Pioneering first-in-class FAAH-HDAC inhibitors as potential multitarget neuroprotective agents

Aiming to simultaneously modulate the endocannabinoid system (ECS) functions and the epigenetic machinery, we selected the fatty acid amide hydrolase (FAAH) and histone deacetylase (HDAC) enzymes as desired targets to develop potential neuroprotective multitarget-directed ligands (MTDLs), expecting to achieve an additive or synergistic therapeutic effect in oxidative stress-related conditions. We herein report the design, synthesis, and biological evaluation of the first-in-class FAAH-HDAC multitarget inhibitors. A pharmacophore merging strategy was applied, yielding 1-phenylpyrrole-based compounds 4a-j. The best-performing compounds (4c, 4f, and 4h) were tested for their neuroprotective properties in oxidative stress models, employing 1321N1 human astrocytoma cells and SHSY5 human neuronal cells. In our preliminary studies, compound 4h stood out, showing a balanced nanomolar inhibitory activity against the selected targets and outperforming the standard antioxidant N-acetylcysteine in vitro. Together with 4f, 4h was also able to protect 1321N1 cells from tert-butyl hydroperoxide or glutamate insult. Our study may provide the basis for the development of novel MTDLs targeting the ECS and epigenetic enzymes.

Polypharmacological Approaches for CNS Diseases: Focus on Endocannabinoid Degradation Inhibition

Polypharmacology breaks up the classical paradigm of “one-drug, one target, one disease” electing multitarget compounds as potential therapeutic tools suitable for the treatment of complex diseases, such as metabolic syndrome, psychiatric or degenerative central nervous system (CNS) disorders, and cancer. These diseases often require a combination therapy which may result in positive but also negative synergistic effects. The endocannabinoid system (ECS) is emerging as a particularly attractive therapeutic target in CNS disorders and neurodegenerative diseases including Parkinson’s disease (PD), Alzheimer’s disease (AD), Huntington’s disease (HD), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), stroke, traumatic brain injury (TBI), pain, and epilepsy. ECS is an organized neuromodulatory network, composed by endogenous cannabinoids, cannabinoid receptors type 1 and type 2 (CB₁ and CB₂), and the main catabolic enzymes involved in the endocannabinoid inactivation such as fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL). The multiple connections of the ECS with other signaling pathways in the CNS allows the consideration of the ECS as an optimal source of inspiration in the development of innovative polypharmacological compounds. In this review, we focused our attention on the reported polypharmacological examples in which FAAH and MAGL inhibitors are involved.

Pd-Catalyzed direct C-H arylation of pyrrolo[1,2-a]quinoxalines

An efficient Pd-catalyzed direct C-H arylation of pyrrolo[1,2-a]quinoxalines with aryl iodides is described, providing a selective route toward a series of 1-arylated and 1,3-diarylated pyrrolo[1,2-a]quinoxalines in good yields. This method features a broad substrate scope, good functional group tolerance and gram-scale synthesis. Furthermore, the C3-thiocyanation of the arylated product is also achieved. We believe that these novel aryl-substituted pyrrolo [1,2-a]quinoxalines will have a variety of applications in organic synthesis and medicinal chemistry.

Discovery of Isatin-Based Carbohydrazones as Potential Dual Inhibitors of Fatty Acid Amide Hydrolase and Monoacylglycerol Lipase

Using ligand-based design strategy, a set of isatin-3-carbohydrazones was designed, synthesized and evaluated for dual fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) inhibition properties. Compound 5-chloro-N'-(5-chloro-2-oxoindolin-3-ylidene)-2-hydroxybenzohydrazide (13 b) emerged as a potent MAGL inhibitor with nanomolar activity (IC₅₀ =3.33 nM), while compound 5-chloro-N'-(1-(4-fluorobenzyl)-2-oxoindolin-3-ylidene)-2-hydroxybenzohydrazide (13 j) was the most potent selective FAAH inhibitor (IC₅₀ =37 nM). Compound 5-chloro-N'-(6-chloro-2-oxoindolin-3-ylidene)-2-hydroxybenzohydrazide (13 c) showed dual FAAH-MAGL inhibitory activity with an IC₅₀ of 31 and 29 nM respectively. Enzyme kinetics studies revealed that the isatin-based carbohydrazones are reversible inhibitors for both FAAH and MAGL. Further, blood-brain permeability assay confirmed that the lead compounds (13 b, 13 c, 13 g, 13 m and 13 q) are suitable as CNS candidates. Molecular dynamics simulation studies revealed the putative binding modes and key interactions of lead inhibitors within the enzyme active sites. The lead dual FAAH-MAGL inhibitor 13 c showed significant antioxidant activity and neuroprotection in the cell-based cytotoxicity assay. In summary, the study yielded three potent FAAH/MAGL inhibitor compounds (13 b, 13 c and 13 j) with acceptable pharmacokinetic profile and thus can be considered as promising candidates for treating neurological and mood disorders.

Discovery of novel hit compounds as potential HDAC1 inhibitors: The case of ligand- and structure-based virtual screening

Histone deacetylases (HDACs) as an important family of epigenetic regulatory enzymes are implicated in the onset and progression of carcinomas. As a result, HDAC inhibition has been proven as a compelling strategy for reversing the aberrant epigenetic changes associated with cancer. However, non-selective profile of most developed HDAC inhibitors (HDACIs) leads to the occurrence of various side effects, limiting their clinical utility. This evidence provides a solid ground for ongoing research aimed at identifying isoform-selective inhibitors. Among the isoforms, HDAC1 have particularly gained increased attention as a preferred target for the design of selective HDACIs. Accordingly, in this paper, we have developed a reliable virtual screening process, combining different ligand- and structure-based methods, to identify novel benzamide-based analogs with potential HDAC1 inhibitory activity. For this purpose, a focused library of 736,160 compounds from PubChem database was first compiled based on 80% structural similarity with four known benzamide-based HDAC1 inhibitors, Mocetinostat, Entinostat, Tacedinaline, and Chidamide. Our inclusive in-house 3D-QSAR model, derived from pharmacophore-based alignment, was then employed as a 3D-query to discriminate hits with the highest predicted HDAC1 inhibitory activity. The selected hits were subjected to subsequent structure-based approaches (induced-fit docking (IFD), MM-GBSA calculations and molecular dynamics (MD) simulation) to retrieve potential compounds with the highest binding affinity for HDAC1 active site. Additionally, in silico ADMET properties and PAINS filtration were also considered for selecting an enriched set of the best drug-like molecules. Finally, six top-ranked hit molecules, CID_38265326, CID_56064109, CID_8136932, CID_55802151, CID_133901641 and CID_18150975 were identified to expose the best stability profiles and binding mode in the HDAC1 active site. The IFD and MD results cooperatively confirmed the interactions of the promising selected hits with critical residues within HDAC1 active site. In summary, the presented computational approach can provide a set of guidelines for the further development of improved benzamide-based derivatives targeting HDAC1 isoform.

Selective Fatty Acid Amide Hydrolase Inhibitors as Potential Novel Antiepileptic Agents

Temporal lobe epilepsy is the most common form of epilepsy, and current antiepileptic drugs are ineffective in many patients. The endocannabinoid system has been associated with an on-demand protective response to seizures. Blocking endocannabinoid catabolism would elicit antiepileptic effects, devoid of psychotropic effects. We herein report the discovery of selective anandamide catabolic enzyme fatty acid amide hydrolase (FAAH) inhibitors with promising antiepileptic efficacy, starting from a further investigation of our prototypical inhibitor 2a. When tested in two rodent models of epilepsy, 2a reduced the severity of the pilocarpine-induced status epilepticus and the elongation of the hippocampal maximal dentate activation. Notably, 2a did not affect hippocampal dentate gyrus long-term synaptic plasticity. These data prompted our further endeavor aiming at discovering new antiepileptic agents, developing a new set of FAAH inhibitors (3a-m). Biological studies highlighted 3h and 3m as the best performing analogues to be further investigated. In cell-based studies, using a neuroblastoma cell line, 3h and 3m could reduce the oxinflammation state by decreasing DNA-binding activity of NF-kB p65, devoid of cytotoxic effect. Unwanted cardiac effects were excluded for 3h (Langendorff perfused rat heart). Finally, the new analogue 3h reduced the severity of the pilocarpine-induced status epilepticus as observed for 2a.

Targeting Endocannabinoid Metabolism: an Arrow with Multiple Tips Against Multiple Sclerosis

Multiple sclerosis (MS) is a chronic, immune-mediated disease of the central nervous system. At present, there is no definitive cure, and the few available disease-modifying options display either poor efficacy or life-threatening side effects. There is clear evidence that relapsing-remitting clinical attacks in MS are driven by inflammatory demyelination and that the subsequent disease steps, being irresponsive to immunotherapy, result from neurodegeneration. The endocannabinoid system (ECS) stands halfway between three key pathomechanisms underlying MS, namely inflammation, neurodegeneration and oxidative stress, thus representing a kingpin for the identification of novel therapeutic targets in MS. This review summarizes the current state of the art in the field of endocannabinoid metabolism modulators and their in vivo effects on relevant animal models. We also highlight key molecular underpinnings of their therapeutic efficacy as well as the potential to turn them into promising clinical candidates.

Multitarget Therapeutic Strategies for Alzheimer's Disease: Review on Emerging Target Combinations

Neurodegenerative diseases represent nowadays one of the major health problems. Despite the efforts made to unveil the mechanism leading to neurodegeneration, it is still not entirely clear what triggers this phenomenon and what allows its progression. Nevertheless, it is accepted that neurodegeneration is a consequence of several detrimental processes, such as protein aggregation, oxidative stress, and neuroinflammation, finally resulting in the loss of neuronal functions. Starting from these evidences, there has been a wide search for novel agents able to address more than a single event at the same time, the so-called multitarget-directed ligands (MTDLs). These compounds originated from the combination of different pharmacophoric elements which endowed them with the ability to interfere with different enzymatic and/or receptor systems, or to exert neuroprotective effects by modulating proteins and metal homeostasis. MTDLs have been the focus of the latest strategies to discover a new treatment for Alzheimer's disease (AD), which is considered the most common form of dementia characterized by neurodegeneration and cognitive dysfunctions. This review is aimed at collecting the latest and most interesting target combinations for the treatment of AD, with a detailed discussion on new agents with favorable in vitro properties and on optimized structures that have already been assessed in vivo in animal models of dementia.

NCS-promoted thiocyanation and selenocyanation of pyrrolo[1,2-a]quinoxalines

An efficient NCS-promoted thiocyanation of pyrrolo[1,2-a]quinoxalines with NH₄SCN or KSCN was developed. Moreover, in the presence of KSeCN, the selenocyanation of pyrrolo[1,2-a]quinoxalines was also achieved.

KI/TBHP-promoted [3 + 2] cycloaddition of pyrrolo[1,2-a]quinoxalines and N-arylsulfonylhydrazones

A series of diverse fused [1,2,4]triazolo[3,4-c]quinoxalines was obtained by an efficient KI/TBHP-promoted [3 + 2] cycloaddition of pyrrolo[1,2-a]quinoxalines and N-arylsulfonylhydrazones.

A perspective review on fatty acid amide hydrolase (FAAH) inhibitors as potential therapeutic agents

Fatty acid amide hydrolase (FAAH) is an important enzyme creditworthy of hydrolyzing endocannabinoids and related-amidated signalling lipids, discovery of which has pioneered novel arena of pharmacological canvasses to unwrap its curative potency in various diseased circumstances. It presents contemporary basis for understanding molecules regulating and mediating inflammatory reactions, pain, anxiety, depression, and neurodegeneration. FAAH inhibitors form vital approach for discovery of therapeutic agents that are concerned with local elevation of endocannabinoids under certain stimuli, debarring adverse/unwanted secondary effects from global activation of cannabinoid receptors by exogenous cannabimimetics. During past decades, several molecules with excellent potency developed through tailor-made approaches entered into clinical trials, but none could reach market. Hence, hunt for novel, non-toxic and selective FAAH inhibitors are on horizon. This review summarizes present perception on FAAH in conjunction with its structure, mechanism of catalysis and biological functions. It also foregrounds recent development of molecules belonging to diverse chemical classes as potential FAAH inhibitors bobbing up from in-depth chemical, mechanistic and computational studies published since 2015-November 2019, focusing on their potency. This review will assist readers to obtain rationale on FAAH as potential target for addressing various disease conditions, acquiring significant knowledge on recently established inhibitor scaffolds and their development potentials. New technologies including MD-MM simulations and 3D-QSAR studies allow mechanistic characterization of enzyme. Assessment of in-vitro and in-vivo efficacy of existing FAAH inhibitors will facilitate researchers to design novel ligands utilizing modern drug design methods. The discussions will also impose precaution in decision making process, quashing possibility of late stage failure.

First dual AK/GSK-3β inhibitors endowed with antioxidant properties as multifunctional, potential neuroprotective agents

The manuscript deals with the design, synthesis and biological evaluation of novel benzoxazinone-based and indole-based compounds as multifunctional neuroprotective agents. These compounds inhibit human adenosine kinase (hAK) and human glycogen synthase kinase 3 beta (hGSK-3β) enzymes. Computational analysis based on a molecular docking approach underlined the potential structural requirements for simultaneously targeting both proteins' allosteric sites. In silico hints drove the synthesis of appropriately decorated benzoxazinones and indoles (5a-s, and 6a-c) and biochemical analysis revealed their behavior as allosteric inhibitors of hGSK-3β. For both our hit 4 and the best compounds of the series (5c,l and 6b) the potential antioxidant profile was assessed in human neuroblastoma cell lines (IMR 32, undifferentiated and neuronal differentiated), by evaluating the protective effect of selected compounds against H₂O₂ cytotoxicity and reactive oxygen species (ROS) production. Results showed a strong efficacy of the tested compounds, even at the lower doses, in counteracting the induced oxidative stress (50 μM of H₂O₂) and in preventing ROS formation. In addition, the tested compounds did not show any cytotoxic effect determined by the LDH release, at the concentration range analyzed (from 0.1 to 50 μM). This study allowed the identification of compound 5l, as the first dual hAK/hGSK-3β inhibitor reported to date. Compound 5l, which behaves as an effective antioxidant, holds promise for the development of new series of potential therapeutic agents for the treatment of neurodegenerative diseases characterized by an innovative pharmacological profile.