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Protein kinase CK2 is associated with a number of human diseases, among them cancer, and is therefore a target for inhibitor development in industry and academia. Six crystal structures of either CK2α, the catalytic subunit of human protein kinase CK2, or its paralog CK2α' in complex with two ATP-competitive inhibitors-based on either a flavonol or a thieno[2,3-d]pyrimidine framework-are presented. The structures show examples for extreme structural deformations of the ATP-binding loop and its neighbourhood and of the hinge/helix αD region, i.e., of two zones of the broader ATP site environment. Thus, they supplement our picture of the conformational space available for CK2α and CK2α'. Further, they document the potential of synthetic ligands to trap unusual conformations of the enzymes and allow to envision a new generation of inhibitors that stabilize such conformations. [ABSTRACT FROM AUTHOR]

The increase of antibiotic resistance amongstMycobacterium tuberculosisstrains has become one of the most pressing problems of modern medicine. Therefore, the search of antibiotics againstM. tuberculosiswith novel mechanisms of action is very important. We have identified inhibitors ofM. tuberculosisleucyl-tRNA synthetase (LeuRS) among the derivatives of 5-phenylamino-2H-[1,2,4]triazin-3-one. The most active compounds 5-(5-chloro-2-hydroxy-phenylamino)-6-methyl-2H-[1,2,4]triazin-3-one and 5-(5-chloro-2-hydroxy-phenylamino)-2H-[1,2,4]triazin-3-one inhibitM. tuberculosisLeuRS with IC50of 7.6 μМ and 7.2 μМ, respectively. It was established that the inhibitory activity of compounds against pathogenic LeuRS is 10-fold better, than for human enzyme. [ABSTRACT FROM AUTHOR]

Protein kinase CK2 is associated with a number of human diseases, among them cancer, and is therefore a target for inhibitor development in industry and academia. Six crystal structures of either CK2α, the catalytic subunit of human protein kinase CK2, or its paralog CK2α' in complex with two ATP-competitive inhibitors-based on either a flavonol or a thieno[2,3-d]pyrimidine framework-are presented. The structures show examples for extreme structural deformations of the ATP-binding loop and its neighbourhood and of the hinge/helix αD region, i.e., of two zones of the broader ATP site environment. Thus, they supplement our picture of the conformational space available for CK2α and CK2α'. Further, they document the potential of synthetic ligands to trap unusual conformations of the enzymes and allow to envision a new generation of inhibitors that stabilize such conformations.

CK2 is a Ser/Thr kinase recruited by tumor cells to avoid cell death. 4'-Carboxy-6,8-dibromo-flavonol (FLC26) is a nanomolar CK2 inhibitor reducing the physiological phosphorylation of CK2 biomarkers and inducing cell death. Its binding mode to the ATP site was predicted to depend primarily on noncovalent interactions not comprising halogen bonds. We confirm this by two independent cocrystal structures which additionally show that FLC26 is selective for an open, protein kinase-untypical conformation of the hinge/helix αD region. The structures suggest how the bromo substituents, found previously in lead optimization studies, contribute to the inhibitory efficacy. In this context, one of the complex structures, obtained by crystallization with the kosmotropic salt NaCl, revealed an unconventional π-halogen bond between the 8-bromo substituent of FLC26 and an aromatic side chain which is absent under low-salt conditions. The kosmotropic salt sensitivity of π-halogen bonds is a novel feature which requires attention in structural comparisons and halogen-bond-based explanations.

Background: Previously, we reported that menadione activated rat, native heme oxygenase-2 (HO-2) and human recombinant heme oxygenase-2 selectively; it did not activate spleen, microsomal heme oxygenase-1. The purpose of this study was to explore some structure-activity relationships of this activation and the idea that redox properties may be an important aspect of menadione efficacy., Methods: Heme oxygenase activity was determined in vitro using rat spleen and brain microsomes as the sources of heme oxygenase-1 and -2, respectively, as well as recombinant, human heme oxygenase-2., Results: Menadione analogs with bulky aliphatic groups at position-3, namely vitamins K1 and K2, were not able to activate HO-2. In contrast, several compounds with similar bulky but less lipophilic moieties at position-2 (and -3) were able to activate HO-2 many fold; these compounds included polar, rigid, furan-containing naphthoquinones, furan-benzoxazine naphthoquinones, 2-(aminophenylphenyl)-3-piperidin-1-yl naphthoquinones. To explore the idea that redox properties might be involved in menadione efficacy, we tested analogs such as 1,4-dimethoxy-2-methylnaphthalene, pentafluoromenadione, monohalogenated naphthoquinones, α-tetralone and 1,4-naphthoquinone. All of these compounds were inactive except for 1,4-naphthoquinone. Menadione activated full-length recombinant human heme oxygenase-2 (FL-hHO-2) as effectively as rat brain enzyme, but it did not activate rat spleen heme oxygenase., Conclusions: These observations are consistent with the idea that naphthoquinones such as menadione bind to a receptor in HO-2 and activate the enzyme through a mechanism that may involve redox properties.

Apoptosis signal-regulating kinase 1 (ASK1) has recently emerged as an attractive therapeutic target for the treatment of cardiac and neurodegenerative disorders. The selective inhibitors of ASK1 may become important compounds for the development of clinical agents. We have identified the ASK1 inhibitor among 3H-naphtho[1,2,3-de]quinoline-2,7-diones using receptor-based virtual screening. In vitro kinase assay revealed that ethyl 2,7-dioxo-2,7-dihydro-3H-naphtho[1,2,3-de]quinoline-1-carboxylate (NQDI-1) inhibited ASK1 with a K(i) of 500 nM. The competitive character of inhibition is demonstrated in Lineweaver-Burk plots. In our preliminary selectivity study this compound exhibited strong specific inhibitory activity toward ASK1.

Due to the emerging role of protein kinase CK2 as a molecule that participates not only in the development of some cancers but also in viral infections and inflammatory failures, small organic inhibitors of CK2, besides application in scientific research, may have therapeutic significance. In this paper, we present a new class of CK2 inhibitors-3-carboxy-4(1H)-quinolones. This class of inhibitors has been selected via receptor-based virtual screening of the Otava compound library. It was revealed that the most active compounds, 5,6,8-trichloro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (7) (IC(50) = 0.3 microM) and 4-oxo-1,4-dihydrobenzo[h]quinoline-3-carboxylic acid (9) (IC(50) = 1 microM), are ATP competitive (K(i) values are 0.06 and 0.28 microM, respectively). Evaluation of the inhibitors on seven protein kinases shows considerable selectivity toward CK2. According to theoretical calculations and experimental data, a structural model describing the key features of 3-carboxy-4(1H)-quinolones responsible for tight binding to CK2 active site has been developed.