Potent haloperidol derivatives covalently binding to the dopamine D2 receptor

Cholecystokinin-Induced Duodenogastric Bile Reflux Increases the Severity of Indomethacin-Induced Gastric Antral Ulcers in Re-fed Mice

BACKGROUND/AIMS

We examined the involvement of cholecystokinin (CCK) in the exacerbation of indomethacin (IND)-induced gastric antral ulcers by gastroparesis caused by atropine or dopamine in mice.

METHODS

Male mice were fed for 2 h (re-feeding) following a 22-h fast. Indomethacin (IND; 10 mg/kg, s.c.) was administered after re-feeding; gastric lesions were examined 24 h after IND treatment. In another experiment, mice were fed for 2 h after a 22-h fast, after which the stomachs were removed 1.5 h after the end of the feeding period. Antral lesions, the amount of gastric contents, and the gastric luminal bile acids concentration were measured with or without the administration of the pro- and antimotility drugs CCK-octapeptide (CCK-8), atropine, dopamine, SR57227 (5-HT3 receptor agonist), apomorphine, lorglumide (CCK1 receptor antagonist), ondansetron, and haloperidol alone and in combination.

RESULTS

IND produced severe lesions only in the gastric antrum in re-fed mice. CCK-8, atropine, dopamine, SR57227 and apomorphine administered just after re-feeding increased bile reflux and worsened IND-induced antral lesions. These effects were significantly prevented by pretreatment with lorglumide. Although atropine and dopamine also increased the amount of gastric content, lorglumide had no effect on the delayed gastric emptying provoked by atropine and dopamine. Both ondansetron and haloperidol significantly inhibited the increase of bile reflux and the exacerbation of antral lesions induced by atropine and dopamine, respectively, but did not affect the effects of CCK-8.

CONCLUSIONS

These results suggest that CCK-CCK1 receptor signal increases bile reflux during gastroparesis induced by atropine and dopamine, exacerbating IND-induced antral ulcers.

Development of Photoswitchable Tethered Ligands that Target the μ-Opioid Receptor

Converting known ligands into photoswitchable derivatives offers the opportunity to modulate compound structure with light and hence, biological activity. In doing so, these probes provide unique control when evaluating G-protein-coupled receptor (GPCR) mechanism and function. Further conversion of such compounds into covalent probes, known as photoswitchable tethered ligands (PTLs), offers additional advantages. These include localization of the PTLs to the receptor binding pocket. Covalent localization increases local ligand concentration, improves site selectivity and may improve the biological differences between the respective isomers. This work describes chemical, photophysical and biochemical characterizations of a variety of PTLs designed to target the μ-opioid receptor (μOR). These PTLs were modeled on fentanyl, with the lead disulfide-containing agonist found to covalently interact with a cysteine-enriched mutant of this medically-relevant receptor.

Gastroparesis Worsens Indomethacin-Induced Gastric Antral Ulcers by Bile Reflux via Activation of 5-HT3 and Dopamine D2 Receptors in Mice

BACKGROUND/AIMS

We examined the contributions of gastric emptying and duodenogastric bile reflux in the formation of gastric antral ulcers induced by NSAIDs in mice.

METHODS

We used the murine re-fed indomethacin (IND) experimental ulcer model. Outcome measures included the appearance of gastric lesions 24 h after IND treatment and the assessment of gastric contents and the concentration of bile acids 1.5 h after re-feeding. The effects of atropine, dopamine, SR57227 (5-HT3 receptor agonist), apomorphine, ondansetron, haloperidol, and dietary taurocholate and cholestyramine were also examined.

RESULTS

IND (10 mg/kg, s.c.) induced severe lesions only in the gastric antrum in the re-fed model. The antral lesion index and the amount of food intake during the 2-h refeeding period were positively correlated. Atropine and dopamine delayed gastric emptying, increased bile reflux, and worsened IND-induced antral lesions. SR57227 and apomorphine worsened antral lesions with increased bile reflux. These effects were prevented by the anti-emetic drugs ondansetron and haloperidol, respectively. The anti-emetic drugs markedly decreased the severity of antral lesions and the increase of bile reflux induced by atropine or dopamine without affecting delayed gastric emptying. Antral lesions induced by IND were increased by dietary taurocholate but decreased by the addition of the bile acid sequestrant cholestyramine.

CONCLUSIONS

These results suggest that gastroparesis induced by atropine or dopamine worsens NSAID-induced gastric antral ulcers by increasing duodenogastric bile reflux via activation of 5-HT3 and dopamine D2 receptors.

Design, Synthesis and Pharmacological Evaluation of Novel Conformationally Restricted N-arylpiperazine Derivatives Characterized as D2/D3 Receptor Ligands, Candidates for the Treatment of Neurodegenerative Diseases

Most neurodegenerative diseases are multifactorial, and the discovery of several molecular mechanisms related to their pathogenesis is constantly advancing. Dopamine and dopaminergic receptor subtypes are involved in the pathophysiology of several neurological disorders, such as schizophrenia, depression and drug addiction. For this reason, the dopaminergic system and dopamine receptor ligands play a key role in the treatment of such disorders. In this context, a novel series of conformationally restricted N-arylpiperazine derivatives (5a–f) with a good affinity for D₂/D₃ dopamine receptors is reported herein. Compounds were designed as interphenylene analogs of the drugs aripiprazole (2) and cariprazine (3), presenting a 1,3-benzodioxolyl subunit as a ligand of the secondary binding site of these receptors. The six new N-arylpiperazine compounds were synthesized in good yields by using classical methodologies, and binding and guanosine triphosphate (GTP)-shift studies were performed. Affinity values below 1 μM for both target receptors and distinct profiles of intrinsic efficacy were found. Docking studies revealed that Compounds 5a–f present a different binding mode with dopamine D₂ and D₃ receptors, mainly as a consequence of the conformational restriction imposed on the flexible spacer groups of 2 and 3.

Development of disulfide-functionalized peptides covalently binding G protein-coupled receptors

A broadly applicable synthesis of peptides incorporating mixed disulfides between cysteine and homocysteine and cysteamine was developed. The method was established using pharmacologically relevant G protein-coupled receptor (GPCR) ligands including the μ-receptor agonist Dmt-DALDA and extended to the orexin derivative Oxa(17-33) and NT(8-13), the C-terminal hexapeptide of neurotensin. The newly developed NT(8-13) analog 6b incorporating an S-functionalized homocysteine revealed covalent binding of the neurotensin receptor 1 (NTSR1) in a radioligand depletion study.

Haloperidol-induced hypokinesia in rats is differentially affected by the light/dark phase, age, and melatonin

It has been well established that the striatal dopaminergic system is compromised with aging, namely D2 receptor function. Also well documented is the age related decline of the neurohormone, melatonin, in both humans and nonhuman animals. What has not been well studied is the possible interaction between the D2 receptor system and the age related decline in melatonin with its unmistakable pattern of synthesis and release exclusively during the dark phase. We tested the effect of the D2 antagonist, haloperidol (1.0 mg/kg ip), in adolescent (2 mo old) and adult rats (10 mo old) in the light (ZT3) and dark phases (ZT 15) in rats kept in a 12 L/12D cycle and the effect of exogenous melatonin (15 mg/kg ip/day x 4 days for a total of 60 mg/kg) on D2 antagonism. Using the bar test, measuring the extrapyramidal side-effect of hypokinesia, we report haloperidol to work differentially depending on both age and phase. Adult rats experienced the effect of the D2 antagonist in both the light and dark phases, while younger rats did not show hypokinetic affects in the dark. By manipulated lighting, we were able to restore the effect of haloperidol in younger rats in the dark phase. We also found ameliorating effects of melatonin lessening time on the bar after treatment with haloperidol, however, this effect was only found in older rats. These data demonstrate the importance of the light/dark cycle and age in the susceptibility of extrapyramidal effects with use of drugs that target D2 receptor function.

Development of covalent antagonists for β1- and β2-adrenergic receptors

The selective covalent tethering of ligands to a specific GPCR binding site has attracted considerable interest in structural biology, molecular pharmacology and drug design. We recently reported on a covalently binding noradrenaline analog (FAUC37) facilitating crystallization of the β₂-adrenergic receptor (β₂AR^H2.64C) in an active state. We herein present the stereospecific synthesis of covalently binding disulfide ligands based on the pharmacophores of adrenergic β₁- and β₂ receptor antagonists. Radioligand depletion experiments revealed that the disulfide-functionalized ligands were able to rapidly form a covalent bond with a specific cysteine residue of the receptor mutants β₁AR^I2.64C and β₂AR^H2.64C. The propranolol derivative (S)-1a induced nearly complete irreversible blockage of the β₂AR^H2.64C within 30 min incubation. The CGP20712A-based ligand (S)-4 showed efficient covalent blocking of the β₂AR^H2.64C at very low concentrations. The analog (S)-5a revealed extraordinary covalent cross-linking at the β₁AR^I2.64C and β₂AR^H2.64C mutant while retaining a 41-fold selectivity for the β₁AR wild type over β₂AR. These compounds may serve as valuable molecular tools for studying β₁/β₂ subtype selectivity or investigations on GPCR trafficking and dimerization.

Emerging and Re-Emerging Warheads for Targeted Covalent Inhibitors: Applications in Medicinal Chemistry and Chemical Biology

Targeted covalent inhibitors (TCIs) are designed to bind poorly conserved amino acids by means of reactive groups, the so-called warheads. Currently, targeting noncatalytic cysteine residues with acrylamides and other α,β-unsaturated carbonyl compounds is the predominant strategy in TCI development. The recent ascent of covalent drugs has stimulated considerable efforts to characterize alternative warheads for the covalent-reversible and irreversible engagement of noncatalytic cysteine residues as well as other amino acids. This Perspective article provides an overview of warheads-beyond α,β-unsaturated amides-recently used in the design of targeted covalent ligands. Promising reactive groups that have not yet demonstrated their utility in TCI development are also highlighted. Special emphasis is placed on the discussion of reactivity and of case studies illustrating applications in medicinal chemistry and chemical biology.