Novel thiazolopyridine derivatives of diflapolin as dual sEH/FLAP inhibitors with improved solubility.

Inflammatory responses are orchestrated by a plethora of lipid mediators, and perturbations of their biosynthesis or degradation hinder resolution and lead to uncontrolled inflammation, which contributes to diverse pathologies. Small molecules that induce a switch from pro-inflammatory to anti-inflammatory lipid mediators are considered valuable for the treatment of chronic inflammatory diseases. Commonly used non-steroidal anti-inflammatory drugs (NSAIDs) are afflicted with side effects caused by the inhibition of beneficial prostanoid formation and redirection of arachidonic acid (AA) into alternative pathways. Multi-target inhibitors like diflapolin, the first dual inhibitor of soluble epoxide hydrolase (sEH) and 5-lipoxygenase-activating protein (FLAP), promise improved efficacy and safety but are confronted by poor solubility and bioavailability. Four series of derivatives bearing isomeric thiazolopyridines as bioisosteric replacement of the benzothiazole core and two series additionally containing mono- or diaza-isosteres of the phenylene spacer were designed and synthesized to improve solubility. The combination of thiazolo[5,4-b]pyridine, a pyridinylen spacer and a 3,5-Cl2-substituted terminal phenyl ring (46a) enhances solubility and FLAP antagonism, while preserving sEH inhibition. Moreover, the thiazolo[4,5-c]pyridine derivative 41b, although being a less potent sEH/FLAP inhibitor, additionally decreases thromboxane production in activated human peripheral blood mononuclear cells. We conclude that the introduction of nitrogen, depending on the position, not only enhances solubility and FLAP antagonism (46a), but also represents a valid strategy to expand the scope of application towards inhibition of thromboxane biosynthesis.

MicroRNA-146a promotes proliferation, migration, and invasion of HepG2 via regulating FLAP.

Abnormal expression of 5-Lipoxygenase Activating Protein (FLAP) has been detected in many tumor cells. MicroRNAs (miRNAs) negatively regulate gene expression post-transcriptionally by binding to the 3'-untranslated region (3'-UTR) of the target mRNA sequences and have been shown to be involved in various types of cancers. Herein, we aimed to demonstrate the expression of miR-146a and FLAP in human HCC tissues and liver cancer cell lines. We demonstrated that miR-146a expression is overexpressed, while FLAP protein and mRNA are suppressed in hepatocellular carcinoma tissues and HepG2 cells compared to para-carcinoma tissues and HL-7702 cells. Dual luciferase reporter gene assay showed that miR-146a-5p can directly target FLAP mRNA. Knockdown of miR-146a also resulted in increased FLAP expression of cancer cells. Additionally, miR-146a silencing or restoration of FLAP led to a reduction of HepG2 cell proliferation, cell cycle progression, migration, and invasion. This study showed that miR-146a has a stimulatory role in HepG2 cells and promotes HepG2 cell migration and invasion by targeting FLAP mRNA. Thus, miR-146a may be a tumor promoter and a potential therapeutic target for the treatment of HCC patients.

Synthesis and structure-activity relationships for some novel diflapolin derivatives with benzimidazole subunit.

A series of derivatives of the potent dual soluble epoxide hydrolase (sEH)/5-lipoxygenase-activating protein (FLAP) inhibitor diflapolin was designed, synthesised, and characterised. These novel compounds, which contain a benzimidazole subunit were evaluated for their inhibitory activity against sEH and FLAP. Molecular modelling tools were applied to analyse structure-activity relationships (SAR) on both targets and to predict solubility and gastrointestinal (GI) absorption. The most promising dual inhibitors of these series are 5a, 6b, and 6c.

Biosynthesis of leukotriene B4.

Leukotriene B4 (LTB4) is a lipid mediator derived from arachidonic acid (AA) by the sequential action of 5-lipoxygenase (5-LOX), 5-lipoxygenase-activating protein (FLAP) and LTA4 hydrolase (LTA4H). It was initially recognized for its involvement in the recruitment of neutrophils and is one of the most potent chemotactic agents known to date. A large body of data has indicated that LTB4 plays a significant role in many chronic inflammatory diseases, such as arthritis, chronic obstructive pulmonary disease (COPD), cardiovascular disease, cancer and more recently, metabolic disorder. In this review, we focus on the biosynthesis of LTB4 and its biological effects. In particular, we will describe a basic biochemical understanding integrated with recent developments in the field of structural biology of the three key enzymes (5-LOX, FLAP and LTA4H) in LTB4 biosynthesis, and also summarize the most outstanding work on in vivo biological and pathogenic roles of these enzymes and the development of enzyme inhibitors.

Effects of a FLAP inhibitor, GSK2190915, in asthmatics with high sputum neutrophils.

Patients with refractory asthma frequently have neutrophilic airway inflammation and respond poorly to inhaled corticosteroids. This study evaluated the effects of an oral 5-lipoxygenase-activating protein (FLAP) inhibitor, GSK2190915, in patients with asthma and elevated sputum neutrophils. Patients received 14 (range 13-16) days treatment with GSK2190915 100 mg and placebo with a minimum 14 day washout in a double-blind, cross-over, randomised design (N = 14). Sputum induction was performed twice pre-dose in each treatment period to confirm sputum neutrophilia, and twice at the end of each treatment period. The primary endpoint was the percentage and absolute sputum neutrophil count, averaged for end-of-treatment visits. GSK2190915 did not significantly reduce mean percentage sputum neutrophils (GSK2190915-placebo difference [95% CI]: -0.9 [-12.0, 10.3]), or mean sputum neutrophil counts (GSK2190915/placebo ratio [95% CI]: 1.06 [0.43, 2.61]). GSK2190915 resulted in a marked suppression (>90%) of sputum LTB4 and urine LTE4, but did not alter clinical endpoints. There were no safety issues. Despite suppressing the target mediator LTB4, FLAP inhibitor GSK2190915 had no short-term effect on sputum cell counts or clinical endpoints in patients with asthma and sputum neutrophilia.

Combined Machine Learning and GRID-Independent Molecular Descriptor (GRIND) Models to Probe the Activity Profiles of 5-Lipoxygenase Activating Protein Inhibitors.

Leukotrienes (LTs) are pro-inflammatory lipid mediators derived from arachidonic acid (AA), and their high production has been reported in multiple allergic, autoimmune, and cardiovascular disorders. The biological synthesis of leukotrienes is instigated by transfer of AA to 5-lipoxygenase (5-LO) via the 5-lipoxygenase-activating protein (FLAP). Suppression of FLAP can inhibit LT production at the earliest level, providing relief to patients requiring anti-leukotriene therapy. Over the last 3 decades, several FLAP modulators have been synthesized and pharmacologically tested, but none of them could be able to reach the market. Therefore, it is highly desirable to unveil the structural requirement of FLAP modulators. Here, in this study, supervised machine learning techniques and molecular modeling strategies are adapted to vaticinate the important 2D and 3D anti-inflammatory properties of structurally diverse FLAP inhibitors, respectively. For this purpose, multiple machine learning classification models have been developed to reveal the most relevant 2D features. Furthermore, to probe the 3D molecular basis of interaction of diverse anti-inflammatory compounds with FLAP, molecular docking studies were executed. By using the most probable binding poses from docking studies, the GRIND model was developed, which indicated the positive contribution of four hydrophobic, two hydrogen bond acceptor, and two shape-based features at certain distances from each other towards the inhibitory potency of FLAP modulators. Collectively, this study sheds light on important two-dimensional and three-dimensional structural requirements of FLAP modulators that can potentially guide the development of more potent chemotypes for the treatment of inflammatory disorders.