Daniela Gündisch

Syntheses and evaluation of halogenated cytisine derivatives and of bioisosteric thiocytisine as potent and selective nAChR ligands.

We have developed one-step syntheses of halogenated derivatives of (-)-cytisine featuring a halogen substituent at positions 3, 5 or 3 and 5 of the 2-pyridone fragment, and prepared the novel bioisosteric thiocytisine by oxygen-sulphur exchange. The affinities of these pyridone-modified analogs of (-)-cytisine for (alpha 4)(2)(beta 2)(3) and alpha 7* nAChRs in rat forebrain membranes were determined by competition with (+/-)-[(3)H]epibatidine and [(3)H]MLA, respectively. The 3-halocytisines 7 possess subnanomolar affinities for (alpha 4)(2)(beta 2)(3) nAChRs, higher than those found for (-)-cytisine as well as for the 5-halocytisines 8 and 3,5-dihalocytisines 6. In contrast to the parent alkaloid the 3-halogenated species display much a higher affinity for the alpha 7* nAChR subtype. The most potent molecule was 3-bromocytisine (7b) with preferential selectivity (200-fold) for the (alpha 4)(2)(beta 2)(3) subtype [K(i)=10 pM (alpha 4 beta 2) and 2.0 nM (alpha 7*)]. Replacement of the lactam with a thiolactam pharmacophore to thiocytisine (12) resulted in a subnanomolar affinity for the (alpha 4)(2)(beta 2)(3) nAChR subtype (K(i)=0.832 nM), but in a drastic decrease of affinity for the alpha 7* subtype; thiocytisine (12) has a K(i) value of 4000 nM (alpha 7*), giving a selectivity of 4800-fold for the neuronal (alpha 4)(2)(beta 2)(3)-nAChR and thus displaying the best affinity-selectivity profile in the series under consideration.

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 β2 subunit (β2*), results in antidepressant-like effects. Previous studies have shown that cytisine, a partial agonist at α4/β2* nAChRs, and a full agonist at α3/β4* and α7 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 α4/β2* 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.

Smoking upregulates α4β2* nicotinic acetylcholine receptors in the human brain

Abstract The role of the α4β2* nicotinic acetylcholine receptors (nAChR) in tobacco addiction in humans is largely unresolved. We visualized brain α4β2* nicotinic acetylcholine receptors of smokers and non-smokers with positron emission tomography using 2-[ 18 F]fluoro-3-(2( S )azetidinylmethoxy)pyridine, commonly known as 2-[ 18 F]F-A-85380. The total brain distribution volume of 2-[ 18 F]F-A-85380 was significantly increased in smokers. Statistical parametric mapping revealed that the most prominent regional differences of distribution volumes (DV) were found in cerebellum and brainstem with an increased uptake in smokers. The up-regulation of α4β2* nAChR upon chronic nicotine exposure via tobacco smoking incorporates subcortical brain regions which may play an important role in nicotine addiction.

Feasibility of [18F]-2-Fluoro-A85380-PET imaging of human vascular nicotinic acetylcholine receptors in vivo.

OBJECTIVES The aim of this feasibility study was to evaluate [(18)F]-2-Fluoro-A85380 for in vivo imaging of arterial nicotinic acetylcholine receptors (nAChRs) in humans. Furthermore, potentially different vascular uptake patterns of this new tracer were evaluated in healthy volunteers and in patients with neurodegenerative disorders. BACKGROUND [(18)F]-2-Fluoro-A85380 was developed for in vivo positron emission tomography (PET) imaging of nAChR subunits in the human brain. These nAChRs are also found in arteries and seem to mediate the deleterious effects of nicotine as a part of tobacco smoke in the vasculature. It has been previously shown that uptake patterns of the radiotracer in the brain differs in patients with neurodegenerative disorders compared with healthy controls. METHODS [(18)F]-2-Fluoro-A85380 uptake was quantified in the ascending and descending aorta, the aortic arch, and the carotids in 5 healthy volunteers and in 6 patients with either Parkinsons disease or multiple system atrophy, respectively, as the maximum target-to-background ratio. The maximal standardized uptake value values, the single hottest segment, and the percent active segments of the [(18)F]-2-Fluoro-A85380 uptake in the arteries were also assessed. RESULTS [(18)F]-2-Fluoro-A85380 uptake was clearly visualized and maximum target-to-background ratio uptake values corrected for the background activity of the tracer showed specific tracer uptake in the arterial walls. Significantly higher uptake values were found in the descending aorta. Comparison between volunteers and patients revealed significant differences, with lower [(18)F]-2-Fluoro-A85380 uptake in the patient group when comparing single arterial territories but not when all arterial territories were pooled together. CONCLUSIONS [(18)F]-2-Fluoro-A85380 can provide specific information on the nAChR distribution in human arteries. Vascular nAChR density seems to be lower in patients with Parkinsons disease or multiple system atrophy. Once confirmed in larger study populations and in the experimental setting, this approach might provide insights into the pathogenic role of nAChRs in the human vasculature.

Carbazole Scaffold in Medicinal Chemistry and Natural Products: A Review from 2010-2015

9H-carbazole is an aromatic molecule that is tricyclic in nature, with two benzene rings fused onto a 5-membered pyrrole ring. Obtained from natural sources or by synthetic routes, this scaffold has gained much interest due to its wide range of biological activity upon modifications, including antibacterial, antimalarial, anticancer, and anti-Alzheimer properties. This review reports a survey of the literature on carbazole-containing molecules and their medicinal activities from 2010 through 2015. In particular, we focus on their in vitro and in vivo activities and summarize structure-activity relationships (SAR), mechanisms of action, and/or cytotoxicity/selectivity findings when available to provide future guidance for the development of clinically useful agents from this template.

Feasibility of 2–deoxy–2–[18F]fluoro–D–glucose– A85380–PET for imaging of human cardiac nicotinic acetylcholine receptors in vivo

SummaryNicotinic acetylcholine receptors mediate the parasympathetic autonomic control of cardiac function. Aim of this study was the assessment of cardiac nicotinic acetylcholine receptor distribution with a novel (α4β2) nicotinic acetylcholine receptor PET ligand (2–deoxy–2– [18F]fluoro–D–glucose–A85380) in humans. Five healthy volunteers without cardiac disease and six patients with either Parkinsons disease or multiple system atrophy without additional overt cardiac disease were evaluated with 2–deoxy–2–[18F]fluoro–D–glucose–A85380 PET–imaging to assess the cardiac parasympathetic innervation and the putative impact of both disorders. 2–deoxy–2– [18F]fluoro–D–glucose–A85380 whole body PET–scans were performed on a Siemens PET/CT biographTM 75.4 min±6.7 after i.v. injection of 371.2±58.1 MBq. Average count rate density of left ventricle ROIs and a standard ROI in the right lung were measured within three consecutive slices of 10.0 mm thickness. Heart–to–lung ratios were calculated in each volunteer and patient.Tracer uptake in the left ventricle could be measured in all of the five volunteers and the six patients. Heart–to–lung ratios in the volunteer group were not different from patients suffering from Parkinsons disease or MSA (3.2 ± 0.5 vs 3.2 ± 0.8 and 2.96±0.7, mean ± SD), respectively.Human cardiac nicotinic acetylcholine receptors can be visualized and measured by 2–deoxy–2– [18F]fluoro–D–glucose–A85380 PET scans both in cardiac–healthy subjects and patients suffering from Parkinsons disease or multiple system atrophy. The heart– as well as the lung–tracer uptake was almost constant throughout all subjects leading to a good targetto– background ratio. These first results suggest no impact of either PD or MSA on cardiac nicotinic acetylcholine receptors.

Nicotinic acetylcholine receptor ligands as potential therapeutics

The nicotinic acetylcholine receptors (nAChRs) belong to a superfamily of ligand-gated ion channels. Neuronal nAChRs are involved in a variety of complex cognitive processes (learning and memory) and therefore in CNS disorders. These include, for example, Alzheimer’s and Parkinson’s disease, attention deficit hyperactivity disorder, Tourette’s syndrome, schizophrenia, depression, pain and tobacco dependence. Thus, nAChRs present a rational target for the treatment of these pathological processes. Over the past years an increasing number of ligands, especially for the α4β2 subtype has been synthesised. Recent developments reveal increased interest in α7 ligands for the treatment of CNS diseases as well as for pain and inflammation. Unfortunately, only a few companies provide biological data in detail, especially regarding subtype selectivity and functionality. This review provides an overview of the recent patent literature focusing mainly on small molecule ligands.

Synthesis and evaluation of N1-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 α4β2(∗), α3β4(∗), α7(∗) and (α1)(2)β1γδ 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 α4β2(∗), α3β4(∗), 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.

Effects of Aβ1−42 fibrils and of the tetrapeptide Pr-IIGL on the phosphorylation state of the τ-protein and on the α7 nicotinic acetylcholine receptor in vitro

In order to investigate the possible links connecting β‐amyloid (Aβ) accumulation, τ‐hyperphosphorylation and nicotinic receptor expression, rat embryonic primary hippocampal cultures were incubated with amyloidogenic peptides. Exposure to 0.5 µm fibrillar Aβ1−42 for 3 days caused retraction of dendrites, shrinkage of cell bodies and a decrease in the expression of microtubule‐associated proteins 2b (MAP2b), without affecting the total number of neurons and their viability. No impact on the τ‐phosphorylation sites Ser‐202, Thr231/Ser235, Ser262 and Ser396/Ser404 was found. The total number of homomeric α7‐nicotinic receptors (α7‐nAChRs) and their affinity for [125I]α‐bungarotoxin remained unaltered. Upon incubation with the putatively protective tetrapeptide propionyl–isoleucine–isoleucine–glycine–leucine (Pr‐IIGL), an analogue of the region [31–34] of Aβ, cell bodies were swollen in the region of the apical dendrite. These morphological alterations, different from those elicited by Aβ1−42, did not involve MAP2 expression changes. In contrast to Aβ1−42, Pr‐IIGL caused a massive hyperphosphorylation of the τ‐protein at Ser‐202 and at Ser396/Ser404. The total number of homomeric α7‐nAChRs and their affinity for [125I]α‐bungarotoxin were unaffected. In conclusion, the present results show a toxic effect of Aβ1−42 on the cytoskeletal structure at concentrations normally present in the brains of Alzheimers disease patients, but raise some doubts about the role of Aβ1−42 fibrils as a direct trigger of τ‐hyperphosphorylation. The tetrapeptide Pr‐IIGL cannot be considered protective with regard to cell morphology. Although it prevents the Aβ1−42‐induced retraction of dendrites, it exhibits other toxic properties. The homomeric α7‐nAChRs were not affected either by Aβ1−42 incubation or by Pr‐IIGL‐induced τ‐hyperphosphorylation.

Bispidine as a Privileged Scaffold

Thediazabicyclic molecule bispidine named by the chemist Carl Mannich in 1930, is a naturally occurring scaffold with interesting features. Bispidine can form different conformers, has high basicity, can attack dichloromethane, has metal ion coordination properties and interacts with nicotinic acetylcholine receptors. In this review we will discuss important properties, synthetic pathways and biological activities of bispidine and some derivatives. Bispidine can function as a scaffold for compounds with very diverse biological activities, e.g. interacting with ion channels, G-protein coupled receptors, and enzymes, and is even used for the development of new in vivo radiotracers.