δ-Opioid mechanisms for ADL5747 and ADL5859 effects in mice: analgesia, locomotion, and receptor internalization.

N,N-diethyl-4-(5-hydroxyspiro[chromene-2,4'-piperidine]-4-yl) benzamide (ADL5859) and N,N-diethyl-3-hydroxy-4-(spiro[chromene-2,4'-piperidine]-4-yl)benzamide (ADL5747) are novel δ-opioid agonists that show good oral bioavailability and analgesic and antidepressive effects in the rat and represent potential drugs for chronic pain treatment. Here, we used genetic approaches to investigate molecular mechanisms underlying their analgesic effects in the mouse. We tested analgesic effects of ADL5859 and ADL5747 in mice by using mechanical sensitivity measures in both complete Freund's adjuvant and sciatic nerve ligation pain models. We examined their analgesic effects in δ-opioid receptor constitutive knockout (KO) mice and mice with a conditional deletion of δ-receptor in peripheral voltage-gated sodium channel (Nav)1.8-expressing neurons (cKO mice). Both ADL5859 and ADL5747, and the prototypical δ agonist 4-[(R)-[(2S,5R)-4-allyl-2,5-dimethyl-piperazin-1-yl]-(3-methoxyphenyl)methyl]-N,N-diethyl-benzamide (SNC80) as a control, significantly reduced inflammatory and neuropathic pain. The antiallodynic effects of all three δ-opioid agonists were abolished in constitutive δ-receptor KO mice and strongly diminished in δ-receptor cKO mice. We also measured two other well described effects of δ agonists, increase in locomotor activity and agonist-induced receptor internalization by using knock-in mice expressing enhanced green fluorescence protein-tagged δ receptors. In contrast to SNC80, ADL5859 and ADL5747 did not induce either hyperlocomotion or receptor internalization in vivo. In conclusion, both ADL5859 and ADL5747 showed efficient pain-reducing properties in the two models of chronic pain. Their effects were mediated by δ-opioid receptors, with a main contribution of receptors expressed on peripheral Nav1.8-positive neurons. The lack of in vivo receptor internalization and locomotor activation, typically induced by SNC80, suggests agonist-biased activity at the receptor for the two drugs.

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.

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.

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.

Antinociceptive activity of the selective iNOS inhibitor AR-C102222 in rodent models of inflammatory, neuropathic and post-operative pain.

Nitric oxide generated by the nitric oxide synthase (NOS) isoforms contributes to pain processing. The selective inhibition of iNOS might represent a novel, therapeutic target for the development of antinociceptive compounds. However, few isoform-selective inhibitors of NOS have been developed. The present experiments examined the anti-inflammatory and antinociceptive activity of a selective inducible nitric oxide (iNOS) inhibitor, AR-C102222, on arachidonic acid-induced ear inflammation, Freund's complete adjuvant (FCA)-induced hyperalgesia, acetic acid-induced writhing, and tactile allodynia produced by L5 spinal nerve ligation (L5 SNL) or hindpaw incision (INC). AR-C102222 at a dose of 100mg/kg p.o., significantly reduced inflammation produced by the application of arachidonic acid to the ear, attenuated FCA-induced mechanical hyperalgesia, and attenuated acetic acid-induced writhing. In the L5 SNL and INC surgical procedures, tactile allodynia produced by both procedures was significantly reduced by 30mg/kg i.p. of AR-C102222. These data demonstrate that the selective inhibition of iNOS produces antinociception in different models of pain and suggest that the iNOS-NO system plays a role in pain processing.

Pharmacological evaluation of the selective spinal nerve ligation model of neuropathic pain in the rat.

Rodent models of neuropathic pain are used to investigate the underlying mechanisms of pain associated with damage to peripheral nerves and to evaluate the efficacy of novel compounds. However, few models have been adequately characterized and the validity of many models remains unclear. The present experiment examined the activity of known anti-allodynic compounds in the L5 spinal nerve ligation (SNL) model of peripheral mononeuropathy in the rat, a modified version of the L5/L6 SNL model [S.H. Kim, J.M. Chung, An experimental model for peripheral neuropathy produced by segmental spinal nerve ligation in the rat, Pain 50 (1992) 355-363]. Tactile sensitivity was measured 7-21 days post-surgery using von Frey monofilaments before and following treatment with gabapentin (30, 60 and 120 mg/kg), morphine (1, 3 and 6 mg/kg), amitriptyline (1.5, 3 and 10 mg/kg), fluoxetine (3, 10 and 30 mg/kg), WIN55,212-2 (0.5, 1 and 2.5 mg/kg), indomethacin (1 and 5 mg/kg) or U-50,488H (3 and 6 mg/kg). Compared to sham-operated control animals, L5 SNL animals displayed significant tactile allodynia in the ipsilateral hindpaw that was completely reversed by treatment with gabapentin, morphine, and WIN55,212-2, partially reversed by amitriptyline and fluoxetine, and unaffected by U-50,488H or indomethacin. The robust effects of the non-selective cannabinoid receptor agonist WIN55,212-2 and morphine support reports in the literature that systemic cannabinoid receptor agonists and opioids are active in neuropathic pain. These results suggest that the L5 SNL model can be utilized to determine the anti-allodynic activity of novel compounds.

Cannabinoid CB2 receptor agonist activity in the hindpaw incision model of postoperative pain.

The identification of peripherally expressed CB2 receptors and reports that the selective activation of cannabinoid CB2 receptors produces antinociception without traditional cannabinergic side effects suggests that selective cannabinoid CB2 receptor agonists might be useful in the management of pain. In a rat hindpaw incision model, we examined the antiallodynic activity of the selective cannabinoid CB2 receptor agonists AM1241 (3-30 mg/kg i.p.), GW405833 (3-30 mg/kg i.p.), and HU-308 (0.3-30 mg/kg i.p.). The rank order for efficacy in the hindpaw incision model following a dose of 10 mg/kg, i.p. was AM1241 > GW405833 = HU-308, and the selective cannabinoid CB2 receptor antagonist, SR144528, reversed the antiallodynic effect of HU-308. Together, these data suggest that selective cannabinoid CB2 receptor agonists might represent a new class of postoperative analgesics.

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.

Potent, orally bioavailable delta opioid receptor agonists for the treatment of pain: discovery of N,N-diethyl-4-(5-hydroxyspiro[chromene-2,4'-piperidine]-4-yl)benzamide (ADL5859).

Selective delta opioid receptor agonists are promising potential therapeutic agents for the treatment of various types of pain conditions. A spirocyclic derivative was identified as a promising hit through screening. Subsequent lead optimization identified compound 20 (ADL5859) as a potent, selective, and orally bioavailable delta agonist. Compound 20 was selected as a clinical candidate for the treatment of pain.

Novel malonamide derivatives as potent kappa opioid receptor agonists.

A novel series of malonamide derivatives was synthesized. These amides were shown to be potent and selective kappa opioid receptor agonists.

Novel phenylamino acetamide derivatives as potent and selective kappa opioid receptor agonists.

A novel series of phenylamino acetamide derivatives was synthesized. These amides were shown to be potent and selective kappa opioid receptor agonists.

Synthesis and evaluation of novel peripherally restricted kappa-opioid receptor agonists.

A series of 3-substituted analogs (3) of the parent kappa agonist, 1, were prepared to limit access to the central nervous system. With the exception of compound 3j, all other compounds bound to the human kappa opioid receptor with high affinity (K(i)=0.31-9.5 nM) and were selective for kappa over mu and delta opioid receptors. Compounds 3c, d, and 3g-i produced potent antinociceptive activity in the rat formalin assay (i.paw) and the mouse acetic acid-induced writhing assay (s.c.), with weak activity in the mouse platform sedation test. The peripheral restriction indices of 3c, d, 3g, and 3i were improved 2- to 7-fold compared to the parent compound 1, and these compounds were approximately 2- to 5-fold more potent than the peripheral kappa agonist ICI 204448.

Potent and highly selective kappa opioid receptor agonists incorporating chroman- and 2,3-dihydrobenzofuran-based constraints.

Two novel chemical classes of kappa opioid receptor agonists, chroman-2-carboxamide derivatives and 2,3-dihydrobenzofuran-2-carboxamide derivatives, were synthesized. These agents exhibited high and selective affinity for the kappa opioid receptor.

Azepinone as a conformational constraint in the design of kappa-opioid receptor agonists.

A new class of kappa-opioid receptor agonists is described. The design of these agents was based upon energy minimization and structural overlay studies of the generic azepin-2-one structure 3 with the crystal structure of arylacetamide kappa agonist 1, ICI 199441. The most active compound identified was ligand 4a (K(i)=0.34 nM), which demonstrated potent antinociceptive activity after oral administration in rodents.