Suppression of inflammation by a synthetic histone mimic

Abstract

Interaction of pathogens with cells of the immune system results in activation of inflammatory gene expression. This response, while vital for immune defence, is frequently deleterious to the host due to the exaggerated production of inflammatory proteins. The scope of inflammatory responses reflects the activation state of signalling proteins upstream of inflammatory genes as well as signal-induced assembly of nuclear chromatin complexes that support mRNA expression1–4. Recognition of post-translationally modified histones by nuclear proteins that initiate mRNA transcription and support mRNA elongation is a critical step in the regulation of gene expression5–10. Here we present a novel pharmacological approach that targets inflammatory gene expression by interfering with the recognition of acetylated histones by the Bromodomain and Extra Terminal domain (BET) family of proteins. We describe a synthetic compound (I-BET) that by “mimicking” acetylated histones disrupts chromatin complexes responsible for the expression of key inflammatory genes in activated macrophages and confers protection against LPS-induced endotoxic shock and bacteria-induced sepsis. Our findings suggest that synthetic compounds specifically targeting proteins that recognize post-translationally modified histones can serve as a new generation of immunomodulatory drugs.

JQ1 affects BRD2-dependent and independent transcription regulation without disrupting H4-hyperacetylated chromatin states

“…In LPS-activated macrophages, BET inhibition reduced the levels of H3ac, H4K5ac, H4K8ac, H4K12ac, and total H4ac on promoters of the induced genes [38]. This reduction is presumably due to increased accessibility of HDAC to the exposed BET protein binding sites by preventing the formation of multi-molecular complexes containing histone acetyltransferases (HATs) and other transcription machineries [38], as shown by the reduced level of positive transcription elongation factor b (P-TEFb/CDK9) and RNA polymerase II on the affected regions [38]. In H23 cells, however, a subset of BRD2-bound genes involved in RNA processing, such as POL2RA and CDK9, was in fact upregulated, and the transcription levels of HATs, such as KAT2A and EP300, were not affected by JQ1.…”

The bromodomain interaction module

“…Additionally, JQ1 was shown to have therapeutic effects in multiple myelomas, through regulation of the Myc oncogenic driver in these tumors [100]. Another benzodiazepine scaffold (IBET) was shown to exhibit great potential as an anti-inflammatory agent, by reducing expression of pro-inflammatory genes in activated macrophages [20].…”

Discovery of Benzotriazolo[4,3-d][1,4]diazepines as Orally Active Inhibitors of BET Bromodomains

“…CPI-3) 13 and with what others have observed with related scaffolds. 4,5 Substitutions at other positions of the benzo ring or at the 1 position of the isoxazole diminished potency (data not shown).…”

“…Specifically, we hypothesized that changing the cyclic imine to a substituted aniline would retain the concave shape important for specific binding to the bromodomain while providing a different metabolic profile for the series. We were also interested in evaluating a modified linker in combination with the reported triazole binding element 4,5 and in finding a replacement for the thiophene group of CPI-3 because of its potential metabolic instability. Here we describe the resulting benzo [b]isoxazolo- [4,5-d]azepine and benzotriazolo [4,3-d] [1,4]diazepine series, which were potent inhibitors of BET bromodomains in biochemical and cellular assays and which allowed for optimization of metabolic stability and demonstration of a pharmacodynamic effect in a mouse model of IL-6 suppression (Scheme 1).…”