Design of α7 nicotinic acetylcholine receptor ligands using the (het)Aryl-1,2,3-triazole core: Synthesis, in vitro evaluation and SAR studies.

We report here the synthesis of a large library of 1,2,3-triazole derivatives which were in vitro tested as α7 nAchR ligands. The SAR study revealed that several crucial factors are involved in the affinity of these compounds for α7 nAchR such as a (R) quinuclidine configuration and a mono C-3 quinuclidine substitution. The triazole ring was substituted by a phenyl ring bearing small OMe/CH2F groups or fluorine atom and by several heterocycles such as thiophenes, furanes, benzothiophenes or benzofuranes. Among the 30 derivatives tested, the two derivatives 10 and 39 with Ki in the nanomolar range were identified (2.3 and 3 nM respectively). They exhibited a strict selectivity toward the α4ß2 nicotinic receptor (up to 1 µM) but interacted with the 5HT3 receptors with Ki around 3 nM. Synthesis, SAR studies and a full description of the derivatives are reported.

Imaging of the striatal and extrastriatal dopamine transporter with (18)F-LBT-999: quantification, biodistribution, and radiation dosimetry in nonhuman primates.

UNLABELLED: The aim of this study was to evaluate the quantification, biodistribution, and radiation dosimetry of the novel dopamine transporter (DAT) radioligand (18)F-(2S,3S)-methyl 8-((E)-4-fluorobut-2-en-1-yl)-3-(p-tolyl)-8-azabicyclo[3.2.1]octane-2-carboxylate ((18)F-LBT-999) in nonhuman primates. METHODS: The brain study was conducted in 4 female rhesus monkeys. PET measurements were conducted for 243 min using the high-resolution research tomograph (HRRT) with the measurement of the metabolite-corrected arterial input function and protein binding. Quantification was performed with kinetic analysis using 2-tissue- and 1-tissue-compartment models, with Logan graphical analysis and with different reference tissue models. The outcome measures were total distribution volume (V(T)), nondisplaceable distribution volume (V(ND)), binding potential relative to the free concentration of radioligand in plasma (BP(F)), and binding potential relative to the concentration of nondisplaceable radioligand in tissue (BP(ND)) = V(T) - V(ND)/V(ND) using the cerebellum as a reference region. For the biodistribution and radiation dosimetry, 2 female cynomolgus monkeys were studied. Whole-body PET scans were obtained using a PET/CT system for approximately 250 min. Estimates of the absorbed radiation dose in humans were calculated using OLINDA/EXM software. RESULTS: (18)F-LBT-999 showed good brain uptake (300% standardized uptake value) and regional distribution according to known DAT density. The 2-tissue-compartment model was the preferred model for the quantification. Late peak equilibrium (120-140 min) and slow washout were observed in the striatum, with high variability of V(T), BP(F), and BP(ND). When the different models were compared with the 2-tissue-compartment model, the underestimation of V(T) or BP(ND) was larger in the caudate and putamen than in the midbrain and thalamus. The reference tissue models were suitable for the quantification. The whole-body distribution study showed that the main routes of excretion of (18)F-LBT-999 were the urinary and gastrointestinal systems, with the bladder being the critical organ. Accumulation of (18)F-LBT-999 was found in the bone and skull, with a relatively high dose estimated for the osteogenic cells. The range of calculated effective dose was 0.021-0.022 mSv/MBq. CONCLUSION: (18)F-LBT-999 seemed to be a suitable PET radioligand for the DAT quantification, particularly for extrastriatal regions. The skull uptake did not seem to be a limitation for brain imaging. The calculated dosimetry estimates based on data in nonhuman primates seemed comparable with those of other clinically used (18)F-labeled radioligands, for example, (18)F-FDG (0.024-0.027 mSv/MBq).

New fluoro-diphenylchalcogen derivatives to explore the serotonin transporter by PET.

A series of fluorinated diphenylchalcogen derivatives, possessing a sulfur or an oxygen bridge, has been prepared with the aim to get a suitable radiotracer to image the SERT in vivo using positron emission tomography (PET). The compounds were synthesized and assayed toward the serotonin (SERT), dopamine (DAT), and norepinephrine (NET) transporters. Among the developed series, five compounds display a high SERT affinity (K(i): 0.27-2.91 nM range) and can be labeled either with carbon-11 or fluorine-18.

[11C]LBT-999: a suitable radioligand for investigation of extra-striatal dopamine transporter with PET.

A new tropane derivative, (E)-N-(4-fluorobut-2-enyl)-2beta-carbomethoxy-3beta-(4'-tolyl)nortropane (LBT-999), was evaluated in baboons as a carbon-11 radioligand for studies of the dopamine transporter (DAT) using positron emission tomography (PET). Brain uptake was high in the striatum (17 and 13% ID/100 mL tissue in the putamen and the caudate, respectively), moderate in the midbrain and thalamus (5 and 3% ID/100 mL tissue, respectively), and low in the cortex and cerebellum (2% ID/100 mL tissue) at 30 min post injection. The striatum-to-cerebellum ratio was high (30 at 110 min post injection). Specific binding was completely blocked following pretreatment with the DAT antagonists GBR12909 (5 mg/kg i.v.) or PE2I (1 mg/kg i.v.). The [(11)C]LBT-999 uptake was decreased by these antagonists in the putamen (-79 and -92%, respectively), caudate (-80 and -91%, respectively), midbrain (-73 and -78%, respectively), and thalamus (-34 and -46%, respectively). The serotonin transporter (SERT) antagonist citalopram (5 mg/kg i.v.) or the norepinephrine transporter antagonist maprotiline (5 mg/kg i.v.) had no effect on LBT specific binding. Pharmacological challenge with PE2I (1 mg/kg i.v.) induced a rapid and almost complete decrease of the specific binding in the putamen (-97%), caudate (-96%), midbrain (-96%), and thalamus (-81%), confirming the reversibility of [(11)C]LBT-999 binding. The high brain uptake of [(11)C]LBT-999 together with its low nonspecific binding (reflected by the very high brain structure-to-cerebellum ratio) indicate that this radiotracer is an excellent candidate for in vivo quantification of the DAT, especially in extrastriatal structures, such as the midbrain.

Involvement of alpha6/alpha3 neuronal nicotinic acetylcholine receptors in neuropsychiatric features of Dementia with Lewy bodies: [(125)I]-alpha-conotoxin MII binding in the thalamus and striatum.

Dementia with Lewy bodies (DLB) is a neurodegenerative disease associated with a range of neuropsychiatric symptoms and reduced expression of neuronal nicotinic acetylcholine receptors (nAChRs) in neocortex, hippocampus, thalamus and basal ganglia. To determine whether there are selective associations between alterations in alpha6/alpha3 neuronal nicotinic acetylcholine receptors (nAChRs) and the two key neuropsychiatric features of DLB, impaired consciousness (IC) and visual hallucinations (VH), quantitative [(125)I]-alpha-conotoxin MII ([(125)I]-alpha-Ctx MII) autoradiography was undertaken on 28 people with DLB and 15 control cases from the Newcastle Brain Bank. There was a highly significant overall trend for reduced thalamic [(125)I]-alpha-Ctx MII binding in DLB (p < 0.001), with significant deficits in the centromedian, ventral lateral and ventroposterior medial thalamic nuclei (p < 0.05), together with caudate and putamen (p < 0.001). [(125)I]-alpha-Ctx MII binding was significantly lower in DLB cases with IC than without IC in the putamen (p < 0.05), however there was no significant association between [(125)I]-alpha-Ctx MII binding and VH. Reductions in [(125)I]-alpha-Ctx MII binding in caudate and putamen were paralleled by similar reductions in [(125)I]PE2I binding. [(125)I]PE2I binding was also significantly lower in DLB cases with IC than without IC in the caudate (p < 0.05) and putamen (p < 0.001). These results demonstrate that deficits in alpha6/alpha3 nAChRs occur in specific brain regions in DLB, may in part be related to the loss of dopaminergic neurons and may contribute to the development of impaired consciousness in the disorder.

Serotoninergic neurotransmission is affected by n-3 polyunsaturated fatty acids in the rat.

We explored the effects of chronic alpha-linolenic acid dietary deficiency on serotoninergic neurotransmission. In vivo synaptic serotonin (5-HT) levels were studied in basal and pharmacologically stimulated conditions using intracerebral microdialysis in the hippocampus of awake 2-month-old rats. We also studied the effects of reversion of the deficient diet on fatty acid composition and serotoninergic neurotransmission. A balanced (control) diet was supplied to deficient rats at different stages of development, i.e. from birth, 7, 14 or 21 days of age. We demonstrated that chronic n-3 polyunsaturated fatty acid dietary deficiency induced changes in the synaptic levels of 5-HT both in basal conditions and after pharmacological stimulation with fenfluramine. Higher levels of basal 5-HT release and lower levels of 5-HT-stimulated release were found in deficient than in control rats. These neurochemical modifications were reversed by supply of the balanced diet provided at birth or during the first 2 weeks of life through the maternal milk, whereas they persisted if the balanced diet was given from weaning (at 3 weeks of age). This suggests that provision of essential fatty acids is durably able to affect brain function and that this is related to the developmental stage during which the deficiency occurs.

Synthesis and biological evaluation of halogenated naphthyridone carboxamides as potential ligands for in vivo imaging studies of substance P receptors.

With the aim of developing new radioligands for in vivo studies of substance P receptors using positron emission tomography or single photon emission computed tomography, 2- and 3-halo naphthyridone-6-carboxamide derivatives were synthesized. Their affinities toward the target receptors were evaluated on CHO cells and compared to the unsubstituted analogue EP 00652218 (IC(50) = 100 nM +/- 20). The IC(50) value was not altered in the case of 2-chloro compound 1 (IC(50) = 100 nM +/- 15) and only slightly reduced for the 2-fluoro and -iodo analogues 6 and 8 (IC(50) = 500 nM +/- 80). A drastic reduction in binding (IC(50) > 1000 nM) was observed for the halogenated compounds 2-5, 7, and 9.

Neither the density nor function of striatal dopamine transporters were influenced by chronic n-3 polyunsaturated fatty acid deficiency in rodents.

We hypothesized that the chronic dietary deficiency of n-3 polyunsaturated fatty acids (n-3 PUFAs) might affect the density and/or function of dopamine transporters (DAT), which have a major role in regulating the synaptic level of dopamine. This hypothesis was tested by investigating DAT in the striatum using three complementary methods in control and deficient rats. The density of DAT was determined by quantitative autoradiography using [(125)I]PE2I, a specific ligand of this transporter. Functional investigations were performed (i) in vitro by measuring [(3)H]dopamine uptake on synaptosomes, and (ii) in vivo using intracerebral microdialysis. The results demonstrated that neither the density nor the function of DAT were influenced by n-3 PUFA deficiency in the striatum. This suggests lower sensitivity to n-3 PUFA deficiency in the striatum than that previously observed in the frontal cortex.