Xylazine as an emerging new psychoactive substance; focuses on both 5-HT7 and κ-opioid receptors' molecular interactions and isosteric replacement

Xylazine, traditionally used as a veterinary sedative, has recently emerged as a new psychoactive substance, being typically ingested in combination with fentanyl derivatives and hence raising significant public health concerns. Despite its increasing prevalence, little is known about its molecular interactions with human neuroreceptors, specifically the serotonin 7 (5-HT7R) and kappa-opioid (KOR) receptors, which play critical roles in mood regulation, consciousness and nociception. Hence, the binding affinity and molecular interactions of xylazine with both 5-HT7R and KOR through docking simulations and molecular dynamics calculations were investigated. These computational approaches revealed critical insights into receptor binding motifs and highlighted structural modifications that could enhance receptor affinity. The isosteric replacements within the xylazine structure to improve its binding efficacy were assessed, demonstrating that minimal structural modifications can potentiate its interaction with 5-HT7R and KOR. These findings may well advance our understanding of xylazine's mechanism of action, possibly contributing to identifying suitable treatment/management approaches in treating xylazine-related overdoses.

Optimization of 4-amino-pyridazin-3(2H)-one as a valid core scaffold for FABP4 inhibitors

Current clinical research suggests that fatty acid-binding protein 4 inhibitors (FABP4is), which are of biological and therapeutic interest, may show potential in treating cancer and other illnesses. We sought to uncover new structures through the optimization of the previously reported 4-amino and 4-ureido pyridazinone-based series of FABP4is as part of a larger research effort to create more potent FABP4 inhibitors. This led to the identification of 14e as the most potent analog with IC50  = 1.57 μM, which is lower than the IC50 of the positive control. Advanced modeling investigations and in silico absorption, distribution, metabolism, and excretion - toxicity calculations suggested that 14e represents a potential candidate for in vivo studies such as FABP4i.

Designing of new tetrahydro-β-carboline-based ABCG2 inhibitors using 3D-QSAR, molecular docking, and DFT tools

Human ATP-binding cassette superfamily G member 2 (ABCG2) protein is a member of the ABC transporter family, which is responsible for multidrug resistance (MDR) in cancerous cells. MDR reduces the effectiveness of chemotherapy in breast cancer, which is one of the leading causes of death in women globally. MDR in cancer cells is one of the immediate signs of progression of resistance; thus, various anticancer drugs can be designed. To reduce MDR, we utilized the tetrahydro-β-carboline (THβC) compound library. We accomplished a three-dimensional quantitative structure-activity relationship (3D-QSAR), scaffold hopping to design a new library of compounds of THβC, and further molecular docking, induced-fit docking (IFD), molecular mechanics energies combined with generalized born and surface area continuum solvation (MM-GBSA), drug-like features, ADMET properties, and density functional theory (DFT) studies were performed. From these studies, the best 3D-QSAR model (r2 = 0.99, q2 = 0.92) was found, and the necessity of electrostatic, steric, and hydrophobic field effects were determined that could modulate bioactivity. Moreover, based on electrostatic, steric, and hydrophobic field notations, new THβC derivatives (3409) were designed. These findings might provide new insight for researchers to perform in vitro and in vivo studies for better antagonists against MDR in treating breast cancer.Communicated by Ramaswamy H. Sarma.

Ligand Growing Experiments Suggested 4-amino and 4-ureido pyridazin-3(2H)-one as Novel Scaffold for FABP4 Inhibition

Fatty acid binding protein (FABP4) inhibitors are of synthetic and therapeutic interest and ongoing clinical studies indicate that they may be a promise for the treatment of cancer, as well as other diseases. As part of a broader research effort to develop more effective FABP4 inhibitors, we sought to identify new structures through a two-step computing assisted molecular design based on the established scaffold of a co-crystallized ligand. Novel and potent FABP4 inhibitors have been developed using this approach and herein we report the synthesis, biological evaluation and molecular docking of the 4-amino and 4-ureido pyridazinone-based series.

Novel Tyrosine Kinase Inhibitors to Target Chronic Myeloid Leukemia

This paper reports on a novel series of tyrosine kinase inhibitors (TKIs) potentially useful for the treatment of chronic myeloid leukemia (CML). The newly designed and synthesized compounds are structurally related to nilotinib (NIL), a second-generation oral TKI, and to a series of imatinib (IM)-based TKIs, previously reported by our research group, these latter characterized by a hybrid structure between TKIs and heme oxygenase-1 (HO-1) inhibitors. The enzyme HO-1 was selected as an additional target since it is overexpressed in many cases of drug resistance, including CML. The new derivatives 1a–j correctly tackle the chimeric protein BCR-ABL. Therefore, the inhibition of TK was comparable to or higher than NIL and IM for many novel compounds, while most of the new analogs showed only moderate potency against HO-1. Molecular docking studies revealed insights into the binding mode with BCR-ABL and HO-1, providing a structural explanation for the differential activity. Cytotoxicity on K562 CML cells, both NIL-sensitive and -resistant, was evaluated. Notably, some new compounds strongly reduced the viability of K562 sensitive cells.

From Far West to East: Joining the Molecular Architecture of Imidazole-like Ligands in HO-1 Complexes

HO-1 overexpression has been reported in several cases/types of human malignancies. Unfortunately, poor clinical outcomes are reported in most of these cases, and the inhibition of HO-1 is considered a valuable and proven anticancer approach. To identify novel hit compounds suitable as HO-1 inhibitors, we report here a fragment-based approach where ligand joining experiments were used. The two most important parts of the classical structure of the HO-1 inhibitors were used as a starting point, and 1000 novel compounds were generated and then virtually evaluated by structure and ligand-based approaches. The joining experiments led us to a novel series of indole-based compounds. A synthetic pathway for eight selected molecules was designed, and the compounds were synthesized. The biological activity revealed that some molecules reach the micromolar activity, whereas molecule 4d inhibits the HO-1 with an IC₅₀ of 1.03 μM. This study suggested that our joining approach was successful, and a novel hit compound was generated. These results are ongoing for further development.

Deep scaffold hopping with multimodal transformer neural networks

Scaffold hopping is a central task of modern medicinal chemistry for rational drug design, which aims to design molecules of novel scaffolds sharing similar target biological activities toward known hit molecules. Traditionally, scaffolding hopping depends on searching databases of available compounds that can't exploit vast chemical space. In this study, we have re-formulated this task as a supervised molecule-to-molecule translation to generate hopped molecules novel in 2D structure but similar in 3D structure, as inspired by the fact that candidate compounds bind with their targets through 3D conformations. To efficiently train the model, we curated over 50 thousand pairs of molecules with increased bioactivity, similar 3D structure, but different 2D structure from public bioactivity database, which spanned 40 kinases commonly investigated by medicinal chemists. Moreover, we have designed a multimodal molecular transformer architecture by integrating molecular 3D conformer through a spatial graph neural network and protein sequence information through Transformer. The trained DeepHop model was shown able to generate around 70% molecules having improved bioactivity together with high 3D similarity but low 2D scaffold similarity to the template molecules. This ratio was 1.9 times higher than other state-of-the-art deep learning methods and rule- and virtual screening-based methods. Furthermore, we demonstrated that the model could generalize to new target proteins through fine-tuning with a small set of active compounds. Case studies have also shown the advantages and usefulness of DeepHop in practical scaffold hopping scenarios.

Growing the molecular architecture of imidazole-like ligands in HO-1 complexes

Up-regulation of HO-1 had been frequently reported in different cases and types of human malignancies. Since poor clinical outcomes are reported in these cases, this enzyme's inhibition is considered a valuable and proven anticancer approach. To identify novel HO-1 inhibitors suitable for drug development, we report a structure-guided fragment-based approach to identify new lead compounds. Different parts of the selected molecules were analyzed, and the different series of novel compounds were virtually evaluated. The growing experiments of the classical HO-1 inhibitors structure led us to different hit-compounds. A synthetic pathway for six selected molecules was designed, and the compounds were synthesized. The biological activity revealed that molecules 10 and 12 inhibit the HO-1 activity with an IC₅₀ of 1.01 and 0.90 μM, respectively. This study suggested that our growing approach was successful, and these results are ongoing for further development.

Discovery of Novel Acetamide-Based Heme Oxygenase-1 Inhibitors with Potent In Vitro Antiproliferative Activity

Heme oxygenase-1 (HO-1) promotes heme catabolism exercising cytoprotective roles in normal and cancer cells. Herein, we report the design, synthesis, molecular modeling, and biological evaluation of novel HO-1 inhibitors. Specifically, an amide linker in the central spacer and an imidazole were fixed, and the hydrophobic moiety required by the pharmacophore was largely modified. In many tumors, overexpression of HO-1 correlates with poor prognosis and chemoresistance, suggesting the inhibition of HO-1 as a possible antitumor strategy. Accordingly, compounds 7i and 7l-p emerged for their potency against HO-1 and were investigated for their anticancer activity against prostate (DU145), lung (A549), and glioblastoma (U87MG, A172) cancer cells. The selected compounds showed the best activity toward U87MG cells. Compound 7l was further investigated for its in-cell enzymatic HO-1 activity, expression levels, and effects on cell invasion and vascular endothelial growth factor (VEGF) extracellular release. The obtained data suggest that 7l can reduce cell invasivity acting through modulation of HO-1 expression.

Machine learning vs. field 3D-QSAR models for serotonin 2A receptor psychoactive substances identification

Serotonergic psychedelics, substances exerting their effects primarily through the serotonin 2A receptor (5HT2AR), continue to comprise a substantial portion of reported new psychoactive substances (NPS). In this paper five quantitative structure-activity relationship (QSAR) models for predicting the affinity of 5-HT2AR ligands have been developed. The resulting models, exploiting the accessibility of the QSAR equations, generate a useful tool for the investigation and identification of unclassified molecules. The models have been built using a set of 375 molecules using Forge software, and the quality was confirmed by statistical analysis, resulting in effective tools with respect to their predictive and descriptive capabilities. The best performing algorithm among the machine learning approaches and the classical field 3D-QSAR model were then combined to produce a consensus model and were exploited, together with a pharmacophorefilter, to explore the 5-HT2AR activity of 523 105 natural products, to classify a set of recently reported 5-HT2AR NPS and to design new potential active molecules. The findings of this study should facilitate the identification and classification of emerging 5-HT2AR ligands including NPS.

Synthesis, in vitro and in silico studies of HO-1 inducers and lung antifibrotic agents

Aim: Dimethyl fumarate (DMF) analogs were synthesized to obtain inducers of HO-1 and antifibrotic agents. Methods: HO-1 expression levels were measured on lung fibroblasts (MRC5). NMR and docking studies were performed. Heme oxygenase activity, gene levels and protein expression have been measured for the most active compound 1a. Collagen production by fibroblast after exposure to TGF-β was measured. Results: Compound 1a showed to be a strong HO-1 inducer. Its activity seems to be mediated by activation of nuclear factor erythroid 2 related factor 2 (Nrf2). TGF-β-induced collagen production was significantly decreased on MRC5, pretreated with DMF or 1a. DMF and 1a have a high potential for treatment of lung fibrotic injuries.

Chromatograpic resolution of phenylethanolic-azole racemic compounds highlighted stereoselective inhibition of heme oxygenase-1 by (R)-enantiomers

Heme oxygenase-1 (HO-1) has been recognized as extensively involved in the development and aggravation of cancer, cell propagation and at in the mechanism of chemoresistance development. Low micromolar HO-1 inhibitors selective towards HO-2 has been recently reported, wherein the azole core and the hydrophobic residues are linked through a phenylethanolic spacer bearing a chiral center. Since less information are known about the stereoselective requirements for HO-1 inhibition, here we report the enantiomeric resolution of 1-(biphenyl-3-yl)-2-(1H-imidazol-1-yl)ethanol (1) and 1-[4-[(4-bromobenzyl)oxy]phenyl]-2-(1H-imidazol-1-yl)ethanol (2), two among the most potent and selective HO-1 inhibitors known thus far when tested as racemates. The absolute configuration was established for 1 by a combination of experimental and in silico derived electronic circular dichroism spectra, while docking approaches were useful in the case of compound 2. Biological evaluation of pure enantiomers highlighted higher HO-1 inhibitory activity of (R)-enantiomers. Docking studies demonstrated the importance of hydrogen bond interaction, more pronounced for the (R)-enantiomers, with a consensus water molecule within the binding pocket. The present study demonstrates that differences in three-dimensional structure amongst compounds 1 and 2 enantiomers affect significantly the selectivity of these HO-1 inhibitors.

Non-competitive heme oxygenase-1 activity inhibitor reduces non-small cell lung cancer glutathione content and regulates cell proliferation

Non-small cell lung cancer (NSCLC) remains the leading cause of cancer-related death mainly due to its high metastatic rate. Impairment of redox homeostasis mechanisms has been previously described in NSCLC and is associated with the disease itself as well as with comorbidities such as smoking. The aim of the present in vitro study was to evaluate the effect of selective and non-competitive inhibition of heme oxygenase-1 (HO-1) on cancer redox homeostasis with particular regards to glutathione (GSH) metabolism related enzymes. NSCLC cell line (A549) was treated with the HO-1 activity inhibitor VP13/47 (10 µM) and we further evaluated cell viability, apoptosis, mitochondrial dysfunction and oxidative stress. Our results showed that VP13/47 significantly reduced HO-1 expression and total HO activity thus, resulting in a significant reduction of cell viability, proliferation and increased apoptosis, mitochondrial dysfunction and oxidative stress. Consistently with increased oxidative stress, we also showed that reduced GSH was significantly decreased and such effect was also accompanied by a significant downregulation of the enzymes involved in its biosynthesis. Taken all together our results show that selective HO-1 inhibition significantly impairs NSCLC progression and may represent a possible pharmacological strategy for new chemotherapy agents.

Repurposing of FDA-Approved Drugs for Treating Iatrogenic Botulism: A Paired 3D-QSAR/Docking Approach†

Botulinum neurotoxin (BoNT) is widely used for the treatment of spasticity, focal dystonia, chronic migraine, facial hemispasm, and facial aesthetic treatments. Generally, treatment with botulinum toxin is a safe procedure when conducted by clinicians with expertise, and local side effects are rare and transient. However, occasionally adverse effects can occur due to the spread of the drug to nontargeted muscles and organs, producing dry mouth, fatigue, and flu-like symptoms, up to signs of systemic botulism, which appears to be more frequent in children treated for spasticity than in adults. In silico 3D-QSAR and molecular docking studies were performed to build a structure-based model on selected potent known botulinum neurotoxin type A inhibitors; this was used to screen the US Food and Drug Administration (FDA) database. Thirty molecules were identified as possible light-chain BoNT/A inhibitors. In this study, we applied a well-established ligand- and structure-based methodology for the identification of hit compounds among a database of FDA-approved drugs. The identification of budesonide, protirelin, and ciclesonide followed by other compounds can be considered a starting point for investigations of selected compounds that could bypass much of the time and costs involved in the drug approval process.

Computational Tools in the Discovery of FABP4 Ligands: A Statistical and Molecular Modeling Approach

Small molecule inhibitors of adipocyte fatty-acid binding protein 4 (FABP4) have received interest following the recent publication of their pharmacologically beneficial effects. Recently, it was revealed that FABP4 is an attractive molecular target for the treatment of type 2 diabetes, other metabolic diseases, and some type of cancers. In past years, hundreds of effective FABP4 inhibitors have been synthesized and discovered, but, unfortunately, none have reached the clinical research phase. The field of computer-aided drug design seems to be promising and useful for the identification of FABP4 inhibitors; hence, different structure- and ligand-based computational approaches have been used for their identification. In this paper, we searched for new potentially active FABP4 ligands in the Marine Natural Products (MNP) database. We retrieved 14,492 compounds from this database and filtered through them with a statistical and computational filter. Seven compounds were suggested by our methodology to possess a potential inhibitory activity upon FABP4 in the range of 97–331 nM. ADMET property prediction was performed to validate the hypothesis of the interaction with the intended target and to assess the drug-likeness of these derivatives. From these analyses, three molecules that are excellent candidates for becoming new drugs were found.

Heme Oxygenase-2 (HO-2) as a therapeutic target: Activators and inhibitors

Heme oxygenase (HO) enzymes are involved in heme catabolism and several physiological functions. Among the different HO isoforms, HO-2 stands out for its neuroprotective properties and modulatory activity in male reproduction. However, unlike the HO-1 ligands, the potential therapeutic applications of HO-2 inhibitors/activators have not been extensively explored yet. Moreover, the physiological role of HO-2 is still unclear, mostly due to the lack of highly selective HO-2 chemical probes. To boost the interest on this intriguing target, the present review updates the knowledge on the structure-activity relationships of HO-2 inhibitors and activators, as well as their potential therapeutic applications. To the best of our knowledge, among HO-2 inhibitors, clemizole derivatives are the most selective HO-2 inhibitors reported so far (IC₅₀ HO-1 >100 μM, IC₅₀ HO-2 = 3.4 μM), while the HO-2 nonselective inhibitors described herein possess IC₅₀ HO-2 values ≤ 10 μM. Furthermore, the development of HO-2 activators, such as menadione analogues, helped to understand the critical moieties required for HO-2 activation. Recent advances in the potential therapeutic applications of HO-2 inhibitors/activators cover the fields of neurodegenerative, cardiovascular, inflammatory, and reproductive diseases further stimulating the interest towards this target.

Structure-Based Approach for the Prediction of Mu-opioid Binding Affinity of Unclassified Designer Fentanyl-Like Molecules

Three quantitative structure-activity relationship (QSAR) models for predicting the affinity of mu-opioid receptor (μOR) ligands have been developed. The resulted models, exploiting the accessibility of the QSAR modeling, generate a useful tool for the investigation and identification of unclassified fentanyl-like structures. The models have been built using a set of 115 molecules using Forge as a software, and the quality was confirmed by statistical analysis, resulting in being effective for their predictive and descriptive capabilities. The three different approaches were then combined to produce a consensus model and were exploited to explore the chemical landscape of 3000 fentanyl-like structures, generated by a theoretical scaffold-hopping approach. The findings of this study should facilitate the identification and classification of new μOR ligands with fentanyl-like structures.

Fourfold Filtered Statistical/Computational Approach for the Identification of Imidazole Compounds as HO-1 Inhibitors from Natural Products

Over-regulation of Heme oxygenase 1 (HO-1) has been recently identified in many types of human cancer, and in these cases, poor clinical outcomes are normally reported. Indeed, the inhibition of HO-1 is being considered as an anticancer approach. Imidazole scaffold is normally present in most of the classical HO-1 inhibitors and seems indispensable to the inhibitory activity due to its strong interaction with the Fe(II) of the heme group. In this paper, we searched for new potentially HO-1 inhibitors among three different databases: Marine Natural Products (MNP), ZINC Natural Products (ZNP) and Super Natural II (SN2). 484,527 compounds were retrieved from the databases and filtered through four statistical/computational filters (2D descriptors, 2D-QSAR pharmacophoric model, 3D-QSAR pharmacophoric model, and docking). Different imidazole-based compounds were suggested by our methodology to be potentially active in inhibiting the HO-1, and the results have been rationalized by the bioactivity of the filtered molecules reported in the literature.

Progress in the development of selective heme oxygenase-1 inhibitors and their potential therapeutic application

Heme oxygenases (HOs) are a family of enzymes involved in the selective catabolism of free circulating heme. While HO-2 is constitutively expressed, HO-1 is strongly overexpressed under stressful stimuli (e.g., oxidative stress). Under these conditions, HO-1 exerts its strong cytoprotective activities and plays a crucial role in stimulating cell survival by removing the pro-oxidant heme and by producing carbon monoxide and biliverdin (promptly reduced to bilirubin). Unfortunately, the broad spectrum of HO-1 cytoprotective effects has been well experimentally documented both in normal and tumor cells, where the enzyme can be overexpressed, making it an exciting target in the management of some type of tumors. Development of non-competitive HO-1 inhibitors dates back in 2002 with the discovery of Azalanstat. Since then, many efforts have been devoted to the identification of selective HO-1 and HO-2 inhibitors and to unravel the molecular determinants responsible for selectivity. Molecular modeling studies supported the identification of chemical features involved in the recognition and inhibition of these enzymes. Herein, medicinal chemistry aspects and in silico studies related to the development of HO inhibitors will be discussed. The purpose of this review is to highlight recent advances in the development of new selective HO-1 and HO-2 inhibitors and covers the last six years (2013-2018).

Morphing of Ibogaine: A Successful Attempt into the Search for Sigma-2 Receptor Ligands

Ibogaine is a psychoactive indole alkaloid with high affinity for several targets including the σ₂ receptor. Indeed, extensive data support the involvement of the σ₂ receptor in neurological disorders, including Alzheimer’s disease, schizophrenia, alcohol abuse and pain. Due to its serious side effects which prevent ibogaine from potential clinical applications, novel ibogaine derivatives endowed with improved σ₂ receptor affinity may be particularly beneficial. With the purpose to facilitate the investigation of iboga alkaloid derivatives which may serve as templates for the design of selective σ₂ receptor ligands, here we report a deconstruction study on the ibogaine tricyclic moiety and a successive scaffold-hopping of the indole counterpart. A 3D-QSAR model has been applied to predict the σ₂ pK_i values of the new compounds, whereas a molecular docking study conducted upon the σ₂ receptor built by homology modeling was used to further validate the best-scored molecules. We eventually evaluated pinoline, a carboline derivative, for σ₂ receptor affinity through radioligand binding assay and the results confirmed the predicted high µM range of affinity and good selectivity. The obtained results could be helpful in the drug design process of new ibogaine simplified analogs with improved σ₂ receptor binding capabilities.

A Pseudouridine Isoxazolidinyl Nucleoside Analogue Structural Analysis: A Morphological Approach

An in silico study has been conducted upon (3′RS,5′SR)-5-[2′-benzyl-5′-hydroxymethyl-1′,2′-isoxazolidin-3′-yl]uracil through a molecular dynamics/docking approach that highlights its potential inhibitory activity upon the wild-type pseudouridine 5′-monophosphate glycosidase. The crystal structure of this compound has been solved by means of X-ray single crystal diffraction and the data inferred were used to predict its crystal morphology. These data were compared with optical microscopy images and confirmed the validity of the computed models. This robust approach, already used for several other different compounds, provides a fast and reliable tool to standardize a crystallization method in order to get similar and good quality crystals. As different crystal shapes could be associated with different polymorphic forms, this method could be considered a fast and cheap screening to choose among different and coexistent polymorphic forms. Furthermore, a match with the original crystal structure of pseudouridine 5′-monophosphate is provided.

FABP4 inhibitors 3D-QSAR model and isosteric replacement of BMS309403 datasets

The data have been obtained from FABP4 inhibitor molecules previously published. The 120 compounds were used to build a 3D-QSAR model. The development of the QSAR model has been undertaken with the use of Forge software using the PM3 optimized structure and the experimental IC₅₀ of each compound. The QSAR model was also employed to predict the activity of 3000 new isosteric derivatives of BMS309403. The isosteric replacement was also validated by the synthesis and the biological screening of three new compounds reported in the related research article “3D-QSAR assisted identification of FABP4 inhibitors: An effective scaffold hopping analysis/QSAR evaluation” (Floresta et al., 2019).

3D-QSAR assisted identification of FABP4 inhibitors: An effective scaffold hopping analysis/QSAR evaluation

Following on the recent publication of pharmacologically relevant effects, small molecule inhibitors of adipocyte fatty-acid binding protein 4 (FABP4) have attracted high interest. FABP4 is mainly expressed in macrophages and adipose tissue, where it regulates fatty acid storage and lipolysis, being also an important mediator of inflammation. In this regard, FABP4 recently demonstrated an interesting molecular target for the treatment of type 2 diabetes, other metabolic diseases and some type of cancers. In the past years, hundreds of effective FABP4 inhibitors have been synthesized. In this paper, a quantitative structure-activity relationship (QSAR) model has been produced, in order to predict the bioactivity of FABP4 inhibitors. The methodology has been combined with a scaffold-hopping approach, allowing to identify three new molecules that act as effective inhibitors of this protein. These molecules, synthesized and tested for their FABP4 inhibitor activity, showed IC₅₀ values between 3.70 and 5.59 μM, with a high level of agreement with the predicted values.

iVS analysis to evaluate the impact of scaffold diversity in the binding to cellular targets relevant in cancer

This study reports the application of inverse virtual screening (iVS) methodologies to identify cellular proteins as suitable targets for a library of heterocyclic small-molecules, with potential pharmacological implications. Standard synthetic procedures allow facile generation of these ligands showing a high degree of core scaffold diversity. Specifically, we have computationally investigated the binding efficacy of the new series for target proteins which are involved in cancer pathogenesis. As a result, nine macromolecules demonstrated efficient binding interactions for the molecular dataset, in comparison to the co-crystallised ligand for each target. Moreover, the iVS analysis led us to confirm that 27 analogues have high affinity for one or more examined cellular proteins. The additional evaluation of ADME and drug score for selected hits also highlights their capability as drug candidates, demonstrating valuable leads for further structure optimisation and biological studies.

A Structure- and Ligand-Based Virtual Screening of a Database of "Small" Marine Natural Products for the Identification of "Blue" Sigma-2 Receptor Ligands

Sigma receptors are a fascinating receptor protein class whose ligands are actually under clinical evaluation for the modulation of opioid analgesia and their use as positron emission tomography radiotracers. In particular, peculiar biological and therapeutic functions are associated with the sigma-2 (σ₂) receptor. The σ₂ receptor ligands determine tumor cell death through apoptotic and non-apoptotic pathways, and the overexpression of σ₂ receptors in several tumor cell lines has been well documented, with significantly higher levels in proliferating tumor cells compared to quiescent ones. This acknowledged feature has found practical application in the development of cancer cell tracers and for ligand-targeting therapy. In this context, the development of new ligands that target the σ₂ receptors is beneficial for those diseases in which this protein is involved. In this paper, we conducted a search of new potential σ₂ receptor ligands among a database of 1517 “small” marine natural products constructed by the union of the Seaweed Metabolite and the Chemical Entities of Biological Interest (ChEBI) Databases. The structures were passed through two filters that were constituted by our developed two-dimensional (2D) and three-dimensional Quantitative Structure-Activity Relationship (3D-QSAR) statistical models, and successively docked upon a σ₂ receptor homology model that we built according to the FASTA sequence of the σ₂/TMEM97 (SGMR2_HUMAN) receptor.

Discovery of High-Affinity Cannabinoid Receptors Ligands through a 3D-QSAR Ushered by Scaffold-Hopping Analysis

Two 3D quantitative structure–activity relationships (3D-QSAR) models for predicting Cannabinoid receptor 1 and 2 (CB₁ and CB₂) ligands have been produced by way of creating a practical tool for the drug-design and optimization of CB₁ and CB₂ ligands. A set of 312 molecules have been used to build the model for the CB₁ receptor, and a set of 187 molecules for the CB₂ receptor. All of the molecules were recovered from the literature among those possessing measured K_i values, and Forge was used as software. The present model shows high and robust predictive potential, confirmed by the quality of the statistical analysis, and an adequate descriptive capability. A visual understanding of the hydrophobic, electrostatic, and shaping features highlighting the principal interactions for the CB₁ and CB₂ ligands was achieved with the construction of 3D maps. The predictive capabilities of the model were then used for a scaffold-hopping study of two selected compounds, with the generation of a library of new compounds with high affinity for the two receptors. Herein, we report two new 3D-QSAR models that comprehend a large number of chemically different CB₁ and CB₂ ligands and well account for the individual ligand affinities. These features will facilitate the recognition of new potent and selective molecules for CB₁ and CB₂ receptors.

Development of new HO-1 inhibitors by a thorough scaffold-hopping analysis

HO-1 inhibition is considered a valuable anticancer approach. In fact, up-regulation of HO-1 had been repeatedly reported in many types of human malignancies, and in these clinical cases, poor outcomes are reported. To identify novel HO-1 inhibitors suitable for drug development, a scaffold-hopping strategy calculation was utilized to design novel derivatives. Different parts of the selected molecule were analyzed and the different series of novel compounds were virtually evaluated. The calculation for the linker moiety of the classical HO-1 inhibitors structure led us to compounds 5 and 6. A synthetic pathway for the two molecules was designed and the compounds were synthesized. The biological activity revealed an HO-1 inhibition of 0.9 and 54 μM for molecules 5 and 6 respectively. This study suggested that our scaffold-hopping approach was successful and these results are ongoing for further development.