Combination of prexasertib and adavosertib causes mitotic catastrophe. (a–d) Quantification of percent of CAL27 and FaDu cells (a) undergoing apoptosis without prior mitosis; (b) entering into mitosis; (c) unable to successfully complete mitosis; (d) undergoing apoptosis after initially entering mitosis over 24 h of live cell imaging following addition of indicated drugs; and (e) representative images of CAL27 cells related to (a–d). Scale bar, 30 um; (f) confocal images of cells, stained with DAPI to visualize nuclei (blue), and antibody to acetylated α-tubulin to visualize mitotic spindle (green), or to phospho-histone H3 to visualize DNA breaks (red), 24 h after treatment with indicated drugs. Scale bar, 10 um. All graphs: *, p ≤ 0.05; relative to vehicle controls.