in addition to its neurotoxic effects, cocaine could foster development of HAD by potentiating viral expression in the brain and that this phenomenon is inhibited by KOR ligands.

Design and Synthesis of Novel Dimeric Morphinan Ligands for κ and μ Opioid Receptors

A novel series of morphinans were synthesized, and their binding affinity at and functional selectivity for micro, delta, and kappa opioid receptors were evaluated. These dimeric ligands can be viewed as dimeric morphinans, which were formed by coupling two identical morphinan pharmacophores (cyclorphan (1) or MCL 101 (2)) with varying connecting spacers. Ligands 6 and 7 with alkyl spacers on the nitrogen position and ligands 8 and 9 in which the two morphinan pharmacophores were coupled by ether moieties at the 3-hydroxyl positions showed significant decrease in affinity at all three opioid receptors. An improvement in the affinity was achieved by introducing an ester moiety as the spacer in the dimeric morphinans. It was observed that the affinity of these ligands was sensitive to the character and length of the spacer. Compound 13 (MCL-139) with a 4-carbon ester spacer, compound 17 (MCL-144) containing a 10-carbon spacer, and compound 19 (MCL-145) with the conformationally constrained fumaryl spacer were the most potent ligands in this series, displaying excellent affinities at micro and kappa receptors (K(i) = 0.09-0.2 nM at micro and K(i) = 0.078-0.049 nM at kappa), which were comparable to the parent compound 2. Ligand 12, a compound containing only one morphinan pharmacophore and a long-chain ester group, had affinity at both micro and kappa receptors almost identical to that of the parent ligand 2. In the [(35)S]GTPgammaS binding assay, ligands 13, 17, and 19 and their parent morphinans 1 and 2 stimulated [(35)S]GTPgammaS binding mediated by the micro and kappa receptors. Compounds 13 and 17 were full kappa agonists and partial micro agonists, while compound 19 was a partial agonist at both micro and kappa receptors. These novel ligands, as well as their interesting pharmacological properties, will serve as the basis for our continuing investigation of the dimeric ligands as potential probes for the pharmacotherapy of cocaine abuse and may also open new avenues for the characterization of opioid receptors.

Synthesis and pharmacology of 8-amino-3-[(tetrahydro-2-furanyl)methyl] benzomorphan

AIM

To design and synthesize new chiral 8-(substituted) amino-analogues of 3-[(tetrahydro-2-furanyl)methyl] benzomorphans, to expand knowledge of the structure-activity relationship (SAR) for 8-aminobenzomorphan.

METHODS

Target compounds were synthesized from the 8-triflate of the optically active 3-[(tetrahydro-2-furanyl)methyl]-2,6-methano-benzomorphans using Pd-catalyzed aminations. Opioid receptor binding experiments were performed to evaluate their biological activities.

RESULTS

Both 8-amino and 8-phenylamino analogues showed lower binding affinity for mu, delta and kappa receptors than corresponding 8-hydroxy-3-[(tetrahydro-2-furanyl)methyl]-2,6-methano-benzomorphan in vitro.

CONCLUSION

The relative poor binding affinity of the target compounds did not warrant conducting the in vivo studies to determine if they have the profile(kappa agonist/mu antagonist) that will be potentially useful in the treatment of drug addiction. Further study is in progress.

Synthesis and biological evaluation of 18-methoxycoronaridine congeners. Potential antiaddiction agents

Variation of the methoxycarbonyl and C-18 substituents of the antiaddictive compound 18-methoxycoronaridine, and contraction of its isoquinuclidine ring segment, provided 15 congeners for SAR evaluation at opioid and alpha3beta4 nicotinic acetylcholine receptors. The opioid activities were relatively low, and the alpha3beta4 nicotinic acetylcholine receptor activities were found to correlate with in vivo antiaddictive activities.

Redefining the structure-activity relationships of 2,6-methano-3-benzazocines. Part 2: 8-formamidocyclazocine analogues

High affinity binding for mu and kappa opioid receptors has been observed in analogues of cyclazocine, ethylketocyclazocine and naltrexone where the prototypic (of opiates) phenolic OH group was replaced with a formamide (-NHCHO) group. For the 8-formamide analogue of cyclazocine, binding is highly enantiospecific (eudismic ratios approximately 2000 for mu and kappa) with K(i) values </=1 nM observed for the (2R,6R,11R)-isomer, (-)-4. A preliminary SAR revealed that affinity is very sensitive to substitution on the formamide appendage.

Effects of mixed-action kappa/mu opioids on cocaine self-administration and cocaine discrimination by rhesus monkeys

kappa-Opioid agonists may functionally antagonize some behavioral effects of cocaine, but the role of mixed kappa/mu receptor activity is unclear. The effects of three mixed kappa/mu agonists (MCL-101, (-)cyclorphan, and Mr2034) and one kappa-selective agonist (enadoline) on cocaine self-administration and cocaine discrimination were compared in rhesus monkeys. Acute treatment with all kappa agonists dose dependently reduced cocaine-maintained responding and produced a downward shift in the cocaine self-administration dose-effect curve (0.001-0.32 mg/kg/inj, i.v.). During 7 days of chronic treatment, (-)cyclorphan (0.0032-0.032 mg/kg/h) and MCL-101 (0.0032-0.032 mg/kg/h) each dose dependently reduced cocaine self-administration maintained by a dose near the peak of the cocaine self-administration dose-effect curve. MCL-101 (0.032 mg/kg/h) produced selective and sustained decreases in cocaine self-administration, whereas (-)cyclorphan (0.032 mg/kg/h) had selective but transient effects. In addition, these mixed kappa/mu agonists produced fewer side effects (some salivation) than the kappa-selective agonist (sedation, salivation, emesis). However, none of these kappa agonists substituted for or antagonized cocaine's discriminative stimulus effects in monkeys trained to discriminate cocaine (0.4 mg/kg, i.m.) from saline. Thus, kappa and mixed kappa/mu-opioid agonists may reduce cocaine self-administration without altering cocaine's discriminative stimulus effects. Mixed kappa/mu agonists appear to offer some advantages over selective kappa agonists as potential treatments for cocaine abuse.

Several delta-opioid receptor ligands display no subtype selectivity to the human delta-opioid receptor

Pharmacological studies performed in vivo suggested that the delta-opioid receptor could exist as two distinct subtypes, delta(1) and delta(2), while in vitro studies are inconclusive. Therefore, we measured the binding and functional selectivity of several putative delta(1)- and delta(2)-opioid receptor-selective compounds in membranes from Chinese hamster ovary cells stably expressing the human delta-opioid receptor. The compounds characterized were the agonists [D-Pen(2),D-Pen(5)]enkephalin (DPDPE, delta(1)) and deltorphin II (delta(2)), and the antagonists 7-benzylidenenaltrexone (BNTX, delta(1)), naltriben (delta(2)), naltrindole 5'-isothiocyanate (delta(2)), and naltrindole (delta(1) and delta(2)). In competition binding assays, all compounds tested showed no preference for the [3H]DPDPE, [3H]deltorphin II, or [3H]naltrindole binding sites. BNTX also showed no selectivity for the delta-opioid receptor over the mu-opioid receptor. In functional assays, the stimulation of [35S]GTPgammaS binding induced by either DPDPE or deltorphin II was potently inhibited by both delta(1)- and delta(2)-opioid receptor-selective antagonists. Together, these results indicate that these compounds are not selective for either the delta(1)- or delta(2)-opioid receptor binding sites in binding or functional assays.

Syntheses and opioid receptor binding affinities of 8-amino-2,6-methano-3-benzazocines

8-Amino-2,6-methano-3-benzazocine derivatives have been made using Pd-catalyzed amination procedures, and their affinities for opioid receptors were assessed. The 8-amino group was hypothesized to be a replacement for the prototypic 8-OH substituent for 2,6-methano-3-benzazocines and related opiates. This OH group is generally required for binding yet is implicated in unfavorable pharmacokinetic characteristics such as low oral bioavailability and rapid clearance via O-glucuronidation. The core structures in which the 8-OH group was replaced were cyclazocine and its enantiomers, ethylketocyclazocine and its enantiomers, ketocyclazocine, and Mr2034. Many new analogues had high affinity for opioid receptors with several in the subnanomolar range. Highest affinity was seen in analogues with secondary 8-(hetero)arylamino appendages. Binding to opioid receptors was enantioselective with the (2R,6R,11R)-configuration preferred and high selectivity for mu and kappa over delta opioid receptors was observed within the series. Several derivatives were shown to have intrinsic opioid-receptor-mediated activity in [(35)S]GTPgammaS assays.

Delta opioid antagonist effects of buprenorphine in rhesus monkeys

Buprenorphine is an opioid with high affinity for delta, mu and kappa opioid receptors. The delta receptor-mediated effects of buprenorphine have not been studied. Thus, the present study examined the delta receptor-mediated effects of buprenorphine in rhesus monkeys. assays of receptor binding and agonist-stimulated GTP S binding confirmed that buprenorphine had high affinity for, and low efficacy at, delta receptors. In an assay of schedule-controlled responding for food presentation in four monkeys, buprenorphine produced little effect alone, but it antagonized the effects of the delta agonist SNC80, the mu agonist morphine and the kappa agonist U50,488. Buprenorphine was approximately 30-fold less potent as a delta antagonist than as a mu or kappa antagonist. In three monkeys trained to discriminate SNC80 from saline, buprenorphine alone produced only saline-appropriate responding, and buprenorphine pretreatment antagonized the discriminative stimulus effects of SNC80. In a fourth monkey, buprenorphine produced a partial substitution for SNC80 that could be blocked by the delta-selective antagonist naltrindole but not by the mu-selective antagonist quadazocine. These results indicate that, in rhesus monkeys, buprenorphine has very low efficacy at delta receptors, and that buprenorphine produces delta receptor-mediated effects with lower potency than it produces mu or kappa receptor-mediated effects.

8-Carboxamidocyclazocine: a long-acting, novel benzomorphan

To obtain benzomorphans with a longer duration of action that may be potential therapeutics for treating cocaine abuse, 8-carboxamidocyclazocine was synthesized. The pharmacological properties of 8-carboxamidocyclazocine were compared with the parent compound cyclazocine. Changing the 8-hydroxyl group on cyclazocine to an 8-carboxamido group resulted in only a 2-fold decrease in the affinity of the compound for the kappa-receptor, and no change in the affinity for the mu-opioid receptor, with both compounds having K(i) values of less than 1 nM, based on radioligand binding assays. In the guanosine 5'-O -(3-[(35)S]thio)triphosphate ([(35)S]GTPgammaS) binding assay, the two compounds produced moderate stimulation of GTP binding to the human kappa- and mu-receptors. When given by i.c.v. injection, the compounds produced less than 60% antinociception in the mouse 55 degrees C warm-water tail-flick test. However, in the mouse writhing test, the compounds had high potency in producing antinociception. Antinociception induced by either 8-carboxamidocyclazocine or cyclazocine was mediated by both kappa- and mu-opioid receptors. Cyclazocine acted as a mu-antagonist in addition to its agonist properties at the mu-receptor, as measured by the inhibition of morphine-induced antinociception. In contrast, 8-carboxamidocyclazocine did not inhibit morphine-induced antinociception, demonstrating that it was not a mu-opioid receptor antagonist in this assay. An i.p. injection of an ED(70) dose of 8-carboxamidocyclazocine produced antinociception that lasted for 15 h in contrast to cyclazocine, which produced antinociception, lasting 2 h. 8-Carboxamidocyclazocine is a novel, long-acting benzomorphan, which possesses pharmacological properties that are distinct from the properties of cyclazocine.

Mixed kappa agonists and mu agonists/antagonists as potential pharmacotherapeutics for cocaine abuse: synthesis and opioid receptor binding affinity of N-substituted derivatives of morphinan

A series of new N-substituted derivatives of morphinan was synthesized and their binding affinity for the three opioid receptors (mu, delta, and kappa) was determined. A paradoxical effect of N-propargyl (MCL-117) and N-(3-iodoprop-(2E)-enyl) (MCL-118) substituents on the binding affinities for the mu and kappa opioid receptors was observed. All of these novel derivatives showed a preference for the mu and kappa versus delta binding.

Kappa-opioid receptors on lymphocytes of a human lymphocytic cell line: morphine-induced up-regulation as evidenced by competitive RT-PCR and indirect immunofluorescence

We have previously shown that classical brain-like kappa opioid receptors (KOR) are constitutively expressed in lymphocytic cells. including human CEM x174 T-B hybrid cells, Jurkat -T4 cells, human peripheral blood mononuclear cells (PBMC), human CD4+ cells and monkey PBMC (Biochem. Biophys. Res. Commun. 209 (1995) 1003). The present study further demonstrates that the KOR of lymphocytes are activated in the presence of extracellular morphine or U50,488H, a KOR selective agonist, and the activation causes an increase in the expression of KOR mRNA, as determined by a quantitative competitive Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR) procedure. The observed agonist-induced KOR up-regulation was blocked by treating the cells with either naloxone (a KOR-partially selective antagonist) or nor-binaltorphimine (a KOR-selective antagonist). Up-regulation of lymphocytic KOR by morphine was also evidenced by flow cytometric analysis of phycoerythrin (PE) amplification of fluorescein isothiocyanate-conjugated arylacetamide labeling of the KOR. Although morphine binds primarily to mu-opioid receptors, together with the previously reported phenomenon that morphine modulation of immune functions also exists in mu-opioid receptor knockout mice, the present study confirms that opioids such as morphine may exert their effects through multiple opioid receptor types and that the effects of morphine or endogenous opioids on immune cells could not be simply adduced from the anticipated effects of a synthetic, selective opioid receptor ligand.

3-Carboxamido analogues of morphine and naltrexone. synthesis and opioid receptor binding properties

In response to the unexpectedly high affinity for opioid receptors observed in a novel series of cyclazocine analogues where the prototypic 8-OH was replaced by a carboxamido group, we have prepared the corresponding 3-CONH(2) analogues of morphine and naltrexone. High affinity (K(i)=34 and 1.7nM) for mu opioid receptors was seen, however, the new targets were 39- and 11-fold less potent than morphine and naltrexone, respectively.

Chronic opioid treatment of the mouse thymoma cell lines R1.G1 and R1EGO leads to down-regulation of the kappa opioid receptor without desensitization of adenylyl cyclase activity

Kappa opioid agonists alter some immune functions of macrophages, and T- and B-lymphocytes. The mouse thymoma cell lines R1.G1 and R1EGO express only kappa-opioid receptors and these kappa-opioid receptors are coupled to an inhibitory GTP-binding regulatory protein. Binding of kappa-opioid agonists to the opioid receptor leads to the inhibition of adenylyl cyclase activity in these cells. In this study, an acute (15 min) and chronic (24 h) treatment of R1.G1 and R1EGO cell with a potent kappa-opioid agonist (-)U50,488 (100 nM) was studied to determine if a kappa-opioid agonist altered receptor number and/or desensitization of adenylyl cyclase activity in these two cell lines. Chronic treatment of both R1.G1 and R1EGO cells with (-)U50,488 lead to down-regulation of the kappa-opioid receptor, measured as a decrease of approximately 50% in the Bmax value for the binding of [3H]U69,593. The binding affinity (Kd value) was not affected after chronic treatment either in R1.G1 or R1EGO cells. There was no difference in the magnitude of inhibition of adenylyl cyclase activity by (-)U50,488 between the acute (15 min) and chronic (24-h) treatment in both cell lines R1.G1 and R1EGO. This study indicates that chronic opioid treatment of mouse thymoma R1.G1 and R1EGO cell lines leads to down-regulation of the receptor, without desensitization. This phenomenon was observed in R1.1 parent mouse thymoma cell line and recently in CHO cells expressing kappa-opioid receptor. This study demonstrates that unlike some neuronal preparations, chronic opioid treatment of the thymoma cell lines resulted in receptor down-regulation without desensitization.

Kappa-opioid receptor agonist suppression of HIV-1 expression in CD4+ lymphocytes

Synthetic kappa-opioid receptor (KOR) agonists have been shown to suppress HIV-1 expression in acutely infected macrophages. In the present study, we examined the effects of the KOR ligand trans-3,4-dichloro-N-methyl-N[2-(1-pyrolidinyl)cyclohexyl]benzeneaceamide methanesulfonate (U50,488) on HIV-1 expression in CD4+ lymphocytes, the main target cell of this virus. When U50,488 was added to activated CD4+ lymphocytes, HIV-1 expression was inhibited in a concentration- and time-dependent manner with maximal suppression (approximately 60%) at 10(-7) M U50,488. The KOR selective antagonist nor-binaltorphimine (nor-BNI) had no effect by itself on viral expression but blocked the antiviral property of U50,488, suggesting that U50,488 was acting via a KOR-related mechanism. Support for the involvement of KOR was provided by the findings that 34% of activated CD4+ lymphocytes were positive for KOR, using an immunofluorescence technique, and that seven additional synthetic KOR ligands also inhibited HIV-1 expression. The results of this study broaden understanding of the antiviral properties of KOR ligands to include cells outside of the nervous system and suggest a potential role for these agents in the treatment of HIV-1 infection.

8-Carboxamidocyclazocine analogues: redefining the structure-activity relationships of 2,6-methano-3-benzazocines

Unexpectedly high affinity for opioid receptors has been observed for a novel series of cyclazocine analogues where the prototypic 8-OH was replaced by a carboxamido group. For mu and kappa opioid receptors, the primary carboxamido derivative of cyclazocine ((+/-)-15) displayed high affinity (Ki=0.41 and 0.53 nM, respectively) nearly comparable to cyclazocine. A high enantiopreference ((2R,6R,11R)-) for binding was also observed. Compound (+/-)-15 also displayed potent antinociception activity in mice when administered icv.