Compound 1 bearing with benzo [cd]indol-2(1H)-one scaffold was identified as an effective BRD4 inhibitor through the AlphaScreen-based high-throughput screening and its high-resolution crystal structure with BRD4_BD1 protein. A series of 48 compounds were designed and synthesized by structural optimization on compound 1. All the compounds have been evaluated for their BRD4 inhibitory activities. The results showed that compounds 23, 24, 28 and 44 are the most potential ones with the IC50 values of 1.02 μM, 1.43 μM, 1.55 μM and 3.02 μM, respectively. According to their co-crystal structures in complex with BRD4_BD1 and the protein thermal shift assays, the binding modes were revealed that the additional indirect hydrogen bonds and hydrophobic interactions make such four compounds more active than 1 against BRD4. Furthermore, compounds 1, 23 and 44 were chosen to evaluate for their antiproliferative activities on the MLL-AF4-expression acute leukemia cell line (MV4-11), other cancer cell lines (MDA-MB-231, A549, 22Rv1) and the non-cancer cell lines (HUV-EC-C, MRC5, RPTEC). The results showed that these compounds exhibited good and selective inhibitory activities against MV4-11 cells with the IC50 values of 11.67 μM, 5.55 μM, and 11.54 μM, respectively, and could act on the cell proliferation by blocking cell cycle at G1 phase. They could markedly down-regulate the expressions of the c-Myc, Bcl-2 and CDK6 oncogenes in MV4-11 in the qRT-PCR and western blot studies, which further demonstrated that compound 1 and its derivatives could serve as a promising therapeutic strategy for MLL leukemia by targeting BRD4_BD1 protein.
Keywords: Acetyl-lysine binding pocket; BRD4 inhibitor; Benzo[cd]indol-2(1H)-one; Bromodomain and extra-terminal domain; Sulfonamide.
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