Monitoring ligand-induced conformational changes for the identification of estrogen receptor agonists and antagonists.

Nuclear receptors are transcription factors that are important targets for current drug discovery efforts as they play a role in many pathological processes. Their activity can be regulated by small molecules like hormones and drugs that can have agonistic or antagonistic functions. These ligands bind to the receptor and account for diverse conformational changes that are crucial determinants for the receptor activity. Here, we set out to develop FLiN (fluorescent labels in nuclear receptors), a direct binding assay that detects conformational changes in the estrogen receptor. The assay is based on the introduction of a cysteine residue and subsequent specific labeling of the receptor with a thiol-reactive fluorophore. Changes in the receptor conformation upon ligand binding lead to differences in the microenvironment of the fluorophore and alter its emission spectrum. The FLiN assay distinguishes between different binding modes and is suitable for high-throughput screening.

Dibenzosuberones as p38 mitogen-activated protein kinase inhibitors with low ATP competitiveness and outstanding whole blood activity.

p38α mitogen-activated protein (MAP) kinase is a main target in drug research concerning inflammatory diseases. Nevertheless, no inhibitor of p38α MAP kinase has been introduced to the market. This might be attributed to the fact that there is no inhibitor which combines outstanding activity in biological systems and selectivity. Herein an approach to the development of such inhibitors on the basis of the highly selective molecular probe Skepinone-L is described. Introduction of a "deep pocket" moiety addressing the DFG motif led to an increased activity of the compounds. Hydrophilic moieties, addressing the solvent-exposed area adjacent to hydrophilic region II, conserved a high activity of the compounds in a whole blood assay. Combined with their outstanding selectivity and low ATP competitiveness, these inhibitors are very interesting candidates for use in biological systems and in therapy.

Targeting the hinge glycine flip and the activation loop: novel approach to potent p38α inhibitors.

The p38 MAP kinase is a key player in signaling pathways regulating the biosynthesis of inflammatory cytokines. Small molecule p38 inhibitors suppress the production of these cytokines. Therefore p38 is a promising drug target for novel anti-inflammatory drugs. In this study, we report novel dibenzepinones, dibenzoxepines, and benzosuberones as p38α MAP kinase inhibitors. Previously reported dibenzepinones and dibenzoxepines were chemically modified by introduction of functional groups or removal of a phenyl ring. This should result in targeting of the hydrophobic region I, the "deep pocket", and the hinge glycine flip of the kinase. Potent inhibitors with IC(50) values in the single digit nanomolar range (up to 3 nM) were identified. Instead of targeting the "deep pocket" in the DFG-out conformation, interactions with the DFG-motif in the in-conformation could be observed by protein X-ray crystallography.

Targeting GSK3 from Ustilago maydis: type-II kinase inhibitors as potential antifungals.

Protein kinases are key enzymes in the complex regulation of cellular processes in almost all living organisms. For this reason, protein kinases represent attractive targets to stop the growth of eukaryotic pathogens such as protozoa and fungi. However, using kinase inhibitors to fight against these organisms bears several challenges since most of them are unselective and will also affect crucial host kinases. Here we present the X-ray structure of glycogen synthase kinase 3 from the fungal plant pathogen Ustilago maydis (UmGSK3) and its inhibition by type-II kinase inhibitors. Despite the high sequence homology between the human and the fungal variant of this vital kinase, we found substantial differences in the conformational plasticity of their active sites. Compounds that induced such conformational changes could be used to selectively inhibit the fungal kinase. This study serves as an example of how species-specific selectivity of inhibitors can be achieved by identifying and addressing the inactive state of a protein kinase. In addition to this, our study gives interesting insights into the molecular plasticity of UmGSK3 by revealing a previously unknown inactive conformation of this important kinase family.