Discovery of aryl-biphenyl-2-ylmethylpiperazines as novel scaffolds for 5-HT7 ligands and role of the aromatic substituents in binding to the target receptor

Chimeric Structures in Mental Illnesses-"Magic" Molecules Specified for Complex Disorders

Mental health problems cover a wide spectrum of diseases, including mild to moderate anxiety, depression, alcohol/drug use disorders, as well as bipolar disorder and schizophrenia. Pharmacological treatment seems to be one of the most effective opportunities to recover function efficiently and satisfactorily. However, such disorders are complex as several target points are involved. This results in a necessity to combine different types of drugs to obtain the necessary therapeutic goals. There is a need to develop safer and more effective drugs. Considering that mental illnesses share multifactorial processes, the paradigm of one treatment with multiple modes of action rather than single-target strategies would be more effective for successful therapies. Therefore, hybrid molecules that combine two pharmacophores in one entity show promise, as they possess the desired therapeutic index with a small off-target risk. This review aims to provide information on chimeric structures designed for mental disorder therapy (i.e., schizophrenia and depression), and new types of drug candidates currently being tested. In addition, a discussion on some benefits and limitations of multifunctional, bivalent drug candidates is also given.

Privileged scaffold-based design to identify a novel drug-like 5-HT7 receptor-preferring agonist to target Fragile X syndrome

Recent preclinical studies have shown that activation of the serotonin 5-HT₇ receptor has the potential to treat neurodevelopmental disorders such as Fragile X syndrome, a rare disease characterized by autistic features. With the aim to provide the scientific community with diversified drug-like 5-HT₇ receptor-preferring agonists, we designed a set of new long-chain arylpiperazines by exploiting structural fragments present in clinically approved drugs or in preclinical candidates (privileged scaffolds). The new compounds were synthesized, tested for their affinity at 5-HT₇ and 5-HT_1A receptors, and screened for their in vitro stability to microsomal degradation and toxicity. Selected compounds were characterized as 5-HT₇ receptor-preferring ligands, endowed with high metabolic stability and low toxicity. Compound 7g emerged as a drug-like 5-HT₇ receptor-preferring agonist capable to rescue synaptic plasticity and attenuate stereotyped behavior in a mouse model of Fragile X syndrome.

Blockade of 5-HT2 receptors with sarpogrelate uncovers 5-HT7 receptors inhibiting the tachycardic sympathetic drive in pithed rats

Our group has previously shown in pithed rats that the cardiac sympathetic drive, which produces tachycardic responses, is inhibited by 5-HT via the activation of prejunctional 5-HT_1B/1D/5 receptors. Interestingly, when 5-HT₂ receptors are chronically blocked with sarpogrelate, the additional role of cardiac sympatho-inhibitory 5-HT_1F receptors is unmasked. Although 5-HT₂ receptors mediate tachycardia in rats, and the chronic blockade of 5-HT₂ receptors unmasked 5-HT₇ receptors mediating cardiac vagal inhibition, the role of 5-HT₇ receptors in the modulation of the cardiac sympathetic tone remains virtually unexplored. On this basis, male Wistar rats were pretreated during 14 days with sarpogrelate (a 5-HT₂ receptor antagonist) in drinking water (30 mg/kg/day; sarpogrelate-pretreated group) or equivalent volumes of drinking water (control group). Subsequently, the rats were pithed to produce increases in heart rate by either electrical preganglionic spinal (C₇ -T₁ ) stimulation of the cardiac sympathetic drive or iv administration of exogenous noradrenaline. The iv continuous infusion of AS-19 (a 5-HT₇ receptor agonist; 10 µg/kg/min) (i) inhibited the tachycardic responses to sympathetic stimulation, but not those to exogenous noradrenaline only in sarpogrelate-pretreated rats. This inhibition was completely reversed by SB258719 (a selective 5-HT₇ receptor antagonist; 1 mg/kg, iv) or glibenclamide (an ATP-sensitive K⁺ channel blocker; 20 mg/kg, iv). These results suggest that chronic 5-HT₂ receptor blockade uncovers a cardiac sympatho-inhibitory mechanism mediated by 5-HT₇ receptors, involving a hyperpolarization due to the opening of ATP-sensitive K⁺ channels. Thus, these findings support the role of 5-HT₇ receptors in the modulation of the cardiac sympathetic neurotransmission.

Electrostatic potential and non-covalent interactions analysis for the design of selective 5-HT7 ligands

Despite the significant improvement of methodology in the field of the in silico drug discovery, the search for selective drugs is still far from trivial. This is especially relevant in the case of designing new medicaments for treatment of central nervous system disorders. In this work, we present a new approach based on the molecular docking and the following electronic properties analysis of ligands' binding poses (electrostatic potential distribution analysis and quantitative topological analysis of the electron density distribution). The proposed protocol significantly increases the success rate of the selective 5-HT₇R ligands against 5-HT_1AR selection from the prepared databases (the rise from 33.3% to 77.8% and from 22.7% to 62.5% for training and testing sets, respectively). The presented approach can be applied as a supportive method in the virtual screening of ligands databases.

Structure-Activity Relationships and Therapeutic Potentials of 5-HT7 Receptor Ligands: An Update

Serotonin 5-HT₇ receptor (5-HT₇R) has been the subject of intense research efforts because of its presence in brain areas such as the hippocampus, hypothalamus, and cortex. Preclinical data link the 5-HT₇R to a variety of central nervous system processes including the regulation of circadian rhythms, mood, cognition, pain processing, and mechanisms of addiction. 5-HT₇R blockade has antidepressant effects and may ameliorate cognitive deficits associated with schizophrenia. 5-HT₇R has been recently shown to modulate neuronal morphology, excitability, and plasticity, thus contributing to shape brain networks during development and to remodel neuronal wiring in the mature brain. Therefore, the activation of 5-HT₇R has been proposed as a therapeutic approach for neurodevelopmental and neuropsychiatric disorders associated with abnormal neuronal connectivity. This Perspective celebrates the silver jubilee of the discovery of 5-HT₇R by providing a survey of recent studies on the medicinal chemistry of 5-HT₇R ligands and on the neuropharmacology of 5-HT₇R.

Novel N-biphenyl-2-ylmethyl 2-methoxyphenylpiperazinylalkanamides as 5-HT7R antagonists for the treatment of depression

5-HT7 receptor (5-HT7R) is a promising target for the treatment of depression and neuropathic pain. 5-HT7R antagonists exhibited antidepressant effects, while the agonists produced strong anti-hyperalgesic effects. In our efforts to discover selective 5-HT7R antagonists or agonists, N-biphenylylmethyl 2-methoxyphenylpiperazinylalkanamides 1 were designed, synthesized, and biologically evaluated against 5-HT7R. Among the synthesized compounds, N-2'-chlorobiphenylylmethyl 2-methoxyphenylpiperazinylpentanamide 1-8 showed the best binding affinity with a Ki value of 8.69nM and it was verified as a novel antagonist according to functional assays. The compound 1-8 was very selective over 5-HT1DR, 5-HT2AR, 5-HT3R, 5-HT5AR and 5-HT6R and moderately selective over 5-HT1AR, 5-HT1BR and 5-HT2CR. The novel 5-HT7R antagonist 1-8 exhibited an antidepressant effect at a dose of 25mg/kg in the forced swimming test in mice and showed a U-shaped dose-response curve which typically appears in 5-HT7R antagonists such as SB-269970 and lurasidone.