Identification of Small Molecules Blocking the Pseudomonas aeruginosa type III Secretion System Protein PcrV.

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that employs its type III secretion system (T3SS) during the acute phase of infection to translocate cytotoxins into the host cell cytoplasm to evade the immune system. The PcrV protein is located at the tip of the T3SS, facilitates the integration of pore-forming proteins into the eukaryotic cell membrane, and is required for translocation of cytotoxins into the host cell. In this study, we used surface plasmon resonance screening to identify small molecule binders of PcrV. A follow-up structure-activity relationship analysis resulted in PcrV binders that protect macrophages in a P. aeruginosa cell-based infection assay. Treatment of P. aeruginosa infections is challenging due to acquired, intrinsic, and adaptive resistance in addition to a broad arsenal of virulence systems such as the T3SS. Virulence blocking molecules targeting PcrV constitute valuable starting points for development of next generation antibacterials to treat infections caused by P. aeruginosa.

Towards small molecule inhibitors of mono-ADP-ribosyltransferases.

Protein ADP-ribosylation is a post-translational modification involved in DNA repair, protein degradation, transcription regulation, and epigenetic events. Intracellular ADP-ribosylation is catalyzed predominantly by ADP-ribosyltransferases with diphtheria toxin homology (ARTDs). The most prominent member of the ARTD family, poly(ADP-ribose) polymerase-1 (ARTD1/PARP1) has been a target for cancer drug development for decades. Current PARP inhibitors are generally non-selective, and inhibit the mono-ADP-ribosyltransferases with low potency. Here we describe the synthesis of acylated amino benzamides and screening against the mono-ADP-ribosyltransferases ARTD7/PARP15, ARTD8/PARP14, ARTD10/PARP10, and the poly-ADP-ribosyltransferase ARTD1/PARP1. The most potent compound inhibits ARTD10 with sub-micromolar IC50.

Chemical probes to study ADP-ribosylation: synthesis and biochemical evaluation of inhibitors of the human ADP-ribosyltransferase ARTD3/PARP3.

The racemic 3-(4-oxo-3,4-dihydroquinazolin-2-yl)-N-[1-(pyridin-2-yl)ethyl]propanamide, 1, has previously been identified as a potent but unselective inhibitor of diphtheria toxin-like ADP-ribosyltransferase 3 (ARTD3). Herein we describe synthesis and evaluation of 55 compounds in this class. It was found that the stereochemistry is of great importance for both selectivity and potency and that substituents on the phenyl ring resulted in poor solubility. Certain variations at the meso position were tolerated and caused a large shift in the binding pose. Changes to the ethylene linker that connects the quinazolinone to the amide were also investigated but proved detrimental to binding. By combination of synthetic organic chemistry and structure-based design, two selective inhibitors of ARTD3 were discovered.

PARP inhibitor with selectivity toward ADP-ribosyltransferase ARTD3/PARP3.

Inhibiting ADP-ribosyl transferases with PARP-inhibitors is considered a promising strategy for the treatment of many cancers and ischemia, but most of the cellular targets are poorly characterized. Here, we describe an inhibitor of ADP-ribosyltransferase-3/poly(ADP-ribose) polymerase-3 (ARTD3), a regulator of DNA repair and mitotic progression. In vitro profiling against 12 members of the enzyme family suggests selectivity for ARTD3, and crystal structures illustrate the molecular basis for inhibitor selectivity. The compound is active in cells, where it elicits ARTD3-specific effects at submicromolar concentration. Our results show that by targeting the nicotinamide binding site, selective inhibition can be achieved among the closest relatives of the validated clinical target, ADP-ribosyltransferase-1/poly(ADP-ribose) polymerase-1.

Discovery of ligands for ADP-ribosyltransferases via docking-based virtual screening.

The diphtheria toxin-like ADP-ribosyltransferases (ARTDs) are an enzyme family that catalyzes the transfer of ADP-ribose units onto substrate proteins by using nicotinamide adenine dinucleotide (NAD(+)) as a cosubstrate. They have a documented role in chromatin remodelling and DNA repair, and inhibitors of ARTD1 and 2 (PARP1 and 2) are currently in clinical trials for the treatment of cancer. The detailed function of most other ARTDs is still unknown. By using virtual screening, we identified small ligands of ARTD7 (PARP15/BAL3) and ARTD8 (PARP14/BAL2). Thermal-shift assays confirmed that 16 compounds, belonging to eight structural classes, bound to ARTD7/ARTD8. Affinity measurements with isothermal titration calorimetry for two isomers of the most promising hit compound confirmed binding in the low micromolar range to ARTD8. Crystal structures showed anchoring of the hits in the nicotinamide pocket. These results form a starting point in the development of chemical tools for the study of the role and function of ARTD7 and ARTD8.

Synthesis and application of a 2-[(4-fluorophenyl)-sulfonyl]ethoxy carbonyl(Fsec) protected glycosyl donor in carbohydrate chemistry.

The 2-[(4-fluorophenyl)sulfonyl]ethoxy carbonyl (Fsec) group for protection of hydroxyl groups has been designed, synthesized, and evaluated. Fsec-Cl was readily prepared in 91% yield over three steps and subsequently used to protect 4-fluorobenzyl alcohol in high yield. The Fsec group was cleaved from the resulting model compound under mild basic conditions e.g., 20% piperidine in DMF and was stable under acidic conditions, e.g., neat acetic acid. The Fsec group was used to protect the unreactive 4-OH in a galactose building block that was later used in the synthesis of 6-aminohexyl galabioside.

Small-molecule screening using a whole-cell viral replication reporter gene assay identifies 2-{[2-(benzoylamino)benzoyl]amino}-benzoic acid as a novel antiadenoviral compound.

Adenovirus infections are widespread in society and are occasionally associated with severe, but rarely with life-threatening, disease in otherwise healthy individuals. In contrast, adenovirus infections present a real threat to immunocompromised individuals and can result in disseminated and fatal disease. The number of patients undergoing immunosuppressive therapy for solid organ or hematopoietic stem cell transplantation is steadily increasing, as is the number of AIDS patients, and this makes the problem of adenovirus infections even more urgent to solve. There is no formally approved treatment of adenovirus infections today, and existing antiviral agents evaluated for their antiadenoviral effect give inconsistent results. We have developed a whole cell-based assay for high-throughput screening of potential antiadenoviral compounds. The assay is unique in that it is based on a replication-competent adenovirus type 11p green fluorescent protein (GFP)-expressing vector (RCAd11pGFP). This allows measurement of fluorescence changes as a direct result of RCAd11pGFP genome expression. Using this assay, we have screened 9,800 commercially available small organic compounds. Initially, we observed approximately 400 compounds that inhibited adenovirus expression in vitro by > or = 80%, but only 24 were later confirmed as dose-dependent inhibitors of adenovirus. One compound in particular, 2-{[2-(benzoylamino)benzoyl]amino}-benzoic acid, turned out to be a potent inhibitor of adenovirus replication.

Synthesis and evaluation of 2-(2-fluoro-4-hydroxymethyl-5-methoxy-phenoxy)acetic acid as a linker in solid-phase synthesis monitored by gel-phase (19)F NMR spectroscopy.

Gel-phase (19)F NMR spectroscopy is a useful monitoring technique for solid-phase organic chemistry due to the high information content it delivers and swift acquisition times, using standard NMR spectrometers. This paper describes the synthesis of the novel linker 2-(2-fluoro-4-hydroxymethyl-5-methoxy-phenoxy)acetic acid in 29% yield over seven steps, using nucleophilic aromatic substitutions on 2,4,5-trifluorobenzonitrile as key steps. Following standard solid-phase synthesis a peptide could be cleaved from the linker using 20% TFA in CH(2)Cl(2) in 30 minutes, in contrast to a previously described monoalkoxy linker that requires 90% TFA in water at elevated temperature. A resin-bound peptide could be successfully glycosylated using only two equivalents of a thioglycoside donor, activated with N-iodosuccinimide and trifluoromethanesulfonic acid, and subsequent cleavage and deprotection gave the target glycopeptide. Direct glycosylation of the linker itself followed by mild acidic cleavage gave a fully protected hemiacetal for further chemical manipulation.