Synthesis and analytical characterization of new thiazol-2-(3H)-ones as human neutrophil elastase (HNE) inhibitors

Design and synthesis of thiadiazole-oxadiazole-acetamide derivatives: Elastase inhibition, cytotoxicity, kinetic mechanism, and computational studies

Considering the biological significance of 1,3,4-thiadiazole/oxadiazole heterocyclic scaffolds, a novel series of 1,3,4-thiadiazole-1,3,4-oxadiazole-acetamide derivatives (7a-j) was designed and synthesized using molecular hybridization. The inhibitory effects of the target compounds on elastase were evaluated, and all of these molecules were found to be potent inhibitors compared to the standard reference oleanolic acid. Compound 7f exhibited the excellent inhibitory activity (IC₅₀ = 0.06 ± 0.02 μM), which is 214-fold more active than oleanolic acid (IC₅₀ = 12.84 ± 0.45 μM). Kinetic analysis was also performed on the most potent compound (7f) to determine the mode of binding with the target enzyme, and it was discovered that 7f inhibits the enzyme in a competitive manner. Furthermore, the MTT assay method was used to assess their toxicity on the viability of B16F10 melanoma cell lines, and all compounds did not display any toxic effect on the cells even at high concentrations. The molecular docking studies of all compounds also justified with their good docking score and among them, compound 7f had a good conformational state with hydrogen bond interactions within the receptor binding pocket, which is consistent with the experimental inhibition studies.

Exploration of nitrogen heterocycle scaffolds for the development of potent human neutrophil elastase inhibitors

Human neutrophil elastase (HNE) is a potent protease that plays an important physiological role in many processes but is also involved in a variety of pathologies that affect the pulmonary system. Thus, compounds able to inhibit HNE proteolytic activity could represent effective therapeutics. We present here a new series of pyrazolopyridine and pyrrolopyridine derivatives as HNE inhibitors designed as modifications of our previously synthesized indazoles and indoles in order to evaluate effects of the change in position of the nitrogen and/or the insertion of an additional nitrogen in the scaffolds on biological activity and chemical stability. We obtained potent HNE inhibitors with IC₅₀ values in the low nanomolar range (10-50 nM), and some compounds exhibited improved chemical stability in phosphate buffer (t_1/2 > 6 h). Molecular modeling studies demonstrated that inhibitory activity was strictly dependent on the formation of a Michaelis complex between the OH group of HNE Ser195 and the carbonyl carbon of the inhibitor. Moreover, in silico ADMET calculations predicted that most of the new compounds would be optimally absorbed, distributed, metabolized, and excreted. Thus, these new and potent HNE inhibitors represent novel leads for future therapeutic development.

Novel Sulfonamide Analogs of Sivelestat as Potent Human Neutrophil Elastase Inhibitors

Human neutrophil elastase (HNE) is involved in a number of essential physiological processes and has been identified as a potential therapeutic target for treating acute and chronic lung injury. Nevertheless, only one drug, Sivelestat, has been approved for clinical use and just in Japan and the Republic of Korea. Thus, there is an urgent need for the development of low-molecular-weight synthetic HNE inhibitors, and we have developed a wide variety of HNE inhibitors with various chemical scaffolds. We hypothesized that substitution of the active fragment of Sivelestat into these HNE inhibitor scaffolds could modulate their inhibitory activity, potentially resulting in higher efficacy and/or improved chemical stability. Here, we report the synthesis, biological evaluation, and molecular modeling studies of novel compounds substituted with the 4-(sulfamoyl)phenyl pivalate fragment necessary for Sivelestat activity. Many of these compounds were potent HNE inhibitors with activity in the nanomolar range (IC50 = 19-30 nM for compounds 3a, 3b, 3f, 3g, and 9a), confirming that the 4-(sulfamoyl)phenyl pivalate fragment could substitute for the N-CO group at position 1 and offer a different point of attack for Ser195. Results of molecular docking of the these pivaloyl-containing compounds into the HNE binding site supported the mechanism of inhibitory activity involving a nucleophilic attack of Ser195 from the catalytic triad onto the pivaloyl carbonyl group. Furthermore, some compounds (e.g., 3a and 3f) had a relatively good stability in aqueous buffer (t1/2 > 9 h). Thus, this novel approach led to the identification of a number of potent HNE inhibitors that could be used as leads for the further development of new therapeutics.

Neutrophil Elastase Inhibitors and Chronic Kidney Disease

End-stage renal disease (ESRD), the last stage of chronic kidney disease (CKD), is characterized by chronic inflammation and oxidative stress. Neutrophils are the front line cells that mediate an inflammatory response against microorganisms as they can migrate, produce reactive oxygen species (ROS), secrete neutrophil serine proteases (NSPs), and release neutrophil extracellular traps (NETs). Serine proteases inhibitors regulate the activity of serine proteases and reduce neutrophil accumulation at inflammatory sites. This review intends to relate the role of neutrophil elastase in CKD and the effects of neutrophil elastase inhibitors in predicting or preventing inflammation.