(A) Cell growth assay following treatment with the indicated doses of volasertib. (B) Cell cycle analysis conducted at 48 h after treatment with volasertib (5 nM). (C) Apoptosis assay conducted at 48 h after treatment with the indicated doses of volasertib. (D) Cell growth assay following transfection with PLK1 or control siRNAs. (E) Cell cycle analysis conducted at 48 h after siRNA transfection. (F) Apoptosis assay conducted at 48 h after siRNA transfection. (G) Cell growth assay following treatment with the various doses of volasertib, JQ1, and their combinations for 72 h. (H) Apoptosis assay conducted at 48 h after a single treatment with volasertib (5 nM), JQ1 (500 nM), and their combination at doses that did not induce significant apoptosis individually. (I) Cell growth assay following treatment with the various doses of volasertib, FX1, and their combinations for 72 h. (J) Apoptosis assay conducted at 48 h after a single treatment with volasertib (5 nM), FX1 (50 μM), and their combination at doses that did not induce significant apoptosis individually. Data are shown as the mean ± SEM of three independent experiments. Significant expression differences are shown as *P < 0.05; **P <0.01.