Inflammation Control: Novel Boron-Based Inhibitors of IL-1beta Release

Abstract

The NLRP3 inflammasome is a high molecular weight structure responsible for sensing and reacting to injury and infection during inflammation. Its activation induces caspase-1 activation and interleukin-1beta (IL-1beta) release, a pro-inflammatory cytokine involved in both acute and chronic inflammatory responses. There is increasing evidence that inappropriate activation of the NLRP3 inflammasome and IL-1beta release is associated with a number of sterile, non-communicable diseases including gout, atherosclerosis, type II diabetes and Alzheimer's disease. Thus the NLRP3 inflammasome is regarded as a therapeutic target for the treatment of sterile inflammation. Medicinal chemistry was used to design and synthesise a library of forty novel boron compounds (termed the NBC series) based on the previously identified NLRP3 inflammasome oxazaborine inhibitors BC7 and BC23. The synthesis of 2,2-diphenyl/diaryl-1,3,2-oxaza/dioxaborines involved the borylation of 1,3-dicarbonyls or beta-enaminone intermediates using diphenyborinic anhydride (DPBA) or mono-/diarylborinic acids. 2,2-Diphenyl-1,3,2-diazaborines were synthesised by reacting oxazaborine BC23 with primary amines. The proposed chelation of two NBC molecules was confirmed using X-ray crystallography. NBC compounds were tested for IL-1beta inhibitory activity in an NLRP3-induced human THP-1 cell line. Structure-activity relationship (SAR) analysis revealed that a boron atom chelated in an oxazaborine ring and the presence of a CCl3 group was essential for IL-1beta inhibitory activity. The most potent compound identified in the series, NBC6, is a specific, irreversible inhibitor of IL-1beta release in THP-1 cells with an IC50 of 0.57 microM, and blocks NLRP3 inflammasome activation in vitro and in vivo. The synthesis of a biotinylated NBC probe for target identification purposes was attempted. A bioorthogonal click chemistry approach using the copper(I)-catalysed azide-alkyne cycloaddition reaction of alkyne NBC21 with a fluorescent azide was successful in BMDM cells. Subsequent chemoproteomic studies using biotin are in progress to elucidate the precise cellular target. Mechanism of action studies suggested that the BC/NBC molecules inhibit by covalent modification, however they were not cysteine modifiers. A hypothesis is that they may inhibit a serine protease and further studies are in progress.

Date of Award	31 Dec 2017
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Sally Freeman (Supervisor), Stuart Allan (Supervisor), Richard Bryce (Supervisor) & David Brough (Supervisor)