Discovery of 2-(Pyrazol-4-yl)-quinazolin-4(3H)-one Derivatives as Subnanomolar BRD4 BD2 Inhibitors with High Selectivity via a Bioisosterism Approach

BRD4, a bromodomain-containing protein, has emerged as an attractive therapeutic target for various diseases. Selective inhibition of the bromodomain is gaining traction as a promising strategy for targeted drug discovery. Based on bioisosterism-guided optimization of RVX-OH (8), a pan-BET inhibitor, we designed and synthesized a series of novel quinazolin-4(3H)-one derivatives as potent BRD4 inhibitors. Among them, 2-(1H-pyrazol-4-yl)quinazolin-4(3H)-one B6 exhibited subnanomolar BRD4 BD2 inhibitory activity with an IC₅₀ value of 0.41 nM and a remarkably 39,683-fold selectivity over BRD4 BD1. 2D ¹H-¹⁵N TROSY spectra distinctly demonstrated the high-affinity binding of B6 to BRD4 BD2. Furthermore, B6 obviously inhibited the lipopolysaccharide (LPS)-induced expression of interleukin (IL)-6. This potent and selective inhibitor B6 with cellular activity will further add to the understanding of individual bromodomains of BRD4 in epigenetic regulation and promote the discovery of novel lead compounds for the treatment of inflammatory diseases.