Exploring the effectiveness of novel benzimidazoles as CB2 ligands: synthesis, biological evaluation, molecular docking studies and ADMET prediction

The progress of small molecules against cannabinoid 2 receptor (CB2R)

The two subtypes of cannabinoid receptors (CBR), namely CB1R and CB2R, belong to the G protein-coupled receptor (GPCR) superfamily and are confirmed as potential therapeutic targets for a variety of diseases such as inflammation, neuropathic pain, and immune-related disorders. Since CB1R is mainly distributed in the central nervous system (CNS), it could produce severe psychiatric adverse reactions and addiction. In contrast, CB2R are predominantly distributed in the peripheral immune system with minimal CNS-related side effects. Therefore, more attention has been devoted to the discovery of CB2R ligands. In view of the favorable profile of CB2R, many high-binding affinity and selectivity CB2R ligands have been developed recently. This paper reviews recent research progress on CB2R ligands, including endogenous CB2R ligands, natural compounds, and novel small molecules, in order to provide a reference for subsequent CB2R ligand development.

Dual allosteric and orthosteric pharmacology of synthetic analog cannabidiol-dimethylheptyl, but not cannabidiol, on the cannabinoid CB2 receptor

Cannabinoid CB2 receptor (CB2R) is a class A G protein-coupled receptor (GPCR) involved in a broad spectrum of physiological processes and pathological conditions. For that reason, targeting CB2R might provide therapeutic opportunities in neurodegenerative disorders, neuropathic pain, inflammatory diseases, and cancer. The main components from Cannabis sativa, such as Δ9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD), have been therapeutically exploited and synthetically-derived analogs have been generated. One example is cannabidiol-dimethylheptyl (CBD-DMH), which exhibits anti-inflammatory effects. Nevertheless, its pharmacological mechanism of action is not yet fully understood and is hypothesized for multiple targets, including CB2R. The aim of this study was to further investigate the molecular pharmacology of CBD-DMH on CB2R while CBD was taken along as control. These compounds were screened in equilibrium and kinetic radioligand binding studies and various functional assays, including G protein activation, inhibition of cAMP production and ß-arrestin-2 recruitment. In dissociation studies, CBD-DMH allosterically modulated the radioligand binding. Furthermore, CBD-DMH negatively modulated the G protein activation of reference agonists CP55,940, AEA and 2-AG, but not the agonist-induced ß-arrestin-2 recruitment. Nevertheless, CBD-DMH also displayed competitive binding to CB2R and partial agonism on G protein activation, inhibition of cAMP production and ß-arrestin-2 recruitment. CBD did not exhibit such allosteric behavior and only very weakly bound CB2R without activation. This study shows a dual binding mode of CBD-DMH, but not CBD, to CB2R with the suggestion of two different binding sites. Altogether, it encourages further research into this dual mechanism which might provide a new class of molecules targeting CB2R.

N-[1,3-Dialkyl(aryl)-2-oxoimidazolidin-4-ylidene]-aryl(alkyl)sulphonamides as Novel Selective Human Cannabinoid Type 2 Receptor (hCB2R) Ligands; Insights into the Mechanism of Receptor Activation/Deactivation

Cannabinoid type 1 (hCB1) and type 2 (hCB2) receptors are pleiotropic and crucial targets whose signaling contributes to physiological homeostasis and its restoration after injury. Being predominantly expressed in peripheral tissues, hCB2R represents a safer therapeutic target than hCB1R, which is highly expressed in the brain, where it regulates processes related to cognition, memory, and motor control. The development of hCB2R ligands represents a therapeutic opportunity for treating diseases such as pain, inflammation and cancer. Identifying new selective scaffolds for cannabinoids and determining the structural determinants responsible for agonism and antagonism are priorities in drug design. In this work, a series of N-[1,3-dialkyl(aryl)-2-oxoimidazolidin-4-ylidene]-aryl(alkyl)sulfonamides is designed and synthesized and their affinity for human hCB1R and hCB2R is determined. Starting with a scaffold selected from the NIH Psychoactive Drug Screening Program Repository, through a combination of molecular modeling and structure-activity relationship studies, we were able to identify the chemical features leading to finely tuned hCB2R selectivity. In addition, an in silico model capable of predicting the functional activity of hCB2R ligands was proposed and validated. The proposed receptor activation/deactivation model enabled the identification of four pure hCB2R-selective agonists that can be used as a starting point for the development of more potent ligands.

Design and synthesis of leucylaniline derivatives as leucyl-tRNA synthetase inhibitors

By simulating the structure of Leu-AMP, 26 leu-arylamine derivatives were designed and synthesized as leucyl-tRNA Synthetase inhibitors; compounds 19 and 24 showed good anti-tuberculosis activity.

DARK Classics in Chemical Neuroscience: Etonitazene and Related Benzimidazoles

Etonitazene and related 2-benzylbenzimidazoles are potent analgetics invented in the research laboratories of the Swiss pharmaceutical giant CIBA in the late 1950s. Though the unprecedented structure distinguishes this class of compounds from poppy-derived and other synthetic analgetics, a range of studies indicate that these drugs are selective μ opioid receptor agonists possessing morphine-like pharmacotoxicological properties in animals as well as humans. Several unscheduled members of this synthetically readily accessible class of opioids that are not controlled under the international and national drug control systems have recently emerged on the illicit drug market. Among them, isotonitazene has been implicated in at least 200 fatalities in Europe and North America. None of the 2-benzylbenzimidazole derivatives have been developed into medicines, but etonitazene and some of its derivatives have been used as receptor probes and in addiction behavior studies in animals. The unique structure has inspired research on such benzimidazoles and related benzimidazolones of which "brorphine" made its debut as one of the newest psychoactive substance to emerge on the illicit opioid drug market in mid-2019. This in-depth review provides a historical introduction, an overview on the chemistry, pharmacological profiles, adverse effects, addiction liability, regulatory status, and the impact on chemical neuroscience of the 2-benzylbenzimidazoles. Structurally related benzimidazoles with opioid and/or analgesic properties are also discussed briefly.

Design, Synthesis and Biological Evaluation of Anti-tuberculosis Agents based on Bedaquiline Structure

Background:

Bedaquiline is a novel anti-tuberculosis drug that inhibits Mycobacterial ATP synthase. However, studies have found that bedaquiline has serious side effects due to high lipophilicity. Recently, the complete structure of ATP synthase was first reported in the Journal of Science.

Objective:

The study aimed to design, synthesise and carry out biological evaluation of antituberculosis agents based on the structure of bedaquiline.

Methods:

The mode of action of bedaquiline and ATP synthase was determined by molecular docking, and a series of low lipophilic bedaquiline derivatives were synthesized. The inhibitory activities of bedaquiline derivatives towards Mycobacterium phlei 1180 and Mycobacterium tuberculosis H37Rv were evaluated in vitro. A docking study was carried out to elucidate the structureactivity relationship of the obtained compounds. The predicted ADMET properties of the synthesized compounds were also analyzed.

Results:

The compounds 5c3, 6a1, and 6d3 showed good inhibitory activities (MIC=15.62 ug.mL-1). At the same time, the compounds 5c3, 6a1, and 6d3 also showed good drug-like properties through molecular docking and ADMET properties prediction.

Conclusion:

The results of in vitro anti-tuberculosis activity assays, docking studies and ADMET predictions indicate that the synthesized compounds have potential antifungal activity, with compounds 6a1 being further optimized and developed as lead compounds.

Design, Synthesis, and Biological Evaluation of Novel Multifunctional Rolipram-Tranilast Hybrids As Potential Treatment for Traumatic Brain Injury

Traumatic brain injury (TBI) is a prevalent public healthcare concern frequently instigated by mechanical shock, traffic, or violence incidents, leading to permanent nerve damage, and there is no ideal treatment for it yet. In this study, a series of Rolipram-Tranilast hybrids were designed and synthesized. The neuroprotective activities of the Rolipram-Tranilast hybrids were evaluated both in vitro and in vivo. Compound 5 has been identified as the strongest neuroprotective molecule among the series with robust anti-oxidant and anti-inflammatory potentials. Compound 5 significantly increased the heme oxygenase-1 (HO-1) levels and the phosphorylated cAMP response elements binding protein (p-CREB) while it down-regulated phosphodiesterase-4 B (PDE4B) expression in vitro. Furthermore, compound 5 remarkably attenuated TBI and had a good safety profile in mice. Taken together, our findings suggested that compound 5 could serve as a novel promising lead compound in the treatment of TBI and other central nervous system (CNS) diseases associated with PDE4B and oxidative stress.

Prediction of the Binding Affinities and Selectivity for CB1 and CB2 Ligands Using Homology Modeling, Molecular Docking, Molecular Dynamics Simulations, and MM-PBSA Binding Free Energy Calculations

Cannabinoids are a group of chemical compounds that have been used for thousands of years due to their psychoactive function and systemic physiological effects. There are at least two types of cannabinoid receptors, CB1 and CB2, which belong to the G protein-coupled receptor superfamily and can trigger different signaling pathways to exert their physiological functions. In this study, several representative agonists and antagonists of both CB1 and CB2 were systematically studied to predict their binding affinities and selectivity against both cannabinoid receptors using a set of hierarchical molecular modeling and simulation techniques, including homology modeling, molecular docking, molecular dynamics (MD) simulations and end point binding free energy calculations using the molecular mechanics/Poisson-Boltzmann surface area-WSAS (MM-PBSA-WSAS) method, and molecular mechanics/generalized Born surface area (MM-GBSA) free energy decomposition. Encouragingly, the calculated binding free energies correlated very well with the experimental values and the correlation coefficient square (R²), 0.60, was much higher than that of an efficient but less accurate docking scoring function (R² = 0.37). The hotspot residues for CB1 and CB2 in both active and inactive conformations were identified via MM-GBSA free energy decomposition analysis. The comparisons of binding free energies, ligand-receptor interaction patterns, and hotspot residues among the four systems, namely, agonist-bound CB1, agonist-bound CB2, antagonist-bound CB1, and antagonist-bound CB2, enabled us to investigate and identify distinct binding features of these four systems, with which one can rationally design potent, selective, and function-specific modulators for the cannabinoid receptors.

Synthesis and Biological Evaluation of Novel (thio)semicarbazone-Based Benzimidazoles as Antiviral Agents against Human Respiratory Viruses

Respiratory RNA viruses are responsible for recurrent acute respiratory illnesses that still represent a major medical need. Previously we developed a large variety of benzimidazole derivatives able to inhibit these viruses. Herein, two series of (thio)semicarbazone- and hydrazone-based benzimidazoles have been explored, by derivatizing 5-acetyl benzimidazoles previously reported by us, thereby evaluating the influence of the modification on the antiviral activity. Compounds 6, 8, 16 and 17, bearing the 5-(thio)semicarbazone and 5-hydrazone functionalities in combination with the 2-benzyl ring on the benzimidazole core structure, acted as dual inhibitors of influenza A virus and human coronavirus. For respiratory syncytial virus (RSV), activity is limited to the 5-thiosemicarbazone (25) and 5-hydrazone (22) compounds carrying the 2-[(benzotriazol-1/2-yl)methyl]benzimidazole scaffold. These molecules proved to be the most effective antiviral agents, able to reach the potency profile of the licensed drug ribavirin. The molecular docking analysis explained the SAR of these compounds around their binding mode to the target RSV F protein, revealing the key contacts for further assessment. The herein-investigated benzimidazole-based derivatives may represent valuable hit compounds, deserving subsequent structural improvements towards more efficient antiviral agents for the treatment of pathologies caused by these human respiratory viruses.

Structural Modifications on CORM-3 Lead to Enhanced Anti-angiogenic Properties Against Triple-negative Breast Cancer Cells

PURPOSE

Carbon monoxide-releasing molecules (CORMs) are a special class of organometallic complexes that have been reported to offer beneficial effects against different conditions including several subtypes of cancer. Especially for the aggressive and poorly treated triplenegative breast cancer (TNBC), early CORMs have been shown to diminish malignant angiogenesis and may be considered as an alternative approach. So, this study aimed at testing novel CORM molecules against angiogenesis in TNBC seeking potent drug candidates for new therapies.

METHODS

Based on previous studies, CORM-3 was chosen as the lead compound and a group of 15 new ruthenium-based CORMs was synthesized and subsequently evaluated in vitro for potential anti-angiogenic properties.

RESULTS

A similar anti-angiogenic behaviour to the lead complex was observed and a new CORM, complex 4, emerged as a promising agent from this study. Specifically, this complex offered better inhibition of the activation of VEGFR2 and other downstream proteins of vascular endothelial cells. Complex 4 also retained the ability of the parent molecule to reduce the upregulated VEGF expression from TNBC cells and inhibit endothelial cell migration and new vessel formation. The lack of significant cytotoxicity and the downregulating activity over the cytoprotective enzyme haem oxygenase-1 (HO-1) in cancer cells may also favour CORMs against this poorly treated subtype of breast cancer.

CONCLUSION

Since the anti-angiogenic approach is one of the few available targeted strategies against TNBC, both CORM-3 and the new complex 4 should be considered for further research as combination agents with existing anti-angiogenic drugs for more effective treatment of malignant angiogenesis in TNBC.

Design of a potent anticancer lead inspired by natural products from traditional Indian medicine

Among the plant constituents of Clerodendrum colebrookianum Walp., acteoside, martinoside, and osmanthuside β6 interact with ROCK, a drug target for cancer. In this study, aglycone fragments of these plant constituents (caffeic acid, ferulic acid, and p-coumaric acid) along with the homopiperazine ring of fasudil (standard ROCK inhibitor) were used to design hybrid molecules. The designed molecules interact with the key hinge region residue Met156/Met157 of ROCK I/II in a stable manner according to our docking and molecular dynamics simulations. These compounds were synthesized and tested in vitro in SW480, MDA-MB-231, and A-549 cancer cell lines. The most promising compound was chemically optimized to obtain a thiourea analog, 6a (IC₅₀ = 25 µM), which has >3-fold higher antiproliferative activity than fasudil (IC₅₀ = 87 µM) in SW480 cells. Treatment with this molecule also inhibits the migration of colon cancer cells and induces cell apoptosis. Further, SPR experiments suggests that the binding affinity of 6a with ROCK I protein is better than that of fasudil. Hence, the drug-like natural product analog 6a constitutes a highly promising new anticancer lead.Communicated by Ramaswamy H. Sarma.