An Aromatic Hydroxyamide Attenuates Multiresistant Staphylococcus aureus Toxin Expression.

Methicillin-resistant Staphylococcus aureus (MRSA) causes severe infections with only few effective antibiotic therapies currently available. To approach this challenge, chemical entities with a novel and resistance-free mode of action are desperately needed. Here, we introduce a new hydroxyamide compound that effectively reduces the expression of devastating toxins in various S. aureus and MRSA strains. The molecular mechanism was investigated by transcriptome analysis as well as by affinity-based protein profiling. Down-regulation of several pathogenesis associated genes suggested the inhibition of a central virulence-related pathway. Mass spectrometry-based chemical proteomics revealed putative molecular targets. Systemic treatment with the hydroxyamide showed significant reduction of abscess sizes in a MRSA mouse skin infection model. The absence of resistance development in vitro further underlines the finding that targeting virulence could lead to prolonged therapeutic options in comparison to antibiotics that directly address bacterial survival.

Target analysis of α-alkylidene-γ-butyrolactones in uropathogenic E. coli.

α-Alkylidene-γ-butyrolactones are quite common in nature and exhibit a broad spectrum of biological activities. We therefore synthesized a small library of xanthatine inspired α-alkylidene-γ-butyrolactones to screen non-pathogenic and uropathogenic E. coli strains by activity based protein profiling (ABPP). The identified targets are involved in cellular redox processes and give first insight into the preferred binding sites of this privileged motif. Furthermore the gene of one protein, c2450, which was only identified in uropathogenic E. coli belongs to a genomic island which encodes a hybrid polyketide/non-ribosomal peptide synthetase (PKS/NRPS). This system is responsible for the synthesis of colibactin, a natural product which causes DNA double strand breaks in eukaryotic cells leading to the activation of the DNA damage checkpoint pathway and subsequent cell cycle arrest. While the role of several proteins that are involved in the colibactin synthesis has been elucidated, the function of c2450 remains elusive. Investigation of the binding site showed that c2450 is modified at a cysteine residue which may be important for the catalytic activity.

Protein reactivity of natural product-derived γ-butyrolactones.

The discovery of novel and unique target-drug pairs for the treatment of human diseases such as cancer and bacterial infections is an urgent goal of chemical and pharmaceutical sciences. Natural products represent an inspiring source of compounds for designing chemical biology methods with applications in target identification and characterization. Inspired by the huge structural diversity of γ-butyrolactones, which constitute up to 10% of all known compounds of natural origin, we extended the "activity-based protein profiling" (ABPP) target identification technology to this promising and so far unexplored natural compound class. We designed and synthesized a comprehensive set of natural product-derived γ-lactones and thiolactones that varied in protein reactivity. Several important bacterial enzymes that are involved in diverse cellular functions such as metabolism (dihydrolipoyl dehydrogenase and 6-phosphofructokinase), cell wall biosynthesis (MurA1 and MurA2), and protein folding (trigger factors) were obtained. Especially protein folding in bacteria could represent a novel strategy for antibiotic intervention and requires chemical tools for characterization and inhibition. Future studies that extend structural modifications to protein reactive α-methylene-γ-butyrolactone as well as to reversible binding γ-lactones and thiolactones will reveal if this premise holds true.