Evidence for investigating GSK-3 inhibitors as potential therapeutics for severe COVID-19.

A key component of severe COVID-19 is a "cytokine storm" i.e., the excessive expression of unneeded cytokines. Previous studies suggest that SARS-CoV-2 proteins can induce macrophages to secrete pro-inflammatory cytokines; a process that may involve Toll-like receptors (TLRs). Glycogen synthase kinase-3 (GSK-3) has been implicated in TLR signal transduction and a selective GSK-3 inhibitor, termed COB-187, dramatically attenuates cytokine expression induced by the TLR ligand lipopolysaccharide (LPS). In the present study, we provide evidence that the SARS-CoV-2 spike protein (S) and the S2 subunit (S2) induce production of CXCL10 (a chemokine elevated in severe COVID-19) by a human macrophage cell line. Further, we report that two clinically relevant GSK-3 inhibitors and COB-187 attenuate S and S2 protein-induced CXCL10 production. Combined, our observations provide impetus for investigating GSK-3 inhibitors as potential therapeutics for severe COVID-19.

A novel GSK-3 inhibitor binds to GSK-3ß via a reversible, time and Cys-199-dependent mechanism.

Glycogen synthase kinase-3 (GSK-3) has been implicated in numerous pathologies making GSK-3 an attractive therapeutic target. Our group has identified a compound termed COB-187 that is a potent and selective inhibitor of GSK-3. In this study, we probed the mechanism by which COB-187 inhibits GSK-3ß. Progress curves, generated via real-time monitoring of kinase activity, indicated that COB-187 inhibition of GSK-3ß is time-dependent and subsequent jump dilution assays revealed that COB-187 binding to GSK-3ß is reversible. Further, a plot of the kinetic constant (kobs) versus COB-187 concentration suggested that, within the range of concentrations studied, COB-187 binds to GSK-3ß via an induced-fit mechanism. There is a critical cysteine residue at the entry to the active site of GSK-3ß (Cys-199). We generated a mutant version of GSK-3ß wherein Cys-199 was substituted with an alanine. This mutation caused a dramatic decrease in the activity of COB-187; specifically, an IC50 in the nM range for wild type versus >100 µM for the mutant. A screen of COB-187 against 34 kinases that contain a conserved cysteine in their active site revealed that COB-187 is highly selective for GSK-3 indicating that COB-187's inhibition of GSK-3ß via Cys-199 is specific. Combined, these findings suggest that COB-187 inhibits GSK-3ß via a specific, reversible, time and Cys-199-dependent mechanism.

Isosteres of ester derived glucose uptake inhibitors.

Glucose transporters (GLUTs) facilitate glucose uptake and are overexpressed in most cancer cells. Inhibition of glucose transport has been shown to be an effective method to slow the growth of cancer cells both in vitro and in vivo. We have previously reported on the anticancer activity of an ester derived glucose uptake inhibitor. Due to the hydrolytic instability of the ester linkage we have prepared a series of isosteres of the ester moiety. Of all of the isosteres prepared, the amine linkage showed the most promise. Several additional analogues of the amine-linked compounds were also prepared to improve the overall activity.

RNA drug discovery: Conformational restriction enhances specific modulation of the T-box riboswitch function.

Antibacterial drug resistance is a global health concern that requires multiple solution approaches including development of new antibacterial compounds acting at novel targets. Targeting regulatory RNA is an emerging area of drug discovery. The T-box riboswitch is a regulatory RNA mechanism that controls gene expression in Gram-positive bacteria and is an exceptional, novel target for antibacterial drug design. We report the design, synthesis and activity of a series of conformationally restricted oxazolidinone-triazole compounds targeting the highly conserved antiterminator RNA element of the T-box riboswitch. Computational binding energies correlated with experimentally-derived Kd values indicating the predictive capabilities for docking studies within this series of compounds. The conformationally restricted compounds specifically inhibited T-box riboswitch function and not overall transcription. Complex disruption, computational docking and RNA binding specificity data indicate that inhibition may result from ligand binding to an allosteric site. These results highlight the importance of both ligand affinity and RNA conformational outcome for targeted RNA drug design.

Identification of a novel selective and potent inhibitor of glycogen synthase kinase-3.

Glycogen synthase kinase-3 (GSK-3) is a multitasking protein kinase that regulates numerous critical cellular functions. Not surprisingly, elevated GSK-3 activity has been implicated in a host of diseases including pathological inflammation, diabetes, cancer, arthritis, asthma, bipolar disorder, and Alzheimer's. Therefore, reagents that inhibit GSK-3 activity provide a means to investigate the role of GSK-3 in cellular physiology and pathophysiology and could become valuable therapeutics. Finding a potent inhibitor of GSK-3 that can selectively target this kinase, among over 500 protein kinases in the human genome, is a significant challenge. Thus there remains a critical need for the identification of selective inhibitors of GSK-3. In this work, we introduce a novel small organic compound, namely COB-187, which exhibits potent and highly selective inhibition of GSK-3. Specifically, this study 1) utilized a molecular screen of 414 kinase assays, representing 404 unique kinases, to reveal that COB-187 is a highly potent and selective inhibitor of GSK-3; 2) utilized a cellular assay to reveal that COB-187 decreases the phosphorylation of canonical GSK-3 substrates indicating that COB-187 inhibits cellular GSK-3 activity; and 3) reveals that a close isomer of COB-187 is also a selective and potent inhibitor of GSK-3. Taken together, these results demonstrate that we have discovered a region of chemical design space that contains novel GSK-3 inhibitors. These inhibitors will help to elucidate the intricate function of GSK-3 and can serve as a starting point for the development of potential therapeutics for diseases that involve aberrant GSK-3 activity.

Synthesis and cytotoxic activity of MOM-ether analogs of isosteviol.

Lung cancer is one of the most common malignancies worldwide. In this Letter, novel MOM-ether analogs of isosteviol were designed and synthesized to be tested for anticancer activities against H1299 lung cancer cell lines. The effects of these derivatives were studied in H1299 human large cell lung carcinoma cells that are null for p53 and compared to normal counterparts NL-20 normal lung epithelial cells. The initial screening of twelve MOM-ether analogs of isosteviol derivatives on H1299 lung cancer cells by MTT assay revealed that two derivatives (an ester and a carbamate) were the most potent in reducing cell viability. The IC50 values for these derivatives were determined to be 14 and 21 µM respectively. We compared the cytotoxicity of the best derivatives in H1299 lung cancer cells and NL-20 normal lung epithelial cells. Both derivatives showed lower cytotoxic effects on NL-20 normal lung epithelial cells. Moreover, both derivatives induced apoptosis in H1299 lung cancer cells more than NL-20 normal lung epithelial cells.

Capturing the Effects of Single Atom Substitutions on the Inhibition Efficiency of Glycogen Synthase Kinase-3ß Inhibitors via Markov State Modeling and Experiments.

Small modifications in the chemical structure of ligands are known to dramatically change their ability to inhibit the activity of a protein. Unraveling the mechanisms that govern these dramatic changes requires scrutinizing the dynamics of protein-ligand binding and unbinding at the atomic level. As an exemplary case, we have studied Glycogen Synthase Kinase-3ß (GSK-3ß), a multifunctional kinase that has been implicated in a host of pathological processes. As such, there is a keen interest in identifying ligands that inhibit GSK-3ß activity. One family of compounds that are highly selective and potent inhibitors of GSK-3ß is exemplified by a molecule termed COB-187. COB-187 consists of a five-member heterocyclic ring with a thione at C2, a pyridine substituted methyl at N3, and a hydroxyl and phenyl at C4. We have studied the inhibition of GSK-3ß by COB-187-related ligands that differ in a single heavy atom from each other (either in the location of nitrogen in their pyridine ring, or with the pyridine ring replaced by a phenyl ring), or in the length of the alkyl group joining the pyridine and the N3. The inhibition experiments show a large range of half-maximal inhibitory concentration (IC50) values from 10 nM to 10 µM, implying that these ligands exhibit vastly different propensities to inhibit GSK-3ß. To explain these differences, we perform Markov State Modeling (MSM) using fully atomistic simulations. Our MSM results are in excellent agreement with the experiments in that they accurately capture differences in the binding propensities of the ligands. The simulations show that the binding propensities are related to the ligands' ability to attain a compact conformation where their two aromatic rings are spatially close. We rationalize this result by sampling numerous binding and unbinding events via funnel metadynamics simulations, which show that indeed while approaching the bound state, the ligands prefer to be in their compact conformation. We find that the presence of nitrogen in the aromatic ring increases the probability of attaining the compact conformation. Protein-ligand binding is understood to be dictated by the energetics of interactions and entropic factors, like the release of bound water from the binding pockets. This work shows that changes in the conformational distribution of ligands due to atom-level modifications in the structure play an important role in protein-ligand binding.

3D-QSAR and 3D-QSSR models of negative allosteric modulators facilitate the design of a novel selective antagonist of human α4ß2 neuronal nicotinic acetylcholine receptors.

Subtype selective molecules for α4ß2 neuronal nicotinic acetylcholine receptors (nAChRs) have been sought as novel therapeutics for nicotine cessation. α4ß2 nAChRs have been shown to be involved in mediating the addictive properties of nicotine while other subtypes (i.e., α3ß4 and α7) are believed to mediate the undesired effects of potential CNS drugs. To obtain selective molecules, it is important to understand the physiochemical features of ligands that affect selectivity and potency on nAChR subtypes. Here we present novel QSAR/QSSR models for negative allosteric modulators of human α4ß2 nAChRs and human α3ß4 nAChRs. These models support previous homology model and site-directed mutagenesis studies that suggest a novel mechanism of antagonism. Additionally, information from the models presented in this work was used to synthesize novel molecules; which subsequently led to the discovery of a new selective antagonist of human α4ß2 nAChRs.

Fused ring aziridines as a facile entry into triazole fused tricyclic and bicyclic heterocycles.

The intramolecular dipolar cycloaddition of an azide with an alkyne has provided a useful entry into triazole fused tricyclic heterocycles containing both the triazole ring and the oxazolidin-2-one ring system. The requisite azido-alkynes have been prepared via a two-step sequence from fused ring aziridines. A series of 6-12 membered rings containing both the oxazolidinone and triazole rings have been prepared. These ring systems have been designed as conformationally restrained analogs of RNA-binding oxazolidinones.

Structure-activity studies of RNA-binding oxazolidinone derivatives.

The structure-activity relationship of a series of oxazolidinones binding to T-box riboswitch antiterminator RNA has been investigated. Oxazolidinones differentially substituted at C-5 were prepared and the ligand-induced fluorescence resonance energy transfer (FRET) changes in FRET-labeled antiterminator model RNA were assayed. Both qualitative and quantitative analysis of the structure-activity relationship indicate that hydrogen bonding and hydrophobic properties play a significant role in ligand binding.

Negative allosteric modulators that target human alpha4beta2 neuronal nicotinic receptors.

Allosteric modulation of neuronal nicotinic acetylcholine receptors (nAChRs) is considered to be one of the most promising approaches for therapeutics. We have previously reported on the pharmacological activity of several compounds that act as negative allosteric modulators (NAMs) of nAChRs. In the following studies, the effects of 30 NAMs from our small chemical library on both human alpha4beta2 (Halpha4beta2) and human alpha3beta4 (Halpha3beta4) nAChRs expressed in human embryonic kidney ts201 cells were investigated. During calcium accumulation assays, these NAMs inhibited nAChR activation with IC(50) values ranging from 2.4 microM to more than 100 microM. Several NAMs showed relative selectivity for Halpha4beta2 nAChRs with IC(50) values in the low micromolar range. A lead molecule, KAB-18, was identified that shows relative selectivity for Halpha4beta2 nAChRs. This molecule contains three phenyl rings, one piperidine ring, and one ester bond linkage. Structure-activity relationship (SAR) analyses of our data revealed three regions of KAB-18 that contribute to its relative selectivity. Predictive three-dimensional quantitative SAR (comparative molecular field analysis and comparative molecular similarity indices analysis) models were generated from these data, and a pharmacophore model was constructed to determine the chemical features that are important for biological activity. Using docking approaches and molecular dynamics on a Halpha4beta2 nAChR homology model, a binding mode for KAB-18 at the alpha/beta subunit interface that corresponds to the predicted pharmacophore is described. This binding mode was supported by mutagenesis studies. In summary, these studies highlight the importance of SAR, computational, and molecular biology approaches for the design and synthesis of potent and selective antagonists targeting specific nAChR subtypes.

Novel inhibitors of basal glucose transport as potential anticancer agents.

Cancer cells commonly show increased levels of glucose uptake and dependence. A potential strategy for the treatment of cancer may be the inhibition of basal glucose transport. We report here the synthesis of a small library of polyphenolic esters that inhibit basal glucose transport in H1299 lung and other cancer cells. These basal glucose transport inhibitors also inhibit cancer cell growth in H1299 cells, and these two activities appear to be correlated.

Natural product derivatives with bactericidal activity against Gram-positive pathogens including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecalis.

We have shown that the intentional engineering of a natural product biosynthesis pathway is a useful way to generate stereochemically complex scaffolds for use in the generation of combinatorial libraries that capture the structural features of both natural products and synthetic compounds. Analysis of a prototype library based upon nonactic acid lead to the discovery of triazole-containing nonactic acid analogs, a new structural class of antibiotic that exhibits bactericidal activity against drug resistant, Gram-positive pathogens including Staphylococcus aureus and Enterococcus faecalis.

Library of 1,4-disubstituted 1,2,3-triazole analogs of oxazolidinone RNA-binding agents.

The design and synthesis of small molecules that target RNA is immensely important in antibacterial therapy. We had previously reported on the RNA binding of a series of 4,5-disubstituted 2-oxazolidinones that bind to a highly conserved bulge region of bacterial RNA. This biological target T box antitermination system, which is found mainly in Gram-positive bacteria, regulates the expression of several amino acid related genes. In an effort to amplify our library, we have prepared a library of 1,4-disubstituted 1,2,3-triazole analogs that entails an isosteric replacement of the oxazolidinone nucleus. The synthesis of the new analogs was enhanced via copper(I) catalysis of an azide and alkyne cycloaddition reaction. A total of 108 1,4-disubstituted 1,2,3-triazole compounds have been prepared. All compounds were evaluated as RNA binding agents.

Modulation of LPS-induced inflammatory cytokine production by a novel glycogen synthase kinase-3 inhibitor.

Sepsis is a serious condition that can lead to long-term organ damage and death. At the molecular level, the hallmark of sepsis is the elevated expression of a multitude of potent cytokines, i.e. a cytokine storm. For sepsis involving gram-negative bacteria, macrophages recognize lipopolysaccharide (LPS) shed from the bacteria, activating Toll-like-receptor 4 (TLR4), and triggering a cytokine storm. Glycogen synthase kinase-3 (GSK-3) is a highly active kinase that has been implicated in LPS-induced cytokine production. Thus, compounds that inhibit GSK-3 could be potential therapeutics for sepsis. Our group has recently described a novel and highly selective inhibitor of GSK-3 termed COB-187. In the present study, using THP-1 macrophages, we evaluated the ability of COB-187 to attenuate LPS-induced cytokine production. We found that COB-187 significantly reduced, at the protein and mRNA levels, cytokines induced by LPS (e.g. IL-6, TNF-α, IL-1ß, CXCL10, and IFN-ß). Further, the data suggest that the inhibition could be due, at least in part, to COB-187 reducing NF-κB (p65/p50) DNA binding activity as well as reducing IRF-3 phosphorylation at Serine 396. Thus, COB-187 appears to be a potent inhibitor of the cytokine storm induced by LPS.

Effect of novel negative allosteric modulators of neuronal nicotinic receptors on cells expressing native and recombinant nicotinic receptors: implications for drug discovery.

Allosteric modulation of nAChRs is considered to be one of the most promising approaches for drug design targeting nicotinic acetylcholine receptors (nAChRs). We have reported previously on the pharmacological activity of several compounds that seem to act noncompetitively to inhibit the activation of alpha3beta4(*) nAChRs. In this study, the effects of 51 structurally similar molecules on native and recombinant alpha3beta4 nAChRs are characterized. These 51 molecules inhibited adrenal neurosecretion activated via stimulation of native alpha3beta4(*) nAChR, with IC(50) values ranging from 0.4 to 13.0 microM. Using cells expressing recombinant alpha3beta4 nAChRs, these molecules inhibited calcium accumulation (a more direct assay to establish nAChR activity), with IC(50) values ranging from 0.7 to 38.2 microM. Radiolabeled nAChR binding studies to orthosteric sites showed no inhibitory activity on either native or recombinant nAChRs. Correlation analyses of the data from both functional assays suggested additional, non-nAChR activity of the molecules. To test this hypothesis, the effects of the drugs on neurosecretion stimulated through non-nAChR mechanisms were investigated; inhibitory effects ranged from no inhibition to 95% inhibition at concentrations of 10 microM. Correlation analyses of the functional data confirmed this hypothesis. Several of the molecules (24/51) increased agonist binding to native nAChRs, supporting allosteric interactions with nAChRs. Computational modeling and blind docking identified a binding site for our negative allosteric modulators near the orthosteric binding site of the receptor. In summary, this study identified several molecules for potential development as negative allosteric modulators and documented the importance of multiple screening assays for nAChR drug discovery.

4,5-Disubstituted oxazolidinones: High affinity molecular effectors of RNA function.

The T box transcription antitermination system is a riboswitch found primarily in Gram-positive bacteria which monitors the aminoacylation of the cognate tRNA and regulates a variety of amino acid-related genes. Novel 4,5-disubstituted oxazolidinones were identified as high affinity RNA molecular effectors that modulate the transcription antitermination function of the T box riboswitch.

Natural products in parallel synthesis: triazole libraries of nonactic acid.

The synthesis of a library of nonactic acid-derived triazoloamide derivatives and their evaluation as antimicrobial agents is described.

The synthesis of 5-substituted ring E analogs of methyllycaconitine via the Suzuki-Miyaura cross-coupling reaction.

Novel 3,5-disubstituted ring E analogs of methyllycaconitine were prepared and evaluated in nicotinic acetylcholine receptor binding assays. The desired analogs were prepared through the Suzuki-Miyaura cross-coupling reaction of methyl 5-bromo-nicotinate. The Suzuki-Miyaura cross-coupling reactions of pyridines with electron withdrawing substituents have not been extensively described previously.

Diastereoselective Synthesis of a Highly Substituted cis-Decahydroquinoline via a Knoevenagel Condensation.

A diastereoselective approach to 3,7,8-trisubstituted cis-decahydroquinolines is described. This ring system forms the core of rings B and E of the norditerpenoid alkaloid methyllycaconitine. This approach starts with a known disubsituted cyclohexene. The remaining carbons are attached via a Knoevenagel condensation followed by an intramolecular lactam formation. The stereochemistry of the substituents is controlled by the cis-substitution of the starting cyclohexene ring.