SoRI 9409, a non-peptide opioid mu receptor agonist/delta receptor antagonist, fails to stimulate [35S]-GTP-gamma-S binding at cloned opioid receptors

Recent work suggests that opioids which combine mu agonist and delta antagonist activity may be non-addicting antinociceptive agents. SoRI 9409 (5'-(4-Chlorophenyl)-17-(cyclopropylmethyl)-6,7-didehydro-3,14-dihydroxy-4,5alpha-epoxypyrido-[2',3':6,7]morphinan) is a naltrexone-derived non-peptide ligand which demonstrates partial mu and kappa agonist activity and antagonist activity at delta receptors. Chronic administration of SoRI 9409 to mice failed to produce tolerance to its antinociceptive effect and SoRI 9409 produced less withdrawal signs than naloxone in acute and chronic morphine dependence models. To further characterize SoRI 9409 we determined its effects in the guanosine 5'-O-(3-[35S]thio)-triphosphate binding assay. SoRI 9409 demonstrated no agonist activity at cloned mu delta, or kappa receptors. Other experiments demonstrated that SoRI 9409 was a potent and selective delta antagonist (K(i) = 0.08 nM) which acted also as an antagonist at mu and kappa receptors. Its profile of activity resembled that of naltrindole (NTI). Viewed collectively, the in vitro data reported here predict that SoRI 9409 should be a mu antagonist in vivo, which is not observed. Resolving these discrepant findings will require additional research.

Opioid peptide receptor studies. 15. Relative efficacy of 4-[(N-allyl-3-methyl-4-piperidinyl)phenylamino]-N,N-diethylbenzamide and related compounds at the cloned human delta-opioid receptor

Previous data obtained from both binding and functional assays demonstrated that (-)-4-[(N-allyl-3-methyl-4-piperidinyl)phenylamino]-N,N-diethylbenzamide [(-)-RTI5989-54] displays selective binding and full agonist activity relative to (+/-)-RTI5989-54 for the delta opioid receptor. The present study was conducted to evaluate the activities of structurally diverse opioid receptor delta ligands in the [(35)S]GTP-gamma-S binding assay, comparing the relationship between receptor binding, activation, efficacy, and intrinsic efficacy. The data, obtained with cloned human delta receptors, demonstrated that (-)-RTI5989-54 behaves like the highly selective delta agonist SNC80. Addition of the hydroxyl group to RTI5989-54 (RTI5989-61) or replacement of the allyl group with the trans-crotyl group on the piperidine nitrogen of RTI-5989-61 (RTI5989-62) increased binding affinity, produced full agonist activity, and decreased intrinsic efficacy at the delta opioid receptor. The order of potency for the EC(50) (GTP-gamma-S) was RTI5989-62 (0.20 nM) > RTI5989-61 (0.43 nM) > SNC80 (1.92 nM) > DPDPE (3.50 nM) > (-)-RTI5989-54 (17.6 nM) > (+/-)-RTI5989-54 (65.6 nM) > (+)-RTI5989-54 (483 nM). RTI5989-61 and RTI5989-62 were fully efficacious, but had intrinsic efficacy values that were 2.2-3.1 times lower than that of DPDPE and SNC80. Comparison of the binding K(i) in competitively inhibiting [(125)I]IOXY binding to the functional K(i) for delta antagonists [Ki (IOXY)/Ki (GTP-gamma-S)] shows that antagonists might antagonize agonist-evoked neurochemical effects with equal magnitude while occupying different proportions of target receptors.

Mutation W284L of the human delta opioid receptor reveals agonist specific receptor conformations for G protein activation

Intrinsic activities of different delta opioid agonists were determined in a [35S]GTPgammaS binding assay using cell membranes from Chinese hamster ovary (CHO) cells stably expressing the wild type (hDOR/CHO) or W284L mutant human delta opioid receptor (W284L/CHO). Agonist binding affinities were regulated more robustly by sodium and guanine nucleotide in W284L/CHO than in hDOR/ CHO cell membranes. The W284L mutation selectively reduced the affinity of SNC 80 while having moderate effect ((-) TAN 67) or no effect (DPDPE) on the affinities of other delta selective agonists. The mutation had opposite effects on the intrinsic activities of agonists belonging to different chemical classes. The effects of the mutation on agonist affinities and potencies were independent from its effects on the intrinsic activities of the agonists. Maximal stimulation of [35S]GTPgammaS binding by SNC 80 was 2-fold higher in W284L mutant cell membranes than in wild type hDOR/CHO cell membranes, despite lower receptor expression levels in the W284L/CHO cells. The binding affinity of SNC 80 however, was significantly reduced (15-fold and 30-fold in the absence or presence of sodium+GDP respectively) in W284L/CHO cell membranes relative to wild type hDOR/CHO membranes. Conversely, the Emax of (-)TAN 67 in the [35S]GTPgammaS binding assay was markedly reduced (0.6-fold of that of the wild type) with only a slight (6-fold) reduction in its binding affinity. The affinity and intrinsic activity of DPDPE on the other hand remained unchanged at the W284L mutant hDOR. The mutation had similar effects on the affinities potencies and intrinsic activities of (-)TAN 67 and SB 219825. The results indicate that delta opioid agonists of different chemical classes use specific conformations for G protein activation.

Increased tumor necrosis factor-alpha and nitric oxide production by rat macrophages following in vitro stimulation and intravenous administration of the delta-opioid agonist SNC 80

Opioids alter immune function by binding to opioid receptors on cells of the immune system, or indirectly by acting on receptors within the central nervous system. Mu-selective opioid agonists are generally associated with immunosuppression, whereas delta-opioid receptor-selective agonists are commonly associated with immunopotentiation. We have previously shown that intracerebroventricular administration of the nonpeptide delta-opioid receptor agonist (+)-4-((alpha R)-alpha-((2S, 5R)-4-allyl-2, 5-dimethyl-1-piperazinyl)-3-methoxybenzyl)-N, N-diethyl-benzamide (SNC 80) did not alter certain parameters of immunocompetence. In the present study, we studied the in vitro and ex vivo effects of SNC 80 on rat macrophage and lymphocyte functions. We showed that SNC 80 at concentrations of 10(-7) M and 10(-6) M, significantly (P < 0.01) stimulated the in vitro production of tumor necrosis factor-alpha (TNF-alpha) (60-100% increase) and nitric oxide (34-67% increase) by resident and LPS-stimulated peritoneal macrophages. Similarly, intravenous administration of SNC 80 (6.8 mg/kg) significantly (P < 0.01) increased the production of TNF-alpha and nitric oxide (2- and 1.5-fold increases respectively, compared with saline-injected control) by LPS-stimulated splenic macrophages. In addition, intravenous injection of SNC 80 plus Con A potentiated ex vivo LPS-stimulated macrophage functions. SNC 80 could potentially be utilized in various clinical situations where immunosuppression is undesirable.

Effect of N-alkyl and N-alkenyl substituents in noroxymorphindole, 17-substituted-6,7-dehydro-4,5alpha-epoxy-3,14-dihydroxy-6,7:2',3'-indolomorphinans, on opioid receptor affinity, selectivity, and efficacy

The N-alkyl analogues (N-ethyl through N-heptyl), branched N-alkyl chain analogues (N-isopropyl, N-2-methylpropyl, and N-3-methylbutyl), and N-alkenyl analogues ((E)-N-3-methylallyl (crotyl), N-2-methylallyl, and N-3,3-dimethylallyl) were prepared in the noroxymorphindole series (17-substituted-6,7-dehydro-4,5alpha-epoxy-3,14-dihydroxy-6,7:2',3'-indolomorphinans), and the effect of the N-substituent on opioid receptor affinity, selectivity, and efficacy was examined using receptor binding assays, [(35)S]GTPgammaS efficacy determinations, and smooth muscle functional assays (electrically stimulated mouse vas deferens and guinea pig ileum). All of the compounds acted as opioid antagonists, including those with N-substituents which usually confer either weak agonist-antagonist behavior (N-ethyl) or potent opioid agonist activity (N-pentyl) in morphinan-like ligands which interact with the mu-receptor. Several N-substituted noroxymorphindoles were found to be more mu/delta-selective than naltrindole (NTI). The N-2-methylallylnoroxymorphindole, in particular, was found to be more selective than NTI in receptor binding assays (mu/delta = 1700 vs 120; kappa/delta = 810 vs 140), as an antagonist in the GTPgammaS assay (mu/delta = 170 vs 140; kappa/delta = 620 vs 160), and considerably more selective than NTI in the functional assays (mu/delta > 2200 vs 90). It also had high affinity for the delta-opioid receptor (K(i) = 4.7 nM in the binding assay) and high antagonist potency (1.2 nM in the GTPgammaS assay; 8.9 nM in the MVD assay).

Antinociceptive effects of delta-opioid agonists in Rhesus monkeys: effects on chemically induced thermal hypersensitivity

The effects of SNC80 and other structurally related delta-opioid receptor agonists were assessed under conditions of chemically induced hypersensitivity to thermal stimuli in four rhesus monkeys. The shaved tail of each monkey was exposed to warm water (38, 42, 46, and 50 degrees C), and the tail-withdrawal latency from each temperature was recorded. The effects of drugs on the temperature that produced a 10-s tail-withdrawal latency (the T(10) value) were examined. Capsaicin (0.01-0.32 mg) injected into the tail of monkeys dose dependently decreased the T(10), indicating that capsaicin increased sensitivity to thermal stimuli. A dose of 0.1 mg of capsaicin decreased the T(10) from 48.0 to 42.1 degrees C (a -5.9 degrees C change) 15 min after injection. SNC80 (1.0-10.0 mg/kg s.c.) dose dependently blocked the capsaicin-induced decrease in the T(10), and 10.0 mg/kg SNC80 fully blocked the effects of capsaicin. The delta-selective antagonist naltrindole (0.1-1.0 mg/kg) dose dependently antagonized the effects of SNC80, whereas a mu-selective dose of the opioid antagonist quadazocine (0.1 mg/kg) did not. Two other delta-selective agonists, SNC162 (1.0-10.0 mg/kg) and SNC243A (1.0-10.0 mg/kg), also dose dependently blocked capsaicin-induced thermal hypersensitivity. In contrast, neither SNC67 (10.0 mg/kg), which is the (-)-enantiomer of SNC80, nor the nonsteroidal anti-inflammatory drug (NSAID) ketorolac (1.0-10.0 mg/kg) modified the effects of capsaicin. SNC80 was also effective in reversing thermal hypersensitivity induced by prostaglandin E(2) (0.0158 mg) and Freund's complete adjuvant (10% concentration). These findings suggest that delta-agonists have antinociceptive effects in primates under conditions of chemically induced thermal hypersensitivity and might be effective under a broader range of conditions than clinically available NSAIDs.

A comparison of cocaine, GBR 12909, and phentermine self-administration by rhesus monkeys on a progressive-ratio schedule

The dopamine reuptake inhibitor GBR 12909 and the dopamine releaser phentermine may have potential for the treatment of cocaine abuse in humans. Pre-session treatment with either drug can decrease cocaine-maintained responding in rhesus monkeys while not affecting food-maintained responding. Both drugs are self-administered, but in some reports the patterns of responding they maintain differ from typical cocaine-reinforced responding. This study compared self-administration of cocaine (1--100 microg/kg/inj), GBR 12909 (3--100 microg/kg/inj), and phentermine (10--170 microg/kg/inj) in rhesus monkeys on a progressive-ratio schedule. Individual unit doses of each drug were available across several consecutive sessions. Cocaine self-administration was typical: the average number of ratios completed per session was a bitonic (increasing/decreasing) function of unit dose. Phentermine self-administration was variable across subjects (two of four monkeys self-administered reliably); one subject exhibited clear signs of behavioral toxicity. Self-administration of GBR 12909 was similarly variable across subjects. In the two subjects that self-administered GBR 12909 reliably, self-administration of small to mid-sized unit doses was enhanced following exposure to large unit doses. These data indicate that differences in self-administration of these drugs can be observed under progressive ratio procedures. Further, the data add to existing evidence suggesting that phentermine and GBR 12909 have at least moderate potential to be abused by humans.

The development of a potential single photon emission computed tomography (SPECT) imaging agent for the corticotropin-releasing hormone receptor type

A high-affinity radioligand for CRHR1 has been prepared that can serve as a template for the development of SPECT imaging agents. The 5-chloro-N-cyclopropylmethyl-N-(2,6-dichloro-4-iodophenyl)-2-methyl-N-propylpyrimidine-4,6-diamine (6b, Ki = 14 nM), and the corresponding 4-bromophenyl analogue (6a, Ki = 21 nM), were synthesized in four steps from compound 3.

Response requirements and unit dose modify the effects of GBR 12909 on cocaine-maintained behavior

Previous studies found that GBR 12909 can decrease cocaine-maintained responding at doses that do not affect food-maintained responding. In this study, the effects of GBR 12909 (0.3-3.0 mg/kg) were further examined by varying the response requirement and unit dose of cocaine. Rhesus monkeys earned food or cocaine under a multiple fixed-ratio (FR) schedule. The FR for food was always 30, but the FR for cocaine was varied from 10-130 and the unit dose was varied from 5.6-56.0 microg/kg per injection. Doses of GBR 12909 were tested in an ascending order, for 5 consecutive sessions each. GBR 12909 selectively decreased cocaine-maintained responding in all monkeys in at least 1 condition. These effects were enhanced with large response requirements and/or small unit doses. The results demonstrate that environmental variables can influence the selectivity of GBR 12909's effects and contribute to a growing debate concerning the evaluation of potential pharmacotherapies for drug abuse.

Opioid peptide receptor studies. 14. Stereochemistry determines agonist efficacy and intrinsic efficacy in the [(35)S]GTP-gamma-S functional binding assay

Previous data obtained with the cloned rat mu opioid receptor demonstrated that stereochemistry affects the four parameters of the ligand-receptor interaction: potency (ED(50)), efficacy (maximal stimulation), intrinsic efficacy (effect as a function of receptor occupation), and binding affinity. This study evaluated the activities of structurally diverse opioid receptor ligands in the [(35)S]GTP-gamma-S binding assay, comparing the relationship between receptor binding, activation, efficacy, and intrinsic efficacy. The data, obtained with cloned rat mu receptors, demonstrated that an analgetic, (-)-5-m-hydroxyphenyl-2-methylmorphan (NIH8508), and its (+)-isomer (NIH8509), behave as partial agonists, but had different intrinsic efficacy in the [(35)S]GTP-gamma-S binding assay. Replacement of the methyl group with the phenethyl group on the piperidine nitrogen of NIH8508 and NIH8509 [(1R,5S)-AH019 and (1S, 5R)-AH019] increased affinity for the mu receptor and eliminated any agonist effect, supporting the hypothesis that certain structural features make these compounds antagonists. These study also show that all of the fully efficacious mu agonists studied here had high levels of intrinsic efficacy, producing a 50% response at about 10% receptor occupancy. Comparison of the binding K(i) in competitively inhibiting [(125)I]IOXY binding to the functional K(i) for opioid antagonists [K(i)(IOXY)/K(i)(GTP-gamma-S)] provides more detailed evidence that the [(35)S]GTP-gamma-S binding assay can be used to reliably determine apparent functional antagonist K(i) values in addition to agonist ED(50), efficacy and intrinsic efficacy.

Amphetamine-type central nervous system stimulants release norepinephrine more potently than they release dopamine and serotonin

A large body of evidence supports the hypothesis that mesolimbic dopamine (DA) mediates, in animal models, the reinforcing effects of central nervous system stimulants such as cocaine and amphetamine. The role DA plays in mediating amphetamine-type subjective effects of stimulants in humans remains to be established. Both amphetamine and cocaine increase norepinephrine (NE) via stimulation of release and inhibition of reuptake, respectively. If increases in NE mediate amphetamine-type subjective effects of stimulants in humans, then one would predict that stimulant medications that produce amphetamine-type subjective effects in humans should share the ability to increase NE. To test this hypothesis, we determined, using in vitro methods, the neurochemical mechanism of action of amphetamine, 3,4-methylenedioxymethamphetamine (MDMA), (+)-methamphetamine, ephedrine, phentermine, and aminorex. As expected, their rank order of potency for DA release was similar to their rank order of potency in published self-administration studies. Interestingly, the results demonstrated that the most potent effect of these stimulants is to release NE. Importantly, the oral dose of these stimulants, which produce amphetamine-type subjective effects in humans, correlated with the their potency in releasing NE, not DA, and did not decrease plasma prolactin, an effect mediated by DA release. These results suggest that NE may contribute to the amphetamine-type subjective effects of stimulants in humans.

Design, synthesis, and monoamine transporter binding site affinities of methoxy derivatives of indatraline

A series of methoxy-containing derivatives of indatraline 13a-f and 17 were synthesized, and their binding affinities for the dopamine, serotonin, and norepinephrine transporter binding sites were determined. Introduction of a methoxy group to indatraline affected its affinity and selectivity greatly. Except for the 4-methoxy derivative 13a,which had the same high affinity at the dopamine transporter binding site as indatraline, the other methoxy-containing analogues (13b-f and 17) exhibited lower affinity than indatraline for the three transporter binding sites. However, some of the analogues were more selective than indatraline, and the 6-methoxy derivative 13c displayed the highest affinity for both the serotonin and norepinephrine transporters. This compound retained reasonable affinity for the dopamine transporter and is a promising template for the development of a long-acting inhibitor of monoamine transporters. Such inhibitors have potential as medications for treatment, as a substitution medication, or for prevention of the abuse of methamphetamine-like stimulants.

Synthesis and transporter binding properties of bridged piperazine analogues of 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine (GBR 12909)

A series of analogues related to 1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)piperazine (2) and 1-¿2-[bis(4-fluorophenyl)methoxy]ethyl¿-4-(3-phenylpropyl)piperazine (3) (GBR 12935 and GBR 12909, respectively), in which the piperazine moiety was replaced by bridged piperazines for structural rigidity, has been designed, synthesized, and evaluated for their ability to bind to the dopamine transporter (DAT) and to inhibit the uptake of (3)H-labeled dopamine (DA). The binding data indicated that compounds 7 and 11, the N-methyl- and N-propylphenyl-3,8-diaza[3.2. 1]bicyclooctane analogues of 3, showed high affinity for the DAT (IC(50) = 8.0 and 8.2 nM, respectively), and 7 had high selectivity at the DAT relative to the serotonin transporter (SERT) (88- and 93-fold for binding and reuptake, respectively). They also displayed linear activity in DA uptake inhibition, possessing a similar binding and reuptake inhibition profile to 3. The N-indolylmethyl analogue 16 showed the highest affinity (IC(50) = 1.4 nM) of the series, with a 6-fold increase over its corresponding N-phenypropyl derivative 11. Interestingly, this compound exhibited a high ratio (29-fold) of IC(50) for the inhibition of DA reuptake versus binding to the DAT. Replacing the piperazine moiety of 2 and 3 with (1S, 4S)-2,5-diazabicyclo[2.2.1]heptane resulted in compounds 23-26, which showed moderate to poor affinity (IC(50) = 127-1170 nM) for the DAT. Substitution of the homopiperazine moiety of 4 with a more rigid 3,9-diazabicyclo[4.2.1]nonane gave compounds 28-33. However, the binding data showed that compound 32 displayed a 10-fold decrease in affinity at the DAT and a 100-fold decrease in selectivity at the DAT relative to the SERT compared to its corresponding homopiperazine compound 4.

Uptake and release effects of diethylpropion and its metabolites with biogenic amine transporters

Three metabolites of diethylpropion (1), (+/-)-2-ethylamino-1-phenyl-propan-1-one (2), (1R,2S)-(-)-N,N-diethylnorephedrine (3a) and (1S,2R)-(-)-N,N-diethylnorephedrine (3b) were synthesized. Their uptake and release effects with biogenic amine transporters were evaluated. A major finding of this study is that the in vivo activity of diethylpropion on biogenic amine transporters is most likely due to metabolite 2 as diethylpropion (1) and the metabolites 3a and 3b showed little or no effect in the assays studied. These studies also revealed that 2 acted as a substrate at the norepinephrine (IC50 = 99 nM) and serotonin transporters (IC50 = 2118 nM) and an uptake inhibitor at the dopamine transporter (IC50 = 1014 nM). The potent action of 2 at the NE transporter supports the hypothesis that amphetamine-type subjective effects may be mediated in part by brain norepinephrine.

Neurochemical neutralization of amphetamine-type stimulants in rat brain by the indatraline analog (-)-HY038

Amphetamine-type stimulants are substrates for the proteins that serve as transporters for the biogenic amines dopamine (DA), serotonin (5HT), and norepinephrine (NE) and release these neurotransmitters from neurons located in the peripheral and central nervous system. Using indatraline as a lead compound, we sought to develop a long-acting depot medication that would neutralize the deleterious effects of amphetamine-type stimulants. Our first efforts produced (+/-)-HY038, and its two stereoisomers, which are hydroxy-substituted analog of indatraline. The K(i) values for [(3)H]DA reuptake inhibition by (-)-HY038 and (+)-HY038 were 3.2 +/- 0.1 and 32 +/- 1 nM. Similar results were obtained for [(3)H]5HT reuptake inhibition. (-)-HY038 and (+)-HY038 were slightly less potent at inhibiting [(3)H]NE reuptake (K(i) values of 20 +/- 2 and 159 +/- 12 nM). Low doses of (-)-HY038 blunted the ability of AMPH to release [(3)H]DA by shifting the AMPH dose-response curve to the right in a dose-dependent manner. (-)-HY038 also inhibited the ability of (+)-methamphetamine and (+/-)-3,4-methylenedioxymethamphetamine ((+/-)-MDMA) to release [(3)H]DA. Low doses of (-)-HY038 blunted the ability of these stimulants to release [(3)H]NE and [(3)H]5HT by shifting their dose-response curves to the right in a manner similar to that seen for inhibition of [(3)H]DA release. These data indicate that (-)-HY038 inhibits the ability of AMPH, (+)-methamphetamine and (+/-)-MDMA to release DA, NE, and 5HT and therefore might have the potential to neutralize the neurotoxic and cardiovascular side-effects of substrate-type stimulants.

Opioid receptor imaging with positron emission tomography and [(18)F]cyclofoxy in long-term, methadone-treated former heroin addicts

Stabilized methadone-maintained former heroin addicts (MTPs) treated with effective doses of methadone have markedly reduced drug craving; reduction or elimination of heroin use; normalized stress-responsive hypothalamic-pituitary-adrenal, reproductive, and gastrointestinal function; and marked improvement in immune function and normal responses to pain, all of which are physiological indices modulated in part by endogenous and exogenous opioids directed at the mu and, in some cases, the kappa-opioid systems. This study was performed to explore opioid receptor binding in MTPs. Fourteen normal, healthy volunteers and 14 long-term MTPs in treatment for 2 to 27 years and receiving 30 to 90 mg/day of methadone were studied with positron emission tomography using tracer amounts of [(18)F]cyclofoxy, an opioid antagonist that labels mu and kappa opioid receptors. Imaging was performed in the morning, 22 h after the last dose of methadone in patients, and concurrent plasma levels of methadone were determined. Five brain regions of specific interest for addiction and pain research (thalamus, amygdala, caudate, anterior cingulate cortex, and putamen) were among the six regions of highest [(18)F]cyclofoxy binding. Specific binding of [(18)F]cyclofoxy was lower by 19 to 32% in these regions in MTPs compared with those in normal volunteers. The degree to which specific binding was lower in caudate and putamen correlated with methadone plasma levels (P <.01 and P <.05, respectively), suggesting that these lower levels of binding may be related to receptor occupancy with methadone and that significant numbers of opioid receptors may be available to function in their normal physiological roles.

N-Cyclohexylethyl-N-noroxymorphindole: a mu-opioid preferring analogue of naltrindole

The position of the indole in the indolomorphinans, which includes the delta opioid antagonist naltrindole, is considered to be responsible for the delta opioid selectivity for this class of ligands. Herein is described the N-cyclohexylethyl substituted N-nor-derivative, which is shown to be mu preferring. Thus, the nature of the N-substituent is equally important to the receptor selectivity for this class of ligands.

Antalarmin blockade of corticotropin releasing hormone-induced hypertension in rats

Central administration of CRH results in endocrinological, cardiovascular, and behavioral effects that suggest stress or anxiety. Among these is a marked pressor response. Parenteral administration of CRH, however, results in hypotension. We used parenteral administration of antalarmin, a novel, small molecule CRH1 receptor antagonist, and alpha-helical CRH(9-41), a peptidic CRHR1/CRHR2 antagonist to attempt to determine the receptor mechanisms through which CRH is acting in both of these situations. Our results suggest that the hypertension produced by central CRH administration is mediated through central CRHR1 receptors, whereas the hypotension produced by parenteral CRH administration is mediated through peripheral CRHR2 receptors.

A practical synthesis of the serotonin 5-HT2A receptor antagonist MDL 100907, its enantiomer and their 3-phenolic derivatives as precursors for [11C]labeled PET ligands

A practical synthesis of the 3-phenolic precursor of MDL 100907, a selective 5-HT2A receptor antagonist, is described. The route was also applied to the enantiomeric series, thus affording the direct precursors of both 3-[11C]MDL 100907 and its enantiomer as ligands for positron emission tomography. Similar methodology was developed for the direct synthesis of MDL 100907 and its enantiomer, MDL 100009. The routes utilized classical optical resolution of the N-nor intermediates in at least 98% enantiomeric excess and easily afforded multigram amounts of the chiral precursors of a variety of N- and 3-O-substituted enantiomers.

Role of delta-opioid receptors in biological processes

Agonists at the delta-opioid receptor were initially investigated as potential analgesic agents that may lack the undesired effects (respiratory depression, constipation, dependence) of mu-opioid agonists such as morphine. These studies have, however, uncovered that the delta-opioid system is involved in many biological processes, and thus delta-opioid-based medications have great therapeutic potential for the treatment of a wide variety of disorders.

Methamphetamine dependence: medication development efforts based on the dual deficit model of stimulant addiction

Converging lines of evidence indicate that withdrawal from prolonged exposure to stimulants and alcohol results in synaptic deficits of both dopamine (DA) and serotonin (5-HT). According to the dual deficit model proposed by the authors, DA dysfunction during cocaine or alcohol withdrawal underlies anhedonia and psychomotor retardation, whereas 5-HT dysfunction gives rise to depressed mood, obsessional thoughts, and lack of impulse control. This model predicts that pharmacotherapies which correct only one of the two neurochemical deficits will not be effective. On the other hand, pharmacotherapies which "correct" both of the proposed DA and 5-HT abnormalities should be effective in treating stimulant and alcohol dependence. This paper reviews two approaches, based on the dual deficit model, taken by our laboratory to develop medications to treat stimulant abuse.

Probes for narcotic receptor-mediated phenomena. 27. Synthesis and pharmacological evaluation of selective delta-opioid receptor agonists from 4-[(alphaR)-alpha-(2S,5R)-4-substituted-2, 5-dimethyl-1-piperazinyl-3-methoxybenzyl]-N,N-diethylbenzamides and their enantiomers

Potent, selective, and efficacious delta-opioid receptor agonists such as (+)-4-[(alphaR)-alpha-(2S,5R)-4-allyl-2, 5-dimethyl-1-piperazinyl-3-methoxybenzyl]-N,N-diethylbenzamide [SNC80, (+)-2] have been found to be useful tools for exploring the structural requirements which are necessary for ligands which interact with the delta-receptor. To determine the necessity for the 4-allyl moiety in (+)-2, this substituent was replaced with a variety of 4-alkyl, 4-arylalkyl, and 4-alkenyl substituents. The corresponding enantiomers of these compounds were also synthesized. The binding affinities for the mu-, delta-, and kappa-opioid receptors and efficacies in the functional GTPgammaS binding assay were determined for the (+)-2 related compounds and their enantiomers. The 4-crotyl analogue was found to have similar delta-receptor affinity and efficacy as (+)-2, but the 4-cyclopropylmethyl analogue, in the functional assay, appeared to be a partial agonist with little antagonist activity.

Assessment of SNC 80 and naltrindole within a conditioned taste aversion design

Although compounds with relative selectivity for the mu and kappa opiate receptors subtypes have been reported to condition taste aversions, it is not known whether systemically administered delta compounds have the ability to produce aversions. To that end, female Long-Evans rats were adapted to water deprivation and were given pairings of a novel saccharin solution and various doses of the selective delta agonist SNC 80 (0.32-10.0 mg/kg; Experiment 1) or the selective delta antagonist naltrindole (1.0-18.0 mg/kg; Experiment 2). For comparison, the relatively selective mu agonist morphine (Experiment 1) and mu antagonist naloxone (Experiment 2) were assessed under identical conditions. Both SNC 80 (Experiment 1) and naltrindole (Experiment 2) were effective as unconditioned stimuli within this design, inducing dose-dependent taste aversions with repeated conditioning trials. Although at no dose did animals injected with SNC 80 differ from those injected with morphine, aversions induced by SNC 80 were acquired at a faster rate than those induced by morphine. Subjects injected with naloxone drank significantly less than those injected with naltrindole at the 10 mg/kg dose, and aversions induced by naloxone at 5.6 and 10 mg/kg were acquired at a faster rate than those induced by naltrindole. Although the basis for opioid agonist- and antagonist-induced taste aversions is not known, the differences between aversions induced by SNC 80 and naltrindole and those induced by morphine and naloxone, respectively, may be a function of their relative selectivity for specific opiate receptor subtypes.

Morphine discriminative control is mediated by the mu opioid receptor: assessment of delta opioid substitution and antagonism

Morphine is an effective training drug in drug discrimination procedures. In subsequent generalization tests in which other opioids are administered, mu opioid agonists selectively substitute for the training drug. Given the relative selectivity of morphine for the mu receptor, such substitution patterns suggest that the mu opioid receptor is mediating the discriminative control of this compound. The present study assessed this selective mediation by examining the ability of the delta opioid agonist SNC80 to substitute for (and the delta opioid antagonist naltrindole to antagonize) morphine stimulus effects in rats trained to discriminate morphine from its vehicle in the conditioned taste aversion baseline of drug discrimination learning. Although morphine and methadone produced dose-related substitution for morphine (10 mg/kg), there was no evidence of substitution for morphine by SNC80 at any dose tested. Further, although naloxone (3.2 mg/kg) completely blocked the discriminative effects of morphine, naltrindole (3.2-10 mg/kg) did not significantly affect the morphine stimulus. These data suggest that the discriminative control established to morphine is mediated by its activity at the mu, but not the delta, receptor.

Development of a novel class of monocyclic and bicyclic alkyl amides that exhibit CB1 and CB2 cannabinoid receptor affinity and receptor activation

CB1 and CB2 cannabinoid receptors can be activated by several different classes of agonists, including cannabinoids such as delta9-tetrahydrocannabinol and 9-nor-9beta-hydroxyhexahydrocannabinol, and eicosanoids such as arachidonylethanolamide. Structure-activity relationship studies have identified potential pharmacophoric elements for binding to cannabinoid receptors by both cannabinoids and eicosanoids. Molecular models have hypothesized conformational, spatial, and pharmacophoric distance requirements based upon radioligand binding data whereby overlap of pharmacophoric elements of the two classes disclose a low energy conformation of arachidonylethanolamide that can occupy the same receptor space as cannabinoid ligands. To test this model, we have developed a novel class of monocyclic and bicyclic alkyl amide cannabinoid receptor ligands. Further, we predicted a spatial conformation for these compounds in a molecular model based on the pharmacophoric and structural requirements for binding to the CB1 cannabinoid receptor.