Pharmacokinetics of ML3403 ({4-[5-(4-Fluorophenyl)-2-methylsulfanyl-3H-imidazol-4-yl]-pyridin-2-yl}-(1-phenylethyl)-amine), a 4-Pyridinylimidazole-Type p38 Mitogen-Activated Protein Kinase Inhibitor

2-Alkylsulfanyl-4(5)-aryl-5(4)-heteroarylimidazoles: An Overview on Synthetic Strategies and Biological Activity

2-Alkylsulfanyl-4(5)-aryl-5(4)-heteroarylimidazoles represent an important class of ATP-competitive protein kinase inhibitors, offering the possibility of multiple interactions with different regions of the target enzyme. The necessity of exploring the effects of diverse chemical decorations around the imidazole core prompted the design of several synthetic routes aimed at achieving both efficiency and flexibility. Additionally, the optimization of established protocols and the extensive use of transition metal-catalyzed cross-coupling reactions have been broadening the spectrum of preparative methodologies within the last decade. This review summarizes the progress in the development of synthetic strategies leading to 2-alkylsulfanyl-4(5)-aryl-5(4)-heteroarylimidazoles and 1-alkyl-2-alkylsulfanyl-4(5)-aryl-5(4)-heteroarylimidazoles and offers a glance at the biological activities of this class of compounds.

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.

In vitro effects of SB202190 on Echinococcus granulosus

Spillage of cyst contents during surgical operation is the major cause of recurrence after hydatid cyst surgery. Instillation of a scolicidal agent into a hepatic hydatid cyst is the most commonly employed measure to prevent this complication. SB202190 is a pyridinyl imidazole derivative and is known to be a specific inhibitor of p38 MAPK. In the present study, the scolicidal effect of SB202190 was investigated. Freshly isolated Echinococcus granulosus protoscolices were subjected to SB202190 treatment (10, 20, 40, and 80 µM), and the effects on parasite viability were monitored by trypan blue staining. Corresponding effects were visualized by scanning and transmission electron microscopy. Dose-dependent protoscolex death within a few days of SB202190 treatment was observed. Although the in vitro scolicidal effect of SB202190 was satisfactory, the in vivo efficacy of this drug and also possible side effects remain to be further investigated.

Critical review of p38 MAP kinase inhibitors: a bioanalytical perspective

p38 MAP kinase is a key enzyme in the proinflammatory response and a large number of compounds have been studied as potential therapeutic drugs. This review summarizes the bioanalytical methods used for the analysis of p38 MAP kinase inhibitors, with a special focus on sample preparation and chromatographic analysis. Biological sample extraction techniques utilized included protein precipitation, liquid–liquid extraction and SPE. Applications include determinations of compounds in a variety of biological fluids and tissues. Extracted samples are typically separated by reverse-phase LC and quantitated either by UV or MS/MS detection. The benefits and limitations of each sample preparation strategy are discussed. The importance of chromatographic separation to avoid matrix effect and interference from endogenous compounds or drug-related biotransformation products are also discussed herein.

Chiral sulfoxides as metabolites of 2-thioimidazole-based p38α mitogen-activated protein kinase inhibitors: enantioselective synthesis and biological evaluation

A number of pharmaceutically important drugs contain asymmetric sulfinyl moieties, so the biological evaluation of chiral sulfoxides as human drug metabolites is important for the development of safe and effective pharmaceuticals. Asymmetric oxidation is one of the most attractive ways to prepare chiral sulfoxides. In combination with different chiral ligands, the iron- and titanium-catalyzed asymmetric oxidations of tri- and tetrasubstituted 2-thioimidazoles afford the corresponding sulfoxides with enantiomeric excesses up to 99% as novel p38α mitogen-activated protein kinase (p38α MAPK) inhibitors. The enantiomerically pure sulfoxides were evaluated on their inhibitory potency against p38α MAPK compared to the respective sulfides and sulfoxide racemates and showed differences in their affinities for the enzyme with IC(50) in the low nanomolar range. In addition, the ability to inhibit the release of tumor necrosis factor-α (TNF-α) from human whole blood (HWB) was examined. Some pyridinylimidazole derivatives showed excellent HWB activity with IC(50) as low as 52 nM.

Novel p38 MAPK inhibitor ML3403 has potent anti-inflammatory activity in airway smooth muscle

SB203580 is the prototypical p38 MAPK inhibitor; however it cannot be used clinically due to liver toxicity. We developed a structural analogue of SB203580 - ML3403 - with equal in vitro and ex vivo p38alpha MAPK inhibition as SB203580, but with reduced activity towards liver cytochrome P450 enzymes. In addition, we developed a selective p38alpha MAPK inhibitor - CP41. The aim of this study is to compare the anti-inflammatory activity of ML3403 and CP41, with SB203580. We compare and contrast the ability of the p38 MAPK inhibitors to repress tumour necrosis factor alpha (TNFalpha)-induced interleukin 6 (IL-6) and interleukin 8 (IL-8) mRNA expression and protein secretion from airway smooth muscle cells. We also examined and compared the binding affinities of ML3403 and SB203580 to the active and inactive p38alpha MAPK. We demonstrate that ML3403 binds to both active and inactive p38 MAPK with high affinity and that it inhibits p38 MAPK-mediated airway smooth muscle synthetic function to an equivalent degree with SB203580. CP41 was not able to reduce IL-6 and IL-8 secretion in airway smooth muscle cells; a function of its higher IC(50) against p38alpha MAPK when compared to SB203580 and ML3403. We show that p38 MAPK-mediated pro-inflammatory pathways in airway smooth muscle cells can be inhibited by ML3403. The anti-inflammatory activity is equivalent to the prototypical p38 MAPK inhibitor SB203580. Our results implicate a future pharmacotherapeutic strategy towards reducing inflammation in asthma and airway remodelling.

Trisubstituted purines are useful tools for developing potent plant mitogen-activated protein kinase inhibitors

A number of compounds have been reported to be specific inhibitors of protein kinases mediated by structural-based selectivity, but the development of specific inhibitors has not yet been addressed in plant science. Here we tested C2, C6, and N9-trisubstituted purines to determine the basic relationship between their chemical structure and inhibitory activity versus a plant mitogen-activated protein kinase (MAPK). Modification of substitution at positions C2 and N9 caused increased inhibitory activity of 6-benzylaminopurine analogs. In the case of 6-isopentenyladenine derivatives, the addition of a methyl group at position N9 caused at least 2-fold increased inhibitory activity, as compared with the addition of an isopropyl group. The data indicate that the selectivity and potency of inhibitors can be improved by modification of the chemical structure, suggesting that trisubstituted purines are powerful tools for probing biological processes and understanding the physiological roles of MAPK signaling.

2-Acylaminopyridin-4-ylimidazoles as p38 MAP kinase inhibitors: Design, synthesis, and biological and metabolic evaluations

Targeting cytokines has become an important focus in the treatment of many inflammatory disorders. p38 MAP kinase (MAPK) is the key enzyme in regulating the biosynthesis and release of pro-inflammatory cytokines such as IL-1beta and TNFalpha. Inhibition of p38 MAPK results in decreased expression of these cytokines. Tri- and tetrasubstituted pyridinylimidazoles are potent inhibitors of p38 MAPK. Substitution on the pyridinyl moiety allows the design of inhibitors that show increased selectivity and activity by targeting the enzyme's hydrophobic region II. The objective of this study was to synthesize novel 1,2,4,5-tetrasubstituted imidazole derivates and to characterize them not only for their ability to inhibit p38 MAPK and modulate cytokine release in human whole blood, but also to evaluate their metabolic stability. Biological data and metabolic studies demonstrate that the introduction of a 2-acylamino function at C2 of the pyridine results in highly efficient and metabolically stable inhibitors relative to C2-alkylamino derivatives. A series of novel candidates was investigated for metabolic stability in human liver microsomes and in human whole blood. Additionally, metabolic S-oxidation was investigated, and possible metabolites were synthesized.

alpha,beta-Unsaturated aldehydes contained in cigarette smoke elicit IL-8 release in pulmonary cells through mitogen-activated protein kinases

Cigarette smoking is the major risk factor for chronic obstructive pulmonary disease (COPD), a syndrome characterized by pulmonary neutrophil infiltration, chronic inflammation, and progressive tissue destruction. We examined here the acute effect of aqueous cigarette smoke extract (CSE) and of two alpha,beta-unsaturated aldehydes (acrolein and crotonaldehyde) contained in CSE in cultured normal human lung fibroblasts and small airway epithelial cells. By examining a panel of 19 cytokines and chemokines, we found that IL-8 release was elevated by CSE as well as by acrolein, whereas other inflammatory mediators were mostly unaffected. CSE-evoked IL-8 release was mimicked by acrolein and crotonaldehyde at concentrations (3-60 microM each) found in CSE and fully prevented by 1 mM alpha,beta-unsaturated aldehydes scavengers N-acetylcysteine (NAC) or sodium 2-mercaptoethanesulfonate. Neither the saturated aldehyde acetaldehyde nor H(2)O(2) evoked IL-8 release. In addition, CSE or crotonaldehyde upregulated the release of IL-8 from alveolar macrophages from both COPD patients and healthy nonsmokers, indicating that this is a response common to cells involved in lung inflammation. CSE-evoked IL-8 release was accompanied by increased phosphorylation of p38 MAPK and ERK1/2. CSE-evoked p38 and ERK1/2 phosphorylation was mimicked by acrolein and inhibited by NAC. IL-8 release elicited by both acrolein and CSE was blocked by pharmacological inhibition of p38 and ERK1/2 phosphorylation. In summary, our data show that alpha,beta-unsaturated aldehydes-evoked phosphorylation of p38 and ERK1/2 underlies IL-8 release elicited by CSE, thus shedding light on the mechanisms through which cigarette smoke can initiate inflammation in the lung.

Characterization and inhibition of a p38-like mitogen-activated protein kinase (MAPK) from Echinococcus multilocularis: antiparasitic activities of p38 MAPK inhibitors

Alveolar echinococcosis (AE), caused by the metacestode larval stage of the fox-tapeworm Echinococcus multilocularis, is a life-threatening disease with very limited treatment options. In search for novel drug targets, we concentrate on factors of the cellular signaling machinery and report herein the characterization of a novel gene, Emmpk2, which is expressed in the parasite's larval stage and which codes for a member of the mitogen-activated protein kinase (MAPK) family. On the amino acid sequence level, the encoded protein, EmMPK2, shares considerable homologies with p38 MAPKs from a wide variety of animal organisms but also displays several distinct differences, particularly in amino acid residues known to be involved in the regulation of enzyme activity. Upon heterologous expression in Escherichia coli, purified EmMPK2 showed prominent autophosphorylation activity and strongly elevated basal activity towards a MAPK substrate, when compared to the closest human orthologue, p38-alpha. EmMPK2 activity could be effectively inhibited in the presence of ML3403 and SB202190, two ATP-competitive pyridinyl imidazole inhibitors of p38 MAPKs, in a concentration-dependent manner. When added to in vitro cultivated metacestode vesicles, SB202190 and particularly ML3403 led to dephosphorylation of EmMPK2 in the parasite and effectively killed parasite vesicles at concentrations that did not affect cultivated mammalian cells. Taken together, these results identify pyridinyl imidazoles as a novel class of anti-Echinococcus compounds and EmMPK2 as a promising target for the development of drugs against alveolar echinococcosis.