Interaction of N1-unsubstituted and N1-benzenesulfonyltryptamines at h5-HT6 receptors

Despite possessing a common tryptaminergic scaffold, examination of 28 (i.e., 14 pairs of) compounds suggests that N1-unsubstituted and N1-benzenesulfonyltryptamines likely bind at h5-HT6 receptors in a dissimilar manner (r2=0.201). Additionally, an examination of two rotationally constrained N1-benzenesulfonyltryptamine analogs indicates that a non-coplanar relationship between the two aryl groups might be preferred for interaction with the receptors.     

Binding of isotryptamines and indenes at h5-HT6 serotonin receptors

To determine if the indolic nitrogen atom is required for the binding of N(1)-benzyltryptamines at h5-HT(6) serotonin receptors, several isotryptamines and indene analogs were examined. The affinity of 3-benzyl-N(1)-(N,N-dimethylaminoethyl)indole (5, K(i)=32nM) and 1-benzyl-3-(N,N-dimethylaminoethyl)indene (11, K(i)=3nM) indicates that the indolic nitrogen atom is not essential for binding.     

Binding of tryptamine analogs at h5-HT1E receptors: a structure-affinity investigation

Structure-affinity requirements for the binding of serotonin (5-HT) analogs at human 5-HT1E receptors were investigated by examining the affinities of >40 tryptamine-related compounds. No tryptamine analog was found to bind with substantially higher affinity than 5-HT. The results indicate that hydrogen bonding plays a key role in the 5-HT1E/receptor interaction. This finding was supported using quantitative structure-activity analysis (QSAR) techniques such as comparative molecular field analysis (CoMFA) and the program QsarIS.     

Binding of methoxy-substituted N1-benzenesulfonylindole analogs at human 5-HT6 serotonin receptors

Comparison of several amine-substituted and methoxy-substituted analogs of N1-(4-aminobenzene)sulfonylindole suggests that these substituents might contribute to the 5-HT6 serotonin receptor affinity of these agents via their electronic effect on the indolic nucleus. Their 1,2,3,4-tetrahydrocarbazole counterparts behave differently.     

Further studies on the binding of N1-substituted tryptamines at h5-HT6 receptors

N(1)-Arylsulfonyl-substituted analogs of N,N-dimethyltryptamine bind at 5-HT(6) receptors. Replacement of the aryl moiety with similarly hydrophobic alkyl substituents results in decreased affinity, as does replacement of a benzenesulfonyl moiety with a benzyl group. Current findings indicate that an aryl (or substituted aryl) sulfonyl (rather than alkylsulfonyl or benzyl) moiety is optimal for high-affinity binding, and further suggest that the N(1)-benzenesulfonyl- and their corresponding N(1)-benzyltryptamine counterparts bind in a different fashion.     

Binding of amine-substituted N1-benzenesulfonylindoles at human 5-HT6 serotonin receptors

An examination of several amine-substituted analogs of N(1)-benzenesulfonylindoles reveals that although they bind at human 5-HT(6) serotonin receptors with high affinity, they are likely to bind in a dissimilar manner.     

Epiminocyclohepta[b]indole analogs as 5-HT6 antagonists

A new series of epiminocyclohepta[b]indoles with potent 5-HT(6) antagonist activity were discovered and optimized using in vitro protocols. One compound from this series was progressed to advanced pharmacokinetic (PK) studies followed by 5-HT(6) receptor occupancy studies. The compound was found to have excellent oral absorption, a highly favorable PK profile and demonstrated pharmacodynamic interaction with the 5-HT(6) receptor as shown by ex vivo autoradiography.     

gamma-Carbolines: binding at 5-HT5A serotonin receptors

Screening of various agents resulted in the identification of 5-methyl-1,2,3,4-tetrahydro-gamma-carboline (1; K(i)=5,300 nM) as a compound with modest affinity for mouse 5-HT(5A) receptors. Structure-affinity studies were conducted resulting in 5-methyl-2-[3-(4-fluorophenoxy)propyl]-1,2,3,4-tetrahydro-gamma-carboline (17; K(i)=13 nM). Although 17 also binds at 5-HT(2) receptors, it serves as a novel lead for the further development of 5-HT(5A) ligands.     

Relative selectivity of some conformationally constrained tryptamine analogs at 5-HT1, 5-HT1A and 5-HT2 recognition sites

In an attempt to define pharmacophoric differences between 5-HT1, 5-HT1A and 5-HT2 recognition sites, a number of rigid analogs were studied and compared to analogous free chain tryptamines. Racemic partial ergolines RU 27849 and RU 28306 showed reduced potency at all 5-HT1 sites, but were at least equipotent to analogous tryptamines at the 5-HT2 site. A nonergoline-like constrained analog of tryptamine was similar in potency to RU 27849 at all 5-HT1 sites, but showed a 4-fold enhancement in potency over RU 27849 and tryptamine at the 5-HT2 site. At all 3 sites, 3-(tetrahydropyridyl) indoles (unless substituted at the indole 2-position) were the most potent rigid analogs studied and represent the most promising class for the development of selective compounds.     

Possible differences in modes of agonist and antagonist binding at human 5-HT6 receptors

A graphics model of the human 5-HT6 receptor was constructed and automated docking studies were performed. The model suggests that 5-HT6 antagonist arylsulfonyltryptamines might bind differently than that of the agonist serotonin. Furthermore, the model explains many of the empirical results from our previous structure-affinity studies.     

Evaluation of isotryptamine derivatives at 5-HT2 serotonin receptors

On the basis that meta-chlorophenylpiperazine (mCPP; 1) is a nonselective 5-HT_2C agonist, that benz-fused tryptamines (e.g., 5) display enhanced 5-HT₂ affinity, and that certain isotryptamines 3 reportedly bind with enhanced affinity and selectivity at 5-HT_2C receptors, we prepared and examined a series of isotryptamine-related analogues as potentially selective 5-HT_2C agonists. None of the compounds displayed selectivity for 5-HT_2C versus 5-HT_2A receptors. Detailed re-examination of a compound previously reported to display 100-fold 5-HT_2C selectivity [i.e., S(+)-5,6-difluoro-α-methylisotryptamine] revealed that its selectivity versus 5-HT_2A receptors was, at best, only 10-fold.     

(±)-Nantenine analogs as antagonists at human 5-HT2A receptors: C1 and flexible congeners

C1 and flexible analogs of (±)-nantenine were synthesized and evaluated for antagonist activity at human 5-HT_2A receptors in a calcium mobilization assay. This work has resulted in the identification of the most potent 5-HT_2A antagonist known based on an aporphine. Our results also suggest that the C1 position may be a key site for increasing 5-HT_2A antagonist activity in this compound series. In addition, the structural rigidity of the aporphine core appears to be required for nantenine to function as a 5-HT_2A antagonist.     

Binding of beta-carbolines at 5-HT(2) serotonin receptors

A series of ring-substituted (i.e., methoxy and bromo) 3,4-dihydro- and 1,2,3,4-tetrahydro-β-carbolines was examined at 5-HT_2A and 5-HT_2C serotonin receptors. Whereas most of the methoxy-substituted derivatives typically displayed affinities similar to their unsubstituted parents, certain (particularly 8-substituted) bromo derivatives displayed enhanced affinity. A binding profile was obtained for selected β-carbolines.     

Interaction of S-activated enkephalin analogs with opiate receptors

Enkephalin analogs containing a thiol activated by a thiomethyl (SCH3)*** or 3-nitro-2-pyridinesulfenyl (Npys) group were synthesized. Incubation of such S-activated enkephalin analogs as [D-Ala2, Leu(CH2S)SCH(3)5]enkephalin or [D-Ala2,Leu(CH2S)Npys5]enkephalin with guinea pig ileum (GPI) resulted in the continuous stimulation of the mu opiate receptors. This sustained GPI-activity was completely reversed with the antagonist naloxone, while subsequent washings elicited again the full enkephalin activity. When GPI showing full enkephalin activity was incubated with 1 mM dithiothreitol, about 70% of the activity was eliminated. Examination of enkephalin analogs containing Cys(Npys) at position 1, 5, or 6 suggested that no other thiols occur near the enkephalin binding site of the mu receptor. From these results, it is considered that only one thiol group exists near the binding site of the mu receptor in GPI. Similar results were also obtained for the mu receptors in mouse vas deferens.     

5—羟色胺受体的分子生物学

把含有编码5-羟色胺受体(5-HTR)的mRNA注入非洲爪蟾卵母细胞内,借助卵母细胞的翻译系统,把5-HTR“移植”到卵母细胞的细胞膜上,借此深入研究5-HTR的配体结合特性以及受体后的信息传递机制。5-HT_(IC)R、5-HT_(IA)R以及5-HT_2R的cDNA相继克隆化成功,确定了这三种5-HTR的一级结构,并对受体的配体结合点、G蛋白的作用部位以及5-HTR的分子构象进行了推测。     

5-HT receptors on identified Lymnaea neurones in culture. Pharmacological characterization of 5-HT1A receptors

The ability of the selective 5-HT_1A receptor agonist R(+)-8-hydroxydipropylaminotetralin hydrobromide (8-OH-DPAT) to bind with 5-HT receptor(s) on cultured, identified neurones in Lymnaea stagnalis was examined. The identified neurones studied were from the buccal ganglia and the serotonin-containing cerebral giant cells (CGCs). 5-HT and its agonists were applied from puffer pipettes, whilst 5-HT antagonists were applied in the bathing medium. At 10⁻³ M, the 5-HT_1A agonist, always produced paroxysmal depolarizing shifts (PDS) while at a lower concentration (10⁻⁴ M), it always mimicked the effects of 10⁻³ M 5-HT. 8-OH-DPAT (10⁻⁴ M) and 5-HT 10⁻³ M produced dose-dependent increases in the responses they evoked. At 10⁻⁴ M, the 5-HT₃ receptor agonist 1-(m-chlorophenyl)-biguanide hydrochloride (m-CPBG), failed to hyperpolarize most of the neurones hyperpolarized by 5-HT. At 10⁻⁴ M, the antagonists ketanserin (5-HT₂), MDL 72222 (5-HT₃), and pindobind-5-HT_1A (5-HT_1A) consistently abolished spike generation ii spontaneously active neurones. Both ketanserin and MDL 72222 failed to block the actions of 8-OH-DPAT and only partially blocked those of 5-HT, but pindobind-5-HT_1A completely, but reversibly,blocked the 8-OH-DPAT effects while greatly reducing those of 5-HT. These results suggest that 5-HT_1A receptor subtypes might be involved in the hyperpolarizing responses of the CGCs and their follower motor neurones in the buccal ganglia of Lymnaea stagnalis to 5-HT. The presence of 5-HT_1A receptors on these neurones can be considered to correspond with those found in mammals because their pharmacological responses resemble those of mammalian 5-HT_1A receptors.     

Hypothalamic 5-HT functional regulation through 5-HT1A and 5-HT2C receptors during pancreatic regeneration

5-HT receptors are predominantly located in the brain and are involved in pancreatic function and cell proliferation through sympathetic nervous system. The objective of this study was to investigate the role of hypothalamic 5-HT, 5-HT1A and 5-HT2C receptor binding and gene expression in rat model of pancreatic regeneration using 60% pancreatectomy. The pancreatic regeneration was evaluated by 5-HT content, 5-HT1A and 5-HT2C receptor gene expression in the hypothalamus of sham operated, 72 h and 7 days pancreatectomised rats. 5-HT content was quantified by HPLC. 5-HT1A receptor assay was done by using specific agonist [3H]8-OH DPAT. 5-HT2C receptor assay was done by using specific antagonist [3H]mesulergine. The expression of 5-HT1A and 5-HT2C receptor gene was analyzed by RT-PCR. 5-HT content was higher in the hypothalamus of 72 h pancreatectomised rats. 5-HT1A and 5-HT2C receptors were down-regulated in the hypothalamus. RT-PCR analysis revealed decreased 5-HT1A and 5-HT2C receptor mRNA expression. The 5-HT1A and 5-HT2C receptors gene expression in the 7 days pancreatectomised rats reversed to near sham level. This study is the first to identify 5-HT1A and 5-HT2C receptor gene expression in the hypothalamus during pancreatic regeneration in rats. Our results suggest the hypothalamic serotonergic receptor functional regulation during pancreatic regeneration.     

Functional characterization of the novel antipsychotic iloperidone at human D2, D3, alpha 2C, 5-HT6, and 5-HT1A receptors

Iloperidone has demonstrated an interesting monoamine receptor profile in radioligand binding studies, with nanomolar affinity for certain noradrenaline, dopamine, and serotonin receptors. In this study, the agonist/antagonist activity of iloperidone was determined in cell lines expressing recombinant human D(2A), D(3), alpha(2C), 5-HT(1A), or 5-HT(6) receptors. With the exception of 5-HT(6) receptors, these receptors are negatively coupled to cyclase. Thus, after stimulation with forskolin, the agonists dopamine (at D(2A) and D(3)), noradrenaline (at alpha(2C)), or 8-OH-DPAT (at 5-HT(1A)) induced a reduction in cAMP accumulation. Conversely, activation of the 5-HT(6) receptor by 5-HT led to an increase in cAMP accumulation. Iloperidone alone was devoid of significant agonist activity but inhibited the agonist response in all 5 cell lines in a surmountable and concentration-dependent fashion. Iloperidone was most potent at D(3) receptors (pK(B) 8.59 +/- 0.20; n = 6), followed by alpha(2C) (pK(B) 7.83 +/- 0.06; n = 15), 5-HT(1A) (pK(B) 7.69 +/- 0.18; n = 10), D(2A) (pK(B) 7.53 +/- 0.04; n = 11) and 5-HT(6) (pK(B) 7.11 +/- 0.08; n = 11) receptors.     

Mechanisms of agonism and inverse agonism at serotonin 5-HT1A receptors

Mechanisms of agonist and inverse agonist action at the serotonin 5-HT1A receptor have been studied using the modulation of guanosine 5'-O-(3-[35S]thiotriphosphate) ([35S]GTPgammaS) binding in membranes of Chinese hamster ovary (CHO) cells expressing the receptor (CHO-5-HTA1A cells). A range of agonists increased [35S]GTPgammaS binding with different potencies and to different maximal extents, whereas two compounds, methiothepin and spiperone, inhibited both agonist-stimulated and basal [5S]GTPgammaS binding, thus exhibiting inverse agonism. Potencies of agonists to stimulate [35S]GTPgammaS binding in membranes from CHO-5-HT1A cells were reduced by adding increasing concentrations of GDP to assays, whereas changes in sodium ion concentration did not affect agonist potency. The maximal effect of the agonists was increased by increasing sodium ion concentrations. The affinities of agonists in ligand binding assays were unaffected by changes in sodium ion concentration. Increasing GDP in the assays of the inverse agonists increased potency for spiperone to inhibit [35S]GTPgammaS binding and had no effect for methiothepin, in agreement with the sensitivity of these compounds to guanine nucleotides in ligand binding assays. Potencies for these inverse agonists were unaffected by changes in sodium ion concentration. These data were simulated using the extended ternary complex model. These simulations showed that the data obtained with agonists were consistent with these compounds achieving agonism by stabilising the ternary complex. For inverse agonists, the simulations showed that the mechanism for spiperone may be to stabilise forms of the receptor uncoupled from G proteins. Methiothepin, however, probably does not alter the equilibrium distribution of different receptor species; rather, this inverse agonist may stabilise an inactive form of the receptor that can still couple to G protein.     

5-hydroxytryptamine is a fast excitatory transmitter at 5-HT3 receptors in rat amygdala.

A fast excitatory synaptic potential mediated by 5-hydroxytryptamine (5-HT) was recorded in rat lateral amygdala neurons in brain slices. The synaptic potential has brief duration (tens of milliseconds), is mimicked by 5-HT, is potentiated by a 5-HT uptake inhibitor, and is blocked by selective 5-HT3 receptor antagonists. The underlying synaptic current reversed polarity at about 0 mV. This is an example of fast neurotransmission in the mammalian brain mediated by an amine rather than an amino acid. The antiemetic, anxiolytic, and perhaps antipsychotic actions of 5-HT3 antagonists might result from blockade of such synapses.