Preclinical Evaluation of the Effects of Trazpiroben (TAK-906), a Novel, Potent Dopamine D2/D3 Receptor Antagonist for the Management of Gastroparesis.

Current therapies for gastroparesis metoclopramide and domperidone carry risks of extrapyramidal symptoms and life-threatening cardiac arrhythmias. Trazpiroben, a novel, potent dopamine D2/D3 receptor antagonist, has low brain permeation and very low affinity for human ether-à-go-go-related gene (hERG) channel inhibition, potentially improving on safety profiles of existing therapies. Trazpiroben demonstrated the following receptor affinities: high for D2 and D3, moderate for D4, and minimal for D1 and D5 It demonstrated moderate affinity for adrenergic α 1B (α 1B) and 5-hydroxytryptamine (5HT) 2A receptors and low potential for off-target adverse events (AEs). Trazpiroben potently inhibited dopamine-activated D2L receptor activation of cognate G-proteins in human embryonic kidney 293 cell membranes and was a neutral D2L receptor antagonist. In vivo, trazpiroben dose-dependently increased prolactin release in orally dosed rat (0.1-1 mg/kg). Additionally, multiple oral doses in the rat (100 mg/kg) and dog (50 mg/kg) for 3 days produced robust plasma exposures and prolactin increases in both species. Trazpiroben inhibited retching/vomiting in the dog with apomorphine-induced emesis with a potency (0.1-1 mg/kg) like that of trazpiroben-mediated prolactin increases in rat. Oral trazpiroben (1, 10, and 30 mg/kg) did not affect rat rotarod performance, suggesting low brain penetration. Trazpiroben concentrations were low in cerebrospinal fluid versus plasma after multiple oral doses for 4 days in rat and dog. Trazpiroben weakly inhibited the hERG channel current (concentration causing half-maximal inhibition of control-specific binding of 15.6 µM), indicating little potential for disrupting cardiac rhythm. Overall, trazpiroben is a potent D2/D3 receptor antagonist designed to avoid the serious potential AEs associated with current gastroparesis therapies. SIGNIFICANCE STATEMENT: Trazpiroben is a novel, potent dopamine D2/D3 selective receptor antagonist designed to avoid adverse effects associated with the current pharmacological therapies metoclopramide and domperidone. Preclinical studies have demonstrated low brain penetration and weak affinity for the hERG channel, indicating that trazpiroben is not expected to be associated with central nervous system or cardiovascular safety issues. With these pharmacological properties, trazpiroben may represent a viable new treatment option for gastroparesis because of a potentially improved safety profile relative to existing therapies.

Design, synthesis and biological evaluation of novel serotonin and dopamine receptor ligands being 6-bromohexyl saccharine derivatives.

Due to numerous side effects of current antidepressants, the search for new, safer bioactive compounds is still a valid research topic in medical chemistry. In our research we decided to synthesize and determine SAR for new hexyl arylpiperazines (LACPs) derivated with saccharin moiety. High biological activity has been explained using molecular modelling methods. The compounds obtained show high affinity for the 5-HT1A (compound 18, Ki = 4 nM - antagonist mode) and D2 (compound 15, Ki = 7 nM - antagonist mode) receptor, and in some cases also 5-HT7 receptor (compound 17, Ki = 20 nM). A preliminary ADME analysis showed that the compounds exhibit CNS drugability properties. We have proved that carbon-chain lengthening may have a beneficial effect on increasing the activity towards serotonin and dopamine receptors.

Synthesis and characterization of a series of chiral alkoxymethyl morpholine analogs as dopamine receptor 4 (D4R) antagonists.

Herein, we report the synthesis and structure-activity relationship of a series of chiral alkoxymethyl morpholine analogs. Our efforts have culminated in the identification of (S)-2-(((6-chloropyridin-2-yl)oxy)methyl)-4-((6-fluoro-1H-indol-3-yl)methyl)morpholine as a novel potent and selective dopamine D4 receptor antagonist with selectivity against the other dopamine receptors tested (<10% inhibition at 1µM against D1, D2L, D2S, D3, and D5).

Investigation of the binding and functional properties of extended length D3 dopamine receptor-selective antagonists.

The D3 dopamine receptor represents an important target in drug addiction in that reducing receptor activity may attenuate the self-administration of drugs and/or disrupt drug or cue-induced relapse. Medicinal chemistry efforts have led to the development of D3 preferring antagonists and partial agonists that are >100-fold selective vs. the closely related D2 receptor, as best exemplified by extended-length 4-phenylpiperazine derivatives. Based on the D3 receptor crystal structure, these molecules are known to dock to two sites on the receptor where the 4-phenylpiperazine moiety binds to the orthosteric site and an extended aryl amide moiety docks to a secondary binding pocket. The bivalent nature of the receptor binding of these compounds is believed to contribute to their D3 selectivity. In this study, we examined if such compounds might also be "bitopic" such that their aryl amide moieties act as allosteric modulators to further enhance the affinities of the full-length molecules for the receptor. First, we deconstructed several extended-length D3-selective ligands into fragments, termed "synthons", representing either orthosteric or secondary aryl amide pharmacophores and investigated their effects on D3 receptor binding and function. The orthosteric synthons were found to inhibit radioligand binding and to antagonize dopamine activation of the D3 receptor, albeit with lower affinities than the full-length compounds. Notably, the aryl amide-based synthons had no effect on the affinities or potencies of the orthosteric synthons, nor did they have any effect on receptor activation by dopamine. Additionally, pharmacological investigation of the full-length D3-selective antagonists revealed that these compounds interacted with the D3 receptor in a purely competitive manner. Our data further support that the 4-phenylpiperazine D3-selective antagonists are bivalent and that their enhanced affinity for the D3 receptor is due to binding at both the orthosteric site as well as a secondary binding pocket. Importantly, however, their interactions at the secondary site do not allosterically modulate their binding to the orthosteric site.

Targeting dopamine D3 and serotonin 5-HT1A and 5-HT2A receptors for developing effective antipsychotics: synthesis, biological characterization, and behavioral studies.

Combination of dopamine D3 antagonism, serotonin 5-HT1A partial agonism, and antagonism at 5-HT2A leads to a novel approach to potent atypical antipsychotics. Exploitation of the original structure-activity relationships resulted in the identification of safe and effective antipsychotics devoid of extrapyramidal symptoms liability, sedation, and catalepsy. The potential atypical antipsychotic 5bb was selected for further pharmacological investigation. The distribution of c-fos positive cells in the ventral striatum confirmed the atypical antipsychotic profile of 5bb in agreement with behavioral rodent studies. 5bb administered orally demonstrated a biphasic effect on the MK801-induced hyperactivity at dose levels not able to induce sedation, catalepsy, or learning impairment in passive avoidance. In microdialysis studies, 5bb increased the dopamine efflux in the medial prefrontal cortex. Thus, 5bb represents a valuable lead for the development of atypical antipsychotics endowed with a unique pharmacological profile for addressing negative symptoms and cognitive deficits in schizophrenia.

Formulation and evaluation of domperidone loaded mineral oil entrapped emulsion gel (MOEG) buoyant beads.

Alginate based mineral oil entrapped emulsion gel (MOEG) buoyant beads of domperidone were prepared by emulsion gelation technique. The prepared beads were evaluated for particle size, surface morphology, buoyancy, actual drug content and entrapment efficiency. Effect of different oils (castor oil, olive oil and linseed oil) and oil concentrations (10%, 15% and 20%, w/w) on uniformity, homogeneity and integrity of the beads was also studied. Density of the formulated beads was found to be ranging between 0.101 and 0.182 g/cm3. The results of the in vitro drug release indicated that linseed oil showed to be good release retardant compared to castor oil and olive oil. Moreover, the beads formulated using 15%, w/w linseed oil were more uniform in shape, exhibited maximum buoyancy and minimal oil leakage. Diffusion exponent (n) value varied from 0.4855 to 0.7710 indicating anomalous drug release behavior involving swelling, diffusion and/or erosion of the polymer matrix.

The interaction of antipsychotic drugs with lipids and subsequent lipid reorganization investigated using biophysical methods.

The interaction of antipsychotic drugs (AP) with lipids and the subsequent lipid reorganization on model membranes was assessed using a combination of several complementary biophysical approaches (calorimetry, plasmon resonance, fluorescence microscopy, X-ray diffraction and molecular modeling). The effect of haloperidol (HAL), risperidone (RIS), and 9-OH-risperidone (9-OH-RIS) was examined on single lipid and mixtures comprising lipids of biological origin. All APs interact with lipids and induced membrane reorganization. APs showed higher affinity for sphingomyelin than for phosphatidylcholine. Cholesterol increased AP affinity for the lipid bilayer and led to the following AP ranking regarding affinity and structural changes: RIS >9-OH-RIS >HAL. Liquid-ordered domain formation and bilayer thickness were differentially altered by AP addition. Docking calculations helped understanding the observed differences between the APs and offer a representation of their conformation in the lipid bilayer. Present results indicate that AP drugs may change membrane compartmentalization which could differentially modulate the signaling cascade of the dopamine D2 receptor for which APs are ligands.

Screening and isolation of a natural dopamine D1 receptor antagonist using cell-based assays.

To develop a cell-based assay to screen for human dopamine D(1) receptor agonists or antagonists from medicinal plant extracts, a stable Chinese hamster ovary (CHO) cell line (CHO-D1R) expressing the human dopamine D(1) receptor was established using an expression vector containing a scaffold attachment region (SAR) element. CHO-D1R cells showed specific binding to [(3)H]-SCH23390 with high affinity (K(d)=1.47+/-0.17 nM) and dose-dependent responses for the dopamine-mediated stimulation of cAMP concentrations (EC(50)=20.6+/-1.44 nM). The screening of medicinal plant extracts using cell-based cAMP assays revealed that an extract of Gleditsia sinensis Lam., which is known to be rich in saponin, had strong antagonist activity for the D(1) receptor. From the activity-guided fractionation and chemical structural analysis of the G. sinensis extract, a compound called gleditsioside F was isolated and was identified to have antagonist activity for the D(1) receptor. Gleditsioside F showed very effective D(1) antagonist activity by inhibiting ligand binding to the D(1) receptor as well as by inhibiting dopamine-mediated increases in cAMP concentration.

Nasal absorption of metoclopramide from different Carbopol 981 based formulations: In vitro, ex vivo and in vivo evaluation.

There is a need for nasal drug delivery of metoclopramide HCI (MTC) in specific patient populations where the use of commercially available intravenous and oral dosage forms may be inconvenient and/or unfeasible. In this perspective, nasal dosage forms (solution, gel and lyophilized powder) of MTC were prepared by using a mucoadhesive polymer Carbopol 981 (CRB 981). The drug release studies of formulations were performed by using a modified horizontal diffusion chamber with cellulose membrane and excised cattle nasal mucosa as diffusion barriers. After the ex vivo experiments, the morphological appearances of the nasal mucosa were analyzed with the light microscopic studies. In vivo experiments were carried on sheep model. The release of MTC from solution and powder formulations was found higher than gel formulation (p < 0.05) and no severe damage was found on the integrity of nasal mucosa after ex vivo experiments. The penetration enhancing effect of dimethyl-beta-cyclodextrin (DM-beta-CD) used in powder formulations was observed in ex vivo and in vivo experiments. In contrast to in vitro and ex vivo experiments the nasal bioavailability of gel formulation was found higher than those of the solution and powder (p < 0.05) and might represent a promising novel tool for the systemic delivery of MTC.

Recent pharmacological studies on natural products in China.

Natural products have been used as medicinal agents for many years. In addition, these compounds have also served as the starting points for semisynthetic analogs with improved properties. This review focuses on recent advances in the pharmacological studies on natural products mainly performed and published in China. Emphasis will be placed on those compounds that show the greatest promise clinically such as huperzine A (9-amino-13-ethylidene-11-methyl-4-azatricyclo[7.3.1.0(3.8)]trideca-3(8),6,11-trien-5-one), s-(-)-3-n-butylphthalide (s-(-)-3-butyl-1(3H)-isobenzofuranone), (-)-clausenamide (3-hydroxy-4-phenyl-5a-hydroxybenzyl-N-methyl-gamma-lactam) and Ginkgo biloba extract and its active components.

11C-Fallypride: radiosynthesis and preliminary evaluation of a novel dopamine D2/D3 receptor PET radiotracer in non-human primate brain.

Fallypride [benzamide, 5-(3-fluoropropyl)-2,3-dimethoxy-N-[(2S)-1-(2-propenyl)-2-pyrrolidinyl]methyl]-, CAS RN 166173-78-0] is a selective dopamine D2/D3 receptor antagonist. Carbon-11 labeled fallypride may serve as a radiotracer for use in biomedical imaging technique positron emission tomography (PET). The precursor, 5-(3-fluoropropyl)-2-hydroxy-3-methoxy-N-[(2S)-1-(2-propenyl)-2-pyrrolidinyl]methyl]benzamide was synthesized from 2-hydroxy-3-methoxy-5-(2-propenyl)benzoic acid, methyl ester in seven steps with approximately 10% overall chemical yield. Using this precursor (11)C-fallypride was produced by radiolabeling with (11)C-methyl iodide in 25-40% radiochemical yields with specific activities of 200-1000 Ci/mmol. PET imaging studies in nonhuman primates with (11)C-fallypride showed radiotracer localization in dopaminergic brain regions such as caudate, putamen, thalamus and cortex. This regional localization of (11)C-fallypride is similar to that observed previously for (18)F-fallypride. The results suggest (11)C-fallypride is a useful PET radiotracer for imaging dopamine D2/D3 receptors.

Synthesis and biological evaluation of hyperforin analogues. Part I. Modification of the enolized cyclohexanedione moiety.

Modification of the St. John's wort acylphloroglucinol constituent, hyperforin (1), by acylation, alkylation, and oxidation resulted in detrimental effects on the inhibition of the synaptosomal accumulation of serotonin, showing the existence of definite structure-activity relationships in this in vitro test system and highlighting the role of the enolized cyclohexanedione moiety for activity on neurotransmitter reuptake.

6-(4-Benzylpiperazin-1-yl)benzodioxanes as selective ligands at cloned primate dopamine D(4) receptors.

A series of novel 6-(4-benzylpiperazin-1-yl)benzodioxanes were prepared and screened at selected dopamine receptor subtypes. 6-(4-[4-Chlorobenzyl]piperazin-1-yl)benzodioxane (2d) had high affinity and selectivity for the D(4) dopamine receptor subtype and was identified as a D(4) antagonist via its attenuation of dopamine-induced GTPgamma(35)S binding at the D(4) receptor.

N-Substituted (2,3-dihydro-1,4-benzodioxin-2-yl)methylamine derivatives as D(2) antagonists/5-HT(1A) partial agonists with potential as atypical antipsychotic agents.

A series of N-substituted 1-(2,3-dihydro-1, 4-benzodioxin-2-yl)methylamine derivatives with D(2) antagonist/5-HT(1A) partial agonist activity has been prepared as potential atypical antipsychotic agents. Optimization of in vitro receptor binding activity and in vivo activity in rodent models of psychosis has led to compound 24, which showed good affinities for human D(2), D(3), and 5-HT(1A) receptors but significantly less affinity for human alpha(1) adrenoceptors and rat H(1) and muscarinic receptors. In rodents, 24 showed functional D(2)-like antagonism and 5-HT(1A) partial agonism. After oral dosing, 24 showed good activity in rodent antipsychotic tests and very little potential to cause extrapyramidal side effects (EPS), as measured by its ability to induce catalepsy in rats only at very high doses. In the light of this promising profile of activity, 24 has been selected for clinical investigation as a novel antipsychotic agent with a predicted low propensity to cause EPS.

Muscarinic agonists with antipsychotic-like activity: structure-activity relationships of 1,2,5-thiadiazole analogues with functional dopamine antagonist activity.

Muscarinic agonists were tested in two models indicative of clinical antipsychotic activity: conditioned avoidance responding (CAR) in rats and inhibition of apomorphine-induced climbing in mice. The standard muscarinic agonists oxotremorine and pilocarpine were both active in these tests but showed little separation between efficacy and cholinergic side effects. Structure-activity relationships of the alkylthio-1,2,5-thiadiazole azacyclic type muscarinic partial agonists are shown, revealing the exo-6-(3-propyl/butylthio-1,2, 5-thiadiazol-4-yl)-1-azabicyclo[3.2.1]octane analogues (4a,b and 9a, b) to be the most potent antipsychotic agents with large separation between efficacy and cholinergic side effects. The lack of enantiomeric selectivity suggests the pharmacophoric elements are in the mirror plane of the compounds. A model explaining the potency differences of closely related compounds is offered. The data suggest that muscarinic agonists act as functional dopamine antagonists and that they could become a novel treatment of psychotic patients.

The discovery of potent and selective dopamine D4 receptor antagonists.

The identification of a novel dopamine receptor subtype, referred to as the D4 receptor, which binds the atypical antipsychotic drug clozapine with high potency, has led to the initiation of a drug discovery program that aims to find novel inhibitors of this receptor subtype. A selective screening strategy was utilized, in which 4500 compounds chosen on the basis of structural similarities to known biogenic amine receptor antagonists were tested against both the D4 and D2 dopamine receptor subtypes. A potent D4-selective compound was discovered.