NMR fragment screening reveals a novel small molecule binding site near the catalytic surface of the disulfide-dithiol oxidoreductase enzyme DsbA from Burkholderia pseudomallei.

The presence of suitable cavities or pockets on protein structures is a general criterion for a therapeutic target protein to be classified as 'druggable'. Many disease-related proteins that function solely through protein-protein interactions lack such pockets, making development of inhibitors by traditional small-molecule structure-based design methods much more challenging. The 22 kDa bacterial thiol oxidoreductase enzyme, DsbA, from the gram-negative bacterium Burkholderia pseudomallei (BpsDsbA) is an example of one such target. The crystal structure of oxidized BpsDsbA lacks well-defined surface pockets. BpsDsbA is required for the correct folding of numerous virulence factors in B. pseudomallei, and genetic deletion of dsbA significantly attenuates B. pseudomallei virulence in murine infection models. Therefore, BpsDsbA is potentially an attractive drug target. Herein we report the identification of a small molecule binding site adjacent to the catalytic site of oxidized BpsDsbA. 1HN CPMG relaxation dispersion NMR measurements suggest that the binding site is formed transiently through protein dynamics. Using fragment-based screening, we identified a small molecule that binds at this site with an estimated affinity of KD ~ 500 µM. This fragment inhibits BpsDsbA enzymatic activity in vitro. The binding mode of this molecule has been characterized by NMR data-driven docking using HADDOCK. These data provide a starting point towards the design of more potent small molecule inhibitors of BpsDsbA.

Fragment screening libraries for the identification of protein hot spots and their minimal binding pharmacophores.

Fragment-based drug design relies heavily on structural information for the elaboration and optimisation of hits. The ability to identify neighbouring binding hot spots, energetically favourable interactions and conserved binding motifs in protein structures through X-ray crystallography can inform the evolution of fragments into lead-like compounds through structure-based design. The composition of fragment libraries can be designed and curated to fit this purpose and herein, we describe and compare screening libraries containing compounds comprising between 2 and 18 heavy atoms. We evaluate the properties of the compounds in these libraries and assess their ability to probe protein surfaces for binding hot spots.

Methyl probes in proteins for determining ligand binding mode in weak protein-ligand complexes.

Structures of protein-ligand complexes provide critical information for drug design. Most protein-ligand complex structures are determined using X-ray crystallography, but where crystallography is not able to generate a structure for a complex, NMR is often the best alternative. However, the available tools to enable rapid and robust structure determination of protein-ligand complexes by NMR are currently limited. This leads to situations where projects are either discontinued or pursued without structural data, rendering the task more difficult. We previously reported the NMR Molecular Replacement (NMR2) approach that allows the structure of a protein-ligand complex to be determined without requiring the cumbersome task of protein resonance assignment. Herein, we describe the NMR2 approach to determine the binding pose of a small molecule in a weak protein-ligand complex by collecting sparse protein methyl-to-ligand NOEs from a selectively labeled protein sample and an unlabeled ligand. In the selective labeling scheme all methyl containing residues of the protein are protonated in an otherwise deuterated background. This allows measurement of intermolecular NOEs with greater sensitivity using standard NOESY pulse sequences instead of isotope-filtered NMR experiments. This labelling approach is well suited to the NMR2 approach and extends its utility to include larger protein-ligand complexes.

Advice on assistance and protection provided by the Scientific Advisory Board of the Organisation for the Prohibition of Chemical Weapons: Part 3. On medical care and treatment of injuries from sulfur mustard.

Blister agents damage the skin, eyes, mucous membranes and subcutaneous tissues. Other toxic effects may occur after absorption. The response of the Scientific Advisory Board (SAB) of the Organisation for the Prohibition of Chemical Weapons (OPCW) to a request from the OPCW Director-General in 2013 on the status of medical countermeasures and treatments to blister agents is updated through the incorporation of the latest information. The physical and toxicological properties of sulfur mustard and clinical effects and treatments are summarised. The information should assist medics and emergency responders who may be unfamiliar with the toxidrome of sulfur mustard and its treatment.

Rapid Elaboration of Fragments into Leads by X-ray Crystallographic Screening of Parallel Chemical Libraries (REFiLX).

A bottleneck in fragment-based lead development is the lack of systematic approaches to elaborate the initial fragment hits, which usually bind with low affinity to their target. Herein, we describe an analysis using X-ray crystallography of a diverse library of compounds prepared using microscale parallel synthesis. This approach yielded an 8-fold increase in affinity and detailed structural information for the resulting complex, providing an efficient and broadly applicable approach to early fragment development.

Advice on assistance and protection from the Scientific Advisory Board of the Organisation for the Prohibition of Chemical Weapons: Part 2. On preventing and treating health effects from acute, prolonged, and repeated nerve agent exposure, and the identification of medical countermeasures able to reduce or eliminate the longer term health effects of nerve agents.

The Scientific Advisory Board (SAB) of the Organisation for the Prohibition of Chemical Weapons (OPCW) has provided advice in relation to the Chemical Weapons Convention on assistance and protection. We present the SAB's response to a request from the OPCW Director-General in 2014 for information on the best practices for preventing and treating the health effects from acute, prolonged, and repeated organophosphorus nerve agent (NA) exposure. The report summarises pre- and post-exposure treatments, and developments in decontaminants and adsorbing materials, that at the time of the advice, were available for NAs. The updated information provided could assist medics and emergency responders unfamiliar with treatment and decontamination options related to exposure to NAs. The SAB recommended that developments in research on medical countermeasures and decontaminants for NAs should be monitored by the OPCW, and used in assistance and protection training courses and workshops organised through its capacity building programmes.

Synthesis of Novel Hybrids Inspired from Bromopyrrole Alkaloids Inhibiting MMP-2 and -12 as Antineoplastic Agents.

Synthesis of novel set of forty semicarbazide/thiosemicarbazide hybrids inspired from marine bromopyrrole alkaloids is reported. Biological screening of these hybrids against a panel of five human cancer cell lines identified a number of hits endowed with interesting cytotoxicity profile. Compounds 5c and 5e (IC50  = 0.03 µm), 5t (IC50  = 0.03 µm), 4s (IC50  = 0.07 µm), and 5n (IC50  = 0.01 µm) displayed maximum cytotoxicity toward hormone-dependent breast cancer cells MCF7, hepatic cancer cells WRL68, colon cancer cells CaCO2 and mouth and oral cancer cells KB403, respectively. The most active hits were further investigated for their potential to inhibit MMP-2 and MMP-12. Compound 5e showed maximum activity (IC50  = 1.8 µm) toward MMP-2. Further, we preformed anti-invasive assay on the most active compounds, where CaCO2 tumor cell migration was significantly decreased (77.9%) by hybrid 5e. The non-toxicity toward human VERO cells (IC50  = 83.1 to 231.8 µm) indicated the selectivity of most active hits (5c, 5e, 5t and 5n) toward cancer cells.

Design, synthesis and evaluation of small molecule imidazo[2,1-b][1,3,4]thiadiazoles as inhibitors of transforming growth factor-ß type-I receptor kinase (ALK5).

A new series of imidazo[2,1-b][1,3,4]thiadiazoles 5(a-g), 6(a-g), 9(a-i) and 12(a-h) were synthesized as transforming growth factor-ß (TGF-ß) type I receptor (also known as activin receptor-like kinase 5 or ALK5) inhibitors. These compounds were evaluated for their ALK5 inhibitory activity in an enzyme assay and their TGF-ß -induced Smad2/3 phosphorylation inhibitory activity in a cell-based assay. Compound 6d, 2-(5-((2-cyclopropyl-6-(4-fluorophenyl) imidazo [2,1-b][1,3,4]thiadiazol-5-yl)methylene)-4-oxo-2-thioxothiazolidin-3-yl) acetic acid, shows prominent ALK5 inhibition (IC50 = 0.0012 µM) and elective inhibition (91%) against the P38αkinase at10 µM. The binding mode of compound 6d by XP docking studies shows that it fits well into the active site cavity of ALK5 by forming broad and tight interactions. Lipinski's rule and in silico ADME pharmacokinetic parameters are within the acceptable range defined for human use thereby indicating their potential as a drug-like molecules.

Novel series of coumarinyl substituted-thiazolidin-2,4-dione analogs as anticancer agents: design, synthesis, spectral studies and cytotoxicity evaluation.

In this research work, a series of eighteen novel coumarinyl substituted thiazolidin-2,4-dione analogs (4a-4r) have been designed by molecular hybridization approach, synthesized and their structures were established on the basis of FTIR, 1H NMR, 13C NMR and elemental (CHN) analysis. These title compounds were screened for their cytotoxicity using MTT assay methodology against five different mammalian cancer cell lines viz. hormone dependant breast adenocarcinoma (MCF7), cervical carcinoma (HeLa), colorectal carcinoma (HT29), lung cancer (A549) and prostate adeno carcinoma (PC3). The cytotoxicity screening studies revealed that MCF-7, HeLa and A549 cancer cell lines were sensitive to all the tested compounds. Though the compounds showed varying degrees of cytotoxicity in the tested cell lines, most significant effect was observed for compounds 4i (1.06, 2.4 and 3.06 µM) and 4o (0.95, 3.2 and 2.38 µM) against MCF7, HeLa and A549 cell lines respectively. In conclusion, the anticancer results of these promising leads strongly encouraged us for additional lead optimization with the aim of developing more potential anticancer agents.

Novel imidazo[2,1-b]-1,3,4-thiadiazoles as promising antifungal agents against clinical isolate of Cryptococcus neoformans.

We herein report the synthesis and in vitro antimicrobial evaluation of twenty five novel hybrid derivatives of imidazo [2,1-b]-1,3,4-thiadiazole containing chalcones (5a-o) and Schiff bases (6a-j) against three fungal strains (Candida albicans, Cryptococcus neoformans and Aspergillus niger). Most of the tested compounds displayed substantial anti-fungal activity with MICs ranging between 1.56 and 100 µg/mL. Compounds 5a, 5b and 5n exhibited promising activity against C. neoformans at a MIC 1.56 µg/mL. In addition, compound 5n also demonstrated significant antifungal activity against the clinical isolates of C. neoformans at MIC 3.125 µg/mL. However, moderate activity was observed for these compounds against four bacterial strains (Staphylococcus aureus, Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa) and Mycobacterium tuberculosis (H37Rv).

Acridone-based antitumor agents: a mini-review.

In the past decades, tricyclic acridone ring system has become one of the major research interests of the medicinal chemists due to the biological significance of this moiety in drug design and drug discovery. Acridone scaffold has substantial bio-potential since it possess crucial activities such as antibacterial, antimalarial, antiviral and anti-neoplastic. The diverse biological activity of acridone and its prospective in reversal of multi-drug resistance has attracted attention of medicinal chemists to explore this scaffold especially to treat multi-drug resistance in cancer. Considering this potential in this review we have summarized the synthesis and the antitumor activities of different acridone derived compounds reported from 2000 to 2014.

An insight into purine, tyrosine and tryptophan derived marine antineoplastic alkaloids.

There is an ever-increasing need for the development of new drugs with safe and improved profile for the treatment of cancer. From time immemorial, nature has been considered as an abundant source of medicinal compounds having therapeutic properties. An enormous chemical diversity is present in thousands and millions of species of microorganisms, marine organisms, plants and animals that can act as potential therapeutic agents against various types of human cancer. Literature survey revealed that many alkaloids isolated from marine cyanobacteria, fungi, algae, sponges and tunicates displayed a wide range of anticancer properties like antiproliferative, antiangiogenic, induction of apoptosis, promoting cytotoxicity by inhibition of topoisomerase activities and tubulin polymerization. In this context, bastadins derived from tyrosine-based alkaloids have been reported as one the important class of anticancer agents. In particular bastadin 6 (24), seems to be a promising natural lead compound for the development of marine natural product-based anticancer therapeutic agents. This review mainly highlights the pharmacologically active scaffolds like purine, tyrosine and tryptophan containing marine alkaloids that exhibit biological activity, including anti-angiogenesis, cytotoxicity and anticancer activity.

Current perspective of natural alkaloid carbazole and its derivatives as antitumor agents.

Throughout our evolution, the importance of natural products for medicine and health has been increasing and it continues to be a key source of novel anticancer drugs, leads and new chemical entities. Among natural products, tricyclic heteroaromatic alkaloids such as carbazoles are an important class of natural and semi-synthetic organic compounds. In the last few decades medicinal role of natural and semi-synthetic carbazoles has expanded significantly, especially as a vital heterocyclic class of antitumor agents. Some of the carbazoles that displayed potential anticancer activity have undergone clinical trials. However, complications arising due to multidrug resistance in clinical trials led to very few of the selected carbazoles being approved for cancer therapy. Planar, polycyclic and aromatic carbazoles exhibit anticancer activity via DNA intercalation. Further many carbazoles can be cytotoxic by inhibiting DNA-dependent enzymes such as telomerase and topoisomerase I/II.