Selective Enhancement of REM Sleep in Male Rats through Activation of MT1 Receptors Located in the Locus Coeruleus Norepinephrine neurons.

Sleep disorders affect millions of people around the world and have a high comorbidity with psychiatric disorders. While current hypnotics mostly increase non-rapid eye movement sleep (NREMS), drugs acting selectively on enhancing rapid eye movement sleep (REMS) are lacking. This polysomnographic study in male rats showed that the first-in-class selective melatonin MT1 receptor partial agonist UCM871 increases the duration of REMs without affecting that of NREMS. The REMS-promoting effects of UCM871 occurred by inhibiting, in a dose-response manner, the firing activity of the locus coeruleus (LC) norepinephrine (NE) neurons, which express MT1 receptors. The increase of REMS duration and the inhibition of LC-NE neuronal activity by UCM871 were abolished by MT1 pharmacological antagonism and by an adeno-associated viral (AAV) vector which selectively knocked down MT1 receptors in the LC-NE neurons. In conclusion, MT1 receptor agonism inhibits LC-NE neurons and triggers REMS, thus representing a novel mechanism and target for REMS disorders and/or psychiatric disorders associated with REMS impairments.Significance Statement Rapid eye movement sleep (REMS) is involved in the processes of memory consolidation and emotional regulation, but drugs selectively enhancing REMS are scant. Herein, we show that the first-in-class selective melatonin MT1 receptor agonist UCM871, by inhibiting the activity of norepinephrine neurons in the locus coeruleus, an important nucleus regulating the sleep/wake cycle, selectively increases the duration of REMS. These findings enhance our current understanding of the neurobiology and pharmacology of REMS and provide a possible novel mechanism and target for disorders associated with REMS dysfunctions.

Melatonin MT1 receptor as a novel target in neuropsychopharmacology: MT1 ligands, pathophysiological and therapeutic implications, and perspectives.

Melatonin (MLT), a neuromodulator mainly acting through two G-protein coupled receptors MT1 and MT2, regulates many brain functions, including circadian rhythms, mood, pain and sleep. MLT and non-selective MT1/MT2 receptor agonists are clinically used in neuropsychiatric and/or sleep disorders. However, the selective roles of the MT1 and MT2 receptors need to be clarified. Here, we review the role of the MT1 receptor in neuropsychopharmacology, describe the anatomical localization of MT1 receptors in the brain, discuss the medicinal chemistry, biochemistry and molecular aspects of the receptor, and explore the findings linking MT1 receptors to psychiatric and neurological disorders. MT1 receptors are localized in brain regions which regulate circadian rhythms, sleep, and mood, such as the suprachiasmatic nucleus, cortex, hippocampus, dorsal raphe nucleus and lateral hypothalamus. Their activation modulates intracellular signaling pathways also targeted by psychoactive drugs, including antidepressants and mood stabilizers. MT1 receptor knockout mice display increased anxiety, a depressive-like phenotype, increased propensity to reward and addiction, and reduced Rapid-Eye-Movement sleep. These behavioral dysfunctions are associated with altered serotonergic and noradrenergic neurotransmissions. Several studies indicate that the MT1, rather than MT2, receptor is implicated in circadian rhythm regulation. The involvement of MT1 receptors in Alzheimer's and Huntington diseases has also been proposed. Postmortem studies in depressed patients have further confirmed the possible involvement of MT1 receptors in depression. Overall, there is substantial evidence indicating a role for MT1 receptor in modulating brain function and mood. Consequently, this MLT receptor subtype deserves to be further examined as a novel target for neuropsychopharmacological drug development.

Enhanced detection for determination of enantiomeric purity of novel agomelatine analogs by EKC using single and dual cyclodextrin systems.

Performing CD-EKC, baseline separation of five agomelatine analogs, potential antidepressant compounds, was achieved. A method for the enantioresolution and determination of enantiomeric purity of these naphthalene derivatives was developed using capillaries dynamically coated with polyethylene oxide and anionic cyclodextrins (highly sulfated CD) as chiral selectors. Operational parameters such as the nature and concentration of the cyclodextrins were investigated. In a second step the implementation of a dual cyclodextrin system was found to strongly enhance the LOD of the analytes. After optimization, best conditions were a 25 mM phosphate buffer at pH 2.5 containing 5% w/v (i.e. 19.7 mM) of highly sulfated-γ-CD and 10 mM of 6-monodeoxy-6-monoamino-ß-CD dual system, leading to resolution of, at least, 3.6 in 35 min. A preliminary validation of the developed method was undertaken: linearity, precision, and LOD and LOQ were evaluated. The latest ones were found equal to 0.25 and 0.82 µM and to 0.31 and 0.96 µM respectively for the first and the second enantiomer of compound 1.

New melatonin (MT1/MT2) ligands: design and synthesis of (8,9-dihydro-7H-furo[3,2-f]chromen-1-yl) derivatives.

Herein we describe the synthesis of novel tricyclic analogues issued from the rigidification of the methoxy group of the benzofuranic analogue of melatonin as MT1 and MT2 ligands. Most of the synthesized compounds displayed high binding affinities at MT1 and MT2 receptors subtypes. Compound 6b (MT1, Ki=0.07nM; MT2, Ki=0.08nM) exhibited with the vinyl 6c and allyl 6d the most interesting derivatives of this series. Functional activity of these compounds showed full agonist activity with EC50 in the nanomolar range. Compounds 6a (EC50=0.8nM and Emax=98%) and 6b (EC50=0.2nM and Emax=121%) exhibited good pharmacological profiles.

Novel conformationally constrained analogues of agomelatine as new melatoninergic ligands.

Novel conformationally restricted analogues of agomelatine were synthesized and pharmacologically evaluated at MT1 and MT2 melatoninergic receptors. Replacement of the N-acetyl side chain of agomelatine by oxathiadiazole-2-oxide (compound 3), oxadiazole-5(4H)-one (compound 4), tetrazole (compound 5), oxazolidinone (compound 7a), pyrrolidinone (compound 7b), imidazolidinedione (compound 12), thiazole (compounds 13 and 14) and isoxazole moieties (compound 15) led to a decrease of the melatoninergic binding affinities, particularly at MT1. Compounds 7a and 7b exhibiting nanomolar affinity towards the MT2 receptors subtypes have shown the most interesting pharmacological results of this series with the appearance of a weak MT2-selectivity.

Synthesis and SAR Studies of Isoquinoline and Tetrahydroisoquinoline Derivatives as Melatonin Receptor Ligands.

In our constant search for new successors of agomelatine, we report herein a new series of compounds resulting from bioisosteric modulation of the naphthalene ring. The isoquinoline and tetrahydroisoquinoline derivatives were synthesized and pharmacologically evaluated. This isosteric replacement of the naphthalene group of agomelatine has led to potent agonist and partial agonist compounds with nanomolar melatonergic binding affinities. Overall, the presence of a nitrogen atom was accompanied with a decrease in the binding affinity toward both MT1 and MT2 and the loss of 5HT2C response, especially for tetrahydroisoquinoline in comparison with the parent compound. Interestingly, due to the presence of this nitrogen atom, a notable improvement in the pharmacokinetic properties was observed for all compounds.

Quinazoline and phthalazine derivatives as novel melatonin receptor ligands analogues of agomelatine.

For further development of successors of Agomelatine through modulation of its pharmacokinetic properties, we report herein the design, synthesis and pharmacological results of a new family of melatonin receptor ligands. Issued from the introduction of quinazoline and phthalazine scaffolds carrying an ethyl amide lateral chain and a methoxy group as bioisosteric ligands analogues of previously developed Agomelatine. The biological activity of the prepared analogues was compared with that of Agomelatine. Quinazoline and phthalazine rings proved to be a versatile scaffold for easy feasible MT1 and MT2 ligands. Potent agonists with sub-micromolar binding affinity were obtained. However, the presence of two nitrogen atoms resulted in compounds with lower affinity for both MT1 and MT2, in comparison with the parent compound, balanced by the exhibition of good pharmacokinetic properties.

Discovery of holoenzyme-disrupting chemicals as substrate-selective CK2 inhibitors.

CK2 is a constitutively active protein kinase overexpressed in numerous malignancies. Interaction between CK2α and CK2ß subunits is essential for substrate selectivity. The CK2α/CK2ß interface has been previously targeted by peptides to achieve functional effects; however, no small molecules modulators were identified due to pocket flexibility and open shape. Here we generated numerous plausible conformations of the interface using the fumigation modeling protocol, and virtually screened a compound library to discover compound 1 that suppressed CK2α/CK2ß interaction in vitro and inhibited CK2 in a substrate-selective manner. Orthogonal SPR, crystallography, and NMR experiments demonstrated that 4 and 6, improved analogs of 1, bind to CK2α as predicted. Both inhibitors alter CK2 activity in cells through inhibition of CK2 holoenzyme formation. Treatment with 6 suppressed MDA-MB231 triple negative breast cancer cell growth and induced apoptosis. Altogether, our findings exemplify an innovative computational-experimental approach and identify novel non-peptidic inhibitors of CK2 subunit interface disclosing substrate-selective functional effects.

Synthesis of 3-phenylnaphthalenic derivatives as new selective MT(2) melatoninergic ligands.

A series of naphthalenic analogues of melatonin were prepared and evaluated as melatonin receptor MT(2) selective ligands. Activity and MT(2) selectivity can be modulated with suitable variations of the C-3 phenyl and the acyl group on the C-1 side chain. Surprisingly, in contrast with what had been previously described in other series (2-benzylindoles, 2-benzylbenzofurans and 3-phenyltetralins), the presence of a C-3 phenyl with a functional group on the meta position seems to be primordial for MT(2) affinity and selectivity. Indeed, N-[2-(3-(3-hydroxymethylphenyl)-7-methoxynaphth-1-yl)ethyl]acetamide (21) is one of the best MT(2) selective ligands described until now and behaves as an antagonist.

Design and synthesis of benzofuranic derivatives as new ligands at the melatonin-binding site MT3.

Benzofuranic analogues of MCA-NAT (5-methoxycarbonylamino-N-acetyltryptamine) have been synthesized and evaluated as melatonin receptor ligands. Introduction of a methoxycarbonylamino substituent in the C-5 position of the benzofurane nucleus obtains MT(3) selective ligands. This selectivity can be modulated with suitable variations of the C-5 position and the acyl group on the C-3 side chain.

Synthesis and biological evaluation of new naphtho- and quinolinocyclopentane derivatives as potent melatoninergic (MT1/MT2) and serotoninergic (5-HT2C) dual ligands.

We recently reported a series of naphthofuranic compounds as constrained agomelatine analogues. Herein, in order to explore alternative ethyl amide side chain rigidification, naphthocyclopentane and quinolinocyclopentane derivatives with various acetamide modulations were synthesized and evaluated at both melatonin (MT1, MT2) and serotonin (5-HT2C) receptors. These modifications has led to compounds with promising dual affinity and high MTs receptors agonist activity. Enantiomeric separation was then performed on selected compounds allowing us to identify levogyre enantiomers (-)-17g and (-)-17k as the highest (MT1, MT2)/5-HT2C dual ligands described nowadays.

New quinolinic derivatives as melatonergic ligands: Synthesis and pharmacological evaluation.

New series of melatonergic ligands issued from two methoxy-quinolinic scaffolds (2-MQ and 3-MQ), were designed and synthesized. Herein we report the synthetic scheme and pharmacological results of the new prepared compounds. Investigation of compound 11a, the strict 2-MQ analogue, revealed the promising potential of this series. Therefore, pharmacomodulation of the acetamide function of 11a has led to compounds with different pharmacological profiles and the emergence of an MT2 selectivity. Besides, sulphonamide 11b showed the most important MT2 selectivity of this series (167 folds) while methyl and ethyl-ureas 11f and 11g represented the most potent melatonergic ligands of this study.

Melatonergic ligands: Design, synthesis and pharmacological evaluation of novel series of naphthofuranic derivatives.

Following our research for new melatonergic ligands, herein we report the design, synthesis and biological evaluation of new series of naphthofuranic derivatives as MT1 and MT2 ligands. Binding affinity results of the prepared compounds revealed good binding affinities at both melatonin receptor subtypes. Particularly, compound 6a behaved as an MT1 partial agonist and MT2 full agonist and exhibited an excellent binding affinity at MT2 (Ki = 0.09 nM). In addition, lateral chain displacement from position 1 to 2 of the furan core had no effect on the binding affinity at both MT1 and MT2, while elongation of this side chain, led to decreased melatonergic binding affinities.

Synthesis and pharmacological evaluation of dual ligands for melatonin (MT1/MT2) and serotonin 5-HT2C receptor subtypes (II).

In this paper we report the investigation of C-3 and ß-acetamide positions of agomelatine analogues. Concomitant insertion of a hydroxymethyl in the ß-acetamide position and aliphatic groups in C-3 position produced a positive effect on both melatonin (MT1, MT2) and serotonin (5-HT2C) binding affinities. In particular, the allyl 6b and ethyl 15a represented the more interesting compounds of this series. Furthermore, the introduction of methyl cycloalkyl groups (compounds 11a, 12a) exhibited no change in both MT2 and 5-HT2C binding affinities while a decrease of MT1 binding affinity occurred leading to an MT2 selectivity. Finally, the acetamide modulation has led to methyl thiourea 11h, with a weak MT2 selectivity.

Synthesis and pharmacological evaluation of a series of the agomelatine analogues as melatonin MT1 /MT2 agonist and 5-HT2C antagonist.

Agomelatine is a naphthalenic analogue of melatonin that is in clinical use for the treatment of major depressive disorders. Interestingly, while agomelatine exhibits potent affinity for melatonin receptors, it binds with only moderate affinity to the serotonin 5-HT2C receptor. Optimization of agomelatine toward this target could further potentiate its clinical efficacy. To explore this hypothesis and to access derivatives in which a key point of agomelatine metabolism is blocked, a series of naphthalenic derivatives was designed and synthesized as novel analogues of agomelatine. Most of the prepared compounds exhibited good binding affinity at the melatonin MT1 and MT2 receptor subtypes. Two compounds, an acetamide and an acrylamide derivative, exhibited good binding affinities at both the human melatonin (MT) receptors and the serotonin 5-HT2C receptor subtype, with pKi values of 7.96 and 7.95 against MT1, 7.86 and 8.68 against MT2, and 6.64 and 6.44 against 5-HT2C, respectively.

Design, synthesis and pharmacological evaluation of new series of naphthalenic analogues as melatoninergic (MT1/MT2) and serotoninergic 5-HT2C dual ligands (I).

As part of our ongoing interest in developing new melatoninergic ligands bearing the same pharmacological profile as agomelatine, we focused our attention on this compound as a lead. Several chemical modifications have been performed on positions C-3 and 8 of the naphthalene ring determined as primary targets for the agomelatine metabolism. Herein we report the modulation of the positions C-3 and 7 in addition of the amide side chain because of this later prominent role in the affinity profile of such ligands. Synthesized compounds were then biologically evaluated at human cloned melatoninergic and serotoninergic receptors and showed different binding affinity and intrinsic activity profiles. Compounds bearing fluoroacetamide group (compounds 4 and 5) showed a high melatoninergic binding affinity particularly towards MT(1) receptor subtype. Thus, the fluoroacetamide 4 exhibited a good melatoninergic (MT(1)/MT(2)) binding affinity (70 pM) higher than the lead. Moreover, other compounds (10a, 10e, 16, 17 and 18) issued from these modulations behaved as MT(1) and MT(2) agonists and exhibited a sub-nanomolar binding affinity towards these receptors. However, only compounds 10e, 17 and 18 showed a sub-nanomolar binding affinity at 5-HT(2C) higher than the agomelatine.

Design and synthesis of naphthalenic derivatives as new ligands at the melatonin binding site MT3.

Naphthalenic analogs of MCA-NAT (5-methoxycarbonylamino-N-acetyltryptamine) have been synthesized and evaluated as melatonin receptor ligands. Introduction of a methoxycarbonylamino substituent at the C-7 position of the naphthalenic nucleus yields MT3 selective ligands. This selectivity can be modulated with suitable variations of the C-7 position and the acyl group on the C-1 side chain. We identified new series of compounds with affinity for the MT3 binding site in the nanomolar range, and singled out a selective ligand, (N-[2-(7-methylsulfamoyl-naphth-1-yl)ethyl]acetamide (17), with a Ki of 4.9 nM and selectivity of 1024 and 2040 versus MT1 and MT2 receptors respectively.