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.

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.

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.

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.

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).

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, in vitro evaluation and molecular docking of a new class of indolylpropyl benzamidopiperazines as dual AChE and SERT ligands for Alzheimer's disease.

During the last decade, the one drug-one target strategy has resulted to be inefficient in facing diseases with complex ethiology like Alzheimer's disease and many others. In this context, the multitarget paradigm has emerged as a promising strategy. Based on this consideration, we aim to develop novel molecules as promiscuous ligands acting in two or more targets at the same time. For such purpose, a new series of indolylpropyl-piperazinyl oxoethyl-benzamido piperazines were synthesized and evaluated as multitarget-directed drugs for the serotonin transporter (SERT) and acetylcholinesterase (AChE). The ability to decrease ß-amyloid levels as well as cell toxicity of all compounds were also measured. In vitro results showed that at least four compounds displayed promising activity against SERT and AChE. Compounds 18 and 19 (IC50 = 3.4 and 3.6 µM respectively) exhibited AChE inhibition profile in the same order of magnitude as donepezil (DPZ, IC50 = 2.17 µM), also displaying nanomolar affinity in SERT. Moreover, compounds 17 and 24 displayed high SERT affinities (IC50 = 9.2 and 1.9 nM respectively) similar to the antidepressant citalopram, and significant micromolar AChE activity at the same time. All the bioactive compounds showed a low toxicity profile in the range of concentrations studied. Molecular docking allowed us to rationalize the binding mode of the synthesized compounds in both targets. In addition, we also show that compounds 11 and 25 exhibit significant ß-amyloid lowering activity in a cell-based assay, 11 (50% inhibition, 10 µM) and 25 (35% inhibition, 10 µM). These results suggest that indolylpropyl benzamidopiperazines based compounds constitute promising leads for a multitargeted approach for Alzheimer's disease.

UFR2709, a Nicotinic Acetylcholine Receptor Antagonist, Decreases Ethanol Intake in Alcohol-Preferring Rats.

Brain nicotinic acetylcholine receptors (nAChRs), a heterogeneous family of pentameric acetylcholine-gated cation channels, have been suggested as molecular targets for the treatment of alcohol abuse and dependence. Here, we examined the effect of the competitive nAChR antagonist UFR2709 on the alcohol consumption of high-alcohol-drinking UChB rats. UChB rats were given free access to ethanol for 24-h periods in a two-bottle free choice paradigm and their ethanol and water intake were measured. The animals were i.p. injected daily for 17 days with a 10, 5, 2.5, or 1 mg/kg dose of UFR2709. Potential confounding motor effects of UFR2709 were assessed by examining the locomotor activity of animals administered the highest dose of UR2709 tested (10 mg/kg i.p.). UFR2709 reduced ethanol consumption and ethanol preference and increased water consumption in a dose-dependent manner. The most effective dose of UFR2709 was 2.5 mg/kg, which induced a 56% reduction in alcohol consumption. Administration of UFR2709 did not affect the weight or locomotor activity of the rats, suggesting that its effects on alcohol consumption and preference were mediated by specific nAChRs.

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.

Galanthamine and other Amaryllidaceae related alkaloids are inhibitors of α7, α4β2 and α3β4 nicotinic acetylcholine receptors

Abstract Galanthamine is an Amaryllidaceae-derived acetylcholinesterase inhibitor used to treat memory impairment in Alzheimer's disease and vascular dementia. There is evidence that galanthamine, in addition to its effects on acetylcholinesterase, may enhance or inhibit brain nicotinic acetylcholine receptors, which could increase or decrease the therapeutic efficacy of galanthamine, respectively. Here, we evaluated the effects of galanthamine and two others Amaryllidaceae acetylcholinesterase inhibitors (haemanthamine and tazettine) analyzed by gas chromatography-mass spectrometry and identified by comparing their mass fragmentation patterns with literature and database NIST vs.2.0 on the agonist responses of brain nicotinic acetylcholine receptors α7, α3β4, (α4)2(β2)3 and (α4)3(β2)2. Using nicotinic acetylcholine receptors expressed heterologously in Xenopus oocytes, in conjunction with two-electrode voltage clamping, we found that galanthamine inhibits the function of nicotinic acetylcholine receptors assayed through a mix competitive and non-competitevely. Nicotinic acetylcholine receptor α7 were significantly more sensitive to inhibition (17 ± 0.6 µM) than the heteromeric receptor, α3β4 (90 ± 3.4 µM). Neither haemanthamine nor tazettine were more potent than galanthamine.

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.

Amphetamine Derivatives as Monoamine Oxidase Inhibitors.

Amphetamine and its derivatives exhibit a wide range of pharmacological activities, including psychostimulant, hallucinogenic, entactogenic, anorectic, or antidepressant effects. The mechanisms of action underlying these effects are usually related to the ability of the different amphetamines to interact with diverse monoamine transporters or receptors. Moreover, many of these compounds are also potent and selective monoamine oxidase inhibitors. In the present work, we review how structural modifications on the aromatic ring, the amino group and/or the aliphatic side chain of the parent scaffold, modulate the enzyme inhibitory properties of hundreds of amphetamine derivatives. Furthermore, we discuss how monoamine oxidase inhibition might influence the pharmacology of these compounds.

3D similarities between the binding sites of monoaminergic target proteins.

The study of binding site similarities can be relevant to understand the interaction of different drugs at several molecular targets. The increasing availability of protein crystal structures and the development of novel algorithms designed to evaluate three-dimensional similarities, represent a great opportunity to explore the existence of electronic and shape features shared by clinically relevant proteins, which could assist drug design and discovery. Proteins involved in the recognition of monoaminergic neurotransmitters, such as monoamine transporters or monoamine oxidases (MAO) have been related to several psychiatric and neurological disorders such as depression or Parkinson's disease. In this work, we evaluated the possible existence of similarities among the binding sites of the serotonin transporter (SERT), the dopamine transporter (DAT), MAO-A and MAO-B. This study was carried out using molecular simulation methodologies linked to the statistical algorithm PocketMatch, which was modified in order to obtain similarities profiles. Our results show that DAT and SERT exhibit a high degree of 3-D similarities all along the pathway that is presumably involved in the substrate transport process. Distinct differences, on the other hand, were found both at the extracellular and the intracellular ends of the transporters, which might be involved in the selective initial recognition of the corresponding substrate. Similarities were also found between the active (catalytic) site of MAO-A and the extracellular vestibule of SERT (the S2 binding site). These results suggest some degree of structural convergence for these proteins, which have different functions, tissue distribution and genetic origin, but which share the same endogenous ligand (serotonin). Beyond the functional implications, these findings are valuable for the design of both selective and non-selective ligands.

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.

Erysodine, a competitive antagonist at neuronal nicotinic acetylcholine receptors, decreases ethanol consumption in alcohol-preferring UChB rats.

Alcohol abuse is a worldwide health problem with high economic costs to health systems. Emerging evidence suggests that modulation of brain nicotinic acetylcholine receptors (nAChRs) may be a therapeutic target for alcohol dependence. In this work, we assess the effectiveness of four doses of erysodine (1.5, 2.0, 4.0 or 8.0 mg/kg/day, i.p.), a competitive antagonist of nAChRs, on voluntary ethanol consumption behavior in alcohol-preferring UChB rats, administered during three consecutive days. Results show that erysodine administration produces a dose-dependent reduction in ethanol consumption respect to saline injection (control group). The highest doses of erysodine (4 and 8 mg/kg) reduce (45 and 66%, respectively) the ethanol intake during treatment period and first day of post-treatment compared to control group. While, the lowest doses of erysodine (1.5 and 2 mg/kg) only reduce ethanol intake during one day of treatment period. These effective reductions in ethanol intake were 23 and 29% for 1.5 and 2 mg/kg erysodine, respectively. Locomotor activity induced by a high dose of erysodine (10 mg/kg) was similar to those observed with saline injection in control rats, showing that the reduction in ethanol intake was not produced by hypolocomotor effect induced by erysodine. This is the first report showing that erysodine reduces ethanol intake in UChB rats in a dose-dependent manner. Our results highlight the role of nAChRs in the reward effects of ethanol and its modulation as a potentially effective pharmacological alternative for alcohol dependence treatment.

Rhodolirium andicola: a new renewable source of alkaloids with acetylcholinesterase inhibitory activity, a study from nature to molecular docking

ABSTRACT Acetylcholinesterase is an important target for control of neurodegenerative diseases causing cholinergic signaling deficit. Traditionally, galanthamine has been used as an Amaryllidaceae-derived acetylcholinesterase inhibitor, although new Amaryllidaceae plants could serve as source for better acetylcholinesterase inhibitors. Therefore, the objective of this study was to characterize the alkaloid composition from bulbs of Rhodolirium andicola (Poepp.) Traub, a native Chilean Amaryllidaceae specie, and assess their inhibitory activity on acetylcholinesterase by in vitro and in silico methodologies. Alkaloidal extracts from R. andicola exhibited an inhibitory activity with IC50 values between 11.25 ± 0.04 and 57.78 ± 1.92 µg/ml that included isolated alkaloid, galanthamine (2.3 ± 0.18 µg/ml), Additionally, 12 alkaloids were detected using gas chromatography-mass spectrometry and identified by comparing their mass fragmentation patterns with literature and database NIST vs.2.0. To better understand the bioactivity of isolated compounds and alkaloidal extracts against acetylcholinesterase, a molecular docking approach was performed. Results suggested that alkaloids such as lycoramine, norpluvine diacetate and 6α-deoxy-tazettine expand the list of potential acetylcholinesterase inhibitors to not only galanthamine. The role of R. andicola as a source for acetylcholinesterase inhibitors is further discussed in this study.

Characterization of a Novel Drosophila SERT Mutant: Insights on the Contribution of the Serotonin Neural System to Behaviors.

A better comprehension on how different molecular components of the serotonergic system contribute to the adequate regulation of behaviors in animals is essential in the interpretation on how they are involved in neuropsychiatric and pathological disorders. It is possible to study these components in "simpler" animal models including the fly Drosophila melanogaster, given that most of the components of the serotonergic system are conserved between vertebrates and invertebrates. Here we decided to advance our understanding on how the serotonin plasma membrane transporter (SERT) contributes to serotonergic neurotransmission and behaviors in Drosophila. In doing this, we characterized for the first time a mutant for Drosophila SERT (dSERT) and additionally used a highly selective serotonin-releasing drug, 4-methylthioamphetamine (4-MTA), whose mechanism of action involves the SERT protein. Our results show that dSERT mutant animals exhibit an increased survival rate in stress conditions, increased basal motor behavior, and decreased levels in an anxiety-related parameter, centrophobism. We also show that 4-MTA increases the negative chemotaxis toward a strong aversive odorant, benzaldehyde. Our neurochemical data suggest that this effect is mediated by dSERT and depends on the 4-MTA-increased release of serotonin in the fly brain. Our in silico data support the idea that these effects are explained by specific interactions between 4-MTA and dSERT. In sum, our neurochemical, in silico, and behavioral analyses demonstrate the critical importance of the serotonergic system and particularly dSERT functioning in modulating several behaviors in Drosophila.

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.

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, binding assays, cytotoxic activity and docking studies of benzimidazole and benzothiophene derivatives with selective affinity for the CB2 cannabinoid receptor.

Herein we report the design, synthesis, bioinformatic and biological studies of benzimidazole and benzothiophene derivatives as new cannabinoid receptor ligands. To test the hypothesis that the lack of a hydrogen bond interaction between benzimidazole and benzothiophene derivatives with Lys192 reduces their affinity for CB1 receptors (as we previously reported) and leads to CB2 selectivity, most of the tested compounds do not exhibit hydrogen bond acceptors. All compounds displayed mostly CB2 selectivity, although this was more pronounced in the benzimidazoles derivatives. Furthermore, docking assays revealed a ∏-cation interaction with Lys109 which could play a key role for the CB2 selectivity index. The series displayed low toxicity on five different cell lines. Derivative 8f presented the best binding profile (Ki = 0.08 µM), high selectivity index (KiCB1/KiCB2) and a low citoxicity. Interestingly, in cell viability experiments, using HL-60 cells (expressing exclusively CB2 receptors), all synthesised compounds were shown to be cytotoxic, suggesting that a CB2 agonist response may be involved.