Design, Synthesis, and in vitro Biological Evaluation of 3,5-Dimethylisoxazole Derivatives as BRD4 Inhibitors

Abstract

BRD4 has been identified as a potential target for blocking proliferation in a variety of cancer cell lines. In this study, 3,5-dimethylisoxazole derivatives were designed and synthesized with excellent stability in liver microsomes as potent BRD4 inhibitors, and were evaluated for their BRD4 inhibitory activities in vitro. Gratifyingly, compound 11 h [3-((1-(2,4-difluorophenyl)-1H-1,2,3-triazol-4-yl)methyl)-6-(3,5-dimethylisoxazol-4-yl)-4-phenyl-3,4-dihydroquinazolin-2(1H)-one] exhibited robust potency for BRD4(1) and BRD4(2) inhibition with IC₅₀ values of 27.0 and 180 nm, respectively. Docking studies were performed to illustrate the strategy of modification and analyze the conformation in detail. Furthermore, compound 11 h was found to potently inhibit cell proliferation in the BRD4-sensitive cell lines HL-60 and MV4-11, with IC₅₀ values of 0.120 and 0.09 μm, respectively. Compound 11 h was further demonstrated to downregulate c-Myc levels in HL-60 cells. In summary, these results suggest that compound 11 h is most likely a potential BRD4 inhibitor and is a lead compound for further investigations.

Keywords: 3,5-dimethylisoxazoles; BRD4; antitumor agents; inhibitors; lysine acetylation.