Treatment with zinc oxide nanoparticles led to caspase-independent cell death. HT29-SCAT3 cells were treated with 0.1% DMSO (vehicle; negative control), ZnO (10 μg/ml), TiO2 (30 μg/ml), FeO (30 μg/ml) and staurosporine (1 μM; positive control) for 18 hrs. The images were collected by an automated high-throughput microscope with a 20× objective (ImageXpress Micro). The addition of a caspase inhibitor IDN6556 (10 μM) did not inhibit cell death induced by ZnO. This experiment was repeated 3 times.