I-BET151 induces cell cycle arrest and apoptosis in myeloma cell lines. (A) Propidium iodide (PI) staining and flow cytometric cell cycle and apoptosis analysis at indicated time points of the myeloma cell line H929 treated with DMSO or 1 μM I-BET151. (B) Cell cycle analysis of H929 cells after 72-hour culture in the presence of escalating concentrations of I-BET151. Cumulative results of apoptosis induction (subG₀/G₁) and inhibition of cell proliferation (S/G₂ phase). Data are shown as mean ± standard error of the mean (SEM) (n = 3). (C) PI/Ki67 staining and flow cytometric cell cycle analysis of the H929 myeloma cells treated with DMSO or 1 μM I-BET151 for 72 hours. (D) Dose- and time-dependent inhibition of H929 cell proliferation by I-BET151 as assessed by a luminescent proliferation assay. Data are shown as mean ± SEM (n = 3). (E) Flow cytometric assessment of bromodeoxyuridine (BrdU) incorporation by H929 myeloma cells after culture with DMSO or 1 μM I-BET151 for 72 hours. (F) Top: Annexin-V/4',6-diamidino-2-phenylindole (DAPI) staining and flow cytometric analysis of cell viability after treating H929 myeloma cells for the indicated time points with 1 μM I-BE151. Bottom: percent apoptosis (ie, Annexin-V+ cells) in each of the 6 myeloma cell lines at 72 hours after treatment with DMSO or I-BET151. *P < .05, **P < .01. (G) Histograms showing the IC₅₀ of I-BET151 against myeloma cell lines cultured in MS5 cell stroma or stroma-free conditions (mean ± SEM; n = 3), as assessed by a luminescent adenosine triphosphate (ATP) detection-based proliferation assay.