Targeting BRD9 by I-BRD9 efficiently inhibits growth of acute myeloid leukemia cells

Background: Acute myeloid leukemia (AML) is characterized by genetic and epigenetic mutations that lead to a block in differentiation as well as unrestrained proliferation. Many epigenetic regulators have been shown to be important for AML initiation and development. Among these, bromodomain-containing protein 9 (BRD9), an epigenetic regulator, was recently identified as a critical factor required for AML development. Hence targeting BRD9 may provide a new therapeutic strategy. Thus, we investigated the role of BRD9 inhibitor I-BRD9 in AML cells and its potential mechanisms.

Methods: Cell Counting Kit-8 (CCK-8) assays were performed to explore the growth inhibitory effects of I-BRD9 on AML cells. Flow cytometry was used to examine the effects of I-BRD9 on apoptosis, Edu incorporation, and cell differentiation. Apoptotic pathway activation was confirmed by western blot. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was employed to analyze cell death and cell cycle-related gene expression.

Results: I-BRD9 significantly reduced AML cells growth. This is accompanied by decreased Edu incorporation and dramatic cell death. Mechanistically, cell death induced by I-BRD9 was largely blocked by the pan-caspase inhibitor Z-VAD-FMK and, to a lesser extent, by Ferrostatin-1.Furthermore, apoptotic markers including the cleavage of PARP, Capase9, and Capsese3, were induced by I-BRD9, which were rescued by pretreatment with Z-VAD-FMK. In addition, I-BRD9 treatment increased IRE3, CDKN1A, and CDKN2B expression in AML cells, possibly leading to the observed decrease in Edu incorporation. Together, these data strongly suggested that I-BRD9 induced growth inhibition in AML cells was dependent on apoptosis and cell cycle inhibition.

Conclusions: Our data support the important role of BRD9 in AML cells; moreover, the BRD9 inhibitor I-BRD9 could be potentially useful in the treatment of AML .