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

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.