Selective Acetamidine-Based Nitric Oxide Synthase Inhibitors: Synthesis, Docking, and Biological Studies

Development of novel nitric oxide production inhibitors based on the 7H-pyrrolo[2,3-d]pyrimidine scaffold

Nitric oxide (NO), the smallest signaling molecule known, can be excessively produced by overexpressed inducible nitric oxide synthase (iNOS), and eventually leads to multiple inflammatory related diseases. Thus, reducing the overexpression of NO represents as very potential anti-inflammatory strategy. In current study, a series of compounds were designed and synthesized based on the hybridization of 7H-pyrrolo[2,3-d]pyrimidine and cinnamamide fragments in order to develop novel NO production inhibitors. Among them, compound S2h displayed a vigorous inhibitory activity on NO production with an IC50 value of 3.21 ± 0.67 µM, which was much lower than that of the positive control Nω-nitro-L-arginine (L-NNA, IC50 = 28.36 ± 3.13 µM). Due to its obeying Lipinski's and Veber's rules that guarantee compounds with good oral bioavailability, S2h effectively suppressed the paw swelling in carrageenan-induced mice. Additionally, compound S2h formed clear interactions with iNOS protein according to the docking analysis. Therefore, compounds S2h is a promising lead compound for further development of potent iNOS inhibitors or anti-inflammatory agents.

Neuronal Nitric Oxide Synthase and Post-Translational Modifications in the Development of Central Nervous System Diseases: Implications and Regulation

In the Central Nervous System (CNS), Nitric Oxide (NO) is mainly biosynthesized by neuronal Nitric Oxide Synthase (nNOS). The dysregulated activation of nNOS in neurons is critical in the development of different conditions affecting the CNS. The excessive production of NO by nNOS is responsible for a number of proteins' post-translational modifications (PTMs), which can lead to aberrant biochemical pathways, impairing CNS functions. In this review, we briefly revise the main implications of dysregulated nNOS in the progression of the most prevalent CNS neurodegenerative disorders, i.e., Alzheimer's disease (AD) and Parkinson's disease, as well as in the development of neuronal disorders. Moreover, a specific focus on compounds able to modulate nNOS activity as promising therapeutics to tackle different neuronal diseases is presented.

Alkaloids from Lepidium meyenii (Maca), structural revision of macaridine and UPLC-MS/MS feature-based molecular networking

Lepidium meyenii Walp., known as Peruvian ginseng, is widely used in ethnomedicine. To date, L. meyenii is cultivated worldwide at high-altitude and is commonly used as a food supplement. However, its medicinal value is still controversial and its mechanism of action remains unknown, due to limited knowledge about the phytochemical constituents of this plant species. In this study, a multidisciplinary approach comprising conventional NMR- and HRMS-based structure elucidation, quantum mechanical calculation of NMR chemical shifts and UPLC-MS/MS feature-based molecular networking was applied to analyse the phytochemical profile of L. meyenii. In the current work, three previously undescribed imidazole alkaloids were identified using extensive spectroscopic techniques (HRMS, NMR), for which the names lepidiline E, F and G were adopted. In addition, two amidine alkaloids were reported, representing an undescribed class of alkaloids in L. meyenii, and 1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid, a well-known β-carboline alkaloid, was also isolated from L. meyenii for the first time. Molecular networks of imidazole, amidine and β-carboline alkaloids in L. meyenii were constructed by the Global Natural Products Social Molecular Networking (GNPS) web platform, resulting in the tentative identification of three undescribed analogues. In addition, the structure of a previously reported compound named 'macaridine' was revised as macapyrrolin C based on density functional theory (DFT) calculations and comprehensive comparison of NMR data.

Inhibition of iNOS by Benzimidazole Derivatives: Synthesis, Docking, and Biological Evaluations

BACKGROUND

Inducible nitric Oxide Synthase (iNOS) plays a key role in the progression of inflammatory diseases by accelerating the production of NO, which makes it an intriguing target to treat inflammation in complex diseases. Therefore, the search is on to develop molecules as selective iNOS inhibitors.

OBJECTIVE

The present work was aimed to design, synthesize and evaluate benzimidazole-coumarin coupled molecules as anti-iNOS agents through in silico and pharmacological studies.

METHODS

A critical study of literature reports on iNOS inhibitors led to the selection of a (un)substituted coumarin nucleus, 2-aminobenzimidazole, and a 4-atom linker as important structural components for iNOS inhibition. Two series of compounds (7-16 and 17-26) were designed and synthesized by coupling these components. The compounds were subjected to docking using iNOS (1QW4) and nNOS (1QW6) as targets. All compounds were evaluated for NO and iNOS inhibitory activities in vitro. The selected compound was finally evaluated for anti-inflammatory activity in vivo using the carrageenan-induced rat paw edema model.

RESULTS

All compounds showed moderate to good inhibition of NO and iNOS in vitro. Compound 12 was the most potent inhibitor of NO and iNOS. Hence, it was evaluated in vivo for toxicity and anti-inflammatory activity. It was found to be safe in acute toxicity studies, and effective in reducing the rat paw edema significantly. Its anti-inflammatory behaviour was similar to that of aminoguanidine, which is a selective iNOS inhibitor.

CONCLUSION

The newly synthesized benzimidazole-coumarin hybrids may serve as potential leads for the development of novel anti-iNOS agents.

Artificial Intelligence, Big Data and Machine Learning Approaches in Precision Medicine & Drug Discovery

Artificial Intelligence revolutionizes the drug development process that can quickly identify potential biologically active compounds from millions of candidate within a short period. The present review is an overview based on some applications of Machine Learning based tools, such as GOLD, Deep PVP, LIB SVM, etc. and the algorithms involved such as support vector machine (SVM), random forest (RF), decision tree and Artificial Neural Network (ANN), etc. at various stages of drug designing and development. These techniques can be employed in SNP discoveries, drug repurposing, ligand-based drug design (LBDD), Ligand-based Virtual Screening (LBVS) and Structure- based Virtual Screening (SBVS), Lead identification, quantitative structure-activity relationship (QSAR) modeling, and ADMET analysis. It is demonstrated that SVM exhibited better performance in indicating that the classification model will have great applications on human intestinal absorption (HIA) predictions. Successful cases have been reported which demonstrate the efficiency of SVM and RF models in identifying JFD00950 as a novel compound targeting against a colon cancer cell line, DLD-1, by inhibition of FEN1 cytotoxic and cleavage activity. Furthermore, a QSAR model was also used to predict flavonoid inhibitory effects on AR activity as a potent treatment for diabetes mellitus (DM), using ANN. Hence, in the era of big data, ML approaches have been evolved as a powerful and efficient way to deal with the huge amounts of generated data from modern drug discovery to model small-molecule drugs, gene biomarkers and identifying the novel drug targets for various diseases.

In Silico Study Examining New Phenylpropanoids Targets with Antidepressant Activity

BACKGROUND

Natural products, such as phenylpropanoids, which are found in essential oils derived from aromatic plants, have been explored during non-clinical psychopharmacology studies, to discover new molecules with relevant pharmacological activities in the central nervous system, especially antidepressant and anxiolytic activities. Major depressive disorder is a highly debilitating psychiatric disorder and is considered to be a disabling public health problem, worldwide, as a primary factor associated with suicide. Current clinically administered antidepressants have late-onset therapeutic actions, are associated with several side effects, and clinical studies have reported that some patients do not respond well to treatment or reach complete remission.

OBJECTIVE

To review important new targets for antidepressant activity and to select phenylpropanoids with antidepressant activity, using Molegro Virtual Docker and Ossis Data Warris, and to verify substances with more promising antidepressant activity.

RESULTS AND CONCLUSION

An in silico molecular modeling study, based on homology, was conducted to determine the three-dimensional structure of the 5-hydroxytryptamine 2A receptor (5- HT2AR), then molecular docking studies were performed and the predisposition for cytotoxicity risk among identified molecules was examined. A model for 5-HT2AR homology, with satisfactory results, was obtained indicating the good stereochemical quality of the model. The phenylpropanoid 4-allyl-2,6-dimethoxyphenol showed the lowest binding energy for 5-HT2AR, with results relevant to the L-arginine/nitric oxide (NO)/cGMP pathway, and showed no toxicity within the parameters of mutagenicity, carcinogenicity, reproductive system toxicity, and skin-tissue irritability, when evaluated in silico; therefore, this molecule can be considered promising for the investigation of antidepressant activity.

A Novel Prodrug of a nNOS Inhibitor with Improved Pharmacokinetic Potential

Under different pathological conditions, aberrant induction of neuronal nitric oxide synthase (nNOS) generates overproduction of NO that can cause irreversible cell damage. The aim of this study was to develop an amidoxime prodrug of a potent nNOS inhibitor, the benzhydryl acetamidine. We synthesized the benzhydryl acetamidoxime, which was evaluated in vitro to ascertain the potential NOS inhibitory activity, as well as conducting bioconversion into the parent acetamidine. The prodrug was also profiled for in vitro physicochemical properties, by determining the lipophilicity, passive permeation through the human gastrointestinal tract and across the blood-brain barrier by PAMPA, and chemical, enzymatic, and plasma stability. The obtained data demonstrate that the amidoxime prodrug shows an improved pharmacokinetic profile with respect to the acetamidine nNOS inhibitor, thus suggesting that it could be a promising lead compound to treat all those pathological conditions in which nNOS activity is dysregulated.

Antiglioma Activity of Aryl and Amido-Aryl Acetamidine Derivatives Targeting iNOS: Synthesis and Biological Evaluation

Nitric oxide is an important inflammation mediator with a recognized role in the development of different cancers. Gliomas are primary tumors of the central nervous system with poor prognosis, and the expression of the inducible nitric oxide synthase correlates with the degree of malignancy, changes in vascular reactivity, and neo-angiogenesis. Therefore, targeting the nitric oxide biosynthesis appears as a potential strategy to impair glioma progression. In the present work a set of aryl and amido-aryl acetamidine derivatives were synthesized to obtain new potent and selective inducible nitric oxide synthase inhibitors with improved physicochemical parameters with respect to the previously published molecules. Compound 17 emerged as the most promising inhibitor and was evaluated on C6 rat glioma cell line, showing antiproliferative effects and high selectivity over astrocytes.

Acetamidine-Based iNOS Inhibitors as Molecular Tools to Counteract Inflammation in BV2 Microglial Cells

Neurodegenerative diseases are associated with increased levels of nitric oxide (NO) mainly produced by microglial cells through inducible nitric oxide synthase (iNOS) whose expression is induced by inflammatory stimuli. NO can both exert cytotoxic functions and induce a metabolic switch by inhibiting oxidative phosphorylation and upregulating glycolytic flux. Here, we investigated whether two newly synthesized acetamidine based iNOS inhibitors, namely CM292 and CM544, could inhibit lipopolysaccharide (LPS)-induced BV2 microglial cell activation, focusing on both inflammatory and metabolic profiles. We found that CM292 and CM544, without affecting iNOS protein expression, reduced NO production and reverted LPS-induced inflammatory and cytotoxic response. Furthermore, in the presence of the inflammatory stimulus, both the inhibitors increased the expression of glycolytic enzymes. In particular, CM292 significantly reduced nuclear accumulation of pyruvate kinase M2, increased mitochondrial membrane potential and oxygen consumption rate, and augmented the expression of pyruvate dehydrogenase, pointing to a metabolic switch toward oxidative phosphorylation. These data confirm the role played by NO in the connection between cell bioenergetics profile and inflammation, and suggest the potential usefulness of iNOS inhibitors in redirecting microglia from detrimental to pro-regenerative phenotype.

Targeting iNOS As a Valuable Strategy for the Therapy of Glioma

Gliomas are the most prevalent primary tumors of the brain and spinal cord. Histologically, they share features of normal glial cells, but whether gliomas originate from normal glial cells, glial or neural precursors, stem cells, or other cell types remains a topic of investigation. The enhanced expression of inducible nitric oxide synthase (iNOS) has been reported as a hallmark of chemoresistance in gliomas, and several lines of evidence have reported that a decreased proliferation of glioma cells could be related to the selective inhibition of iNOS. This review aims to summarize the current understanding of iNOS expression and activity modulation in the regulation of glioma pathogenesis, along with compounds that could act as therapeutic agents against glioma.

Druggability profile of stilbene-derived PPAR agonists: determination of physicochemical properties and PAMPA study

PPAR agonists represent a new therapeutic opportunity for the prevention and treatment of neurodegenerative disorders, but their pharmacological success depends on favourable pharmacokinetic properties and capability to cross the BBB. In this study, we assayed some PPAR agonists previously synthesized by us for their physicochemical properties, with particular references to lipophilicity, solubility and permeability profiles, using the PAMPA. Although tested compounds showed high lipophilicity and low aqueous solubility, the results revealed a good overall druggability profile, encouraging further studies in the field of neurodegenerative diseases.

Inducible nitric oxide synthase inhibitors: A comprehensive update

Inducible nitric oxide synthase (iNOS), which is expressed in response to bacterial/proinflammatory stimuli, generates nitric oxide (NO) that provides cytoprotection. Overexpression of iNOS increases the levels of NO, and this increased NO level is implicated in pathophysiology of complex multifactorial diseases like Parkinson's disease, Alzheimer's disease, multiple sclerosis, rheumatoid arthritis, and inflammatory bowel disease. Selective inhibition of iNOS is an effective approach in treatment of such complex diseases. l-Arginine, being a substrate for iNOS, is the natural lead to develop iNOS inhibitors. More than 200 research reports on development of nitric oxide synthase inhibitors by different research groups across the globe have appeared in literature so far. The first review on iNOS, in 2002, discussed the iNOS inhibitors under two classes that is, amino acid and non-amino acid derivatives. Other review articles discussing specific chemical classes of iNOS inhibitors also appeared during last decade. In the present review, all reports on both natural and synthetic iNOS inhibitors, published 2002 onwards, are studied, classified, and discussed to provide comprehensive information on iNOS inhibitors. The synthetic inhibitors are broadly classified into two categories that is, arginine and non-arginine analogs. The latter are further classified into amidines, five- or six-membered heterocyclics, fused cyclics, steroidal type, and chalcones analogs. Structures of the most/significantly potent compounds from each report are provided to know the functional groups important for incurring iNOS inhibitory activity and selectivity. This review is aimed to provide a comprehensive view to the medicinal chemists for rational designing of novel and potent iNOS inhibitors.

The Selective Acetamidine-Based iNOS Inhibitor CM544 Reduces Glioma Cell Proliferation by Enhancing PARP-1 Cleavage In Vitro

Gliomas are the most aggressive adult primary brain tumors. Expression of inducible Nitric Oxide Synthase has been reported as a hallmark of chemoresistance in gliomas and several studies have reported that inhibition of inducible Nitric Oxide Synthase could be related to a decreased proliferation of glioma cells. The present work was to analyze the molecular effects of the acetamidine derivative compound 39 (formally CM544, N-(3-{[(1-iminioethyl)amino]methyl}benzyl) prolinamide dihydrochloride), a newly synthetized iNOS inhibitor, in a C6 rat glioma cell model. There is evidence of CM544 selective binding to the iNOS, an event that triggers the accumulation of ROS/RNS, the expression of Nrf-2 and the phosphorylation of MAPKs after 3 h of treatment. In the long run, CM544 leads to the dephosphorylation of p38 and to a massive cleavage of PARP-1, confirming the block of C6 rat glioma cell proliferation in the G1/S checkpoint and the occurrence of necrotic cell death.

Involvement of NOS2 Activity on Human Glioma Cell Growth, Clonogenic Potential, and Neurosphere Generation

Aberrant nitric oxide synthase 2 (NOS2) expression has been suggested as an interesting therapeutic target that is being implicated as a component of the molecular profile of several human malignant tumors, including glioblastoma, which is the most aggressive brain tumor with limited therapeutic options and poor prognosis. The aim of the present work was to evaluate the effect of 1400W, a specific NOS2 inhibitor, on human glioma cells in terms of clonogenic potential, proliferation, migration rate, and neurosphere generation ability. NOS2 expression was determined by Western blotting. Nitric oxide (NO) production was measured through nitrite level determination. The trypan blue exclusion test and the plate colony formation assay were performed to evaluate cell proliferation and clonogenic potential. Cell proliferation and migration ability was assessed by the in vitro wound-healing assay. Neurosphere generation in a specific stemcell medium was investigated. NOS2 was confirmed to be expressed in both the glioma cell line and a human glioma primary culture, and overexpressed in relative derived neurospheres. Experiments that aimed to evaluate the influence of 1400W on U-87 MG, T98G (glioblastoma cell lines) and primary glioma cells sustained the crucial role played by NOS2 in proliferation, colony formation, migration, and neurosphere generation, thus supporting the emerging relevance of a NOS2/NO system as a prognostic factor for glioma malignancy and recurrence.

Discovery of N-{3-[(ethanimidoylamino)methyl]benzyl}-l-prolinamide dihydrochloride: A new potent and selective inhibitor of the inducible nitric oxide synthase as a promising agent for the therapy of malignant glioma

In mammalian cells, aberrant iNOS induction may have detrimental consequences, and seems to be involved in the proliferation and progression of different tumors, such as malignant gliomas. Therefore, selective inhibition of iNOS could represent a feasible therapeutic strategy to treat these conditions. In this context, we have previously disclosed new acetamidines able to inhibit iNOS with a very high selectivity profile over eNOS or nNOS. Here we report the synthesis of a new series of compounds structurally related to the leading scaffold of N-[(3-aminomethyl)benzyl] acetamidine (1400 W), together with their in vitro activity and selectivity. Compound 39 emerged as the most promising molecule of this series, and it was ex vivo evaluated on isolated and perfused resistance arteries, confirming a high selectivity toward iNOS inhibition. Moreover, C6 rat glioma cell lines biological response to 39 was investigated, and preliminary MTT assay showed a significant decrease in cell metabolic activity of C6 rat glioma cells. Finally, results of a docking study shed light on the binding mode of 39 into NOS catalytic site.

Thiadiazoline- and Pyrazoline-Based Carboxamides and Carbothioamides: Synthesis and Inhibition against Nitric Oxide Synthase

Two new families of pyrazoline and thiadiazoline heterocycles have been developed. Their inhibitory activities against two different isoforms of nitric oxide synthase (inducible and neuronal NOS) are reported. The novel derivatives were synthesized combining the arylthiadiazoline or arylpyrazoline skeleton and a carboxamide or carbothioamide moiety, used as starting material ethyl 2-nitrobenzoates or substituted nitrobenzaldehydes, respectively. The structure-activity relationships of final molecules are discussed in terms of the R1 radical effects in the aromatic ring, the Y atom in the heterocyclic system, the X heteroatom in the main chain, and the R2 substituent in the carboxamide or carbothioamide rest. In general, thiadiazolines (5a–e) inhibit preferentially the neuronal isoform; among them, 5a is the best nNOS inhibitor (74.11% at 1 mM, IC50 = 420 μM). In contrast, pyrazolines (6a–r) behave better as iNOS than nNOS inhibitors, 6m being the best molecule of this series (76.86% at 1 mM of iNOS inhibition, IC50 = 130 μM) and the most potent of all tested compounds.

The Positive Regulation of eNOS Signaling by PPAR Agonists in Cardiovascular Diseases

Increasing evidence shows that activation of peroxisome proliferator-activated receptors (PPARs) plays an essential role in the regulation of vascular endothelial function through a range of mechanisms, including non-metabolic. Among these, the PPAR-mediated activation of endothelial nitric oxide synthase (eNOS) appears to be of considerable importance. The regulated and sustained bioavailability of nitric oxide (NO) in the endothelium is essential to avoid the development of cardiovascular diseases such as hypertension or atherosclerosis. Therefore, a deeper understanding of the different effects of specific PPAR ligands on NO bioavailability could be useful in the development of novel or multi-targeted PPAR agonists. In this review, we report the most meaningful and up-to-date in vitro and in vivo studies of the regulation of NO production performed by different PPAR agonists. Insights into the molecular mechanisms of PPAR-mediated eNOS activation are also provided. Although findings from animal studies in which the activation of PPARα, PPARβ/δ, or PPARγ have provided clear vasoprotective effects have been promising, several benefits from PPAR agonists are offset by unwanted outcomes. Therefore, new insights could be useful in the development of tissue-targeted PPAR agonists with more tolerable side effects to improve treatment options for cardiovascular diseases.

Indazole, Pyrazole, and Oxazole Derivatives Targeting Nitric Oxide Synthases and Carbonic Anhydrases

Nitric oxide (NO) is an essential endogenous mediator with a physiological role in the central nervous system as neurotransmitter and neuromodulator. A growing number of studies have demonstrated that abnormal nitrergic signaling is a crucial event in the development of neurodegeneration. In particular, the uncontrolled production of NO by neuronal nitric oxide synthase (nNOS) is observed in several neurodegenerative diseases. Moreover, it is well recognized that specific isoforms of human carbonic anhydrase (hCA) physiologically modulate crucial pathways of signal processing and that low expression of CA affects cognition, leading to mental retardation, Alzheimer's disease, and aging-related cognitive impairments. In light of this, dual agents that are able to target both NOS (inhibition) and CA (activation) could be useful drug candidates for the treatment of Alzheimer's disease, aging, and other neurodegenerative diseases. In the present work, we show the design, synthesis, and in vitro biological evaluation of new nitrogen-based heterocyclic compounds. Among the tested molecules, 2-amino-3-(4-hydroxyphenyl)-N-(1H-indazol-5-yl)propanamide hydrochloride (10 b) was revealed to be a potent dual agent, able to act as a selective nNOS inhibitor and activator of the hCA I isoform.

Screening of NOS activity and selectivity of newly synthesized acetamidines using RP-HPLC

Nitric Oxide Synthase (NOS) inhibitors could play a powerful role in inflammatory and neurodegenerative diseases. In this work, novel acetamidine derivatives of NOS were synthesized and the inhibitor activity was evalued. To screen the activity and selectivity, the l-citrulline residue, after the enzymatic NOS assay, was derivatized with o-phthaldialdehyde/N-acetyl cysteine (OPA/NAC) and then evaluated by RP-HPLC method with fluorescence detection. All compounds did not affect the activity of endothelial and neuronal isoforms, while nine of them possessed a percentage of iNOS activity at 10μM lower than 50%, and were selected for IC50 evaluation. Among them, a compound emerged as a very potent (IC50 of 53nM) and selective iNOS inhibitor.