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The Gram-negative pathogen Pseudomonas aeruginosa produces an intercellular alkyl quinolone signaling molecule, the Pseudomonas quinolone signal. The pqs quorum sensing communication system that is characteristic for P. aeruginosa regulates the production of virulence factors. Therefore, we consider the pqs system a novel target to limit P. aeruginosa pathogenicity. Here, we present small molecules targeting a key player of the pqs system, PqsR. A rational design strategy in combination with surface plasmon resonance biosensor analysis led to the identification of PqsR binders. Determination of thermodynamic binding signatures and functional characterization in E. coli guided the hit optimization, resulting in the potent hydroxamic acid derived PqsR antagonist 11 (IC(50) = 12.5 μM). Remarkably it displayed a comparable potency in P. aeruginosa (IC(50) = 23.6 μM) and reduced the production of the virulence factor pyocyanin. Beyond this, site-directed mutagenesis together with thermodynamic analysis provided insights into the energetic characteristics of protein-ligand interactions. Thus the identified PqsR antagonists are promising scaffolds for further drug design efforts against this important pathogen.

The human pathogen Pseudomonas aeruginosa employs alkyl quinolones for cell-to-cell communication. The Pseudomonas quinolone signal (PQS) regulates various virulence factors via interaction with the transcriptional regulator PqsR. Therefore, we consider the development of PqsR antagonists a novel strategy to limit the pathogenicity of P. aeruginosa. A fragment identification approach using surface plasmon resonance screening led to the discovery of chemically diverse PqsR ligands. The optimization of the most promising hit (5) resulted in the oxadiazole-2-amine 37 showing pure antagonistic activity in Escherichia coli (EC50 = 7.5 μM) and P. aeruginosa (EC50 = 38.5 μM) reporter gene assays. 37 was able to diminish the production of the PQS precursor HHQ in a PqsH-deficient P. aeruginosa mutant. The level of the major virulence factor pyocyanin was significantly reduced in wild-type P. aeruginosa. In addition, site-directed mutagenesis in combination with isothermal titration calorimetry and NMR INPHARMA experiments revealed that the identified ligands bind to the same site of PqsR by adopting different binding modes. These findings will be utilized in a future fragment-growing approach aiming at novel therapeutic options for the treatment of P. aeruginosa infections.

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Using the microdialysis technique and sensitive HPLC procedures for the determination of acetylcholine (ACh) and ethanol, we investigated the release of ACh in rat hippocampus after acute ethanol administration. Systemic administration of ethanol (0.8 and 2.4 g/kg i.p.) led to peak ethanol concentrations of 21 and 42 mM in the hippocampus, respectively. The high dose caused a long-lasting inhibition of basal ACh release by up to 33%. Local infusion of scopolamine (1 microM) enhanced hippocampal ACh release up to eightfold in the presence of neostigmine (10 microM), and this stimulated release was also inhibited after systemic ethanol administration (by up to 45%). The low dose of ethanol (0.8 g/kg) led to a delayed stimulation of hippocampal ACh release. A stimulatory effect on ACh release was also observed when ethanol (50-100 mM) was infused directly into the hippocampus or into the septal area, i.e. to the origin of the cholinergic septohippocampal pathway; thus, the stimulatory effect may be mediated by a direct effect on cholinergic fibres. We conclude that ethanol exerts dual modulatory effects on the activity of the septohippocampal cholinergic fibres, depending on the dose and the site of administration. It is suggested that the inhibition of hippocampal ACh release by intoxicating doses of ethanol may contribute to the well-known cognitive and amnesic effects of ethanol intake.

Inhibition of 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1) is a novel and attractive approach to reduce the local levels of the active estrogen 17β-estradiol in patients with estrogen-dependent diseases like breast cancer or endometriosis. With the aim of optimizing the biological profile of 17β-HSD1 inhibitors from the hydroxyphenylnaphthol class, structural optimizations were performed at the 1-position of the naphthalene by introduction of different heteroaromatic rings as well as substituted phenyl groups. In the latter class of compounds, which were synthesized applying Suzuki-cross coupling, the 3-methanesulfonamide 15 turned out to be a highly potent 17β-HSD1 inhibitor (IC(50) = 15 nM in a cell-free assay). It was also very active in the cellular assay (T47D cells, IC(50) = 71 nM) and selective toward 17β-HSD2 and the estrogen receptors α and β. It showed a good membrane permeation and metabolic stability and was orally available in the rat.

An attractive target that has still to be explored for the treatment of estrogen-dependent diseases, such as breast cancer and endometriosis, is the enzyme responsible for the last step in the biosynthesis of estradiol (E2): 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1). It catalyzes the reduction of the weakly active estrone (E1) into E2, which is the most potent estrogen in humans. Inhibition of 17β-HSD1 lowers intracellular E2 concentrations and thus presents a therapeutic target for estrogen-dependent pathologies. Recently, we reported a new class of highly active and selective 17β-HSD1 inhibitors: bicyclic substituted hydroxyphenylmethanones. Here, further structural variations on the bicyclic moiety are described, especially focusing on the exchange of its hydroxy function. Twenty-nine novel inhibitors were synthesized and evaluated for 17β-HSD1 inhibition in a cell-free and cellular assay, for selectivity toward 17βHSD2 and estrogen receptors (ER) alpha and beta, as well as for metabolic stability. The best compound exhibited IC50 values of 12 nM (cell-free assay) and 78 nM (cellular assay), high selectivity for 17β-HSD1, and reasonable metabolic stability. A molecular docking study provided insight into the protein-ligand interactions of this compound with 17β-HSD1.