Effects of CDK4/6 inhibitors in MLL-rearranged AML cell lines. (A) Cell proliferation assay. ML-2, MV4-11, MOLM-13, THP-1, and NOMO-1 cells were cultured in the presence of DMSO, palbociclib (500 nM), or abemaciclib (500 nM). (B) Cell-cycle analysis. Flow cytometric analysis of cell lines treated with DMSO, palbociclib (500 nM), or abemaciclib (500 nM) for 24 hours and stained with propidium iodide. (C) Comparison of percentages of G2/M and S phase cells. (D) Immunoblot analysis revealed significantly lower expression of cyclin D3 proteins in THP-1 cells transfected with siRNA against human cyclin D3 transcript (left column: siCCND3) than in THP-1 cells transfected with non-targeting siRNA (right column: siControl). (E-G) THP-1 cells transfected with siCCND3 showed significant impairment in cell proliferation (E) and cell-cycle progression from G1 to S phase (F-G) compared with those transfected with nontargeting siRNA. (H) Schematic figure showing that the cyclin D3-CDK4/6 complex promotes cell-cycle progression and CDK4/6 inhibitors are promising therapeutic agents in MLL-rearranged AML cells. Data are presented as the mean ± standard error of 3 independent experiments. ***P < .001, *P < .05.