Cetuximab and U3-1287 induced apoptosis in CtxRclones. (A) Combinatorial treatment with cetuximab and U3-1287 activates Caspase 3/7 compared to either drug alone in CtxR clones. Caspase-3/7 activity was determined by Caspase 3/7-Glo assay. Data represent means ± s.e.m from 3 independent experiments (n = 9). *p <0.05 or **p <0.01. (B) The percentage of Annexin v-positive/propidium iodide-negative cells was increased significantly after the combination of cetuximab and U3-1287 treatment compared to vehicle, cetuximab or U3-1287 alone in the CtxR clones. Cells were plated and allowed to adhere for 24 h prior to treatment with vehicle, cetuximab (20 ug/mL), U3-1287 (50 ug/mL) or the combination of cetuximab (20 ug/mL) and U3-1287 (50 ug/mL) for 24 h prior to Annexin-v analysis via flow cytometry. Data points are represented as mean ± s.e.m. (n = 3). *p <0.05 or **p ≤0.001. Flow cytometry profile in HC4 cells represents Annexin-V-FITC staining in x-axis and PI in y-axis. The number represents the percentage of cells in each condition.