Efficacy of Novel Highly Specific Bromodomain-Containing Protein 4 Inhibitors in Innate Inflammation–Driven Airway Remodeling

Abstract

NFκB/RelA triggers innate inflammation by binding to Bromodomain-Containing Protein 4 (BRD4), an atypical histone acetyltransferase (HAT). Although RelA·BRD4 HAT mediates acute neutrophilic inflammation, its role in chronic and functional airway remodeling is not known. We observed that BRD4 is required for TLR3 mediated mesenchymal transition, a cell-state change that is characteristic of remodeling. We therefore tested novel highly selective BRD4 inhibitors, ZL0420 and -0454, on chronic airway remodeling produced by repetitive TLR3 agonist challenges, and compared their efficacy with nonselective BET protein inhibitors, JQ1 and RVX208. We observed that ZL0420 and -0454 more potently reduced poly(I:C)-induced weight loss, fibrosis assessed by micro-CT and second harmonic generation microscopy; these measures correlated with collagen deposition observed in histopathology. Importantly the ZL inhibitors were more effective than that of nonselective BET inhibitors at equivalent doses. The ZL inhibitors had significant effects on lung physiology, reversing TLR3-associated airway hyper responsiveness (AHR) and increasing lung compliance in vivo. At the molecular level, ZL inhibitors reduced elaboration of the TGF β-induced growth program, preventing mucosal mesenchymal transition, disrupting BRD4 HAT activity, and complex formation with RelA. We also observed that ZL0454 treatment blocked poly(I:C)-associated expansion of the αSMA1+/COL1A+ myofibroblast population, and prevented myofibroblast transition in a co-culture system. We conclude that 1) BRD4 is a central effector of mesenchymal transition that results in paracrine activation of myofibroblasts, mechanistically linking innate inflammation to AHR and fibrosis, and 2) highly selective BRD4 inhibitors may be effective in reversing the effects of repetitive airway viral infections on innate inflammation-mediated remodeling.

RSV Reprograms the CDK9•BRD4 Chromatin Remodeling Complex to Couple Innate Inflammation to Airway Remodeling

“…The essential functional role of CDK9•BRD4 in RSV-induced IIR has been demonstrated by disruption of P-TEFb recruitment by RelA Ser 276 site mutation [52], siRNA-mediated silencing of CDK9 and BRD4 [24,52,53,61], and small-molecule inhibition of CKD9 and BRD4 [34,48,53]. Consequently, CDK9•BRD4 are molecules receiving significant attention as a target for pharmacological manipulation of viral and allergen-inducible mucosal inflammation [48,[62][63][64][65][66].…”

A Bromodomain-Containing Protein 4 (BRD4) Inhibitor Suppresses Angiogenesis by Regulating AP-1 Expression

“…The family of bromodomain and extra-terminal domain (BET) proteins is composed of bromodomain-containing protein 2 (BRD2), BRD3, BRD4, and bromodomain testis-specific protein (BRDT). BRD4, an epigenetic reader, is one of the most important BET proteins and plays an important role in angiogenesis and the development of inflammation-associated diseases, cardiovascular diseases, central nervous system disorders and cancers ( Belkina and Denis, 2012 ; Shi et al., 2014 ; Padmanabhan et al., 2016 ; Tian et al., 2016 ; Wu et al., 2017 ; Liu et al., 2018 ; Tan et al., 2018 ; Tian et al., 2018 ; Tian et al., 2019a ; Tian et al., 2019b ; Zhao et al., 2019 ). Similar to other BET family members, BRD4 contains two highly conserved N -terminal bromodomains (BDs), BD1 and BD2, which can recognize acetylated lysine residues and non-histone proteins to transcriptionally regulate gene expression, cell cycle progression, cell proliferation, and apoptosis ( Dey et al., 2000 ; Kanno et al., 2004 ; Dey et al., 2009 ).…”

“…BRD4 BD2 recognizes and binds to diacetylated histone H3 and recruits non-histone proteins ( Filippakopoulos et al., 2012 ; Shi et al., 2014 ; Liu et al., 2017 ). BRD4 is considered a promising therapeutic target in various human diseases ( Filippakopoulos and Knapp, 2014 ; Cully, 2017 ; Liu et al., 2017 ; Cochran et al., 2019 ; Niu et al., 2019 ; Tian et al., 2019a ; Tian et al., 2019b ; Zhao et al., 2019 ; Alamer et al., 2020 ; Brasier and Zhou, 2020 ). Consequently, discovery and development of BRD4 inhibitors is urgently needed and has attracted increasing attention.…”

BETting on Novel Treatments for Asthma: Bromodomain 4 Inhibitors

“…Poly(I:C)-induced RelA-BRD4 binding was disrupted by these BRD4 inhibitors in association with blockade of the EMT program. The study by Tian and colleagues (9) provides convincing in vitro and in vivo data indicating that BRD4 inhibition can prevent poly(I:C)/TLR3-induced airway remodeling. In addition to efficacy end-points in this murine model, they assessed the toxicity of these selective BRD4 inhibitors by analyzing blood chemistry, examining morphological changes in lung, kidney, and liver.…”

“…In this issue of the Journal, Tian and colleagues (pp. 68-83) report that BRD4 inhibitors suppress inflammation-driven airway remodeling using in vitro and in vivo approaches (9). They report that BRD4 is required for polyinosinic:polycytidylic acid (poly(I:C))-activated, Toll-like receptor 3 (TLR3)-dependent epithelial-mesenchymal transition (EMT) of airway epithelial cells.…”