Structure-based design of bacterial nitric oxide synthase inhibitors

Simple monocyclic pyrimidine analogs as microtubule targeting agents binding to the colchicine site

Complex natural products that bind to tubulin/microtubules come under the broad category of microtubule binding agents. The design of simplified analogs of previously reported bicyclic, microtubule depolymerizer, pyrrolo[2,3-d]pyrimidine, provided valuable structure-activity relationship data and led to the identification of novel monocyclic pyrimidine analogs of which 12 was 47-fold more potent (EC50 123 nM) for cellular microtubule depolymerization activity and 7.5-fold more potent (IC50 24.4 nM) at inhibiting the growth of MDA-MB-435 cancer cells, suggesting significantly better binding of the target within the colchicine site of tubulin compared to lead compound 1. This compound and others of this series of monocyclic pyrimidine analogs were able to overcome multidrug resistance due to the expression of the βIII-isotype of tubulin and P-glycoprotein. In vivo evaluation of the most potent analog 12 in an MDA-MB-435 xenograft mouse model indicated, along with paclitaxel, that both compounds showed a trend towards lower tumor volume however neither compound showed significant antitumor activity in the trial. To our knowledge these are the first examples of simple substituted monocyclic pyrimidines as colchicine site binding antitubulin compounds with potent antitumor activity.

Synthesis, DFT investigations, antioxidant, antibacterial activity and SAR-study of novel thiophene-2-carboxamide derivatives

Synthetic strategy for the synthesis of thiophene 2-carboxamide derivatives substituted with hydroxyl, methyl and amino groups at position-3 was proposed. The strategy includes the cyclization of the precursor ethyl 2-arylazo-3-mercapto-3-(phenylamino)acrylate derivatives, 2-acetyl-2-arylazo-thioacetanilide derivatives and N-aryl-2-cyano-3-mercapto-3-(phenylamino)acrylamide derivatives with N-(4-acetylphenyl)-2-chloroacetamide in alcoholic sodium ethoxide. IR, ¹H NMR, and mass spectroscopic analyses were used to characterize the synthesized derivatives. In addition, molecular, electronic properties of the synthesized products were studied by the density functional theory (DFT) where they exhibited close HOMO-LUMO energy gap (ΔE_H-L) in which the amino derivatives 7a-c have the highest while the methyl derivatives 5a-c were the lowest. Using the ABTS method, the antioxidant properties of the produced compounds were evaluated, where amino thiophene-2-carboxamide 7a exhibit significant inhibition activity 62.0% compared to ascorbic acid The antibacterial activity against two pathogenic Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis) and two of pathogenic Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) revealed that 7b records the highest activity index compared to ampicillin 83.3, 82.6, 64.0, 86.9%, respectively. Furthermore, the thiophene-2-carboxamide derivatives were docked with five different proteins with the use molecular docking tools and the results explained interactions between amino acid residue of enzyme and compounds. Compounds 3b and 3c showed the highest binding score with 2AS1 protein.

Potential of substituted quinazolines to interact with multiple targets in the treatment of cancer

The efficacy of quinazoline-based antiglioma agents has been attributed to their effects on microtubule dynamics.1,2 The design, synthesis and biological evaluation of quinazolines as potent inhibitors of multiple intracellular targets, including microtubules and multiple RTKs, is described. In addition to the known ability of quinazolines 1 and 2 to cause microtubule depolymerization, they were found to be low nanomolar inhibitors of EGFR, VEGFR-2 and PDGFR-β. Low nanomolar inhibition of EGFR was observed for 1-3 and 9-10. Compounds 1 and 4 inhibited VEGFR-2 kinase with activity better than or equal to that of sunitinib. In addition, compounds 1 and 2 had similar potency to sunitinib in the CAM angiogenesis assay. Multitarget activities of compounds in the present study demonstrates that the quinazolines can affect multiple pathways and could lead to these agents having antitumor potential caused by their activity against multiple targets.

Cu-Catalyzed switchable synthesis of functionalized pyridines and pyrroles

A switchable synthesis of functionalized pyridines and pyrroles via Cu-catalyzed cascade reactions with N-sulfonyl azadienes and alkynes.

Emerging Roles of Nitric Oxide Synthase in Bacterial Physiology

Nitric oxide (NO) is a potent inhibitor of diverse cellular processes in bacteria. Therefore, it was surprising to discover that several bacterial species, primarily Gram-positive organisms, harboured a gene encoding nitric oxide synthase (NOS). Recent attempts to characterize bacterial NOS (bNOS) have resulted in the discovery of structural features that may allow it to function as a NO dioxygenase and produce nitrate in addition to NO. Consistent with this characterization, investigations into the biological function of bNOS have also emphasized a role for NOS-dependent nitrate and nitrite production in aerobic and microaerobic respiration. In this review, we aim to compare, contrast, and summarize the structure, biochemistry, and biological role of bNOS with mammalian NOS and discuss how recent advances in our understanding of bNOS have enabled efforts at designing inhibitors against it.

Secretome of Intestinal Bacilli: A Natural Guard against Pathologies

Current studies of human gut microbiome usually do not consider the special functional role of transient microbiota, although some of its members remain in the host for a long time and produce broad spectrum of biologically active substances. Getting into the gastrointestinal tract (GIT) with food, water and probiotic preparations, two representatives of Bacilli class, genera Bacillus and Lactobacillus, colonize epithelium blurring the boundaries between resident and transient microbiota. Despite their minor proportion in the microbiome composition, these bacteria can significantly affect both the intestinal microbiota and the entire body thanks to a wide range of secreted compounds. Recently, insufficiency and limitations of pure genome-based analysis of gut microbiota became known. Thus, the need for intense functional studies is evident. This review aims to characterize the Bacillus and Lactobacillus in GIT, as well as the functional roles of the components released by these members of microbial intestinal community. Complex of their secreted compounds is referred by us as the "bacillary secretome." The composition of the bacillary secretome, its biological effects in GIT and role in counteraction to infectious diseases and oncological pathologies in human organism is the subject of the review.

Staphylococcus aureus nitric oxide synthase (saNOS) modulates aerobic respiratory metabolism and cell physiology

Nitric oxide (NO) is generated from arginine and oxygen via NO synthase (NOS). Staphylococcus aureus NOS (saNOS) has previously been shown to affect virulence and resistance to exogenous oxidative stress, yet the exact mechanism is unknown. Herein, a previously undescribed role of saNOS in S. aureus aerobic physiology was reported. Specifically, aerobic S. aureus nos mutant cultures presented with elevated endogenous reactive oxygen species (ROS) and superoxide levels, as well as increased membrane potential, increased respiratory dehydrogenase activity and slightly elevated oxygen consumption. Elevated ROS levels in the nos mutant likely resulted from altered respiratory function, as inhibition of NADH dehydrogenase brought ROS levels back to wild-type levels. These results indicate that, in addition to its recently reported role in regulating the switch to nitrate-based respiration during low-oxygen growth, saNOS also plays a modulatory role during aerobic respiration. Multiple transcriptional changes were also observed in the nos mutant, including elevated expression of genes associated with oxidative/nitrosative stress, anaerobic respiration and lactate metabolism. Targeted metabolomics revealed decreased cellular lactate levels, and altered levels of TCA cycle intermediates, the latter of which may be related to decreased aconitase activity. Collectively, these findings demonstrate a key contribution of saNOS to S. aureus aerobic respiratory metabolism.

The latest advances in the discovery of nitric oxide hybrid drug compounds

INTRODUCTION

There is a great interest in Nitric oxide (NO) within medicinal chemistry since it's involved in human signaling pathways. Prodrugs or hybrid compounds containing NO-donor scaffolds linked to an active compound are valuable, due to their potential for modulating many pathological conditions due to NO's biological properties when released in addition to the native drug. Compounds that selectively inhibit nitric oxide synthase isoforms (NOS) can also increase therapeutic capacity, particularly in the treatment of chronic diseases. However, search for bioactive compounds to efficiently and selectively modulate NO is still a challenge in drug discovery. Areas covered: In this review, the authors highlight the recent advances in the strategies used to discover NO-hybrid derivatives, especially those related to anti-inflammatory, cardiovascular, anticancer and anti-microorganism activities. They also focus on: nitric oxide synthase inhibitors, NO delivery materials and other related activities. Expert opinion: The process of molecular hybridization can be used to obtain NO-releasing compounds that also interact with different targets. The main problem with this approach is to control NO multiple actions in the right biological system. However, the use of NO-releasing groups with many different scaffolds leads to new molecular structures for bioactive compounds, suggesting synergies.

Targeting Bacterial Nitric Oxide Synthase with Aminoquinoline-Based Inhibitors

Nitric oxide is produced in Gram-positive pathogens Bacillus anthracis and Staphylococcus aureus by the bacterial isoform of nitric oxide synthase (NOS). Inhibition of bacterial nitric oxide synthase (bNOS) has been identified as a promising antibacterial strategy for targeting methicillin-resistant S. aureus [Holden, J. K., et al. (2015) Chem. Biol. 22, 785-779]. One class of NOS inhibitors that demonstrates antimicrobial efficacy utilizes an aminoquinoline scaffold. Here we report on a variety of aminoquinolines that target the bacterial NOS active site, in part, by binding to a hydrophobic patch that is unique to bNOS. Through mutagenesis and crystallographic studies, our findings demonstrate that aminoquinolines are an excellent scaffold for further aiding in the development of bNOS specific inhibitors.

Nitric Oxide Synthase as a Target for Methicillin-Resistant Staphylococcus aureus

Bacterial infections associated with methicillin-resistant Staphylococcus aureus (MRSA) are a major economic burden to hospitals, and confer high rates of morbidity and mortality among those infected. Exploitation of novel therapeutic targets is thus necessary to combat this dangerous pathogen. Here, we report on the identification and characterization, including crystal structures, of two nitric oxide synthase (NOS) inhibitors that function as antimicrobials against MRSA. These data provide the first evidence that bacterial NOS (bNOS) inhibitors can work synergistically with oxidative stress to enhance MRSA killing. Crystal structures show that each inhibitor contacts an active site Ile residue in bNOS that is Val in the mammalian NOS isoforms. Mutagenesis studies show that the additional nonpolar contacts provided by the Ile in bNOS contribute to tighter binding toward the bacterial enzyme.

Elucidating nitric oxide synthase domain interactions by molecular dynamics

Nitric oxide synthase (NOS) is a multidomain enzyme that catalyzes the production of nitric oxide (NO) by oxidizing L-Arg to NO and L-citrulline. NO production requires multiple interdomain electron transfer steps between the flavin mononucleotide (FMN) and heme domain. Specifically, NADPH-derived electrons are transferred to the heme-containing oxygenase domain via the flavin adenine dinucleotide (FAD) and FMN containing reductase domains. While crystal structures are available for both the reductase and oxygenase domains of NOS, to date there is no atomic level structural information on domain interactions required for the final FMN-to-heme electron transfer step. Here, we evaluate a model of this final electron transfer step for the heme-FMN-calmodulin NOS complex based on the recent biophysical studies using a 105-ns molecular dynamics trajectory. The resulting equilibrated complex structure is very stable and provides a detailed prediction of interdomain contacts required for stabilizing the NOS output state. The resulting equilibrated complex model agrees well with previous experimental work and provides a detailed working model of the final NOS electron transfer step required for NO biosynthesis.

Inhibitor Bound Crystal Structures of Bacterial Nitric Oxide Synthase

Nitric oxide generated by bacterial nitric oxide synthase (NOS) increases the susceptibility of Gram-positive pathogens Staphylococcus aureus and Bacillus anthracis to oxidative stress, including antibiotic-induced oxidative stress. Not surprisingly, NOS inhibitors also improve the effectiveness of antimicrobials. Development of potent and selective bacterial NOS inhibitors is complicated by the high active site sequence and structural conservation shared with the mammalian NOS isoforms. To exploit bacterial NOS for the development of new therapeutics, recognition of alternative NOS surfaces and pharmacophores suitable for drug binding is required. Here, we report on a wide number of inhibitor-bound bacterial NOS crystal structures to identify several compounds that interact with surfaces unique to the bacterial NOS. Although binding studies indicate that these inhibitors weakly interact with the NOS active site, many of the inhibitors reported here provide a revised structural framework for the development of new antimicrobials that target bacterial NOS. In addition, mutagenesis studies reveal several key residues that unlock access to bacterial NOS surfaces that could provide the selectivity required to develop potent bacterial NOS inhibitors.