Behavioral Study of 3- and 5-Halocytisine Derivatives in Zebrafish Using the Novel Tank Diving Test (NTT).

Anxiety is a serious mental disorder, and recent statistics have determined that 35.12% of the global population had an anxiety disorder during the COVID-19 pandemic. A mechanism associated with anxiolytic effects is related to nicotinic acetylcholine receptor (nAChR) agonists, principally acting on the α4ß2 nAChR subtype. nAChRs are present in different animal models, including murine and teleosteos ones. Zebrafish has become an ideal animal model due to its high human genetic similarities (70%), giving it high versatility in different areas of study, among them in behavioral studies related to anxiety. The novel tank diving test (NTT) is one of the many paradigms used for studies on new drugs related to their anxiolytic effect. In this work, an adult zebrafish was used to determine the behavioral effects of 3- and 5-halocytisine derivatives, using the NTT at different doses. Our results show that substitution at position 3 by chlorine or bromine decreases the time spent by the fish at the bottom compared to the control. However, the 3-chloro derivative at higher doses increases the bottom dwelling time. In contrast, substitution at the 5 position increases bottom dwelling at all concentrations showing no anxiolytic effects in this model. Unexpected results were observed with the 5-chlorocytisine derivative, which at a concentration of 10 mg/L produced a significant decrease in bottom dwelling and showed high times of freezing. In conclusion, the 3-chloro and 3-bromo derivatives show an anxiolytic effect, the 3-chlorocytisine derivative being more potent than the 3-bromo derivative, with the lowest time at the bottom of the tank at 1mg/L. On the other hand, chlorine, and bromine at position 5 produce an opposite effect.

Pharmacological Characterization of 4-Methylthioamphetamine Derivatives.

Amphetamine derivatives have been used in a wide variety of pathologies because of their pharmacological properties as psychostimulants, entactogens, anorectics, and antidepressants. However, adverse cardiovascular effects (sympathomimetics) and substance abuse problems (psychotropic and hallucinogenic effects) have limited their use. 4-Methylthioamphetamine (MTA) is an amphetamine derivative that has shown to inhibit monoamine uptake and monoamine oxidase. However, the pharmacological characterization (neurochemical, behavioral, and safety) of its derivatives 4-ethylthioamphetamine (ETA) and 4-methylthio-phenil-2-butanamine (MT-But) have not been studied. In the current experiments, we show that ETA and MT-But do not increase locomotor activity and conditioned place preference with respect to MTA. At the neurochemical level, ETA and MT-But do not increase in vivo DA release in striatum, but ETA and MT-But affect the nucleus accumbens bioaccumulation of DA and DOPAC. Regarding cardiovascular effects, the administration of MTA and ETA increased the mean arterial pressure and only ETA significantly increases the heart rate. Our results show that the pharmacological and safety profiles of MTA are modulated by changing the methyl-thio group or the methyl group of the aminoethyl chain.

Nicotinic Antagonist UFR2709 Inhibits Nicotine Reward and Decreases Anxiety in Zebrafish.

Zebrafish is becoming a popular animal model in neuropharmacology and drug discovery, mainly due to its ease of handling and low costs involved in maintenance and experimental work. This animal displays a series of complex behaviours that makes it useful for assessing the effects of psychoactive drugs. Here, adult zebrafish were used for assessment of the anxiolytic and anti-addictive properties of UFR2709, a nicotinic receptor (nAChR) antagonist, using two behavioural paradigms to test for addiction, the novel tank diving test to assess anxiety and the conditioned place preference (CPP). Furthermore, the expression of nAChR subunits α4 and α7 was measured in the zebrafish brain. The results show that UFR2709 exhibits an anxiolytic effect on zebrafish and blocks the effect evoked by nicotine on CPP. Moreover, UFR2709 significantly decreased the expression of α4 nicotinic receptor subunit. This indicates that UFR2709 might be a useful drug for the treatment of nicotine addiction.

Synthesis, Docking, 3-D-Qsar, and Biological Assays of Novel Indole Derivatives Targeting Serotonin Transporter, Dopamine D2 Receptor, and Mao-A Enzyme: In the Pursuit for Potential Multitarget Directed Ligands.

A series of 27 compounds of general structure 2,3-dihydro-benzo[1,4]oxazin-4-yl)-2-{4-[3-(1H-3indolyl)-propyl]-1-piperazinyl}-ethanamides, Series I: 7(a-o) and (2-{4-[3-(1H-3-indolyl)-propyl]-1-piperazinyl}-acetylamine)-N-(2-morfolin-4-yl-ethyl)-fluorinated benzamides Series II: 13(a-l) were synthesized and evaluated as novel multitarget ligands towards dopamine D2 receptor, serotonin transporter (SERT), and monoamine oxidase-A (MAO-A) directed to the management of major depressive disorder (MDD). All the assayed compounds showed affinity for SERT in the nanomolar range, with five of them displaying Ki values from 5 to 10 nM. Compounds 7k, Ki = 5.63 ± 0.82 nM, and 13c, Ki = 6.85 ± 0.19 nM, showed the highest potencies. The affinities for D2 ranged from micro to nanomolar, while MAO-A inhibition was more discrete. Nevertheless, compounds 7m and 7n showed affinities for the D2 receptor in the nanomolar range (7n: Ki = 307 ± 6 nM and 7m: Ki = 593 ± 62 nM). Compound 7n was the only derivative displaying comparable affinities for SERT and D2 receptor (D2/SERT ratio = 3.6) and could be considered as a multitarget lead for further optimization. In addition, docking studies aimed to rationalize the molecular interactions and binding modes of the designed compounds in the most relevant protein targets were carried out. Furthermore, in order to obtain information on the structure-activity relationship of the synthesized series, a 3-D-QSAR CoMFA and CoMSIA study was conducted and validated internally and externally (q2 = 0.625, 0.523 for CoMFA and CoMSIA and r2ncv = 0.967, 0.959 for CoMFA and CoMSIA, respectively).

Minimal Structural Changes Determine Full and Partial Nicotinic Receptor Agonist Activity for Nicotine Analogues.

Neuronal α4ß2 nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels (LGIC) that have been implicated in nicotine addiction, reward, cognition, pain disorders, anxiety, and depression. Nicotine has been widely used as a template for the synthesis of ligands that prefer α4ß2 nAChRs subtypes. The most important therapeutic use for α4ß2 nAChRs is as replacement therapy for smoking cessation and withdrawal and the most successful therapeutic ligands are partial agonists. In this case, we use the N-methylpyrrolidine moiety of nicotine to design and synthesize new α4ß2 nicotinic derivatives, coupling the pyrrolidine moiety to an aromatic group by introducing an ether-bonded functionality. Meta-substituted phenolic derivatives were used for these goals. Radioligand binding assays were performed on clonal cell lines of hα4ß2 nAChR and two electrode voltage-clamp experiments were used for functional assays. Molecular docking was performed in the open state of the nAChR in order to rationalize the agonist activity shown by our compounds.

Synthesis of Novel Nicotinic Ligands with Multimodal Action: Targeting Acetylcholine α4ß2, Dopamine and Serotonin Transporters.

Nicotinic acetylcholine receptors (nAChRs), serotonin transporters (SERT) and dopamine transporters (DAT) represent targets for the development of novel nicotinic derivatives acting as multiligands associated with different health conditions, such as depressive, anxiety and addiction disorders. In the present work, a series of functionalized esters structurally related to acetylcholine and nicotine were synthesized and pharmacologically assayed with respect to these targets. The synthesized compounds were studied in radioligand binding assays at α4ß2 nAChR, h-SERT and h-DAT. SERT experiments showed not radioligand [3H]-paroxetine displacement, but rather an increase in the radioligand binding percentage at the central binding site was observed. Compound 20 showed Ki values of 1.008 ± 0.230 µM for h-DAT and 0.031 ± 0.006 µM for α4ß2 nAChR, and [3H]-paroxetine binding of 191.50% in h-SERT displacement studies, being the only compound displaying triple affinity. Compound 21 displayed Ki values of 0.113 ± 0.037 µM for α4ß2 nAChR and 0.075 ± 0.009 µM for h-DAT acting as a dual ligand. Molecular docking studies on homology models of α4ß2 nAChR, h-DAT and h-SERT suggested potential interactions among the compounds and agonist binding site at the α4/ß2 subunit interfaces of α4ß2 nAChR, central binding site of h-DAT and allosteric modulator effect in h-SERT.

Role of the Cys Loop and Transmembrane Domain in the Allosteric Modulation of α4ß2 Nicotinic Acetylcholine Receptors.

Allosteric modulators of pentameric ligand-gated ion channels are thought to act on elements of the pathways that couple agonist binding to channel gating. Using α4ß2 nicotinic acetylcholine receptors and the α4ß2-selective positive modulators 17ß-estradiol (ßEST) and desformylflustrabromine (dFBr), we have identified pathways that link the binding sites for these modulators to the Cys loop, a region that is critical for channel gating in all pentameric ligand-gated ion channels. Previous studies have shown that the binding site for potentiating ßEST is in the C-terminal (post-M4) region of the α4 subunit. Here, using homology modeling in combination with mutagenesis and electrophysiology, we identified the binding site for potentiating dFBr on the top half of a cavity between the third (M3) and fourth transmembrane (M4) α-helices of the α4 subunit. We found that the binding sites for ßEST and dFBr communicate with the Cys loop, through interactions between the last residue of post-M4 and Phe170 of the conserved FPF sequence of the Cys loop, and that these interactions affect potentiating efficacy. In addition, interactions between a residue in M3 (Tyr309) and Phe167, a residue adjacent to the Cys loop FPF motif, also affect dFBr potentiating efficacy. Thus, the Cys loop acts as a key control element in the allosteric transduction pathway for potentiating ßEST and dFBr. Overall, we propose that positive allosteric modulators that bind the M3-M4 cavity or post-M4 region increase the efficacy of channel gating through interactions with the Cys loop.

Synthesis and biological evaluation of potential acetylcholinesterase inhibitors based on a benzoxazine core.

With the purpose of expanding the structural variety of chemical compounds available as pharmacological tools for the treatment of Alzheimer's disease, we synthesized and evaluated a novel series of indole-benzoxazinones (Family I) and benzoxazine-arylpiperazine derivatives (Family II) for potential human acetylcholinesterase (hAChE) inhibitory properties. The most active compounds 7a and 7d demonstrated effective inhibitory profiles with Ki values of 20.3 ± 0.9 µM and 20.2 ± 0.9 µM, respectively. Kinetic inhibition assays showed non-competitive inhibition of AChE by the tested compounds. According to our docking studies, the most active compounds from both series (Families I and II) showed a binding mode similar to donepezil and interact with the same residues.

Synthesis and Docking of Novel 3-Indolylpropyl Derivatives as New Polypharmacological Agents Displaying Affinity for 5-HT1A R/SERT.

A series of novel 3-indolylpropyl derivatives was synthesized and evaluated for their binding affinities at the serotonin-1A receptor subtype (5-HT1A R) and the 5-HT transporter (SERT). Compounds 11b and 14b exhibited the highest affinities at the 5-HT1A R (Ki = 43 and 56 nM), whereas compounds 11c and 14a were the most potent analogs at the SERT (Ki = 34 and 17 nM). On the other hand, compounds 14b and 11d showed potent activity at both targets, displaying a profile that makes them promising leads for the search for novel potent ligands with a dual mechanism of action. Molecular docking studies in all the compounds unveiled relevant drug-target interactions, which allowed rationalizing the observed affinities.

Non-equivalent ligand selectivity of agonist sites in (α4ß2)2α4 nicotinic acetylcholine receptors: a key determinant of agonist efficacy.

The α4ß2 nicotinic acetylcholine receptor (nAChR) is the most abundant nAChR type in the brain, and this receptor type exists in alternate (α4ß2)2α4 and (α4ß2)2ß2 forms, which are activated by agonists with strikingly differing efficacies. Recent breakthroughs have identified an additional operational agonist binding site in the (α4ß2)2α4 nAChR that is responsible for the signature sensitivity of this receptor to activation by agonists, yet the structural mechanisms determining agonist efficacy at this receptor type are not yet fully understood. In this study, we characterized the ligand selectivity of the individual agonist sites of the (α4ß2)2α4 nAChR to determine whether differences in agonist selectivity influence agonist efficacy. Applying the substituted cysteine accessibility method to individual agonist sites in concatenated (α4ß2)2α4 receptors, we determined the agonist selectivity of the agonist sites of the (α4ß2)2α4 receptor. We show that (a) accessibility of substituted cysteines to covalent modification by methanesulfonate reagent depends on the agonist site at which the modification occurs and (b) that agonists such as sazetidine-A and TC-2559 are excluded from the site at the α4/α4 interface. Given that additional binding to the agonist site in the α4/α4 interface increases acetylcholine efficacy and that agonists excluded from the agonist site at the α4/α4 interface behave as partial agonists, we conclude that the ability to engage all agonist sites in (α4ß2)2α4 nAChRs is a key determinant of agonist efficacy. The findings add another level of complexity to the structural mechanisms that govern agonist efficacy in heteromeric nAChRs and related ligand-gated ion channels.

Multiple binding sites in the nicotinic acetylcholine receptors: An opportunity for polypharmacolgy.

For decades, the development of selective compounds has been the main goal for chemists and biologists involved in drug discovery. However, diverse lines of evidence indicate that polypharmacological agents, i.e. those that act simultaneously at various protein targets, might show better profiles than selective ligands, regarding both efficacy and side effects. On the other hand, the availability of the crystal structure of different receptors allows a detailed analysis of the main interactions between drugs and receptors in a specific binding site. Neuronal nicotinic acetylcholine receptors (nAChRs) constitute a large and diverse family of ligand-gated ion channels (LGICs) that, as a product of its modulation, regulate neurotransmitter release, which in turns produce a global neuromodulation of the central nervous system. nAChRs are pentameric protein complexes in such a way that expression of compatible subunits can lead to various receptor assemblies or subtypes. The agonist binding site, located at the extracellular region, exhibits different properties depending on the subunits that conform the receptor. In the last years, it has been recognized that nAChRs could also contain one or more allosteric sites which could bind non-classical nicotinic ligands including several therapeutically useful drugs. The presence of multiple binding sites in nAChRs offers an interesting possibility for the development of novel polypharmacological agents with a wide spectrum of actions.

Design, synthesis, biological evaluation and binding mode modeling of benzimidazole derivatives targeting the cannabinoid receptor type 1.

A series of N-acyl-2,5-dimethoxyphenyl-1H-benzimidazoles were designed based on a CoMFA model for cannabinoid receptor type 1 (CB1) ligands. Compounds were synthesized and radioligand binding affinity assays were performed. Eight novel benzimidazoles exhibited affinity for the CB1 receptor in the nanomolar range, and the most promising derivative compound 5 displayed a K(i) value of 1.2 nM when compared to CP55,940. These results confirm our previously reported QSAR model on benzimidazole derivatives, providing new information for the development of small molecules with high CB1 affinity.

Synthesis and biological screening of novel indolalkyl arenes targeting the serotonine transporter.

A series of functionalized indolylalkylarenes 3-16(a and b) were synthesized and their affinities for the serotonin transporter were investigated in vitro. Compounds 3-12(a and b) were obtained by nucleophilic substitution of 3-(1H-indol-3-yl)propyl-4-methylbenzenesulfonates 2(a and b) with a series of azaheterocycles. Compounds 14-16(a and b) were prepared in a two-step sequence by reaction of 3-(1H-indol-3-yl)-2-methylpropanal with substituted 1,2-phenylenediamines. Compounds 3b, 4b, and 5b showed good binding affinities (K(i) = 33.0, 48.0, and 17 nM, respectively). The other synthesized compounds showed moderate or no affinity in the binding studies.

Early-life exposure to sex hormones promotes voluntary ethanol intake in adulthood. A vulnerability factor to drug addiction.

While there is extensive research on alcohol dependence, the factors that make an individual vulnerable to developing alcoholism haven't been explored much. In this study, we aim to investigate how neonatal exposure to sex hormones affects alcohol intake and the regulation of the mesolimbic pathway in adulthood. The study aimed to investigate the impact of neonatal exposure to a single dose of testosterone propionate (TP) or estradiol valerate (EV) on ethanol consumption in adult rats. The rats were subjected to a two-bottle free-choice paradigm, and the content of dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) in the nucleus accumbens (NAcc) was measured using HPLC-ED. The expression of critical DA-related proteins in the mesolimbic pathway was evaluated through RT-qPCR and western blot analysis. Supraphysiological neonatal exposure to EV or TP resulted in increased ethanol intake over four weeks in adulthood. In addition, the DA and DOPAC content was reduced and increased in the NAcc of EV and TP-treated rats, and ß-endorphin content in the hypothalamus decreased in EV-treated rats. The VTA µ receptor and DA type 2 form short receptor (D2S) expression were significantly reduced in EV and TP male rats. Finally, in an extended 6-week protocol, the increase in ethanol consumption induced by EV was mitigated during the initial two hours post-naloxone injection. Neonatal exposure to sex hormones is a detrimental stimulus for the brain, which can facilitate the development of addictive behaviors, including alcohol use disorder.

Synthesis, docking and pharmacological evaluation of novel homo- and hetero-bis 3-piperazinylpropylindole derivatives at SERT and 5-HT1A receptor.

A series of 3-(3-(4-(3-(1H-indol-3-yl)propyl)piperazin-1-yl)propyl)-1H-indole derivatives (3a-d and 5a-f) as homo- and hetero-bis-ligands, were synthesized and evaluated for in vitro affinity at the serotonin transporter (SERT) and the 5-HT1A receptor. Compounds 5b and 5f showed nanomolar affinities for both targets. The experimental data were rationalized according to results obtained from docking experiments. These findings are in agreement with our proposal that bis-indole derivatives can bind both targets, and might serve as leads in the quest of ligands endowed with a dual mechanism of action.

Neonicotinic analogues: selective antagonists for α4ß2 nicotinic acetylcholine receptors.

Nicotine is an agonist of nicotinic acetylcholine receptors (nAChRs) that has been extensively used as a template for the synthesis of α4ß2-preferring nAChRs. Here, we used the N-methyl-pyrrolidine moiety of nicotine to design and synthesise novel α4ß2-preferring neonicotinic ligands. We increased the distance between the basic nitrogen and aromatic group of nicotine by introducing an ester functionality that also mimics acetylcholine (Fig. 2). Additionally, we introduced a benzyloxy group linked to the benzoyl moiety. Although the neonicotinic compounds fully inhibited binding of both [α-(125)I]bungarotoxin to human α7 nAChRs and [(3)H]cytisine to human α4ß2 nAChRs, they were markedly more potent at displacing radioligand binding to human α4ß2 nAChRs than to α7 nAChRs. Functional assays showed that the neonicotinic compounds behave as antagonists at α4ß2 and α4ß2α5 nAChRs. Substitutions on the aromatic ring of the compounds produced compounds that displayed marked selectivity for α4ß2 or α4ß2α5 nAChRs. Docking of the compounds on homology models of the agonist binding site at the α4/ß2 subunit interfaces of α4ß2 nAChRs suggested the compounds inhibit function of this nAChR type by binding the agonist binding site.

Design, synthesis, binding and docking-based 3D-QSAR studies of 2-pyridylbenzimidazoles--a new family of high affinity CB1 cannabinoid ligands.

A series of novel 2-pyridylbenzimidazole derivatives was rationally designed and synthesized based on our previous studies on benzimidazole 14, a CB1 agonist used as a template for optimization. In the present series, 21 compounds displayed high affinities with Ki values in the nanomolar range. JM-39 (compound 39) was the most active of the series (KiCB1 = 0.53 nM), while compounds 31 and 44 exhibited similar affinities to WIN 55212-2. CoMFA analysis was performed based on the biological data obtained and resulted in a statistically significant CoMFA model with high predictive value (q2 = 0.710, r2 = 0.998, r2pred = 0.823).

Synthesis, 5-hydroxytryptamine1A receptor affinity and docking studies of 3-[3-(4-aryl-1-piperazinyl)-propyl]-1H-indole derivatives.

A series of 3-[3-(4-aryl-1-piperazinyl)-propyl]-1H-indole derivatives (12a-h) was synthesized and evaluated for binding affinity at the human 5-hydroxytryptamine(1A) receptor (5-HT(1A)R) compounds (12b) and (12h) showed the highest 5-HT(1A) receptor affinity (IC(50)=15 nM). Molecular docking studies with all the compounds in a homology model of 5-HT(1A) showed that the main interaction anchoring the ligand in the receptor was a charge-reinforced bond between the protonated nitrogen atom (N-4) of the piperazine ring and Aspartate(3.32).

UFR2709, an Antagonist of Nicotinic Acetylcholine Receptors, Delays the Acquisition and Reduces Long-Term Ethanol Intake in Alcohol-Preferring UChB Bibulous Rats.

Alcoholism is a worldwide public health problem with high economic cost and which affects health and social behavior. It is estimated that alcoholism kills 3 million people globally, while in Chile it is responsible for around 9 thousand deaths per year. Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels expressed in the central nervous system, and they were suggested to modulate the ethanol mechanism involved in abuse and dependence. Previous work demonstrated a short-term treatment with UFR2709, a nAChRs antagonist, which reduced ethanol intake using a two-bottle free-choice paradigm in University of Chile bibulous (UChB) rats. Here, we present evidence of the UFR2709 efficacy in reducing the acquisition and long-term ethanol consumption. Our results show that UFR2709 (2.5 mg/kg i.p.) reduces the seek behavior and ethanol intake, even when the drug administration was stopped, and induced a reduction in the overall ethanol intake by around 55%. Using naïve UChB bibulous rats, we demonstrate that UFR2709 could delay and reduce the genetically adaptive impulse to seek and drink ethanol and prevent its excessive intake.

Molecular determinants for competitive inhibition of alpha4beta2 nicotinic acetylcholine receptors.

The Erythrina alkaloids erysodine and dihydro-beta-erythroidine (DHbetaE) are potent and selective competitive inhibitors of alpha4beta2 nicotinic acetylcholine receptors (nAChRs), but little is known about the molecular determinants of the sensitivity of this receptor subtype to inhibition by this class of antagonists. We addressed this issue by examining the effects of DHbetaE and a range of aromatic Erythrina alkaloids on [(3)H]cytisine binding and receptor function in conjunction with homology models of the alpha4beta2 nAChR, mutagenesis, and functional assays. The lactone group of DHbetaE and a hydroxyl group at position C-16 in aromatic Erythrina alkaloids were identified as major determinants of potency, which was decreased when the conserved residue Tyr126 in loop A of the alpha4 subunit was substituted by alanine. Sensitivity to inhibition was also decreased by substituting the conserved aromatic residues alpha4Trp182 (loop B), alpha4Tyr230 (loop C), and beta2Trp82 (loop D) and the nonconserved beta2Thr84; however, only alpha4Trp182 was predicted to contact bound antagonist, suggesting alpha4Tyr230, beta2Trp82, and beta2Thr84 contribute allosterically to the closed state elicited by bound antagonist. In addition, homology modeling predicted strong ionic interactions between the ammonium center of the Erythrina alkaloids and beta2Asp196, leading to the uncapping of loop C. Consistent with this, beta2D196A abolished sensitivity to inhibition by DHbetaE or erysodine but not by epierythratidine, which is not predicted to form ionic bonds with beta2Asp196. This residue is not conserved in subunits that comprise nAChRs with low sensitivity to inhibition by DHbetaE or erysodine, which highlights beta2Asp196 as a major determinant of the receptor selectivity of Erythrina alkaloids.