The selective mu-opioid receptor antagonist ADL5510 reduces levodopa-induced dyskinesia without affecting antiparkinsonian action in MPTP-lesioned macaque model of Parkinson's disease.

In Parkinson's disease (PD), dyskinesia develops following long-term treatment with 3,4-dihydroxyphenylalanine (L-dopa). Given the prominent role of the opioid system in basal ganglia function, nonselective opioid receptor antagonists have been tested for antidyskinetic efficacy in the clinic (naltrexone and naloxone), although without success. In the current study, ADL5510, a novel, orally active opioid antagonist with mu opioid receptor selectivity, was examined in L-dopa-treated 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) macaques. Antidyskinetic effects were compared with those of naltrexone. Parkinsonian monkeys with established L-dopa-induced dyskinesia (LID) received acute challenges with L-dopa (subcutaneously) in combination with either vehicle, ADL5510 (0.1, 1, 3 or 10 mg/kg by mouth), or naltrexone (1, 3, or 10 mg/kg subcutaneously). Following treatments, behavior was monitored for 6 hours. Parameters assessed were total activity, parkinsonism, and dyskinesia. ADL5510 (1, 3, and 10 mg/kg) reduced activity and LID (chorea and dystonia) without affecting the antiparkinsonian benefits of L-dopa. The antidyskinetic effect of ADL5510 showed a U-shaped dose-response. It was inactive at 0.1 mg/kg, efficacious at 1 and 3 mg/kg (72% and 40% reductions, respectively), and then less effective at 10 mg/kg. The quality of ON time produced by L-dopa was improved, as indicated by a reduction in the percentage of ON time spent experiencing disabling dyskinesia (70% and 61% reductions with 1 and 3 mg/kg, respectively, compared with L-dopa). Naltrexone, in contrast, did not alleviate LID or affect the antiparkinsonian actions of L-dopa. Mu-selective opioid antagonists have the potential to form the basis of novel antidyskinetic therapies for PD.

Novel sulfamoyl benzamides as selective CB(2) agonists with improved in vitro metabolic stability.

A lead optimization campaign in our previously reported sulfamoyl benzamide class of CB(2) agonists was conducted to improve the in vitro metabolic stability profile in this series while retaining high potency and selectivity for the CB(2) receptor. From this study, compound 14, N-(3,4-dimethyl-5-(morpholinosulfonyl)phenyl)-2,2-dimethylbutanamide, was identified as a potent and selective CB(2) agonist exhibiting moderate in vitro metabolic stability and oral bioavailability. Compound 14 demonstrated in vivo efficacy in a rat model of post-surgical pain.

The involvement of the mu-opioid receptor in gastrointestinal pathophysiology: therapeutic opportunities for antagonism at this receptor.

The localization of opioid receptors and their endogenous peptide ligands within the gastrointestinal (GI) tract and their role in the coordination of propulsion and secretion underscores the importance of opioid receptors in the maintenance of GI homeostasis. The peripherally acting micro-opioid receptor antagonists alvimopan and methylnaltrexone (MNTX) are currently under investigation as therapeutic agents to treat the deleterious GI side effects associated with opioid administration. These compounds have demonstrated efficacy in numerous animal models of GI function, and clinical studies have revealed their efficacy in the treatment of postoperative ileus (POI) and opioid-induced bowel dysfunction. Preservation of opioid-mediated analgesia has been demonstrated for these compounds in both the preclinical and clinical settings. Future studies exploring the benefits of selective antagonism of the peripheral mu-opioid receptor in the treatment of other GI conditions may open new therapeutic opportunities for alvimopan and MNTX.

Nascent structure-activity relationship study of a diastereomeric series of kappa opioid receptor antagonists derived from CJ-15,208.

Cyclic tetrapeptide c[Phe-pro-Phe-trp] 2, a diastereomer of CJ-15,208 (1), was identified as a potent dual kappa/mu opioid receptor antagonist devoid of delta opioid receptor affinity against cloned human receptors: K(i) (2)=3.8nM (kappa), 30nM (mu); IC(50) ([(35)S]GTPgammaS binding)=140nM (kappa), 21nM (mu). The d-tryptophan residue rendered 2 ca. eightfold and fourfold more potent at kappa and mu, respectively, than the corresponding l-configured tryptophan in the natural product 1. Phe analogs 3-10, designed to probe the effect of substituents on receptor affinity and selectivity, possessed K(i) values ranging from 14 to 220nM against the kappa opioid receptor with mu/kappa ratios of 0.45-3.0. An alanine scan of 2 yielded c[Ala-pro-Phe-trp] 12, an analog equipotent to 2. Agents 2 and 12 were pure antagonists in vitro devoid of agonist activity. Ac-pro-Phe-trp-Phe-NH(2)16 and Ac-Phe-trp-Phe-pro-NH(2)17 two of the eight possible acyclic peptides derived from 1 and 2, were selective, modestly potent mu ligands: K(i) (16)=340nM (mu); K(i) (17)=360nM (mu).

Discovery of N-(3-(morpholinomethyl)-phenyl)-amides as potent and selective CB2 agonists.

Recently sulfamoyl benzamides were identified as a novel series of cannabinoid receptor ligands. Replacing the sulfonamide functionality and reversing the original carboxamide bond led to the discovery of N-(3-(morpholinomethyl)-phenyl)-amides as potent and selective CB(2) agonists. Selective CB(2) agonist 31 (K(i)=2.7; CB(1)/CB(2)=190) displayed robust activity in a rodent model of postoperative pain.

Novel pyridine derivatives as potent and selective CB2 cannabinoid receptor agonists.

Replacement of the phenyl ring in our previous (morpholinomethyl)aniline carboxamide cannabinoid receptor ligands with a pyridine ring led to the discovery of a novel chemical series of CB2 ligands. Compound 3, that is, 2,2-dimethyl-N-(5-methyl-4-(morpholinomethyl)pyridin-2-yl)butanamide was identified as a potent and selective CB2 agonist exhibiting in vivo efficacy after oral administration in a rat model of neuropathic pain.

CB2 selective sulfamoyl benzamides: optimization of the amide functionality.

Previous research within our laboratories identified sulfamoyl benzamides as novel cannabinoid receptor ligands. Optimization of the amide linkage led to the reverse amide 40. The compound exhibited robust antiallodynic activity in a rodent pain model when administered intraperitoneally. Efficacy after oral administration was observed only when ABT, a cytochrome P450 suicide inhibitor, was coadministered.

Use of receptor chimeras to identify small molecules with high affinity for the dynorphin A binding domain of the kappa opioid receptor.

A series of 2-substituted sulfamoyl arylacetamides of general structure 2 were prepared as potent kappa opioid receptor agonists and the affinities of these compounds for opioid and chimeric receptors were compared with those of dynorphin A. Compounds 2e and 2i were identified as non-peptide small molecules that bound to chimeras 3 and 4 with high affinities similar to dynorphin A, resulting in K(i) values of 1.5 and 1.2 nM and 1.3 and 2.2 nM, respectively.

Discovery of a series of aminopiperidines as novel iNOS inhibitors.

Nitric oxide (NO), a mediator of various physiological and pathophysiological processes, is synthesized by three isozymes of nitric oxide synthase (NOS). Potential candidate clinical drugs should be devoid of inhibitory activity against endothelial NOS (eNOS), since eNOS plays an important role in maintaining normal blood pressure and flow. A new series of aminopiperidines as potent inhibitors of iNOS were identified from a HTS lead. From this study, we identified compound 33 as a potent iNOS inhibitor, with >25-fold selectivity over eNOS and 16-fold selectivity over nNOS.

Novel trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidines as mu opioid receptor antagonists with improved opioid receptor selectivity profiles.

A series of N-substituted trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidines, mu opioid receptor antagonists, analogs of alvimopan, were prepared using solid phase methodology. This study led to the identification of a highly selective mu opioid receptor antagonist, which interacts selectively with mu peripheral receptors.

Sulfamoyl benzamides as novel CB2 cannabinoid receptor ligands.

Sulfamoyl benzamides were identified as a novel series of cannabinoid receptor ligands. Starting from a screening hit 8 that had modest affinity for the cannabinoid CB(2) receptor, a parallel synthesis approach and initial SAR are described, leading to compound 27 with 120-fold functional selectivity for the CB(2) receptor. This compound produced robust antiallodynic activity in rodent models of postoperative pain and neuropathic pain without traditional cannabinergic side effects.

Elucidation of the bioactive conformation of the N-substituted trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine class of mu-opioid receptor antagonists.

The series of trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidines have been widely investigated as opioid receptor antagonists. One of our research goals was to explore the bioactive conformation of the N-phenethyl trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine derivative 3, prototypical mu-opioid antagonist in this series. In this effort, the rotational degrees of freedom of the N-substituent of 3 were limited by incorporation of an ethylene bridge between the piperidine 2- or 6-position of 3 and the benzylic position of the N-phenethyl moiety. The overall modification led to a novel series of fused bicyclic derivatives of the octahydroquinolizine chemical class, conformationally restricted analogue of 3. The constrained analogues 6 and 9 showed high affinity toward the mu-opioid receptor. Compound 6 was found to be a mu-opioid antagonist, whereas the constrained analogue 9 displayed potent mu-agonist activity in vitro. This study provides additional information about the molecular determinants for mu recognition, the structural features affecting ligand binding, and the structure function relationships.

Synthesis and pharmacological evaluation of novel octahydro-1H-pyrido[1,2-a]pyrazine as mu-opioid receptor antagonists.

To better understand structural requirements for a mu ligand of the trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine class to interact with the mu opioid receptor, we have described in the previous article (Le Bourdonnec, B. et al. J. Med. Chem. 2006, 25, 7278-7289) new, constrained analogues of the N-phenethyl derivative 3. One of the active constrained analogues, compound 4, exhibited subnanomolar mu-opioid receptor affinity (K(i) = 0.62 nM) and potent mu-opioid antagonist activity (IC(50) = 0.54 nM). On the basis of structure 4, a new series of mu-opioid receptor antagonists were designed. In these compounds the octahydroquinolizine template of 4 was replaced by an octahydro-1H-pyrido[1,2-a]pyrazine scaffold. The new derivatives were tested for their binding affinities and in vitro functional activity against the cloned human mu-, delta-, and kappa-opioid receptors. From this study, we identified compound 36, which displays high affinity toward the mu-opioid receptor (K(i) = 0.47 nM), potent mu in vitro antagonist activity (IC(50) = 1.8 nM) and improved binding selectivity profile mu/kappa and mu/delta, when compared to 4.

Pharmacological characterization of human kappa/mu opioid receptor chimeras that retain high affinity for dynorphin A.

Arylacetamide analgesics that stimulate kappa opioid receptors in the central nervous system mediate dysphoria and psychosis as well as analgesia. However, the naturally occurring peptide agonist, dynorphin A, is analgesic in the absence of dysphoria and psychosis, indicating that the therapeutic effects of kappa opioid agonists may be separated from their side effects. As part of our effort to discover kappa opioid receptor analgesics lacking side effects, we designed and constructed two mu/kappa chimeric receptors, composed primarily of amino acid residues derived from the mu opioid receptor, that were expected to bind dynorphin A with high affinity. In one, extracellular loop 2 and transmembrane domain 4 were derived from the kappa opioid receptor and in the other, only extracellular loop 2 was derived from the kappa opioid receptor. Most competitors of [(3)H]diprenorphine binding from a variety of structural classes bound to the chimeras with affinities similar to those with which they bound to the mu opioid receptor. In contrast, dynorphin A analogs bound to the chimeras with affinities similar to those with which they bound to the kappa opioid receptor. Pharmacological characterization of [(35)S]GTPgammaS binding mediated by the chimera with extracellular loop 2 derived from the kappa opioid receptor showed that it behaved as if it were mu opioid receptor with high affinity for dynorphin A analogs. These chimeras may be useful in identifying novel kappa receptor agonists that bind to the second extracellular loop of the receptor and share the desirable therapeutic profile of dynorphin A.

[(3)H]Alvimopan binding to the micro opioid receptor: comparative binding kinetics of opioid antagonists.

Alvimopan is a novel peripheral micro opioid antagonist in clinical development for the management of post-operative ileus and opioid-induced bowel dysfunction. We hypothesized that the long duration of action of alvimopan might be related to a slower dissociation rate from the micro opioid receptor compared to other shorter acting antagonists. The dissociation rate of alvimopan from the micro opioid receptor (t(1/2)=30--44 min) was comparable to that of the long acting partial agonist buprenorphine (t(1/2)=44 min), but was slower than those of the antagonists naloxone (t(1/2)=0.82 min) and N-methylnaltrexone (t(1/2)=0.46 min). Also, increases in the apparent affinities and potencies of buprenorphine and alvimopan, but not of naloxone and methylnaltrexone, were observed upon preincubation with the micro opioid receptor. Consistent with its long duration of action, alvimopan has a slow dissociation rate from the micro opioid receptor compared to other shorter acting antagonists and may be more potent if administered prior to dosing with exogenous opioids.

Structure-activity relationships of dynorphin a analogues modified in the address sequence.

The peptide [Pro3]Dyn A(1-11)-NH2 2 exhibits high affinity (K(i) = 2.4 nM) and over 2000-fold selectivity for the opioid receptor. Stepwise removal of the C-terminal residues from this ligand demonstrated that its positively charged Arg residues, particularly Arg6 and Arg7, were crucial for binding to the kappa receptor. Analogues shorter than seven amino acids lacked significant affinity for opioid receptors. Comparison with a series of truncated analogues of Dyn A showed that the relative losses in binding potency differed only slightly between the two series. The neutral residues Ile8 and Pro10 could be removed without significant loss in affinity for the kappa receptor. Their replacement, in the Pro3 analogue, with additional Arg residues led to analogues with improved kappa affinity (e.g., [Pro3,Arg8]Dyn A(1-11)-NH2 20: K(i)(kappa) = 0.44 nM). This type of modification did not compromise the high kappa selectivity of the Pro3 analogues. These findings support the view that a negatively charged domain in the putative second extracellular loop of the kappa receptor selectively recognizes residues 6-11 of dynorphin through electrostatic interactions. As with parent compound 2, analogue 20 and related compounds displayed kappa antagonist properties.

Synthesis and biological activities of cyclic lanthionine enkephalin analogues: delta-opioid receptor selective ligands.

The synthesis and biological test results of a series of enkephalin analogues incorporating the lanthionine modification are presented. The syntheses of four monosulfide-bridged analogues of enkephalins, Tyr-c[D-Ala(L)-Gly-Phe-D-Ala(L)]-OH (1a), Tyr-c[D-Val(L)-Gly-Phe-D-Ala(L)]-OH (1b), Tyr-c[D-Ala(L)-Gly-Phe-Ala(L)]-OH (1c), and Tyr-c[D-Val(L)-Gly-Phe-Ala(L)]-OH (1d), where Ala(L) and Val(L) denote the lanthionine amino acid ends linked by a monosulfide bridge to form the lanthionine structure, were successfully carried out via preparation of the linear peptide on solid support and cyclization in solution. In vitro binding assays against mu-, delta-, and kappa-opioid receptors and in vitro tests using GPI and MVD assays revealed that the dimethyl lanthionine analogues 1b and 1d, denoted as D-Val(L) in position 2, show substantial selectivity toward the delta-opioid receptor, while the unsubstituted analogues 1a and 1c, denoted as D-Ala(L) in position 2, bind to both mu- and delta-opioid receptors. The in vivo thermal escape assay by intrathecal administration showed that the analogues 1b and 1d are among the most potent ligands at producing antinociception through the delta-opioid receptor. The picomolar potencies of analogues 1a and 1c in the intrathecal (it.) assay strongly indicate that mu- and delta-opioid receptors interact synergistically to modulate the antinociceptive responses.

Antipruritic and antihyperalgesic actions of loperamide and analogs.

Loperamide and three of its analogs were evaluated for their ability to inhibit binding to cloned human opioid receptor subtypes and to produce antipruritus and antinociception following local s.c. administration to rodents. All four compounds were fully efficacious agonists with affinities of 2 to 4 nM for the cloned human mu opioid receptor. Local s.c. injection of loperamide, ADL 01-0001 or ADL 01-0002 at the same site as the introduction of the pruritogenic compound 48/80 resulted in antipruritic activity in a mouse model of itch. Similarly, i.paw or i.pl. administration of compounds ADL 01-0001, ADL 01-0002 and ADL 01-0003 to inflamed paws caused potent antinociception, inhibiting late phase formalin-induced flinching, Freund's adjuvant-induced mechanical hyperalgesia and tape stripping-induced mechanical hyperalgesia. Loperamide and its analogs were efficacious in animal models of itch and inflammatory pain, and may have potential therapeutic utility as antipruritic and antihyperalgesic agents.

Design and Synthesis of Imidazopyrimidine Derivatives as Potent iNOS Dimerization Inhibitors.

A series of imidazopyrimidine derivatives with the general formula I was synthesized and identified as potent inhibitors of iNOS dimer formation, a prerequisite for proper functioning of the enzyme. Stille and Negishi coupling reactions were used as key steps to form the carbon-carbon bond connecting the imidazopyrimidine core to the central cycloalkenyl, cycloalkyl and phenyl ring templates.

Spirocyclic delta opioid receptor agonists for the treatment of pain: discovery of N,N-diethyl-3-hydroxy-4-(spiro[chromene-2,4'-piperidine]-4-yl) benzamide (ADL5747).

Selective, nonpeptidic delta opioid receptor agonists have been the subject of great interest as potential novel analgesic agents. The discoveries of BW373U86 (1) and SNC80 (2) contributed to the rapid expansion of research in this field. However, poor drug-like properties and low therapeutic indices have prevented clinical evaluation of these agents. Doses of 1 and 2 similar to those required for analgesic activity produce convulsions in rodents and nonhuman primates. Recently, we described a novel series of potent, selective, and orally bioavailable delta opioid receptor agonists. The lead derivative, ADL5859 (4), is currently in phase II proof-of-concept studies for the management of pain. Further structure activity relationship exploration has led to the discovery of ADL5747 (36), which is approximately 50-fold more potent than 4 in an animal model of inflammatory pain. On the basis of its favorable efficacy, safety, and pharmacokinetic profile, 36 was selected as a clinical candidate for the treatment of pain.