Type III secretion inhibitors for the management of bacterial plant diseases.

The identification of chemical compounds that prevent and combat bacterial diseases is fundamental for crop production. Bacterial virulence inhibitors are a promising alternative to classical control treatments, because they have a low environmental impact and are less likely to generate bacterial resistance. The major virulence determinant of most animal and plant bacterial pathogens is the type III secretion system (T3SS). In this work, we screened nine plant extracts and 12 isolated compounds-including molecules effective against human pathogens-for their capacity to inhibit the T3SS of plant pathogens and for their applicability as virulence inhibitors for crop protection. The screen was performed using a luminescent reporter system developed in the model pathogenic bacterium Ralstonia solanacearum. Five synthetic molecules, one natural product and two plant extracts were found to down-regulate T3SS transcription, most through the inhibition of the regulator hrpB. In addition, for three of the molecules, corresponding to salicylidene acylhydrazide derivatives, the inhibitory effect caused a dramatic decrease in the secretion capacity, which was translated into impaired plant responses. These candidate virulence inhibitors were then tested for their ability to protect plants. We demonstrated that salicylidene acylhydrazides can limit R. solanacearum multiplication in planta and protect tomato plants from bacterial speck caused by Pseudomonas syringae pv. tomato. Our work validates the efficiency of transcription reporters to discover compounds or natural product extracts that can be potentially applied to prevent bacterial plant diseases.

Screening for Inhibitors of Acetaldehyde Dehydrogenase (AdhE) from Enterohemorrhagic Escherichia coli (EHEC).

Acetaldehyde dehydrogenase (AdhE) is a bifunctional acetaldehyde-coenzyme A (CoA) dehydrogenase and alcohol dehydrogenase involved in anaerobic metabolism in gram-negative bacteria. This enzyme was recently found to be a key regulator of the type three secretion (T3S) system in Escherichia coli. AdhE inhibitors can be used as tools to study bacterial virulence and a starting point for discovery of novel antibacterial agents. We developed a robust enzymatic assay, based on the acetaldehyde-CoA dehydrogenase activity of AdhE using both absorption and fluorescence detection models (Z' > 0.7). This assay was used to screen ~11,000 small molecules in 384-well format that resulted in three hits that were confirmed by resynthesis and validation. All three compounds are noncompetitive with respect to acetaldehyde and display a clear dose-response effect with hill slopes of 1-2. These new inhibitors will be used as chemical tools to study the interplay between metabolism and virulence and the role of AdhE in T3S regulation in gram-negative bacteria, and as starting points for the development of novel antibacterial agents.

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.

Inhibitory activity of the isoflavone biochanin A on intracellular bacteria of genus Chlamydia and initial development of a buccal formulation.

Given the established role of Chlamydia spp. as causative agents of both acute and chronic diseases, search for new antimicrobial agents against these intracellular bacteria is required to promote human health. Isoflavones are naturally occurring phytoestrogens, antioxidants and efflux pump inhibitors, but their therapeutic use is limited by poor water-solubility and intense first-pass metabolism. Here, we report on effects of isoflavones against C. pneumoniae and C. trachomatis and describe buccal permeability and initial formulation development for biochanin A. Biochanin A was the most potent Chlamydia growth inhibitor among the studied isoflavones, with an IC50 = 12 µM on C. pneumoniae inclusion counts and 6.5 µM on infectious progeny production, both determined by immunofluorescent staining of infected epithelial cell cultures. Encouraged by the permeation of biochanin A across porcine buccal mucosa without detectable metabolism, oromucosal film formulations were designed and prepared by a solvent casting method. The film formulations showed improved dissolution rate of biochanin A compared to powder or a physical mixture, presumably due to the solubilizing effect of hydrophilic additives and presence of biochanin A in amorphous state. In summary, biochanin A is a potent inhibitor of Chlamydia spp., and the in vitro dissolution results support the use of a buccal formulation to potentially improve its bioavailability in antichlamydial or other pharmaceutical applications.

Design of a general-purpose European compound screening library for EU-OPENSCREEN.

This work describes a collaborative effort to define and apply a protocol for the rational selection of a general-purpose screening library, to be used by the screening platforms affiliated with the EU-OPENSCREEN initiative. It is designed as a standard source of compounds for primary screening against novel biological targets, at the request of research partners. Given the general nature of the potential applications of this compound collection, the focus of the selection strategy lies on ensuring chemical stability, absence of reactive compounds, screening-compliant physicochemical properties, loose compliance to drug-likeness criteria (as drug design is a major, but not exclusive application), and maximal diversity/coverage of chemical space, aimed at providing hits for a wide spectrum of drugable targets. Finally, practical availability/cost issues cannot be avoided. The main goal of this publication is to inform potential future users of this library about its conception, sources, and characteristics. The outline of the selection procedure, notably of the filtering rules designed by a large committee of European medicinal chemists and chemoinformaticians, may be of general methodological interest for the screening/medicinal chemistry community. The selection task of 200K molecules out of a pre-filtered set of 1.4M candidates was shared by five independent European research groups, each picking a subset of 40K compounds according to their own in-house methodology and expertise. An in-depth analysis of chemical space coverage of the library serves not only to characterize the collection, but also to compare the various chemoinformatics-driven selection procedures of maximal diversity sets. Compound selections contributed by various participating groups were mapped onto general-purpose self-organizing maps (SOMs) built on the basis of marketed drugs and bioactive reference molecules. In this way, the occupancy of chemical space by the EU-OPENSCREEN library could be directly compared with distributions of known bioactives of various classes. This mapping highlights the relevance of the selection and shows how the consensus reached by merging the five different 40K selections contributes to achieve this relevance. The approach also allows one to readily identify subsets of target- or target-class-oriented compounds from the EU-OPENSCREEN library to suit the needs of the diverse range of potential users. The final EU-OPENSCREEN library, assembled by merging five independent selections of 40K compounds from various expert groups, represents an excellent example of a Europe-wide collaborative effort toward the common objective of building best-in-class European open screening platforms.

N-acylated derivatives of sulfamethoxazole and sulfafurazole inhibit intracellular growth of Chlamydia trachomatis.

Antibacterial compounds with novel modes of action are needed for management of bacterial infections. Here we describe a high-content screen of 9,800 compounds identifying acylated sulfonamides as novel growth inhibitors of the sexually transmitted pathogen Chlamydia trachomatis. The effect was bactericidal and distinct from that of sulfonamide antibiotics, as para-aminobenzoic acid did not reduce efficacy. Chemical inhibitors play an important role in Chlamydia research as probes of potential targets and as drug development starting points.

Statistical molecular design: a tool to follow up hits from small-molecule screening.

In high-throughput screening (HTS) a robust assay is used to interrogate a large collection of small organic molecules in order to find compounds, hits, with a desired biological activity. The hits are then further explored by an iterative process where new compounds are designed, purchased, or synthesized, followed by an evaluation in one or more assays. Statistical molecular design (SMD) is a useful method to select a balanced, varied, and information-rich compound collection based on hits from HTS in order to create a foundation for development of optimized compounds with improved properties. In this chapter, we describe the use of SMD to explore a hit obtained from small-molecule screening.