Magic mushroom extracts in lipid membranes

The active hallucinogen of magic mushrooms, psilocin, is being repurposed to treat nicotine addiction and treatment-resistant depression. Psilocin belongs to the tryptamine class of psychedelic compounds which include the hormone serotonin. It is believed that psilocin exerts its effect by binding to the serotonin 5-HT_2A receptor. However, recent in-vivo evidence suggests that psilocin may employ a different mechanism to exert its effects. Membrane-mediated receptor desensitization of neurotransmitter receptors is one such mechanism. We compare the impact of the neutral and charged versions of psilocin and serotonin on the properties of zwitterionic and anionic lipid membranes using molecular dynamics simulations and calorimetry. Both compounds partition to the lipid interface and induce membrane thinning. The tertiary amine in psilocin, as opposed to the primary amine in serotonin, limits psilocin's impact on the membrane although more psilocin partitions into the membrane than serotonin. Calorimetry corroborates that both compounds induce a classical melting point depression like anesthetics do. Our results also lend support to a membrane-mediated receptor-binding mechanism for both psilocin and serotonin and provide physical insights into subtle chemical changes that can alter the membrane-binding of psychedelic compounds.     

Structure and activity of membrane receptors: Modeling and computational simulation of ligand recognition in a three-dimensional model of the 5-hydroxytryptamine1A receptor

A three-dimensional molecular model of the transmembrane domain of the 5-HT_1A receptor (5-HT_1AR) is presented in the context of a general strategy for modeling the macromolecular structure of a guanine nucleotide binding, regulatory protein coupled receptor (GPCR). The model of the 5-HT_1AR rests on the definition of the putative residues of the ligand-binding site guided by criteria based on specific models proposed from structure-activity studies and on published results of modifications of GPCRs using methods of molecular biology. The resulting requirements for matching recognition sites in the agonist-binding pocket define the molecular details of the interaction between the agonist 5-HT and the human 5-HT_1AR that includes: (1) the interaction between the protonated amine moiety and the conserved negative Asp-116, located in TMH 3; (2) the hydrogen bond between the hydroxyl group and Thr-199, located in TMH 5; and (3) the interaction complex between the aromatic ring portion of the ligand and the neutral form of His-192, located in TMH 5. Results from quantum mechanical calculations of the interaction between an agonist and the proposed recognition pocket of the 5-HT_1AR model suggest a trigger of the receptor activation mechanism resulting from ligand binding. The antagonist-binding pocket of the human 5-HT_1AR is inferred from the interaction sites of pindolol with the receptor model: (1) the ionic interaction between the protonated amine of the ligand and the side chain of the conserved Asp-116, located in TMH 3; and (2) the hydrogen bonds between the ether oxygen and the hydroxyl group of the ligand and Asn-385, located in TMH 7. Use of the model is proposed to facilitate the identification of the structural elements of agonists and antagonists that are key for their specific functions, in order to achieve the design of new compounds with predetermined pharmacological properties.     

Synthesis, structure–affinity relationships, and modeling of AMDA analogs at 5-HT2A and H1 receptors: Structural factors contributing to selectivity

Histamine H₁ and serotonin 5-HT_2A receptors present in the CNS have been implicated in various neuropsychiatric disorders. 9-Aminomethyl-9,10-dihydroanthracene (AMDA), a conformationally constrained diarylalkyl amine derivative, has affinity for both of these receptors. A structure–affinity relationship (SAFIR) study was carried out studying the effects of N-methylation, varying the linker chain length and constraint of the aromatic rings on the binding affinities of the compounds with the 5-HT_2A and H₁ receptors. Homology modeling of the 5-HT_2A and H₁ receptors suggests that AMDA and its analogs, the parent of which is a 5-HT_2A antagonist, can bind in a fashion analogous to that of classical H₁ antagonists whose ring systems are oriented toward the fifth and sixth transmembrane helices. The modeled orientation of the ligands are consistent with the reported site-directed mutagenesis data for 5-HT_2A and H₁ receptors and provide a potential explanation for the selectivity of ligands acting at both receptors.     

Synthesis of novel 5-substituted-2-aminotetralin analogs: 5-HT1A and 5-HT7 G protein-coupled receptor affinity, 3D-QSAR and molecular modeling

The serotonin 5-HT₇ G protein-coupled receptor (GPCR) is a proposed pharmacotherapeutic target for a variety of central and peripheral indications, albeit, there are no approved drugs selective for binding 5-HT₇. We previously reported that a lead analog based on the 5-substituted-N,N-disubstituted-1,2,3,4-tetrahydronaphthalen-2-amine (5-substituted-2-aminotetralin, 5-SAT) scaffold binds with high affinity at the 5-HT₇ GPCR, and can treat symptoms of autism in mouse models; subsequently, the lead was found to have high affinity at the 5-HT_1A GPCR. Herein, we report the synthesis of novel 5-SAT analogs to develop a 3-dimensional quantitative structure—affinity relationship (3D-QSAR) at the human 5-HT₇ receptor for comparison with similar studies at the highly homologous 5-HT_1A receptor. We report 35 new 5-SAT ligands, some with very high affinity (K_i ≤ 1 nM) and stereoselectivity at 5-HT₇ + or 5-HT_1A receptors, several with modest selectivity (up to 12-fold) for binding at 5-HT₇, and, several ligands with high selectivity (up to 40-fold) at the 5-HT_1A receptor. 3D-QSAR results indicate that steric extensions at the C(5)-position improve selectivity for the 5-HT₇ over 5-HT_1A receptor, while steric and hydrophobic extensions at the chiral C(2)-amino position impart 5-HT_1A selectivity. In silico receptor homology modeling studies, supplemented with molecular dynamics simulations and binding free energy calculations, were used to rationalize experimentally-determined receptor selectivity and stereoselective affinity results. The data from these studies indicate that the 5-SAT chemotype, previously shown to be safe and efficacious in rodent paradigms of neurodevelopmental and neuropsychiatric disorders, is amenable to structural modification to optimize affinity at serotonin 5-HT₇ vs. 5-HT_1A GPCRs, as may be required for successful clinical translation.     

Structural manipulation of aporphines via C10 nitrogenation leads to the identification of new 5-HT7AR ligands

Aporphine alkaloids containing a C10 nitrogen motif were synthesized and evaluated for affinity at 5-HT_1AR, 5-HT_2AR, 5-HT₆R and 5-HT_7AR. Three series of racemic aporphines were investigated: 1,2,10-trisubstituted, C10 N-monosubstituted and compounds containing a C10 benzofused aminothiazole moiety. The 1,2,10-trisubstituted series of compounds as a group displayed modest selectivity for 5-HT_7AR and also had moderate 5-HT_7AR affinity. Compounds from the C10 N-monosubstituted series generally lacked affinity for 5-HT_2AR and 5-HT₆R and showed strong affinity for 5-HT_1A or 5-HT_7AR. Compounds in this series that contained an N6-methyl group were up to 27-fold selective for 5-HT_7AR over 5-HT_1AR, whereas compounds with an N6-propyl substituent showed a reversal in this selectivity. The C10 benzofused aminothiazole analogues showed a similar binding profile as the C10 N-monosubstituted series i.e. strong affinity for 5-HT_1AR or 5-HT_7AR, with selectivity between the two receptors being similarly influenced by N6-methyl or N6-propyl substituents. Compounds 29 and 34a exhibit high 5-HT_7AR affinity, excellent selectivity versus dopamine receptors and function as antagonists in 5-HT_7AR cAMP-based assays. Compounds 29 and 34a have been identified as new lead molecules for further tool and pharmaceutical optimization.     

Molecular basis for cis-urocanic acid as a 5-HT2A receptor agonist

The underlying mechanisms of urocanic acid (UA) to induce immune suppression remain elusive until the recent finding that cis-UA acts via the serotonin, 5-hydroxytryptamine (5-HT) receptor subtype 5-HT_2A. In the present study, the interactions of cis-UA to 5-HT_2A receptor were explored and compared with those of 5-HT to the same receptor using computational docking. Similar binding modes were observed for cis-UA and 5-HT with 5-HT_2A receptor and the former possessed relatively higher binding affinity, which may account for cis-UA being a serotonin receptor agonist. Moreover, the molecular basis for the distinct binding affinities between the trans- and cis-UA with 5-HT_2A receptor was also provided.     

Discovery of DSP-1053, a novel benzylpiperidine derivative with potent serotonin transporter inhibitory activity and partial 5-HT1A receptor agonistic activity

We have previously shown that SMP-304, a serotonin uptake inhibitor with weak 5-HT_1A partial agonistic activity, may act under high serotonin levels as a 5-HT_1A antagonist that improves the onset of paroxetine in the rat swimming test. However, SMP-304 is mostly metabolized by CYP2D6, indicating limited efficacy among individuals and increased side effects. To reduce CYP2D6 metabolic contribution and enhance SERT/5-HT_1A binding affinity, we carried out a series of substitutions at the bromine atom in the left part of the benzene ring of SMP-304 and replaced the right part of SMP-304 with a chroman-4-one. This optimization work led to the identification of the antidepressant candidate DSP-1053 as a potent SERT inhibitor with partial 5-HT_1A receptor agonistic activity. DSP-1053 showed low CYP2D6 metabolic contribution and a robust increase in serotonin levels in the rat frontal cortex.     

Binding thermodynamics of serotonin to rat-brain 5-HT1a, 5HT2a and 5-HT3 receptors

The thermodynamic parameters ΔG° , ΔH° and Δs° of the binding equilibrium of serotonin to 5-HT_1A, 5-HT_2A and 5-HT₃ rat-brain membrane receptors have been determined by means of affinity constant measurements at six temperatures in the range 0 –35 ° C and van't Hoff plots. At variance with 5-HT_1A and 5-HT₃, the binding at the 5-HT_2A receptors is strongly endothermic and entropy-driven. Comparison with the results obtained by other authors on 5-HT_2A receptors in rats and humans suggests that the observed differences can be explained by a single amino acid difference in the receptor sequence between these two species.     

Prefrontal Serotonergic Denervation Induces Increase in the Density of 5-HT<Subscript>2A</Subscript> Receptors in Adult Rat Prefrontal Cortex

The 5-HTergic system and particularly 5-HT_2A receptors have been involved in prefrontal cognitive functions, but the underlying mechanisms by which the serotonin (5-HT) system modulates these processes are still unclear. In this work, the effects of prefrontal 5-HTergic denervation on the density and expression levels of 5-HT_2A receptors were evaluated by immunohistochemical and molecular biology studies in the prefrontal cortex (PFC). The [³H]-Ketanserin binding study revealed an increase in the B_max, along with no change in the binding affinity (K_D) for 5-HT_2A receptors. The increase in PFC of 5-HT_2A receptor density in response to denervation was accompanied by increase in 5-HT_2A receptor mRNA and protein levels. This increase in the number of 5-HT_2A receptors may be interpreted as an adaptive plastic change, i.e., hypersensitivity; resulting from the selective pharmacological lesion of the raphe-proceeding 5-HTergic fibers to the PFC. Based on previous evidence, this could be strongly related to the abnormal expression of short-term memory.     

Synthesis and evaluation of a series of 2-substituted-5-thiopropylpiperazine (piperidine)-1,3,4-oxadiazoles derivatives as atypical antipsychotics

Background

It is important to develop novel antipsychotics that can effectively treat schizophrenia with minor side-effects. The aim of our work is to develop novel antipsychotics that act on dopamine D₂ and D₃, serotonin 5-HT_1A and 5-HT_2A receptors with low affinity for the serotonin 5-HT_2C and H₁ receptors, which can effectively cure positive symptoms, negative symptoms and cognitive impairment without the weight gain side-effect.

Methodology/Principal Findings

A series of 2-substituted-5-thiopropylpiperazine (piperidine) -1,3,4-oxadiazoles derivatives have been synthesized and the target compounds were evaluated for binding affinities to D₂, 5-HT_1A and 5-HT_2A receptors. Preliminary results indicated that compounds 14, 16 and 22 exhibited high affinities to D₂, 5-HT_1A and 5-HT_2A receptors among these compounds. Further binding tests showed that compound 22 had high affinity for D₃ receptor, and low affinity for serotonin 5-HT_2C and H₁ receptors. In addition, compound 22 inhibited apomorphine-induced climbing behavior and MK-801-induced hyperactivity with no extrapyramidal symptoms liability in mice. Moreover, compound 22 exhibited acceptable pharmacokinetic properties.

Conclusions/Significance

Compound 22 showed an atypical antipsychotic activity without liability for extrapyramidal symptoms. We anticipate compound 22 to be useful for developing a novel class of drug for the treatment of schizophrenia.     

Design,synthesis and molecular modelling of new bulky Fananserin derivatives with altered pharmacological profile as potential antidepressants

It is now known that many neurotransmitter systems are responsible for diseases of the central nervous system (CNS). One of the most common CNS disease is depression. Considering that in the treatment and the genesis of depression, the most important are the serotonin receptors from 5-HT_1A, 5-HT_2A, 5-HT₆ and 5-HT₇ groups, and dopamine D₂R this article describes searching for group of new ligands for mentioned receptors. In the searching for potentially useful compound, we decided to start from the structure of well-known Fananserin. We tried to developed new derivatives, with changed profile of activity compared to Fananserin. Literature analysis and virtual screening emerged group of halogenated long-chain arylpiperazines derivatives of 1,8 naphthosultam/lactam with hexyl carbon chain to synthesis. The compounds obtaining method was developed with a microwave assisted synthesis. Reactions were carried out in acetonitrile, water or in solvent-free conditions. The obtained compounds were tested for their affinity for the serotonin receptors mentioned above. The work managed to obtain compounds acting on selected serotonin receptors, including multifunctional 5-HT_1A/5-HT₇/D₂ ligand 5k, dual 5-HT_1A/D₂ ligand 5j and selective 5-HT_1A ligands 5r and 5c. The SAR analysis showed a visible dependence of affinity for the 5-HT₆ receptors from structure of ligands. This relationship was discussed using molecular docking methods. A conformal analysis was also performed for selected ligands and the Fukui indexes were calculated using the DFT (B3LYP/6-311+G (d,p) level of theory) methods. The conducted research and analysis using molecular docking methods allows for selecting further pathways of structural modifications in the design of new ligands for serotonin receptors belonging to the group mentioned. What is more, conducted research show the potential using of Fukui indices to predict the biological activity of new molecules.     

Molecular modeling study of 4-phenylpiperazine and 4-phenyl-1,2,3,6-tetrahydropyridine derivatives: A new step towards the design of high-affinity 5-HT1A ligands

The main feature of many drugs having a 5-HT_1A affinity is the presence of an arylpiperazine moiety. Indeed, the protonated nitrogen and the aromatic ring of the arylpiperazine compounds are considered crucial for the interaction with the receptor. However, the replacement of the piperazine moiety by a 1,2,3,6-tetrahydropyridine ring in 4-arylpiperazine-ethyl carboxamide derivatives was recently shown to be highly favourable for 5-HT_1A affinity. In order to better understand the favourable effect of this chemical modification, we performed a conformational analysis of these compounds mainly based on the position of the phenyl ring relative to the piperazine and tetrahydropyridine moiety. In the piperazine compounds, the phenyl ring preferentially adopts a perpendicular orientation, whereas an almost planar orientation seems to be the most favourable conformation for the tetrahydropyridine compounds. Therefore, this conformational difference appears as a key for a better interaction with the receptor binding site. This result will serve for the designing high-affinity 5-HT_1A ligands.     

The 5-HT1A receptor: an overview of recent advances

Progress in the field of neuronal receptor research has accelerated during the last few years due to developments in pharmacology and molecular biology. This is particularly true in the case of the serotonin 5-HT_1A receptor. In 1983 the very selective, high affinity 5-HT_1A agonist 8-OH-DPAT was developed which allowed the pharmacology and distribution of the 5-HT_1A receptor in the central nervous system of the rat and man to be extensively characterized. By 1987, the gene encoding this receptor protein was cloned and sequenced, allowing not only elucidation of its structure, but also better insight into the nature of its coupling to transmembrane signal transduction systems. Thus in a short period of time considerable knowledge has accumulated on how serotonin exerts its functions in the central nervous system via the 5-HT_1A receptor. In the present review we will briefly discuss some of the latest developments regarding the 5-HT_1A receptor.     

Delineating the Site of Interaction of the 5-HT3A Receptor with the Chaperone Protein RIC-3

The serotonin type 3A (5-HT_3A) receptor is a homopentameric cation-selective member of the pentameric ligand-gated ion channel (pLGIC) superfamily. Members of this superfamily assemble from five subunits, each of which consists of three domains: extracellular (ECD), transmembrane (TMD), and intracellular domain (ICD). Previously, we have demonstrated that the 5-HT_3A-ICD is required for the interaction between 5-HT_3A and the chaperone protein resistance to inhibitors of choline esterase (RIC-3). Additionally, we have shown that 5-HT_3A-ICD fused to maltose-binding protein (MBP) directly interacts with RIC-3, without the involvement of other protein(s). To elucidate the molecular determinants of this interaction, we developed different MBP-fused 5-HT_3A-ICD constructs by deleting large segments of its amino acid sequence. We expressed seven engineered ICDs in Escherichia coli and purified them to homogeneity. Using a RIC-3 affinity pull-down assay, the interaction between MBP-5HT_3A-ICD constructs and RIC-3 was investigated. In summary, we identify a 24-amino-acid-long segment of the 5-HT_3A-ICD as a molecular determinant for the interaction between the 5-HT_3A-ICD and RIC-3.     

Synthesis and computer-aided analysis of the role of linker for novel ligands of the 5-HT6 serotonin receptor among substituted 1,3,5-triazinylpiperazines

A series of 2-amino-4-(4-methylpiperazin-1-yl)-1,3,5-triazines was designed based on previously published 2-amino-4-benzyl-(4-methylpiperazin-1-yl)-1,3,5-triazines in order to evaluate the role of a linker between the triazine moiety and an aromatic substituent for the human serotonin 5-HT₆ receptor affinity. As new linkers two carbon atoms (ethyl or ethenyl) or an oxyalkyl chain (methoxy, 2-ethoxy, 2-propoxy) were introduced. Affinities of the compounds for the 5-HT₆R as the main target, and for the 5-HT_1AR, 5-HT₇R and D₂R as competitive ones, were determined in the radioligand binding assays. Docking to the 5-HT₆R homology model was performed to support SAR analysis. Results showed that the branching of the methoxyl linker increased affinity for the human 5-HT₆R whereas an unsaturated bond within the linker dramatically reduced desirable activity. Both experimental and theoretical studies confirmed the previously postulated beneficial role of the aromatic size for interaction with the 5-HT₆R. Thus, the largest naphthyl moiety yielded the highest activity. In particular, 4-(4-methylpiperazin-1-yl)-6-(1-(naphthalen-1-yloxy)ethyl)-1,3,5-triazin-2-amine (24), the most potent 5-HT₆R agent found (K_i = 23 nM), can be a new lead structure for further search and development.     

New dual ligands for the D2 and 5-HT1A receptors from the group of 1,8-naphthyl derivatives of LCAP

More than 300 million people are suffering from depression, one of the civilization diseases in the 21st century. Serotonin 5-HT_1AR and dopamine D₂R play an important role in the treatment and pathogenesis of depression. Moreover, in recent years, the efficacy of dual 5-HT_1A/D₂ receptors ligands has been demonstrated in the fight against depression. In this work the new bulky arylpiperazine derivatives (LCAP) were synthesized in microwave radiation field. The affinities for the selected serotonin (5-HT_1A,5-HT_2A,5-HT₆,5-HT₇) and dopamine (D₂) receptors have been evaluated in vitro. Compounds 5.3a, 5.4, 5.1c, 5.3d, 5.2a are promising dual 5-HT_1AR/D₂R ligands. The SAR analysis were additionally supported with molecular docking studies.     

9-Aminomethyl-9,10-dihydroanthracene (AMDA) analogs as structural probes for steric tolerance in 5-HT2A and H1 receptor binding sites

Synthesis, radioligand binding and molecular modeling studies of several 9-aminomethyl-9,10-dihydroanthracene (AMDA) analogs were carried out to determine the extent of the steric tolerance associated with expansion of the tricyclic ring system and amine substitution at 5-HT_2A and H₁ receptors. A mixture of (7,12-dihydrotetraphene-12-yl)methanamine and (6,11-dihydrotetracene-11-yl)methanamine in a 75–25% ratio was found to have an apparent K_i of 10 nM at the 5-HT_2A receptor. A substantial binding affinity for (7,12-dihydrotetraphene-3-methoxy-12-yl)methanamine at the 5-HT_2A receptor (K_i = 21 nM) was also observed. Interestingly, this compound was found to have 100-fold selectivity for 5-HT_2A over the H₁ receptor (K_i = 2500 nM). N-Phenylalkyl-AMDA derivatives, in which the length of the alkyl chain varied from methylene to n-butylene, were found to have only weak affinity for both 5-HT_2A and H₁ receptors (K_i = 223 to 964 nM). Our results show that large rigid annulated AMDA analogs can be sterically accommodated within the proposed 5-HT_2A binding site.