Differential modulation of brain nicotinic acetylcholine receptor function by cytisine, varenicline, and two novel bispidine compounds: emergent properties of a hybrid molecule.

Partial agonist therapies for the treatment of nicotine addiction and dependence depend on both agonistic and antagonistic effects of the ligands, and side effects associated with other nAChRs greatly limit the efficacy of nicotinic partial agonists. We evaluated the in vitro pharmacological properties of four partial agonists, two current smoking cessation drugs, varenicline and cytisine, and two novel bispidine compounds, BPC and BMSP, by using defined nAChR subtypes expressed in Xenopus laevis oocytes and human embryonic kidney 293 cells. Similar to varenicline and cytisine, BPC and BMSP are partial agonists of α4ß2 nAChRs, although BMSP produced very little activation of these receptors. Unlike varenicline and cytisine, BPC and BMSP showed desired low activity. BPC produced mecamylamine-sensitive steady-state activation of α4* receptors that was not evident with BMSP. We evaluated the modulation of α4*- and α7-mediated responses in rat lateral geniculate nucleus (LGN) neurons and hippocampal stratum radiatum (SR) interneurons, respectively. The LGN neurons were sensitive to a very low concentration of varenicline, and the SR interneuron responses were also sensitive to varenicline at a submicromolar concentration. Although 300 nM BPC strongly inhibited the ACh-evoked responses of LGN neurons, it did not inhibit the α7 currents of SR interneurons. Similar results were observed with 300 nM BMSP. Additionally, the bispidine compounds were efficacious in the mouse tail suspension test, demonstrating that they affect receptors in the brain when delivered systemically. Our data indicate that BPC and BMSP are promising α4ß2* partial agonists for pharmacotherapeutics.

The 3,7-diazabicyclo[3.3.1]nonane scaffold for subtype selective nicotinic acetylcholine receptor ligands. Part 2: carboxamide derivatives with different spacer motifs.

3,7-Diazabicyclo[3.3.1]nonane (bispidine) based nicotinic acetylcholine receptor (nAChR) ligands have been synthesized and evaluated for nAChRs interaction. Diverse spacer motifs were incorporated between the hydrogen bond acceptor (HBA) part and a variety of substituted (hetero)aryl moieties. Bispidine carboxamides bearing spacer motifs often showed high affinity in the low nanomolar range and selectivity for the α4ß2(∗) nAChR. Compounds 15, 25, and 47 with Ki values of about 1 nM displayed the highest affinities for α4ß2(∗) nAChR. All evaluated compounds are partial agonists or antagonists at α4ß2(∗), with reduced or no effects on α3ß4(∗) with the exception of compound 15 (agonist), and reduced or no effect at α7 and muscle subtypes.

The 3,7-diazabicyclo[3.3.1]nonane scaffold for subtype selective nicotinic acetylcholine receptor (nAChR) ligands. Part 1: the influence of different hydrogen bond acceptor systems on alkyl and (hetero)aryl substituents.

3,7-Diazabicyclo[3.3.1]nonane is a naturally occurring scaffold interacting with nicotinic acetylcholine receptors (nAChRs). When one nitrogen of the 3,7-diazabicyclo[3.3.1]nonane scaffold was implemented in a carboxamide motif displaying a hydrogen bond acceptor (HBA) functionality, compounds with higher affinities and subtype selectivity for α4ß2(∗) were obtained. The nature of the HBA system (carboxamide, sulfonamide, urea) had a strong impact on nAChR interaction. High affinity ligands for α4ß2(∗) possessed small alkyl chains, small un-substituted hetero-aryl groups or para-substituted phenyl ring systems along with a carboxamide group. Electrophysiological responses of selected 3,7-diazabicyclo[3.3.1]nonane derivatives to Xenopus oocytes expressing various nAChR subtypes showed diverse activation profiles. Compounds with strongest agonistic profiles were obtained with small alkyl groups whereas a shift to partial agonism/antagonism was observed for aryl substituents.

Synthesis and evaluation of N(1)-alkylindole-3-ylalkylammonium compounds as nicotinic acetylcholine receptor ligands.

In this study thirty-three novel indole derivatives were designed and synthesized based on the structure of deformylflustrabromine B (1), a metabolite isolated from the marine bryozoan Flustra foliacea L. The syntheses were carried out using standard methodologies and in good yields. The molecules were tested for their affinities for the α4ß2(∗), α3ß4(∗), α7(∗) and (α1)(2)ß1γδ nicotinic acetylcholine receptor (nAChR) subtypes. Binding assays showed that, among these ligands, compound 7c exhibited the highest affinity with K(i)=136.1, 93.9 and 862.4nM for the α4ß2(∗), α3ß4(∗), and α7(∗) nAChRs subtypes, respectively. These results indicated that the indole core might be a useful scaffold for the development of new potent and selective nAChR ligands.

Multiple Dose Pharmacokinetics of Tapentadol Oral Solution for the Treatment of Moderate to Severe Acute Pain in Children Aged 2 to <7 Years.

Background: This prospective, open-label trial was conducted to fulfil a post-approval commitment made to the competent authorities to extend the indication of the strong opioid analgesic tapentadol hydrochloride oral solution (OS) to the pediatric population. Patients and Methods: The trial assessed the pharmacokinetic (PK) profile of tapentadol, tapentadol-O-glucuronide and tapentadol-O-sulfate after administration of multiple doses of tapentadol OS (1.25 mg tapentadol/kg bodyweight every 4 h for up to 72 h) in children aged 2 to <7 years after a painful event that produces acute pain requiring treatment with a strong analgesic. The obtained PK data were integrated into a previously developed population PK (popPK) model based on single-dose data and then a model-based PK evaluation was performed. The primary trial endpoint was the area under the concentration-time curve at steady state for the dosing interval (AUCτ,ss) for tapentadol. Results: Ten children received tapentadol OS; all completed the trial. Multiple administrations of the trial medication resulted in tapentadol serum concentrations within the concentration range predicted by the previously developed popPK model. The estimated model-based AUCτ,ss values for tapentadol ranged from 142 to 321 h•ng/mL. They were within the predicted exposure range with no higher than expected accumulation for the employed dosing regimen and also within the targeted steady state exposure range observed in adults receiving multiple doses of immediate release tapentadol 50 to 100 mg. The treatment regimen was safe and well tolerated. Conclusion: The findings confirm the linear and predictable PK profile of tapentadol hydrochloride. The good agreement between the observed data and the model predictions shows the value of modelling and simulations in the planning and analysis of pediatric clinical trials and the ability to utilize the established PK models to predict multiple dose exposure.

Tapentadol prolonged release in patients with chronic low back pain: real-world data from the German Pain eRegistry.

Aim: Comparison of tapentadol prolonged release (PR) with other oral WHO-III PR opioid analgesics (morphine, oxycodone ± naloxone, hydromorphone) in routine medical care of chronic low back pain. Patients & methods: Noninterventional, retrospective 12-week study using anonymized clinical practice data from the German Pain eRegistry. Six effectiveness, tolerability, and safety criteria were aggregated in a primary composite end point (treatment responder). Propensity scoring matched 2331 datasets per treatment cohort. Results: All six single criteria showed significantly better outcomes for tapentadol PR (all parameters p < 0.001). There were significantly more treatment responders under tapentadol PR (65.7 vs 14.2%; p < 0.001). Conclusion: Tapentadol PR showed significantly better effectiveness and tolerability in severe chronic low back pain unsuccessfully treated with WHO-I/II analgesics compared with the other oral WHO-III PR opioids investigated.

Lay abstract Chronic low back pain is a common condition often resulting in impaired functioning in daily life and reduced quality of life and well-being of the patient. In case treatment with less potent pain medications is unsuccessful, opioid treatment might be required. Our study compared the effectiveness and tolerability of the prolonged release formulation of the atypical opioid tapentadol with other strong opioids commonly used for chronic pain treatment in Germany (morphine, hydromorphone, oxycodone ± naloxone). Anonymized patient data from German clinical practices collected in a pain registry were used (2331 comparable patients per treatment group). Patients receiving 12 weeks of tapentadol treatment experienced significantly greater pain relief, greater improvements in daily living activities, sleep, and quality of life compared with those receiving the other strong opioids investigated. Neuropathic pain components (pain features resembling nerve pain, often described as shooting, burning or stabbing pain) were reduced to a greater extent in the tapentadol treatment group. Tapentadol was also significantly better tolerated. This study showed that tapentadol is effective and well tolerated in chronic low back pain treatment in routine medical practice in patients still in considerable pain despite treatment with less potent pain medications.

Cytisine-based nicotinic partial agonists as novel antidepressant compounds.

Nicotine and other nicotinic agents are thought to regulate mood in human subjects and have antidepressant-like properties in animal models. Recent studies have demonstrated that blockade of nicotinic acetylcholine receptors (nAChRs) including those containing the beta2 subunit (beta2(*)), results in antidepressant-like effects. Previous studies have shown that cytisine, a partial agonist at alpha4/beta2(*) nAChRs, and a full agonist at alpha3/beta4(*) and alpha7 nAChRs, has antidepressant-like properties in several rodent models of antidepressant efficacy; however, it is not clear whether more selective partial agonists will also be effective in these models. We tested cytisine and two derivatives, 5-bromo-cytisine (5-Br-Cyt) and 3-(pyridin-3'-yl)-cytisine (3-pyr-Cyt) for their ability to act as a partial agonist of different nAChR subtypes and to show antidepressant-like activity in C57/BL6 mice in the tail suspension, the forced-swim, and the novelty-suppressed feeding tests. 3-pyr-Cyt was a partial agonist with very low efficacy at alpha4/beta2(*) nAChRS but had no agonist effects at other nAChRs normally targeted by cytisine, and it was effective in mouse models of antidepressant efficacy. Animals showed dose-dependent antidepressant-like effects in all three behavioral paradigms. 5-Br-Cyt was not effective in behavioral tests when administered peripherally, probably because of its inability to penetrate the blood-brain barrier, because it efficiently reduced immobility in the tail suspension test when administered intraventricularly. These results suggest that novel nicotinic partial agonists may provide new possibilities for development of drugs to treat mood disorders.

Nicotinic acetylcholine receptor ligands, a patent review (2006-2011).

INTRODUCTION: Nicotinic acetylcholine receptors (nAChRs), pentameric ligand-gated cation channels, are potential targets for the development of therapeutics for a variety of disease states. AREAS COVERED: This article is reviewing recent advances in the development of small-molecule ligands for diverse nAChR subtypes and is a continuation of an earlier review in this journal. EXPERT OPINION: The development of nAChR ligands with preference for α4ß2 or α7 subtypes for the treatment of central nervous system disorders are in the most advanced developmental stage. In addition, there is a fast growing interest to generate so-called PAMs, positive allosteric modulators, to influence the channels' functionalities.