Cell viability of CK-treated cells and IC50 concentration of CK against neuroblastoma cells. (a) SK-N-MC cells were treated with 0, 20, 40, 80, 100 µM of CK and cultured at 37°C, 5% CO2 incubator for 48 h, and then the OD450 of the cells was measured (Mean ± SE, * p < 0.01). (b) Cell viability of each treatment group was expressed as a percentage based on the control group. The IC50 concentration of CK for 50% survival of neuroblastoma was determined by plotting a linear regression curve.