Figure 2: Drug combination effects in U2-OS osteosarcoma cells. The CellTiter-Blue assay was used to monitor viability in treated wells relative to untreated wells (% of untreated). Caspase 3/7 activation was measured after 24-hour concurrent treatments. (a) Vorinostat plus etoposide concurrent treatment. Cell viability was measured after 72-hour drug treatment. Vertical axis represents mean viability result for 5 independent experiments (). Apoptosis panel shows percent caspase 3/7 activation relative to untreated controls (100%). (b) Sorafenib plus topotecan concurrent and sequential drug treatment effects on cell viability. Sequential treatment consisted of a 24-hour pretreatment with sorafenib followed by the addition of topotecan. Cell viability was measured 48 hours after topotecan addition. (c) Dasatinib plus topotecan concurrent treatment. 72-hour cell viability assays were performed at constant drug ratios of 2 : 1 and 1 : 1. Caspase 3/7 activation was assayed after a 24-hour concurrent drug treatment (1 : 1 ratio) as in (a).