Opioid Receptor Binding Properties Research Articles

Transdermal Buprenorphine, Opioid Rotation to Sublingual Buprenorphine, and the Avoidance of Precipitated Withdrawal

Buprenorphine is an opioid, used in the United States and abroad for both analgesia and addiction, with unique opioid receptor binding properties. There are several pharmacological features of buprenorphine that make it an emerging option for the long-term treatment of chronic pain-its respiratory suppression ceiling effect, its efficacy in neuropathic pain and hyperalgesic states, and its decreased suppression of the immune and endocrine systems compared with other long-acting opioids. Previous studies have shown that high-dose sublingual buprenorphine is an effective treatment of chronic pain patients not responding to other opioids. Guidelines for the introduction of sublingual buprenorphine, termed buprenorphine induction, include an opioid-free "withdrawal" period of 12-48 hours to avoid an anticipated and accelerated opioid withdrawal, a syndrome described in this article as precipitated withdrawal. The requirement of a period of opioid abstinence before buprenorphine use may present a significant barrier to its adoption for chronic pain. We present a case series of a novel method of sublingual buprenorphine introduction without an induction period, using the recently Food and Drug Administration-approved low-dose transdermal buprenorphine (Butrans; Purdue Pharma L.P.) as a bridge medication. In these cases, buprenorphine was started in opioid-dependent chronic noncancer pain patients who had taken short-acting opioid medications within hours of the initiation of the rotation. This method avoids the painful abstinence period and did not result in precipitated withdrawal or other significant adverse effects.

N-terminal guanidinylation of the cyclic 1,4-ureido-deltorphin analogues: the synthesis, receptor binding studies, and resistance to proteolytic digestion.

The synthesis of a series of N-guanidinylated cyclic ureidopeptides, analogues of 1,4-ureido-deltorphin/dermorphine tetrapeptide is described. The δ- and μ-opioid receptor affinity of new guanidinylated analogues and their non-guanidinylated precursors was determined by the displacement radioligand binding experiments. Our results indicate that the guanidinylation of cyclic 1,4-ureidodeltorphin peptide analogues does not exhibit a uniform influence on the opioid receptor binding properties, similarly as reported earlier for some linear peptides. All analogues were also tested for their in vitro resistance to proteolysis during incubation with large excess of chymotrypsin, pepsin, and papain by means of mass spectroscopy. Guanidinylated ureidopeptides 1G-4G showed mixed μ agonist/δ agonist properties and high enzymatic stability indicating their potential as therapeutic agents for treatment of pain.

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 μ, δ and κ opioid receptors was observed when the OH → CONH 2 switch was applied. For 4,5α-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.

Redefining the structure–activity relationships of 2,6-methano-3-benzazocines. Part 6: Opioid receptor binding properties of cyclic variants of 8-carboxamidocyclazocine

A series of 7,8- and 8,9-fused pyrimidinone, aminopyrimidine and pyridone derivatives of 8-carboxamidocyclazocine (8-CAC) have been prepared and evaluated in opioid receptor binding assays. Targets were designed to corroborate a pharmacophore hypothesis regarding the bioactive conformation of the carboxamide of 8-CAC. In addition to the results from this study strongly supporting this pharmacophore hypothesis, a number of novel compounds with high affinity to opioid receptors have been identified.

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 μ opioid receptor was achieved though the N-(2-(4′-methoxybiphenyl-4-yl)ethyl) analogue of 8-CAC. High binding affinity to μ and very high binding affinity to κ 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.

Sensitivity of dopamine systems to opioidergic stimulation in alcoholism: a PET study with [18F]fallypride

It is widely accepted that the mesolimbic dopamine (DA) system plays a major role in the rewarding effects of alcohol consumption. In addition there is increasing evidence that alcohol interferes with endogenous opioid mechanisms which in return modulate dopaminergic transmission in the mesolimbic pathway. It is assumed that alcohol has (acute and chronic) effects on the binding properties of opioid receptors. Opioid agonists with affinity for µ opioid receptors are expected to develop their rewarding effect by activation of the mesolimbic dopamine system which ascends from the ventral tegmentum to the nucleus accumbens. The aim of the present study was to test for differences in sensitivity of DA reward systems to opioidergic stimulation in alcohol-dependent patients and healthy controls. D2-like DA receptors were quantified with PET and [18F]fallypride as the radiotracer in 8 male detoxified alcohol dependent patients and 8 age matched controls. Subjects underwent dynamic PET scans over 180 minutes. To test for a group difference in DA release between baseline and experimental condition, participants were scanned twice, the second time after application of the short-acting µ-opiate agonist remifentanil. Binding potentials (BP) were calculated by means of the simplified reference tissue model. DA release was calculated as percent change in BP. Craving was assessed in both conditions. The results will be presented and discussed in the light of current models of addiction.

Synthesis and opioid receptor binding properties of a highly potent 4-hydroxy analogue of naltrexone

Very high affinity for opioid receptors (e.g., K i = 0.052 nM for μ) has been observed in the rationally designed naltrexone analogue 5. SAR and physical data supports the hypothesis that the 4-OH group of 5 stabilizes the 3-carboxamido group in the putative bioactive conformation.

ChemInform Abstract: 3‐Carboxamido Analogues of Morphine and Naltrexone: Synthesis and Opioid Receptor Binding Properties.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

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

High-affinity binding to μ opioid receptors has been identified in a series of novel 3-carboxamido analogues of morphine and naltrexone.

Selective protection and functionalization of morphine: synthesis and opioid receptor binding properties of 3-amino-3-desoxymorphine derivatives.

As part of an effort to identify novel opioid receptor interactive agents, we recently prepared a series of 8-(substituted)amino analogues of cyclazocine. We found the chiral 8-phenylamino (NHC(6)H(5)) cyclazocine derivative to have subnanomolar affinity for kappa opioid receptors and a 2-fold lower affinity for mu, opioid receptors. To determine if the benefits of (substituted)amino groups could be extended to the morphine core structure, we have made five novel 3-amino-3-desoxymorphine derivatives of general structure 5 where RR'N = H(2)N, CH(3)NH, (CH(3))(2)N, C(6)H(5)NH, and C(6)H(5)CH(2)NH. Relative to morphine, these derivatives had 38-273-fold, 11-41-fold, and 10-141-fold lower affinity for mu, delta, and kappa opioid receptors, respectively. Target compounds were made via Pd-catalyzed amination of a morphine 3-trifluoromethylsulfonate substrate where the 6-OH group was protected with a tert-butyldiphenylsilyl group. To make 6-tert-butyldiphenylsilyloxymorphine selectively, a new high-yield method was developed whereby morphine was bis-silylated using normal conditions followed by selective removal of the 3-tert-butyldiphenylsilyl group with catalytic tetrabutylammonium fluoride.

New opioid affinity labels containing maleoyl moiety

Opioid receptor binding properties and pharmacological profiles of novel peptides containing maleoyl function were determined in order to develop new affinity labels. Based on the enkephalin structure peptide ligands were synthesized and tested. Both in in vitro receptor binding experiments and pharmacological studies, all ligands showed agonist character with relatively high affinity (K i values in the nanomolar range) and good to moderate selectivity. Replacement of Gly 2 in the enkephalin frame with D-Ala led to higher affinities with a small decrease in selectivity. The longer peptide chains resulted in compounds with high percentage (up to 86%) of irreversible binding. The selectivity pattern of the ligands is in good agreement with the data obtained from the pharmacological assays (guinea pig ileum and mouse vas deferens bioassays). The newly synthesized peptides could be used in further studies in order to determine more detailed characteristics of the ligand-receptor interaction.

Interaction of agonist peptide [ 3H]Tyr- d-Ala-Phe-Phe-NH 2 with μ-opioid receptor in rat brain and CHO-μ/1 cell line

Opioid receptor binding properties of [ 3H]Tyr- d-Ala-Phe-Phe-NH 2 (TAPP) were characterized in rat brain and Chinese hamster ovary (CHO) cells expressing the rat μ-receptor. In rat brain, [ 3H]TAPP labeled a single class of opioid sites with a dissociation constant (K d) of 0.31 nM and maximal number of binding sites (B max) of 119 fmol/mg protein. In CHO-μ/1 cell membranes, the K d and B max values were 0.78 n M and 1806 fmol/mg protein, respectively. Binding to rat brain was demonstrated to be pharmacologically identical to that obtained with CHO-μ/1 cell membranes and modulated by Na + ions and guanine nucleotides. The high affinity and selectivity of [ 3H]TAPP together with its low non-specific binding make this radioligand a useful tool for labeling the native and cloned μ-opioid receptor.

Endogenous opioid systems and alcohol addiction.

Alcohol exerts numerous pharmacological effects through its interaction with various neurotransmitters and neuromodulators. Among the latter, the endogenous opioids play a key role in the rewarding (addictive) properties of ethanol. Three types of opioid receptors (mu, delta and kappa) represent the respective targets of the major opioid peptides (beta-endorphin, enkephalins and dynorphins, respectively). The rewarding (reinforcing) properties of mu- and delta-receptor ligands are brought by activation of the mesolimbic dopamine system which ascends from the ventral tegmentum of the midbrain (VTA) to rostral structures; of these, the nucleus accumbens (NAC) is of particular importance in drug addiction. In contrast, dysphoria results from activation of kappa-receptors. The neurochemical manifestations of these opposing effects are, respectively, increases and decreases in dopamine release in the NAC. Several lines of evidence indicate that alcohol interferes with endogenous opioid mechanisms which are closely linked with dopamine transmission in the mesolimbic pathway. The view that condensation products of dopamine and alcohol-derived aldehyde (tetrahydroisoquinolines) play a role remains controversial. There is, however, much information on the direct (acute and chronic) effects of alcohol on the binding properties of opioid receptors, as well as modulation of opioid peptide synthesis and secretion (e.g. a suggested increase in beta-endorphin release). In view of the reinforcing properties of alcohol, it is relevant to consider behavioural studies involving alcohol self-administration in rodents and primates. Low doses of morphine have been found to increase, and higher doses of the opiate to decrease, alcohol consumption. Conversely, opioid antagonists such as naloxone and naltrexone (which bind to non-selectively opioid receptors) have been shown to decrease alcohol consumption under various experimental conditions. Similar results have been reported when selective mu- or delta-receptor antagonists are administered. Results obtained in genetic models of high preference for alcohol also support the view that alcohol intake depends on the activity of the endogenous opioid reward system and that alcohol consumption may serve to compensate for inherent deficits in this system. One hypothetical model proposes that reward results from activation of mu-opioid receptors in the VTA and/or delta-receptor in the NAC; both these nuclei are targets of endogenous beta-endorphin. It is suggested that alcohol interferes with this reward pathway either directly or indirectly. The available experimental data accord well with those obtained from clinical studies which opioid antagonists have been used to prevent relapse in alcoholics. Conceptual considerations concerning communalities between various forms of addictions are also discussed in this review.

O-21-6 - Opioid receptor binding properties of [ 3H]Buprenorphine in rat brain

-The localization of 5-HT-moduline, an endogenous cerebral tetrapeptide (LSAL) which specifically interacts with 5-HT1B receptors (Rousselle et al., 1996; Massot et al., 1996) was examined in mouse brain using an immunocytochemistry technique with a polyclonal anti-peptide antibody highly specific for this tetrapeptide. Highest levels of 5-HT-moduline immunoreactivity were observed in the cerebral cortex including cingulate, retrosplenial, parietal and pyriform cortical areas and in the basal ganglia. Intense immunoreactivity also occurred in the hippocampus, subiculum, various hypothalamic and thalamic nuclei and in some midbrain regions such as the substantia nigra and the superior colliculi. Immunoreactive neurons generally showed intense and extensive labelling of the perikarya and dendritic arborizations with moderate to heavy characteristic deposits of reaction product along plasma membranes and within cytoplasm while the nuclei were devoid of reaction product. The results obtained indicated that 5-HT-moduline immunoreactivity was heterogenously distributed in neuronal structures of mouse brain. The distribution of 5-HT-moduline immunoreactivity closely correlated with that of 5-HT-moduline specific binding sites as visualized by autoradiography (Massot et al., 1996). Moreover, it seems to overlap with the distribution of serotonergic innervation and also with that of 5-HT1B receptors in mouse brain (Boschert et al., 1994; Bruinvels et al., 1994; Chopin et al., 1994; Langlois et al., 1995). These data provide evidence that 5-HT-moduline immunoreactivity is located in cells with the morphological appearance of neurones. Its localization in brain areas which also contain 5-HT1B receptors, is in good agreement with previous demonstrations that this peptide specifically interacts with 5-HT1B receptors to regulate their functional activity and accordingly controls the modulatory activity of the serotoninergic system on various CNS functions.

Tandem mass spectrometry analysis of synthetic opioid peptide analogs

Five synthetic opioid peptides that were designed to have specific opioid receptor-binding properties were studied by low energy collision-induced dissociation (CID) tandem mass spectrometry (MS/MS). The MS/MS data are required for the analysis of those peptides in ovine plasma in a study to determine the placental transfer of the peptide to the fetus. The synthetic enkephalin-related peptides were: Tyr-D-Arg-Phe-Lys-NH2, (DALDA), N,N-diallyl-Tyr-Aib-Aib-Phe-Leu-OH, (ICI 174,864), Tyr-D-Thr-Gly-Phe-Leu-Thr, (DTLET), Tyr-D-Pen-Gly-Phe-D-Pen-OH, (DPDPE), and D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2, (CTAP). Liquid secondary ion mass spectrometry (LSIMS) was used for sample desorption-ionization, and a hybrid (E1BE2qQ) tandem mass spectrometer was used to collect the product-ion spectra. A protonated molecule ion, [M + H]+, was observed for each peptide. Amino acid sequence-determining fragment ion were produced by CID and collected by MS/MS for the three linear peptides, and also for the two disulfide-bond-containing peptides in their unreduced and dithiothreitol (DTT)-reduced forms. The detection level for the [M + H]+ ion of DTLET was ca. 3 pmol; and the stabilities of the CTAP and ICI analogs in plasma were studied.

Synthesis of [ [formula omitted]-ALA 2, 4′- 125I-PHE 3, GLU 4] deltorphin and characterization of its δ opioid receptor binding properties

Both [ d -Ala 2, Glu 4]Deltorphin and [ d -Ala 2, 4′-I-Phe 3, Glu 4]Deltorphin are highly selective ligands for δ, relative to μ, opioid receptors. Radiolabeled [ d -Ala 2, 4′- 125I-Phe 3, Glu 4]Deltorphin ([ 125I]Deltorphin) was prepared with a specific activity of 2200 Ci/mmol from [ d -Ala 2, 4′-NH 2-Phe 3, Glu 4]Deltorphin through a diazonium salt intermediate. The inhibition of [ 125I]Deltorphin binding to rat brain membranes by ligands selective for μ, δ, and κ opioid receptors is consistent with binding by the radioligand to a single site having the properties of a δ opioid receptor. The results of these studies are in good agreement with those obtained by structurally different δ opioid receptor ligands. The similarity between the δ receptor site labeled by [ 125I]Deltorphin and those labeled by other δ receptor agonists, in contrast to differences seen by in vivo studies of their analgesic effects, is discussed.

Studies on Analgesic Oligopeptides. VII. Solid Phase Synthesis and Biological Properties of Tyr-D-Arg-Phe-.BETA.Ala-NH2 and its Fluorinated Aromatic Amino Acid Derivatives.

Tyr-D-Arg-Phe-beta Ala-NH2 (I) and its six fluorinated analogs were synthesized. Their opioid receptor binding properties were examined in vitro and their analgesic activity in vivo using the mouse writhing test. It was found that I was one of the most selective and potent mu-receptor agonists reported to date. [Tyr(2F)1](VI) and [Tyr(3F)1](V) derivatives of I showed similar biological properties to those of I. Since these peptides resist enzymatic degradation, it is expected that they are excellent reagents for the studies of function of mu-receptor-mediated biological properties in vivo and in vitro.

Solid phase synthesis and opioid receptor binding properties of presumable dermorphin precursor derivatives.

Presumable dermorphin precursor peptide derivatives comprised of 35 amino acids and their fragments, which are based on the amino acid sequence determined by recombinant deoxyribonucleic acid (DNA) techniques, were synthesized by the solid phase method. A 35-residue peptide amide containing L-Ala2-dermorphin sequence at the N-terminus (1) as well as its D-Ala2 isomer (2) and the C-terminal 20-residue peptide amide were found to be unexpectedly stable against aminopeptidase M digestion and in rat brain membrane fractions mixture, suggesting that the C-terminal Glu-rich moiety of 1 and 2 serves to protect from enzymatic breakdown. In the opioid receptor binding assay, 2 showed 40 and 25-fold higher affinities than 1 for mu and delta-receptors, respectively. The N-terminal 15-residue peptide fragment of 2 showed greatly increased affinities for both receptors, being one half of those of dermorphin, whereas that of 1 showed low affinities. Opioid receptor binding properties of these synthetic peptides may be useful in investigation of the processing to dermorphin.

Studies on analgesic oligopeptides. VI. Further studies of synthesis and biological properties of tripeptide alkylamides, Tyr-D-Arg-Phe-X.

Nine analogs based on a structure of Tyr-D-Arg-Phe-X (X = alkylamides or alkylhydrazide containing electron-withdrawing atoms or groups) were newly synthesized and their biological properties were examined by the opioid receptor binding properties of mu-, delta- and kappa-receptors, guinea-pig ileum (GPI) assay and analgesic activity in the tail pinch test after subcutaneous administration in mice. Analogs with X = NHCF2CF3, Sar-ol, or NH(CH2)2CN showed potent activities in the GPI and analgesic assays and high affinity for mu-receptor. An analog with X = taurinamide was found to possess 4-fold higher mu-receptor selectivity than that of [D-Ala2, MePhe4, Gly-ol5]enkephalin (DAGO). The receptor binding properties of previously reported analogs [Chem. Pharm. Bull., 33, 1528 (1985); ibid., 33, 4865 (1985); ibid., 36, 4834 (1988)] were also examined for overall discussion of the structure-activity relationships of this series of tripeptide amides.

Characterization of kappa opioid receptors in neurosecretosomes from bovine posterior pituitary.

The binding properties of opioid receptors on isolated nerve terminals (neurosecretosomes) from bovine posterior pituitaries were characterized. Both [3H]etorphine and [3H]ethylketocyclazocine ([3H]EKC) showed high-affinity binding with complex binding isotherms, consistent with the presence of multiple classes of binding sites. [D-Ala2,D-Leu5]enkephalin showed no specific binding and failed to displace [3H]etorphine at high concentrations, indicating the absence of mu, delta, or benzomorphan (kappa 2) sites. Mathematical modelling of the data suggested the presence of three classes of binding sites. The first was of high affinity with Kd values of 0.9 and 2.0 nM for etorphine and EKC, respectively. The second class of sites appeared to bind etorphine with a KD of 150 nM, and EKC with extremely low affinity (unmeasurable binding). The third class of sites was characterized by KD values of 7 and 2 microM for etorphine and EKC, respectively. These results indicate that the nerve terminals of bovine posterior pituitary contain opioid binding sites of the kappa type. Furthermore, these binding sites appear heterogeneous, consisting of at least two and possibly more subtypes or states.