Pyridinylimidazoles as GSK3ß Inhibitors: The Impact of Tautomerism on Compound Activity via Water Networks.

Glycogen synthase kinase-3ß (GSK3ß) is involved in many pathological conditions and represents an attractive drug target. We previously reported dual GSK3ß/p38α mitogen-activated protein kinase inhibitors and identified N-(4-(4-(4-fluorophenyl)-2-methyl-1H-imidazol-5-yl)pyridin-2-yl)cyclopropanecarboxamide (1) as a potent dual inhibitor of both target kinases. In this study, we aimed to design selective GSK3ß inhibitors based on our pyridinylimidazole scaffold. Our efforts resulted in several novel and potent GSK3ß inhibitors with IC50 values in the low nanomolar range. 5-(2-(Cyclopropanecarboxamido)pyridin-4-yl)-4-cyclopropyl-1H-imidazole-2-carboxamide (6g) displayed very good kinase selectivity as well as metabolical stability and inhibited GSK3ß activity in neuronal SH-SY5Y cells. Interestingly, we observed the importance of the 2-methylimidazole's tautomeric state for the compound activity. Finally, we reveal how this crucial tautomerism effect is surmounted by imidazole-2-carboxamides, which are able to stabilize the binding via enhanced water network interactions, regardless of their tautomeric state.

Pyridinylimidazoles as dual glycogen synthase kinase 3ß/p38α mitogen-activated protein kinase inhibitors.

Compounds simultaneously inhibiting two targets that are involved in the progression of the same complex disease may exhibit additive or even synergistic therapeutic effects. Here we unveil 2,4,5-trisubstituted imidazoles as dual inhibitors of p38α mitogen-activated protein kinase and glycogen synthase kinase 3ß (GSK3ß). Both enzymes are potential therapeutic targets for neurodegenerative disorders, like Alzheimer's disease. A set of 39 compounds was synthesized and evaluated in kinase activity assays for their ability to inhibit both target kinases. Among the synthesized compounds, potent dual-target-directed inhibitors showing IC50 values down to the low double-digit nanomolar range, were identified. One of the best balanced dual inhibitors presented in here is N-(4-(2-ethyl-4-(4-fluorophenyl)-1H-imidazol-5-yl)pyridin-2-yl)cyclopropanecarboxamide (20c) (p38α, IC50 = 16 nM; GSK3ß, IC50 = 35 nM) featuring an excellent metabolic stability and an appreciable isoform selectivity over the closely related GSK3α. Our findings were rationalized by computational docking studies based on previously published X-ray structures.

Mycobacterium tuberculosis Strains H37ra and H37rv have equivalent minimum inhibitory concentrations to most antituberculosis drugs.

Background: Mycobacterium tuberculosis (Mtb) strains H37Ra and H37Rv are commonly used to study new and re-evaluate old antituberculous agents with respect to their pharmacodynamic effects in vitro. The differences in membrane proteins and, in particular, differences in carrier proteins between Mtb H37Ra and Mtb H37Rv may have an impact on antibiotic potency. The question of whether H37Ra can be used as a reliable surrogate for H37Rv and clinical strains has not been addressed sufficiently. The purpose of this study is to provide a full comparison of susceptibility data of the most common antituberculosis (TB) agents against both Mtb strains. Methods: In addition to a literature review, in vitro checkerboard susceptibility study was conducted comparing the in vitro minimum inhibitory concentration (MIC) of 16 common antituberculous drugs against H37Ra and H37Rv. Heifets-Sanchez TB agar drug susceptibility plates were utilized. Results: Half of the antibiotics demonstrated similar growth inhibition against both strains, while slightly differing MIC values were found for 7 of 16 drugs. With the exception of rifampicin, no marked difference in MIC against H37Ra and H37Rv was observed. Conclusion: While neither the attenuated (H37Ra) nor the virulent strain (H37Rv) is a clinical strain, both strains predicted MICs of clinical isolates equally well, when comparing the current in vitro results to clinical susceptibility data in the literature. H37Ra comes with the benefits of lower experimental costs and less administrative barriers including the requirement of a biosafety Level III environment.

From 2-Alkylsulfanylimidazoles to 2-Alkylimidazoles: An Approach towards Metabolically More Stable p38α MAP Kinase Inhibitors.

In vitro and in vivo metabolism studies revealed that 2-alkylsulfanylimidazole ML3403 (4-(5-(4-fluorophenyl)-2-(methylthio)-1H-imidazol-4-yl)-N-(1-phenylethyl)pyridin-2-amine) undergoes rapid oxidation to the sulfoxide. Replacing the sulfur atom present in the two potent p38α mitogen-activated protein (MAP) kinase inhibitors ML3403 and LN950 (2-((5-(4-fluorophenyl)-4-(2-((3-methylbutan-2-yl)amino)pyridin-4-yl)-1H-imidazol-2-yl)thio)ethan-1-ol) by a methylene group resulted in 2-alkylimidazole derivatives 1 and 2, respectively, having a remarkably improved metabolic stability. The 2-alkylimidazole analogs 1 and 2 showed 20% and 10% biotransformation after 4 h of incubation with human liver microsomes, respectively. They display a 4-fold increased binding affinity towards the target kinase as well as similar in vitro potency and ex vivo efficacy relative to their 2-alkylsulfanylimidazole counterparts ML3403 and LN950. For example, 2-alkylimidazole 2, the analog of LN950, inhibits both the p38α MAP kinase as well as the LPS-stimulated tumor necrosis factor-α release from human whole blood in the low double-digit nanomolar range.

Insights into effective RNAi gained from large-scale siRNA validation screening.

Transfection of chemically synthesized short interfering RNAs (siRNAs) enables a high level of sequence-specific gene silencing. Although siRNA design algorithms have been improved in recent years, it is still necessary to prove the functionality of a given siRNA experimentally. We have functionally tested several thousand siRNAs for target genes from various gene families including kinases, phosphatases, and cancer-related genes (e.g., genes involved in apoptosis and the cell cycle). Some targets were difficult to silence above a threshold of 70% knockdown. By working with one design algorithm and a standardized validation procedure, we discovered that the level of silencing achieved was not exclusively dependent on the siRNA sequences. Here we present data showing that neither the gene expression level nor the cellular environment has a direct impact on the knockdown which can be achieved for a given target. Modifications of the experimental setting have been investigated with the aim of improving knockdown efficiencies for siRNA-target combinations that show only moderate knockdown. Use of higher siRNA concentrations did not change the overall performance of the siRNA-target combinations analyzed. Optimal knockdown at the mRNA level was usually reached 48-72 hours after transfection. Target gene-specific characteristics such as the accessibility of the corresponding target sequences to the RNAi machinery appear to have a significant influence on the knockdown observed, making certain targets easy or difficult to knock down using siRNA.